IP Multimedia Subsystem IMS Agenda Background n IMS

IP Multimedia Subsystem (IMS) 江培文

Agenda Background n IMS Definition n IMS Architecture n IMS Entities n IMS-CS Interworking n

Background - AMPS n Advanced Mobile Phone System (AMPS) ¨ First generation (1 G) cellular network ¨ Analog mobile phone system ¨ Standardized by ANSI ¨ Operate in the 800 MHz band ¨ Voice call

Background - GSM n Global System for Mobile communications (GSM) ¨ Second generation (2 G) cellular network ¨ Digital mobile phone system ¨ Most GSM networks operate in 900 MHz or 1800 MHz bands ¨ Each radio channel bandwidth is 200 k. Hz ¨ Standardized by ETSI ¨ Voice call, short message service

Background - GPRS n General Packet Radio Service (GPRS) ¨ 2. 5 G packet oriented mobile network ¨ Provide data rates from 56 up to 114 kbps ¨ Standardized by ETSI/3 GPP ¨ Short Message Service (SMS), Wireless Application Protocol (WAP), Multimedia Messaging Service (MMS), Internet Access

Background - EDGE n Enhanced Data rates for GSM Evolution (EDGE) ¨ 2. 75 G packet oriented mobile network ¨ Data rate up to 236. 8 kbps ¨ Standardized by 3 GPP ¨ Multimedia services, Internet access

Background - WCDMA n Wideband Code Division Multiple Access (WCDMA) ¨ Third generation (3 G) cellular network ¨ 1885– 2025 MHz for uplink band 2110– 2200 MHz for downlink band ¨ Each radio channel bandwidth is 5 MHz ¨ Data rate up to 384 kbps ¨ Standardized by 3 GPP ¨ The world's first commercial WCDMA network, FOMA, was launched by NTT Do. Co. Mo in Japan in 2001.

Background - HSDPA n High Speed Downlink Packet Access (HSDPA) ¨ 3. 5 G packet oriented mobile network ¨ Adaptive Modulation and Coding (AMC) n Depend on signal quality and cell usage n QPSK in initial scheme, 16 QAM in good radio condition. ¨ Data rate up to 14. 4 Mbps for downlink and 384 kbps for uplink ¨ Standardized by 3 GPP (since release 5)

Background - LTE n Long Term Evolution (LTE) ¨ Fourth generation (4 G) cellular network? ¨ Orthogonal FDMA (OFDMA) for downlink and Single Carrier FDMA (SC-FDMA) for uplink ¨ Support Multiple-Input and Multiple-Output (MIMO) n n n Improve communication performance Increase data throughput Without additional bandwidth or transmit power ¨ Channel bandwidth between 1. 5 and 20 MHz ¨ All IP Network (AIPN) ¨ Data rate up to 326. 4 Mbps for downlink and 86. 4 Mbps for uplink ¨ Standardized by 3 GPP (since release 8)

IMS Definition 3 GPP Release 5 introduced the IMS as part of 3 GPP specifications in March 2002 n The IMS is supposed to be a standardized access-independent IP-based architecture that interworks with existing voice and data networks for both fixed (e. g. , PSTN, Internet) and mobile (e. g. , GSM, WCDMA) users n

IMS in Converged Networks

IMS Architecture

IMS Entities Routing and Session Management n Databases n Services n Interworking Functions n Support Functions n

Routing and Session Management n Call Session Control Functions (CSCF) ¨ Proxy Call Session Control Function (P-CSCF) ¨ Interrogating Call Session Control Function (I- CSCF) ¨ Serving Call Session Control Function (S-CSCF)

P-CSCF The first contact point for users within the IMS n SIP compression n IPSec security association n Interaction with Policy Decision Function (PDF) n Emergency session detection n

I-CSCF Obtain the name of the S-CSCF or Application Server (AS) from the Home Subscriber Server (HSS) n Assign an S-CSCF based on received capabilities from the HSS n Route incoming requests to an assigned SCSCF or AS n

S-CSCF Handle registration process n Store service profile n Make routing decision n Maintain session state n

IMS Entities Routing and Session Management n Databases n Services n Interworking Functions n Support Functions n

Databases Home Subscriber Server (HSS) n Subscription Locator Function (SLF) n

HSS n The main data storage for all subscriber and service-related data ¨ User identities n Private and public user identities ¨ Registration information ¨ Access parameters n Allocated S-CSCF names ¨ Service triggering information

SLF n The resolution mechanism that enables the ICSCF, the S-CSCF and the AS to find the address of the HSS that holds the subscriber data for a given user identity when multiple and separately addressable HSSs have been deployed by the network operator.

IMS Entities Routing and Session Management n Databases n Services n Interworking Functions n Support Functions n

Services Multimedia Resource Function Controller (MRFC) n Multimedia Resource Function Processor (MRFP) n Application Server (AS) n

MRFC A signalling plane node n Provide the mechanism for bearer-related services such as announcement n Handle SIP communication to/from the SCSCF n Control the MRFP n

MRFP A media plane node n Mix the incoming media streams for multiple parties n Process the media stream source for multimedia announcements n

AS Provide value-added multimedia services n Process the incoming SIP sessions from the SCSCF n Originate SIP requests n Send accounting information to the charging functions n

IMS Services Presence n Multimedia Chat n Push to talk Over Cellular (POC) n Conferencing n

IMS Entities Routing and Session Management n Databases n Services n Interworking Functions n Support Functions n

Interworking Functions For exchanging signalling and media between IMS and CS Core Network n Breakout Gateway Control Function (BGCF) n Media Gateway Control Function (MGCF) n Signalling Gateway (SGW) n IMS Media Gateway (IMS-MGW) n

BGCF It chooses where a breakout to the CS domain occurs n If the breakout happens in the same network, then the BGCF selects a MGCF to handle the session. n If the breakout takes place in another network, then the BGCF forwards the session to another BGCF in a selected network. n

MGCF Send a converted request via the Signalling Gateway (SGW) to the CS CN n Control the IMS Media Gateway (IMS-MGW) n Perform protocol conversion between SIP and ISDN User Part (ISUP) n

SGW Perform signalling conversion at the transport level between the IP-based transport of signalling and the Signalling System No. 7 (SS 7) n i. e. , between SCTP and SS 7 n

IMS-MGW Provide the user plane link between CS domain and IMS domain n Perform transcoding for the user plane traffic n i. e. , between TDM and RTP n

IMS Entities Routing and Session Management n Databases n Services n Interworking Functions n Support Functions n

Support Functions Policy Decision Function (PDF) n Security Gateway (SEG) n

PDF Session establishment in the IMS involves the end-to-end messages exchange using SIP and SDP n The P-CSCF forwards the relevant SDP information to the PDF n The PDF authorizes the IP flows of the media components and transfers the authorized IP Qo. S parameters to the GGSN to establish an IMS session n

SEG Protect control plane traffic between security domains n Enforce the security policy of a security domain n Coincide with operator borders n

IMS-CS Interworking

CS-IMS Interworking

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