IP Multimedia Subsystem (IMS) 江培文

IP Multimedia Subsystem(IMS)

江培文

Agenda

Background IMS Definition IMS Architecture IMS Entities IMS-CS Interworking

Background - AMPS

Advanced Mobile Phone System (AMPS)First generation (1G) cellular network Analog mobile phone system Standardized by ANSI Operate in the 800 MHz bandVoice call

Background - GSM

Global System for Mobile communications (GSM)Second generation (2G) cellular network Digital mobile phone system Most GSM networks operate in 900 MHz

or 1800 MHz bandsEach radio channel bandwidth is 200

kHzStandardized by ETSIVoice call, short message service

Background - GPRS

General Packet Radio Service (GPRS) 2.5G packet oriented mobile networkProvide data rates from 56 up to 114

kbpsStandardized by ETSI/3GPP Short Message Service (SMS), Wireless

Application Protocol (WAP), Multimedia Messaging Service (MMS), Internet Access

Background - EDGE

Enhanced Data rates for GSM Evolution (EDGE)2.75G packet oriented mobile networkData rate up to 236.8 kbps Standardized by 3GPP Multimedia services, Internet access

Background - WCDMA

Wideband Code Division Multiple Access (WCDMA)Third generation (3G) cellular network1885–2025 MHz for uplink band and 2110–2

200 MHz for downlink band Each radio channel bandwidth is 5 MHz Data rate up to 384 kbps Standardized by 3GPP The world's first commercial WCDMA netwo

rk, FOMA, was launched by NTT DoCoMo in Japan in 2001.

Background - HSDPA

High Speed Downlink Packet Access (HSDPA) 3.5G packet oriented mobile networkAdaptive Modulation and Coding (AMC)

Depend on signal quality and cell usage QPSK in initial scheme, 16QAM in good radio

condition. Data rate up to 14.4 Mbps for downlink

and 384 kbps for uplinkStandardized by 3GPP (since release 5)

Background - LTE

Long Term Evolution (LTE) Fourth generation (4G) cellular network? Orthogonal FDMA (OFDMA) for downlink and

Single Carrier FDMA (SC-FDMA) for uplink Support Multiple-Input and Multiple-Output

(MIMO) 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 3GPP (since release 8)

IMS Definition

3GPP Release 5 introduced the IMS as part of 3GPP specifications in March 2002

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

IMS in Converged Networks

IMS Architecture

IMS Entities

Routing and Session Management Databases Services Interworking Functions Support Functions

Routing and Session Management

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

SIP compression IPSec security association Interaction with Policy Decision

Function (PDF) Emergency session detection

I-CSCF

Obtain the name of the S-CSCF or Application Server (AS) from the Home Subscriber Server (HSS)

Assign an S-CSCF based on received capabilities from the HSS

Route incoming requests to an assigned S-CSCF or AS

S-CSCF

Handle registration process Store service profile Make routing decision Maintain session state

IMS Entities

Routing and Session Management Databases Services Interworking Functions Support Functions

Databases

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

HSS

The main data storage for all subscriber and service-related dataUser identities

Private and public user identitiesRegistration informationAccess parameters

Allocated S-CSCF namesService triggering information

SLF

The resolution mechanism that enables the I-CSCF, 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 Databases Services Interworking Functions Support Functions

Services

Multimedia Resource Function Controller (MRFC)

Multimedia Resource Function Processor (MRFP)

Application Server (AS)

MRFC

A signalling plane node Provide the mechanism for bearer-relat

ed services such as announcement Handle SIP communication to/from the

S-CSCF Control the MRFP

MRFP

A media plane node Mix the incoming media streams for

multiple parties Process the media stream source for

multimedia announcements

AS

Provide value-added multimedia services

Process the incoming SIP sessions from the S-CSCF

Originate SIP requests Send accounting information to the

charging functions

IMS Services

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

IMS Entities

Routing and Session Management Databases Services Interworking Functions Support Functions

Interworking Functions

For exchanging signalling and media between IMS and CS Core Network

Breakout Gateway Control Function (BGCF)

Media Gateway Control Function (MGCF) Signalling Gateway (SGW) IMS Media Gateway (IMS-MGW)

BGCF

It chooses where a breakout to the CS domain occurs

If the breakout happens in the same network, then the BGCF selects a MGCF to handle the session.

If the breakout takes place in another network, then the BGCF forwards the session to another BGCF in a selected network.

MGCF

Send a converted request via the Signalling Gateway (SGW) to the CS CN

Control the IMS Media Gateway (IMS-MGW)

Perform protocol conversion between SIP and ISDN User Part (ISUP)

SGW

Perform signalling conversion at the transport level between the IP-based transport of signalling and the Signalling System No. 7 (SS7)

i.e., between SCTP and SS7

IMS-MGW

Provide the user plane link between CS domain and IMS domain

Perform transcoding for the user plane traffic

i.e., between TDM and RTP

IMS Entities

Routing and Session Management Databases Services Interworking Functions Support Functions

Support Functions

Policy Decision Function (PDF) Security Gateway (SEG)

PDF

Session establishment in the IMS involves the end-to-end messages exchange using SIP and SDP

The P-CSCF forwards the relevant SDP information to the PDF

The PDF authorizes the IP flows of the media components and transfers the authorized IP QoS parameters to the GGSN to establish an IMS session

SEG

Protect control plane traffic between security domains

Enforce the security policy of a security domain

Coincide with operator borders

IMS-CS Interworking

CS-IMS Interworking

Thank You