From: Chris Home (clarson52@comcast.net)
Date: Fri Feb 14 2003 - 16:22:21 GMT-3
Here is an excellent link on QoS and even provides recommendations for DSCP
values for different apps. Video is recommended with a lower DSCP value then
voice. The link also discusses the relative priority model of classifying
traffic. Very good read.
http://www.cisco.com/application/pdf/en/us/guest/netsol/ns17/c649/ccmigratio
n_09186a00800d67ed.pdf
----- Original Message -----
From: "P729" <p729@cox.net>
To: <ccielab@groupstudy.com>
Sent: Friday, February 14, 2003 1:20 PM
Subject: Re: QoS need confirm-- a bit long
> "A strict priority queue (PQ) allows delay-sensitive data such as voice to
> be de-queued and sent before packets in other queues are de-queued."
> "Bandwidth command: Provides low latency: No"
>
> A dilemma I'm currently wrestling with is "what if you have two forms of
> delay-sensitive traffic, say voice and streaming video?" Both need to be
> de-queued ahead of other non-priority traffic, yet one can't "starve" the
> other... The delay tolerance of the video stream is not known, but even if
> it were (it is likely to be more tolerant due to startup synchronization
and
> buffering, but with larger packet sizes), how could one "interleave" the
two
> types of priority traffic to stay within their respective jitter budgets?
> Are there ways to tune WRR/CBWFQ/etc. to provide more than one "pseudo"
> low-latency queue?
>
> Thoughts/experience anyone?
>
> Regards,
>
> Mas Kato
> https://ecardfile.com/id/mkato
>
> ----- Original Message -----
> From: "Brian McGahan" <brian@cyscoexpert.com>
> To: "'Pang Gery'" <pang_gery@yahoo.com.hk>; <ccielab@groupstudy.com>
> Sent: Friday, February 14, 2003 7:57 AM
> Subject: RE: QoS need confirm-- a bit long
>
>
> Gery,
>
> The bandwidth and the priority statement are different.
>
> The bandwidth statement is used to guarantee bandwidth for a
> certain traffic class. This is a *minimum* guarantee for this class of
> traffic. During periods of congestion, traffic in this class may still
> burst above the configured rate, however it is always guaranteed the
> minimum that is specified.
>
> The priority statement is used to guarantee low latency for
> traffic. The priority statement is a *maximum* guarantee for this class
> of traffic. All traffic that conforms to the configured rate is
> guaranteed low latency (always dequeued first), however during periods
> of congestion, all traffic over the configured rate is dropped. During
> periods of non-congestion, excess traffic may be transmitted, however it
> is not guaranteed low latency.
>
> For more information see the following article, "Comparing the bandwidth
> and priority Commands of a QoS Service Policy"
>
> http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a
> 0080103eae.shtml
>
>
> HTH
>
> Brian McGahan, CCIE #8593
> Director of Design and Implementation
> brian@cyscoexpert.com
>
> CyscoExpert Corporation
> Internetwork Consulting & Training
> Toll Free: 866-CyscoXP
> Outside US: 847.674.3392
> Fax: 847.674.2625
>
>
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Pang Gery
> > Sent: Thursday, February 13, 2003 6:43 AM
> > To: ccielab@groupstudy.com
> > Subject: QoS need confirm-- a bit long
> >
> > Hi Group,
> >
> > I have just reviewed the QoS part and make the following brief notes.
> My
> > focus is on whether the feature take effect with and without
> congestioin.
> > Could you please help to review and correct me if my concept is wrong?
> >
> > 1.1 Policy-based routing and QoS via BGP
> >
> > They just classify packets, will not drop packet, and take effect
> with
> > and w/o congestion.
> >
> > 1.2 CAR
> >
> > It can classify and drop packet, and take effect with and w/o
> > congestion.
> >
> > 2.1 Priority Queue / Custom Queue Ip RTP / FR RTP / CBWFQ / LLQ
> >
> > Take effect only when congestion.
> >
> > 2.2 Question: is the bandwidth command used in policy-map of CBWFQ
> same
> > as the priority command used in LLQ?
> >
> > My feeling is the bandwidth is used for data and priority is
> used
> > for real-time traffic like voice. Also, bandwidth sets the minimum
> amount
> > allocated for 'that traffic' at congestion, when there is no
> congestion,
> > 'that traffic' can use more available bandwidth.
> >
> > However, the priority command guarantee the maximum resources for
> > specific traffic whether there is congestion or not.
> >
> > 3. GTS / FRTS
> >
> > They are not congestion management and will do the shapping with or
> > without congestion.
> >
> > Am I right?
> >
> > Thank you very much.
> >
> > Gery Pang
> >
> >
> >
> > Yahoo! =l)G/d(%+H=c .I$U<i,y$h&V
> > http://voicemail.yahoo.com.hk
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