Abstract:
A machine-to-machine communication proxy node is presented herein. The proxy node may be used as a translation device in machine-to-machine communications. For example, if an application server in a packet based network initiates communication with device in a mobile network, the proxy node may be utilized to translate application domain specific device identities coded in the format of Session Initiation Protocol (SIP) and Uniform Resource Identifier&#39;s (URI&#39;s) to mobile specific identities such as IMSI and establish communication connection in the mobile network. This identifying of mobile devices may be utilized to replace the commonly used E.164 Mobile Subscriber Integrated Services Digital Network (MSISDN) numbers for identifying mobile devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Submission Under 35 U.S.C. §371 for U.S. National Stage Patent Application of International Application Number: PCT/EP2010/051867, filed Feb. 15, 2010 entitled “MACHINE-TO-MACHINE DEVICE TRIGGERING USING SESSION INITIATION PROTOCOL UNIFORM RESOURCE IDENTIFIER,” the entirety of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Machine-to-machine communication in cellular networks. 
     BACKGROUND 
     With Machine-to-Machine (M2M) communication being more and more deployed in cellular networks, problems with how to address the M2M devices (user equipment; UE&#39;s) for Mobile Terminated Communication from M2M application servers arise. With the use of dynamic IP address assignments, a mechanism where the M2M application server gets to know the IP address of the device needs to be present. In some applications the device/UE itself can contact the M2M application server and inform about its presence and IP address, but in other applications the communication needs to be initiated from the M2M application server side, where the application server may not know the IP address of the device. 
     Another problem with the growing interest in M2M cellular communications is that each device/UE today is assigned an E.164 Mobile Subscriber Integrated Services Digital Network (MSISDN) number. With the expected growth of M2M devices being 50 Billion and beyond, these identities will soon be exhausted. This has been pointed out by the International Telecommunications Union (ITU) which has asked 3GPP to find new solutions for addressing mobile devices. It is even suggested that the E.164 MSISDN shall not be mandatory for M2M devices anymore, as these numbers are mainly targeted for human communication. 
     SUMMARY 
     Currently Mobile Terminated Communication with M2M devices is often based on Short Message Service (SMS) where the E.164 MSISDN is required for addressing. The E.164 MSISDN is a number assigned to an M2M device to uniquely identify the device in a mobile network. This solution does not scale for a large number of M2M devices. The Short Message Service Centers (SMSCs) also have problems in meeting the delay and response time requirements that many M2M applications have (e.g. for emergency type of applications). 
     It is also a problem that Public Land Mobile Network (PLMN) specific identifiers need to be used in the development of the M2M applications in servers outside the PLMN. This solution creates unnecessary dependencies between the two domains. Furthermore, this also results in development being slowed due to the constraints for how to allocate the various identities. 
     For some M2M applications, which include infrequent communication with small amounts of data (e.g., a monthly reading of an electricity meter), the relatively large amount of overhead of signaling (e.g., attach, bearer &amp; periodic) in mobile system can be a problem when large sets of M2M devices are present in the network. 
     Thus, solutions directed towards the resolution of the above mentioned deficiencies are presented herein. Example embodiments provide the replacement of E.164 MSISDN with Session Initiation Protocol (SIP) and Uniform Resource Identifier&#39;s (URI&#39;s) for identifying M2M devices, thereby freeing more resources to be used for human involved communications. Example embodiments also provide a decoupling of PLMN identities from M2M applications outside of the PLMN. Thus, externally from the PLMN, SIP and SIP URI&#39;s may be used in place of the PLMN identities. This enables the M2M application service provider to be free to use his formation in the identification of associated M2M devices. The chosen identities are transparent to the mobile operator and are seen and treated in the same manner as any other URI&#39;s. 
     Example embodiments may also involve a combined SIP server and mapping function at the border between the Packet Data Network (PDN), where a M2M application server may be located, and the PLMN, where the M2M device may be located. The SIP server may act as a SIP Proxy on behalf of the device and taking a full user agent role. At this border, the SIP URI may be translated to PLMN internal information and vice versa. Examples of PLMN internal information may include, but are not limited to, an International Mobile Subscriber Identity (IMSI), IP-address(es) of the device, temporary identifiers used for paging (e.g., a Packet—Temporary Mobile Subscriber Identity (P-TMSI), and a System architecture evolution—Temporary Mobile Subscriber Identity (S-TMSI)) if the device is idle or no bearers have been activated, and cell(s) where the device has been last reported its location. If the device has several PDP contexts/PDN connections or if the device uses both IP version 4 and IP version 6 simultaneously there may multiple IP addresses. In that case the PLMN internal information may include characteristics of the IP address information e.g. IP version, quality of service or priority of the corresponding bearer etc. 
