From: Brian Lodwick (xpranax@xxxxxxxxxxx)
Date: Thu Oct 18 2001 - 09:59:08 GMT-3
Ron,
It sounds like you have quite a grasp on this information. I'd like to run
something by you and see if you can help clear something up I've been having
difficulties with?
In the best documentation I have found on VoIP over Frame-Relay QOS it
notes the ideal Tc value is 10ms. It also says that 10ms is the lowest
configurable value. I understand this is optimum because it will provide for
very small time gaps between packets. The problem I am encountering is how
to mathmatically calculate this formula.
I found something saying something saying it was Tc = Bc/CIR
But then it goes on to say In this example we have a CIR to 64000, and have
set the Bc to 600 (forcing the Tc to it's minumum configurable value)
Wouldn't that give you a Tc of 106.66....?
>>>Brian
>From: "Ron Royston" <ccie6824@hotmail.com>
>Reply-To: "Ron Royston" <ccie6824@hotmail.com>
>To: John.K.Feuerherd@WellsFargo.COM, ccielab@groupstudy.com
>Subject: Re: QOS configs
>Date: Wed, 17 Oct 2001 17:20:20 -0500
>
>No. I believe they are different. Scott Keagy talks about this in
>"Integrating Voice and Data Networks". CIR is typically expressed in Bps
>and is the AVERAGE rate of traffic guaranteed by the carrier; Bc and Be are
>expressed per unit of time, Tc, and are the ACTUAL number of bits that the
>carrier commits to transport. Cisco routers take CIR as Bps, and Bc as
>Bits.
>
>The only practical reason that you should use the latter of your examples
>is
>to malipulate the value of Tc, which plays an important role in controlling
>pausing time (which can manifest itself as jitter and delay in real-time
>apps.) You don't explicitly configure Tc, you configure Bc and CIR and IOS
>implies the Tc from there.
>
>I believe that these are the same (note the Be, not Bc):
>
>map-class frame-relay sample1
> frame-relay traffic-rate 9600 19200
> no frame-relay adaptive-shaping
>-and-
>map-class frame-relay sample2
> frame-relay cir 9600
> frame-relay be 19200
>
>Having the bc set to 19200, as in your example, would double the Tc to 2
>seconds, telling the router to push out 2xCIR bits every 2 seconds at the
>port speed. If the port speed is high, and the CIR low, your data gets
>sent
>in short bursts followed by a long pauses and will likely exceed your CIR
>from the carriers vantage point. The carrier's Tc is less than 2 seconds,
>so they'll be getting 2 seconds worth of bits in less than 1 second if your
>port speed is high enough, and they'll De, discard eligible, that data.
>Right?
>
>-Ron
>
>PS IMHO, CCO needs more understandable info on this subject, but you can
>check out, http://www.cisco.com/warp/customer/125/21.shtml. That's all I
>can find.
>
>
>
>
>
>>From: John.K.Feuerherd@WellsFargo.COM
>>Reply-To: John.K.Feuerherd@WellsFargo.COM
>>To: ccielab@groupstudy.com
>>Subject: QOS configs
>>Date: Tue, 16 Oct 2001 19:56:49 -0700
>>
>>Hello all,
>> I have a quick question about traffic shaping. I think I understand
>>this, but I just want to make sure:
>>
>>This two configs are basically the same right.....
>>
>>map-class frame-relay sample1
>> frame-relay traffic-rate 9600 19200
>> no frame-relay adaptive-shaping
>>
>>
>>map-class frame-relay sample2
>> frame-relay cir 9600
>> frame-relay bc 19200
>>
>>Thanks in advance!
>>
>>JF
>>John Feuerherd
>>Wells Fargo Bank
>>CCNP CCDP
>>1-505-766-6118 <- Office
>>1-505-301-1966 <- Cell
>>John.K.Feuerherd@Wellsfargo.com
>>MAC: Q2129-074
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