[cisco-voip] Intercluster trunks and H323 outbound faststart

[Wes Sisk]

Let's take a step back for clarification please.
can you elaborate on what you mean by 'clipping'?
how far apart are your 2 clusters in terms of msec round trip time?
also, do you use low bit rate (LBR) codecs (729, iLBC) over the 
intercluster trunks?

CM's software MTP does not support LBR codecs only G.711.  If you are 
attempting to invoke an MTP and there is no capabilities match CM will 
default to connecting the call anyway but disabling supplementary 
services. This could also lead to additional delay.

In general inbound faststart will not help without the remote peer 
supporting outbound faststart.  If you noted any difference with only 
inbound fast start enabled it is either a fluke or there is something 
else going on in the network that needs clarification.  The only item I 
can think of that would trigger this is some type of SBC or CUBE 
anchoring calls between 2 clusters.  Do you have any such device between 
the clusters?

with 150msec RTT to remote sites you may want to review this previous 
conversation on cisco-voip:
http://www.gossamer-threads.com/lists/cisco/voip/114051


/Wes


On Wednesday, September 16, 2009 3:07:45 AM, Blenkarn, Gary 
<Gary.Blenkarn at fmglobal.com> wrote:
>
> Hi
>
>  
>
> We have 2 CCM 6.1 clusters.  They are connected via a non gatekeeper 
> controlled trunk.  In terms of latency some of the phones are one way 
> 150ms.  We have been getting instances of voice clipping.  Therefore 
> as the SRND states we have implemented Fast start.  Inbound fast start 
> is configured both ends and makes a small difference.  Though outbound 
> Fast start makes the voice clipping worse?  The outbound fast start 
> requires the use of an MTP.  It is currently using the software MTP of 
> the Call Managers in each cluster. 
>
>  
>
> Can anybody provide any information how best practice wise outbound 
> fast start should be setup please?  Should we be using a hardware MTP 
> for instance on each Cluster?
>
>  
>
> Thank you
>
>  
>
> *Gary Blenkarn*
>
> Senior Data Networking Analyst
>
>  
>
>
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