     Example embodiments may involve an optimized registration procedure for M2M devices in the 3GPP network. The optimized registration procedure may include utilizing a field in the Protocol Configuration Options (PCO) where attach/bearer activation messages may be used to convey a device identity to the SIP server/mapping function (i.e. to register the device). 
     Furthermore, example embodiments may also include a possibility to initiate paging from the SIP server/mapping function if the M2M device is idle, or has no bearers activated (and hence no IP address is available), or the device is in some other detach state only listening to the paging channel at frequent or infrequent intervals. 
     Example embodiments also include a SIP server/mapping function where small amounts of data, which are included in the SIP signaling (e.g., an SIP Invite), is translated to SMS messages and sent to the M2M device, e.g., using IMSI (no E.164 MSISDN would be required). For optimized real-time performance the SMS may be delivered directly to the Mobile Management Entity/Serving General packet radio service Support Node (MME/SGSN) or even a Radio Access Network (RAN) node (e.g., eNodeB/RNC/BSC) without passing the SMSC. Bypassing the SMSC avoids store-and-forward delays as well as reduces the amount of required communications signaling. This mechanism may be bi-directional, i.e., answers from the M2M device may be mapped and sent back using SIP signaling (e.g., SIP 200 OK) to the originating application server. 
     DEFINITIONS 
     APN—Access point name 
     DSCP—DiffServ Code Point 
     GGSN—Gateway General packet radio service Support Node 
     HSS—Home Subscriber Server 
     IE—Information Element 
     IMSI—International Mobile Subscriber Identity 
     M2M—Machine-to-Machine 
     MME—Mobile Management Entity 
     MSISDN—Mobile Subscriber Integrated Services Digital Network 
     MTC—Mobile Type Communication 
     P-TMSI-Packet—Temporary Mobile Subscriber Identity 
     PCO—Protocol Configuration Options 
     PDN—Packet Data Network 
     PGW—Packet data Network Gateway 
     PLMN—Public Land Mobile Network 
     QCI—QoS Class Identifier 
     RAN—Radio Access Network 
     S-TMSI—System architecture evolution—Temporary Mobile Subscriber Identity 
     SGSN—Serving General packet radio service Support Node 
     SIP—Session Initiation Protocol 
     SMS—Short Message Service 
     SMSC—Short Message Service Center 
     URI—Uniform Resource Identifier 
     UE—User Equipment 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. 
       The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
         FIG. 1  is a schematic of a Machine-to-Machine communication network according to example embodiments; 
         FIG. 2  is a block diagram of a machine-to-machine proxy node included in the communication network of  FIG. 1 ; 
         FIG. 3  is a flow chart of example operational steps which may be taken by the proxy node of  FIG. 2 : 
         FIG. 4  is a message sequence diagram of device registration; 
         FIG. 5  is a message sequence diagram of device deregistration; 
         FIG. 6  is a message sequence diagram of a machine application initiated communication with a registered device; 
         FIG. 7  is a message sequence diagram of a machine application initiated communication with an unregistered device; and 
         FIG. 8  is a message sequence diagram of a small data transfer communication. 
     
    
    
     DETAILED DESCRIPTION 
     In the description below the term M2M Device and MTC Device are used interchangeably. It should further be appreciated that an M2M device may function as an M2M application server in attempting to communicate with another M2M device. Therefore, the example embodiments describing functions of the M2M application server may also be applied to an M2M device. 
