The problem of unrecognized ACK messages at Verizon for our cancelled outgoing calls

The problem of unrecognized ACK messages at Verizon for our cancelled outgoing calls

Emin Gabrielyan

2007-05-23

The flow graph of an answered call (correct behaviour):

The left side (128.179.67.76) represents a SIP phone. The middle part (212.249.15.4 and 195.129.125.74) represents our SIP server with two interfaces. The right side (212.190.89.137) represents the SIP server of Verizon.

The flow graph of a cancelled call (wrong behaviour):

[png], [txt]

It seems that Verizon does not understand our ACK and continuously retransmits the 487-Request-Cancelled.

The contents of messages are available [pdf], [ps].

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