1219 Response Codes 01

486 忙

The callee's end system was contacted successfully, but the callee is

   currently not willing or able to take additional calls at this end

   system.  The response MAY indicate a better time to call in the

   Retry-After header field.  The user could also be available

   elsewhere, such as through a voice mail service.  Status 600 (Busy

   Everywhere) SHOULD be used if the client knows that no other end

   system will be able to accept this call.

 

21.4.25 487 Request Terminated

 

   The request was terminated by a BYE or CANCEL request.  This response

   is never returned for a CANCEL request itself.

 

21.4.26 488 Not Acceptable Here

   The response has the same meaning as 606 (Not Acceptable), but only

   applies to the specific resource addressed by the Request-URI and the

   request may succeed elsewhere.

21.4.27 491 Request Pending

 

   The request was received by a UAS that had a pending request within

   the same dialog.  Section 14.2 describes how such "glare" situations

   are resolved. 同向对冲

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