round trip time between CUCM servers

[Turbo727]

Hi,

I need to put cucm subscriber at a different location to add redundancy to the phone system. I understand Cisco recommends RTT no more than 80ms. Is the 80ms average rtt or max rtt. what if it goes slightly over say 90ms?

thanks.                  

[Gajanan Pande]

It is just a recommended value of max 80ms RTT. If the latency goes beyond it, will not result into immediate break down of everything but thats the time when you will start seeing issues. Therefore, it is a BU recommended value after careful testing/consideration to ensure smooth functioning in CoW deployment.

GP.

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[Chris Deren]

I don't think it is recommended value, but rather maximum value supported. So, sure the system may not have issues when the latency is over 80 ms,but if you call TAC they may refuse to work on it until latency is resolved. The actual recommended latency is 40 ms as if you go beyond 40 ms up to 80 ms the bandwidth requirements increase and a formula is available in SRND.

HTH,

Chris

[acampbell]

Hi,

I am with Chris on this (+5 C)

From the CUCM 8 SRND

http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/8x/models.html#wp1044021

•Delay

The maximum one-way delay between any two Unified CM servers should not exceed 40 msec, or 80 msec round-trip time. Measuring the delay is covered in Delay Testing. Propagation delay between two sites introduces 6 microseconds per kilometer without any other network delays being considered. This equates to a theoretical maximum distance of approximately 3000 km for 20 ms delay or approximately 1860 miles. These distances are provided only as relative guidelines and in reality will be shorter due to other delay incurred within the network.

Regards,
Alex.
Please rate useful posts.

[will.alvord]

You may run into quirky phone re-registration issues or gateways depending on protocol.  There are a couple of sccp phone keepalive settings you can tweak in the callmanager service params, but you might be okay.  If you're just looking to add redundancy, maybe SRST on the remote gateway (assuming that's your deployment model) would be a better option.  Just my 2 cents.