SIP is a VoIP protocol in Application Layer of OSI arch

1. Introduction to
Session Iinitiation Protocol
(a VoIP protocol)
2007-10-16William.L
wiliwe@gmail.com

2. Agenda
Introduction
Architecture
SIP Message Format
Call Flows

3. Introduction
An application-layer signaling protocol
Create, Modify, and Terminate sessions
SIP is ASCII text-based
SIP incorporates elements of two widely used Internet
protocols:
HTTP SIP borrowed a client-server design and the use of
URLs and URIs
SMTP SIP borrowed a text-encoding scheme and header style
SIP uses e-mail-like names for addresses
UserName@Host-Domain

4. Architecture (1/2)
Client-Server architecture --- the same as HTTP
Client
originates message
Server
responds to or forwards message
Elements
SIP User Agents
takes direction or input from a user and acts as an agent on their
behalf to set up and tear down media sessions with other user
agents.
SIP Servers
Registrar
Proxy
Redirect

5. Architecture (2/2)
Request
Response
Server Client

6. SIP Message (1/8)
SIP Message
Message Headers
Request / Status Line
Message Body
C R L F

7. INVITE sip:allen@10.7.1.228:5060 SIP/2.0
Via: SIP/2.0/UDP 22.3.56.790:5060;branch=z9G4bK0e8d
From: sip:carol@22.3.56.790:5060
To: sip:bob@22.3.56.789:5060
Call-ID: 1234567890@10.8.2.106
Cseq: 1 INVITE
Content-Type: applcation/sdp
Content-Length: 224
v=0
o=jessica 0 0 IN IP4 10.7.1.229
s=Session SDP
c=IN IP4 10.7.1.229
m=audio 5004 RTP/AVP 0 3 5
a=rtpmap:0 PCMU/8000
SIP Message (2/8)

8. SIP
Request
Message Via: SIP/2.0/UDP
22.3.56.790:5060;branch=z9G4bK0e8d
From: sip:carol@22.3.56.790:5060
To: sip:bob@22.3.56.789:5060
Call-ID: 1234567890@10.8.2.106
Cseq: 1 INVITE
Content-Type: applcation/sdp
Content-Length: 224
INVITE sip:allen@22.3.56.789:5060 SIP/2.0
v=0
o=jessica 0 0 IN IP4
10.7.1.229
s=Session SDP
c=IN IP4 10.7.1.229
m=audio 5004 RTP/AVP 0 3 5
a=rtpmap:0 PCMU/8000
C R L F
SIP Message (3/8)

9. SIP Message (4/8)

10. GET /2001/Talks/0710-ep-grid/all.htm,access HTTP/1.1
User-Agent: W3C ChACL agent
Host: www.w3.org
Accept: text/xml
Accept-Encoding: deflate, gzip, x-gzip, identity, *;q=0
Authorization: Basic xxxxxxxxxxxxxxxxxxxx
Connection: Keep-Alive, TE
TE: deflate, gzip, chunked, identity, trailers
HTTP Message Request
HTTP/1.0 200
Date: Sat, 07 Jul 2001 14:08:12 GMT
Server: Apache/1.3.6 (Unix) PHP/3.0.15
WWW-Authenticate: Basic realm="W3CACL“
Content-length: 301
Content-Type: text/xml<?xml version="1.0"?>
<!-- Session-Id: 994514895.830925 --><rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:s="http://www.w3.org/2001/02/acls/ns#"> <rdf:Description
aboutEach="#B1"> <s:hasAccessTo
rdf:resource="http://www.w3.org/2001/Talks/0710-ep-grid/all.htm"/>
</rdf:Description></rdf:RDF>
HTTP Message Response
SIP Message (5/8)
SIP messages’ format
is the same as HTTP
ones

11. 6 Methods defined for request
REGISTER
INVITE
ACK
BYE
CANCEL
OPTONS
SIP Message (6/8)

12. Status codes
Informational – 1xx
Success – 2xx
Redirection – 3xx
Client-Error – 4xx
Server-Error – 5xx
Global-Failure – 6xx
SIP Message (7/8)

13. Most header fields and its using are the
same as that defined in HTTP and SMTP
SIP Message (8/8)

14. Call Flows
Registration
Basic Call
Re-INVITE – modify the session’s parameter
No Answer – use CANCEL method
Busy
Call Hold
3-way Conference -- The third party is added

15. Registration

16. Registration_Register_request

17. Registration_Register_response

18. Request
Response
bob@biloix.com
Registrar
User
Agent
Entity
Location
Server
Bob
192.0.2.4
use
store bob@biloix.com : 192.0.2.4

19. Basic Call
1
2
3
4
5
6

20. Basic Call_message_1

21. Basic Call_message_2

22. Basic Call_message_3
Bob Off-hook

23. Basic Call_message_4

25. Basic Call_message_5
Bob On-hook

26. Basic Call_message_6

27. Basic Call_the session is terminated

28. Session with re-INVITE (IP Address Change)
9
6

29. F6
Session with re-INVITE – Bob’s Original IP address

30. F9
Session with re-INVITE – Bob’s new IP address

31. Unsuccessful --- No Answer

32. Unsuccessful --- Busy

33. Call
Hold

34. Call Hold_message_Request
F5

35. Call Hold_message_Response
F6

36. Three-Way Conference --- Third Party is Added

37. Three-Way Conference - Message_1
F5

38. F8
Three-Way Conference - Message_2

39. Three-Way Conference - start to 3-way conference

40. References
RFC-3261 SIP:Session Initiation Protocol
Understanding the Session Initiation Protocol, Alan B.
Johnstone , 2/e, 2004
draft-ietf-sipping-service-examples-10.txt, March 5,
2006
draft-ietf-sipping-conferencing-models-01.txt, January
2003
RFC 3665 Session Initiation Protocol (SIP) Basic Call
Flow Examples,
, December 2003
http://www.in2eps.com/xrai/ztk-ietf-wg-rai-sip.html