SIP - The Basics
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SIP is a protocol for setting up and managing sessions over the internet, including voice and video calls. It allows users to locate each other and establish communication sessions between endpoints. SIP sets up sessions but does not handle the actual media, like audio, which is transported separately using protocols like RTP. SIP works by routing request and response messages between user agents through proxies and servers to initiate, negotiate, and terminate communication sessions.
SIP - The Basics
- 1. About SIP SIP The Basics Jonas Borjesson @borjessonjonas
- 2. NOTE ● This version has been adapted to be viewed without transitions. ● Go to aboutsip.com to download the original version. ● Also be sure to check out vimeo.com/aboutsip for any recorded presentations. @borjessonjonas
- 3. This is SIP! @borjessonjonas
- 4. SIP is about communication! Gaming Voice Video Chat Presence Whatever @borjessonjonas
- 5. SIP is about sessions ● A session represents a p2p relationship between two SIP endpoints. ● SIP helps you: ● Setup sessions. ● Negotiate what you want to do with the session ● Tear down sessions ● Session can be anything ● Voice/video/gaming/your own whatever ● SIP only helps you establish and manage the session, you decide what to do! @borjessonjonas
- 6. SIP is about finding your friends ● Before you can “call” your friends (establish a session), you must find them! ● No magic though... you need to tell someone where you are... a t o g et W en t coffee /Bob @borjessonjonas
- 7. No Magic Hey, I 'm comin g ove r, nee d a coff ee too . .. ? Hey, have you seen Bob? ! He is over at Cafe Capuchino aboutsip.com ! Tell my friends that I bob@aboutsip.com am online at Cafe Capuchino @borjessonjonas
- 8. Basic User Scenario Proxy INVITE sip:bob@aboutsip.com INVITE sip:bob@192.168.0.100 180 Ringing 180 Ringing 200 OK 200 OK ACK ACK audio @borjessonjonas
- 9. SIP Components ● User Agents (UA) ● User Agent Client (UAC) ● User Agent Server (UAS) ● Servers ● Proxy – forwards the request to the next hop ● Registrar – accepts registrar requests ● Redirect Server – finds alternative locations ● Location Service – stores bindings. (note, all SIP components are logical components and a such one server can act as all of the roles) @borjessonjonas
- 10. SIP Messages ● Request/Response model ● UAC sends the request, UAS responds ● Requests starts with a request line ● INVITE sip:alice@example.com SIP/2.0 ● Methods ● INVITE, ACK, BYE, CANCEL, REGISTER, OPTIONS ● And many more... @borjessonjonas
- 11. SIP Messages ● SIP responses starts with a status line ● SIP/2.0 200 OK ● Response Codes: ● 1xx – Provisional. INVITE ● 2xx – Success. 180 Ringing ● 3xx – Redirection. 500 Server Error ● 4xx – Client Error. ● 5xx – Server Error. ● 6xx - Global Failures. @borjessonjonas
- 12. INVITE Request INVITE sip:bob@aboutsip.com SIP/2.0 To: <sip:bob@aboutsip.com> From: <sip:alice@aboutsip.com>;tag=987lkajsdf89au Call-ID: lkjasdf90989lkj CSeq: 1 INVITE Content-Type: application/sdp Content-Length: 450 Record-Route: <sip:192.168.1.52:5060;transport=tcp;lr> Via: SIP/2.0/TCP 192.168.0.122:5060;branch=xxx;rport ... Contact: <sip:192.168.0.122:3156;transport=TCP> @borjessonjonas
- 13. 200 OK Response SIP/2.0 200 OK To: <sip:bob@aboutsip.com>;tag=89uasdkfjoiu From: <sip:alice@aboutsip.com>;tag=987lkajsdf89au Call-ID: lkjasdf90989lkj CSeq: 1 INVITE Via: SIP/2.0/TCP 192.168.0.122:5060;branch=xxx;rport ... Contact: <sip:192.168.0.22:3156;transport=TCP> Record-Route: <sip:192.168.1.52:5060;transport=tcp;lr> Content-Type: application/sdp Content-Length: 451 @borjessonjonas
- 14. SIP Headers ● Headers carries important information about e.g. routing or request and responses. ● Similar in syntax and meaning to HTTP ● The more important headers: ● To & From ● Via ● Contact ● Call-ID ● Route & Record-Route ● CSeq @borjessonjonas
- 15. Addressing ● SIP-address is used to locate and communicate with other users. ● sip:alice@example.com ● sips:alice@example.com ● Each user typically have an Address of Record (AOR) through which that user can be contacted. @borjessonjonas
- 16. What about the actual Audio ● SIP doesn't care about audio ● SIP only cares about managing sessions* ● Allows any type of sessions to be established, such as an audio session. ● SDP + RTP = gets audio going ● SDP – describes e.g. an audio session ● RTP carries the actual audio @borjessonjonas
- 17. Summary ● SIP != VoIP ● SIP can do VoIP but is so much more ● SIP actually doesn't care about audio at all ● SIP helps you route messages through the network. ● SIP helps to locate your friends. @borjessonjonas
- 18. More presentations and material at aboutsip.com Thanks! @borjessonjonas