From: Joe Chang (changjoe@earthlink.net)
Date: Fri Feb 14 2003 - 17:24:48 GMT-3
From the CD:
"When a packet is to be sent out an interface, the priority queues on that
interface are scanned for packets in descending order of priority. The high
priority queue is scanned first, then the medium priority queue, and so on.
The packet at the head of the highest queue is chosen for transmission. This
procedure is repeated every time a packet is to be sent. "
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/qos_
c//qcprt2/qcdconmg.htm#1001407
----- Original Message -----
From: "OhioHondo" <ohiohondo@columbus.rr.com>
To: "Brian McGahan" <brian@cyscoexpert.com>; "'P729'" <p729@cox.net>;
<ccielab@groupstudy.com>
Sent: Friday, February 14, 2003 4:35 PM
Subject: RE: QoS need confirm-- a bit long
> I have a question on Priority Queuing.
>
> When the highest priority queue is emptied, the next highest queue is
> serviced AND the highest priority queue is not checked again until that
> queue is emptied. Some thing like:
>
> Empty pri-1 (highest queue)
> Check pri-2 (next highest queue)
> Empty pri-2
>
> Check pri-1 (if there is data, empty pri-1)
> Check pri-2 (if there is data, empty pri-2 and go back to pri-1)
> Check pri-3
>
> If it works this way it should be totally unacceptable for real time
data --
> at least on E1 circuits and below.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Brian McGahan
> Sent: Friday, February 14, 2003 1:54 PM
> To: 'P729'; ccielab@groupstudy.com
> Subject: RE: QoS need confirm-- a bit long
>
>
> My impression of the LLQ was that inside this PQ, it is FIFO. I
> haven't seen any documents that support or deny this though. I was
> actually having a discussion about this yesterday with a student, and
> they were asking the same question. Maybe it's time to open a TAC case
> on it ;)
>
> 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
> > P729
> > Sent: Friday, February 14, 2003 12:20 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
This archive was generated by hypermail 2.1.4 : Sat Mar 01 2003 - 11:06:23 GMT-3