From: beda jain (bpjain@xxxxxxxxx)
Date: Tue Aug 13 2002 - 14:54:36 GMT-3
Hi,
I have question on Be. some doc says Be= AR - CIR, some docs say Be= (AR -
CIR)/8.
where Tc=125ms. which one is correct,
Thanks,
Beda
At 09:36 AM 8/13/2002 -0700, ccie candidate wrote:
> Hi ;
>i would like to contribute in this topic .
>
>i have spent great time in the past trying to understand this FRTS , and
>as usual , Cisco never puts full info about one subject in one place or
>one document , you have to dig many places ..print lots of docs .....anyway .
>
>what you have said is nearly right , but let me add some more to it , i
>might be wrong too ...so you can correct me .
>
>Mincir is the amount you pay for , the only guranteed thing here proviced
>by the Service provided
>it is also the vlaue where the traffic throtled down when you face any
>congestion in your network .
>
>Cir is the normal or average rate at which you transmit you data when the
>network is not congested .
>
>now to Bc and Be and Tc .
>
>Tc is the time interval , it takes the value from 10Msec to 125 Msec so
>you can say the following
>Tc =Bc /Cir if <125 Msec
>Tc = 125 msec if Bc/Cir > 125 !!!
>Tc recommended to be 10 msec in case of voice .
>
>so Tc cannot go for more than 125 msec
>
>Bc is the amount of bits which you can send under normal conditions of the
>network ( it is like the Mtu ).
>
>Be is the amount you can send over the Bc when the network is not
>congested ,however this amount of Data will be DE and can be droped first
>in case of congestion .
>
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>--
>
>On Mon, 12 Aug 2002 22:30:38
> Frank B wrote:
> >Hey folks...sorry about the re-hash but after receiving my last post I
> >reread it and realized a couple of SNAFUs within.
> >
> >My statement: "Bc is commonly set to 1/8 of the CIR" is not exactly
> >correct. CIR is a rate of bits per second, Bc is in bits making Tc just
> >a time period in seconds (basic algebra-the bits canx each other out and
> >there's only seconds remaining...right?) well, you get it.
> >
> >My 2nd foul-up: I found that Be is set to zero bits by default (not
> >sure what I was thinking)...making Bc the max you can transmit in a
> >given time interval by default. I should think things through before I
> >transmit.
> >
> >Guess I don't get partial credit huh? Later, Frank
> >
> >
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> >Frank B
> >Sent: Monday, August 12, 2002 9:38 PM
> >To: 'Mark Vann'; ccielab@groupstudy.com
> >Cc: 'Andri Bersvendsen'
> >Subject: RE: FRTS
> >
> >
> >Mark,
> > The way I attempt to keep it straight in my warped mind is that
> >what you're paying the carrier for is the "minimum" you ever want to
> >transmit at--else you're being ripped off ;-> So, the rate they give
> >you (whether they call CIR or whatever) should be configured on a Cisco
> >router as equal the minCIR. The CIR (in Cisco-eese) is the rate you
> >want to transmit at under uncongested conditions--usually set to the
> >access rate (aka port speed) and of course this can't possibly be faster
> >than the access rate of the interface.
> >
> >Tc=Bc/CIR --this is usually 125ms because Bc is commonly set to 1/8 of
> >the CIR...but doesn't have to be!
> >
> >BTW....that's also why there's usually 8 time periods per second. Which
> >brings us to Be (which you didn't ask about but we're so close)
> >
> >Be is the amount you can transmit over and above the Bc within that
> >first time period of each second...IF you have credit built up (not to
> >exceed the volume of the infamous and invisible token bucket right?) I
> >beleve that by default Be=Bc which in that case gives you the limit of
> >Bc in each time period within each second--not 100% sure about that one
> >though.
> >
> >Now I hope you don't mind a question on the topic from me...where in an
> >"official" Cisco document does it state that upon receipt of a BECN
> >within a given time interval that the transmit rate is decreased by 25
> >percent? I've seen it around (and on page 385 of Solie's book for
> >example) but is this in fact correct? And in any event, is this
> >configurable?...and the obvious follow-on "How do you do it?"
> >
> >Thanks and aloha man! Frank
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> >Andri Bersvendsen
> >Sent: Sunday, August 11, 2002 10:42 PM
> >To: Mark Vann; ccielab@groupstudy.com
> >Subject: Re: FRTS
> >
> >
> >Bc = 1/8 of CIR only if Tc=125mS (this is the normal/default value for
> >Tc).
> >
> >Bc = CIR*Tc
> >
> >Example:
> >
> >Bc=?
> >CIR=64000
> >Tc=0.125
> >
> >Bc=64000*0.125
> >Bc=8000
> >Bc=8Kbps
> >
> >CIR do not have anything with port speed (also called access rate (AR))
> >to do. It must be lower than the access rate.
> >
> >And now LAB14:
> >
> >On page 382 the following information is given:
> >
> >port speed (JPL)=1.544 Mbps
> >CIR=32Kbps.
> >port speed (nasa_houston)=64Kbps
> >
> >In FRTS you must configure MinCIR=32Kbps.
> >And Bc is calculated from CIR in FRTS.
> >
> >
> >
> >>Can someone please clarify something for me? When
> >>cisco says that bc = 1/8 of cir, that basically means
> >>that 8/CIR=Bc . If this is so are they refering to CIR
> >>being the provider CIR or the CIR that is used in TS ,
> >>such as Port speed? I am just trying to figure out how
> >>Karl Solie arrived at this values on lab 14 in the
> >>preparation volume 1.
> >>Thanks
> >>
> >>
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