     In many applications, M2M servers in packet based networks may need to retrieve or send data from/to M2M devices. For example, the amount of usage of a utility monitored by a meter may need to be reported to a service provider.  FIG. 1  illustrates a communications network which may be employed in machine-to-machine (M2M) communications according to example embodiments. The network  100  may include two distinct sub-networks. For example, a mobile based network  101 , in which a M2M device  102  may be located, and a packet based network  103 , in which a M2M application server  104  may be located. An M2M application server  104  located in a specific Packet Data Network (PDN)  106  may initiate communication and request data from a M2M device  102 . An M2M proxy  108  may function as a session initiator where, for example, the device identity is in the format of a SIP URI, may be translated to, for example, an IP address of the M2M device  102  and returned M2M application server  104 . The M2M proxy  108  may act as a translator of control plane information between the sub-networks  101  and  103 . The M2M proxy  108  may also accept subscriptions of state changes for M2M Devices. In this case the M2M proxy will notify or publish to the requesting entity (e.g. M2M application server) the changed information (e.g. IP address, device status etc) of a device each time the information is changed. 
     As an overview,  FIG. 2  provides a schematic of an example M2M proxy  108  and  FIG. 3  is a flow diagram illustrating example operational steps which may be taken by the proxy  108 . The M2M proxy  108  may include a receiver  112 , which may be configured to receive a communication request  110  ( 200 ). The communication request  110  may include a device specific identifier associated with the first network domain (e.g., an IMSI in a mobile based network). The receiver  112  may abstract the device specific identifier from the request and send the identifier  114  to a translator  116 . The translator may be employed to translate the identifier  114  into a translated identifier, where the translated identifier is associated with a second network domain (e.g.; a packet based network) ( 202 ). The translator  116  may thereafter send the translated identifier  118  to a transmitter  120 . The transmitter  120  may send a status relating to a machine in the first network domain, the status being defined by the translated identifier ( 204 ). 
     In example embodiments, the M2M proxy  108 ,  FIG. 2 , may serve as a Session Initiation Protocol (SIP) server towards the external PDN  106  and the M2M application server  104 . The receiver  112  may abstract the device specific identifier from the session initiation request  111  and send the identifier  114  to the translator  116 . The translator may be employed to translate the identifier  114  into a translated identifier. The translator  116  may thereafter send the translated identifier  118  to the transmitter  120 . The transmitter  120  may thereafter return the requested information to the requesting entity e.g. a M2M Application Server  104  as the status  111 . 
     In example embodiments, the M2M proxy may serve as a Session Initiation Protocol (SIP) server towards the external PDN  106  and the M2M application server  104  by returning session related information of one or several sessions being initiated. The M2M proxy  108  may act as a SIP server towards one or several requesting clients. That is, the M2M proxy  108  controlling the M2M devices  102  may, in example embodiments, serve multiple M2M Application Servers  104  independently and simultaneously. The M2M proxy  108  may also act as a 3GPP functional entity in the mobile sub-network  101 . The mobile sub-network, or the Public Land Mobile Network (PLMN), may include a number of communication devices and interfaces. For example, the PLMN may include Radio Access Networks (RANs), Servicing General packet radio service Support Nodes (SGSN), Mobility Management Entities (MME), Gateway General packet radio service Support Nodes (GGSN), Packet data Network Gateways (PGW), and/or Home Subscriber Server (HSS), etc. 
     In acting as a functional entity, the M2M proxy  108  may manage messages and identifying information which is provided from the PLMN. Specifically, in one example embodiment, the M2M proxy  108  may maintain a mapping table  109  and  120  storing information such as externally used device identifiers, the PLMN internal International Mobile Subscriber Identity (IMSI), SGSN/Mobility Management Entity (MME) address, one or more IP address of the device and QoS and priority related information of the IP addresses (e.g. QCI, DSCP etc). The mapping table  109  may be organized such that every entry of a PLMN based identifier may be associated with its associated PDN based identifier and vice versa.  FIGS. 4 through 8  more specific provide examples of how the M2M proxy  108  may be utilized in machine communications. It should be appreciated that in all example embodiments, the M2M Proxy may be a function in the GGSN/PGW or inside some other node at the PLMN border or being a standalone functional entity. 
     Device Registration/Deregistration 
     In creating and maintaining a mapping table, a M2M device  102  may initiate a device registration with the M2M proxy  108 . As a result of device registration, the M2M proxy  108  may easily translate necessary device identifications, store device information and status such as IP address(es) or locations, for the mobile sub-network  101  and provide these on request from the packet based network  103 . 
