[cisco-voip] Intercluster trunks and H323 outbound faststart

[Blenkarn, Gary]

Hi Wes

Thank you very much for your reply.  Answers to your questions:


*         Clipping - losing the first 2 seconds from the receiver like their hello.

*         2 Clusters are 200ms apart.

*         LBR rate codec G729 is used across trunk.

Therefore I am assuming that I need to do a hardware MTP on the gateways that my CCM's cluster is at and add it the MRGL that is on the trunks each side.  A question from your article, are there any negatives in using the 'Bundle Outbound Messages Timer' parameter?

Regards

Gary

From: Wes Sisk [mailto:wsisk at cisco.com]
Sent: 16 September 2009 14:35
To: Blenkarn, Gary
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] Intercluster trunks and H323 outbound faststart

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><mailto: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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