Subject: [Sip] Sending 200 OK after receiving ACK

From: Surya Santosh <[email-masked]>
Date: Tue, 14 Dec 2004 17:58:17 +0530

Hi All,

I have a doubt regarding the processing of ACK  by the UA. The UA , even 
after receving ACK from the other UA is still sending 200 OK's.

I am using the following configuration.

Host1------------Firewall---------------------------Internet
                                          |
                                          |
                                        Host2

I am using AOL instant messenger on both the hosts. I started video from 
Host2 to Host1. As AOL video uses SIP for connection establishment, Host1 
sends SIP INVITE to HOST2 and the following figure depicts the flow of the 
packets between the two UA's.

Host1--------------------------------------Host2
INVITE---------------------->
           <---------------------  100 Trying
           <---------------------  180 Ringing
           <---------------------- 200 OK
ACK    ----------------------->

After receiving the ACK, Host 2 is still sending 200 OK's . It is happening 
often but not all the times.
I have attached the capture of both success case and failure case. Could 
anyone please help me in finding out why Host2 is sending 200 OK' s even 
after receiving ACK.

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