[cisco-voip] MTP and transcoders with intercluster trunk

[Ryan Ratliff]

Inline.

-Ryan

> On Aug 12, 2011, at 7:19 AM, Damian Turburville wrote:
> 
> Hi,
> Scenario as follows
> 
> CUCM 6.1 placing calls across a WAN link to another CUCM 6.1 but with firewalls in the way. As advised by other members of this fine forum I would need MTP's at either end to provide a fixed IP we can use on the firewalls for NAT.

You can use MTPs or even TRPs (trusted relay point) which would serve essentially the same function in this purpose.  

> We want to use G.729 across the WAN link to conserve bandwidth, I believe that since most IP phones (we use 7911, 7912, 7937, 7942 and 7960's) support G.729 natively that normally if a call is placed from IP phone to IP phone (even across a WAN link?) no transcoder will be required. Is this still the case if MTP's are involved? Or will transcoders be required?

As long as you have IOS MTPs then you can do 729 just fine.  As soon as you mention 729 the software MTPs on CUCM are ruled out.   The CUCM region settings determine that highest bandwidth available for a call which in turn determines the highest quality audio codec that all parties involved in the call support.  When using MTPs be sure to account for them when looking at capabilities.

> Also as a related question, what variant of G.729 does CUCM 6.1 use? In the Region settings it is just down as G.729 but is this a high or medium complexity variant? This may be important to know in order to provision the right type of HW transcoders.

The Region value is really a number.  Since all variants of 729 use the same bandwidth the Region does not account for nor care about variants.   You are correct that it is important to know the variant when provisioning IOS MTPs.  You will be much better off from a voice quality perspective by not allowing the 729b variants anywhere in the network.  You can disable them via Service Parameter in CUCM and not allow them on the MTPs.  Your users will have bad enough audio quality on 729 you may as well not expose them to the joys of VAD while they are at it.    If you had the endpoints to support the newer low-bandwidth codecs like iLBC or iSAC.

There were enhancements to the recent CUCM versions to prefer audio quality in combination with bandwidth and link loss.  You can find the list at http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/admin/8_6_1/ccmsys/a02sycfg.html#wp1155995.


> 
> Many thanks,
> Damian
> _______________________________________________
> cisco-voip mailing list
> cisco-voip at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-voip
> 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://puck.nether.net/pipermail/cisco-voip/attachments/20110812/0b6c03fd/attachment.html>