According to RFC 3261 (section 8.1.1.5), as @Juha Heinanen mentioned, the Cseq value can be arbitrary, It means the CSeq value can start from any number. But according to RFC 3261 (section 22.2), as @Henning Westerholt mentioned, the value of CSeq must increment for 401 (Unauthorized) or 407 (Proxy Authentication Required) responses.

Then for those who want to use the Sems project, keep in mind that the Sems does not follow these specifications.

With Best Regards

On Mon, Dec 20, 2021 at 7:43 PM Juha Heinanen <jh@tutpro.com> wrote:

Mojtaba writes:

> So, I have to manage the value of CSeq by Kamailio or have some update in
> Sems so that at least could relay the Cseq without changing.
> What do you think?

If your Kamailio is between SEMS and Asterisk, you could try to increase
CSeq value by some constant in all requests from SEMS to Asterisk.

-- Juha