SIP: Multiple (different) incoming calls with identical Call-ID.

Discussion in 'VOIP' started by simon@mungewell.org, Mar 22, 2006.

  1. Guest

    Hi All,
    I am attempting to figure out the solution to the problem where a
    multi-pressence UA can have multiple incoming calls with the same
    Call-ID (along with To and From). This situation can arise when a call
    is forwarded between accounts and happens to arrive at the UA via
    different accounts/routes.

    http://www.ietf.org/rfc/rfc3261.txt says
    --- page 12
    Call-ID contains a globally unique identifier for this call,
    generated by the combination of a random string and the softphone's
    host name or IP address. The combination of the To tag, From tag,
    and Call-ID completely defines a peer-to-peer SIP relationship
    between Alice and Bob and is referred to as a dialog.
    ---

    For example with FreeWorldDialup, a user can place a 'perminant
    forward' on an account. This causes an incoming call that account to
    ring both the account's UA and that of the forward destination.

    If a UA is registered to both accounts it will receive 2 INVITEs with
    identical call tags (Call-ID, To & From), hence the 'dialogues' are not
    unique.

    This example uses the 'Call Me' service from the FWD webpages to
    initiate call. My application receives the following 'INVITES'
    ---
    INVITE sip::5063;transport=udp SIP/2.0
    CSeq: 2 INVITE
    Via: SIP/2.0/UDP 69.90.155.70;branch=z9hG4bKca7f.beaf88d4.3
    Via: SIP/2.0/UDP 69.90.155.70;branch=z9hG4bKca7f.aeaf88d4.0
    Via: SIP/2.0/UDP 69.90.168.5:5060
    User-Agent: eDial Server
    From: ""
    <sip:>;tag=94919237611626883
    Call-ID:
    To: sip:
    Contact: sip:69.90.168.5:5060
    ---
    INVITE sip::5064;transport=udp SIP/2.0
    CSeq: 2 INVITE
    Via: SIP/2.0/UDP 69.90.155.70;branch=z9hG4bKca7f.aeaf88d4.4
    Via: SIP/2.0/UDP 69.90.168.5:5060
    User-Agent: eDial Server
    From: ""
    <sip:>;tag=94919237611626883
    Call-ID:
    To: sip:
    Contact: sip:69.90.168.5:5060
    ---

    Although this example is deliberately caused, this situation could
    exist in real world situations presumably un-intentionally.

    This situation will not be detected by the proxies as a call loop, as
    it is not a loop - they only see two unique requests as they look at
    the 'via' information.

    At present the application solely uses the Call-ID to identify call
    channels,
    this 'feature' is causing it to get confussed - treating the two
    channels as a single enitity and therefore be unable to converse
    correctly to the two SIP INVITEs.

    Any suggestions on how to guard against this (ie, detect it), or to
    harden the UA so that it can distinguish between these type of multiple
    incoming calls?

    Yours,
    Simon.
     
    , Mar 22, 2006
    #1
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