491 Message


Can anybody tell me why Asterisk responds INVITE for call retrival with 491 Request Pending.


UAS Behavior

Section 13.3.1 describes the procedure for distinguishing incoming
re-INVITEs from incoming initial INVITEs and handling a re-INVITE for
an existing dialog.

A UAS that receives a second INVITE before it sends the final
response to a first INVITE with a lower CSeq sequence number on the
same dialog MUST return a 500 (Server Internal Error) response to the
second INVITE and MUST include a Retry-After header field with a
randomly chosen value of between 0 and 10 seconds.

A UAS that receives an INVITE on a dialog while an INVITE it had sent
on that dialog is in progress MUST return a 491 (Request Pending)
response to the received INVITE.

For any Questions refer RFC 3261 .(Refer Section no : 14.2)