[cisco-voip] WAN failure in call manager

Fri Dec 11 09:21:28 EST 2009

neat suggestion. i just read up on eem. pretty powerful stuff. 

on the corollary, you could also monitor when a phone registered before your MGCP gateways and then force the MGCP gateways to register as well using similar ACLs. 

i likes it! 

--- 
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: "Wes Sisk" <wsisk at cisco.com> 
To: "Lelio Fulgenzi" <lelio at uoguelph.ca> 
Cc: cisco-voip at puck.nether.net, "anand" <anand.eee at gmail.com>, "Karen Cheng" <kaz.cheng at gmail.com> 
Sent: Friday, December 11, 2009 9:13:12 AM GMT -05:00 US/Canada Eastern 
Subject: Re: [cisco-voip] WAN failure in call manager 

to be creative one could write an EEM script to monitor for gateway losing connectivity to mgcp call agent and then implement an ACL blocking all ip connectivity from the phone subnet toward the CM servers. that would effectively have the router control the phone rehome as well. 

/wes 

On Thursday, December 10, 2009 5:54:30 PM, Lelio Fulgenzi <lelio at uoguelph.ca> wrote: 

Good point Wes. That's what I was trying to say with respect to the last paragraph, but reading it again, I didn't make that point clear. 

Yes, the gateway does maintain connectivity for it's local ports (PRI, FXS, etc) and when it looses connectivity it triggers it's local ports to register via SRST to itself (or another SRST router). 

However, regardless of that, even if a router can still talk to the CUCM cluster, it will accept SRST registrations from phones. (see last message sent). 

But I love how you manage to start with "it depends.... " ;) 

--- 
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: "Wes Sisk" <wsisk at cisco.com> 
To: "Karen Cheng" <kaz.cheng at gmail.com> 
Cc: "Lelio Fulgenzi" <lelio at uoguelph.ca> , cisco-voip at puck.nether.net , "anand" <anand.eee at gmail.com> 
Sent: Thursday, December 10, 2009 5:45:03 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [cisco-voip] WAN failure in call manager 

it depends. 

For MGCP functionality the gateway is monitoring CM. When failure is detected router follows the configured fallback apllication, usually h.323 
http://www.cisco.com/en/US/docs/voice_ip_comm/cusrst/admin/srst/configuration/guide/srs_wlan.html#wp1351962 

That is only for the gateway though. 

Phones monitor CM connecvity. When phone loses connectivity to CM they attempt to register with SRST router. When they register they tell the router about their configuration. 

To that end it is both phone initiated and gateway initiated. The gateway does not control all logic, nor does the phone control all logic. 

/Wes 

On Thursday, December 10, 2009 5:32:16 PM, Karen Cheng <kaz.cheng at gmail.com> wrote: 

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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