3GPP IP Multimedia Subsystem

National Chung Cheng UniversityDept. Computer Science & Information Engineering

3GPP IP Multimedia Subsystem

Chiang, Wei-Kuo (江為國)

Assistant Professor Department of CSIE National Chung Cheng University Office : EA 311 Phone : 05-2720411~33126 Email : [email protected]

URL : http://www.cs.ccu.edu.tw/~wkchiang/

National Chung Cheng University


Mobile Communication Networks 3GPP IP Multimedia Subsystem2

Next Generation Network

Internet Telecom & Wireless Communication

IP

MGCF

CSCF

T-SGW MGWMGW

WLAN

GPRS

CSCFSIP

Server

PSTN

InternetWireless App.Server

3rd Parties App.



Outline

Softswitch

Softswitch Architecture

Softswitch Operations

3GPP All IP Network

Network Architecture

Network Entities

3GPP IMS CSCF

Entities Behavior

Message Flows



Softswitch Overview (1/2)

Softswitch: Emulating Circuit Switching in Software

IN/SCP

PSTN

Local Switch

PSTN

Local SwitchSTP SS7 Network

IP Network

RTP Streams

MGC MGC

Trunk

GatewayTrunk

Gateway

SIP-T

SGSG

SIGTRAN

MEGACO

IP Phone

9000 Personalized VoIP

Service System

Application Server



Softswitch Overview (2/2)

Softswitch Provides Open Layered Architecture

• Solutions in a proprietary box

• Expensive

• Little room for innovation

Circuit-Switched

Transport

Hardware

Call Control &

Switching

Services &

Applications

P

R

O

P

R

I

E

T

A

R

Y

• Solutions are open standards-based

• Customers choose best-in-class products

• Open standards enable lower cost for innovation

Soft-Switched

Transport Hardware

Softswitch Call Control

Services, Applications & Features

(Management, Provisioning and

Back Office)

Open Protocols APIs

Open Protocols APIs

Open APIs for 3rd Party App develop.

Best-in-class Access Devices.

Scalable, Open Interfaces for Comm.



Softswitch Architecture (1/2)

CO

Switch

STP

SCP

CO

Switch

STP

SCP

Signaling Layer

Transport Layer

IP

SIP-T

Media

Server

RTP

SIP-?/

MGCP

SIP-TSI

Media

Gateway

Controller

MGCP/

MEGACO

Phones

App.

Server

Media

Gateway

Controller

SIGTRAN

SSA/SCTP

MGCP/MEGACOTrunking

Gateway

Signaling

(SS7)

Gateway

SS7 TCAP

ISUP/TCAP



Softswitch Architecture (2/2)

Media Gateway Controller (MGC)

provides basic call control, signaling,

manages resources, generates CDR

Application Server (AS) hosts enhanced services:

calling card, 800 translation, voice mail, follow-me

provides service/AP interfaces

access to underlying service & switching functions

Media Server (MS)

provides specialized resources:

IVR, conferencing, facsimile functions

AS can access MS to utilize resources on MS



Local

Switch

STP

SCP

STP STP STP

Local

Switch

STP

Local

Switch

Trunking

Gateway

Signaling

(SS7)

Gateway

Media

Gateway

Controller

Trunking

Gateway

Signaling

(SS7)

Gateway

Routing

Directory

Softswitch Operations (1/2)

Basic Call Control

12 ISUP ACM

13 ISUP ANM

ISUP ACM

ISUP ANM

ISUP IAM ISUP IAM

1

23

4 5

6 7

8

910

14

11

SIGTRAN

MGCP/MEGACOVoice Voice

RTP



Softswitch Operations (2/2)

Inter-Softswitch Communications

Local

Switch

STP

Trunking

Gateway

Signaling

(SS7)

Gateway

Media

Gateway

Controller

STP

Trunking

Gateway

STP

Media

Gateway

Controller

Signaling

(SS7)

Gateway

STP STP

Domain A Domain B

Local

Switch

Routing

Directory

3

1

5

2

ISUP IAM

4

SIGTRAN

MGCP/MEGACO

6 SIP-T

7

9

16

Voice

RTP

8

ISUP IAM

12

13

Voice

10

11

14 ISUP ACM

15 ISUP ANM

ISUP ACM

ISUP ANM



MGCP/

MEGACO

Phones

Trunking

Gateway

Signaling

Gateway

MGC

SIGTRAN

SSA/SCTP

RTP

MGCP/MEGACO

SS7 TCAP

ISUP/TCAP

Softswitch Protocols (1/3)

