Alcatel Carrier Internetworking Solutions Switch/Router ユーザーズマニュアル

Page 29-12

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. FECN flag
set in frames experi-
encing congestion.

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.