RE: FRTS

From: ccie candidate (ccie1@xxxxxxxxx)
Date: Tue Aug 13 2002 - 13:36:05 GMT-3

   
 Hi ;
i would like to contribute in this topic .

i have spent great time in the past trying to understand this FRTS , and as usu
al , 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 b
e wrong too ...so you can correct me .

Mincir is the amount you pay for , the only guranteed thing here proviced by th
e Service provided
it is also the vlaue where the traffic throtled down when you face any congesti
on in your network .

Cir is the normal or average rate at which you transmit you data when the netwo
rk 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 netw
ork ( it is like the Mtu ).

Be is the amount you can send over the Bc when the network is not congested ,ho
wever this amount of Data will be DE and can be droped first in case of congest
ion . 

--

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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