       FIG. 4  provides a detailed message sequence diagram of device registration, according to example embodiments. First, the M2M device (or Machine Type Communication [MTC] device)  102  may create a bearer by sending a Create PDP context request or a Create PDN Connection request. The MTC device may include in the bearer request an application specific device identity in the Protocol Configuration Option (PCO) field. The device identity may be forwarded to the GGSN/PGW transparently, or unchanged ( FIG. 4 , step  1 ). 
     The GGSN/PGW  107  may in-turn allocate an IP address for the MTC device. If the device identity field is present in the PCO Information Element (IE), the GGSN/PGW  107  may forward the device identity together with the IMSI, IP address, and/or SGSN/MME address to the M2M proxy  108  ( FIG. 4 , step  2 ). The information may be forwarded as a request using, for example, a Radius or Diameter protocol, or any other Authentication, Authorization, and Accounting (AAA) protocol known in the art. The address of the M2M proxy  108  may be preconfigured in the GGSN/PGW  107  (e.g. per Access point name (APN)) or retrieved by any other means known in the art. 
     Thereafter, the M2M proxy  108  may send an accept message to the GGSN/PGW  107  after a mapping entry has been established or updated in the M2M proxy  108  ( FIG. 4 , step  3 ). In an alternative embodiment, a Radius/Diameter server in the M2M proxy  108  may also allocate the IP address for the device. In this case, the assigned IP address is also returned to the GGSN/PGW  107  in the accept message. Upon receipt of the Access Request, the GGSN/PGVV. SGSN/MME, and RAN may create a bearer using a Create PDP context response or a Create PDN Connection response ( FIG. 4 , step  4 ). 
     Upon the completion of communication between the M2M application server  104  and the M2M Device  102 , the bearers in the Mobile based network  101 , may or may not be deactivated. The M2M Device  102  may initiate the bearer deactivation on its own initiative or on command from the M2M Application server  104  using any standard or proprietary protocol between the two. An example of device bearer deactivation is provided in  FIG. 5 . When the bearer(s) are deactivated for a device, a Deactivate PDP Context request or Deactivate PDN Connection request may be forwarded up to the GGSN/PGW  107  ( FIG. 5 , step  1 ). The GGSN/PGW  107  may thereafter notify the M2M proxy  108  by using, for example, Radius or Diameter protocol ( FIG. 5 , step  2 ). The M2M proxy  108  may thereafter remove the bearer related information from the mapping table  109  for the particular device, e.g. the IP address. The removal of bearer related information results in the device needing to be paged and a bearer created if an M2M application server (MTC Server/MTC User) wants to established a session with the device in the future ( FIG. 7 ). If the M2M Device  102  is unreachable (e.g. not attached or not listening to any paging channel) and the paging will fail or if the M2M proxy  108  has status information about the device saying that it is unreachable, any SIP invite will be given an negative response (e.g., ‘Client Gone’). After updating the mapping table  109 , the M2M proxy  108  may send an acknowledgement or accounting response to the GGSN/PGW  107  ( FIG. 5 , step  3 ). The GGSN/PGW  107  may in-turn forward a Deactivate PDP Context response of Deactivate PDN Connection response message onto the MTC device  102  and the hearer deactivation will proceed as normal ( FIG. 5 , step  4 ). 
     Device Triggering (with and without Extablished Bearers) 
     For many M2M applications there may be an interest to poll communications between MTC devices and the M2M application server. This may be because an MTC user may want to be in control of communication from MTC devices, and therefore does not allow MTC devices to randomly access the application server. Polling may also be useful for MTC devices that are not continuously attached to a network (e.g., devices that do not have continuous PDP/PDN connection). Thus, it may be beneficial to trigger MTC devices to attach and/or establish a PDP/PDN connection based on a trigger indication from the M2M application server. 
     A way to be able to address and trigger MTC devices both when they are attached with bearers and attached without bearers may be to identify MTC devices using SIP URI&#39;s. The identity of a device, for example “123456,” could then be part of a SIP URI coded into the user part (e.g., as sip:123456@mtc-provider-name.operator-name.com). A device which knows its own identity registers in the network, and the device identity together with the IP address of the UE, is stored in a M2M Proxy. An MTC User or MTC Server may then easily retrieve the IP address of the MTC Device using basic session signalling. In the example configuration the MTC Proxy takes a full UA role and may immediately respond to a Session Request with a Session Response returning the IP address of the particular MTC Device. Thereafter, the normal application specific UDP/TCP/IP communication can start. 
