[cisco-voip] SIP session timer in IOS gateway

Fri Sep 23 16:54:53 EDT 2016

Hmm, good idea. But oh man, what a hack that would be. I might play around with this on my desk but not sure I’d feel comfortable with it in production. I’ll have to ponder if there could be weird edge cases when the timers get restarted by hold/resume, caller ID updates, etc.

At the rate I’m going, eventually I’ll have so much SIP header hacking that I might as well have just written my own SIP stack! Some of the SIP interop baloney I’m encountering makes FXO disconnect signaling look like a rock-solid worldwide standard in comparison! And this is with SIP on only one side of my gateways. I guess the fun is really going to start when we replace the PRIs with SIP trunks. Arrrrrrrrrrrgggggh.

-mn

From: bmeade90 at gmail.com [mailto:bmeade90 at gmail.com] On Behalf Of Brian Meade
Sent: September-23-16 2:38 PM
To: Norton, Mike <mikenorton at pwsd76.ab.ca>
Cc: Daniel Pagan <dpagan at fidelus.com>; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] SIP session timer in IOS gateway

Maybe an outbound sip-profile to modify the Session-Expires header to advertise to the other side a smaller SE value while CUBE still thinks it has 1800 seconds to wait?

I don't think the CUBE would change it's internal timer based on adjusting the SIP header via sip-profiles.

On Fri, Sep 23, 2016 at 4:30 PM, Norton, Mike <mikenorton at pwsd76.ab.ca<mailto:mikenorton at pwsd76.ab.ca>> wrote:
No that’s not the problem. The length of the SE timer isn’t what I’m talking about.

(BTW it is possible to adjust the SE. They added that as an additional parameter to the “min-se” command in 15.something.)

In my case I’m using 1800 and that is getting negotiated successfully. If I use something else, that also gets negotiated successfully. Cranking up the min-se causes the proper 422 response and second INVITE attempt, etc. Everything is occurring exactly as the RFC says it should. But the RFC is too vague!

For example, with SE=1800, the IOS gateway sends the BYE “slightly before” 1800 seconds, around 1665 seconds - which is perfectly valid according to the RFC. The other side is doing the refreshes. It does the refresh “before” 1800 seconds, around 1688 seconds - which is perfectly valid according to the RFC (halfway, i.e. 900, is recommended but not required; the only requirement is “before” 1800).

My problem is that IOS’s “slightly before” occurs around 1665 seconds and the other side’s “before” occurs around 1688 seconds. Neither side is in the wrong but the RFC has a stupid hole here. I need IOS to wait until closer to 1800.

-mn

From: Daniel Pagan [mailto:dpagan at fidelus.com<mailto:dpagan at fidelus.com>]
Sent: September-23-16 2:23 PM
To: Daniel Pagan <dpagan at fidelus.com<mailto:dpagan at fidelus.com>>; Norton, Mike <mikenorton at pwsd76.ab.ca<mailto:mikenorton at pwsd76.ab.ca>>; cisco-voip at puck.nether.net<mailto:cisco-voip at puck.nether.net>
Subject: RE: SIP session timer in IOS gateway

I should be more specific… the min-SE specifies the minimum value the UAS is willing to accept from the Session-Expires header sent by the UAC. If your INVITE has an SE if 1800, and the incoming dial-peer has a min-SE of 3600, then CUBE will reply back to the UAC with a 422 final response - this 422 will contain its own min-SE header with value of 3600. The UAC should ACK the 422 and *should* follow-up with another INVITE where the Session-Expires timer value is 3600. This is one way to force CUBE to manipulate the incoming SE. I felt my previous explanation was missing some information and might have been a bit too vague.

“If the response to a session refresh request is a 422 (Session Interval Too Small) response message, then the UAC MAY retry the request.”

CUCM, if it’s the UAC, will retry the INVITE. I can’t speak to other call-agents though. But I still suggest, if possible, to address the main problem of your session expiration.

Hope this helps.

- Dan

From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Daniel Pagan
Sent: Friday, September 23, 2016 4:12 PM
To: Norton, Mike <mikenorton at pwsd76.ab.ca<mailto:mikenorton at pwsd76.ab.ca>>; cisco-voip at puck.nether.net<mailto:cisco-voip at puck.nether.net>
Subject: Re: [cisco-voip] SIP session timer in IOS gateway

Adjusting the SE on standard CUBE is not possible from what I’ve experienced and tested. One way around it though is to set your Min-SE timer on the incoming dial-peer on CUBE. The UAC sending the INVITE will receive a 422 response back, from CUBE, and will include an updated min-se timer. The new min-SE value in the 422 will then be copied, by the UAC, into the Session-Expires header within a second INVITE. The question I feel I should ask though… is why try manipulating the SE/minSE timers to get around a failed session refresh instead of addressing the session refresh itself? Of course this is only masking another problem.

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From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Norton, Mike
Sent: Friday, September 23, 2016 4:01 PM
To: cisco-voip at puck.nether.net<mailto:cisco-voip at puck.nether.net>
Subject: [cisco-voip] SIP session timer in IOS gateway

I’d like to adjust IOS’s behavior around the SIP session-expires timer. Wondering if anybody knows if the command I need exists...

According to RFC 4028:

“If the side not performing refreshes does not receive a session refresh request before the session expiration, it SHOULD send a BYE to terminate the session, slightly before the session expiration.”

My problem stems from the fact that “slightly before” is left open to the imagination. The RFC “recommends” not more than 32 seconds but does not have any specific “requirement.” The default behaviour of IOS seems to use a longer value. I.e., it sends the BYE a little too prematurely for my situation. I need IOS to let the timer get closer to expiring before it issues the BYE.

I know it’s a long-shot, but someone please tell me there is a command for adjusting this! Not finding anything in the docs. Hoping to avoid having to disable the session timer or crank it up to 11. I love SIP interop, it’s so much fun! :-(

-mn

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