[cisco-voip] Intercluster trunks and H323 outbound faststart

[Wes Sisk]

Gary,

Yes. need hardware mtp in the MRGL.  I do not recall offhand if it needs 
to be in the ICT MRGL or in the device's MRGL.  My first guess would be 
the device's MRGL.  A quick test will verify.

For your MTP's remember that round trip to them can add additional delay 
in signaling.  Just something to keep in mind when planning the design 
and considering impacts.

The only downside to bundling outbound messages is potential additional 
delay.  ccm.exe must hold up SCCP messages in order to bundle them into 
a single outbound message.  Holding the messages will introduce slight 
delay.  the goal is to have the hold be less time than the latency cased 
by TCP RTT.


Have you reviewed CM traces or packet captures for a specific instance 
of delay to confirm the specific problem?  Just to make sure we're 
chasing the correct problem.

/wes

On Wednesday, September 16, 2009 10:23:01 AM, Blenkarn, Gary 
<Gary.Blenkarn at fmglobal.com> wrote:
>
> 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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