[cisco-voip] Speed up skinny?

[Keith Klevenski]

Wes,

Thanks for the reply.  Running CM 7.02.  I'm quite sure its RTT as we're talking 600-800ms with 100 byte packets although the link speeds are 128/256kbps so we're not breaking any speed records here.  ;)  If I change the SCCP gateway to H323 and configure the usual dial-peers the delay is gone.  Convert back to SCCP and it's back.

I don't see any way around it based on the round trip requirement you mentioned.  Thanks for the confirmation.

-Keith

From: Wes Sisk [mailto:wsisk at cisco.com]
Sent: Monday, August 03, 2009 3:39 PM
To: Keith Klevenski
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] Speed up skinny?

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><mailto: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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