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the key Ki from the IMS services identity module (ISIM) contained in the UICC card, calculates locally from the random number (RAND) received, the authentication code AUTN and RES and the keys IK and CK. 11) If the authentication code calculated, AU is identical to that received, the IMS network is authenticated and the Alice's UA entity (or Bob's) sends to the P-CSCF entity a second SIP REGISTER request comprising its identity private, the authentication code RES answer in parameter response of the Authorization header. The REGISTER request, in the header Security-Verify, includes the security data received in the header Security-Server in the response 401 Unauthorized. REGISTER sip:ims.mnc01.mcc208.3gppnetwork.org SIP/2.0 Authorization: Digest username="alice_private@homeA.net", realm="ims.mnc01.mcc208.3gppnetwork.org", nonce=base64 (RAND + AUTN + server specific data), algorithm=AKAv1-MD5, uri="sip:ims.mnc01.mcc208.3gppnetwork.org", , response="6629fae49393a05397450978507c4ef1" Security-Client: ipsec-3gpp; alg=hmac-sha-1-96; spi- - c=23456789; spi-s=12345678; port-c=2468; port-s=1357 Security-Verify ipsec-3gpp; q=0.1; alg=hmac-sha-1-96; spi-c=98765432; spi-s=87654321; port-c=8642; port-s=7531 . . . 12) The P-CSCF entity transfers the message REGISTER to the I-CSCF entity. Basic Procedures 13) I-CSCF entity transmits to the HSS entity the DIAMETER LIR (Location-Information-Request) message to retrieve the IP address of S- CSCF entity. 14) The HSS entity provides the IP address of the S-CSCF entity in the DIAMETER LIA (Location-Information-Answer) message. 15) I-CSCF entity sends to the S-CSCF the REGISTER request. The S-CSCF entity compares the value of the RES received from the UA entity with that of the RES received from the HSS entity. If the two values are identical, the mobile is authenticated. 16) The S-CSCF entity sends to the HSS entity the DIAMETER SAR (Server-Assignment-Request) message to retrieve the mobile profile. 17) The HSS entity transmits the profile of the mobile in a DIAMETER SAA (Server-Ass

ignment-Answer) message. The mobile profile contains the logic to invoke the telephony application server (TAS) that provides supplementary telephone services and authorized media. The S-CSCF entity responds to the mobile with a SIP 200 OK message including its identity in the Service Route header. The registration is effective for a duration indicated in the parameter expires in the header Contact. The mobile has to renew its registration before expiration of that time, by way of the same procedure as for initial registration. The S-CSCF entity indicates, in the header P-Associated-URI, the identities registered implicitly, in addition to that indicated in the header to. SIP/2.0 200 OK Contact: <sip : 192.0.2.101>;expires=600000 P-Associated-URI: <sip:+1-212-555-1111@homeA.net user=phone> VoLTE and ViLTE 18), 19), 20) The SIP 200 OK response follows the reverse path taken by the REGISTER request, through the Via headers. 21) The S-CSCF entity registers the mobile with the TAS entity. 22) The TAS entity sends to the HSS entity the DIAMETER UDR (User- Data-Request) message to retrieve the mobile service data. 23) The answer is provided by the DIAMETER UDA (User-Data- Answer) message. 24) The TAS entity responds with 200 OK message to the SIP REGISTER request. 25) Alice's UA entity (or Bob's) generates a SUBSCRIBE request to receive notifications for registration. The identity of the S-CSCF entity of the domain (homeA. net), contained in the header Route, is learned during the registration of Alice's UA entity, information from the header Service Route. If Alice's UA entity has multiple identities, it indicates in the header P -Preferred-Identity which among them is the preferred one (sip:alice@homeA.net). Alice's UA entity defines in the header Event the type of event which it wishes to subscribe (value reg for registration). Alice's UA entity publishes the duration of the subscription in the header Expires. The value must not be greater than that indicated during registration in the response 200 OK of the REGISTE

R request. Alice's UA entity defines the format of the notifications of registration events in the header Accept (application/reginfo+xml) 26) The P-CSCF entity removes the headers Route containing its own identity and replaces the header P-Preferred-Identity with the header -Asserted-Identity containing Alice's asserted URI identity. Basic Procedures The P-CSCF adds the headers Via and Record Route containing its own identity. The header Record Route enables us to construct the route taken by subsequent requests. The S-CSCF authorizes the subscription with the response 200 OK because it trusts the content of the header P-Asserted-Identity inserted by the P-CSCF and because Alice has subscribed to the registration event service. 27), 28) The response 200 OK is routed through the addresses contained in the headers Via. 29) Receipt of the message 200 OK triggers a subscription on the part of the P-CSCF entity to discover the state of registration of Alice's UA entity. 30) The S-CSCF entity responds with 200 OK. 31) The 200 OK response to the REGISTER message triggers the SUBSCRIBE request from the TAS entity to have knowledge of the registration status of Alice's UA entity (or Bob's). 32) The S-CSCF entity responds with 200 OK. 33), 34) The S-CSCF entity notifies Alice's UA entity of the registration of its identities by sending a NOTIFY request. The S-CSCF reports the state of the subscription in the header Subscription-State (value active) and its duration in the parameter expires. The notification of registration elements is produced in an XML (eXtensible markup language) document of type reginfo attached to the SIP (session initiation protocol) message. 35), 36) The 200 OK response of the mobile is routed from addresses contained in the Via headers. 37) The S-CSCF entity notifies to the P-CSCF entity the registration status of Alice's UA entity (or Bob's) by sending a NOTIFY request. 38) The P-CSCF entity responds with 200 OK. VoLTE and ViLTE 39) The S-CSCF entity notifies to the TAS entity the registration sta

tus of Alice's UA entity (or Bob's) by sending a NOTIFY request. 40) The TAS entity responds with 200 OK. 3.3. Deregistration The deregistration process to the IMS network is described in Figure 3.3. 1), 2) The deregistration phase starts when the Alice's UA entity (or Bob's) transmits a REGISTER message which parameter expires of the header Contact has a zero value. 3) The I-CSCF entity transmits to the HSS entity the DIAMETER LIR message to retrieve the IP address of S-CSCF. P-CSCF I-CSCF S-CSCF SIP REGISTER SIP REGISTER DIAMETER LIR DIAMETER LIA SIP REGISTER DIAMETER SAR DIAMETER SAA SIP NOTIFY SIP NOTIFY SIP 200 OK SIP 200 OK SIP NOTIFY SIP 200 OK SIP NOTIFY SIP 200 OK SIP 200 OK SIP 200 OK SIP 200 OK Figure 3.3. Mobile deregistration to IMS network Basic Procedures 4) The HSS entity provides the IP address of the S-CSCF entity in the DIAMETER LIA message. 5) The I-CSCF entity sends to the S-CSCF entity the REGISTER request. 6) The S-CSCF entity transmits to the HSS entity the DIAMETER SAR message informing about deregistration of the mobile. The HSS entity still retains the identity of the S-CSCF entity to allow the use of services when the mobile is not registered, such as call forwarding to voicemail. 7) The HSS entity transmits the DIAMETER SAA message to acknowledge the previous request. 8), 9) The S-CSCF entity informs Alice's UA entity (or Bob's) of its deregistration in a NOTIFY message. 10), 11) The 200 OK message is a response to the NOTIFY request. 12) The S-CSCF entity informs the TAS entity about the deregistration of Alice's UA entity in a NOTIFY message. 13) The 200 OK message is a response to the NOTIFY request. 14) The S-CSCF entity informs the P-CSCF entity about the deregistration of Alice's UA entity in a NOTIFY message. 15) The 200 OK message is a response to the NOTIFY request. 16), 17), 18) The 200 OK message is a response to the REGISTER request. 3.4. Detachment The detachment procedure to the EPS network is described in Figure 3.4. 1) Upon receipt of 200 OK response to the REGISTER re

quest for deregistration, Alice's UA entity (or Bob's) starts the detachment phase and passes to the MME entity the EMM DETACH REQUEST message. 86 VoLTE and ViLTE EMM ATTACH REQUEST message carries ESM PDN DISCONNECT REQUEST message. ESM PDN DISCONNECT REQUEST EMM DETACH REQUEST RRC ULInformationTransfer S1 -AP UPLINK NAS TRANSPORT GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE ESM DEACTIVATE EPS BEARER CONTEXT REQUEST DIAMETER CCR EMM DETACH ACCEPT DIAMETER CCA S1-AP UE CONTEXT RELEASE COMMAND RRC ConnectionRelease S1-AP UE CONTEXT RELEASE COMPLETE Figure 3.4 Mobile detachment to EPS network EMM ATTACH REQUEST message is carried by RRC ULInformation Transfer message on the radio interface LTE-Uu and S1-AP UPLINK NAS TRANSPORT message on the S1-MME interface. 2) The MME entity sends to the SGW entity the GTPv2-C DELETE SESSION REQUEST message to deactivate the default bearer used for telephone signaling. 3) The SGW entity responds with the GTPv2-C DELETE SESSION RESPONSE message. 4) The SGW entity sends to the PGW entity the GTPv2-C DELETE SESSION REQUEST message to deactivate the default bearer. 5) The PGW entity responds with the GTPv2-C DELETE SESSION RESPONSE message. 6) The PGW entity sends to the PCRF entity the DIAMETER CCR message to inform about the deactivation of the default bearer. Basic Procedures 7) The PCRF entity responds to the PGW entity with the DIAMETER CCA message. 8) The MME entity confirms the detachment to Alice's UA entity in the EMM DETACH ACCEPT message. EMM DETACH ACCEPT message carries ESM DEACTIVATE EPS BEARER CONTEXT REQUEST message. EMM DETACH ACCEPT message is carried by RRC Connection Release message on the radio interface LTE-Uu and S1-AP UE CONTEXT RELEASE COMMAND message on the S1-MME interface. 9) The eNB entity confirms the context deactivation in S1-AP EU CONTEXT RELEASE COMPLETE message. 3.5. Establishment of VoLTE session The establishment of the VoLTE session includes the following operations:

- the negotiation of the characteristics of real-time transport protocol (RTP) streams via session description protocol (SDP); - the establishment of dedicated bearer to the RTP stream. 3.5.1. Originating side The procedure for establishing the VoLTE session on the outgoing call is described in Figure 3.5. 1) Alice's UA entity generates an initial INVITE request sent to Bob's URI (sip : bob@homeB.net). Alice's UA entity specifies in the header Require that Bob's UA entity must support the precondition of resource reservation before activating the ringing of the telephone. Alice's UA entity indicates in the header Supported that it supports the acknowledgement of provisional responses of 1xx type (value 100rel). VoLTE and ViLTE P-CSCF S-CSCF SIP INVITE SIP 100 Trying SIP INVITE SIP 100 Trying SIP INVITE SIP 100 Trying SIP 183 Session Progress SIP 183 Session Progress DIAMETER AAR DIAMETER RAR GTPv2-C CREATE BEARER REQUEST GTPv2-C CREATE BEARER REQUEST ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB SETUP REQUEST RRC ConnectionReconfiguration ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-APE-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 183 Session Progress SIP PRACK SIP PRACK SIP PRACK SIP 200 OK SIP 200 OK SIP 200 OK SIP UPDATE SIP UPDATE SIP UPDATE SIP 200 OK SIP 200 OK SIP 200 OK SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 200 OK SIP 200 OK DIAMETER AAR DIAMETER RAR DIAMETER RAA DIAMETER AAA SIP 180 Ringing SIP ACK SIP ACK SIP ACK Figure 3.5. Establishment of VoLTE session: originating side Alice's UA entity indicates in the header Allow the different supported methods (INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER and MESSAGE). Basic Procedures Alice's UA entity sends an SDP offer in the initial INVITE request to Bob's UA entity. The offer lists the media (audio) that Alice wishes to use for that session and lists the different codecs supported as well. Alice's UA entity indicates in

the SDP offer (a=curr:qos local none, a=curr:qos remote none) that the resource reservation has not been established for the local and remote UA entities. Alice's UA entity indicates in the SDP offer (a=des:qos mandatory local sendrecv) that the precondition of resource reservation is mandatory for the local UA entity. Alice's UA entity indicates in the SDP offer (a=des:qos none remote sendrecv) that the precondition of resource reservation is unknown for the remote UA entity. INVITE sip:bob@homeB.net SIP/2.0 Require: precondition, sec-agree Proxy-Require: sec-agree Supported: 100rel Allow: INVITE, ACK, CANCEL, BYE, PRACK, UPDATE, REFER, MESSAGE Content-Type: application/sdp Content-Length : (...) a=curr:qos local none a=curr:qos remote none a=des:qos mandatory local sendrecv a=des:qos none remote sendrecv 2) The P-CSCF entity responds to the mobile with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 3) The P-CSCF entity removes the header Route containing its own identity. VoLTE and ViLTE The P-CSCF entity replaces the header P-Preferred-Identity - with the header -Asserted-Identity - containing the asserted URI of Alice. The P-CSCF entity adds the headers Via and Record Route containing its own identity. The header Record Route enables us to construct the route to be taken by subsequent requests. The P-CSCF entity forwards the request to the S-CSCF entity whose identity is contained in the header Route. 4) The S-CSCF entity responds to P-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 5) The S-CSCF entity removes the header Route containing its own identity. The S-CSCF entity adds the headers Via and Record Route containing its own identity. The HSS entity has provided, during registration, the S-CSCF entity with the user profile, containing the types of media authorized by the service offered. The S-CSCF entity examines the information contained in the SDP message carried by the INVITE request. If the S-C

SCF finds that these do not conform to the service profile, it sends to Alice's UA entity a negative response 488 Not Acceptable Here. The S-CSCF entity retrieves the destination domain name (homeB. net) from Bob's URI and forwards the INVITE request to the entity in charge of the interconnection with the domain (homeB net). 6) The homeB. net domain responds to S-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 7) In the response 183 Session Progress, Bob's UA entity gives an SDP response in which it chooses a type of codec from those proposed by Alice's UA entity. Basic Procedures The 183 Session Progress response contains in the header Record Route IP addresses of entities that the subsequent requests must pass through. The 183 Session Progress response also indicates that a resource reservation is also required of Bob's side before establishing a session. a=curr:qos local none a=curr:qos remote none a=des:gos mandatory local sendrecv a=des: qos mandatory remote sendrecv 8) The S-CSCF entity forwards the 183 Session Progress response to the P-CSCF entity. The identity of the P-CSCF entity assigned to Bob's UA entity was learned during the registration (information contained in the Path header). The establishment of a dedicated bearer, assigned to voice, is coupled with the establishment of a default bearer and assigned to telephone signaling. This dedicated bearer is coupled with the default bearer assigned to telephone signaling, in that the bearer terminations are the same for both types of bearer. The establishment of the dedicated bearer is triggered by the P-CSCF entity from the analysis of telephone signaling exchanged between the terminals that want to establish a telephone call. 9) The P-CSCF entity sends to the PCRF entity the DIAMETER AAR (authenticate and authorize request) message to verify that the media settings are authorized by the EPS network and to trigger the establishment of dedicated bearer. 10) The PCRF entity consults its SPR dat

abase to retrieve the level of QoS to apply (QCI = 1) and transmits the DIAMETER RAR (Re-Auth- Request) message to the PGW entity containing the characteristics of the stream to establish. VoLTE and ViLTE 11) The PGW entity sends to the SGW entity the GTPv2-C CREATE BEARER REQUEST message containing the TEID identifier of the S5 bearer that the SGW entity will need to use in the GTP-U header when sending traffic to the PGW entity. 12) The SGW entity sends to the MME entity the GTPv2-C CREATE BEARER REQUEST message containing the TEID identifier of the S1 bearer that the eNB entity will need to use in the GTP-U header while sending traffic to the SGW entity. 13) The MME entity sends to the mobile the ESM ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST message carried by the S1-AP E-RAB SETUP REQUEST message on the S1-MME interface and by the RRC ConnectionReconfiguration message on the LTE-Uu interface. The S1-AP E-RAB SETUP REQUEST message contains the TEID identifier that the MME entity has received from the SGW entity. The RRC ConnectionReconfiguration message contains the logical channel identifier (LCID) of the dedicated bearer. 14) The mobile responds to the MME entity by the ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT message carried by the RRC ConnectionReconfigurationComplete message on the LTE-Uu interface and by the S1-AP E-RAB SETUP RESPONSE message on the S1-MME interface. The S1-AP E-RAB SETUP RESPONSE message contains the TEID identifier of the S1 bearer that the SGW entity will need to use in the GTP-U header when it sends traffic to the eNB entity. 15) The MME entity responds to the SGW entity by the GTPv2-C CREATE BEARER RESPONSE message containing the TEID identifier that the MME entity has received from the eNB entity. 16) The SGW entity responds to the PGW entity with the C-GTPv2 CREATE BEARER RESPONSE message containing the TEID identifier of the S5 bearer that PGW entity will need to use in the GTP-U header when it sends traffic to the SGW entity. Basic Procedures The dedicated bearer has

been established at this stage. It will remain blocked by the PGW entity until Bob picks up the call. 17) The PGW entity responds to the PCRF entity with the DIAMETER RAA (Re-Auth Answer) message. 18) The PCRF entity responds to the P-CSCF entity with the DIAMETER AAA (Authenticate-Authorize-Answer) message. 19) The P-CSCF entity forwards the 183 Session Progress response to the Alice's UA entity. 20), 21), 22) Alice's entity sends the subsequent PRACK request to acknowledge the provisional response 183 Session Progress. Alice's UA entity indicates in the Route headers the identities of CSCF entities processing the request, namely P / C-CSCF entities in the domains (homeA. net) and (homeB.net). 23), 24), 25) The 200 OK Message is the response to the PRACK request. 26), 27), 28) When Alice's UA entity has confirmation of the resource reservation, it indicates this to Bob's UA entity in an SDP offer (a=curr:qos local sendrecv) contained in an UPDATE request. a=curr:qos local sendrecv a=curr:qos remote none a=des:qos mandatory local sendrecv a=des: gos mandatory remote sendrecv 29), 30), 31) When Bob's UA entity has confirmation of the resource reservation, it notifies Alice's UA entity in an SDP offer contained in the response 200 OK to the UPDATE request. a=curr:qos local sendrecv a=curr:qos remote sendrecv a=des:gos mandatory local sendrecv a=des:qos mandatory remote sendrecv VoLTE and ViLTE 32), 33), 34) When the resource reservations are effective at both ends, Bob's telephone can ring and a response 180 Ringing is transmitted to Alice's UA entity, generating a ring back tone for her. 35), 36) When Bob picks up the phone, the 200 OK response to the INVITE request is sent to the PCSCF entity. 37) The P-CSCF entity sends to the PCRF entity the DIAMETER AAR message to indicate that Bob took the call. 38) The PCRF entity transmits to the PGW entity the RAR DIAMETER message to unblock the dedicated bearer. 39) The PGW entity responds to the PCRF entity with the DIAMETER AAR message. 40) The PCRF entity responds to

DIAMETER RAA DIAMETER AAA SIP 200 OK SIP 200 OK SIP 200 OK SIP ACK SIP ACK SIP ACK Figure 3.6. Establishment of VoLTE session: terminating side VoLTE and ViLTE 5) The I-CSCF entity adds the header Via, does not add a Record Route and forwards the request to the S-CSCF entity. The subsequent requests, therefore, do not pass through the I-CSCF entity. 6) The S-CSCF entity responds to the I-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 7) The S-CSCF entity verifies that the types of media proposed by Alice's UA entity correspond to the services offered to Bob. The S-CSCF entity adds a header Record Route containing its own identity. The S-CSCF entity modifies the initial request, replacing Bob's URI with his IP address. The link between the URI and the IP address was created at registration. The S-CSCF entity adds Bob's URI to the header P-Called-Party- - ID SO that Bob knows which URI the INVITE request refers to. The S-CSCF entity transfers the request to the P-CSCF entity. The IP address of the P-CSCF entity was learnt at registration (information contained in the header Path). 8) The P-CSCF entity responds to the S-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. 9) The P-CSCF entity adds a header Record Route containing its own identity and forwards the request to Bob's UA entity, whose IP address is included in the URI of the request. 10) Bob's UA entity entity responds to the P-CSCF entity with 100 Trying message that allows for blocking the retransmission timer of the INVITE request. Bob's UA entity stores the different headers Record Route, which it will later use to route subsequent requests. Basic Procedures 11) Bob's UA entity sends a response 183 Session Progress to Alice's UA entity. The response is routed on the basis of the Via headers received from the request INVITE. The response 183 Session Progress contains the Record Route headers received from the request INVITE. This enabl

es Alice's UA entity to retrieve the IP addresses of the CSCF entities that need to process the subsequent requests. Bob's UA entity indicates the value 100rel in the header Require to indicate that the response requires acknowledgement from Alice's UA entity. To correlate the acknowledgement with the response, Bob's UA entity inserts the header RSeq. In the response 183 Session Progress, Bob's UA entity gives an SDP response in which it chooses a type of codec from those proposed by Alice's UA entity. Bob's UA entity indicates in the SDP message of the 183 Session Progress response that resource reservation is also necessary on its part before establishing a session. 12) to 21) On receiving of the 183 Session Progress response, the P-CSCF entity initiates the establishment of dedicated bearer. They are identical to messages 9 to 18 described in the preceding paragraph. 22), 23), 24) The 183 Session Progress response is transmitted to the domain homeA. net. 25), 26), 27) Subsequent PRACK request is received from the domain homeA. net, indicating that Alice's UA entity has acknowledged receiving 183 Session Progress response. 28), 29), 30) The 200 OK message is the response to the PRACK request. 31), 32), 33) Subsequent UPDATE request is received from the domain homeA. net, indicating that the dedicated bearer on the Alice's side is established. 34), 35), 36) The 200 OK message is the response to the UPDATE request, indicating that the dedicated bearer on the Bob's side is established. VoLTE and ViLTE 37) to 40) The 180 Ringing response to the initial INVITE request is sent to the domain homeA. net, indicating that the Bob's phone is ringing. 41) The 200 OK response to the initial INVITE request indicates that Bob picks up his phone. 42) The P-CSCF entity sends the PCRF entity the DIAMETER AAR message to indicate that Bob took the call. 43) The PCRF entity transmits to the PGW entity the DIAMETER RAR message to unblock the dedicated bearer. 44) The PGW entity responds to the PCRF entity with the DIAMETER AAR messa

