After Receiving An Out of Order Sequence (CSeq) Request Can SIP Server Add a "Retry-After" Header in Its 500 (Server Internal Error) Response (Doc ID 1580419.1)

Last updated on MARCH 04, 2024

Applies to:

Goal

When the SIP Container receives an out of order sequence request (CSeq number is too low) then it MUST respond with a 500 (Server Internal Error).  A typical out of order call flow scenario may occur when a UA (User Agent) sends two messages at nearly the same time (less than 1 millisecond apart).  If the second message (higher CSeq number) reaches, or is processed, by the other UA first, for whatever reason, then the first message (lower CSeq number) must be rejected and the SIP session ended.

Sent:

   ----> MESSAGE (CSeq=10)
   <---- 200 OK  (CSeq=10)
   ----> MESSAGE (CSeq=11)
   ----> MESSAGE (CSeq=12)

Received (out of order):

   ----> MESSAGE (CSeq=10)
   <---- 200 OK  (CSeq=10)
   ----> MESSAGE (CSeq=12)
   ----> MESSAGE (CSeq=11)
   <---- 500 (Internal Server Error)

In these type of cases, is it possible to configure SIP Container to add a Retry-After Header in its 500 error response so the UA may re-initiate the session?

Solution

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