       FIG. 6  provides a detailed message sequence diagram depicting the triggering of a device  102  having bearers. When the M2M application server  104  wants to communicate with the MTC device  102 , a session request e.g. using a SIP invite including a SIP URI with the packet based device identity may be sent to the M2M proxy  108  ( FIG. 6 , step  1 ). The address to the M2M proxy  108  may be obtained, for example, by the Domain Name System (DNS) resolving the Fully Qualified Domain Name (FQDN) host part of the SIP URI or by other means known in the art. 
     Thereafter, the M2M proxy  108  may use the received packet based device identity to search in the mapping table  109  for a corresponding PLMN based identifier and location (e.g. SGSN or MME address; or translated identifier  118 ). In doing so, the M2M proxy  108  also ensures that the MTC device  102  has an IP address (e.g., a bearer has been established). If an IP address exists, the M2M proxy  108  may immediately return a session response (e.g. an SIP 200 OK message; or status  111 ) with the IP address of the MTC device  102  to the requesting M2M application server  104  ( FIG. 6 , step  2 ). Once the M2M application server  104  has obtained the IP address of the MTC device  102 , IP communication according to any application specific protocols may commence ( FIG. 6 , step  3 ). 
     The session request and response can in an alternative embodiment be implemented using a subscribe/notify mechanism. In such a case the first session request will indicating a subscription to the M2M Proxy  108 . The M2M Proxy will then send a session notification every time the information about a M2M device  102  has been changed. That is, the M2M application server  104  will then continuously be updated of any status change of any information in the mapping table  109 . 
       FIG. 7  provides a detailed message sequence diagram depicting the triggering of a device without a bearer, but with an entry in the mapping table  109 . If there is no entry at all in the mapping table  109  (i.e. the device has never registered), a SIP invite will be given an immediate negative response (e.g. ‘Not found’). 
     According to example embodiments, the triggering of a device without a bearer may be achieved with the use of paging to locate the device in the PLMN. First, when the M2M application server  104  wants to communicate with the MTC device  102 , a session request (e.g. a SIP invite; request  110 ) including the URI with the device identity (identity  114 ) is sent to the M2M proxy  108  ( FIG. 7 , step  1 ). Similarly to the example of  FIG. 6 , the address of the M2M proxy  108  may be obtained by the DNS resolving the FQDN host part of the URI or by other means known in the art. 
     In the case that the MTC device  102  is non-stationary (e.g., the M2M device is allowed to move according to subscription information), the M2M proxy  108  may request location information from the HSS ( FIG. 7 , step  2 A). The HSS may respond with the address to the SGSN/MME where the MTC device  102  may be reached ( FIG. 7 , step  2 B). For stationary devices, the SGSN/MME address may be stored in the M2M proxy  108  to save HSS signaling. 
     Thereafter, a paging notification may be sent by the M2M proxy  108  to the SGSN/MME where the MTC device  102  is known ( FIG. 7 , step  3 ). The SGSN/MME may in return send a paging message to the MTC device  102  ( FIG. 7 , step  4 ). The paging message sent by the SGSN/MME may be a normal paging or an optimized paging for M2M devices. In the meantime, the M2M proxy  108  may send a SIP 100 Trying message (e.g., status  111 ) to the M2M application server  104  indicating that communication establishment will be attempted and that this may take some time ( FIG. 7 , step  5 ). 
     If the MTC device  102  wasn&#39;t attached but can still receive the paging notification, the MTC device  102  will thereafter attach to the network ( FIG. 7 , step  6 ). The MTC device  102  may then send a bearer request (i.e. Create PDP Context request or Create PDN Connection request) to the network and thereafter the bearer may be created ( FIG. 7 , steps  7 A and  7 B). The bearer request may include an application specific device identity in the PCO field. 
     Upon receiving the request from the MTC device  102 , the GGSN/PGW  107  may allocate an IP address for the MTC device  102 . The GGSN/PGW  107  may also notify the M2M proxy  108  that the MTC device now has a bearer. The GGSN/PGW  107  may provide the M2M proxy  108  with the device identity together with the IMSI, IP address, and SGSN/MME address ( FIG. 7 , step  8 A) and other bearer related information (e.g. QoS, priority etc). An Access Request using the Radius or Diameter protocol may be used, or any other protocol known in the art ( FIG. 7 , step  8 B). The address of the M2M proxy  108  may be preconfigured in the GGSN/PGW  107  (e.g., per APN) or retrieved by some other means. 
