[asterisk-users] Request Pending retransmitions

["Guillén Melo, Joaquin"]

Hi, im trying to build a UAC and I'm coming up with some trouble whenever I receive a SIP 491 Request Pending Response. This happens because I try to place a call on hold using an Invite request rigth before Asterisk sends me a Re-Invite for the same call. I respond to the 491 response with an ACK however for some strange reason Asterisk doesn't accept the ACK and insists on retransmitting the 491 Response. Asterisk replies with the following 491 response: 

SIP/2.0 491 Request Pending 
Via: SIP/2.0/UDP 10.110.7.89:5070;branch=z9hG4bK5a668c33f196837c3602266b23b389e0;received=10.110.7.89 
From: <sip:30001 at 10.110.7.20:5070>;tag=SIPTester 
To: <sip:30008 at 10.110.7.20>;tag=as2ea72122 
Call-ID: 0dd43bb5a64eb5a2fb0114193821f037 at 10.110.7.89 
CSeq: 5 INVITE 
User-Agent: Asterisk PBX 
Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY 
Supported: replaces 
Content-Length: 0 
X-Asterisk-HangupCause: Normal 



And I send the following ACK: 



ACK sip:30008 at 10.110.7.20 SIP/2.0 
Call-ID: 0dd43bb5a64eb5a2fb0114193821f037 at 10.110.7.89 
Max-Forwards: 70 
From: <sip:30001 at 10.110.7.20:5070>;tag=SIPTester 
To: <sip:30008 at 10.110.7.20>;tag=as2ea72122 
Via: SIP/2.0/UDP 10.110.7.89:5070;branch=z9hG4bK5a668c33f196837c3602266b23b389e0 
CSeq: 5 ACK 
Content-Length: 0 

However this doesn't seem to be valid because Asterisk insists be resending the same 491 Response until it sends 6 messages and the decides to destroy the dialog: 

Aug 21 11:21:06 <http://www.voip-info.org/boards/Aug%2021%2011:21:06>  WARNING9686 <http://www.voip-info.org/boards/9686> : chan_sip.c:1967 retrans_pkt: Maximum retries exceeded on transmission 0dd43bb5a64eb5a2fb0114193821f037 at 10.110.7.89 for seqno 5 (Critical Response) - See doc/sip-retransmit.txt. 
Aug 21 11:21:06 <http://www.voip-info.org/boards/Aug%2021%2011:21:06>  WARNING9686 <http://www.voip-info.org/boards/9686> : chan_sip.c:1989 retrans_pkt: Hanging up call 0dd43bb5a64eb5a2fb0114193821f037 at 10.110.7.89 - no reply to our critical packet (see doc/sip-retransmit.txt). 

Does anyone have a clue of what it is I'm doing wrong? Do I have to send a CANCEL request of the hold's INVITE? 

Thanks in advance!

 

Joaquín 

 

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