[c-nsp] DTS traffic shaping & voice queuing

[Djerk Geurts]

http://www.cisco.com/warp/public/105/policevsshape.html

Last part of this page explains a little. Any additional facts are still
welcome...

> -----Original Message-----
> From: cisco-nsp-bounces at puck.nether.net 
> [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Djerk Geurts
> Sent: Tuesday, December 21, 2004 10:47 AM
> To: Cisco NSP
> Subject: RE: [c-nsp] DTS traffic shaping & voice queuing
> 
> 
> Is there any Cisco documentation which details the complete 
> process as all that I can find is either the LLQ (in detail), 
> the policing/shaping or the combination between the two. But 
> nowhere is the adverse effect of policing and/or shaping on 
> the PQ traffic discussed.
> 
> So all I can do is assume that it will work without too much 
> delay. Thanks for the reply but I need to convince ppl based 
> on facts and figured. We are conducting our tests but I'd 
> like to make a well founded statement rather than an "I 
> belive it is so" one...
> 
> Djerk
> 
> > -----Original Message-----
> > From: Rodney Dunn [mailto:rodunn at cisco.com]
> > Sent: Monday, December 20, 2004 4:24 PM
> > To: Djerk Geurts
> > Cc: Cisco NSP
> > Subject: Re: [c-nsp] DTS traffic shaping & voice queuing
> > 
> > 
> > On Mon, Dec 20, 2004 at 09:51:56AM +0100, Djerk Geurts wrote:
> > > Who can tell me how voice is processed when doing DTS (QoS)
> > 
> > Depends to what level you are asking.
> > The most basic is:
> > 
> > shaping creates backpressure to the queueing engine by
> > saying the interface can transmit at X rate.
> > Once the queueing kicks in when the shaper is allowed
> > to send more data the queueing code determines which
> > packets (in what order) are given to the shaper to send.
> > 
> > No congestion, it's FIFO for all traffic.
> > 
> > > 
> > > The principle is to have a hyrarchical policy-map with the parent
> > > shaping to CIR and the child doing the actual QoS queuing and 
> > > bandwidth statements according to the set classes.
> > 
> > Yep.
> > 
> > The purpose is to apply QoS to a Fast-Ethernet
> > > sub-interface where the sub-interface should be rate limited.
> > 
> > That's fine.  It should work on an IOS router.  There are
> > some gotchas where the driver code didn't work just right for 
> > the shaping (ie: ethernet interfaces).  I don't remember the 
> > details of which but I know I've seen it before.  As for a L3 
> > switch like the 65xx I'm not sure about this.  I don't think 
> > it will do shaping.
> > 
> > > 
> > > As far as I know now:
> > > Shape average = Commits to CIR (best as I need to commit to CIR)
> > > Shape peak    = Sends Bc & Be (not good when doing voice? 
> > If Be=0 then the
> > > same as average?)
> > >
> > 
> > It all depends on how the downstream handles the traffic.
> > Most people just do "shape average <CIR>" and leave it as that.
> > 
> >  
> > > - Shaping delays traffic upon congestion as it's queued in
> > the shaping
> > > process. Which is not good for voice traffic.
> > 
> > Not true.  Shaping simply acts as the gateway to the wire on
> > how fast it lets data go out.  You will introduce queueing 
> > delay in the QOS queues but that's what you get when you have 
> > congestion. You put your VOICE in a priority (LLQ) so the 
> > queueing code makes sure those packets get out first so there 
> > is little to no delay in that class.
> > 
> > The other classes will see some small amount of delay but in
> > a BW class that just means that the queueing code will 
> > guarantee that the class gets the configured amount of BW 
> > over time.  It does NOT mean it will go out first.  That's 
> > what LLQ is for.  Send the voice first.
> > 
> > > 
> > > - Policing no queueing happens but packets are just
> > dropped. This is
> > > not good for voice either.
> > 
> > Not a good idea.
> > 
> > > 
> > > Regards,
> > > 
> > > --
> > > Djerk Geurts
> > > 
> > > 
> > > _______________________________________________
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> > 
> 
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