Transcript Service routing in 3GPP IP Multimedia Subsystem

Agenda
• Introduction to 3GPP
• Introduction to SIP
• IP Multimedia Subsystem
• Service Routing in IMS
• Implementation
• Conclusions
Service routing in 3GPP IP Multimedia
Subsystem
Teemu Jalava
Supervisor: Raimo Kantola
Instructor: M.Sc. Markus Isomäki, Nokia Research Center
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
Iu
Uu
End user
terminal
Radio Access Network
AS
Core Network
Session Initiation Protocol (SIP)
• Creation, modification and termination of
multimedia sessions
Client 1
INVITE
100 Trying
INVITE
180 Ringing
• Request - Reply based transactions
200 OK
200 OK
ACK
ACK
• ASCII based, clear text, similar to HTTP
• Uses UDP or TCP
Client 2
180 Ringing
• RCF 2543 -> RCF 3261
• Easy to make new extensions
Proxy
Media streams
BYE
BYE
• URL addressing
• sip:[email protected]
200 OK
200 OK
SIP sample packet
Method name
First line
Headers
Empty
line
Message
payload
Request URI
INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP 130.23.16.19:32746
;branch=z9hG4bKCabU9qqUgvZD
From: <sip:[email protected]>;tag=uce5728c0
To: <sip:[email protected]>
Call-ID: f24793c0-c9a3-11d5-c48d-14064620c566
CSeq: 4 INVITE
Contact: <sip:[email protected]:32746>
Content-Type: application/sdp
Content-Length: 143
v=0
o=alice 1756606023 1 IN IP4 130.23.16.19
s=c=IN IP4 130.23.16.19
m=audio 5004 RTP/AVP 8 0
a=rtpmap:8 PCMA/8000
a=rtpmap:0 PCMU/8000
SIP Routing
• SIP proxy takes care of user location resolving
• [email protected] -> [email protected]
• 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)
Call State Control Function (CSCF)
Interrogating-CSCF
Subscription
Location Function
• Hides topology and configuration
HSS
Diameter
Dx
UA
Mw
P-CSCF
(User Agent)
SIP
Proxy-CSCF
• First contact point
• Provides provicy control and QoS authorization
• Local services, like emergency calls and local
numbering
AS
Diameter
Cx
ISC
Cx
SIP
Mw
I-CSCF
SIP
Visited
Domain
Apclication
Server
Sh
SLF
• Accesspoint to domain
Gm
Home
Subscriber
Server
S-CSCF
SIP
Home
Domain
Serving-CSCF
• Session control services
• Registration, AS usage, charging, etc
IMS Session overview
UA1
UA1's visited network
UA1’s home network
P-CSCF
S-CSCF
I-CSCF
(optional)
I-CSCF
UA2
I-CSCF
S-CSCF
I-CSCF
P-CSCF
UA2’s home network
UA2’s visited network
Application servers
Roles:
• SIP proxy
• redirect server
• Back-to-back-useragent (B2BUA)
Using:
• Call Processing Lanquage (CPL)
• SIP Common Gateway Interface
•
(CGI)
SIP Servets
• User Agent
How:
• Forking
• SUBSCRIBE NOTIFY
• MESSAGE
• Third party call control
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 ofofservice
Example
servicerouting
routing
AS 1
P-CSCF
2. INVITE
AS 2
S-CSCF
5.
7. INVITE
1. INVITE
ITE
V
IN
E
3.
T
I
V
IN
.
4
IN
VI
TE
6.
IN
VI
TE
Terminating network
AS 3
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?