     Upon receiving the information from the GGSN/PGW  107 , the M2M proxy  108  may create or update the mapping table  109  with the associated PLMN and PDN identifications for the device to be used in future communications, and with any bearer related information e.g. IP address(es), QoS etc. The M2M proxy  108  may then return a SIP 200 OK message with the IP address(es) of the MTC device  102  to the requesting M2M application server  104  ( FIG. 7 , step  9 ). The 200 OK message may optionally be sent with a certain delay after the Access Accept message has been sent in order to allow for the bearer to be fully established ( FIG. 7 , step  8 B). Thereafter, IP communication may commence according to any application specific protocols ( FIG. 7 , step  10 ). The session request and response can in an alternative embodiment be implemented using a subscribe/notify mechanism as described for  FIG. 6  above. 
     In another example embodiment, triggers may be broadcast using, for example, the Cell Broadcast Service (CBS), or any other broadcast mechanism known in the art. A Cell Broadcast Center (CBC) may be utilized under the control of a mobile network operator. Connected to a CBC may be one or more Cell Broadcast Entities (CBE) which may originate CBS messages. A mobile network operator may make an interface available to the CBC to trusted third parties to interconnect their CBE to the CBC of the mobile network operator. The MTC devices may be programmed to monitor a present CB channel(s), even when they are not attached to the network, and have assigned an Unique Paging Identity (UPID). This way the M2M application server of the third party is able to send CBS messages, including one or more UPIDs to its MTC device in certain areas based on location information available to the M2M application server. 
     Small Data Communication with Minimized Signaling 
     In many instances, the M2M application server  104  may need to send a small amount of data to the MTC device  102  and vice versa.  FIG. 8  provides an example of small data communication with minimized signaling to an unregistered MTC device. First, the M2M application server  104  may initiate communication by sending a SIP Invite message (e.g., communication request  110 ) to the M2M proxy  108  ( FIG. 8 , step  1 ). The SIP Invite message may include an URI with the device identity (identity  114 ) and the small data to be transmitted. The address of the M2M proxy  108  may be obtained by the DNS resolving the FQDN part of the URI. 
     For the case of non-stationary MTC devices, the M2M proxy  108  may request location information from the HSS ( FIG. 8 , step  2 A). The HSS may respond with, for example, the address to the SGSN/MME where the device may be reached ( FIG. 8 , step  2 B). For stationary devices, the SGSN/MME address may be stored in the M2M proxy  108  to save HSS signaling. 
     The M2M proxy  108  may thereafter send an SMS notification to the SGSN/MME responsible for the device ( FIG. 8 , step  3 ). The SMS notification may include the IMSI associated with the device and the small data. The SGSN/MME may in-turn send the SMS message including the small data to the MTC device  102  ( FIG. 8 , step  4 ). The MTC device  102  may respond by sending an SMS back to the SGSN/MME ( FIG. 8 , step  5 ). The SMS message of step  5  may be empty, and will then be treated as just an acknowledgement of the received SMS message of step  4 . Alternatively, the SMS message of step  5  may include small data the MTC device may wish to send back 
     The SGSN/MME may return the SMS message from the MTC device  102  to the M2M proxy  108  ( FIG. 8 , step  6 ). The M2M proxy  108  may then update the mapping table  109  and register the MTC device  102 . The M2M proxy  108  then sends an SIP 200 OK message (e.g., status  111 ) back to the M2M application server  104  ( FIG. 8 , step  7 ). If the MTC device  102  responded with some data, the small data is included in the 200 OK message. If the MTC device  102  has a bearer activated, the M2M proxy  108  may optionally in step  3  send the small data in a User Datagram Protocol (UDP)/IP packet to the MTC device. The device may in that case also respond with a UDP/IP packet to the M2M proxy  108 . A subsequent SIP 200 OK will then follow. 
     While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims. 
     It should be understood that certain processes disclosed herein may be implemented in hardware, firmware, or software. If implemented in software, the software may be stored on any form of computer readable medium, such as random access memory (RAM), read only memory (ROM), compact disk read only memory (CD-ROM), and so forth. In operation, a general purpose or application specific processor loads and executes the software in a manner well understood in the art.