ge. 45) The PCRF entity responds to the P-CSCF entity with the DIAMETER AAA message. 46), 47), 48) The P-CSCF entity forwards the 200 OK response to the INVITE request to the domain homeA.net. 49), 50), 51) The ACK request of the 200 OK response is received from the domain homeA. net. 3.6. Termination of VoLTE session The termination of the session can be triggered by UA, P-CSCF or IMS- GWF entity, using the BYE method. Termination of the session can be initiated by either (Alice's or Bob's) UA entity when the communication has finished. The P-CSCF entity can also end the session if the mobile is no longer within radio coverage. The PCRF entity sends this information to the P-CSCF entity by way of a DIAMETER ASR (Abort-Session-Request) message. The IMS-GWF entity is an application server which controls the session in the case of pre-paid use. When the user's credit is exhausted, the IMS-GWF entity ends the session. Two BYE requests are needed to terminate the session: one request sent to Alice's UA entity and the second to Bob's UA entity. Basic Procedures 3.6.1. Initiated side The procedure for clearing the VoLTE session initiated by the UA entity, at the initiated side, is described in Figure 3.7. P-CSCF S-CSCF SIP BYE SIP BYE SIP BYE DIAMETER STR DIAMETER RAR DIAMETER RAA DIAMETER STA SIP 200 OK SIP 200 OK SIP 200 OK GTPv2-C DELETE BEARER REQUEST GTPv2-C DELETE BEARER REQUEST ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB RELEASE COMMAND RRC ConnectionReconfiguration ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfiguration Complete S1-AP E-RAB RELEASE RESPONSE GTPv2-C DELETE BEARER RESPONSE GTPv2-C DELETE BEARER RESPONSE Figure 3.7. Termination of VoL TE session: initiated side 1), 2), 3) The release of the session is initiated by Alice's UA entity (or Bob's), which forwards the BYE request to the domain homeB. net homeA. net). 4) On receipt of the BYE request, the P-CSCF entity informs the PCRF entity for the release of the session in the DIAMETER STR (Session- Termina

tion-Request) message. 5) The PCRF entity requests the PGW entity to release of dedicated bearer in the DIAMETER RAR message. 6) The PGW entity acknowledges the DIAMETER RAR request by the RAR DIAMETER RAA message. 7) The PCRF entity acknowledges the DIAMETER STR request by the DIAMETER STA (Answer-Session-Termination) message. VoLTE and ViLTE 8), 9), 10) Alice's UA entity (or Bob's) receives the 200 OK response to the BYE request from the domain homeB net (or homeA net). 11) Upon receipt of the DIAMETER RAR message, the PGW entity initiates the removal of dedicated bearer by the GTPv2 C-BEARER DELETE REQUEST message. 12) The SGW entity transmits the GTPv2 C-BEARER DELETE REQUEST message to continue the dedicated bearer release request. 13) The MME entity sends the ESM DEACTIVATE EPS BEARER CONTEXT REQUEST message to Alice's UA entity (or Bob's) to inform about the deactivation of the dedicated bearer. The ESM DEACTIVATE EPS BEARER CONTEXT REQUEST message is carried by the RRC ConnectionReconfiguration message on the radio interface LTE-Uu and the S1-AP E-RAB RELEASE COMMAND message on the S1-MME interface. 14) The UA entity confirms the deactivation of the dedicated bearer in the ESM DEACTIVATE EPS BEARER CONTEXT ACCEPT message. The ESM DEACTIVATE EPS BEARER CONTEXT ACCEPT message is carried by the RRC ConnectionReconfigurationComplete message on the radio interface LTE-Uu and the S1-AP E-RAB RELEASE RESPONSE message on the S1-MME interface. 15) The MME entity responds to the SGW entity with the GTPv2-C DELETE BEARER RESPONSE message that acknowledges the release request of the dedicated bearer. 16) The SGW entity responds to the PGW entity with the GTPv2-C DELETE BEARER RESPONSE message that acknowledges the release request of the dedicated bearer. 3.6.2. Received side The procedure for clearing the VoLTE session initiated by the UA entity, at the received side, is described in Figure 3.8. Basic Procedures 1), 2), 3) Bob's UA entity (or Alice's) receives the BYE request, from domain homeA. net (or homeB net), e

nding the session. 4) to 7) As described earlier, these messages are used to trigger the release of the dedicated bearer. 8), 9), 10) Bob's UA entity (or Alice's) sends the 200 OK response to the BYE request, to the domain homeA. net (or homeB net). 11) to 16) As described earlier, these messages are used to remove the dedicated bearer. P-CSCF S-CSCF SIP BYE SIP BYE SIP BYE DIAMETER STR DIAMETER RAR DIAMETER RAA DIAMETER STA SIP 200 OK GTPv2-C DELETE BEARER REQUEST SIP 200 OK GTPv2-C DELETE BEARER REQUEST SIP 200 OK ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB RELEASE COMMAND RRC ConnectionReconfiguration ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-AP E-RAB RELEASE RESPONSE GTPv2-C DELETE BEARER RESPONSE GTPv2-C DELETE BEARER RESPONSE Figure 3.8. Termination of VoLTE session: received side 3.7. Establishment of ViLTE session The procedure for establishing the ViLTE session is identical to that described for the VoLTE session when the SDP protocol associated with the initial INVITE request contains the negotiation of the two media, audio and video, with a proposal for codecs for both media. Similarly, the 183 Session Progress response defines the codec selected among the proposals, for each media. 102 VoLTE and ViLTE Upon receipt of the 183 Session Progress response, the P-CSCF entity triggers to the PCRF entity to establish two dedicated bearers: - one dedicated bearer (QCI = 1) for audio flow; - one dedicated bearer (QCI=2) for video flow. The ViLTE session can also be added to a VoLTE session. The procedure of the addition of the video stream for the ViLTE session, at the initiated side, is described in Figure 3.9. P-CSCF S-CSCF SIP UPDATE SIP UPDATE SIP UPDATE SIP 200 OK SIP 200 OK DIAMETER AAR DIAMETER RAR GTPv2-C CREATE BEARER REQUEST GTPv2-C CREATE BEARER REQUEST ESM ACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB SETUP REQUEST RRC ConnectionReconfiguration ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurat

ionComplete S1-AP E-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 200 OK Figure 3.9. Adding a video stream: initiated side 1), 2), 3) Alice's UA entity (or Bob's) forwards the UPDATE request to the domain homeB. net (or homeA. net). The UPDATE request can be replaced by the re-INVITE request and contains a new SDP offer on both audio and video streams. The S-CSCF entity controls that Alice's UA entity (or Bob's) is authorized to establish a ViLTE session. Basic Procedures 4), 5) The 200 OK response to the UPDATE request contains the SDP response in which Bob's UA entity (or Alice's) retains a codec from those proposed by Alice's UA entity (or Bob's). 6) to 15) Upon receipt of the 200 OK response, the P-CSCF entity initiates the establishment of dedicated bearer for the video stream. 16) The P-CSCF entity forwards the 200 OK response to Alice's UA entity (or Bob's). The procedure of the addition of the video stream for the ViLTE session, at the received side, is described in Figure 3.10. P-CSCF S-CSCF SIP UPDATE SIP UPDATE SIP UPDATE SIP 200 OK DIAMETER AAR DIAMETER RAR GTPv2-C CREATE BEARER REQUEST GTPv2-C CREATE BEARER REQUEST ESM ACTIVATE DEDICATE EPS BEARER CONTEXT REQUEST S1-AP E-RAB SETUP REQUEST RRC ConnectionReconfiguration ESM ACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-AP E-RAB SETUP RESPONSE GTPv2-C CREATE BEARER RESPONSE GTPv2-C CREATE BEARER RESPONSE DIAMETER RAA DIAMETER AAA SIP 200 OK SIP 200 OK Figure 3.10. Adding a video stream: received side 1), 2), 3) The UPDATE request received from the domain homeA. net (or homeB net) is transmitted to Bob's UA entity (or Alice's). The S-CSCF entity controls that Bob's UA (or Alice's) is authorized to establish a ViLTE session. 4) Bob's UA entity (or Alice's) selects a codec for the video stream among the proposals received in the SDP offer associated with the UPDATE request. VoLTE and ViLTE The UA entity responds with 200 OK message containing the select

ed codec. 5) to 14) Upon receipt of the 200 OK response, the P-CSCF entity initiates the establishment of dedicated bearer for the video stream. 15), 16) The P-CSCF entity forwards the 200 OK response to the domain homeA net (or homeB net). 3.8. Termination of ViLTE session The procedure for clearing the ViLTE session is identical to that described for the VoLTE session if the two streams, audio and video, need to be released. The release of the ViLTE session may be limited to the removal of the video stream, the audio stream being retained. The procedure of the removal of the video stream, at the initiated side, is described in Figure 3.11. 1), 2), 3) Alice's UA entity (or Bob's) takes the initiative in removing the video flow by sending the UPDATE message to the domain homeB net (or homeA. net). The deletion of the video flow is indicated in the SDP message, which contains the port number of the video stream set to ZERO. 4) to 7) As described earlier, these messages are used to trigger the release of the dedicated bearer for the video stream. 8), 9), 10) Bob's UA entity (or Alice's) sends the 200 OK response to the UPDATE request to the domain homeA. net (or homeB.net) The deletion of the video flow is indicated in the SDP message, which contains the port number of the video stream set to ZERO. 11) to 16) As described earlier, these messages are used to remove the dedicated bearer for the video stream. Basic Procedures P-CSCF S-CSCF SIP UPDATE Homes SIP UPDATE SIP UPDATE DIAMETER STR DIAMETER RAR DIAMETER RAA DIAMETER STA SIP 200 OK SIP 200 OK SIP 200 OK GTPv2-C DELETE BEARER REQUEST GTPv2-C DELETE BEARER REQUEST ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-APE-RAB RELEASE COMMAND RRC ConnectionReconfiguration ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplete S1-AP E-RAB RELEASE RESPONSE GTPv2-C DELETE BEARER RESPONSE GTPv2-C DELETE BEARER RESPONSE Figure 3.11. Removing a video stream: initiated side The procedure of the removal of the video stream, at the receiv

ed side, is described in Figure 3.12. P-CSCF S-CSCF SIP UPDATE SIP UPDATE SIP UPDATE DIAMETER STR DIAMETER RAR DIAMETER RAA DIAMETER STA SIP 200 OK SIP 200 OK GTPv2-C DELETE BEARER REQUEST SIP 200 OK GTPv2-C DELETE BEARER REQUEST ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT REQUEST S1-AP E-RAB RELEASE COMMAND RRC ConnectionReconfiguration ESM DEACTIVATE DEDICATED EPS BEARER CONTEXT ACCEPT RRC ConnectionReconfigurationComplet S1-AP E-RAB RELEASE RESPONSE GTPv2-C DELETE BEARER RESPONSE GTPv2-C DELETE BEARER RESPONSE Figure 3.12. Removing a video stream: received side VoLTE and ViLTE 1), 2), 3) Bob's UA entity (or Alice's) receives the UPDATE request, from the domain homeA. net (or homeB. net), indicating the removal of the video stream. 4) to 7) As described earlier, these messages are used to trigger the release of the dedicated for to the video stream. 8), 9), 10) Bob's UA entity (or Alice's) sends the 200 OK response to the UPDATE request to the domain homeA.net (or homeB. net), indicating the suppression of the video flow. 11) to 16) As described earlier, these messages are used to remove the dedicated bearer for the video stream. 3.9. Emergency call If the mobile detects the emergency call, it performs a particular resource reservation with the EPS network to transmit the INVITE request. The mobile will replace the number dialed by the user by the uniform resource name (URN) which defines the type of emergency call. INVITE urn service: SOS SIP/2.0 The EPS network establishes a bearer (QCI = 5) whose allocation and retention priority (ARP) is higher than that established during the attachment of the mobile. If the mobile does not detect the emergency call, the INVITE request is transmitted on the normal bearer (QCI = 5). If the P-CSCF entity detects the emergency call, it can answer the mobile with an emergency call indication (Figure 3.13). Upon receiving the INVITE message, the P-CSCF entity requests the PCRF entity for the ECGI identifier of the cell where the mobile is located. The P-CSCF entity inserts that

identifier in the INVITE request that it transfers to the Emergency CSCF entity (E-CSCF), in the following two cases (Figure 3.13): Basic Procedures - the mobile is not registered, because it has no UICC card or because it is on a visited network that has no roaming agreement with the home network; - the mobile is already registered with the S-CSCF entity and a specific registration for the emergency call is not required. If a specific registration for the emergency call is required, the P-CSCF entity informs the mobile (Figure 3.13). User dials an emergency call The mobile detects the The mobile send a P-CSCFentity détects emergency call normal service request the emergency call P-CSCF entity inserts an emergency indication information Starting the procedure of the detected emergency call the mobile sends an P-CSCF entity accepts E-CSCF entity The mobile is emergency service processes the registered anonymous call request anonymous call the mobile sends an P-CSCF entity accepte emergency service the emergency service E-CSCF entity request awith normal processes the request awith normal emergency call registration registration Emergency registration procedure The mobile sends an E-CSCF entity emergency service request processes the with an emergency emergency call registration Figure 3.13. Conditions for the transmission of the emergency call The REGISTER request shall insert in the header Contact the parameter SOS to indicate that it is a registration for an emergency call. REGISTER sip: ims mnc01 mcc208 3gppnetwork.org SIP/2.0 Contact: <sip 192.0.2.101>; expires=600000; SOS; Radio Interface Procedures 4.1. Radio interface At the LTE-Uu radio interface, between the user equipment (UE) and the evolved node base station (eNB), traffic data, corresponding to an IP Internet protocol (IP) packet and signaling data, corresponding to an radio resource control (RRC) message, are encapsulated by the data link layer broken down into three sub-layers (Figure 4.1): - packet data convergence protocol (PDCP); - radio link co

ntrol (RLC) protocol; - medium access control (MAC) protocol. Three types of channels are defined (Figure 4.1): - the logical channel defines the data structure at the interface between the RLC and MAC sub-layers; - the transport channel defines the data structure at the interface between the MAC sub-layer and the physical layer; - the physical channel defines the data structure between the two parts making up the physical layer, firstly, the coding and, secondly, the modulation and the multiplexing. The RRC messages can carry non-access stratum (NAS) messages exchanged between the mobile and the mobility management entity (MME). VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. © ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE message Traffic flow Control flows message Packet sub-layer sub-layer Logical channels sub-layer Transport (UL-SCH) RACH DL-SCH channels Physical layer Physical PUCCH PUSCH (PRACH (PDCCH)PDSCH Channels Uplink (PCFICH) PHICH Downlink Figure 4.1. Radio interface structure. For a color version of the figure, see www.iste.co.uk/perez/volte.zip 4.1.1. Data link sub-layer 4.1.1.1. PDCP protocol The PDCP protocol is used for RRC signaling messages, relating to dedicated control data and for the traffic IP packets. The PDCP protocol performs the following functions: - compression of the data traffic headers using the robust header compression (ROHC) mechanism; - security of data traffic (confidentiality) and RRC signaling (integrity and confidentiality); - the delivery in sequence of the RRC messages and the IP packets; - the recovery of PDCP frames lost during the handover. Several PDCP instances can be activated simultaneously: - two instances for signaling radio bearers (SRB1 and SRB2) relating to RRC signaling data: Radio Interface Procedures - the SRB1 bearer is used for the transmission of an RRC message that can carry a NAS message, - the SRB2 bearer is used for the transmission of a NAS message

only; - one instance for each data radio bearer (DRB) relating to data traffic. Header compression is based on the ROHC mechanism for which multiple algorithms have been defined by the request for comments (RFC) specifications of the Internet engineering task force (IETF) standards body (Table 4.1). Profile identifier Compressed headers References 0x0000 uncompressed RFC 4995 0x0001 RTP/UDP/IP RFC 3095, RFC 4815 0x0002 UDP/IP RFC 3095, RFC 4815 0x0003 ESP/IP RFC 3095, RFC 4815 0x0004 RFC 3843, RFC 4815 0x0006 TCP/IP RFC 4996 0x0101 RTP/UDP/IP RFC 5225 0x0102 UDP/IP RFC 5225 0x0103 ESP/IP RFC 5225 0x0104 RFC 5225 Table 4.1. ROHC specifications Header compression is based on the observation that in a session, a number of fields are invariant, such as IP addresses or port numbers. Header compression is particularly effective when the size of the IP packet payload is relatively low, which is the case for voice (Figure 4.2). The decompressor uses the PDCP feedback control message to inform the compressor that decompression is successful or that synchronization between compression and decompression has been lost. VoLTE and ViLTE 12,2 kbps 12,2 kbps 244 bits every 20 ms 244 bits every 20 ms 12 bytes 8 bytes 4 bytes 20 bytes 28,2 kbps 13,8 kbps 564 bits every 20 ms 276 bits every 20 ms Figure 4.2. Header compression 4.1.1.2. RLC protocol The RLC protocol provides control of the radio link between the mobile and the eNB entity. The mobile can simultaneously activate multiple RLC instances, with each instance corresponding to a PDCP instance. The RLC protocol operates in three modes: - acknowledged mode (AM): session information protocol (SIP) uses this mode; - unacknowledged mode (UM): real-time transport protocol (RTP) uses this mode. - transparent mode (TM) for which no header is added. The RLC protocol performs the following operations: - retransmission in the case of error via the automatic repeat request (ARQ) mechanism, for the acknowledged mode only; - concatenation, segmentation and reassembly of PDCP frames both

in the acknowledged and unacknowledged mode; - possible re-segmentation of PDCP frames, in the acknowledged mode, during retransmission of the RLC frame; - re-sequencing of received data, both in the acknowledged and unacknowledged mode; - detection of duplicate data both in the acknowledged and unacknowledged mode. Radio Interface Procedures 4.1.1.3. MAC protocol The MAC protocol provides the following functions: - multiplexing of RLC frames from multiple instances in a transport block; - resource allocation via a scheduling mechanism; - management of retransmission in case of error via the hybrid automatic repeat request (HARQ) mechanism; - management of the random access procedure. 4.1.2. Logical channels The broadcast control channel (BCCH) is a unidirectional common control channel, used only in the downlink for RRC broadcasting of master information block (MIB) and system information block (SIB) messages. The paging control channel (PCCH) is a unidirectional common control channel, used only in the downlink to transport RRC messages for paging. The common control channel (CCCH) is a bidirectional common control channel, used to transmit the first RRC signaling messages when the mobile connects to the eNB entity. The dedicated control channel (DCCH) is a bidirectional dedicated control channel, used to transmit RRC messages when the mobile is connected to the eNB entity. The dedicated traffic channel (DTCH) is a dedicated bidirectional channel, used to transmit unicast IP packets. The multicast control channel (MCCH) is a unidirectional channel used for transmitting RRC messages for control information associated with IP packets transmitted in broadcast mode. The multicast traffic channel (MTCH) is a unidirectional channel used to transmit IP packets in broadcast mode to the mobile. 114 VoLTE and ViLTE 4.1.3. Transport channels 4.1.3.1. Downlink The broadcast channel (BCH) supports the BCCH logical channel including the RRC message relating to MIB system information. The paging channel (PCH) supports the PCC

H logical channel. The downlink shared channel (DL-SCH) multiplexes the CCCH, DCCH, DTCH and BCCH logical channels. The BCCH logical channel includes the RRC messages relating to SIB system information. The MCCH and MTCH logical channels are mapped to the DL-SCH transport channel if the number of mobiles concerned by transmitted IP packets in broadcast mode is low. The multicast channel (MCH) multiplexes the MCCH and MTCH logical channels if the number of mobiles concerned by IP packets transmitted in broadcast mode is significant. 4.1.3.2. Uplink The random access channel (RACH) does not transport logical channels. It is used by the mobile for random access to the eNB entity. The RACH transport channel only carries a preamble to initialize the connection with the eNB entity. The uplink shared channel (UL-SCH) multiplexes the DCCH, CCCH and DTCH logical channels. 4.1.4. Physical layer 4.1.4.1. Transmission chain The transmission chain consists of two sub-sets: - for each direction of transmission, the first sub-set comprises the error detection code, the error correction code and the bit rate matching; - for the downlink direction, the second sub-set includes modulation, mapping on spatial layers, precoding, resource element mapping and inverse fast Fourier transform (IFFT) to generate the orthogonal frequency division multiple access (OFDMA) signal (Figure 4.3). Radio Interface Procedures Transport block Control information Error detection code Modulation Error correction code Mapping on spatial layers Precoding Rate matching Physical channel Mapping on resource elements OFDMA signal Figure 4.3. Transmission chain: downlink - for the uplink direction, the second sub-set includes modulation, mapping to resource elements and inverse Fourier transform IFFT. The generation of the single carrier frequency division multiple access (SC-FDMA) signal introduced a fast Fourier transform (FFT). The spatial layer mapping and precoding are implemented only for Release 10 (Figure 4.4). Transport block Control information Erro

r detection code Modulation Error correction code Rate adaptation Mapping on spatial layers Relactor Precoding Physical channel Mapping on resource elements SC-FDMA signal Figure 4.4. Transmission chain: uplink 116 VoLTE and ViLTE 4.1.4.2. Frequency-division multiplexing Support for both transmission directions uses two bandwidths matched in the frequency division duplex (FDD) mode or a single bandwidth in the time-division duplex (TDD) mode. For the FDD mode, each transmission direction operates simultaneously in the assigned bandwidth. For the TDD mode, both directions of transmission operate alternately in the same bandwidth, meaning each direction is assigned a portion of time. The bandwidth of the radio channel is flexible and can take several values: 1.4 MHz, 3 MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz. Carrier aggregation (CA) involves combining the use of several component carriers (CC) or radio channels to increase the cell bit rate. The aggregation can be performed on five radio channels, bringing the maximum bandwidth to 100 MHz. The radio channel is formed in the frequency domain of an orthogonal frequency-division multiplexing (OFDM) with sub-carrier spacing of 15 kHz or 7.5 kHz. 4.1.4.3. Time-division multiplexing Two structures of time frames are defined according to the FDD or TDD mode. The type-1 structure defined for the FDD mode lasts 10 ms and contains 10 sub-frames (Figure 4.5). Each sub-frame is made up of two time slots. Frame 10 ms Sub-frame 123456789 01234567891 0.5 ms Figure 4.5. Structure of the frame in FDD mode Radio Interface Procedures For the uplink, the signals transmitted by different mobiles must be temporally aligned, to the reception by the eNB entity. The mobiles must, therefore, be synchronized temporally by the eNB entity which conveys the timing advance (TA) to them, to be applied for the uplink. The type-2 structure defined for the TDD mode also lasts 10 ms and contains two half-frames of 5 ms each (Figure 4.6). Each half-frame comprises five sub-frames and the second sub-fra

me can correspond to a special sub-frame containing three particular fields: - a field for the downlink pilot time slot (DwPTS) which can contain data; - a field for the uplink pilot time slot (UpPTS) which can contain data or a preamble; - a gap period (GP), between the two preceding fields. This interval time facilitates the compensation of a time difference between different mobiles and avoids an overlap between the two transmission directions. Frame 10 ms Half-frame Half-frame Sub-frame DwPTS UpPTS DwPTS UpPTS 45678910 0.5 ms Figure 4.6. Structure of the frame in TDD mode 118 VoLTE and ViLTE The sub-frames are attributed to the data for the uplink and downlink according to diverse configurations (Table 4.2): - sub-frames 0 and 5 are always allocated to traffic in the downlink; - sub-frame 1 is always allocated to the special sub-frame containing the three particular fields; - sub-frame 2 is always allocated to traffic in the uplink; - sub-frame 6 can be allocated to the special sub-frame containing three particular fields for a periodicity of 5 ms; - sub-frames 3, 4, 7, 8, 9 are allocated to the downlink or uplink traffic according to the selected configuration. Number of the sub-frame Configuration Periodicity 012345678 DSUUUDSUUU 5 ms DSUUDDSUUD 5 ms DSUDDDSUDD 10 ms DSUUUDDDDD 10 ms DSUUDDDDDD 10 ms DSUDDDDDDD DSUUUDSUUD D (Downlink) / U (Uplink) / S (Special) Table 4.2. TDD frame configuration Radio Interface Procedures Each time slot comprises of 3 or 6 or 7 OFDM symbols (Figure 4.7). 1 slot = 15360 Ts Normal cyclic prefix Symbol 1 slot = 15360 Ts Extended cyclic prefix Symbol Figure 4.7. Time slot structure An OFDM symbol corresponds to a number of bits which depends on the modulation used: - 2 bits in the case of a quadrature phase-shift keying (QPSK) modulation whose constellation contains 4 different symbols; - 4 bits in the case of a quadrature amplitude modulation (16-QAM) whose constellation contains 16 different symbols; - 6 bits in the case of a 64-QAM modulation whose constellation contain 64 d

