Next Generation Mobile Communications Ecosystem Type C Application Server* Network Subcription Policy Policy Application Application Rules Databases Server Server 8/OSA-API Network Policy and OSA Service Management Charging Capacity Layer/OSS Rules SCMCS Server Function Controller TylGx Element Proxy Service Breakout Management Position Call Session Call Session Gateway Layer Server Control Control Control Function Function Function Managed Position Network Interrogating Media Media Determining Entity Entity Call Session Resource Gateway Control Function Control Function Controller Function Mobile Station odma2000 Access Network Access Media Gateway Resource Media BSC/RNC Function Gateway Processor Mobile IP Attendant Other Access Networks Border 43/Mb Agent Router Legacy MS Domain TJA/E/R-41 Support Network Figure 9.7 3GPP2 network architecture model reflecting common IMS entities. Reproduced with permission from C 2008 3GPP2 [10] material. 3GPP2 MMD specifies the Tx interface [X.S0013-013-0 v1.0] between a PCRF and an Application Function (AF), and the Ty interface [X.S0013-014-0 v1.0] between a PCRF and an Access Gateway. In 3GPP Release 8, both the Rx interface [TS 29.214] and the Gx interface [TS 29.212] are enhanced and new Gxx interface [TS 29.212] and S9 interface [TS 29.215] are specified. The functionality for Tx and Ty interfaces are incorporated into the Release 8 within Rx, Gx, Gxx and S9 interfaces. MGW: The Media Gateway (MGW) is equivalent to the IMS-MGW (IMS Media Gateway) in [TS 23.002]. IMS, Services and Applications 9.8 Protocols IMS uses a large number of protocols to perform its functions; but some of the key ones are reused from the Internet. The most important one is SIP (Session Initiation Protocol) which was originally designed by Henning and Schulzrinne of Columbia University and Mark Handley of University College London in 1996. Others include Diameter, MEGACO, and COPS: SIP: In November 2000, SIP was accepted as a 3GPP signaling protocol and permanent element of the IMS architecture. 