[SR-Users] Is ACK required in a re-invite?

[Alex Balashov]

On 08/15/2016 05:42 PM, Jay Li wrote:
> Dear All,
>
> I just have a basic SIP question on re-invite. I wonder if "ACK" is
> required in a re-invite scenario, like re-invite -> 200 OK -> ACK. What
> I've seen is for some reason, my PSTN doesn't send a "ACK" back to me
> after my 200 OK response to their re-invite. I don't know if not sending
> an ACK in a re-invite is an allowed behavior. Thanks.

Yes, an ACK is required. Per RFC 3261 § 14.1 ("UAC behavior"):

    The rules for transmitting a re-INVITE and for
    generating an ACK for a 2xx response to re-INVITE are
    the same as for the initial INVITE (Section 13.2.1).

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Alex Balashov | Principal | Evariste Systems LLC
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