1. SIP, Presence and Instant Messaging

2. Session Initiation Protocol (SIP)
Developed in mmusic Group in IETF
Proposed standard RFC2543, February 1999
Work began 1995
Part of Internet Multimedia Conferencing Suite
Main Functions
Invite users to sessions
Find the user’s current location, match with their capabilities and preferences in order to deliver invitation
Carry opaque session descriptions
Modification of sessions
Termination of sessions

3. Protocol Components User Agent User Agent Client (UAC)
End systems
Send SIP requests
User Agent Server (UAS)
Listens for call requests
Prompts user or executes program to determine response
User Agent
UAC + UAS
Redirect Server
“Network” server; redirects users to try other server
Proxy Server
“Network Server” Proxies request to another server Can “fork” request to multiple servers, creating a search tree
Registrar
receives registrations regarding current user locations

4. SIP Architecture Request Response Media SIP Redirect Server1 2 3 4 5 6 7 8 9 10 11 12
SIP Client
SIP Redirect
Server
SIP Proxy
(User Agent Server)
Location Service 13 14

5. SIP Message Syntax Many header fields from http
Payload contains a media description
SDP - Session Description Protocol
INVITE SIP/2.0
From: J. Rosenberg
Subject: That pay increase
To: Eric Sumner
Via: SIP/2.0/UDP pc13.dynamicsoft.com
Call-ID:
Content-type: application/sdp
CSeq: 4711 INVITE
Content-Length: 187
v=0
o=jdrosen IN IP s=
c=IN IP
t=0 0
m=audio 3456 RTP/AVP 0

6. SIP Benefits Integration with IP Applications Scalability
MIME
URIs
DNS
Scalability
Stateless operation
SRV usage
Multi-hop networks
Session Independence
Usable for interactive games, chat, voice, video
Recoverability
State stored in messages
Re-opening of TCP connections
Extension Management
Adding headers
Adding methods
Adding bodies
Require and Proxy-Require
Interoperability
New Services!
Integration with IM, presence, , web

7. What Does Presence Have to Do With SIP?
How to Deliver Presence
Need a network that can identify users independent of location
Need a way to forward subscription requests to server handling that user
Need a way for user to tell server its location and other presence data
Need a network which can forward notifications to subscribers
Needs to scale
Needs to deliver messages in real time
What Does a SIP Network Do?
Identifies users independent of location
Forwards requests (INVITE or otherwise) to server handling user
REGISTER allows network to tell server its location and other information [later]
Can forward messages back to originators in reverse direction
Scales
Delivers messages in real time (call setup delays)

8. SIP Already Provides Publication Capability
REGISTER is a Publication Message for Locations
Allows for SIP and Other URL Types
Multiple Entities Can Publish for the Same Address
SIP Caller Preferences Extension Allows for Attributes for Locations
Mobile, landline
Home, business
Preferences
Audio, video - MIME capability
Registrar
Registrar

9. SIP Extension for Presence
REGISTER
SUBSCRIBE
NOTIFY
Presence Agent +
Proxy/Registrar =
Presence Server
Proxy
Subscriber
Presentity
New Entity: Presence Agent
Purely logical entity
Knows presence state of user
Receives SUBSCRIBE requests
Generates NOTIFY requests
Co-located with proxy/registrar or User Agent
Basic Operation
Subscriber send SUBSCRIBE
Routed to PA using normal SIP
PA authorizes subscriber
Acceptance contains presence state
NOTIFY sent when state changes
Routed using SIP Record-Route

10. Features of SIP For Presence Extension
End Users Can Perform Notifications
Scalability
Presence Agent Function Can Migrate
Network provides service when user is offline
When user is online, subscriptions migrate to user
Authorization is orthogonal
Multiple Entities Can Generate Presence Information for One Presentity
Mobile phone, PDA, laptop and desktop PC
Traditional SIP Proxies Route SUBSCRIBE and NOTIFY
Presence Data is Orthogonal

11. SIP Extension for Instant Messaging
Operation of Extension
Messages carried in SIP messages
New method - MESSAGE
Routed to recipient using normal SIP techniques
Simple extension
Features
Any MIME data can be sent
TCP for large messages
Routed by existing proxies and registrars
Possible to have a different client for IM and communications

12. Advantages of Using SIP for Presence and IM
Unifies Major Communications Services
Voice/video IM
Presence
Shared Databases
Shared Proxies
Shared Servers

13. Advantages of Using SIP For Presence and IM
Reduces Management Costs
One infrastructure instead of two
One NOC instead of two
One set of managers instead of two
Enables New Combined Services
Combined services integrate voice, video, IM, presence, web amd
These new services will be a “killer app” for communications on the Internet
Delivery of combined services is greatly simplified by alignment of presence and communication signaling protocols

14. Information Resource Jonathan Rosenberg