ifferent symbols. The introduction of a guard time between the symbols facilitates the removal of inter-symbol interference. The guard time of a time slot is found at the beginning of the symbol. It contains the copy of the end of the symbol in order to avoid a very high dynamic for the amplifiers. This copy is called the cyclic prefix (CP). The normal cyclic prefix is used in case the delay between the different reflected signals is low, which is the case in cells with a smaller diameter. 120 VoLTE and ViLTE The extended cyclic prefix is used in case the delay between the different reflected signals is significant, which is the case in cells of a large diameter. 4.1.4.4. Spatial multiplexing Four modes characterize the transmission system on the radio channel (Figure 4.8). It should be noted that the term input is applied to the input of the radio channel and the term output to the output of the same channel. Figure 4.8. Transmission modes The single input single output (SISO) mode is the basic signal propagation mode in which a transmitting and a receiving antenna are used. The single input multiple output (SIMO) mode is characterized by the use of a single transmitting antenna and multiple receiving antennas. The SIMO mode is often referred to as receive diversity. The transmitted bit rate is identical to the SISO mode. On the other side, the selection of the received signal allows the receiver to protect against fading of the radio signal. The multiple input single output (MISO) mode features multiple transmit antennas and a single reception antenna. The same signal is transmitted on the transmit antennas. The MISO mode is often referred to as transmit Radio Interface Procedures diversity. As for the SIMO mode, the MISO mode allows the receiver to protect against radio signal fading. The MISO mode is also used for beamforming, directed towards the mobile, by controlling different phases of the emitted signals. The multiple input multiple output (MIMO) uses multiple antennas for transmission and reception. It

improves bit rate by allowing the transmission of several different signals on the same frequency and at the same time. 4.1.5. Physical signals 4.1.5.1. Downlink The primary synchronization signal (PSS) ensures the frequency synchronization of the OFDMA signal and timing synchronization at the half-frame level. The secondary synchronization signal (SSS) provides time synchronization at the frame level. The cell-specific reference signal (RS) is a signal specific to the cell used to perform coherent demodulation of the received signal which is based on the calculation of the transfer function of the radio channel. The MBMS single frequency network reference signal (MBSFN RS) is transmitted only in the physical multicast channel (PMCH) to perform coherent demodulation of the received signal. The UE-specific RS physical signal is a specific signal to the mobile used to perform coherent demodulation of the received signal, to measure the power of the received signal and for beamforming. The positioning reference signal (PRS) is used by the mobile to determine its location from the observed time difference of arrival (OTDOA) mechanism. The channel state information reference signal (CSI RS) improves the measurement of the received signal and the interference level from that supplied from the cell-specific RS physical signal. VoLTE and ViLTE The power of the CSI RS physical signal is either transmitted to determine the level of the received signal, or suppressed to measure the level of interference. 4.1.5.2. Uplink The demodulation reference signal (DM-RS) associated with the physical uplink shared channel (PUSCH) is used for estimation and synchronization of the PUSCH physical channel. The DM-RS physical signal associated with the physical uplink control channel (PUCCH) is used for estimation and synchronization of the PUCCH physical channel. The sound reference signal (SRS) allows the eNB entity to measure the quality of the signal for the uplink, in a frequency band higher than that allocated to the mobile. This mea

surement cannot be obtained by the DM-RS physical signal because the DM-RS is associated with the PUSCH or PUCCH physical channels. The measurement performed by the eNB entity allows it to set the frequency location of the resource allocated to the mobile for the uplink direction, and the modulation and coding scheme. 4.1.6. Physical channels 4.1.6.1. Downlink The physical broadcast channel (PBCH) transmits the BCH transport channel containing the system information corresponding to the MIB message. The physical control format indicator channel (PCFICH) transmits the control format indicator (CFI) indicating the size of the physical downlink control channel (PDCCH). The physical HARQ indicator channel (PHICH) transmits the HARQ indicator (HI) which indicates a positive (ACK) or negative (NACK) acknowledgment for the uplink data received, in the physical uplink shared channel (PUSCH). Radio Interface Procedures The PDCCH physical channel transmits downlink control information (DCI): - allocation of resources and the modulation and coding scheme, for the data in the PDSCH and PUSCH physical channels; - transmission power of the PUCCH and PUSCH physical channels. The physical downlink shared channel (PDSCH) transmits the DL-SCH and PCH transport channels. The physical multicast channel (PMCH) transmits the MCH transport channel. 4.1.6.2. Uplink The physical random access channel (PRACH) contains a preamble used by the mobile when it needs to perform a random access, which is the first stage of the connection of the mobile to the eNB entity. The PUCCH physical channel uses three types of format to transport the uplink control information (UCI): - formats 1, la and 1b transport the UCI information relating to the scheduling request to obtain resource on the PUSCH physical channel and to the positive (ACK) or negative (NACK) acknowledgment, corresponding to the HARQ mechanism, for the data received on the PDSCH physical channel; - formats 2, 2a and 2b transport UCI information relating to the signal status reports for

the signal received on the PDSCH physical channel and the positive (ACK) or negative (NACK) acknowledgments; - format 3 transports the same information as format 1 by adapting it to the aggregation of radio channels introduced in Release 10. The PUSCH physical channel transmits the UL-SCH transport channel and the UCI control information. For Releases 8 and 9, the simultaneous transmission of PUSCH and PUCCH physical channels is not supported. The transmission of UCI information in the PUSCH physical channel is carried out, on the one hand, together with the transfer of traffic data or RRC VoLTE and ViLTE control, while for the transfer of aperiodic UCI information reports, on the other. For Release 10, the simultaneous transmission of the PUSCH and PUCCH physical channels is supported. The transmission of UCI information in the PUCCH physical channel is maintained when the data traffic or RRC control need to be transferred to the PUSCH physical channel. 4.2. Procedures 4.2.1. Access control 4.2.1.1. Acquisition of the PRACH physical channel The procedure of access to the eNB entity is developed for accessing the physical random access channel (PRACH) that the mobile is going to use to carry out the random access. The different physical channels and physical signals processed by the mobile for the acquisition of the PRACH physical channel can be found in Table 4.3. Physical channels Physical signals Acquisition of the parameters Frequency synchronization Time synchronization Parameter N ID (2) Time synchronization Length of the cyclic prefix Parameter NO ID Cell-Specific RS Coherent demodulation Bandwidth of the channel. for the downlink Parameter of the PHICH physical channel PCFICH Size of the PDCCH physical channel PDCCH Detection of the SI-RNTI identity PDSCH SIB1 and SIB2 system information Table 4.3. Acquisition of the PRACH physical channel Radio Interface Procedures The PSS physical signal facilitates the following functions: - frequency synchronization; - time synchronization at the level of the OFDM sym

After having withdrawn the resource elements allocated to the cell- specific RS physical signal, to the PCFICH and PHICH physical channels, the mobile can analyze the PDCCH physical channel. The PDCCH physical channel transports the information which facilitates the recovery of the System Information Base 1 and 2 (SIB1 and SIB2) messages contained in the PDSCH physical channel from the detection of the system information radio network temporary identifier (SI-RNTI). The SIB1 message provides the following information: - the bandwidth of the radio channel, for the uplink; - the configuration of the type-2 time frame; - the scheduling of the other SIB system information. The SIB2 message provides the information related to the configuration of radio resources allocated to the PRACH physical channel. 4.2.1.2. Random access The random access procedure is initialized by the mobile and is required by the following cases: - when establishing the connection to the eNB entity; - when changing the cell during the session (handover); Radio Interface Procedures - when updating timing advance (TA); - when re-establishing the connection to the eNB entity. The random access procedure is said to be with contention when the mobile chooses the used resource (PRACH channel, preamble) randomly. This occurs for the establishment or re-establishment phases of the connection. The random access procedure is said to be without contention when the eNB entity is providing the resource to be used to the mobile. This happens for the handover or the updating of the timing advance TA. 4.2.1.2.1. Random access with contention The random access procedure with contention, during the establishment or re-establishment of the connection to the eNB entity is described in Figure 4.9. PRACH (preamble) PRACH (preamble) PRACH (preamble) PDCCH (RA-RNTI) PDSCH / MAC RAR (TA, UL Grant ,TC-RNTI) PUSCH / MAC / RRC ConnectionRequest PDCCH (TC-RNTI) PDSCH / MAC (CRI) / RRC ConnectionSetup PUSCH/ MAC (C-RNTI) / RRC ConnectionSetupComplete Figure 4.9. Random acce

ss with contention The mobile transmits the preamble in the PRACH physical channel. This preamble is chosen randomly in a list communicated by the eNB entity in the SIB2 system information. VoLTE and ViLTE In case the eNB entity does not respond, the mobile retransmits the preamble while increasing the transmission power. The maximum number of retransmissions is shown by the SIB2 system information or the RRC Connection Reconfiguration message. The risk of contention is linked to the fact that several mobiles can access the same PRACH physical channel and use the same preamble. When the eNB entity receives the PRACH physical channel, it calculates the timing advance and transmits to the mobile: - the DCI control information in the PDCCH physical channel, recovered from random access RNTI (RA-RNTI) identity. The mobile retrieves the description of its data in the PDSCH physical channel; - the random access response (MAC RAR) frame containing the index of the preamble, the timing advance TA, the resource to use (UL Grant) for the transmission in the PUSCH physical channel and the temporary cell RNTI (TC-RNTI) identity. This identity is temporary as several mobiles may consider that this identity is allocated to them, thereby leading to contention. The mobile initializes its timing advance and responds with the RRC Connection Request message containing: - the shortened temporary mobile subscriber identity (S-TMSI), if the mobile is already attached; - a random number in the contrary case. When the eNB entity receives the RRC Connection Request message, it transmits to the mobile: - the DCI control information in the PDCCH physical channel, recovered from the TC-RNTI identity. The mobile retrieves the description of its data in the PDSCH physical channel; - the header MAC RAR containing the UE CRI (contention resolution identity) control element. This control element reproduces the identity in the RRC Connection Request message, thereby resolving the contention issue; - the RRC ConnectionSetup message. The TC-RNTI id

entity becomes the C-RNTI, the definitive identity allocated to mobile. Radio Interface Procedures The mobile indicates its C-RNTI in the control element of the MAC frame and confirms the connection through the RRC ConnectionSetupComplete message. 4.2.1.2.2. Random access without contention The random access procedure without contention, when changing the cell during the session, is described in Figure 4.10. During the procedure of handover based on the X2 interface, the target eNB entity provides the characteristics of the radio interface to the source eNB entity in a message X2-AP HANDOVER REQUEST ACK. This message contains the information element handover command which specifies the preamble that the mobile must use during the random access procedure to the target eNB entity. The source eNB entity forwards the information element handover command in the RRC Connection Reconfiguration message which triggers the handover for the mobile. Source Target RRC ConnectionReconfiguration X2-AP HANDOVER REQUEST ACK (preamble) (preamble) PRACH (preamble) PRACH (preamble) PRACH (preamble) PDCCH (RA-RNTI) PDSCH / MAC RAR (TA, UL Grant ,TC-RNTI) PUSCH / RRC ConnectionReconfigurationComplete Figure 4.10. Random access without contention in case of changing the cell during the session The random access procedure comprises as before the preamble transmission by the mobile and the MAC RAR frame by the eNB entity. VoLTE and ViLTE The mobile connection is finalized when the mobile transmits the RRC Connection Reconfiguration Complete message. 4.2.2. Data transfer 4.2.2.1. Scheduling Data scheduling is the operation carried out by the eNB entity which consists of providing resource blocks (RB) to the mobiles and in controlling transmission power, for the downlink and the uplink direction. In the time domain, the allocation of the resources corresponds to a sub- frame of a TTI (Transmission Time Interval) duration of a millisecond, which represents two resource blocks (RB). In the frequency domain, the eNB entity can give the mobile

several resource blocks, each block corresponds to a frequency band of 180 kHz, formed from an orthogonal frequency division multiplexing (OFDM) of 12 sub-carriers spaced 15 kHz or 24 sub-carriers spaced 7.5 kHz. In the space domain, the mobile can receive and transmit different resource blocks, simultaneously and in the same frequency band, thanks to the MIMO mechanism. For the downlink, the scheduling algorithm takes into account the following information: - the information recovered by the mobiles, in relation to the channel quality indicator (CQI), to the precoding matrix indicator (PMI) and to the number of spatial layers from the signal received on the PDSCH physical channel; - the information recovered by the adjacent eNB entities under the inter cell interference coordination (ICIC) mechanism, in relation to the relative narrowband tx power (RNTP) power transmission; - the information transmitted by the MME entity in relation to the category of the mobile and to the QoS class identifier (QCI) level; - the local information related to the state of the memory, to the need of retransmission, to the state of available resources and to the measure intervals constructed for the mobile. Radio Interface Procedures For the uplink, the scheduling algorithm takes into account the following information: - the information recovered by the mobiles, in relation to the power headroom report (PHR) and the buffer status report (BSR); - the information recovered by the adjacent eNB entities under the ICIC mechanism, in relation to the interference overload indication (IOI) and to high interference indication (HII); - the information recovered by the MME entity in relation to the category of the mobile and to the QCI level; - the local information related to the level of quality measured on the SRS physical signal, to the need for retransmission, to the state of available resources and to the measure intervals constructed for the mobile. The results of the scheduling make up the DCI control information communicated in the P

DCCH physical channel. The DCI control information in formats 0 and 4 facilitates the scheduling of the data in the PUSCH physical channel. The DCI control information in formats 1, 1A, 1B, 1C, 1D and 2, 2B, 2C facilitates the scheduling of data in the PDSCH physical channel. The DCI control information in format 3 facilitates the transmit power control (TPC) of the PUSCH and PUCCH physical channels. The allocation of the resources is shown by the radio network temporary identifier (RNTI) specific to a mobile (C-RNTI, SPS C-RNTI and TPC- RNTI) or to a set of mobiles (P-RNTI, RA-RNTI, TC-RNTI and SI-RNTI). In the FDD mode, the resource allocation for the uplink, signaled in the PDCCH physical channel of the sub-frame n, is applicable to the sub-frame n+4 ms. In the TDD mode, the shift between signaling in the PDCCH physical channel and transmission in the PUSCH physical channel depends on the configuration of the time frame and the number of the sub-frame of the PDCCH physical channel (Table 4.4). 132 VoLTE and ViLTE Configuration of the Number of the sub-frame of the PDCCH physical channel time frame Table 4.4. Shift between signaling in the PDCCH channel and transmission in the PUSCH channel For configuration 0 of the time frame, the shift between signaling in the PDCCH physical channel and transmission in the PUSCH channel depends on the value of the two bits Uplink Index of DCI control information in formats 0 and 4: - for the most significant bit at ONE and the least significant bit at ZERO, the shift is provided in Table 4.5; - for the most significant bit at ZERO and the least significant bit at ONE, the shift is fixed at 7 ms; - for the most significant bit at ONE and the least significant bit at ONE, the mobile can transmit in the two sub-frames previously defined. Configuration of the Number of the sub-frame of the PDCCH physical channel time frame 0123456789 Table 4.5. Shift for configuration 0 of the time frame 4.2.2.2. DRX function The discontinuous reception (DRX) function determines the moments when

the mobile must analyze the PDCCH physical channel, which allows it Radio Interface Procedures to avoid processing this channel every millisecond and in this way to preserve the consumption of its battery (Figure 4.11). shortDRX-Cycle onDurationTimer longDRX-Cycle onDurationTimer drx-InactivityTimer drxShortCycleTimer Figure 4.11. DRX function For a color version of the figure, see www.iste.co.uk/perez/volte.zip An inactivity timer drx-Inactivity Timer of the DRX function is triggered when the mobile receives data on the PDCCH physical channel. This timer is reinitialized each time that the mobile receives data on the PDCCH physical channel. When the timer drx-Inactivity Timer expires, the mobile starts an optional period for the short cycle corresponding to the timer drxShort Cycle Timer. During the short cycle, the mobile analyzes the PDCCH physical channel in a duration corresponding to the timer onDurationTimer. During the short cycle, the triggering of the active period is provided by the following formula: [(SFN * 10) + (sub-frame number)] modulo (shortDRX-Cycle) = (drxStartOffset) modulo (shortDRX-Cycle) When the timer drxShort Cycle Timer expires, the mobile starts the long cycle period for which the triggering of the active period is provided by the following formula: [(SFN * 10) + (sub-frame number)] modulo (longDRX-Cycle) = drxStartOffset The parameter configuration of the DRX function is indicated in the RRC messages of establishment or re-establishment of the connection. VoLTE and ViLTE The eNB entity indicates the activation of the DRX function while using the DRX control element in the MAC frame. The timer drx-Retransmission Timer defines an inactive period of the DRX function during an expected HARQ retransmission. The timer drx-Retransmission Timer starts after the round trip HARQ timer associated with the HARQ retransmission. 4.2.2.3. SPS function The semi-persistent scheduling (SPS) function is applied to the applications that have a periodic character, for example the voice which produces a b

lock every 20 milliseconds. The SPS function allows the eNB entity to avoid announcing the DCI control information in the PDCCH physical channel. The SPS function is configured by the eNB entity in RRC messages of establishment or re-establishment of the connection or establishment of Data Radio Bearer (DRB) containing the following parameter: - SPS C-RNTI identifier; - allocation periodicity, for example a transmission every 20 sub-frames for the voice; - number of the HARQ process of retransmission in case of errors, for the downlink. When the SPS function has been configured, the eNB entity uses the DCI control information transmitted in the PDCCH physical channel to activate or release it. When the SPS function has been configured, the mobile must, nevertheless, continue the analysis of the PDCCH physical channel, for the defined sub-frames by the DRX function to detect the DCI control information in relation to the allocation release. When the SPS function has been activated for the downlink, the sub- frame allocation of the PDSCH physical channel corresponds to the following formula: Radio Interface Procedures (10 * SFN + sub-frame) = [(10 * SFNstart time + subframestart time) + N * semiPersistSchedIntervalDL modulo 10240 The SFN start time and sub frame start time parameters correspond to the values of the frame and sub-frame number when the SPS function has been activated. The semiPersistSchedIntervalDL parameter corresponds to the allocation periodicity of resources for the downlink. When the SPS function has been activated for the uplink, the sub-frame allocation of the PUSCH physical channel corresponds to the following formula: (10 * SFN + sub-frame) = [(10 * SFNstart time + subframestart time) + N * semiPersistSchedIntervalUL + Subframe_Offset * (N modulo 2)] modulo 10240 The semiPersistSchedIntervalUL parameter corresponds to the allocation periodicity of resources for the uplink. The Subframe_Offset parameter is optional and its value is equal to ZERO for the FDD mode and is indicated in Table 4.6

for the TDD mode. Configuration of the Number of the subf-rame during Sub-frame_Offset sub-frame the SPS activation sans objet 2 and 7 3 and 8 2 and 3 sans objet sans objet Table 4.6. Value of optional parameter Subframe_Offset 136 VoLTE and ViLTE 4.2.2.4. HARQ function In case of error, the retransmission implements two mechanisms: - the automatic repeat request (ARQ) mechanism elaborated by the RLC layer; - the hybrid ARQ (HARQ) mechanism established at the physical layer level, under the MAC layer control. The ARQ mechanism takes over from the HARQ mechanism if the retransmissions at the physical layer level have failed. The ARQ is applied only to the flow of traffic and signaling using the acknowledged mode (AM) of the RLC protocol. On the other hand, taking its speed into consideration, the HARQ mechanism is applied to the flow using the AM mode and unacknowledged mode (UM) of the RLC protocol. A different redundancy version facilitates the retransmission of selected data: - for the chase combining mechanism, the retransmission contains the same sequence. The improvement of the error corrector code is due to the increase of the signal to noise ratio; - for the incremental redundancy mechanism, the retransmission contains some different sequences. The improvement of the error corrector code is due to the increase of the number of redundancy bits. The first transmission corresponding to the redundancy version (RV0) contains the initial sequence to transmit and redundancy bits generated by the error corrector code, whose number is determined by the coding rate. The HARQ mechanism functions with a window of one data unit. When a transport block is transmitted, the transmitter must wait for the reception of the acknowledgement before sending the following transport block. This disposition penalizes the rate of the mobile and this restriction is removed thanks to the implementation of several HARQ parallel processes. Radio Interface Procedures The combination of HARQ parallel processes and of the retransmission me

chanism provokes a de-sequencing of the blocks received by the destination. The RLC layer assures the re-sequencing of different blocks received. For the downlink, the HARQ mechanism is adaptive because the retransmission can modify the transmission parameters. For the downlink, the HARQ mechanism is asynchronous because a HARQ process transmission is not constrained by an imposed period. For the uplink, the HARQ mechanism is adaptive or non-adaptive. It is non-adaptive if the retransmission must use the same initial transmission parameters. For the uplink, the HARQ mechanism is synchronous because the HARQ process transmission must be done according to a defined timing. 4.2.2.4.1. Data transfer for uplink The number of HARQ entities for transmission mode 2 (mode with MIMO) is double that of transmission mode 1 (mode without MIMO), because one HARQ entity is allocated to each transport block: - one transport block is used for transmission mode 1; - two transport blocks are used for transmission mode 2. In case of the carrier aggregation (CA), a HARQ entity is developed for each radio channel. For the FDD mode, by the HARQ entity, the HARQ process number has a fixed value: - value equal to 8 for transmission mode 1; - value equal to 16 for transmission mode 2. Figure 4.12 described the HARQ mechanism for the transmission mode 1 in the FDD mode. The transmission moments for each HARQ process is synchronous, with an 8 ms periodicity. 138 VoLTE and ViLTE The PHICH physical channel transports the HARQ indicator (ACK or NACK bits) for each transport block, 4 milliseconds after the transmission of the data in the PUSCH physical channel. Under a HARQ process, if a transport block is acknowledged, a new transport block can be transmitted 8 milliseconds later. If a transport block is not acknowledged, the RV1 redundancy version is transmitted 8 milliseconds later. The HARQ processes used depend on the transmission moment of transport blocks. The 8 HARQ processes are systematically used if the eNB entity allocates every mil

