[Serusers] ACK before INVITE on re-INVITE causes Cisco AS's to return a 500 error

[Evan Borgstrom]

Hey all,

	This has more to do with Asterisk & Cisco AS's IMO but I thought it
would be interesting to get some responses from this group before I
begin the battle with Cisco to get a bug report underway.

	We have an Asterisk box acting as a PBX sending calls to our SER
instances. The asterisk box has "reinvite=yes" in the sip.conf file
which causes Asterisk to send a re-INVITE for the call once it receives
the 200 OK. This re-INVITE has it's SDP changed to that of the IP Phone
behind the Asterisk box so that all media doesn't need to traverse it.
This works fine except in certain instances where messages get out of
order and it causes our Cisco GW's to error the call with a generic 500
message. When the messages are in the correct order the 500 error does
not appear.

	So here's the situation, user behind the asterisk box picks up the
phone and dials a PSTN destination. Asterisk fires off the initial
invite and everything proceeds as normal and we eventually receive the
200 OK message to which the Asterisk box replies with ACK and a new
INVITE that come in this order (X = Asterisk, Y = SER, Z = Cisco):

U 2005/11/15 16:51:51.557322 X.X.X.X:5060 -> Y.Y.Y.Y:5060
ACK

#
U 2005/11/15 16:51:51.557948 X.X.X.X:5060 -> Y.Y.Y.Y:5060
INVITE

	SER accordingly processes the two messages and replies 100 Trying to
the new INVITE message. Here's where the problem occurs, SER then sends
these messages out to the PSTN gateway but the order has been reversed:

#
U 2005/11/15 16:51:51.558937 Y.Y.Y.Y:5060 -> X.X.X.X:5060
SIP/2.0 100 trying

#
U 2005/11/15 16:51:51.559000 Y.Y.Y.Y:5060 -> Z.Z.Z.Z:5060
INVITE

#
U 2005/11/15 16:51:51.559657 Y.Y.Y.Y:5060 -> X.X.X.X:5060
ACK

	When this happens the Cisco GW replies with a 500 error message and the
following is sent to the Cisco's logs:

#
U 2005/11/15 16:51:51.711355 Z.Z.Z.Z:5060 -> Y.Y.Y.Y:5060
SIP/2.0 500 Server Internal Error.


Nov 15 21:51:51.613: HandleUdpSocketReads :Msg enqueued for SPI with
IPaddr: Y.Y.Y.Y:5060
Nov 15 21:51:51.613: *****CCB found in UAS Request table. ccb=0x653BCD0C
Nov 15 21:51:51.613: CCSIP-SPI-CONTROL:  act_sentsucc_new_message
Nov 15 21:51:51.617: CCSIP-SPI-CONTROL: act_sentsucc_new_message_request
Nov 15 21:51:51.617:  Queued event from SIP SPI : SIPSPI_EV_SEND_MESSAGE
Nov 15 21:51:51.617: sip_stats_status_code
Nov 15 21:51:51.617: sipSPICheckRequest: CheckRequest fail on method 102
error code: 2 and status: 500


	Is there any parameter that I can set to ensure that message leave SER
in the order they enter? Should the Cisco be able to handle this
condition (I check a number of different sections of the RFC but
couldn't find anything specific for either side)?

Thanks,
Evan