From: Bob Sinclair (bsin@cox.net)
Date: Sun Dec 21 2003 - 23:19:14 GMT-3
Alec,
That sounds right to me. It is guaranteed a minimum of 384 during
congestion but is shaped to 512.
-Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Pun, Alec CL" <Alec.CL.Pun@pccw.com>
To: "Bob Sinclair" <bsin@cox.net>; "Alec" <clapun@graduate.hku.hk>;
<ccielab@groupstudy.com>
Sent: Sunday, December 21, 2003 9:08 PM
Subject: RE: CAR / Shaping question
> Thanks Bob.
>
> For 3) Can I interpret class cust2 such that it is rate-limited between
384K
> and 512K since the shaping and scheduling refers to the same queue ?
>
> rgds,
> alec
>
> -----Original Message-----
> From: Bob Sinclair [mailto:bsin@cox.net]
> Sent: Monday, December 22, 2003 8:38 AM
> To: Alec; ccielab@groupstudy.com
> Subject: Re: CAR / Shaping question
>
>
> Alec,
>
> For an in-depth discussion of these issues I highly recommend the book
DQOS
> by William Odom (Cisco Press). He has years of experience teaching this
> material, and he explains it well an in depth.
>
> Regarding your point 1, I would say you are correct.
>
> Regarding your point 2, the "shape average" command permits bc+be burst
only
> after a period of quiet has built up a surplus. The "shape peak" command
> allows bc+be in every interval.
>
> Regarding your point 3, the shaping command makes a decision to queue
> out-of-profile packets, whereas the bandwidth command is a scheduling
> process that determines which queue will next be serviced.
>
> Mr. Odom puts it this way:
>
> "the shaper must make the decision bout whether to put a packet into a
> shaping queue, and then the shaper decides when the next packet can be
taken
> from a shaping queue, and then the queuing scheduler decides which packet
> to service next from the shaping queues." page 367.
>
> In your example, I would say that class cust2 traffic is rate-limited,
but
> that traffic is guaranteed a minimum of 384 Kbps in competition with other
> traffic on that interface.
>
> HTH,
>
> -Bob Sinclair
> CCIE #10427, CISSP, MCSE
> www.netmasterclass.net
>
> ----- Original Message -----
> From: "Alec" <clapun@graduate.hku.hk>
> To: <ccielab@groupstudy.com>
> Sent: Sunday, December 21, 2003 12:28 PM
> Subject: CAR / Shaping question
>
>
> > Hi group,
> >
> > 1) The Bc & Be calculation is different between CAR and shaping ??
> > In CAR, setting Be=Bc effectively disables excess burst size whereas in
> > Shaping, Be=Bc will NOT disable Be but will assign a burst size = Bc.
Am
> I
> > correct ?
> > 2) what's the difference between shape [average | peak] ? The command
> > reference doesn't explain clearly.
> > 3) What's the purpose of using both bandwidth and shaping in the
> policy-map
> > simutaneously ? As far as I know, both bandwidth and shaping are talking
> > about egress queueing. Isn't that when we apply shaping to certain BW,
> that
> > BW is already reserved in the egress queue. The following example
seems
> to
> > imply the shaping value always greater than the bandwidth value. Any
> input
> > is welcome!
> >
> > The following example is copied from the configuration guide :
> >
> > Router(config)# policy-map shape-cbwfq
> > Router(config-pmap)# class cust1
> > Router(config-pmap-c)# shape average 384000
> > Router(config-pmap-c)# bandwidth 256
> > Router(config-pmap)# class cust2
> > Router(config-pmap-c)# shape peak 512000
> > Router(config-pmap-c)# bandwidth 384
> > Router(config-pmap-c)# configure terminal
> > Router(config)# interface Serial 3/3
> > Router(config-if)# service out shape-cbwfq
> >
> >
> > thanks
> > alec
> >
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