On 6/28/17 1:11 AM, Parveen Aggarwal wrote:
Dear Expert,

Is it valid to send deRegister request i.e. REGISTER with expires=0 before
receiving final response for previous registration request i.e. REGISTER
with expires >0  ?

As per RFC 3261,
It is mentioned for new REGISTER request only

UAs MUST NOT send a new registration (that is, containing new Contact
    header field values, as opposed to a retransmission) until they have
    received a final response from the registrar for the previous one or
    the previous REGISTER request has timed out.

I see no particular reason why this should be considered an error. However it might not be wise. It would be possible for the two requests to get reordered, so that the unregister is processed before the register. Both would appear to succeed, but the end state of the registrar would be different.

Another consideration is whether these are done using the same Call-ID. (In the same pseudo-dialog.) I don't think it will generally make any difference, but it may present issues if you are also requesting a temporary gruu with the registration.

        Thanks,
        Paul
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