[reSIProcate] Question for how to handle 491 message from SIP server

[Wenwei Xu]

When two calling parties try to hold the call (send an Invite message)
simultaneously, the SIP server will send 491 message (pending request) to
both parties. Then InviteSession::start491Timer() will get called. After
that, the two UA's can't hold/unhold anymore but wait till timeout by the
SIP server (a 481 message). Is this the right way or shall we implement a
491 message handler in the reciprocate stack library such that the UA can
have some control when this happens?

Thanks a lot.

Wenwei Xu