[sipcore] Does a forking proxy send 481?

Christer Holmberg <christer.holmberg@ericsson.com> Wed, 22 December 2010 22:22 UTC

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From: Christer Holmberg <christer.holmberg@ericsson.com>
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Date: Wed, 22 Dec 2010 23:24:31 +0100
Thread-Topic: Does a forking proxy send 481?
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Subject: [sipcore] Does a forking proxy send 481?
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A minor old school SIP question to think about when getting prepared for the holidays:

Fact: A stateful proxy forks an INVITE.

Fact: Some early dialogs are created.

Fact: The proxy receives a 4xx response on early dialog ED1.

Fact: The proxy does not forward the 4xx response, as it waits for final responses on the other early dialogs.

Fact: The UAC sends an in-dialog request on ED1 (since it is not aware that ED1 has been terminated).

Question: Does the forking proxy send a 481 response to the request, or does it forward it towards the remote UAS previously associated with ED1?

The reason I ask is because of a question whether there should always be a 2xx response to a PRACK, even if the associated dialog has been terminated. But, a proxy that does not know PRACK would of course send a 481.