Download IP Multimedia Subsystem (IMS)

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 band
 Voice 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 bands
 Each radio channel bandwidth is 200
kHz
 Standardized by ETSI
 Voice call, short message service
Background - GPRS

General Packet Radio Service (GPRS)
 2.5G
packet oriented mobile network
 Provide data rates from 56 up to 114
kbps
 Standardized 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 network
 Data 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 network
 1885–2025 MHz for uplink band and
2110–2200 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
network, FOMA, was launched by NTT
DoCoMo in Japan in 2001.
Background - HSDPA

High Speed Downlink Packet Access
(HSDPA)
 3.5G
packet oriented mobile network
 Adaptive 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 uplink
 Standardized by 3GPP (since release 5)
Background - LTE

Long Term Evolution (LTE)
 Fourth generation
 Orthogonal FDMA
(4G) cellular network?
(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 IPbased 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 (PCSCF)
 Interrogating Call Session Control
Function (I-CSCF)
 Serving Call Session Control Function (SCSCF)
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 data
 User

identities
Private and public user identities
 Registration
information
 Access parameters

Allocated S-CSCF names
 Service
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 bearerrelated 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 (IMSMGW)
 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