Concept of MGCP/MEGACO

CO

Switch

STP

SCP

PSTN

Phones

Media

Gateway

MGC

Connection

Create

Delete

Modify

Event Notification

Request

Status

Query

Response

Success

Failure

Event

Notify

Status

Report

Dumb Client

Stateless

Intelligent

Server




IETF SIGTRAN - for SS7 over IP

ISUPTCAP

SCCP

MAP

MTP

OSI Layers

Application

Presentation

Session

Transport

Network

Data Link

Physical

INAP

SS7 Protocol Stack

ISUPTCAP

SCCP

MAP

SCN Signaling Adaptation

(SSA)

Common Signaling Transport

(CST)

IP

INAP

SIGTRAN Protocol Stack



CO

Switch

PSTN

Phones

Trunking

Gateway

MGCP/MEGACOCO

SwitchTGW


SIP-T (SIP for Telephones) : RFC 3372 (Sept.2002)

interface between softswitches

MGCMGC

STP

SCP

Signaling

Gateway

SIGTRAN

SSA/SCTP

SS7 TCAP

ISUP/TCAP

STP

SCP

SG

SIP-T

SIP Message +

Mid-call control

Header

ISUP

SDP

. . .

ISUP/SS7

Messages

MTP

ISUP

ISUP/IP

Messages

ISUP

IP

SIP

UA

SS Adapt.

SCTP



IP-PSTN Convergence

CO

Switch

STP

SCP

CO

Switch

STP

SCP

Trunking

Gateway

Signaling

(SS7)

GatewayMedia

Gateway

Controller

Residential

Gateway

RTP

SS7 TCAP

ISUP/TCAPMGC

SG

TGW

SIP-T

SIP

Phones

SIP

Server

SIP

Server

SIP-TSIAS

MS

SIP-?



Outline

Softswitch



3GPP All IP Network


Network Entities

3GPP IMS CSCF

Entities Behavior

Message Flows



3GPP All IP Network

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF

Signaling (SS7 or IP based)

Circuit

Packet (user traffic / signaling)

Call control function



備忘稿

3GPP All IP網路希望藉由packet technologies和IP telephony

在IP網路上提供即時和非即時服務。它主要包含3GPP Release 4

和Release 5的部分，是由Release 99演進過來。在RAN部分支援GERAN和UTRAN，而CN的部分則以GPRS為基礎。

除了少數的連線是用電路(circuit)外（例如：RNC到MS、連接PSTN連線），其餘的 link 均將信令(signaling)以及封包(packet)

分開傳送。在 PS-domain （也就是圖中的上半部）中，撥打電話是利用 VoIP

的方式；為了向下相容性(backward compatibility)的考量，下半部元件主要是用來與舊有終端機連線（legacy terminal）。

其中CSCF的角色類似於 SIP 中的 proxy server 的角色；而 HSS

(Home Subscriber Server)則類似於 HLR 的角色。



備忘稿這是3GPP制定的Release 4 & 5 Network Architecture。

藍色虛線以下的部分是指Release 4制定的範圍，以上的部分則是Release 5。

若是您有聽過R99，那它跟R4的差別就在 - R4利用了Soft-switch 將 Signal與Media的架構精神，將原先的 MSC (Mobile Station Center)分割成MSCServer負責Signal、Media Gateway負責Media；也同樣用在GMSC上。

Release 4 制定的部分，稱之為 Circuit Switched Domain；Release 5制定的部分，稱之為Packet Switched Domain。3G的GPRS 部分延續2.5G的功能與角色，使得無線手機能夠對IP網路作Data Access資料的存取。而HSS(Home Subscriber Server)則類似2G GSM 系統的 HLR (Home LocationRegister)，當然為求提供更多的Services，3G的 HSS需具備支援較多的功能。

至於 CSCF (Call Session Control Function) 主要是負責 Call Control 通話控制。MRF (Multimedia Resource Function)是作 Media Mixing, PlayAnnouncement,支援Multi-party Conferencing，類似 H.323裡面的MCU，Soft-switch 架構中的 Media Server 。

依此3GPP制定的架構來看 - 未來將是一個 All IP Core Network。



Circuit-Switched Services

RNC

Node B

Node B

MS

MS

T-SGW

PSTN

MSC Server

Legacy mobile

signaling network

HSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

Nc

Nb

Iu_CS

(control part)

