通 shuntongzhang@gmail.com wrote:

In urecord.c:get_ucontact_by_instance, REGISTER without instance-id will check cseq number(must be higher), REGISTER with instance-id will not check cseq number.

what is the difference?why not check cseq in REGISTER with instance-id?

Hi

I am not familiar with the mentioned code, but from outbound rfc point of view it seem to be related to detecting device even if it has restarted.

See 5626 for more: https://tools.ietf.org/html/rfc5626#section-3.1