[Serusers] rewrite & ACK forwarding problem

[Sean P. Robertson]

I have the same problem and posed it to the group yesterday ([Serusers]
Ignored 200 OK message.) So far the only workaround that I have found is to
use the rules in my gateway to rewrite the dialed digits before sending them
to the PSTN PRI, thus leaving the origianl URI intact for SIP
communications.

One person told me that this is a bug in the Cisco ATA, but it happens on my
IPDialog phones also.  It seems to me that the INVITE is being processed by
the SER dial rules and is rewritten, but the ACK is not.

Sean
_______________________________________________

Sean Robertson

NETXUSA
p. 800-289-6389
f.  864-233-4344                  "Ask me about Voice over IP."
http://www.netxusa.com/

----- Original Message -----
From: "Alexander Mayrhofer" <axelm at nic.at>
To: <serusers at lists.iptel.org>
Sent: Friday, June 27, 2003 12:15 PM
Subject: [Serusers] rewrite & ACK forwarding problem


>
> Hi,
>
> we're running SER together with a PSTN Gateway. Before a call get's
> forwarded to the gateway, we are rewriting the request URI to make
> rewriting on the GW as simple as possible:
>
> route {
> ...
>    strip(3);  # +43xxx -> xxx
>    prefix("0"); # xxx -> 0xxx
>    rewritehostport(xxx.xxx.xxx.xxx, 5060); # request to gateway
>    route(1);
>    break;
> ...
>
> SIP call flow looks like (record route enabled):
>
> (1) phone -> SER
> INVITE sip:*43699xxxxxxxx at nic.at43.at SIP/2.0
>
> (2) SER -> phone
> SIP/2.0 100 trying -- your call is important to us
>
> (3) SER -> GW
> INVITE sip:0699xxxxxxxx at xx.xx.xx.xx:5060 SIP/2.0
>
> (4) GW -> SER
> SIP/2.0 100 Trying
>
> (5) GW -> SER
> SIP/2.0 183 Session Progress
>
> (6) SER -> phone
> SIP/2.0 183 Session Progress
>
> (7) GW -> SER
> SIP/2.0 180 Ringing
>
> (8) SER -> phone
> SIP/2.0 180 Ringing
>
> (9) GW -> SER
> SIP/2.0 200 OK
> Contact: <sip:0699xxxxxxxx at xx.xx.xx.xx:5060>
>
> (10) SER -> phone
> SIP/2.0 200 OK
> Contact: <sip:0699xxxxxxx at xx.xx.xx.xx:5060>
>
> [ call established, we can talk, but ... ]
>
> (11) phone -> SER
> ACK sip:0699xxxxxxxx at xx.xx.xx.xx:5060 SIP/2.0
>
> --> Here starts the problem. That ACK (11) never gets forwarded to the
> Gateway, so after a few seconds, the GW starts over at (9). Those three
> packets (9-11) repeat a few times until GW runs into a timeout and drops
> the call.
>
> I have the impression that SER can't match the packet to the previous
> requests because of the rewritten URI. Is that correct?
>
> The only output at debug level 3 is:
>
> Warning: sl_send_reply: I won't send a reply for ACK!!
>
> Is that a routing goof somewhere in our scripts or is that a more
> generic problem? Is the problem that the warning indicates somehow
> related to the fact that the ACK is not being forwarded?
>
> Help appreciated.
>
> cheers
>
> axelm
>
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