Mh

Gr

Iu_CS

(user traffic)

Mc


Circuit





備忘稿

All IP 架構中的 MSC Server 與舊有的 MSC 功能不盡相同。承襲了 MGCP/MEGACO 的概念，All IP 架構中將 MSC 的功能中的信令(signaling)以及媒體資料(media)分開成兩個元件：MSC Server 以及 MGW

(Media Gateway)。MSC Server 只處理信令的部份，利用 MGCP 或 MEGACO 來控制 MGW 來處理媒體資料的轉送。



Packet-Switched Services

RNC

Node B

Node B

MS

MS

SGSN InternetGGSN

HSS

Gi

Gr Gc

GnIu_PS

Gi


Circuit





Real-Time PS Services

RNC

Node B

Node B

MS

MS

SGSN InternetGGSN

Legacy mobile

signaling network

CSCFHSS

R-SGW

Gi

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

GiMg

Gi

MrMRF


Circuit





Interworking with PSTN

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

GGSN

Legacy mobile

signaling network

CSCFHSS

MGW

R-SGW

McGi

Gi

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Gi

MGCF

Mg

Gi

MrMRF


Circuit





Home Subscriber Server

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF


Circuit





HSS (1/2)

HSS (Home Subscriber Server) is the master

database for a given user.

Functionalities

The HLR functionality required by the PS-Domain

The circuit switched part of the HLR

User control functions required by the IP

multimedia (IM) subsystem

HSS

MSC Server GMSC Server SGSN GGSN R-SGW CSCF

D C Gr Gc Mh Cx



備忘稿

在All IP網路中的HSS相當於2G、2.5G和Release 99

的HLR角色。其主要工作是負責maintain使用者相關的資訊。除了原本HLR的功能之外，HSS也必須和IM子系統相溝通。



HSS (2/2)

MAP termination

Addressing protocol termination

Authentication, Authorization protocol

termination

IP multimedia control termination

MAP

termination

Addressing

Protocol

termination

Authentication

Authorization

protocol

termination

IP

multimedia

control protocol

termination

HSS

C,D,

Gr,Gc Mh Cx



Media Gateway Control

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF


Circuit





MGCF & MGW

Media Gateway Control Function

Being PSTN signaling termination point

Performing protocol conversion between the

legacy (e.g., ISUP) and the All-IP network call

control protocols

Media Gateway

Being PSTN transport termination point

Interfacing UTRAN over Iu



備忘稿

這裡的MGCF/MGW所扮演的角色，和之前MGCP/MEGACO中所介紹的網路元件類似。但在這裡，Media gateway除了界接PSTN外，也透過Iu介面和UTRAN連接。



MSC Server

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF


Circuit





MSC Server

Mainly comprising the call control and mobility

control parts of a GSM/UMTS MSC

Performing the connection control for media

channels in a MGW

MSC server + MGW = MSC



備忘稿

在All IP網路中的MSC server只包含原本MSC中的call

control和mobility control的部分。它負責控制UTRAN這一端的media gateway。所以說，MSC

server + MGW就可包含一個完整的MSC。



MRF

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF


Circuit





MRF

Multimedia Resource Function

Performing multi-party call and multimedia

conferencing functions

The same function as an MCU in the H.323

network



備忘稿

這個元件類似於H.323網路中的MCU，負責多方通話的控制。



T-SGW & R-SGW

RNC

Node B

Node B

MS

MS

SGSN

T-SGW

Internet

PSTN

MSC Server

GGSN

Legacy mobile

signaling network

CSCFHSS

MGWMGW

GMSC Server

R-SGW

MAP

MAP Mc

McGi

Gi

Nc

Nb

Iu_CS

(control part)

Mh

Gr Gc

Cx

Mm

Ms

GnIu_PS

Iu_CS

(user traffic)

Gi

Mc

MGCF

Mg

Gi

MrMRF


Circuit





T-SGW & R-SGW

Transport Signaling Gateway Function

Mapping call related signaling (i.e., SS7/ISUP)

from PSTN/PLMN on an IP bearer and sending it

to the MGCF

Providing PSTN/PLMNIP transport level address

mapping

Roaming Signaling Gateway Function

Providing communication (i.e., SS7/MAP) with a

2G/R99 MSC/VLR



備忘稿

T-SGW (Transport Signaling Gateway Function)