lisecond of resources to the mobile. Process Transmission instants of data on PUSCH physical channel number Reception instants of ACK/NACK on PHICH physical channel Figure 4.12. HARQ function in the FDD mode Data transfer for uplink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip For the TDD mode, the HARQ process number, under the HARQ entity, depends on the type of configuration of the time frame and transmission mode (Table 4.7). Radio Interface Procedures 139 Configuration of the time frame 00123456 Number of sub-frames / uplink Transmission mode 1 042321 Transmission mode 2 Table 4.7. HARQ process number in the TDD mode Data transfer for uplink The shift which is given in milliseconds, between the transmission of a block in the PUSCH physical channel and the reception of the HI indicator in the PHICH physical channel, is shown in Table 4.8. Number of the sub frame having received HI Configuration of the time frame Table 4.8. Shift between the PUSCH and PHICH physical channels Figure 4.13 describes the HARQ mechanism for configuration 1 of the time frame in the TDD mode. 140 VoLTE and ViLTE Transmission instants of data on PUSCH physical channel Sub-frame number Reception instants of ACK/NACK on PHICH physical channel process number Figure 4.13. HARQ function in the TDD mode, for configuration 1 Data transfer for uplink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip The transport block transmitted in sub-frame 2 or 7 (sub-frame 3 or 8 respectively) receives the HI indicator with a shift of 4 milliseconds (6 milliseconds respectively). Under a HARQ process, if a transport block is acknowledged, a new transport block can be transmitted 10 milliseconds later. If a transport block is not acknowledged, the RV1 redundancy version is transmitted 10 milliseconds later. 4.2.2.4.2. Data transfer for downlink Contrary to the uplink, a single HARQ entity is developed independently of the transmission mode. In case of the aggregation of radio channels, a HARQ entity is develo

ped for each radio channel. As the process number is shown in the DCI control information, the number of open HARQ processes is not fixed and depends on transmission needs. Radio Interface Procedures For the FDD mode, the number of open HARQ processes is less than or equal to 8. The eight HARQ processes are only open if the eNB entity allocates resources to the mobile every millisecond. The PUCCH or PUSCH physical channel transports the ACK or NACK indicator with a shift of 4 milliseconds after the transmission of the transport block in the PDSCH physical channel. Under a HARQ process, if a transport block is acknowledged, a new transport block can be transmitted. If a transport block is not acknowledged, the RV1 redundancy version is transmitted. In the two cases, the moment used by the HARQ process is not imposed by timing as is the case for the uplink. For the TDD mode, the HARQ process number, by the HARQ entity depends on the configuration of the time frame (Table 4.9). Configuration of the time frame Number of sub-frames downlink HARQ process number Table 4.9. HARQ process number in the TDD mode data transfer for the downlink Table 4.10 shows the number of ACK/NACK bits to be transmitted, through the HARQ entity in the PUCCH physical channel, depending on the configuration of the time frame, for transmission mode 1. The indicated values are doubled in the case of transmission mode 2. Configuration of the time frame Number of sub-frames for the PUCCH physical channel Number of ACK / NACK bits Number of bits through sub-frame Table 4.10. Number of ACK / NACK bits to be transmitted in the PUCCH physical channel for the TDD mode and the transmission mode 1 142 VoLTE and ViLTE In certain cases, the capacity of the PUCCH physical channel is insufficient for recovering all the ACK / NACK information: format la has a capacity of one bit; format 1b has a capacity of 2 or 4 bits. Two methods are defined to reduce the number of bits: coupling carried out from a logical AND of various ACK / NACK information: - the NACK

information of a transport block involves the retransmission of all the transport blocks which are linked to it, - in case an ACK / NACK bit is generated by a sub-frame, the coupling generates a bit transmitted in format 1a, in case two ACK / NACK bits are generated by the sub-frame, the coupling generates two bits transmitted in format 1b (Figure 4.14); Transmission instants of data on PDSCH physical channel Sub-frame number Reception instants of ACK/NACK on PUSCH / PUCCH physical channel 0123456789012345 8 ACK/ NACK bits Figure 4.14. Coupling ACK / NACK information Configuration 2 of the time frame Data transfer for downlink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip multiplexing of ACK / NACK information in the PUCCH physical channel: Radio Interface Procedures format 1b is used for transporting 4 bits of information, each bit corresponding to ACK / NACK information generated by a sub-frame, - in case two bits are generated by the sub-frame, the two ACK / NACK corresponding bits are linked by a logical AND (Figure 4.15), the NACK information of a transport block of a sub-frame involves the retransmission of the other transport block of the same sub-frame. Transmission instants of data on PDSCH physical channel Sub-frame number Reception instants of ACK/NACK on PUSCH / PUCCH physical channel >0123456789012345 8 ACK / NACK bits Figure 4.15. Multiplexing ACK / NACK information Configuration 2 of the time frame data transfer for uplink. For a color version of the figure, see www.iste.co.uk/perez/volte.zip 4.2.2.5. TTI bundling function Real-time applications like the voice are sensitive to the packet jitter. The RTP protocol facilitates the correction of the jitter introduced in the network, with a maximum value of 40 ms and packets having a jitter greater than this value are suppressed. The retransmission mechanism of the HARQ function results in an increase of the packet jitter for each retransmission (for example 8 ms in the FDD mode). The HARQ mechanism may be counter-productive in

this case. 144 VoLTE and ViLTE The TTI bundling function consists of transmitting, in four consecutive sub-frames, four redundancy versions, without waiting for the return of HI information, in order to reduce the value of the jitter. The same modulation and coding scheme and the same frequency band are used for transmission of the four redundancy versions. The TTI bundling function is limited to the transmission for the uplink. The TTI bundling function is not supported for the aggregation of radio channels. In the FDD mode, the number of HARQ processes is reduced to 4 (Figure 4.16). The HI information is transmitted 4 ms after the last redundancy version. If the HI information corresponds to a NACK, the four redundancy versions are retransmitted with a 16 ms delay. Transmission instants of data on PUSCH physical channel number process Reception instants of ACK/NACK on PHICH physical channel Figure 4.16. TTI bundling function in the FDD mode For a color version of the figure, see www.iste.co.uk/perez/volte.zip In the TDD mode, the TTI bundling function is only applicable in configurations 0, 1 and 6 of the time frame. The HARQ processes number is limited to 3 for the configurations 0 and 6 and to 2 for the configuration 1 (Figure 4.17). Radio Interface Procedures Transmission instants of data on PUSCH physical channel Sub-frame number Reception instants of ACK/NACK on PHICH physical channel L01234567890123456789012345678901 process number Figure 4.17. TTI function bundling in the TDD mode for configuration For a color version of the figure, see www.iste.co.uk/perez/volte.zip Service Profiles 5.1. Subscription data 5.1.1. Subscription to the EPS network When subscribing to the evolved packet system (EPS), the user is assigned a private international mobile subscriber identity (IMSI) which is associated with a profile on the telephone service (Figure 5.1). User profile APN-Configuration-Profile APN-Configuration APN-Configuration-Profile PDN-Type Service-Selection Subscriber-Status Network-Access-Mode EPS-Subscri

bed-QoS Profile MSISDN VPLMN-Dynamic-Address-Allowed STN-SR ICS-Indicator Figure 5.1. Subscription data to EPS network The home subscriber server (HSS) stores the service profile data that is transmitted to the mobility management entity (MME) when attaching the mobile or when changing the profile service. The "PDP-Type" field indicates the version of IP (Internet Protocol): IPv4, IPv6, IPv4 or IPv6, IPv4 and IPv6. VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. 148 VoLTE and ViLTE The "service-selection" field contains the access point name (APN): ims in the case of voice or conversational video service, SOS in the case of emergency call. The "EPS-subscribed-QoS profile" field indicates the value of the QoS class identifier (QCI) and the allocation and retention priority (ARP). The "VPLMN-dynamic-address-allowed" field indicates whether roaming is allowed or not. The "subscriber-status" field indicates whether the telephone service is allowed or not. The "network-access-mode" field indicates whether the telephone service is available in packet-switched (PS) and circuit-switched (CS) mode or in PS mode only. The "MSISDN" field contains the mobile subscriber number. The "STN-SR" field contains the session transfer number for SRVCC, used during the PS-CS inter-system handover, in the case of the implementation of the e-SRVCC function (enhanced Single Radio Voice Call Continuity). The "ICS-indicator" field indicates whether IMS centralized services are available or not. 5.1.2. Subscription to the IMS network When subscribing to the IP multimedia subsystem (IMS), the user is assigned a IMS private user identity (IMPI) to which are associated one or more service profiles (Figure 5.2). The HSS entity stores data relating to a user's service profile which is transmitted to the serving call session control function (S-CSCF) when the registration of the user or when a change of the service pr

ofile. Each service profile includes one or more IMS public user identity (IMPU) in the form of an SIP URI or TEL URI and a service logic in the form of initial filter criteria (iFC) (Figure 5.2). Service Profiles The field "core network service authorization" of the service profile structure contains an integer number representing the type of media (audio, video) that the user has the right to negotiate in the session description protocol (SDP) message (Figure 5.2). Initial Filter Criteria User profile Priority Private User Identity 0 to 1 1 to n Service Profile n Trigger Point Service Profile 2 1 to n Service Point Trigger n Service Profile 1 Service Point Trigger 2 1 to n Public Identity n Service Point Trigger 1 Public Identity 2 Request URI SIP Method Public Identity 1 SIP Header Session Case Session Description 0 to n Initial Filter Criteria n Initial Filter Criteria 2 Application Server Initial Filter Criteria 1 SIP URI Default Handling Core Network Service Authorization Service Information Figure 5.2. Subscription data to the IMS network The first field of iFC data is priority, which determines the order in which the criteria need to be evaluated. The next field relates to the trigger point, which is a collection of filters (service point triggers) Each filter consists of a logical operation carried out on the basis of the following parameters: Request-URI: the value of the uniform resource identifier (URI) of the request; - SIP Method: the type of method of the request; - SIP Header: the content of the headers; 150 VoLTE and ViLTE - Session Case: the type of call (outgoing or incoming), for a registered or unregistered mobile; - Session Description: the content of the fields of the SDP message. The iFC data also contain the public identity of the telephony application server (TAS) to which the S-CSCF entity transfers the request if the conditions are all fulfilled. The field "default handling" defines the treatment that needs to be applied to the request (continuation or cessation) if the S-CSCF entity c

annot contact the telephony application server. The field "service information" contains data which are transparent for the HSS and S-CSCF entities. These data are handled only by the telephony application server. 5.2. VoLTE profile service 5.2.1. Supplementary telephone services The user agent (UA) indicates that it supports supplementary telephone service by adding in the REGISTER and INVITE requests, the parameter g.3gpp.icsi-ref associated with the header Contact. Contact: <sip:192.0.2.101>;expires=600000;+g.3gpp. .icsi- ef="urn:urn-7:3A3gpp-service-ims.icsi.mmtel" - Table 5.1 lists the supplementary telephone service. The shaded boxes represent supplementary telephone service described in this chapter. 5.2.1.1. Communication diversion CDIV consists of diverting a call (from Alice to Bob) to a different destination (Carol). In this scenario, CDIV is implemented by the telephony application server associated with the callee's (i.e. Bob's) S-CSCF entity. Service Profiles (Communication DIVersion) (Originating Identification Presentation) (Originating Identification Restriction) (Terminating Identification Presentation) (Terminating Identification Restriction) (Message Waiting Indication) (Communication hold) (CONFerence calling) (Communication Waiting) (Communication Barring) (Explicit Communication Transfer) (Malicious Communication Identification) (Completion of Communications to Busy Subscriber) (Completion of Communications on No Reply) (Advice Of Charge) (Closed User Group) (Customised Alerting Tone) (Customised Ringing Signal) (Flexible Alerting) Table 5.1. Supplementary telephone service 152 VoLTE and ViLTE 5.2.1.1.1. CFU Communication forwarding unconditional (CFU) consists systematically forwarding an incoming call to another destination. However, the outgoing calls initiated by Bob's UA entity are not affected by this service. Optionally, a subscription service may be offered to Bob, giving him an indication that CFU is active. This information is transmitted to him when Bob initializes a communicatio

n. The different exchanges relating to CFU are shown in Figure 5.3. S-CSCF P-CSCF Carol SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP 181 Call Is Being Forwarded SIP 181 Call Is Being Forwarded SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP 200 OK (SDP Carol) SIP 200 OK (SDP Carol) SIP 200 OK (SDP Carol) SIP 200 OK (SDP Carol) SIP 200 OK (SDP Carol) SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 5.3. CFU Service Profiles 1) The INVITE request transmitted by Alice's UA entity is received by Bob's S-CSCF entity. The INVITE message contains the SDP message of Alice's UA entity. 2) As the result of the iFC data handling is positive, the request is transmitted to the telephony application server. 3), 4) The telephony application server responds to Alice's UA entity with the 181 Call Is Being Forwarded. This message alerts Alice's UA entity that the call has been transferred. 5), 6), 7) The telephony application server generates an INVITE request, sent to Carol's UA entity. This request includes the SDP message from the INVITE request received from Alice's UA entity. 8), 9), 10) Carol's UA entity responds to the telephony application server with the message 200 OK. The response contains the SDP message of Carol's UA entity. 11), 12) The telephony application server transfers the SDP message from Carol's UA entity in the message 200 OK transmitted to Alice's UA entity. 13), 14) The ACK request from Alice's UA entity acknowledges receipt of the message 200 OK from the telephony application server. 15), 16), 17) The ACK request from the telephony application server acknowledges receipt of the message 200 OK from Carol's UA entity. The media flow is then established between Alice's and Carol's UA entities. 5.2.1.1.2. CFB Communication forwarding on busy user (CFB) consists of forwarding an incoming call when the callee (Bob) is busy. The different exchanges relating to CFB are shown in Figure 5.4. 154 VoLTE and ViLTE 1) to 5) The INVITE request transmitted by Alice's UA entity to Bob's UA enti

ty passes through the telephony application server associated with Bob's S-CSCF entity. 6), 7), 8) Bob's UA entity responds with the message 486 Busy Here. This message is intercepted by the telephony application server, which implements communication forwarding to Carol's UA entity. The following exchanges are identical to those shown for CFU (3 to 17). S-CSCF P-CSCF Carol SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP 486 Busy Here SIP 486 Busy Here SIP 486 Busy Here Figure 5.4. CFB 5.2.1.1.3. CFNR Communication forwarding on no reply (CFNR) involves forwarding an incoming call in the case of the lack of a response from the callee (Bob). The different exchanges relating to CFNR are shown in Figure 5.5. 1) to 5) The INVITE request submitted by Alice's UA entity is received by Bob's UA entity. 6) to 10) On receiving the INVITE request, Bob's UA entity responds with the message 180 Ringing. This message passes through the telephony application server which starts a timer. Service Profiles 11), 12) At the expiration of the timer, the TAS entity responds to Alice's UA entity with the message 181 Call Is Being Forwarded. This message can alert Alice's UA entity that her call was being transferred. 13), 14), 15) The TAS entity stops the ringing by sending the CANCEL request to Bob's UA entity. 16), 17), 18) Bob's UA entity responds with the 200 OK message to the CANCEL request. S-CSCF P-CSCF Carol SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 181 Call Is Being Forwarded SIP 181 SIP CANCEL SIP CANCEL SIP CANCEL SIP 200 OK SIP 200 OK SIP 200 OK SIP 487 Request Terminated SIP 487 Request Terminated SIP 487 Request Terminated SIP ACK SIP ACK SIP ACK Figure 5.5. CFNR VoLTE and ViLTE 19), 20), 21) Bob's UA entity responds with the message 487 Request Terminated to the INVITE request. 22), 23), 24) The A

CK request from the telephony application server acknowledges the receipt of the message 487 Request Terminated from Carol's UA entity. The following exchanges are identical to those described for CFU (5 to 5.2.1.1.4. CFNL Communication forwarding on not logged-in (CNFL) consists of diverting an incoming call if the callee (Bob) is not logged in with the S-CSCF entity. The different exchanges relating to CFNL are identical to those for CFU. 5.2.1.1.5. CD Communication deflection enables the callee (Bob) to deflect a call if he does not want to answer the caller (Alice). The different exchanges relating to CD are shown in Figure 5.6. S-CSCF P-CSCF Carol SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP INVITE (SDP Alice) SIP 302 Moved Temporarily SIP 302 Moved Temporarily SIP 302 Moved Temporarily Figure 5.6. CD Service Profiles 1) to 5) The INVITE request submitted by Alice's UA entity is received by Bob's UA entity. 6), 7), 8) Bob's UA entity responds with the message 302 Moved Temporarily. The response contains Carol's URI, to which the call should be forwarded. The response is intercepted by the TAS entity, which diverts the communication to Carol's UA entity. The following exchanges are identical to those described for CFU (5 to 17). 5.2.1.2. Identification presentation 5.2.1.2.1. OIP and OIR Originating identification presentation (OIP) consists of presenting the callee (Bob) with the identification of the caller (Alice), asserted by the IMS network. Alice's UA inserts into the INVITE request the header P P-Preferred- Identity, containing the public identity IMPU. INVITE sip:bob@homeB.net SIP/2.0 P-Preferred-Identity:<sip:alice@home1.net> The P-CSCF (Proxy-CSCF) entity replaces this header with the header P-Asserted-Identity. The value of this header is presented to Bob's UA entity if the identity of Alice was registered. Otherwise, the P-CSCF entity inserts in the header P-Asserted-Identity Alice's identity registered by default. INVITE sip:bob@homeB.net SIP/2.0

P-Asserted-Identity:<sip:alice@homel.net> Originating identification restriction (OIR) consists of hiding Alice's identification from the callee (Bob). 158 VoLTE and ViLTE Alice's UA entity can temporarily mask the presentation of her identity. It has to perform the following operations: - it has to fill in the header From with the following value: <sip:anonymous@anonymous.invalid> - it has to indicate the value id in the header Privacy SO that the identity present in the header P-Asserted-Identity - is not presented to INVITE sip: :bob@homeB.net SIP/2.0 From: "anonymous" <sip:anonymous@anonymous.invalid>;tag=xy: P-Asserted-Identity:<sip:alice@homel.net> Privacy:id If Alice has subscribed to OIR, her telephony application server has to insert the value id into the header Privacy. It also has to modify the value of the header From to erase Alice's identity. If Alice has subscribed to OIR, Alice's UA entity can raise the restriction temporarily by inserting the value none in the header Privacy. If Bob has not subscribed to OIP or if the header Privacy has the value id, his telephony application server has to remove the header P-Asserted-Identity, modify the value of the header From and remove Alice's identity. 5.2.1.2.2. TIP and TIR Terminating identification presentation (TIP) consists of showing Alice, in the response 183 Session Progress, the identity of the callee (Bob or Carol in the case of communication forwarding), certified by the IMS network. SIP/2.0 183 Session Progress P-Asserted-Identity: - <sip:bob@homeB.net> Service Profiles If Alice has not subscribed to TIP or if the messages received contain the header Privacy with the value id, her telephony application server has to remove the header P-Asserted-Identity - and modify the value of the header From, deleting Bob's or Carol's identity. Terminating identification restriction (TIR) consists of hiding Bob or Carol's identity from Alice. The callee's UA entity (i.e. Bob's or Carol's) can temporarily mask the presentation of his/her identity by adding th

e value id to the header Privacy in the response. If the callee (Bob or Carol) has subscribed to TIR, their telephony application server has to insert the header Privacy with the value id. If the callee (Bob or Carol) has subscribed to TIR, they can temporarily raise the restriction by indicating the value none in the header Privacy. 5.2.1.3. Message waiting indication Message waiting indication (MWI) enables the telephony application server to indicate that a communication has occurred and that a voicemail (for instance) has been recorded. In this case, the TAS entity fulfills the function of a voicemail messaging service. An MWI is transmitted if the user has subscribed to the MWI service. Alice's UA entity transmits a SUBSCRIBE request to subscribe to the MWI service. This message contains the header event with the value message-summary. It indicates in the header Accept the type of message body (value application/simple-message-summary). SUBSCRIBE sip:Alice@homeA.net SIP/2.0 Event: message-summary Accept: pplication/simple-message-summary The request is transmitted to the telephony application server by the S-CSCF entity following the iFC data processing. 160 VoLTE and ViLTE The telephony application server verifies that the subscription for Alice's identity, contained in the header P-Asserted-Identity, is authorized and responds with 200 OK. Otherwise, the response is 403 Forbidden. When the subscription has been successful, the telephony application server immediately sends a NOTIFY request to synchronize the current state of the messages waiting. This initial notification contains only brief information about the recorded messages. NOTIFY sip:Alice@homeA.net SIP/2.0 Subscription-State: active; expires=86399 Event: message-summary Content-Type: application/simple-message-summary Content-Length: (...) Messages-Waiting: yes Message-Account: sip:Alice@homeA.net Voice-Message: 2/1 (1/0) Video-Message: 0/1 (0/0) The message body of the NOTIFY request contains the following fields: - Message-Account: this field i

message. 13) to 16) Alice's UA entity sends a re-INVITE to Bob's UA entity to resume the parked communication. Recovery is achieved by modifying the attributes of the media flow in the SDP message (a=sendrecv). 17) to 20) Bob's UA entity responds positively with the message 200 20) to 24) Alice's UA entity acknowledges the response with the ACK message. 5.2.1.5. Conference The CONF service is provided by an application server comprising the multimedia resource function controller (MRFC) and MRF processor (MFRP). The MRFP entity enables the media flows to be added together. The MRFC entity plays the part of a UA entity and controls the MRFP entity. The different exchanges relating to establishing the conference service are shown in Figure 5.8. Two UA entities (Alice and Bob) are communicating. Alice decides to invite Carol and to activate the conference service. Alice puts Bob on hold, initializes a session with Carol, establishes a session with the conference bridge (MFRP) and transfers the two sessions established with Bob and Carol to the conference bridge. When Alice's UA entity has established the sessions with Bob, Carol and the conference bridge, she begins the transfer of the session established with Bob to the conference bridge by sending the request REFER to the MRFC entity. Service Profiles The REFER request includes the header Refer - to containing the references of the dialog initialized with Bob's UA entity (Bob's URI, header Call - Id, parameters tag in the headers From and To). Alice P-CSCF S-CSCF P-CSCF Carol Session established between Alice and Bob Audio flow Alice places Bob on HOLD Session established between Alice and Carol Audio flow Session established between Alice and conference bridge Audio flow SIP REFER SIP REFER SIP REFER SIP 202 SIP 202 SIP 202 SIP ACK SIP ACK SIP ACK Transfer of the session established between SIP INVITE Alice and Bob to the conference bridge SIP INVITE SIP INVITE SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP NOTIFY SIP NOTIFY SIP NOTIFY Audio flow SIP 200 SIP

