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Sip Tutorial Preview


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  • 1. Fundamentals of SIP Fall VoiceCon 2009, San Francisco David A. Bryan Cogent Force, LLC
  • 2. Outline
    • Background on VoIP
    • What is SIP?
    • SIP Components
    • SIP Messages
    • Locating Users and Establishing Sessions
    • Routing in SIP
    • Media with SIP
    • SIMPLE
    • NATs, Firewalls, and SIP
    • P2PSIP
    • References
  • 3. Session Border Controller SIP/IP network SIP/IP network Session Border Controller (SBC) SIP Server SIP Server
  • 4. Basic Call Flow SIP Server INVITE INVITE 100 Trying 180 Ringing 180 Ringing 200 OK 200 OK ACK ACK BYE BYE Bi-directional Media between endpoints 200 OK 200 OK
  • 5. INVITE message INVITE SIP/2.0 SIP request, method is INVITE, target is an AoR (for Bob) Via: SIP/2.0/TCP Via header tracks where it has been (more on this later) From: Alice <>; tag=ss95cbav Message is from Alice, and this is the SIP URL for Alice. The tag is unique to this call and selected by Alice’s UA To: Bob <> Alice is trying to contact Bob at his SIP URL (a tag will be selected by Bob’s UA later Call-ID: Call-ID is a unique ID to track this particular call (selected by Alice’s UA) CSeq: 1 INVITE Used to track which responses go with which messages. Responses to this invite will also have a CSeq of 1 INVITE Max-Forwards: 10 Used in routing (more on this later) Contact: <;transport=tcp> How to contact Alice directly. Notice this is a contact (has a host) … snip…
  • 6. Forking
    • While somewhat complicated, many features require “forking”
      • Send a message to more than one entity Need to track (and manage both sides)
    • Parallel forking (send to more than one at a time)
        • Ring both desk and mobile at once, cancel the call to whichever fails to pickup
    • Can also use redirection (sequential)
        • Ring desk phone, then try mobile if no answer
    • Can combine
        • Ring desk phone and mobile, then VM if no answer
  • 7. Thank You! I hope to see you in San Francisco!