I think your instructor was thinking of the DE bit.
Have a look at http://www.frforum.com/basicguide/chap3.html#basictrail - the
basic guide to frame relay networking.
Excerpt (this refers to a diagram but you can probably work out what they're
saying without the diagram)...
"Let's suppose Node B is approaching a congestion condition. This could be
caused by a temporary peak in traffic coming into the node from various sources
or by a peak in the amount of traffic on the link between B and C. Here is how
forward congestion notification would occur:
Node B would detect the onset of congestion based on internal measures such as
memory buffer usage or queue length.
Node B would signal Node C (the downstream node, toward the destination) of the
congestion by changing the forward ECN (FECN) contained within the frames
destined for Node C from 0 to 1.
All interim downstream nodes, as well as the attached user device, would thus
learn that congestion is occurring on the DLCI(s) affected. "
There is a similar description of BECNs.
JMcL
---------------------- Forwarded by Jenny Mcleod/NSO/CSDA on 19/09/2000 09:18 am
---------------------------
"Miller, Nathan (AZ15)" <[EMAIL PROTECTED]> on 19/09/2000 01:44:36 am
Please respond to "Miller, Nathan (AZ15)" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
cc: (bcc: JENNY MCLEOD/NSO/CSDA)
Subject: More on FECNs and BECNs
I have received conflicting answers to this question from a number of
sources to include a Cisco Certified Instructor in a CIT course, so I am
posting the question here with hope that someone "out there" can clear this
up. I have been told that when a frame enters a router with the BECN or
FECN bit high is this an indicator that there is congestion on a port on a
frame switch that the frame has traversed (I don't question this). The
piece of the instructor's explanation that I have a problem with is that the
only frames that get the bit flipped are those that are part of a PVC that
is running outside its CIR. He stated that the traffic moving through the
same congested port on other PVCs (those running under CIR) will not be
tagged even though they are moving through a congested port. I thought that
every frame traversing the congested port gets the FECN or BECN bit flipped
(depending on direction). I have found support for this in a couple of
books, but I have seen nothing that says definitively that ALL frames
through the congested port get tagged.
Many thanks in advance!
Nathan Miller
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