200 SIP 200 Clearing of the session established between Alice and Bob Transfer of the session established between Alice and Carol to the conference bridge Audio flow Clearing of the session established between Alice and Carol Figure 5.8. CONF 164 VoLTE and ViLTE The MRFC entity sends a NOTIFY request to Alice's UA entity to indicate that the transfer has been activated. The header Subscription- State assumes the value active. The MRFC entity initializes an INVITE request to Bob's UA entity, using the parameters communicated in the REFER request in the header Replaces. The session is established between Bob's UA entity and the conference bridge. The MRFC entity sends a NOTIFY request to Alice's UA entity to communicate that the transfer has been terminated. The header Subscription-State assumes the value terminated. Alice's UA entity sends a BYE request to Bob's UA entity to release the previously-established session. 5.2.1.6. Communication waiting Communication waiting (CW) gives information to the caller telling them that the callee is on a different communication but that he has been notified of the call. Two possible scenarios may occur: - if the telephony application server knows the callee's status and if the service is activated (case 1), it inserts the communication waiting indication into the INVITE request sent to the callee; - otherwise (case 2), the TAS entity is informed of the situation in the response given by the callee. The different exchanges relating to communication waiting, for case 1, are shown in Figure 5.9. 1), 2), The INVITE request containing the SDP message of the caller is transferred to Bob's TAS entity. 3), 4), 5) The telephony application server adds a second XML message (application/vnd. 3gpp. CW+xml) giving the communication waiting indication, to the message body containing an SDP message (application/sdp) in the INVITE request, received from the S-CSCF entity. Service Profiles The telephony application server indicates in the header Content- Type that multiple messages appear in

the message body (value multipart/mixed) S-CSCF P-CSCF SIP INVITE (SDP) SIP INVITE (SDP) SIP INVITE (SDP / XML) SIP INVITE (SDP / XML) SIP INVITE (SDP / XML) SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing SIP 180 Ringing (Alert-Info) SIP 180 Ringing (Alert - Info) SIP 200 OK SIP 200 OK SIP 200 OK SIP 200 OK SIP 200 OK SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 5.9. CW The telephony application server also includes in this header a parameter boundary corresponding to the boundary between the messages (value boundary1). 166 VoLTE and ViLTE -boundary1 Content-Type application/sdp (SDP message) -boundary1 Content-Type: application/vnd.3gpp.cw+xml <?xml version="1.0"? <ims-cw xmlns="urn:3gpp:ns:cw:1.0"> <communication-waiting-indication/: </ims-cw> -boundary1- 6), 7), 8) On receiving the message 180 Ringing, the telephony application server implements the CFNR, to transfer the call to a third party, in case Bob does not pick the waiting communication up. 9), 10) To the message 180 Ringing received from the P-CSCF entity, the TAS may optionally add the indication to the caller of a call waiting in the header Alert-Info (value urn:alert: service: call-waiting). 11) to 15) Bob's UA entity decides to take the call and end the current call or park his correspondent, and responds to the INVITE request with the message 200 OK. 16) to 20) The caller's UA entity caller acknowledges the 200 OK response with the ACK message. In the second case, the telephony application server relays the INVITE request, without enriching the message body. However, as before, it inserts the header Alert-Info into the response 180 Ringing. 5.2.1.7. Communication rejection 5.2.1.7.1. ICB Incoming communication barring (ICB) enables the callee (Bob) to reject an incoming call belonging to a certain category of communication. The rule may include the URI of the caller, present in the header P-Asserted- Identity or Referred- - By (in the case of call forwarding). Bob's telephony application server responds to Alice's UA entity with the message 6

03 Decline. Service Profiles 5.2.1.7.2. OCB Outgoing communication barring (OCB) is able to block an outgoing communication belonging to a certain category of communication. Bob's telephony application server responds to Alice's UA entity with the message 603 Decline. 5.2.1.7.3. ACR Anonymous communication rejection (ACR) enables Bob to reject an anonymous communication. Bob's TAS entity rejects the communication because the INVITE request contains the header Privacy with the value id. It responds to the INVITE request with the message 433 Anonymity Disallowed. 5.2.2. Audio flow The SDP message contains the types of audio codecs proposed by the caller and the codec selected by the callee, among the following list of codecs: - adaptative multi-rate (AMR); - AMR-WB (Wide Band); - enhanced voice services (EVS). 5.2.2.1. AMR codec The AMR codec provides the analog/digital conversion of an audio signal in the frequency band 300-3400 Hz. The AMR codec produces 20 ms frames and the resulting flow can have the following values: 12.2 kbps, 10.2 kbps, 7.95 kbps, 7.40 kbps, 6.70 kbps, 5.90 kbps, 5.15 kbps and 4.75 kbps. The AMR codec uses discontinuous transmission (DTX) associated with voice activity detection (VAD) and comfort noise generation (CNG) to reduce the flow rate during periods of silence. The SDP offer contains the values of the payload type field of the real- time transport protocol (RTP) header that identifies the codec type used. VoLTE and ViLTE m=audio 49152 RTP/AVP 97 98 a=rtpmap : 97 AMR/8000/1 a=rtpmap 98 AMR/8000/1 a=fmtp : 98 octet-align=1 The value 97 corresponds to the bandwidth-efficient format, for which only the payload is aligned on byte boundaries, fewer padding bits being thus added. The value 98 corresponds to byte-aligned format, where all fields in the payload of the RTP segment are aligned individually on byte boundaries (a = fmtp: 98 byte-align = 1). The value of 97 for the payload type field is listed first as the corresponding format has priority. 5.2.2.2. AMR-WB codec The AMR-WB codec h

as the same technical features as the AMR codec and improves voice quality by increasing the bandwidth (50-7000 Hz) for the audio signal. Several configurations (A, B, C) and several rates per configuration are defined: - configuration A: 6.6 kbps, 8.85 kbps and 12.65 kbps; - configuration B: 6.6kbps, 8.85 kbps, 12.65 kbps and 15.85 kbps; - configuration C: 6.6 kbps, 8.85 kbps, 12.65 kbps and 23.85 kbps. The SDP offer is more important because it must include the AMR and AMR-WB codecs and can propose, for each type of codec, both formats: - the values 97 and 99 of the Payload Type field correspond to the bandwidth-efficient format for AMR-WB and AMR codecs; - the values 98 and 100 of the payload type field correspond to the byte- aligned format for AMR-WB and AMR codecs. The values 97 and 98 of the payload type field are listed first because the AMR-WB codec has priority over the AMR codec. Service Profiles m=audio 49152 RTP/AVP 97 98 99 100 a=rtpmap : 97 AMR-WB/16000/1 a=rtpmap 98 AMR-WB/16000/1 a=fmtp: 98 octet-align=1 a=rtpmap : 99 AMR/8000/1 a=rtpmap : 100 AMR/8000/1 a=fmtp : 100 octet-align=1 5.2.2.3. EVS codec The EVS concept is a new family of codecs whose different types depend on the bandwidth of the audio signal: - Narrow band (NB), for an audio signal whose bandwidth is 300-3400 - Wide band (WB), for an audio signal whose bandwidth is 50-7000 Hz; - Super wide band (SWB), for an audio signal whose bandwidth is 50- 14000 Hz; - Full band (FB), for an audio signal whose bandwidth is 20-20000 Hz. The flow rates obtained have the following values: 5.9 kbps, 7.2 kbps, 8 kbps, 9.6 kbps, 13.2 kbps, 16.4 kbps, 24.4 kbps, 32 kbps, 48 kbps, 64 kbps, 96 kbps and 128 kbps. The rate for the NB type is in the range between 5.9 and 24.4 kbps. The rate for the WB type is in the range between 5.9 and 128 kbps. The rate for the SWB type is in the range between 9.6 and 128 kbps. The rate for the SWB type is in the range between 16.4 and 128 kbps. The NB-type and WB-type EVS codecs provide the following improvements compare

d to the AMR and AMR-WB codecs: - for the same quality, the rate is decreased; - for achieving equivalent rate, the quality is improved. The SWB-type and FB-type EVS codecs are reserved for coding music signals. 170 VoLTE and ViLTE The SDP offer relating to EVS codec must also include the AMR and AMR-WB codecs, EVS codec having priority. The rate required for reservation of resources in the 4G network is equal to 42 kbps (field b = AS: 42). The EVS codec is WB-type because the sampling frequency is 16000 Hz. The rate of WB-type EVS codec is in the range between 5.9 and 24.4 kbps. m=audio 49152 RTP/AVP 97 98 99 100 101 b=AS: 42 a=rtpmap: 97 EVS/16000/1 a=fmtp: 97 br=5.9-24.4 a=rtpmap : 98 AMR-WB/16000/1 a=rtpmap: 99 AMR-WB/16000/1 a=fmtp: 99 octet-align=1 a=rtpmap : 100 AMR/8000/1 a=rtpmap : 101 AMR/8000/1 a=fmtp: 101 octet-align=1 5.3. ViLTE profile service 5.3.1. Supplementary conversational video service The supplementary telephone service described for VoLTE service is extended for the ViLTE service, with supplements for communication hold and conference. In the case of communication hold, the IMS network can take the decision to reduce the bandwidth for audio and video streams. In the case of conference, the following configurations are possible: - a UA entity invited to the conference can only enable the audio stream and disable the video stream indicating in the SDP message, a value equal to ZERO for the port number; - a UA entity participating in a conversational video conference can disable the video stream and keep the audio stream; Service Profiles - if the UA entity responsible for the conversational video conference removes the video stream, the IMS network may decide to convert conversational video conference in an audio conference for all participants. 5.3.2. Video flow The SDP message contains the types of video codecs proposed by the caller and the codec selected by the callee, among the following codecs list: - H.264 codec, with constrained baseline profile (CBP), level 1.2; H.265 with main profi

le (MP) level 3.1 main tier. 5.3.2.1. H.264 codec H.264 profile is identified by the parameter profile-level-id - in the SDP offer. The maximum image size (number of pixels) and the maximum number of frames per second for the CBP profile level 1.2 can take several values: - size 176 X 144, 60.6 frame/s; - size 320 X 240, 20 frame/s; - size 352 X 288, 15.2 frame/s. Several actual sizes of the image can be negotiated and are identified by the parameter a = imageattr in the SDP offer. The maximum rate supported by the profile is equal to 384 kbps. The reserved actual reserved is indicated by the parameter b = AS in the SDP offer. m=video 49154 RTP/AVP 99 b=AS: 315 a=rtpmap : 99 H264/90000 a=fmtp 99 profile-level-id=42e00d a=imageattr:! send [x=176, y=144] [x=224,y=176] [x=272,y=224] [x=320,y=240] recv (x=176,y=144] [x=224, y=176] [x=272,y=224] [x=320,y=240] 172 VoLTE and ViLTE 5.3.2.2. H.265 codec The H.265 codec presents the following improvements compared to H.264 codec: - for the same quality, the rate is decreased; - for an equivalent rate, the quality is improved. The maximum image size (number of pixels) and the maximum number of frames per second for the MP profile level 3.1 main tier can take several values: - size 720 x 576, 75 frame/s; - size 960 x 540, 60 frame/s; - size 1280 x 720,33.7frame/s. In the following example, the mobile is equipped with a 5-inch screen which supports an 848 X 480 frame size and 25 frames per second. The SDP offer provides H.265 codec, H.264 level 3.1 for the frame size 848 X 480 and H.264 level 1.2 for the frame size 320 X 240. The required rate is equal to 690 kbps for a H.264 level 3.1 and 540 kb/s for the H.265 codec. The rate indicated by the parameter b = AS is the maximum rate. m=video 49154 RTP/AVP 98 97 100 99 b=AS: 690 a=rtpmap : 100 H264/90000 a=fmtp: 100 profile-level-id=42e01f a=imageattr: 100 send x=848,y=480] recv [x=848,y=480] a=rtpmap 99 H264/90000 a=fmtp 99 profile-level-id=42e01 a=imageattr:99 send x=320,y=240] recv [x=320,y=240] a=rtpmap: 98 H265/90000 a=fmtp

: 98 profile-id=1 level-id=93 a=imageattr:98 send [x=848,y=480] recv [x=848,y=480] a=rtpmap:97 H265/90000 a=fmtp:97 profile-id=1; level-id=93 a=imageattr: 97 send [x=320,y=240] recv [x=320,y=240] Interconnections 6.1. Interconnection CS network 6.1.1. Functional architecture The CS (Circuit-Switched) network is the public switched telephone network (PSTN) or public land mobile network (PLMN) implementing time- division multiplexing (TDM). The functional architecture of the IMS network for interconnection to the CS network is described in Figure 6.1. The interconnection between the IMS network and the CS network implements new entities: - breakout gateway control function (BGCF), to determine the entity in charge of interconnection, only for outgoing calls; - media gateway control function (MGCF), performing the translation of telephone signaling and for controlling the interconnection gateway; - IMS-MGW (media gateway), adapting the transport formats of traffic flows and signaling flows between the IMS and CS networks. The BGCF entity processes the INVITE requests sent by the serving call session control function (S-CSCF) in case the session needs to be forwarded to an interconnection. This relates to calls to the users connected to the PSTN or PLMN networks. VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. 174 VoLTE and ViLTE From the telephone number, the BGCF entity determines the next hop for the routing of the SIP message. It has to choose the MGCF entity that is responsible for interconnection with the PSTN or PLMN networks. If the interconnection entity is in a third-party network, the BGCF entity transmits the SIP message to another BGCF entity in that third-party network. Traffic flow Control flow P-CSCF E-CSCF I-CSCF S-CSCF Third-party operator PSTN/PLMN Figure 6.1. Functional architecture of IMS network interconnection with CS network The MGCF entity controls the establishm

ent, the maintenance and the release of the connections in the IMS-MGW entity. A connection represents an association between an end-point related to the interface with the PSTN or PLMN networks and an end-point related to the interface with the IP network. The MGCF entity performs the translation between SIP (Session Initiation Protocol) signaling used in the IMS network and telephone Interconnections signaling at the interconnection between IMS or CS networks, using the following protocols: - ISUP (ISDN User Part), for interconnection in TDM mode, with PSTN and PLMN networks; - BICC (Bearer Independent Call Control), for interconnection in IP mode with the PLMN networks corresponding to the Release 4; - SIP-I (SIP with encapsulated ISUP), for interconnection in IP mode with the PLMN networks corresponding to the Release 4. H.248 signaling is used by the MGCF entity to control the IMS-MGW interconnection gateway, whose deployment is mandatory for the interconnection in TDM mode (case of ISUP signaling) and optional for the interconnection in IP mode (the case of BICC or SIP-I signaling). The IMS-MGW performs the conversion of protocols relating to the media flows between the two end-points. It contains the treatments carried out on the media flows, such as transcoding (modification of the type of codec between the two end-points), echo cancellation and transmission of tones and announcements. 6.1.2. Protocol architecture 6.1.2.1. ISUP signaling The protocol ISUP defines the procedures used to establish, manage and release the circuits which transport the voice signals. Initial address message (IAM) is transmitted between digital switches to notify the request for establishment of a communication. It contains the telephone numbers of the caller and the callee; Address complete message (ACM) is returned by the destination switch to indicate that the ringing has been activated for the callee. Answer message (ANM) is transmitted by the destination switch to indicate that the callee has picked up the telephone. Relea

se (REL) message is sent to release the resources when a user hangs up the telephone. 176 VoLTE and ViLTE Release complete (RLC) message is transmitted to acknowledge the REL message. 6.1.2.2. BICC signaling The BICC protocol is used for signaling exchanged between, on one hand, the MGCF entity of the IMS network, and, on the other hand, the entity of the CS network responsible for interconnection of the telephone signaling. The BICC protocol was developed from the ISUP protocol that it is similar for basic call procedures and functions of supplementary telephone services basically. The BICC protocol also implements a mechanism which allows for the exchange of information linked to the support command of the media flow on the IP network between, on one hand, the IMS-MGW interconnection gateway, and, on the other hand, the entity of the CS network responsible for interconnection of the media flow. This information concerns IP addresses, UDP port numbers, types of media (voice, video and data) and formats used for this media (codecs for voice and video protocols for data). This information is tunneled in BICC messages containing signaling such as for example the IAM message for communication establishment or in the BICC APM (Application Transport Mechanism) message which does not transport any signaling information. The IP bearer control protocol (IP BCP) protocol is a control protocol for media flow which aims to ensure the exchange of necessary information to establish or modify media flow characteristics. The IPBCP protocol is initialized by the IMS-MGW and passed to the MGCF entity thanks to the H.248 protocol, for which a specific package is defined. The package defines additional properties which can appear in the terminations and contexts. The IPBCP protocol defines four types of message: - REQUEST message is sent by the MGCF entity to launch a request to establish or modify a media flow on the IP network; Interconnections - ACCEPTED message is sent by the MGCF entity which receives a message of media flow e

stablishment or modification, if it accepts the request; - CONFUSED message is sent by the MGCF entity in response to a media flow modification or establishment if it cannot deal with the received request message; - REJECTED message is sent by the MGCF entity in response to a request for media flow establishment or modification if it refuses the request. The bearer control tunnelling protocol (BCTP) protocol is used for the encapsulation of support control protocol for media flow. The header of the BCTP protocol contains the following indications: - the version of the BCTP protocol; - the type of support control protocol for media flow. 6.1.2.3. SIP-I signaling SIP-I signaling allows for the transport of ISUP messages encapsulated by SIP messages. The ISUP IAM message is carried by the SIP INVITE message. The ISUP ACM message is carried by the provisional response SIP 180 Ringing to the SIP INVITE request. The ISUP ANM message is carried by the SIP 200 OK response to the SIP INVITE request. The ISUP REL message is carried by the SIP BYE message. The ISUP RLC message is carried by the SIP 200 OK response to the SIP BYE request. 6.1.2.4. H.248 signaling The connection model describes the logical entities contained in the IMS- MGW entity that the MGCF entity can control. The main abstractions used in this connection model are contexts and terminations. 178 VoLTE and ViLTE A termination sends and/or collects several flows. The media flow parameters are encapsulated in the termination. A context is a package of allocated terminations. The NULL context contains all terminations which are not allocated to another termination, as is the case with idle time-slots on the TDM-mode interface. H.248 messages have a header which contains the identity of the transmitter and the version of the protocol. Several transactions can be concatenated in a H.248 message. The transactions contained in a message are dealt with independently and no order is predetermined. Each transaction is indicated by a transaction identifier and consis

ts of one or several actions (Figure 6.2). An action consists of a series of commands to modify or examine the context property. Each action usually specifies a context identifier (Figure 6.2). Each command consists of an identifier and a termination descriptor. The descriptor contains the parameters of a termination concerning a command. A descriptor consists of a name and a list of elements (Figure 6.2). H.248 Message Message Transaction Transaction Transaction Transaction header Transaction Action Action Action identifier Context Command Command Command identifier Termination Termination identifier descriptor Figure 6.2. H.248 structure message The terminations which are physical entities have a semi-permanent existence like a time-slot in a time-division multiplexing (TDM). Interconnections The temporary terminations are real-time transport protocol (RTP) flow, in the case of the interface with the IP network. The protocol provides commands to manipulate the logical entities, the contexts and the terminations of the connection model. ADD command adds a termination to a context. Applied to the first termination of a context, it also serves to create a context. MODIFY command modifies the properties of a termination. SUBTRACT command disconnects a termination from its context and sends back statistics about the participation of this termination in this context. Applied to the last termination of a context, it serves to cancel this context. MOVE command moves a termination to another context. AuditValue command sends back the current states of the properties and statistics associated with the terminations. AuditCapabilities command sends back all the possible values of termination properties authorized by the IMS-MGW gateway. NOTIFY command allows the IMS-MGW gateway to inform the MGCF entity about the development of events in this gateway. ServiceChange command allows the IMS-MGW gateway to signal to the MGCF entity that a termination or a group of terminations is about to be disabled or has just been enabled.

This command is also used by the IMS-MGW to register with the MGCF entity. The MGCF entity can also use this command to request the IMS- MGW to disable a termination or a group of terminations. Most commands are reserved for the specific use of the MGCF entity to control the IMS-MGW gateway. The exceptions are NOTIFY and ServiceChange commands, the first being sent by the IMS-MGW and the second being able to be sent by one of the two entities. VoLTE and ViLTE 6.1.2.5. Interfaces The Mi interface is the reference point between the S-CSCF and BGCF entities. This interface supports SIP and SDP signaling. The Mj interface is the reference point between the BGCF and MGCF entities. This interface supports SIP and SDP signaling. The Mg interface is the reference point between the CSCF and MGCF entities. This interface supports SIP and SDP signaling. The Mn interface is the reference point between the MGCF and IMS- MGW entities. This interface supports H.248 signaling. The IMS-MGW performs the conversion of the transport protocols relating to the signaling exchanged between the MGCF, depending on signaling transport over IP (SIGTRAN) model, the PSTN and PLMN networks, depending on signaling system 7 (SS7) model (Figure 6.3). SS7 transport SIGTRAN transport Layer 2 Layer 2 Interconnection Layer 1 Layer 1 IMS / PSTN or PLMN Figure 6.3. Transport of ISUP signaling The IMS-MGW performs, in the case of the ISUP signaling, the conversion of protocols relating to the media flows between the two end- points, corresponding, firstly, to RTP flow, and, secondly, to TDM flow (Figure 6.4). Interconnections IMS-MGW G.711 G.711 Codec Codec Codec G.704 G.704 G.703 G.703 Telephone handset Network Layer 2 Interconnection IMS / PSTN or PLMN (CS mode) Layer 1 Interconnection IMS/EPS Figure 6.4. Voice transport 6.1.3. Session establishment 6.1.3.1. Session establishment initiated by IMS network The procedure for establishing the session corresponds to a call generated by the Alice's user agent (UA) connected to the IMS network to Bob's telep

hone terminal connected to a CS network. The procedure for establishing the session initiated by the IMS network for ISUP or BICC telephone signaling is illustrated in Figure 6.5. 1) The call is generated by Alice's UA entity, by way of an INVITE request whose identity TEL URI contains the telephone number of the callee. The S-CSCF entity carries out an ENUM resolution with the DNS server, to convert the TEL URI into a SIP URI. The INVITE message contains the session description protocol (SDP) message of Alice's UA entity. As the callee is not a client of the IMS network, the response from the DNS server is negative and the S-CSCF entity then routes the INVITE request to the BGCF entity. VoLTE and ViLTE S-CSCF network SIP INVITE (SDP Alice) SIP 100 Trying SIP INVITE (SDP Alice) SIP 100 Trying ISUP/BICC IAM SIP 183 Session in Progress (SDP IMS-MW) SIP 183 Session in Progress (SDP IMS-MW) SIP PRACK SIP PRACK SIP 200 OK SIP 200 OK SIP UPDATE (SDP Alice) SIP UPDATE (SDP Alice) ISUP / BICC COT SIP 200 OK (SDP IMS-GW) SIP 200 OK (SDP IMS GW) ISUP / BICC ACM SIP 180 Ringing SIP 180 Ringing ISUP / BICC ANM SIP 200 OK SIP 200 OK SIP ACK SIP ACK Figure 6.5. Session establishment initiated by IMS network ISUP or BICC signaling 2) The BGCF entity responds to the S-CSCF entity with the 100 Trying message that allows the blocking of the retransmission timer of the INVITE request. 3) The BGCF entity determines the MGCF entity which interconnects with the CS network, either from an ENUM resolution, or from internal correspondence tables, and forwards the INVITE request. 4) The MGCF entity responds to the BGCF entity with the 100 Trying message that allows the blocking of the retransmission timer of the INVITE request. Interconnections 5) The MGCF entity converts the INVITE request into an ISUP/BICC IAM message. This message is transmitted to the IMS-MGW using SIGTRAN transport, and then to the network in CS mode. When the MGCF entity receives the INVITE request, it performs the following operations with the IMS-MGW gateway, in t