主要是把 ISUP, SS7 兩種信令做一個對映(mapping)。以便於 PSTN/PLMN的網路信令可以在 IP 網路上傳輸，反之也相同。

R-SGW (Roaming Signaling Gateway Function)

的功能去 query 外部的資料庫（例如：GSM/GPRS中的VLR等）

T-SGW 和 R-SGW 都可稱為 Signaling gateway。兩者的不同在於，T-SGW 負責轉換和通話相關的信令(如:

ISUP)。而R-SGW負責和舊有的2G/Release 99的MSC/VLR相溝通。



Outline

Softswitch



3GPP All IP Network


Network Entities

3GPP IMS CSCF

Entities Behavior

Message Flows



IP Multimedia Subsystem (1/2)

IP Multimedia (IM) CN subsystem

Comprising all CN elements for provision of

multimedia services.

The IM subsystem (IMS) utilizes the PS domain

to transport multimedia signaling and bearer

traffic.

The IMS attempts to be conformant to IETF

“Internet standards”.

SIP (Session Initiation Protocol) has been

selected as the interfaces between the IM CN

elements.



IP Multimedia Subsystem (2/2)

Internet3G/UMTS

App.Server

HSS

S-CSCF

GPRS

• Presence Server• OSA Gateway• ...

MRF

P-CSCF

I-CSCF

Visited Network External Network

Home Network

Signaling

Media



UE presence in IMS

Home Network

IM Subsystem

Visited Network

IM Subsystem

Inter-Network

IM Backbone

Internet

Intranets

UE

GGSN

BG

BG

SGSN

PDP Context

Visited Network

Gi

Virtual presence of UE

in visited network IM subsystem

(UE’s IP-address is here)

UE shall acquire the necessary IP address(es) as

part of the PDP context activation procedure(s)



Identification of IM Users

Private user identities

Assigned by the home network operator

Stored on USIM (UMTS Subscriber Identity Module)

Stored within the HSS (use for registration)

Contained in all registration requests passed from UE

to home network (for authentication)

Not used for routing of SIP messages

Public user identities

Every IM subscriber shall have one or more public

user identities.

The public user identity shall take the form of SIP

URL or E.164 number. (SIP URL for routing of SIP)



Call Session Control Function

The main function entity in 3G IM Subsystem

Behaves as SIP Proxy server

CSCFs may have different capabilities

Terminal and node behaviours should be

consistent, regardless of whether the user is

roaming

Three kinds of CSCFs defined

Proxy CSCF (P-CSCF)

Interrogating CSCF (I-CSCF)

Serving CSCF (S-CSCF)



Proxy CSCF

P-CSCF is the first contact point for the handset Its address is discovered by UEs following PDP

context activation procedure.

Behaving like a Proxy server

Also behaving as a User Agent in abnormal conditions

Functions

Forward SIP register request from the UE to I-CSCF

determined using the home domain name.

Forward SIP messages from the UE to the SIP server

(e.g. S-CSCF) whose name the P-CSCF has received as

a result of registration procedure.

Detect an emergency session and select a S-CSCF to

handle emergency sessions.

Authorization of bearer resources & QoS management.



Interrogating CSCF

I-CSCF is the contact point within an operator’s network for all connections destined to a subscriber of that network operator.

That is,I-CSCF is the first contact point within an

operator’s network for incoming call signaling.

Registration Assigning a Serving CSCF to a user performing SIP

registration

Session Flow Routing a SIP request received from the S-CSCF(Serving

Originating UE) towards the S-CSCF(Serving Terminating

UE)

Obtaining the S-CSCF address from HSS



I-CSCF(THIG)

Topology Hiding Inter-network Gateway

In the I-CSCF, the operator may use a Topology

Hiding Inter-network Gateway (THIG) function to

hide the configuration, capacity, and topology

of the network from the outside.

When an I-CSCF(THIG) is chosen to meet the

hiding requirement then for sessions traversing

across different operators domains, the I-

CSCF(THIG) may forward the SIP request or

response to another I-CSCF(THIG) allowing the

operators to maintain configuration

independence.



Serving CSCF

S-CSCF performs session control services for the UE

Maintaining a session state as needed by the

network operator for support of the services

Registration

As a Registrar, it accepts registration requests

and makes its information available through the

location server (e.g., HSS).

Session-related/-unrelated Flows

As a Proxy Server, it accepts requests & services

them internally or forwards them on.

