From: P729 (p729@cox.net)
Date: Fri Feb 14 2003 - 15:20:11 GMT-3
"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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