he case of ISUP interconnection: - it transfers to the IMS-MGW gateway the SDP message associated with the INVITE request; - it commands the constitution of the context and the end-points at the level of the IMS-MGW gateway; - it retrieves the characteristics of the media flow of the interface on the IP side and on the TDM side of the IMS-MGW gateway. In the case of a BICC interconnection, the configuration of the IMS- MGW gateway can for example correspond to a transcoding of voice: adaptive multi-rate/narrow band (AMR/NB) codec, at the 4G network side; - half rate (HR) or full rate (FR) codec, at 2G network side. 6), 7) The MGCF entity transmits the response 183 Session Progress to the INVITE request in which the SDP messages recovered from the IMS-MGW gateway is inserted. 8), 9) The subsequent PRACK request acknowledges of the provisional response 183 Session Progress. 10), 11) The 200 OK message is the response to the PRACK request. 12), 13) The confirmation of the resource reservation on the 4G network is indicated to the MGCF entity in an SDP offer contained in the UPDATE request. 14) The MGCF entity transmits to the CS network the ISUP/BICC COT to inform him that the resource is available on the caller's side. 15), 16) The 200 OK message is the response to the UPDATE request. VoLTE and ViLTE 17) The network operating in CS mode reserves the resources and responds with an ISUP ACM message indicating that the call has been presented to the callee. 18), 19) The MGCF entity transmits the provisional response 180 Ringing to the INVITE request to trigger the ring back tone at Alice's UA entity. 20) When the callee hangs up, the MGCF entity receives the ISUP/BICC ANM message. The MGCF entity connects the end-points at the level of the IMS-MGW gateway. 21), 22) The MGCF entity sends the definitive response 200 OK to Alice's UA entity for stopping the ring back tone. 23), 24) The 200 OK response is acknowledged by the ACK request. The procedure for establishing the session initiated by the IMS network for SIP-I sig

naling is shown in Figure 6.6. The procedure for establishing the session initiated by the IMS network for SIP-I signaling, takes that described for ISUP/BICC signaling, with the following modifications. 5) The ISUP IAM message is transmitted in a SIP INVITE message that also contains the SDP message of Alice's UA entity. 6) The CS network responds to MGCF entity with the 100 Trying message which allows the blocking of the retransmission timer of the INVITE request. 7) The provisional response 183 Session in Progress to the INVITE request is generated by the CS network and contains the SDP message of the gateway of this network. 12) The PRACK request is extended to the CS network. 13) The 200 OK response to the PRACK request is generated by the CS network. Interconnections S-CSCF network SIP INVITE (SDP Alice) SIP 100 Trying SIP INVITE (SDP Alice) SIP 100 Trying SIP INVITE (SDP Alice / ISUP IAM) SIP 100 Trying SIP 183 Session in Progress (SDP Réseau CS) SIP 183 Session in Progress (SDP Réseau CS) SIP 183 Session in Progress (SDP Réseau CS) SIP PRACK SIP PRACK SIP PRACK SIP 200 OK SIP 200 OK SIP 200 OK SIP UPDATE (SDP Alice) SIP UPDATE (SDP Alice) SIP UPDATE (SDP Alice) SIP 200 OK SIP 200 OK (SDP Réseau CS) SIP 200 OK (SDP Réseau CS) (SDP Réseau CS) SIP 180 Ringing (ISUP ACM) SIP 180 Ringing SIP 200 OK SIP 180 Ringing (ISUP ANM) SIP 200 OK SIP 200 OK SIP ACK SIP ACK SIP ACK Figure 6.6. Session establishment initiated by IMS network SIP-I signaling 18) The UPDATE request is extended to the CS network. 19) The 200 OK response to the UPDATE request is generated by the CS network. VoLTE and ViLTE 22) The ISUP ACM message is transmitted in the provisional response 180 Ringing to the INVITE request. 25) The ISUP ANM message is transmitted in the 200 OK response to the INVITE request. 30) The IP ACK request is extended to the CS network. 6.1.3.2. Session establishment initiated by CS network The procedure for establishing the session corresponds to a call initiated by the telephone terminal of Alice connected to the CS n

etwork to Bob's UA entity connected to the IMS network. The procedure for establishing the session initiated by the CS network for the BICC or ISUP signaling is described in Figure 6.7. S-CSCF I-CSCF network SIP INVITE ISUP/BICCIAM (SDP IMS-MGW) SIP 100 Trying DIAMETER LIR DIAMETER LIA SIP INVITE (SDP IMS-MGW) SIP 100 Trying SIP 183 Session in Progress (SDP Bob) SIP 183 Session in Progress (SDP Bob) SIP PRACK SIP 200 OK ISUP / BICC COT SIP UPDATE (SDP IMS_MGW) SIP 200 OK (SDP Bob) SIP 180 Ringing SIP 180 Ringing SIP 200 OK ISUP / BICC ACM SIP 200 OK ISUP/BICC ANM SIP ACK Figure 6.7. Session establishment initiated by CS network ISUP or BICC signaling Interconnections 1) The call is generated by the CS network, and results, at the level of the MGCF entity, in the receipt of the message ISUP/BICC IAM. The MGCF entity creates the end-points with the IMS-MGW gateway and retrieves the message, describing the characteristics of the termination of the IMS-MGW gateway on the IP side. 2) The MGCF entity generates an INVITE request with the identity TEL URI containing the telephone number contained in the message ISUP/BICC IAM, associating the SDP message given by the IMS-MGW gateway and forwards the INVITE message to the Interrogating-CSCF (I-CSCF). The MGCF entity shall indicate in the SDP message that the preconditions for the resource reservation are needed. 3) The I-CSCF entity responds to the MGCF entity with the 100 Trying message that allows the blocking of the retransmission timer of the INVITE request. 4) The I-CSCF entity sends to the home subscriber server (HSS) the DIAMETER LIR (Location-Information-Request) message to retrieve the IP address of the S-CSCF entity which registered Bob's UA entity. 5) The HSS entity provides the IP address of the S-CSCF entity in the DIAMETER LIA (Location-Information-Answer) message. 6) The I-CSCF entity forwards the SIP INVITE request to the S-CSCF entity. 7) The S-CSCF entity responds to the I-CSCF entity with the 100 Trying message that allows the blocking of the retransmiss

ion timer of the INVITE request. 8), 9) On receipt of the message 183 Session in Progress, the MGCF entity transfers the SDP message from the Bob's UA entity to the IMS-MGW gateway, thereby supplementing the characteristics of the end- point on the IP network. 10) The PRACK request acknowledges the provisional response 183 Session in Progress. VoLTE and ViLTE 11) The 200 OK message is the response to the PRACK request. 12) The message ISUP/BICC COT tells the MGCF entity that the resource has been reserved on the CS network. 13) The confirmation of the resource reservation on the CS network is indicated to Bob's UA entity in an SDP offer contained in the UPDATE request. 14) The confirmation of the resource reservation on the 4G network is indicated to the MGCF entity in an SDP offer contained in the 200 OK response to the INVITE request. 15), 16) When Bob's UA entity has confirmation of the resource reservation in the 4G network, the telephone rings and the MGCF entity receives the message 180 Ringing. 17) The MGCF entity generates the message ISUP / BICC ACM, sent to the CS network. 18), 19) When Bob picks up, the MGCF entity receives the message 200 OK and connects the end-points of the IMS MGW. 20) The MGCF entity transmits the message ISUP / BICC ANM to the network in CS mode. 21) The 200 OK response is acknowledged by the ACK request. The procedure for establishing the session generated by the CS network for SIP-I signaling is described in Figure 6.8. The procedure for establishing the session generated by the CS network for SIP-I signaling, takes that described for ISUP/BICC signaling, with the following modifications. 1) The ISUP IAM message is transmitted in the INVITE message which also contains the SDP message of the CS network gateway. 2) The MGCF entity responds to the CS network with the 100 Trying message that allows the blocking of the retransmission timer of the INVITE request. Interconnections S-CSCF I-CSCF network SIP INVITE (SDP Réseau CS ISUP IAM) SIP 100 Trying SIP INVITE (SDP Réseau CS) SIP 1

00 Trying DIAMETER LIR DIAMETER LIA SIP INVITE (SDP Réseau CS) SIP 100 Trying SIP 183 Session in Progress SIP 183 (SDP Bob) Session in Progress SIP 183 (SDP Bob) Session in Progress (SDP Bob) SIP PRACK SIP PRACK SIP 200 OK SIP 200 OK SIP UPDATE (SDP Réseau CS) SIP UPDATE (SDP Réseau CS) SIP 200 OK (SDP Bob) SIP 200 OK SIP 180 Ringing (SDP Bob) SIP 180 Ringing SIP 180 Ringing SIP 200 OK (ISUP ACM) SIP 200 OK SIP 200 OK (ISUP ANM) SIP ACK SIP ACK Figure 6.8. Session establishment initiated by CS network SIP-I signaling 11) The provisional response 183 Session in Progress to the INVITE request is extended to the CS network. 12) The PRACK request is generated by the CS network. 15) The 200 OK response to the PRACK request is extended to the CS network. VoLTE and ViLTE 16) The UPDATE request is generated by the CS network. 19) The 200 OK response to the UPDATE request is extended to the CS network. 22) The ISUP ACM message is transmitted in the provisional response 180 Ringing to the INVITE request. 25) The ISUP ANM message is transmitted in the 200 OK response to the INVITE request. 26) The ACK request is generated by the CS network. 6.1.4. Session termination 6.1.4.1. Session termination initiated by IMS network Procedure for the release of the session initiated by the IMS network is displayed in Figure 6.9. S-CSCF network SIP BYE SIP BYE ISUP/BICC REL SIP BYE (ISUP REL) ISUP / BICC RLC SIP 200 OK (ISUP RLC) SIP 200 OK SIP 200 OK Figure 6.9. Session clearing initiated by IMS network ISUP, BICC or SIP-I signaling 1), 2) The UA entity terminates the communication by generating the BYE request. 3) Upon receipt of the BYE request, the MGCF entity removes the end- points of the IMS-MGW gateway and generates the message ISUP/BICC REL to the CS network, in the case of ISUP/BICC signaling. In the case of SIP-I signaling, the ISUP REL message is carried in the BYE request. Interconnections 4) In the case of ISUP/BICC signaling, the CS network responds with the message ISUP / BICC RLC. In the case of SIP-I signaling, the ISUP

interconnection with other IMS networks is described in Figure 6.11. Alice's network (HomeA net) Bob's network (HomeB net) P-CSCF S-CSCF I-CSCF S-CSCF P-CSCF RTP flow SIP flow Figure 6.11. Interconnection with IMS network functional architecture of IMS network In case of an outgoing call, the S-CSCF entity detects that the called subscriber belongs to a different domain and forwards the INVITE request to the BGCF entity that retains its search function of the entity in charge of control interconnection. The interconnection border control function (IBCF) is the gateway that allows the access of the SIP flow to another IMS network. The IBCF entity can make the translation of IP addresses and port numbers, corresponding to the network address and port translation (NAPT). The IBCF entity can perform the translation of IP addresses, port numbers and conversion of IPv4 to IPv6, corresponding to the NAPT-PT (Protocol Translation) function. The IBCF entity performs the masking of the topology of the IMS network, The IBCF entity performs the withdrawal of some headers of the SIP message based on the rules established by the operator, corresponding to the function topology hiding interconnect gateway (THIG). Interconnections The transition gateway (TrGW) is the entity that anchors the RTP stream and allows access traffic to another IMS network. The TrGW entity may perform filtering, transcoding and NAPT or NAPT-PT translation of the RTP streams under the control of the IBCF entity. The interconnection between IMS networks is provided by: - the Ici interface between IBCF entities for the SIP flow; - the Izi interface between TrGW entities for the RTP stream. 6.2.2. Session establishment Table 6.1 summarizes the IP addresses and port numbers for the different RTP streams. Alice's UA TrGW (HomeA. net) IP address 192.0.2.1 192.0.2.2 Port number 49170 56743 TrGW (HomeA. net) TrGW (HomeB net) IP address 178.15.1.1 178.15.1.2 Port number 62111 33248 TrGW (HomeB.net) Bob's UA IP address 190.1.15.1 190.1.15.2 Port number 12538 2415

2 Table 6.1. RTP flow characteristics The procedure for establishing the session is illustrated in Figure 6.12. To simplify the presentation, responses 100 Trying, 180 Ringing and precondition mechanisms are avoided. 194 VoLTE and ViLTE Alice's network (HomeA net) Bob's network (HomeB.net) S-CSCF I-CSCF SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP ACK Figure 6.12. Interconnection with IMS network session establishment 1) The S-CSCF entity receives from the P-CSCF entity the INVITE message whose associated SDP message contains the characteristics of the RTP streams of Alice's UA entity. INVITE SIP tel:+4687197378 SIP/2.0 Route: sip:scscf1.operatorHA.net; Content-Type application/sdp Content-Length: ( C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 2) The S-CSCF entity detects that Alice's and Bob's UA entities are in different domains and transfers the INVITE message to the BGCF entity. The S-CSCF entity removes its identity from the Route header and performs the ENUM resolution on the URI identity of the destination to which it adds the iotl parameter indicating the direction of the request (homeA-Homeb) Interconnections The BGCF entity selects the IBCF entity and forwards the INVITE message without changing the SDP message. INVITE <sip:+46107197378@operatorHb.net;user=phone;iotl=homeA- homeB> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 3) The IBCF entity of the HomeA. net network selects the IBCF entity of the HomeB. net network and forwards the INVITE message including the SDP message which replaces the characteristics of the RTP streams received from Alice's UA entity with those communicated the TrGW entity of the HomeA. net network. INVITE <sip:+46107197378@operatorHb.net;user=phone;iotl=homeA- homeB> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.1 m=audio 62111 RTP/AVP 96 9

7 4) The IBCF entity of the HomeB. net network transfers to the I-CSCF entity the INVITE message including the SDP message which replaces the characteristics of the RTP streams received from the IBCF entity of the HomeA. net network with those communicated by the TrGW entity of the HomeB. net network. The I-CSCF entity retrieves from the HSS entity the identity of the S-CSCF entity and forwards the INVITE message without changing the SDP message. 196 VoLTE and ViLTE INVITE ip:+46107197378@operatorHb.net;user=phone;iotl=homeA- homeB> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.2 m=audio 12538 RTP/AVP 97 98 5) I-CSCF entity receives the provisional response 183 Session in Progress from the S-CSCF entity with the associated SDP message containing the RTP streams characteristics of Bob's UA entity. SIP/2.0 183 Session Progres Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.1 m=audio 24152 RTP/AVP 97 98 The I-CSCF entity forwards to the IBCF entity of the HomeB net network the provisional response 183 Session in Progress without changing the SDP message. 6) The IBCF entity of the HomeB net network transfers to the IBCF entity of the HomeA. net network the provisional response 183 Session in Progress including the SDP message which replaces the characteristics of the RTP streams received from Bob's UA entity with those provided by the TrGW entity of the HomeB. net network. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.2 m=audio 33248 RTP/AVP 97 98 7) The IBCF entity of the HomeA. net network transfers to the BGCF entity the provisional response 183 Session in Progress including Interconnections the SDP message which replaces the characteristics of RTP streams received from the IBCF entity of the HomeB. net network with those communicated by the TrGW entity of the HomeA. net network. SIP/2.0 183 Session Progress Content-Type - application/sdp Content-Length: (...) C=IN IP4 192.0.2.2 m=audio 56743 RTP/AVP 97 98 Ha

ndover 7.1. Introduction Handover is the mechanism that maintains the current session (the voice or the conversational video communication) when the mobile changes the radio cell. During the inter-system handover, cell change takes place without mobile network changes. During the intra-system handover, serving gateway (SG) and PDN gateway (PGW) entities play the role of an anchor point, which will hide the terminal mobility from the IMS network. There are two types of intra-system handover: - X2-based handover, from the name of the interface between the eNB entities; - S1-based handover, from the name of the interface between the MME (Mobility Management Entity) and eNB entities. X2-based handover occurs if both eNB entities, the source and the target, belong to the same group (pool) and the X2-AP interface has been enabled. VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE During X2-based handover, the MME entity does not change, which is not the case of SGW entity that can be relocated or not. S1-based handover occurs for the following four cases: - X2-AP interface between two eNB entities of the same group was not activated, the MME must not be relocated and the SGW entity may be relocated (scenario described in section 7.3.1); - both eNB entities belong to two different groups, the MME entity must be relocated and the SGW entity may be relocated (scenario described in section 7.3.2) or not. During the inter-system handover, cell change is accompanied by a change of network, the mobile being transferred from 4G network to 2G or 3G networks. There are two types of inter-system handover: - packet-switched (PS-PS) handover, for which the mobile does not change the mode when changing the network; - circuit-switched (PS-CS) handover, for which the mobile is also changing the mode. In the case of a voice or conversational video communication, PS-PS inter-system handover oc

curs only if the voice over high speed packet access (VoHSPA) service is available on 3G network. During PS-PS inter-system handover, the SGW entity acts as an anchor point, which will hide the terminal mobility to the IMS network. PS-CS inter-system handover is described relative to the service centralization and continuity in Chapter 8. The handover procedure is activated by the source eNB entity from measurements on the radio signal made by: - the eNB entity for the uplink direction; - the mobile for the downlink direction, for the serving and neighboring cells. These measures are recovered by the eNB entity in RRC MeasurementReport messages. Handover The handover procedure takes place in three phases: - the preparation phase corresponding to the decision of cell change and resource reservation; - the execution phase corresponding to the mobile connection to the target eNB entity; - the completion phase corresponding to the establishment of final bearers and the release of the old resources. The intra-system handover is carried out with a disconnection of the mobile with the eNB entity, whose duration depends on the following: - the synchronization of the mobile on the primary synchronization signal (PSS) and secondary synchronization signal (SSS) transmitted by the target eNB entity; - the discovery of the physical random access channel (PRACH); - the random access procedure; - the connection procedure to the target eNB entity. During the preparation of the intra-system handover, a unidirectional and temporary bearer is created between the source and target eNB entities for the downward direction. During the execution of the handover, the incoming data are forwarded to the target eNB entity that stores and delivers it to the mobile when it connects. For voice and conversational video communication, this operation causes an increase in packet jitter, which is corrected using the real-time transport protocol (RTP), to a certain limit. If the jitter of packets from end to end becomes too large, the packets are d

ropped. 7.2. Handover based on X2 7.2.1. Handover based on X2 without relocation The functional architecture of the handover based on X2 without relocation of the SGW entity is described in Figure 7.1. VoLTE and ViLTE E-UTRAN Source S1-MME LTE-Uu S1-U S1-MME LTE-Uu Target Figure 7.1. Handover based on X2 without relocation functional architecture The X2-based handover procedure without relocation of the SGW entity is described in Figure 7.2: - the preparation phase includes messages 1 and 2; - the implementation phase includes messages 3 to 5; - the completion phase includes messages 6 to 15. 1) On receipt of the RRC MeasurementReport message, the source eNB entity decides to perform a cell change and transmits to the target eNB entity the message X2-AP HANDOVER REQUEST containing the context of the mobile, particularly the tunnel endpoint identifier (TEID) of the S1 bearer provided by the SGW entity. 2) The target eNB entity responds with the message X2-AP HANDOVER REQUEST ACK, containing the technical characteristics of the radio interface in the information element. Handover command and the TEID identifier of the unidirectional X2 temporary bearer built between source and target eNB entities. 3) The source eNB entity eNB starts the execution phase by sending to the mobile the message RRC ConnectionReconfiguration containing information element handover. Handover 4) The source eNB entity sends to the target eNB the sequence numbers of the packet data convergence protocol (PDCP) in the message X2-AP SN STATUS TRANSFER and incoming data that have not been acknowledged by the mobile and that the target eNB entity will store until the mobile is able to receive them. 5) When the RRC connection is established between the mobile and the target eNB entity, the mobile transmits the message RRC ConnectionReconfigurationComplete, which will trigger the transfer of incoming data stored by the target eNB entity to the mobile. Source Target Traffic Radio Bearer S1 Bearer S5 Bearer Incoming data Outgoing data X2-AP HANDOVER R

EQUEST X2-AP HANDOVER REQUEST ACK RRC ConnectionReconfiguration X2-AP SN STATUS TRANSFER RRC Connection aReconfiguration Complete Traffic S1 Bearer S5 Bearer Incoming data X2 Bearer Radio Bearer Traffic Radio Bearer S1 Bearer S5 Bearer Outgoing data S1-AP PATH SWITH REQUEST GTPv2-C MODIFY BEARER REQUEST GTPv2-C MODIFY BEARER REQUEST DIAMETER CCR DIAMETER CCA GTPv2-C MODIFY BEARER RESPONSE GTPv2-C MODIFY BEARER RESPONSE GTP-U EM GTP-U EM Traffic Radio Bearer S1 Bearer S5 Bearer Incoming data S1-AP PATH SWITH REQUEST ACK X2-AP UE CONTEXT RELEASE Figure 7.2. Handover based on X2 without relocation procedure VoLTE and ViLTE 6) The target eNB entity starts the completion phase and transmits to the MME entity the message S1-AP SWITH PATH REQUEST containing the following information: - the TEID identifier of the S1 bearer that the SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity; - the E-UTRAN cell global identifier (ECGI). 7) The MME determines that the SGW entity shall not change and transfers this information to the SGW entity in the message GTPv2-C MODIFY BEARER REQUEST. 8) The SGW entity transfers the ECGI identifier of the cell to the PGW entity in the message GTPv2-C MODIFY BEARER REQUEST. 9) The PGW entity transfers the ECGI identifier of the cell to the policy and charging rules function (PCRF) in the message DIAMETER credit- control-request (CCR). 10) The PCRF entity responds to the PGW entity with the message DIAMETER credit-control-answer (CCA) to acknowledge the request. 11) The PGW entity responds to the SGW entity with the message GTPv2-C MODIFY BEARER RESPONSE to acknowledge the request. 12) The SGW entity responds to the MME entity with the message GTPv2-C MODIFY BEARER RESPONSE message to acknowledge the request. 13) The target eNB entity transmits to the mobile the traffic received from the source eNB entity until it receives the GTP-U EM (End Marker) messages of the SGW entity, from which the traffic will be received directly. 14) The MME responds to the target e

