Hello,

when the call is established, there is one request (the INVITE) from caller to callee. Then the ACK also from caller to callee. But there is no request from callee to caller at that moment. Each side is using its own cseq value, the callee doesn't have to use the latest cseq from caller plus one when it sends a request (like a re-INVITE or the BYE). In practice the cseq 0 is not usually used by an UA, so that's why the keepalive for that direction is using it.

Cheers,

Daniel

On Thu, Jan 2, 2020 at 10:07 PM Alex Balashov <abalashov@evaristesys.com> wrote:

On Thu, Jan 02, 2020 at 09:26:23PM +0100, Daniel-Constantin Mierla wrote:

> the cseq 0 is because in that direction was no request sent
> end-to-end.

Also, sorry, but I didn't quite understand this.

--
Alex Balashov | Principal | Evariste Systems LLC

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