IP Multimedia Subsystem
Interfaces description

IP Multimedia Subsystem

Section Title: Interfaces description
Table Section Text: None

Interface name	IMS entities	Description	Protocol	Technical specification

Cr	MRFC, AS	Used by MRFC to fetch documents (e.g. scripts, announcement files, and other resources) from an AS.	TCP/SCTP channels

Cx	(I-CSCF, S-CSCF), HSS	Used to send subscriber data to the S-CSCF; including filter criteria and their priority. Also used to furnish CDF and/or OCF addresses.	Diameter	TS29.229, TS29.212

Dh	AS (SIP AS, OSA, IM-SSF) SLF	Used by AS to find the HSS holding the user profile information in a multi-HSS environment. DH_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.	Diameter

Dx	(I-CSCF or S-CSCF) SLF	Used by I-CSCF or S-CSCF to find a correct HSS in a multi-HSS environment. DX_SLF_QUERY indicates an IMPU and DX_SLF_RESP return the HSS name.	Diameter	TS29.229, TS29.212

Gm	UE, P-CSCF	Used to exchange messages between SIP user equipment (UE) or Voip gateway and P-CSCF	SIP

Go	PDF, GGSN	Allows operators to control QoS in a user plane and exchange charging correlation information between IMS and GPRS network	COPS (Rel5), diameter (Rel6+)

Gq	P-CSCF, PDF	Used to exchange policy decisions-related information between P-CSCF and PDF	Diameter

Gx	PCEF, PCRF	Used to exchange policy decisions-related information between PCEF and PCRF	Diameter	TS29.211, TS29.212

Gy	PCEF, OCS	Used for online flow-based bearer charging. Functionally equivalent to Ro interface	Diameter	TS23.203, TS32.299

ISC	S-CSCF AS	Reference point between S-CSCF and AS. Main functions are to : Notify the AS of the registered IMPU, registration state and UE capabilities Supply the AS with information to allow it to execute multiple services Convey charging function addresses	SIP

Ici	IBCFs	Used to exchange messages between an IBCF and another IBCF belonging to a different IMS network.	SIP

Izi	TrGWs	Used to forward media streams from a TrGW to another TrGW belonging to a different IMS network.	RTP

Ma	I-CSCF AS	Main functions are to: Forward SIP requests which are destined to a public service identity hosted by the AS Originate a session on behalf of a user or public service identity, if the AS has no knowledge of a S-CSCF assigned to that user or public service identity Convey charging function addresses	SIP

Mg	MGCF -> I,S-CSCF	ISUP signalling to SIP signalling and forwards SIP signalling to I-CSCF	SIP

Mi	S-CSCF -> BGCF	Used to exchange messages between S-CSCF and BGCF	SIP

Mj	BGCF -> MGCF	Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in the same IMS network to send SIP message from BGCF to MGCF	SIP

Mk	BGCF -> BGCF	Used for the interworking with the PSTN/CS domain, when the BGCF has determined that a breakout should occur in another IMS network to send SIP message from BGCF to the BGCF in the other network	SIP

Mm	I-CSCF, S-CSCF, external IP network	Used for exchanging messages between IMS and external IP networks	SIP

Mn	MGCF, IM-MGW	Allows control of user-plane resources	H.248

Mp	MRFC, MRFP	Allows an MRFC to control media stream resources provided by an MRFP.	H.248

Mr Mr'	S-CSCF, MRFC AS, MRFC	Used to exchange information between S-CSCF and MRFC Used to exchange session controls between AS and MRFC	Application server sends SIP message to MRFC to play tone and announcement. This SIP message contains sufficient information to play tone and announcement or provide information to MRFC, so that it can ask more information from application server through Cr Interface.	SIP

Mw	P-CSCF, I-CSCF, S-CSCF, AGCF	Used to exchange messages between CSCFs. AGCF appears as a P-CSCF to the other CSCFs	SIP

Mx	BGCF/CSCF, IBCF	Used for the interworking with another IMS network, when the BGCF has determined that a breakout should occur in the other IMS network to send SIP message from BGCF to the IBCF in the other network	SIP

P1	AGCF, A-MGW	Used for call control services by AGCF to control H.248 A-MGW and residential gateways	H.248

P2	AGCF, CSCF	Reference point between AGCF and CSCF.	SIP

Rc	MRB, AS	Used by the AS to request that media resources be assigned to a call when using MRB in-line mode or in query mode	SIP, in query mode (not specified)

Rf	P-CSCF, I-CSCF, S-CSCF, BGCF, MRFC, MGCF, AS	Used to exchange offline charging information with CDF	Diameter	TS32.299

Ro	AS, MRFC, S-CSCF	Used to exchange online charging information with OCF	Diameter	TS32.299

Rx	P-CSCF, PCRF	Used to exchange policy and charging related information between P-CSCF and PCRF Replacement for the Gq reference point.	Diameter	TS29.214

Sh	AS (SIP AS, OSA SCS), HSS	Used to exchange User Profile information (e.g., user-related data, group lists, user-service-related information or user location information or charging function addresses (used when the AS has not received the third-party REGISTER for a user)) between an AS (SIP AS or OSA SCS) and HSS.	Diameter

Si	IM-SSF, HSS	Transports CAMEL subscription information, including triggers for use by CAMEL-based application services information.	MAP

Sr	MRFC, AS	Used by MRFC to fetch documents (scripts and other resources) from an AS	HTTP

Ut	UE and SIP AS (SIP AS, OSA SCS, IM-SSF) PES AS and AGCF	Facilitates the management of subscriber information related to services and settings	HTTP(s), XCAP

z	POTS, Analog phones and VoIP gateways	Conversion of POTS services to SIP messages

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