NB entity with the message S1-AP SWITH PATH REQUEST ACK to acknowledge the request. 15) The target eNB entity informs the source eNB entity that the handover was achieved with the message X2-AP EU CONTEXT RELEASE SO that it releases the context associated with the mobile. Handover 7.2.2. Handover based on X2 with relocation The functional architecture of the handover based on X2 with relocation of the SGW entity is shown in Figure 7.3. The X2-based handover procedure with relocation of SGW entity for the completion phase is illustrated in Figure 7.4. E-UTRAN Source Former LTE-Uu S1-MME S1-MME LTE-Uu Target Figure 7.3. Handover based on X2 with relocation functional architecture The preparation and execution phases are identical to those described for the handover based on X2 without relocation. 1) The target eNB entity starts the completion phase and transmits to the MME entity the message S1-AP SWITH PATH REQUEST containing TEID and ECGI identifiers. 2) The MME entity determines that the SGW entity must be relocated and transfers this information as well as the IP address of the entity PGW to the new SGW entity in the message GTPv2-C CREATE SESSION REQUEST. VoLTE and ViLTE 3) The new SGW entity forwards the ECGI identifier of the cell to the PGW entity in the message GTPv2-C MODIFY BEARER REQUEST that contains the TEID identifier that the PGW entity will use when it sends traffic to the new SGW entity. 4) The PGW entity forwards the ECGI identifier of the cell to the PCRF entity in the DIAMETER CCR message. Source Target Former Traffic S1 Bearer S5 Bearer Incoming data X2 Bearer Radio Bearer Radio Bearer S1 Bearer S5 Bearer Traffic Outgoing data S1-AP PATH SWITH REQUEST GTPv2-C CREATE SESSION REQUEST GTPv2-C MODIFY BEARER REQUEST DIAMETER CCR DIAMETER CCA GTPv2-C MODIFY BEARER RESPONSE GTPv2-C CREATE SESSION RESPONSE S1-AP PATH SWITH REQUEST ACK Traffic Bearer Radio Bearer S1 Bearer S5 Incoming data Bearer Radio Bearer S1 Traffic Bearer S5 Outgoing data X2-AP UE CONTEXT RELEASE GTPv2-C DELETE SESSION REQUEST GTP

v2-C DELETE SESSION RESPONSE Figure 7.4. Handover based on X2 with relocation completion phase 5) The PCRF entity responds to the PGW entity with the DIAMETER CCA message to acknowledge the request. 6) The PGW entity responds to the SGW entity with the message GTPv2-C MODIFY BEARER RESPONSE containing the TEID identifier that the new SGW entity will use when it sends traffic to the PGW entity. 7) The new SGW entity responds to the MME entity with the message GTPv2-C CREATE SESSION RESPONSE containing the TEID identifier Handover that the target eNB entity will use in the GTP-U header when sending traffic to the new SGW entity. 8) The MME entity responds to the target eNB entity with the message S1-AP SWITH PATH REQUEST ACK containing the TEID identifier provided by the new SGW entity. 9) The target eNB entity informs the source eNB entity that the handover was achieved with the message X2-AP EU CONTEXT RELEASE that it releases the context associated with the mobile. 10) The MME entity controls the release of the context of the former SGW entity with the message GTPv2-C DELETE SESSION REQUEST. 11) The former SGW entity responds to the MME entity with the message GTPv2-C DELETE SESSION REQUEST to acknowledge the request. 7.3. Handover based on S1 7.3.1. Handover based on S1 without relocation The functional architecture for the handover based on S1 without relocation of the MME and SGW entities corresponds to Figure 7.1, for which the X2 interface between the source and target eNB entities is deactivated. The MME is no longer transparent to the handover mechanism and acts as a signaling relay for the handover control between the source and target eNB entities. The temporary bearer built between the source and target eNB entities for incoming data passes through the SGW entity. The handover procedure based on S1 without relocation of the MME and SGW entities is given in Figure 7.5: - the preparation phase includes messages 1 to 6; - the execution phase includes messages 7 to 10; - the completion phase includes messa

ges 11 to 22. VoLTE and ViLTE Source Target Traffic Radio Bearer S1 Bearer S5 Bearer Incoming data Outgoing data S1-AP HANDOVER REQUIRED S1-AP HANDOVER REQUEST S1-AP HANDOVER REQUEST ACK GTPv2-C CREATE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE S1-AP HANDOVER COMMAND RRC ConnectionReconfiguration S1-AP eNB STATUS TRANSFER S1-AP MME STATUS TRANSFER RRC ConnectionReconfiguration Complete Traffic S1 Bearer S5 Bearer Incoming data Temporary Bearer Radio Bearer Temporary Bearer Traffic Radio Bearer S1 Bearer S5 Bearer Outgoing data S1-AP HANDOVER NOTIFY GTPv2-C MODIFY BEARER REQUEST GTPv2-C MODIFY BEARER REQUEST DIAMETER CCR DIAMETER CCA GTPv2-C MODIFY BEARER RESPONSE GTPv2-C MODIFY BEARER RESPONSE GTP-U EM (Bearer S1) GTP-U EM (Bearer temporaire) GTP-U EM (Bearer temporaire) Traffic Radio Bearer S1 Bearer S5 Bearer Incoming data S1-AP UE CONTEXT RELEASE REQUEST S1-AP UE CONTEXT RELEASE COMPLETE GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE Figure 7.5. Handover based on S1 without relocation procedure Handover 1) The source eNB entity initiates the preparation phase of the handover by sending the message S1-AP HANDOVER REQUIRED to the MME entity. 2) The MME entity sends to the target eNB entity the message S1-AP HANDOVER REQUEST to perform the reservation of resources. 3) The target eNB entity responds to the MME entity with the message S1-AP HANDOVER REQUEST ACK containing the following information: - the TEID identifier of the temporary bearer that the SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity; - the TEID identifier of the S1 bearer that the SGW entity will use in GTP-U header when it sends traffic to the target eNB entity; - the technical characteristics of the radio interface in the information element handover command. 4) The MME entity forwards the TEID identifier relating to the temporary bearer to the SGW entity in the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL R

EQUEST. 5) The SGW entity acknowledges the creation of the temporary bearer with the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE containing the TEID identifier of the temporary bearer that the source eNB entity will use in the GTP-U header when it will send traffic to the SGW entity. 6) The preparation phase ends when the MME entity sends to the source eNB entity the message S1-AP HANDOVER COMMAND containing the following information: - the TEID identifier of the temporary bearer that the source eNB entity will use in the GTP-U header when it sends traffic to the SGW entity; - the technical characteristics of the radio interface of the target eNB entity in the information element handover command. 7) The source eNB entity starts the execution phase by sending to the mobile the RRC ConnectionReconfiguration message containing the information element Handover Command. VoLTE and ViLTE 8) The source eNB entity transmits to the MME entity the sequence numbers of the PDCP protocol with the message SI-AP SN STATUS TRANSFER. 9) The MME entity forwards the sequence numbers to the target eNB entity in the message SI-AP MME STATUS TRANSFER. Incoming data that have not been acknowledged by the mobile which the target eNB entity will store until the mobile is able to receive are transmitted in the temporary bearer. 10) When the RRC connection is established between the mobile and the target eNB entity, the mobile transmits the message RRC ConnectionReconfigurationComplete, which will trigger the transfer of incoming data stored by the target eNB entity to the mobile. 11) The completion phase starts when the target eNB entity notifies the MME entity with the message S1-AP HANDOVER NOTIFY containing the ECGI identity of the cell. 12) The MME entity forwards to the SGW entity the message GTPv2-C MODIFY BEARER REQUEST containing the ECGI identity of the cell and the TEID identifier of the S1 bearer that the SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity. 13) The SGW entity tr

ansfers the ECGI identifier of the cell to the PGW entity in the message GTPv2-C MODIFY BEARER REQUEST. 14) The PGW entity transfers the ECGI identifier of the cell to the PCRF entity in the DIAMETER CCR message. 15) The PCRF entity responds to the PGW entity with the DIAMETER CCA message to acknowledge the request. 16) The PGW entity responds to the SGW entity with the message GTPv2-C MODIFY BEARER RESPONSE to acknowledge the request. 17) The SGW entity responds to the MME entity with the message GTPv2-C MODIFY BEARER RESPONSE to acknowledge the request. 18) The target eNB entity transmits to the mobile the traffic received from the source eNB entity by the temporary bearer until it receives a Handover GTP-U EM message from the SGW entity from which the traffic will be received directly from the S1 bearer. 19) The release of the context of the mobile at the source eNB entity is triggered by the MME entity by sending the message S1-AP UE CONTEXT RELEASE REQUEST. 20) The source eNB entity responds to the MME entity with the message S1-AP and acknowledges the message received. 21) The release of the temporary bearer at the SGW entity is triggered by the MME entity by sending the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST. 22) The SGW entity responds to the MME entity with the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE to acknowledge the received message. 7.3.2. Handover based on S1 with relocation The functional architecture for the handover based on S1 with the relocation of the MME and SGW entities is described in Figure 7.6. E-UTRAN Source Former S1-MME Former LTE-Uu LTE-Uu S1-MME Target Figure 7.6. Handover based on S1 with relocation functional architecture 212 VoLTE and ViLTE 7.3.2.1. Preparation phase The S1-based handover procedure with the relocation of the MME and SGW entities is described in Figure 7.7 for the preparation phase. 1) The source eNB entity initializes the preparation phase of the handover by sending the message S1-AP HANDOVER REQUIRED to the former MME entity.

2) The former MME entity selects a new MME entity and transmits the message GTPv2-C FORWARD RELOCATION REQUEST containing the following information: - the IP address of the PGW entity; - the TEID identifier relative to the S5 bearer that the new SGW entity will use in the GTP-U header when it sends traffic to the PGW entity. 3) The new MME decides to relocate the SGW entity and passes to the new SGW entity the message GTPv2-C CREATE SESSION REQUEST containing the information received. Source Target Former Former Radio Bearer S1 Bearer S5 Bearer S1-AP HANDOVER REQUIRED GTPv2-C FORWARD RELOCATION REQUEST GTPv2-C CREATE SESSION REQUEST GTPv2-C CREATE SESSION REQUEST S1-AP HANDOVER REQUEST S1-AP HANDOVER REQUEST ACK GTPv2-C CREATE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE GTPv2-C FORWARD RELOCATION RESPONSE GTPv2-C CREATE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE S1-AP HANDOVER COMMAND Figure 7.7. Handover based on S1 with relocation preparation phase Handover 4) The new SGW entity responds with the message GTPv2-C CREATE SESSION REQUEST containing the TEID identifier of the S1bearer that the target eNB entity will use in the GTP-U header when it sends traffic to the new SGW entity. 5) The new MME entity transmits to the target eNB entity the message S1-AP HANDOVER REQUEST to perform the reservation of resources. 6) The target eNB entity responds to the new MME entity with the message S1-AP HANDOVER REQUEST ACK containing the following information: - the TEID identifier of the temporary bearer that the new SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity; - the TEID identifier of the S1 bearer that the new SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity; - the technical characteristics of the radio interface in the information element handover command. 7) The new MME entity forwards the TEID identifier relating to the temporary bearer to the SGW entity i

n the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL REQUEST. 8) The new SGW entity acknowledges the creation of the temporary bearer by the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE containing the TEID identifier of the temporary bearer that the former SGW entity will use in the GTP-U header when it will send traffic to the new SGW entity. 9) The new MME entity responds to the former MME entity with the message GTPv2-C FORWARD RELOCATION REQUEST containing the following information: - the TEID identifier of the temporary bearer that the former SGW entity will use in the GTP-U header when it sends traffic to the new SGW entity; - the technical characteristics of the radio interface of the target eNB entity in the information element Handover Command. 10) The former MME entity forwards the TEID identifier relating to the temporary bearer to the former SGW entity in the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL REQUEST. 214 VoLTE and ViLTE 11) The former SGW entity acknowledges the creation of the temporary bearer with the message GTPv2-C CREATE INDIRECT FORWARDING TUNNEL RESPONSE containing the TEID identifier of the temporary bearer that the source eNB entity will use in the GTP-U header when it will send traffic to the former entity SGW. 12) The preparation phase ends when the former MME entity transmits to the source eNB entity the message S1-AP HANDOVER COMMAND containing the following information: - the TEID identifier from the temporary bearer that the source eNB entity will use in the GTP-U header when it sends traffic to the former SGW entity; - the technical characteristics of the radio interface of the target eNB entity in the information element handover command. 7.3.2.2. Execution phase The S1-based handover procedure with relocation of the MME and SGW entities is described in Figure 7.8 for the execution phase. Source Target Former Former RRC ConnectionReconfiguration S1-AP eNB STATUS TRANSFER GTPv2-C FORWARD ACCESS CONTEXT NOTIFICATION GTPv2-C FORWARD ACCESS CONTEXT ACKNOW

LEDGE S1-AP MME STATUS TRANSFER RRC ConnectionReconfigurationComplete S1 Bearer S5 Bearer Temporary Bearer Temporary Radio Bearer Temporary Bearer Radio Bearer S1 Bearer S5 Bearer Figure 7.8. Handover based on S1 with relocation execution phase 1) The source eNB entity starts the execution phase by sending to the mobile the RRC ConnectionReconfiguration message containing the information element handover command. Handover 2) The source eNB entity transmits to the former MME entity the sequence numbers of the PDCP protocol with the message SI-AP SN STATUS TRANSFER. 3) The former MME entity forwards the sequence numbers to the new MME entity in the message GTPv2-C FORWARD ACCESS CONTEXT NOTIFICATION. 4) The new MME entity responds to the former MME entity with the message GTPv2-C FORWARD ACCESS CONTEXT ACKNOWLEDGE to acknowledge the message received. 5) The new MME entity forwards the sequence numbers to the target eNB entity in the message SI-AP MME STATUS TRANSFER. Incoming data that have not been acknowledged by the mobile which the target eNB entity will store until the mobile is able to receive are transmitted in the temporary bearer. 6) When the RRC connection is established between the mobile and the target entity, mobile transmits ConnectionReconfigurationComplete message, which will trigger the transfer of incoming data stored by the target eNB entity to the mobile. 7.3.2.3. Completion phase The S1-based handover procedure with the relocation of the MME and SGW entities is shown in Figure 7.9 for the completion phase. 1) The completion phase starts when the target eNB entity notifies the new MME entity with the message S1-AP HANDOVER NOTIFY containing the ECGI identity of the cell. 2) The new MME entity informs the former MME entity that the handover is completed with the message GTPv2-C FORWARD RELOCATION COMPLETE NOTIFICATION. 3) Former MME entity responds to the new MME entity with the message GTPv2-C FORWARD RELOCATION COMPLETE ACKNOWLEDGE to acknowledge the message received. VoLTE and ViLTE 4) The new

MME entity forwards to the new SGW entity in the message GTPv2-C MODIFY BEARER REQUEST containing the ECGI identity of the cell and the TEID identifier of the S1 bearer that the new SGW entity will use in the GTP-U header when it sends traffic to the target eNB entity. Source Target Former Former S1-AP HANDOVER NOTIFY GTPv2-C FORWARD RELOCATION COMPLETE NOTIFICATION GTPv2-C FORWARD RELOCATION COMPLETE ACKNOWLEDGE GTPv2-C MODIFY BEARER REQUEST GTPv2-CMODIFY BEARER REQUEST GTPv2-C MODIFY BEARER RESPONSE GTPv2-C MODIFY BEARER RESPONSE GTP-U EM (S1 Bearer) GTP-U EM (Temporary Bearer) GTP-U EM (Temporary Bearer) GTP-U EM (Temporary Bearer) Radio Bearer S1 Bearer S5 Bearer S1-AP UE CONTEXT RELEASE REQUEST S1-AP UE CONTEXT RELEASE COMPLETE GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE Figure 7.9. Handover based on S1 with relocation completion phase 5) The new SGW entity forwards the ECGI identifier of the cell to the PGW entity in the message GTPv2-C MODIFY BEARER REQUEST. The PGW entity transfers the ECGI identifier of the cell to the PCRF entity in the DIAMETER RRC message. Handover The PCRF entity responds to the PGW entity with the DIAMETER CCA message to acknowledge the request. 6) The PGW entity responds to the new SGW entity with the message GTPv2-C MODIFY BEARER RESPONSE to acknowledge the request. 7) The new SGW entity responds to the new MME entity with the message GTPv2-C MODIFY BEARER RESPONSE to acknowledge the request. 8) The target eNB entity transmits to the mobile the traffic received from the source eNB entity by the temporary bearer until it receives the message GTP-U EM of the new SGW entity, from which the traffic will be received directly by the S1 bearer. 9) The release of the context of the mobile at the source eNB entity is triggered by the former MME entity by sending the messa

ge S1-AP EU CONTEXT RELEASE REQUEST. 10) The source eNB entity responds to the former MME entity with the message S1-AP EU CONTEXT RELEASE COMPLETE to acknowledge the received message. 11) The release of the temporary bearer at the former SGW entity is triggered by the former MME entity by sending the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST. 12) The former SGW entity responds to the former MME entity with the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE to acknowledge the received message. 13) The release of the context at the former SGW entity is triggered by the former MME entity by sending the message GTP-C DELETE SESSION REQUEST. 14) The former SGW entity responds to the former MME entity with the message GTP-C DELETE SESSION RESPONSE to acknowledge the received message. VoLTE and ViLTE 15) The release of the temporary bearer at the new SGW entity is triggered by the new MME entity by sending the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL REQUEST. 16) The new SGW entity responds to the new MME entity with the message GTPv2-C DELETE INDIRECT FORWARDING TUNNEL RESPONSE to acknowledge the received message. 7.4. PS-PS inter-system handover 7.4.1. Functional architecture PS-PS inter-system handover impacts the serving GPRS support node (SGSN) of 2G/3G mobile network and possibly the radio network controller (RNC) if the feature Direct Tunnel is implemented. The SGSN entity plays for 2G/3G mobile networks the same role as the MME entity for a 4G mobile network. The RNC entity plays for a 3G mobile network the same role as the eNB entity regarding the control of the mobile connection and the allocation of resources on the radio interface. The feature Direct Tunnel, specific to a 3G mobile network, allows for direct transfer traffic between the RNC and gateway GPRS support node (GGSN) entities without passing through the SGSN entity. The GGSN entity plays for 2G/3G mobile networks the same role as the PGW entity for 4G mobile network. The SGW entity ensures the anchor point of 2

G/3G mobile networks: - anchoring the traffic is carried by the SGSN entity that connects to the SGW entity if the feature Direct Tunnel is not available; - anchoring the traffic is carried by the RNC entity that connects to the SGW entity if the feature Direct Tunnel is available. The functional architecture for the PS-PS inter-system handover is described in Figure 7.10. Handover E-UTRAN Source S1-MME LTE-Uu GERAN UTRAN Figure 7.10. PS-PS inter-system handover functional architecture The S3 interface is the reference point between the SGSN and MME entities: - this interface supports GTPv2-C (GPRS Tunnel Protocol Control) signaling; - this interface allows the exchange of messages related to the management of PS-PS inter-system handover. The S4 interface is the reference point between the SGW and SGSN entities: - this interface is deployed if the feature Direct Tunnel is not available; - this interface supports GTPv2-C signaling for the control plane and GTP-U (GPRS Tunnel Protocol User) tunneling for the traffic plane; - GTPv2-C signaling ensures the construction of S4 bearer built between the SGW and SGSN entities. The S12 interface is the reference point between the SGW and RNC entities: - this interface is deployed if the feature Direct Tunnel is available; - this interface supports the GTP-U tunneling for the traffic plane. VoLTE and ViLTE 7.4.2. Procedure The procedure for PS-Ps inter-system handover is shown in Figure 7.11: - the preparation phase includes messages 1 to 8; - the execution phase includes messages 9 and 10; - the completion phase includes messages 11 to 21. During the preparation phase, a temporary bearer is constructed to route the incoming data: - the temporary bearer may be direct if the data is routed directly from the eNB entity to the 2G/3G radio access network; - the temporary bearer may be indirect if the incoming data passes through the SGW and SGSN entities. The procedure for PS-PS inter-system handover is elaborated with the following assumptions in hand: - the temporary bearer b

uilt between the eNB and RNC entities is a direct bearer; - the feature Direct Tunnel is not available. 1) to 4) The messages are equivalent to messages 1 to 4 described for the preparation phase of the handover based on S1 with relocation of the MME and SGW entities. 5) The SGSN entity transmits to the RNC entity the message RANAP RELOCATION REQUEST to reserve resources in the radio access network. 6) The RNC entity responds with the message RANAP RELOCATION REQUEST ACK to acknowledge the request. 7), 8) The messages are equivalent to messages 11 and 12 described for the preparation phase of the handover based on S1 with relocation of the MME and SGW entities. 9) The message is equivalent to the message 1 described for the execution phase of the handover based on S1 with relocation of the MME and SGW entities. Handover Source Former Radio Bearer S1 Bearer S5 Bearer S1-AP HANDOVER REQUIRED GTPv2-C FORWARD RELOCATION REQUEST GTPv2-C CREATE SESSION REQUEST GTPv2-C CREATE SESSION REQUEST RANAP RELOCATION REQUEST RANAP RELOCATION REQUEST ACK GTPv2-C FORWARD RELOCATION RESPONSE S1-AP HANDOVER COMMAND RRC ConnectionReconfiguration RRC HandovertoUTRANComplete S1 Bearer S5 Bearer Temporary Radio Bearer Radio Bearer S1 Bearer S5 Bearer RANAP RELOCATION COMPLETE GTPv2-C FORWARD RELOCATION COMPLETE NOTIFICATION GTPv2-C FORWARD RELOCATION COMPLETE ACKNOWLEDGE GTPv2-C MODIFY BEARER REQUEST GTPv2-CMODIFY BEARER REQUEST GTPv2-C MODIFY BEARER RESPONSE GTPv2-C MODIFY BEARER RESPONSE Radio Bearer S1 Bearer S5 Bearer S1-AP UE CONTEXT RELEASE REQUEST S1-AP UE CONTEXT RELEASE COMPLETE GTPv2-C DELETE SESSION REQUEST GTPv2-C DELETE SESSION RESPONSE Figure 7.11. PS-PS inter-system handover procedure 10) The mobile confirms its connection to the RNC entity with the RRC HandovertoUTRANComplete message. 11) The RNC entity informs the SGSN entity about the connection of the mobile with the message RANAP RELOCATION COMPLETE. 222 VoLTE and ViLTE 12) to 17) The messages are equivalent to messages 2 to 7 described for the completion phase of th

Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE The mobility management entity (MME) located in the visited network is connected to the home subscriber server (HSS) located in the home network via the S6a interface. The S9 interface between the home policy charging and rules function (H-PCRF) and the V-PCRF (Visited PCRF) entity is optional. If the S9 interface is not deployed, the rules applying to mobile traffic in roaming are stored in the subscription profile repository (SPR) associated with the V- PCRF entity. During the mobile registration, the S9 interface carries the DIAMETER messages of the Gx interface exchanged between V-PCRF and PGW entities for the establishment of the default support (default bearer) assigned to the SIP flow. During the establishment of the session, S9 interface carries the DIAMETER messages of the Rx interface exchanged between the V-PCRF entity and the proxy call session control function (P-CSCF) in the IMS for the establishment of the dedicated bearer allocated to the RTP stream. 8.1.2. Roaming applied to the IMS network The functional architecture of roaming applied to the IMS network is described in Figure 8.2, when the RTP stream passes through the home network. The roaming interface is between the P-CSCF entity located in the visited network and the S-CSCF (Serving CSCF) entity located in the home network. The interconnection border control function (IBCF) can make the translation of IP addresses and port numbers, corresponding to the network address and port translation (NAPT). The IBCF entity can perform the translation of IP addresses, port numbers and conversion of IPv4 to IPv6, corresponding to the NAPT-PT (Protocol Translation) function. The IBCF entity performs the withdrawal of some headers of the SIP message based on the rules established by the operator, corresponding to the function topology hiding interconnect gateway (THIG). Roaming The transition gateway (TrGW) may perform filtering,

transcoding and NAPT or NAPT-PT translation of the RTP streams under the control of the IBCF entity. Alice's visited network (VisitedA.net) Alice's home network (HomeA. net) P-CSCF IBCF-1 IBCF-2 S-CSCF TrGW-1 TrGW-2 IBCF-3 RTP flow SIP flow TrGW-4 TrGW-3 IBCF-4 P-CSCF IBCF-6 IBCF-5 Bob 's visited network (VisitedB.net) Bob's home network (HomeB net) Figure 8.2. Roaming applied to the IMS network: nominal routeing The IBCF entity of Alice's home network (Bob's home network, respectively) consists of two IBCF-2 and-3 IBCF instances (IBCF-4 and IBCF-5, respectively). The IBCF entity of Alice's home network (Bob's home network, respectively) controls the TrGW-2 entity (TrGW-3, respectively). Roaming interfaces between the home network and the visited network are provided by: - Ici interfaces required for SIP flow between IBCF-1 and IBCF-2 instances for Alice's network and between IBCF-5 and IBCF-6 instances for Bob's network; - Izi interfaces for the RTP stream between TrGW-1 and TrGW-2 entities for Alice's network and between TrGW-3 and TrGW-4 entities for Bob's network. 226 VoLTE and ViLTE The interfaces for the interconnection between IMS networks performing, on the one hand, the outgoing call and, on the other hand, the incoming call is provided by: - Ici interface between IBCF-3 and IBCF-4 instances for the SIP flow; - Izi interface between the TrGW-2 and TrGW-3 entities for the RTP stream. The functional architecture of roaming applied to the IMS network is described in Figure 8.3, when the RTP flows does not pass through the home network of the caller, corresponding to the optimal media routeing (OMR). Alice's visited network (VisitedA.net) Alice' home network (HomeA. net) P-CSCF IBCF-1 IBCF-2 S-CSCF TrGW-1 TrGW-2 IBCF-5 IBCF-4 IBCF-3 SIP flow RTP flow TrGW-4 TrGW-3 IBCF-6 P-CSCF IBCF-8 IBCF-7 Bob' visited network (VisitedB.net) Bob's home network (HomeB.net) Figure 8.3. Roaming applied to IMS network: optimal routeing The IBCF entity of Alice's visited network consists of three instances, IBCF-1, IBCF-4 and I

BCF-5, and controls the TrGW-1 entity. The transit and roaming function (TRF) is located in the visited network of the caller (Alice). The TRF entity receives the initial request SIP INVITE from the S-CSCF entity of the home network of the caller and forwards the request to the home network of the called party (Bob). Roaming Roaming interfaces are provided by: - Ici interfaces between the IBCF-1 and-2 IBCF instances, between the IBCF-3 and IBCF-4 instances and between the IBCF-7 and IBCF-8 instances, for the SIP stream; - Izi interface between the GW-3 and TrGW-4 entities, for the RTP stream. The interfaces for the interconnection is provided by: - Ici interface between the IBCF-5 and IBCF-6 instances for the SIP flow; - Izi interface between the TrGW-1 and TrGW-3 entities for the RTP stream. Figure 8.4 provides an example of SDP announcements containing the characteristics (IP addresses, port numbers and domain name) of the RTP stream. INVITE (190.1.15.1, 16789) S-CSCF (178.15.1.1, 62111) Domain (192.0.2.1, 49170) 183 (0.0.0.0, 16511) (192.0.2.4, 16511) Ha operatorH IBCF-2 IBCF-3 TrGW-2 TrGW-2 INVITE (179.14.1.2, 34500) (190.1.15.1, 16789) (178.15.1.1, 62111) (192.0.2.1, 49170) 183 (0.0.0.0, 16511) (192.0.2.4, 16511) Domain Xa operatorX INVITE (178.15.1.1, 62111) (192.0.2.1, 49170) 183 (0.0.0.0, 16511) (192.0.2.4, 16511) IBCF-1 IBCF-4 INVITE TrGW-1 TrGW-1 INVITE (192.0.2.1, 49170) (192.0.2.4, 16511) (192.0.2.1, 49170) (192.0.2.4, 16511) P-CSCF IBCF-5 TrGW-1 RTP flow Domain Va operatorV Figure 8.4. SDP announcements: optimal routeing The SIP INVITE request generated by the various IBCF entities maintains in the SDP message the characteristics of RTP streams VoLTE and ViLTE (IP address, port number and domain name) of the previous announcements. The IBCF-4 instance must detect from the SIP INVITE request received from the IBCF-3 instance that a looping from the home network has been achieved and must implement the OMR routeing for the RTP stream, to provide to the IBCF-5 instance the SDP message generated by Alice

's UA entity. The response SIP 183 Session Progress from the IBCF-5 instance contains in the SDP message the characteristics of RTP streams provided by the TrGW-1 entity, which need to be transferred to Alice's UA entity. The IBCF-4 instance replaces the IP address provided by the IBCF-5 instance by the undetermined IP address 0.0.0.0 as the IP address has no meaning in the home and transit networks. The IBCF-4 instance, however, maintains in the SDP message the RTP stream characteristics provided by the IBCF-5 instance. The undetermined IP address is deleted by IBCF-1 instance and the IP address provided by the IBCF-5 instance is restored. 8.2. Procedures 8.2.1. Session establishment for nominal routeing 8.2.1.1. Originating side The session establishment procedure for the nominal routeing of the RTP streams, relating to the outgoing call, is described in Figure 8.5. To simplify the presentation, responses 100 Trying and 180 Ringing and precondition mechanisms are not shown. Table 8.1 summarizes the IP addresses and the port numbers of the RTP flows, established, on the one hand, between Alice's UA entity and the TrGW-1 entity, and on the other hand, between the TrGW-1 and TrGW-2 entities. Roaming 229 P-CSCF IBCF-1 IBCF-2 S-CSCF IBCF-3 SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 8.5. Session establishment for nominal routeing originating side Alice's UA TrGW-1 IP address 192.0.2.1 192.0.2.2 Port number 49170 TrGW-1 TrGW-2 IP address 178.15.1.1 190.1.15.2 Port number 62111 12538 Table 8.1. RTP flow characteristics in the case of nominal routeing originating side 1) Alice's UA entity transmits to the P-CSCF entity the SIP INVITE request, whose SDP message contains the characteristics (IP address and port number) of the RTP stream. INVITE SIP: tel:+4687197378; SIP/2.0 Route: <sip:pcscf1.visitedVA.net;lr> Content-Type application/sdp Content-Length: (...) C=IN IP4 192.0.2.1 m=audi

o 49170 RTP/AVP 96 97 230 VoLTE and ViLTE 2) The P-CSCF entity selects the IBCF entity of the visited network (IBCF-1 instance) and transfers the SIP INVITE request. The P-CSCF entity removes its uniform resource identifier (URI) in the Route header and adds that of the S-CSCF entity of the home network, indicating in the iotl parameter the direction of request (visitedA- homeA). INVITE SIP: tel:+4687197378; SIP/2.0 Route: ksip:scscf1.operatorHA.net;lr;iotl=visitedA- homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 . . . 3) The IBCF-1 instance selects the IBCF entity of the home network (IBCF-2 instance) and transfers the SIP INVITE message, whose SDP message replaces the characteristics of RTP streams received from the Alice's UA entity by those provided by the TrGW-1 entity. INVITE SIP: tel:+4687197378; SIP/2.0 Route: k<sip:scscf1.operatorHA.net;lr;iotl=visitedA- homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.1 m=audio 62111 RTP/AVP 96 97 The IBCF-2 instance forwards to the S-CSCF entity the SIP INVITE message without changing the SDP message. 4) The S-CSCF entity transfers to the IBCF-3 instance the SIP INVITE message having the following transactions: - it withdraws its URI identity in the route header; Roaming 231 - it performs the ENUM resolution on the URI identity of the destination to which it adds the iotl parameter indicating the direction of the request (homeA-homeB). INVITE <sip:+46107197378@operatorY;user=phone;iotl=homeA-homeB> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.1 m=audio 62111 RTP/AVP 96 97 When the IBCF-3 instance has received the SIP INVITE request, it generates a new SIP INVITE request to Bob's home network. 5) On receipt of the SIP 183 Session Progress message from Bob's home network, the IBCF-3 instance generates the SIP 183 Session Progress message to the S-CSCF entity whose associated SDP message contains the characteristics of the flow RTP communicated by the Tr

GW-2 entity. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.2 m=audio 12538 RTP/AVP 97 98 The SIP 183 Session Progress message is forwarded without changing the SDP message to the IBCF-1 instance. 6) The IBCF-1 instance forwards to the P-CSCF entity the SIP 183 Session Progress message, whose SDP message replaces the RTP stream characteristics received from the IBCF-3 instance with those provided by the entity TrGW-1. 232 VoLTE and ViLTE SIP/2.0 183 Session Progress Content- - Type application/sdp Content-Length - : (...) C=IN IP4 192.0.2.2 m=audio 9452 RTP/AVP 97 98 The SIP 183 Session Progress message is forwarded without changing the SDP message to Alice's UA entity. 8.2.1.2. Terminating side The session establishment procedure for the nominal routeing of the RTP streams, relating to the outgoing call, is described in Figure 8.6. Table 8.2 summarizes the IP addresses and the port numbers of the RTP streams, established, on the one hand, between Bob's UA entity and TrGW-4 entity, and, on the other hand, between TrGW-3 and TrGW-4 entities. P-CSCF IBCF-6 IBCF-5 S-CSCF IBCF-4 SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP INVITE SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 8.6. Session establishment for nominal routeing terminating side Roaming 233 Bob's UA TrGW-4 IP address 193.0.2.1 193.0.2.2 Port number 49170 TrGW-4 TrGW-3 IP address 179.15.1.1 191.1.15.2 Port number 62111 12538 Table 8.2. RTP flow characteristics in the case of nominal routeing terminating side 1) Upon receipt of the SIP INVITE request from Alice's home network, the IBCF-4 instance generates the SIP INVITE message to the S-CSCF entity, whose SDP message contains the RTP stream characteristics provided by the TrGW-3 entity. INVITE <sip:+46107197378@operatorY;user=phone;iotl=homeA-homeB> SIP/2.0 Content-Type application/sdp Content-Length: (...) C=IN IP4 191.1.15.2 m=audio 12538 RTP/AVP 96 97 2) The S-CSCF entity

inserts Bob's IP address instead of the phone number into the SIP URI identity of the SIP INVITE request. The S-CSCF entity adds the Route header containing the URI identity of the P-CSCF entity and iotl parameter indicating the direction of the request (homeB-visitedB). The IBCF-5 instance forwards to the IBCF (IBCF-6 instance) entity the SIP INVITE message without changing the SDP message. 234 VoLTE and ViLTE INVITE <sip:193.0.2.1@operatorY> SIP/2.0 Route: <sip:pcscf1.visitedVB.net;lr;iotl=homeB-visitedB> Content-Type: application/sdp Content-Length: (...) C=IN IP4 191.1.15.2 m=audio 12538 RTP/AVP 96 97 3) The IBCF-6 instance transfers to the P-CSCF entity the SIP INVITE message, whose SDP message replaces the RTP stream characteristics received from TrGW-3 entity with that communicated by the TrGW-4 entity. INVITE <sip:193.0.2.1@operatorY> SIP/2.0 Route: :<sip:pcscf1.visitedVB.net;lr;iotl=homeB-visitedB> Content-Type: application/sdp Content-Length: (...) C=IN IP4 193.0.2.2 m=audio 9452 RTP/AVP 96 97 4) The P-CSCF entity removes its identity from the Route header and transfers the SIP INVITE message to Bob's UA entity. INVITE <sip: :193.0.2.1@operatorY> SIP/2.0 Content-Type: application/sdp Content-Length: (...) C=IN IP4 193.0.2.2 m=audio 9452 RTP/AVP 96 97 . . . 5) Alice's UA entity generates the SIP 183 Session Progress message to the P-CSCF entity, whose associated SDP message contains the RTP stream characteristics. Roaming 235 SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 193.0.2.1 m=audio 59170 RTP/AVP 97 98 The SIP 183 Session Progress message is forwarded without changing the SDP message to the IBCF-6 instance. 6) The IBCF-6 instance forwards to the IBCF-5 instance SIP 183 Session Progress message, whose SDP message replaces the RTP stream characteristics received from the Bob's UA entity with those provided by the TrGW-4 entity. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: ( ) C=IN IP4 179.15.1.1 m=audio 62111 RTP/AVP 97 98 The

SIP 183 Session Progress message is forwarded without changing the SDP message to the IBCF-4 instance. 8.2.2. Session establishment for optimal routeing The session establishment procedure for the OMR routeing of the RTP streams, relating to the outgoing call, is shown in Figure 8.7. 1) Alice's UA entity transmits to the P-CSCF entity the SIP INVITE request, whose SDP message contains the characteristics (IP address and port number) of the RTP stream. 236 VoLTE and ViLTE INVITE SIP: el:+4687197378; SIP/2.0 Route: <sip:pcscf1.visitedVA.net;I lr> Content-Type : application/sdp Content-Length: ( C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 Alice's visited network (VisitedA.net) Alice's home network Alice' visited network (VisitedA net) (HomeA.net) P-CSCF IBCF-1 IBCF-2 S-CSCF IBCF-3 IBCF-4 IBCF-5 INVITE INVITE INVITE INVITE INVITE INVITE INVITE INVITE SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 183 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP 200 SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK SIP ACK Figure 8.7. Session establishment for optimal routeing originating side 2) The P-CSCF entity removes its URI identity in the Route header and adds that of the S-CSCF entity of the home network, indicating in the iotl parameter the direction of request (visitedA-homeA). The P-CSCF entity selects the IBCF entity of the visited network (IBCF-1 instance) and transfers the SIP INVITE request, whose Feature- Caps header contains the URI identity of the TRF entity. Roaming 237 INVITE SIP: tel:+4687197378; SIP/2.0 Route: <sip:scscf1.operatorHA.net;lr;iotl=visitedA- homeA> Feature- Caps:*;+g.3gpp.trf="<sip:trf1.visitedV.net;iotl=homeA- visitedA>" Content-Type: application/sap Content-Length: (...) C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 3) The IBCF-1 instance selects the IBCF entity of the home network (IBCF-2 instance) and transfers the SIP INVITE message, whose SDP message replaces the RTP stream characteristics received from Alice's UA entity with those provided by the TrGW-1 e

ntity. The SIP message also contains the instances 1 and 2 of the a=visited-realmpopulated with the following information: - the domain name to which Alice's UA entity is connected (va.operatorV.net), the IP address and the RTP stream port number of Alice's UA entity; - the domain name of the network to which the IBCF-1 instance is connected (xa1.operatorX.net), the IP address and the port number of the RTP stream provided by the TrGW-1 entity for the specified domain name. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:scscf1.operatorH.net;lr;iotl=visitedA-homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 178.15.1.1 m=audio 62111 RTP/AVP 96 97 a=visited-realm: Va. .operatorV. net IN IP4 192.0.2.1 49170 a=visited-realm: Xal.operatorX.net IN IP4 178.15.1.1 62111 238 VoLTE and ViLTE 4) The IBCF-2 instance forwards to the S-CSCF entity the SIP INVITE message, whose SDP message replaces the RTP stream characteristics received from the IBCF-1 instance with those provided by the TrGW-2 entity. The SIP message adds the instance 3 of the header a=visited-realm populated with the domain name of the network to which the instance IBCF-2 is connected (Ha.operatorH.net) the IP address and the port number of the RTP stream provided by the TrGW-2 entity for the specified domain name. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:scscf1.operatorH.net;lr;iotl=visitedA-homeA> Content-Type: application/sdp Content-Length: (...) C=IN IP4 190.1.15.1 m=audio 16789 RTP/AVP 96 97 a=visited-realm: Va.operatorV. net IN IP4 192.0.2.1 49170 a=visited-realm: Xal.operatorH.net IN IP4 178.15.1.1 62111 a=visited-realm: Ha.operatorH.net IN IP4 190.1.15.1 16789 5) The S-CSCF entity transfers to the IBCF-3 instance the SIP INVITE message whose header Feature-Caps indicates that the loop to Alice's visited network is activated. The S-CSCF entity withdraws its URI identity in the Route header and adds that the TRF entity of the visited network, indicating in the iotl parameter the direction of the request (homeA-visitedA). INVIT

E SIP: tel:+4687197378; SIP/2.0 Route:<sip:trf1.visitedV.net;lr;iotl=homeA-visitedA> Feature-Caps:*;+g.3gpp.loopback=<"homenetwork_A"> Content-Type: application/sdp Content-Length: (...) Roaming 239 C=IN IP4 190.1.15.1 m=audio 16789 RTP/AVP 96 97 a=visited-realm:] Va.operatorV.: . net IN IP4 192.0.2.1 49170 a=visited-realm: 2 Xal.operatorH.net IN IP4 178.15.1.1 62111 a=visited-realm:3 Ha.operatorH.net IN IP4 190.1.15.1 16789 6) The IBCF-3 instance transfers to the IBCF entity of the visited network (IBCF-4 instance) the SIP INVITE message, whose SDP message replaces the RTP stream characteristics received from the IBCF-2 instance with those reported by the TrGW-2 entity. The SIP message adds the instance 4 of the header a=visited-realm populated with the domain name of the network to which the IBCF-3 instance is connected (Xa2.operatorX.net), the IP address and the port number of the RTP, stream provided by the TrGW-2 entity for the specified domain name. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:trf1.visitedV.net;lr;iotl=homeA-visitedA> Feature-Caps:*;+g.3gpp.loopback=<"homenetwork-A"> Content-Type: application/sdp Content-Length: (...) C=IN IP4 179.14.1.2 m=audio 34500 RTP/AVP 96 97 a=visited-realm: 1 Va.operatorV. . net IN IP4 192.0.2.1 49170 a=visited-realm: Xal.operatorX.net IN IP4 178.15.1.1 62111 a=visited-realm: Ha.operatorH.net IN IP4 190.1.15.1 16789 a=visited-realm: Xa2.operatorX.net IN IP4 179.14.1.2 34500 240 VoLTE and ViLTE 7) Upon receipt of the SIP INVITE message, the IBCF-4 instance detects that the case of optimal routeing is possible. The IBCF-4 instance transfers to the TRF entity the SIP INVITE message, whose SDP message replaces the RTP stream characteristics of the IBCF-3 instance with those of the instance 1 of the header a=visited- realm. Instances 2 to 4 of the header a=visited-realmare deleted. INVITE SIP: tel:+4687197378; SIP/2.0 Route:<sip:trf1.visitedV.net;lr;iotl=homeA-visitedA> Feature-Caps:*;+g.3gpp.loopback=<"homenetwork-A"> Content-Type: application/sdp Content-Length: ( C

=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 a=visited-realm: Va.operatorV. net IN IP4 192.0.2.1 49170 . . . 8) The TRF entity performs ENUM resolution on the URI identity of the destination to which it adds the iotl parameter indicating the direction of the request (visitedA-homeB), withdraws its URI identity in the Route header and transfers the SIP INVITE request to the IBCF-5 instance. INVITE SIP: <sip:+46107197378@operatorY;user=phone;iotl=visitedA- homeB> SIP/2.0 Feature-Caps:*;+g.3gpp.loopback=<"homenetwork-A"> Content-Type: application/sdp Content-Length: (...) C=IN IP4 192.0.2.1 m=audio 49170 RTP/AVP 96 97 . . . a=visited-realm: Va. operatorV . net IN IP4 192.0.2.1 49170 Roaming 241 When the IBCF-5 instance received the SIP INVITE request, it generates a new request to the SIP INVITE Bob's home network. 9) Upon receipt of the SIP 183 Session Progress message from Bob's home network, the IBCF-5 instance generates to the TRF entity, the SIP 183 Session Progress message, whose associated SDP message contains RTP stream characteristics reported by the TrGW-1 entity. The SIP message also contains the instance 1 of the header a=visited-realm populated with the domain name to which the IBCF-5 instance is connected the IP address and the RTP stream port number of the TrGW-1 entity. SIP/2.0 183 Session Progress Content-Type application/sdp Content-Length: (...) C=IN IP4 192.0.2.4 m=audio 16511 RTP/AVP 97 98 a=visited-realm: Va. operatorV.net IN IP4 192.0.2.4 16511 The SIP 183 Session Progress message is forwarded without changing the SDP message to the IBCF-4 instance. 10) The IBCF-4 instance transfers to the IBCF entity of the visited network (IBCF-3 instance), the SIP 183 Session Progress message whose SDP message replaces the IP address of the RTP stream of the IBCF-5 instance by 0.0.0.0 value. SIP/2.0 183 Session Progress Content-Type: application/sdp Content-Length: (...) C=IN IP4 0.0.0.0 m=audio 16511 RTP/AVP 97 98 a=visited-realm: Va. operatorV.net IN IP4 192.0.2.4 16511 The SIP 183 Session Progress messa

ge is forwarded without changing the SDP message to the IBCF-1 instance. 242 VoLTE and ViLTE 11) The IBCF-1 instance forwards to the P-CSCF entity the SIP 183 Session Progress message, whose SDP message replaces the RTP stream characteristics received from the IBCF-4 instance with those of the instance 1 of the header a=visited-realm and removes it. The SIP 183 Session Progress message is forwarded without changing the SDP message to Alice's UA entity. SIP/2.0 183 Session Progress Content-Type application/sdp Content-Length: (...) C=IN IP4 192.0.2.4 m=audio 16511 RTP/AVP 97 98 Service Centralization and Continuity 9.1. ICS function IMS centralized services (ICS) allow for centralizing IMS services regardless of whether the mode of the mobile network is circuit-switched (CS) or packet-switched (PS). The role of the network in CS mode becomes equivalent to that of the network in PS mode: it is restricted to the construction of bearers which handle telephone signaling and voice or conversational video. 9.1.1. Functional architecture The functional architecture of the ICS function is described in Figure 9.1, for the case where the mobile-services switching centre (MSC) server and the user equipment (UE) implement ICS. The mobile attached to the network in CS mode can use the Gm interface for session initiation protocol (SIP) if both CS and PS modes are available simultaneously. The mobile attached to the network in CS mode can use the Ut interface to configure its services to the telephony application server (TAS) if both CS and PS modes are available simultaneously. The ICS function introduces a new entity in the IMS network, the service centralization and continuity application server (SCC AS). VoLTE and ViLTE: Voice and Conversational Video Services over the 4G Mobile Network, First Edition. André Perez. C ISTE Ltd 2016. Published by ISTE Ltd and John Wiley & Sons, Inc. VoLTE and ViLTE Ut (XCAP) (DIAMETER) (DIAMETER) I2 (SIP) Mx / Mi (SIP) Server NAS (CM) Gm (SIP) (CS flow) Mb (RTP flow) Figure 9.1. MSC server and