As a User Agent, it may terminate & independently

generate SIP transactions.

Interaction with Service Platforms for support of

services



ENUM DNS Translation

The S-CSCF shall support the ability to

translate the E.164 address contained in a

request-URI in the non-SIP URL to SIP URL

Using ENUM DNS translation mechanism

RFC 2916

If the translation fails, then the session may

be routed to the PSTN or appropriate

notification shall be sent to the mobile.

Database aspects of ENUM are outside the

scope of 3GPP.



Registration Diagram

P-SCSF

S-CSCF

P-CSCF

GGSN

SGSN

Radio Access Network

GGSN

SGSN


I-CSCF

HSS

1. P-CSCF & GPRS within the same network.

2. Forward to I-CSCF by “home domain name.

3. User can register in the P-CSCF network ?

5. Request info about required S-CSCF cap. ?

4,6. Responses & Information.

7. Select S-CSCF.

8,9. Send S-CSCF to HSS for the subscriber.

10,11. Download user profile to access service.

12. Send Register info to Service Platform.

3,5 4,6

7

10,118,9 12

11

22

Home Network

Visited Network

App.

Server



Application Level Registration

I-CSCFP-CSCFUE HSS1. Register

S-CSCF

Visited/Home Network Home Network

2. Register3. Cx-Query

4. Cx-Query Resp.

5. Cx-Select-Pull

6. Cx-Select-Pull Resp.

7. Register

8. Cx-Put

9. Cx-Put-Resp.

10. Cx-Pull

11. Cx-Pull-Resp.

13. 200 OK

14. 200 OK15. 200 OK

12. Service Control

User can register in

the P-CSCF network ?

Request info about

required S-CSCF cap. ?

Send S-CSCF name to

HSS for the subscriber

Download user profile

to access service.

Store P-CSCF addressIf I-CSCF(THIG),

Encrypt S-CSCF

Send Register info

to Service Platform



Proxy-CSCF Discovery

1. PDP Context Activation

3. DNS - Query/Response

2. DHCP - Query/Response 2. DHCP -Relay

1. Activate PDP Context Request

3. Activate PDP Context Accept

1. Create PDP Context Request

3. Create PDP Context Response

DHCP server DNS serverUE GGSN

UE SGSN GGSN

2. Get IP address(es)

of P-CSCF(s)

Use of DHCP (Dynamic Host Configuration Protocol)

Transfer the P-CSCF address with the PDP

Context Activation signaling to the UE

GGSN acts as a DHCP Relay Agent

1.Create PDP context bearer ( TS 23.060)

2.UE requests a DHCP server

2a. P-CSCF domain name

2b. IP addresses of DNS servers

3. UE performs a DNS query

to retrieve P-CSCF(s) IP addresses

During PDP Context Activation signalling

1. UE indicates the request of P-CSCF

IP address(es) in PDP context request

1a. the indication forwarded to GGSN

2. GGSN gets IP-CSCF IP addresses

(internal configure, implement choice)

3. P-CSCF IP forwarded to UE



Call Setup Diagram

S-CSCF

P-CSCF

GGSN

SGSN


I-CSCF

HSS App.

Server

1

2

Originating Home Network

Visited/Home

Network

S-CSCFI-CSCF

HSS

4 5

6

Terminating Home Network

3

P-CSCF

GGSN

SGSN


8

7

App.

Server

Originating Terminating

Visited/Home

Network



Session Flow Procedures(1/2)

UE#1 S-CSCF#1 S-CSCF#2 UE#2

One of the S-CSCF to S-CSCF Invite

sequence information flows inserted

here

One of the MO Invite

Sequence information

flows inserted here

One of the MT Invite

Sequence information

flows inserted here

MO: Mobile Origination

MT: Mobile Termination



UE#1 S-CSCF#1 S-CSCF#2 UE#2

INVITE

Ringing

200 OK

ACK

SDP

Final SDP

Reserv Success

Session Flow Procedures(2/2)



CSCF Roles & Features

CSCF

P-CSCF(Proxy)

I-CSCF(Interrogating)

S-CSCF(Serving)

Behaving like Features/FunctionsRegister

Forward SIP register to I-CSCF by home domain name.

Session Flow

Forward SIP messages from UE to SIP server (S-CSCF)

as a result of registration procedure.

Detect an emergency session and select a S-CSCF to

handle emergency sessions.

