From: Scott Morris (swm@emanon.com)
Date: Fri Feb 14 2003 - 15:59:00 GMT-3
You only have ONE low latency queue on the network. So if you allocate
more than one class into this queue, the capacity becomes additive, but
the LLQ is served in a FIFO fashion. So there wouldn't necessarily be
starvation of one over the other, other than the speed at which packets
come in.
Scott
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
P729
Sent: Friday, February 14, 2003 1:20 PM
To: ccielab@groupstudy.com
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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