Service routing in 3GPP IP Multimedia Subsystem

Teemu Jalava

Supervisor: Raimo Kantola

Instructor: M.Sc. Markus Isomäki, Nokia Research Center

Agenda

• Introduction to 3GPP

• Introduction to SIP

• IP Multimedia Subsystem

• Service Routing in IMS

• Implementation

• Conclusions

3rd Generation Partnership Project (3GPP)

• The 3rd Generation Partnership Project (3GPP) is a collaboration agreement that brings together a number of telecommunications standards bodies and telecommunications companies.

• Release ’99 was renamed Release 3

• Release 4 was out March 2001- IP network

• Release 5 should be ready in summer 2002- IP multimedia

• Release 6- All IP network

3GPP Network Architecture

DOCUMENTTYPE

TypeUnitOrDepartmentHereTypeYourNameHere TypeDateHere

Radio Access Network Core Network

IuUu

End userterminal

AS

Session Initiation Protocol (SIP)

• Creation, modification and termination of multimedia sessions

• RCF 2543 -> RCF 3261

• Request - Reply based transactions

• Easy to make new extensions

• ASCII based, clear text, similar to HTTP

• Uses UDP or TCP

• URL addressing

• sip:teemu.jalava@nokia.com

Proxy Client 2Client 1

INVITEINVITE

100 Trying

180 Ringing

180 Ringing

200 OK

200 OK

ACK

ACK

Media streams

BYE

BYE

200 OK

200 OK

SIP sample packet

INVITE sip:bob@brown.com SIP/2.0Via: SIP/2.0/UDP 130.23.16.19:32746 ;branch=z9hG4bKCabU9qqUgvZDFrom: <sip:alice@wonder.net>;tag=uce5728c0To: <sip:bob@brown.com>Call-ID: f24793c0-c9a3-11d5-c48d-14064620c566CSeq: 4 INVITEContact: <sip:alice@130.23.16.19:32746>Content-Type: application/sdpContent-Length: 143

v=0o=alice 1756606023 1 IN IP4 130.23.16.19s=-c=IN IP4 130.23.16.19m=audio 5004 RTP/AVP 8 0a=rtpmap:8 PCMA/8000a=rtpmap:0 PCMU/8000

Method name Request URI

Headers

Messagepayload

Emptyline

First line

SIP Routing

• SIP proxy takes care of user location resolving

• teemu.jalava@nokia.com -> user1@130.233.20.40

• using registrar, DNS (ENUM in case of tel URL) or other means

• DNS Service Resource Records (SRV RR) can be used to locate a SIP proxy in an other domain

• via header is needed to ensure packets route the same way back

• record-route header is needed is sertain proxies need to be in the routing path

IP Multimedia Subsystem (IMS)

UA P-CSCF I-CSCF S-CSCF

Gm Mw Mw

SLF

Dx Cx

HSS AS

Cx

SIP SIPSIP

SIPDiameter

Sh

Visited Domain

Home Domain

ISC

HomeSubscriber

Server ApclicationServer

SubscriptionLocation Function

Diameter

Call State Control Function (CSCF)

• First contact point

• Provides provicy control and QoS authorization

• Local services, like emergency calls and local numbering

Proxy-CSCF

• Accesspoint to domain

• Hides topology and configuration

Interrogating-CSCF

• Session control services

• Registration, AS usage, charging, etc

Serving-CSCF

(User Agent)

IMS Session overview

P-CSCF

I-CSCF

UA2’s visited network

UA1

UA2

UA1’s home network

S-CSCF

I-CSCF

P-CSCF

S-CSCF

I-CSCF

I-CSCF

(optional)

UA2’s home network

UA1's visited network

Application serversRoles:

• SIP proxy

• redirect server

• Back-to-back-user-agent (B2BUA)

• User Agent

How:

• Forking

• SUBSCRIBE - NOTIFY

• MESSAGE

• Third party call control

Using:• Call Processing Lanquage (CPL)

• SIP Common Gateway Interface (CGI)

• SIP Servets

What:• Presence

• Instant Messaging

• Group services

Application example: Presence

• Presence enables user to express willingness and availability to communicate

• Can be used with phonebook to make a "buddy list"

• Presence updates with REGISTER method

• Presence download with SUBSCRIBE - NOTIFY

Example of service routingExample of service routing

P-CSCF S-CSCF

AS 1

AS 2

AS 3

1. INVITE 2. INVITE

3. INVIT

E

4. INVIT

E

5. INVITE6. INVITE

7. IN

VITE

Terminating network

S-CSCF routing decisions

• Based of Filter Criteria downloaded from Home Subscriber Server (HSS) at user registration

• User profile

• Filter Criteria• Address of the Application Server to be contacted.

• Priority

• Trigger Points (method, presence or apsence of any header, header content, etc)

• Default Handling

• Optional Service Information

Implementation

• Proof of concept work

• S-CSCF from a SIP proxy• Adding filtering

• Integrated user profile

• Configuring user profile

• Testing with network containing Presence AS, redirection AS and SIP-SMSGW

Conclusions

• SIP based services are easy to make and integrate to the IMS network

• Configuration is easy

• Scalable sollution, AS and S-CSCF duplication

• Release 5 has been delayed from jan 2002 to june 2002, some features have been postponed to Release 6

• Some pressure from 3GPP to IETF to finalize new SIP RFC and SIP compression

These might have some impact to service routing issues

• Questions?