Re: CSeq reset on re-INVITE

On Fri, Oct 28, 2022 at 6:28 PM David Cunningham <[email protected]>
wrote:

> Hello,
>
> We have a problem where Asterisk is resetting the CSeq on a re-INVITE, and
> the phone receiving the re-INVITE is rejecting it, probably as a result of
> that. Would anyone be able to offer any insight please?
>
> The scenario is:
>
> Phone A makes call 1 to Asterisk which dials call 2 to phone B, which
> answers the call.
>
> Phone B puts call 1 on hold, makes call 3 to Asterisk which dials call 4
> to phone C, which answers the call.
>
> Phone B does an attended REFER transfer of call 2 to call 3, taking itself
> out of the call. Asterisk bridges the remaining calls, so phones A and C
> are now talking to each other.
>
> Asterisk sends a re-INVITE to phone A with a P-Asserted-Identity, to tell
> phone A the updated details of phone C that it's talking to. However phone
> A rejects the re-INVITE with a "404 Not found" error.
>
> The only explanation I can see for the "404 Not found" error is that call
> 1 was set up with "CSeq: 954698786 INVITE", whereas the re-INVITE Asterisk
> sends with the P-Asserted-Identity has "CSeq: 102 INVITE". Why is Asterisk
> resetting the CSeq on the re-INVITE, and doesn't this appear to be
> incorrect?
>

It's not incorrect. Each direction has its own CSeq[1]. From Phone A to
Asterisk can be 954698786 and from Asterisk to Phone A can be 102.

[1] https://www.rfc-editor.org/rfc/rfc3261#section-12.2.1.1

-- 
Joshua C. Colp
Asterisk Project Lead
Sangoma Technologies
Check us out at www.sangoma.com and www.asterisk.org

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