[cisco-voip] WAN failure in call manager

Karen Cheng kaz.cheng at gmail.com
Thu Dec 10 17:32:16 EST 2009


Hi Lelio,

I don't believe that part about the phone triggering the SRST function is
true. From memory I believe the SRST router is the one that detects the WAN
failure in which after a certain amount of time (dependent on how many
servers in the CM cluster) it reconfigures itself to be the call agent
instead. It then also continues to monitor connectivity to the CM cluster
and once backup will again wait (dependent on how it is configured, wait
until no calls are active etc) before handing the call agent functions back
to the CM cluster.

I may be wrong though.

Karen

On Fri, Dec 11, 2009 at 8:21 AM, Lelio Fulgenzi <lelio at uoguelph.ca> wrote:

> Correct, during the SRST mode, the CUCM cluster is not controlling
> anything. The phones register to the SRST router using a "simplified"
> configuration they store in memory. The tell the router what DNs it is
> supposed to have, and the router configures the appropriate dial-peers. Then
> using the dynamic dial peers it can call other phones, or using the static
> dial-peers (ones you program) a phone can call off-net using PSTN.
>
> Interesting thing is this, SRST is "always on" waiting for a device to
> register to it. The device is what controls when it talks to the SRST router
> or not. That's how you can test registering devices to the router when the
> WAN really isn't down.
>
> It also means that if there is some way or scenario that your phones may
> not be able to talk to CUCM, but your router can, you will have phones that
> can call each other, but not out the PSTN because the gateways are still
> registered to CUCM. That is, of course, if you have MGCP gateways. If you
> have H323 gateways, I think it's a moot point.
>
> Of course, I could be wrong on one or two points, and would be happy to
> learn something new. ;)
>
>
>
> ---
> Lelio Fulgenzi, B.A.
> Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1
> (519) 824-4120 x56354 (519) 767-1060 FAX (JNHN)
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> "Bad grammar makes me [sic]" - Tshirt
>
>
>
> ----- Original Message -----
> From: "anand" <anand.eee at gmail.com>
> To: cisco-voip at puck.nether.net
> Sent: Thursday, December 10, 2009 5:15:00 PM GMT -05:00 US/Canada Eastern
> Subject: Re: [cisco-voip] WAN failure in call manager
>
> Hi,
>
> I have been breaking my head to understand the exact functions of SRST.
> During the WAN failure, SRST router takes PSTN path.My question is during
> this time will the call manager controls the call or Call Manager is
> completely out of operation(I mean it does not take any part in the call
> control on the PSTN path).
>
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