Alcatel Omni Switch/Router, User Manual

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Congestion Control
Page 29-12
Notification By FECN
Frame Relay headers also contain a congestion control bit called
FECN
(Forwards Explicit
Congestion Notification), which is usually pronounced “Feckon.” Like
BECN
, the
FECN
bit also
notifies a
WSX
or Bridge/Router of congestions problems. However, it is set by the Frame
Relay network in frames that are actually experiencing congestion. When the
WSX
receives
frames with their
FECN
bit set, it knows that congestion is already occurring on the virtual
circuit in the direction that these
FECN
frames are travelling. The
WSX
reacts by reducing the
data flow down to the
CIR
for data in the opposite direction. If the
FECNs
persist, then data
flow is stepped down even further. Data flow will gradually increase back up to the normal
rate as soon as
FECNs
or
BECNs
are no longer received.
Congestion Notification Using a FECN
Congestion. FECN flag
set in frames experi-
encing congestion.
Frame Relay Virtual Circuit
WSX or Bridge/Rout-
e r a t t h i s e n d
receives FECN and
can adjust traffic flow
down to the CIR, or
below, for outgoing
traffic in the opposite
direction.