Agenda

1
Agenda

• Introduction to 3GPP
• Introduction to SIP
• IP Multimedia Subsystem
• Service Routing in IMS
• Implementation
• Conclusions

2
Service routing in 3GPP IP Multimedia Subsystem
Teemu Jalava Supervisor Raimo Kantola Instructor
M.Sc. Markus Isomäki, Nokia Research Center
3
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

4
3GPP Network Architecture
AS
5
Session Initiation Protocol (SIP)
Proxy
Client 2
Client 1

• Creation, modification and termination of
  multimedia sessions
• RCF 2543 -gt RCF 3261
• Request - Reply based transactions
• Easy to make new extensions
• ASCII based, clear text, similar to HTTP
• Uses UDP or TCP
• URL addressing
• sipteemu.jalava_at_nokia.com

INVITE
INVITE
100 Trying
180 Ringing
180 Ringing
200 OK
200 OK
ACK
ACK
Media streams
BYE
BYE
200 OK
200 OK
6
SIP sample packet
7
SIP Routing

• SIP proxy takes care of user location resolving
• teemu.jalava_at_nokia.com -gt user1_at_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

8
IP Multimedia Subsystem (IMS)
Call State Control Function (CSCF)
Interrogating-CSCF

• Accesspoint to domain
• Hides topology and configuration

(User Agent)
Serving-CSCF
Proxy-CSCF

• Session control services
• Registration, AS usage, charging, etc

• First contact point
• Provides provicy control and QoS authorization
• Local services, like emergency calls and local
  numbering

9
IMS Session overview
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Application servers

• Roles
• 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

11
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

12
Example of service routing
Example of service routing
13
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

14
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

15
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

16
Thank you!

• Questions?