[SIPForum-discussion] Delayed 100 Trying

Paul Kyzivat pkyzivat at alum.mit.edu
Tue Aug 11 19:44:52 UTC 2015

On 7/21/15 3:11 AM, Raj Kumaradass wrote:
> Hello,
> I have observed a case where in 100Trying & 180ringing response for a
> initial INVITE message is delayed beyond 32seconds(TCP transport being
> used here) causes the client B to remain in a hung call state, as the T1
> timer expiry eventually causes dialog cleanup at the server side as below.
> Client A ------  Server ------- Client B
>                         --- INVITE ----->
>                         @32seconds(T1 timer) fires and cleansup the dialog
>                         after say 40 seconds
>                         <---100 Trying---
>                         <--- 180 Ringing --
> In such case, is there any standard described way to get this cleaned up
> at Client B side as well?  Is this covered up in any drafts?

Unless the 180 is reliable, there is nothing more for B to do about it. 
And there is nothing to do about the 100. But B will eventually need to 
send some sort of final response. (Success or failure.) When that 
happens, A will presumably drop it, without sending an ACK. When B 
doesn't get the ACK it will retransmit the final response. After all the 
retries have been sent B should time out and terminate the dialog.


More information about the discussion mailing list