1. Alfredo Terzoli / Mosioua Tsietsi
RTMMoIP
Alfredo Terzoli / Mosioua Tsietsi

2. PLAN Getting to know SIP better: essential structure of SIP messages
Beyond the single User Agent: more complex SIP networks
Have you played with SJPhone? Some thoughts on your ‘telecommunication status’ right now

3. SIP messages Either a REQUEST or a RESPONSE Uniform structure:
Start line
Headers (some mandatory, most optional)
(optional) Body
Request: start line carries a method
Response: start line carries a status

4. User Agents Request Response UAS – server UAS – server UAC – client

5. Requests/Methods
INVITE
REGISTER
BYE
ACK
CANCEL
INFO

6. Responses / Status(es)
1xx provisional information
2xx success
3xx redirection
4xx client error
5xx server failure
6xx global failure

7. Headers
Quite a few:
To, From, Cseq, Contact, Subject, Via, Accept, Accept-Language, Accept-Encoding, Authorization, Content-Type, Content-Length, Date, Encryption, Expires, Hide, In-Reply-To, Organization, Max-Forwards, etc

8. Body
Not compulsory
Typically a description of the session, typically done using SDP, Session Description Protocol
BTW, the session description includes what other protocols to use for the actual session. For voice/video session, typically RTP (Real Time Protocol)

9. While exploring…
A very useful resource while making sense of SIP and related protocols is the RFC sourcebook that you can find at
(folllow the links ‘RFC sourcebook>Protocols’)

10. Ok, we are ready for some fun!
Let’s go checking SIP messages in a UA-to-UA situation, using Ethereal.
We won’t be exhaustive in our analysis: SIP is simple, but it is still a full blown protocols for real entities living in a complex environment!
Naturally, we will quickly check some of the related protocols (SDP, RTP)

11. Introducing the server

12. Types of SIP servers Proxy (as in the previous slide) Redirect
Stateful, stateless
Redirect
Registration

13. Our SIP server, SER
Sip Express Router (sip.ict.ru.ac.za) in our system acts as proxy & registration server, never as a redirect server
Open source, large volume
Info about it at

14. Your telecommunication ‘status’
Your SIP soft/hard phones
Internet
Asterisk
SER
iLanga Core
Rhodes PBX
Telkom

15. Call through a proxy

16. Questions?