Phones registered to the SRST gateway but the gateway didnt go to the SRST mode

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Feb 11th, 2010
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When the Wan link flapped many phones registered with the srst router,

but the sh ccm command on the gateway shows that the gateway didnt go into the srst mode.

Any idea why this happened?

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Tommer Catlin Thu, 02/11/2010 - 07:55
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can post a copy of your gateway configuration?

Also some other items to check:

SRST is configured in CUCM for the router IP address.

SRST profile this router is in the Device Pool

The Device pool is assigned to the IP phones at that site.

Everything needs to be reset, reloaded to get this load information. (Device pool, phones rebooted)

On the router, there are statements at the bottom that relate to SRST operations (number of e-phones)  There is also a statement in the beginning of the router programming to enable this.

Can you see the phones registered on the SRST router?

When a call comes in, where does it go to?

munawar.zeeshan Thu, 02/11/2010 - 08:43
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Could you check #show call-manager-fallback.

I hope syntax is correct.

Rgds, Munawar

dominthomas Thu, 02/11/2010 - 09:44
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Thanks guys...

I have checked the srst configuration and its correct.

"SRST is configured in CUCM for the router IP address.

SRST profile this router is in the Device Pool

The Device pool is assigned to the IP phones at that site." All configurations correct...

What actually I am confused is why the gateway didnt fall into srst mode..

Both the phones and gateway communicate with the callmanager through the same wan link.

Is there a time delay(say 1 minute) for the gateway to fall into SRST mode once it come to know that CCM is unreachable?

The WAN link flap was for less than a 2 minutes and once the WAN link came up the phones registered back to the callmanager.


jleehawkins Thu, 02/11/2010 - 11:08
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Is it safe to assume your gateway is an MGCP gateway?

Can you run this command and post the output?

show run | section mgcp|ccm|Serial|controller

Even though the phones and gateway connect with the CUCM over the same wan link both of them use different protocols to communicate with.  The phone I assume are using SCCP and the gateway I assume is MGCP.  When the phones lose their SCCP TCP connection with the CUCM the phone will register with its configured SRST device.  The MGCP gateway must be configured to fall-back to H.323 when the ISDN Q.931 backhaul is broken.

Review this webpage:

Based on my assumptions of your setup I am guessing you may be missing this command:

ccm-manager fallback-mgcp


Tommer Catlin Thu, 02/11/2010 - 11:26
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Also, if your WAN link is flapping, SRST is not going to work.  The WAN link going up and down every two minutes will cause the phones and gateway to keep bouncing.  It takes time for SRST to get settled in.  (Depending on the number phones, router, WAN link, etc)  Id say if the link is down for 2 minutes, then comes backup, SRST is not going to work.  IF the link is down for 5 or more minutes, SRST will work.  But if the link is up/down every 2 minutes.. it does not work how you think it would.  Patience 


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