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CME Redundancy

In the SRND for CME, page 2-1, it was mentioned that

"The single-site model has the following design characteristics:

? Single Cisco Unified CallManager Express (Cisco Unified CME) router or dual Cisco Unified CME

router for redundancy"

I would like to have a setup with two CME routers on the same LAN, the intention is to have redundancy and automatic failover should one of the CME router go down.

1. Please let me know how can I achieved this? Any documents or configuration guide would be great!

2. In addition to the automatic failover, is it possible to have load balancing between the two CME routers?

3. Usually CME is deployed with incoming calls from PSTN. However, my client have the incoming calls from a satellite system and I am in the process of checking what will be the signal type from this satellite system. Have anyone done this kind of implemetation before?

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Re: CME Redundancy

Hi,

Please see the following document on how to configure redundant CME support:

http://cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a008080d461.html#wp1024559

Load balancing is not support, neither necessary because a single route has all the performance needed to support the phones.

Particular attention must be given to how to connect the external lines for redundancy. The document above suggest a method for analog phone lines, other methods are available for digital interfaces.

Note with CME you will not have an easy way to configure very low bit-rate codecs that are often desired on satellite links, however you will be able to use G.729 very easily.

A workaround about this problem, is to have in the router, hairpinned ISDN BRI or PRI interfaces that will allow any type of transcoding to work.

Hope this helps, please rate post if it does!

3 REPLIES
Hall of Fame Super Gold

Re: CME Redundancy

Hi,

Please see the following document on how to configure redundant CME support:

http://cisco.com/en/US/products/sw/voicesw/ps4625/products_configuration_guide_chapter09186a008080d461.html#wp1024559

Load balancing is not support, neither necessary because a single route has all the performance needed to support the phones.

Particular attention must be given to how to connect the external lines for redundancy. The document above suggest a method for analog phone lines, other methods are available for digital interfaces.

Note with CME you will not have an easy way to configure very low bit-rate codecs that are often desired on satellite links, however you will be able to use G.729 very easily.

A workaround about this problem, is to have in the router, hairpinned ISDN BRI or PRI interfaces that will allow any type of transcoding to work.

Hope this helps, please rate post if it does!

New Member

Re: CME Redundancy

Thanks for the information. It really helps me to get started. With reference to your reply, further questions are

The document mentioned the use of splitters for analog FXO lines for redundancy connection.

1. Like to know if Cisco sells such a splitter? If yes, what is the name and part number? If no, would you be able to recommend one?

2. How about digital interfaces?

3. What if the incoming calls are using IP?

For the codec,

1. Am I correct to say it is best to use the G.729 codec?

2. For the workaround, I understand the idea conceptually but am not sure how this is being implemented?

Thanks a million!

Hall of Fame Super Gold

Re: CME Redundancy

Hi,

the pots splitter is nothing, you can buy or build you own anywhere. Just like when you have two telephones on a line.

Digital interfaces are more complicated. The easier is ISDN BRI, because it has a bus and you can connect multiple router to S/T bus.

For T1/ E1 you can either buy a mechanically actuated switch, or again build a splitter, however in this case one interface must be kept shut down all the time. I suggest that in case of problem, someone manually change the cable from an interface to another.

For IP is also very simple, as you configure two destination in the remote router, if the first doesn't work, it would use the second one.

G.729 may not be a good codec for satellite. It must be tested, if packets are delayed or lost, the voice quality goes down dramatically. ILPC would theoretically more suited unfortunately is not easy to use with CME phone, for transcoding you must use the technique I outlined before. It is made configuring all call to go outside via PRI. Same calle come back in the same router via another ISDN port, At this point number are massaged as necessary and the codec of you choice can be applied. A similar process may need to be used on the remote router too.

Now there is one thing that must be said. The routers are very reliable. Especially for customer that never had voip, is better to design for simplicity first and add redundancy later. After all, when they buy a regular PBX or whatever, ther eis zero redundnacy in these products. And these are build much cheaper thatn routers.

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