[cisco-voip] WAN failure in call manager

[Lelio Fulgenzi]

The phone doesn't trigger the SRST function, it just controls it's own behaviour, i.e. when it tries to register to the SRST router. In order for this to work, SRST has to always be up. 

Again, I could be wrong, but I've tested this in the past. The remote router is fully connected, WAN is up and everything, MGCP gateways are registered to CUCM. Then, using an ACL, I block a few phones here at HQ from talking to the CUCM cluster. Within seconds they register to the remote router in SRST mode. 

Now, does the remote router automatically go into SRST mode when the first registering device talks to it? Perhaps, but I don't see any log entries that would suggest that. 

Some supporting(?) details: 



router#show call-manager-fallback 
CONFIG (Version=4.0(2)) 
===================== 
<snip> 
max-dn 500 dual-line 
</snip> 

kc-vgw#show dial-peer voice summary 
AD PRE PASS OUT 
TAG TYPE MIN OPER PREFIX DEST-PATTERN FER THRU SESS-TARGET STAT PORT 
<snip> 
20001 pots up down 5 50/0/1 
20002 pots up down 5 50/0/2 
20003 pots up down 5 50/0/3 
. 
. 
. 
20498 pots up down 5 50/0/498 
20499 pots up down 5 50/0/499 
20500 pots up down 5 50/0/500 
</snip> 


The router has the dynamic dial-peers (no DEST-PATTERN) ready to go, all 500 of them, ready to assign to phones as they register. 


--- 
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: "Karen Cheng" <kaz.cheng at gmail.com> 
To: "Lelio Fulgenzi" <lelio at uoguelph.ca> 
Cc: "anand" <anand.eee at gmail.com>, cisco-voip at puck.nether.net 
Sent: Thursday, December 10, 2009 5:32:16 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [cisco-voip] WAN failure in call manager 

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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