Re: Counting Send DE Frames for Frame Relay MIB

Fred Baker <fred@cisco.com> Fri, 25 August 1995 04:31 UTC

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Date: Thu, 24 Aug 1995 21:29:08 -0700
To: artb@xylan.com
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From: Fred Baker <fred@cisco.com>
Subject: Re: Counting Send DE Frames for Frame Relay MIB
Cc: iplpdn@CNRI.Reston.VA.US

At 2:08 PM 8/22/95, artb@xylan.com wrote:
>I don't agree that the switch is very likely to discard the traffic.  Certainly
>there's a likelihood, and, if the switch is implemented correctly, a greater
>likelihood than for non-DE traffic but there are other factors involved.  The
>switch should discard the DE traffic if it is congested,

A correctly implemented switch has three traffic windows for each DTE:

        traffic within Bc
        traffic within Bc+Be and not within Bc
        Other traffic

traffic is within Bc if the switch receives it from the DTE with DE=0 and
with certain timing characteristics, and leaves DE=0.

traffic is not within Bc and is within Be if DE=0 and Bc is exhausted and
Be is not, or if DE=1 and Be is not exhausted.

traffic is outside Bc+Be if DE=0 but both Bc and Be are exhausted, or if
DE=1 and Be is exhausted. Such traffic drops like a stone.

Be generally has one of two values:
        the size of one, maybe two, frames (8K bits is common)
or      infinite

If Be is infinite, your comments are reasonably accurate; DE is only of
interest when an intermediate switch is forced to discard traffic. If Be ==
8K bits, the traffic is discarded en mass at the ingress point. I guess the
argument depends on whose network you are using your equipment over.

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
So Bill Gates has paid Mick and the boys 12 million dollars to use "Start It
Up" to sell Windows 95.

For those who don't know the song, it's the one that goes "You make a grown
man cry...".

Food for thought