Alfredo Terzoli / Mosioua Tsietsi RTMMoIP Alfredo Terzoli / Mosioua Tsietsi

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

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

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

Requests/Methods INVITE REGISTER BYE ACK CANCEL INFO

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

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

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)

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

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)

Introducing the server

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

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 www.iptel.org

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

Call through a proxy

Questions?