[cisco-voip] Quick failover and SRST

[Ryan Ratliff]

Agreed, while you can only have three CUCM servers in a CM group the SRST reference is an extra layer of redundancy that allows the phones to have basic functionality in case all CUCM servers are unreachable. 

With respect to the time it takes to failover it is very dependent on phone model (7940/60s will be slower then newer phones) and what the phone is doing.  If the phone is active and thus sending lots of packets to CUCM if the network goes down then the TCP retransmits will lead to the TCP connection getting dropped long before the SCCP keepalives are lost.  

I'm actually writing up a document for the CSC that talks about this in further detail.  I'll be sure to communicate here when it's completed.

-Ryan

On Dec 12, 2010, at 3:51 PM, Go0se wrote:

“most of the reading I have done implies about 40 seconds is required to recognize failure of the primary, and initiate handoff to the subscriber.” – if I am reading correctly, you are talking about failover from the publisher callmanager to the subscriber callmanager.  If this is the case typically it’s much faster than 40 seconds It’s a matter of a few seconds. It depends, however, on what all you have.
 
As a side note, Cisco recommends when you have more than one callmanager that you “home” your phones to the subscriber during normal operations and then allow the phones to failover to the publisher if the subscriber fails. Having the phones run off of the subscriber reduces the workload on publisher resources.
 
“should I keep SRST now that I will have redundant CMs?” – What is the likelihood that any building could lose connectivity to both CMs at the same time? If it is possible then your answer is yes. If you already have SRST it won’t hurt anything to leave it in place.
 
Thanks,
 
Go0se
 
My blog:
http://atc.go0se.com
 
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From: cisco-voip-bounces at puck.nether.net [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of David Zhars
Sent: Sunday, December 12, 2010 9:28 AM
To: cisco-voip at puck.nether.net
Subject: [cisco-voip] Quick failover and SRST
 
We have 7 buildings all connected via fiber.  Each building has a 2801 for SRST and 911 handling.

As an upgrade, we are going to install a redundant CM (version 8.x).  I have one site that needs quick failover, and most of the reading I have done implies about 40 seconds is required to recognize failure of the primary, and initiate handoff to the subscriber.  I know there are some settings to speed this up as well.

My quesiton is, should I keep SRST now that I will have redundant CMs?  Could they somehow assist in that 40 second timeframe, or are they sort of the subscriber when you don't have a redundant CM?  What would I gain by keeping SRST with a redundant CM?  

And I'm just curious, but how does Cisco license the redundant CM?  Same prices and maintenance as a regular CM?

thank you!
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