From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Sat Jun 17 2006 - 09:26:52 ART
Ken,
Most of the time FECN is an informative bit, that
may be used simply for statistical purposes.
On the over hand, BECN frames actually signal source to
slow down, but that would work okay only if data exchange
is bidirectional.
Now, for a good example of FECN usefulness consider
"frame-relay fecn-adapt" command wihin map-class.
(Or it's equivalent "shape fecn-adapt" with MQC).
Imagine that you have unidirectional stream of packets
(e.g. video feed) that overloads your FR network. You
will have a lot of FECN bit set packets in direction from
sender to receivers, but not a single packet backwards,
so no BECN frames will arrive to sender.
Here you may use fecn-adapt, that enables reflection
of FECN bit in special FR frames back to sender with
BECN bit set. In this way, a FECN signalling is converted
to BECNs, that actually signal sender to slow down sending rate.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos_r/qrfcmd9.htm#wp1103558
HTH
-- Petr Lapukhov, CCIE #16379 petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com Toll Free: 877-224-8987 Outside US: 775-826-4344 24/7 Support: http://forum.internetworkexpert.com Live Chat: http://www.internetworkexpert.com/chat/
This archive was generated by hypermail 2.1.4 : Sat Jul 01 2006 - 07:57:33 ART