North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: OT? cRTP header compression

  • From: Thomas Kernen
  • Date: Thu Apr 11 15:15:37 2002


Matthew,

Cisco-NAS and Cisco-Voice ml's didn't provide any feedback regarding my
initial question which was cRTP vs CPU usage.
Never seen any info about the fact that cRTP is not CEF switched in 12.2
on AS5300s, OTOH I've not seen any info that does specify which chassis
handles cRTP CEF switched.
>From CCO:
"With Release 12.1, if TCP or RTP header compression is enabled, it
occurs by default in the fast-switched path or the Cisco Express
Forwarding-switched (CEF-switched) path, depending on which switching
method is enabled on the interface. If neither fast-switching nor CEF
switching is enabled, if RTP header compression is enabled, it will
occur in the process-switched path as before"

Cheers
Thomas

----- Original Message -----
From: "Mathew Lodge" <mathew@cplane.com>
To: "Pena, Antonio" <Antonio_Pena@verestar.com>; "'Thomas Kernen'"
<tkernen@deckpoint.ch>; <nanog@merit.edu>
Sent: Thursday, April 11, 2002 1:47 PM
Subject: RE: OT? cRTP header compression


>
> At 08:55 PM 4/10/2002 -0700, Pena, Antonio wrote:
> >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.
>
> 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.
>
> 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.h
tml
> >
>
>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
> >antonio_pena@verestar.com
> >http://www.verestar.com
> >
> >
> >-----Original Message-----
> >From: Thomas Kernen [mailto:tkernen@deckpoint.ch]
> >Sent: Wednesday, April 10, 2002 1:11 PM
> >To: nanog@merit.edu
> >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
>