presence allows multiple people to subscribe to same call. It works for a small group of people having sharedl line

1. Sip Events and Presence
Shadhin Rahman

2. Overview
 General introduction of Sip
 Sip transaction and dialog
 Presence architecture
 Sip Events architecture and behavior
 Security considerations

3. SIP Introduction
 Sip user agent and sip network server
 Client initiates a call and server routes the
call
 Server is responsible for name resolution
and user location
 Sip proxy receives calls and send it to its
destination or next hop.

4. Image source http://www.cafesip.org/projects/jiplet/sip_registrar.jpg
Image source http://www.cafesip.org/projects/jiplet/sip_registrar.jpg

5. Sip Methods
 Invite is for session request
 Ack confirms a request
 Cancel is to end a pending request
 Bye to end a session
 Register to keep track of user location

6. Sip Return Code
 Sip has http like return code
 100 trying
 180 ringing
 200 Ok
 302 moved permanently
 401 unauthorized
 503 service unavailable
 603 declined

7. Sip Transaction and Dialog
 Transaction occurs between a client and a server
and comprises all messages from the first request
sent from the client to the server up to a final
response sent from the server to the client.
 Dialog is a peer-to-peer SIP relationship between
two UAs that persists for some time. A dialog is
identified by a Call-ID, a local tag and a remote
tag.

8. Sip Transaction Dialog
Image source http://www.informatik.uni-
Image source http://www.informatik.uni-
bremen.de/~prelle/terena/cookbook/Cookbook_D2/figures/chapter2/dialog.png
bremen.de/~prelle/terena/cookbook/Cookbook_D2/figures/chapter2/dialog.png

9. Presence
 Presence is user’s reachability and willingness to
communicate its current status information
 User subscribe to an event and receive notification
 Presence user agent
 Presence agent
 Presence server
 Watcher

10. Image source http://msdn.microsoft.com/en-us/library/bb896003.aspx
Image source http://msdn.microsoft.com/en-us/library/bb896003.aspx

11. Presence Overview
 Subscribe request
 Presence agent should authenticate and send
acknowledgement
 State changes should be notified to
subscriber
 Ability to refresh and terminate subscription
 Presence agent should be able to allow or
terminate subscription

12. Presence Flow
Image source http://download.oracle.com/docs/cd/B32110_01/ocms.1013/b31497/about_sdp.htm#BABDHHCJ
Image source http://download.oracle.com/docs/cd/B32110_01/ocms.1013/b31497/about_sdp.htm#BABDHHCJ

13. Sip Events Introduction
 Sip was initially introduced as a signaling
protocol
 Lack of method to emulate constant
communication and update status between
entity
 Three more method was introduced namely
Publish , Subscribe and Notify

14. Simple Sip Events
Image source http://www.cisco.com/en/US/i/100001-200000/190001-200000/190001-191000/190463.jpg
Image source http://www.cisco.com/en/US/i/100001-200000/190001-200000/190001-191000/190463.jpg

15. Sip Event definitions
 Event Package
 Event Templates
 Notification
 Notifier
 State Agent
 Subscriber
 Subscription

16. Description of Subscribe
 Subscription Duration
 Identification of subscribe event or event
classes
 Optional accept header.

17. Subscriber Actions
 Requesting a subscription.
 Refreshing subscription.
 Unsubscribing.
 Confirmation of subscription.

18. Description of Notify
 Event headers
 Message body
 Check for valid event type
 Ensure local authentication and
authorization.
 Notification should sent after removal of
subscription.

19. Notifier Responds
 Initial subscribe transaction processing.
489 bad event.
• Confirmation of subscription
creation/refreshing.
• Authentication/Authorization of subscribe
request.
403 forbidden, 603 declined.

20. Description of Publish
 Publishes event state
 Create, modify and remove state
 Event publication agent
 Event state compositor
 Duration of any event is well defined

21. Processing Publish Request
 Event state compositor keeps track of state
for each Address-of-record
 Esc inspects request uri
 Esc examines event header
 Esc process expires header field
 Esc stores the event state in the body of the
message

22. SUBSCRIBE sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP
host.example.com;branch=z9hG4bKnashds7
To: <sip:presentity@example.com>
From: <sip:watcher@example.com>;tag=12341234
Call-ID: 12345678@host.example.com
CSeq: 1 SUBSCRIBE
Max-Forwards: 70
Expires: 3600
Event: presence
Contact: sip:user@host.example.com
Content-Length: 0

23. SIP/2.0 200 OK
Via: SIP/2.0/UDP
host.example.com;branch=z9hG4bKnashds7
;received=192.0.2.1
To:
<sip:presentity@example.com>;tag=abcd1234
From:
<sip:watcher@example.com>;tag=12341234
Call-ID: 12345678@host.example.com
CSeq: 1 SUBSCRIBE
Contact: sip:pa.example.com
Expires: 3600
Content-Length: 0

24. NOTIFY sip:user@host.example.com SIP/2.0
Via: SIP/2.0/UDP
pa.example.com;branch=z9hG4bK8sdf2
To:
<sip:watcher@example.com>;tag=12341234
From:
<sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@host.example.com
CSeq: 1 NOTIFY
Max-Forwards: 70
Event: presence
Subscription-State: active; expires=3599
Contact: sip:pa.example.com
Content-Type: application/pidf+xml
Content-Length: ...

25. SIP/2.0 200 OK
Via: SIP/2.0/UDP
pa.example.com;branch=z9hG4bK8sdf2
;received=192.0.2.2
To:
<sip:watcher@example.com>;tag=12341234
From:
<sip:presentity@example.com>;tag=abcd1234
Call-ID: 12345678@host.example.com
CSeq: 1 NOTIFY

26. PUBLISH sip:presentity@example.com SIP/2.0
Via: SIP/2.0/UDP
pua.example.com;branch=z9hG4bK652hsge
To: <sip:presentity@example.com>
From:
<sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
Max-Forwards: 70
Expires: 3600
Event: presence
Content-Type: application/pidf+xml
Content-Length: ...

27. SIP/2.0 200 OK
Via: SIP/2.0/UDP
pua.example.com;branch=z9hG4bK652hsge
;received=192.0.2.3
To:
<sip:presentity@example.com>;tag=1a2b3c4d
From:
<sip:presentity@example.com>;tag=1234wxyz
Call-ID: 81818181@pua.example.com
CSeq: 1 PUBLISH
SIP-ETag: dx200xyz
Expires: 1800

28. Security Consideration
 Access control.
 Notifier privacy mechanism.
 Denial of service attacks.
 Replay Attacks.
 Man-in-the-middle attacks.
 Confidentiality.

29. Implementation of Security
 Sip registration
 TLS
 Digest Authentication
 S/MIME

30. References
 Rfc 3856 http://www.ietf.org/rfc/rfc3856.txt
 Rfc 3265 http://www.ietf.org/rfc/rfc3265.txt
 Rfc 2778 http://www.ietf.org/rfc/rfc2778.txt
 Rfc 3261 http://www.ietf.org/rfc/rfc3261.txt
 Rfc 3903 http://www.ietf.org/rfc/rfc3903.txt
 http://en.wikipedia.org/wiki/Session_Initiation_Protocol

31. Summery
 Presence is a way to have sustained stateful
communication
 Sip serves well for presence requirements
 Sip presence deployment must confirm
security measurements

32. Question ?