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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical RE: OT? cRTP header compression
At 08:55 PM 4/10/2002 -0700, Pena, Antonio wrote: As well as increasing sample size (thereby increasing the payload:header ratio), the other thing to try is turning on voice activity detection (VAD, AKA silence suppression). For human conversation, this typically reduces packet rates by around 60%, enabling you to squeeze more conversations onto the link. It also has the side effect of reducing CPU utilization per call on your Cisco voice gateways. Note that turning on VAD does decrease the perceived voice quality a little, so whether it is worth it depends on where you want to make the trade-off between cost and voice quality.I had some kind of experience doing cRTP over Cisco routers, we use Cisco 7204 & 7206 Routers on the IP Gateways and Cisco's 3600 and 5300 as VoIP gateways, as well we had a small setup using a Cisco 2611 router on the termination router. Also, cRTP is not CEF switched on the 5300 in 12.2, AFAIK. It was on 26xx/36xx, but 5300 architecture (and hence switching code) is different. That may have changed since I last looked 6 months ago -- best bet is to ask on the Cisco-NAS mailing list at http://www.cisco.com/warp/public/471/cisco-nas.html Cheers, Mathew The trick is change the VoIP payload size of each packet to reduce the packets per second in a half improving the performance over the routers, also we are using as Cisco recommends TCP & RTP headers compression over the circuits using only MLPPP encapsulation. Also please note that using cRTP and Compression you have increased the switching delay over the circuit and for that reason you may need also to have more processing power of the router. Below you can see a Cisco site where you can check the recommendations for this setup and also based on that information I created a Bandwidth calculator on an excel sheet, if you want it, just drop me an email, I will send it you. http://www.cisco.com/warp/public/788/voice-qos/voip-mlppp.html http://www.cisco.com/warp/public/788/pkt-voice-general/bwidth_consume.html http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos _c/fqcprt6/qcfcrtp.htm http://www.cisco.com/warp/public/105/compression-qos.html Bye Antonio J. Pena Manager, Network Engineering ( /_ _ _ __/_ _ |_/(-/ (-_) /(// Verestar, inc. 1901 Main street Santa Monica, CA, 90405 Phone(310)382-3300 Direct(310)382-3409 [email protected] http://www.verestar.com -----Original Message----- From: Thomas Kernen [mailto:[email protected]] Sent: Wednesday, April 10, 2002 1:11 PM To: [email protected] Subject: OT? cRTP header compression I'm looking for real world experience related to deploying cRTP header compression on Cisco routers related to VoIP flows. We are trying to evalute what type of hardware (ie: CPU power since cRTP is CEF switched since 12.2x IIRC) is required to handle 96/192/384 VoIP calls over a single circuit (HDLC/PPP/FR). This is related to specific overseas circuits where the cost of the circuit is still very expensive vs the cost for the extra hardware to handle the header compression. I'm disregarding all QoS info at this stage. Cheers Thomas
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