Authorization of bearer resources & QoS management.

Proxy server

User Agent

(abnormal cases)

Proxy server

User Agent

(register reject)

Register

Assigning a Serving CSCF to the subscriber.

Session Flow

Routing a SIP request from another network towards

the S-CSCF(Serving Terminating UE)

Obtaining the S-CSCF address from HSS

Registrar

Proxy Server

User Agent

Register

As a Registrar, store registration info to HSS.

Session-related/unrelated Flow

S-CSCF performs session control services for the UE.

Interaction with Service Platforms.

Maintaining a session state as needed by the network

operator for support of the services.



IP Version Interworking

DNS

P-CSCF

IP-CAN

UEIPv6

S-CSCF I-CSCF

IMS-ALG

TrGW

IMS network

Mx

HSS

Ix

Mx

Other networkthat uses a different IP version

Signaling

Bearer

Note that the standardisation and functional requirements of Mx & Ix reference points are FFS.



IMS ALG & TrGW

IMS Application Level Gateway (ALG)

The IMS ALG needs to modify the SIP message bodies and

headers that have IP address association indicated.

The IMS ALG will request NA(P)T-PT to provide the bindings

data between the different IP addresses (IPv6 to IPv4 and

vice versa) upon session initiation, and will release the

bindings at session release.

The TrGW is a NA(P)T-PT

NAT-PT binds addresses in IPv6 network with addresses in

IPv4 network and vice versa

to provide transparent routing between the two IP domain

without requiring any changes to end points, like the UE.

IP-Connectivity Access Network:

that provides the underlying IP transport connectivity

between the UE and the IMS entities.

An example of an "IP-Connectivity Access Network" is GPRS.



Originating towards IPv4

UE(A) IP-CAN P-CSCF(A) S-CSCF(A) IMS-ALG TrGW User side(B)

2. S- CSCF

determines via DNS

query that the domain

of the terminating end

supports IPv4 only

1. Session Initiation

3. Link in the IMS-ALG and get

TrGW IPv4 addr/port information

for user (A)

.4.Session Initiation continues

5.5.5.Session signalling path

established

6. Media path established 6



Terminating from IPv4

UE(A) IP-CAN P-CSCF(A) S-CSCF(A)I-CSCF/IMS-ALG

TrGW User side(B)

2. IMS-ALG determines (viaDNS or preconfigured) theterminating I-CSCF and getsthe IPv6 addr/port for user(A) from TrGW & forwardsrequest to ICSCF so I-CSCF sees User (B) as IPv6

5.5.5.Session signalling path

established

6. Media path established 6

1. Session Initiation

3. Session

Initiation4. Session Initiation



Useful Web Sites

International Packet Comm. Consortium

(IPCC) http://www.packetcomm.org/

International Softswitch Consortium(ISC)

IETF SIP & SIPPING Working Groups http://www.cs.columbia.edu/~hgs/sip/

http://www.ietf.org/html.charters/sip-charter.html

http://www.sipcenter.com/

3GPP-Third Generation Partnership Project http://www.3gpp.org/



3GPP All IP Network TS 23.002 “Network architecture”

TS 23.221 “Architectural requirements”

3GPP IP Multimedia Subsystem

TS 23.228 V7.0.0 (2005-06)

IP Multimedia Subsystem (IMS);

Stage 2(Release 7)

TS 23.228 “IP multimedia subsystem (IMS)”

TS 23.218 “IP multimedia (IM) call model”

TS 24.228 “Signaling flows based on SIP & SDP”

TS 24.229 “Call control based on SIP and SDP”

3GPP Specifications (1/2)



QoS related specs (P-CSCF) TS 23.107 “QoS concept and architecture”

TS 23.207 “End-to-End QoS concept & architecture”

TS 29.208 “End-to-End QoS signaling flows”

Security related specs (P-CSCF) TS 33.102 “Security architecture”

TS 33.203 “Access security for IP-based services”

TS 33.210 “IP network layer security”

Cx Interface specs (S-CSCF, I-CSCF) TS 29.228 “IP Multimedia (IM) Subsystem Cx Interface;

Signaling flows and message contents”

TS 29.229 “Cx Interface based on the Diameter

protocol; Protocol details”

3GPP Specifications (2/2)

Mobile All-IP Networking LaboratoryDepartment of Computer Science & Information Engineering

Any Question?


Documents

3GPP IP Multimedia Subsystem