[cisco-voip] Speed up skinny?

[Wes Sisk]

What CM version are you on?

Only recent optimization available is Advanced CM service parameter 
"Bundle Outbound SCCP Messages Timer" to enable bundling of SCCP 
messages. More messages per packet = fewer ACKs = fewer round trips.  
Much further back there was an effort to streamline the number of 
messages required to setup SCCP call.

SCCP capabilities are exchanged at device registration so it does not 
suffer the same issue as h.323 where capabilities must exchange during 
every call setup.  There is no MSD equivalent.  SCCP overall is a much 
lighter protocol at the point of call signaling.  The only round trip 
requirement in SCCP is OpenReceiveChannel/OpenReceiveChannelAck with 
remote IP:Port.  StartMediaTransmission is required and cannot be sent 
until IP:Port is received from far end device.  Unfortunately this 
exchange is required with no way to bypass this round trip for SCCP.

One area we commonly see issues is shared lines at remote sites.  This 
is covered in SRND:
http://www.cisco.com/en/US/docs/voice_ip_comm/cucm/srnd/6x/netstruc.html#wp1045582

Is it really RTT or is it possibly link speed that is causing the issue?

/Wes



On Monday, August 03, 2009 4:11:50 PM , Keith Klevenski 
<KKlevenski at cstcorp.net> wrote:
>
> Is there any mechanism to 'speed up' skinny call setup like faststart 
> in h323?  Satellite provider migrated to skinny gateways (SCCP 
> controlled FXS ports) from h323 gateways.  All analog phones.  It was 
> noticed that inbound PSTN calls (through h323 gateway) were losing the 
> first second or so of the call when the called party picked up.  This 
> made sense to me as the skinny gateway must tell CM the phone has gone 
> offhook then CM tells the gateway to tell the phone to stop ringing 
> and send media stream to the PSTN gateway.  This is over a 600-700ms 
> satellite link so the delay would be reasonable.  The rest of the call 
> is perfect.  If the same skinny gateway is changed to h323 the delay 
> is not present since h323 gets the IP address where to send the stream 
> during call setup if I'm not mistaken so the delay isn't present, but 
> neither are the features of skinny controlled fxs ports...
>
>  
>
> To me this is all reasonable and makes perfect sense.  The question 
> the customer has is if there is any mechanism to speed up the skinny 
> signaling.  I wouldn't think so based on the master/slave nature of 
> the skinny protocol.  I've configured voice call send-alert, voice rtp 
> send-recv, progress_ind setup enable 3, and all that, but nothing 
> helps and I can understand why.
>
>  
>
> Can anyone confirm if there is a way to speed up skinny call setup 
> over high latency links?  Running CM 7.0, SCCP controlled FXS.
>
>  
>
> Thanks!
>
> -Keith
>
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