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Frame
FLAG
The flag field holds the "Start of frame" marker.
LINK INFO
This field holds the logical connection address and control fields as described here:
DLCI
DLCI (data link connection identifier) identifies the logical connections.
C/R
Command/Response bit related to congestion control.
EA
EA (extended address) is used to extend the header field to support DLCI addresses of
more than 10 bits.
FECN
FECN (forward explicit congestion notification) warns receivers about network
congestion.
BECN
BECN (backward explicit congestion notification) warns senders about network
congestion.
DE
DE (discard eligibility) indicates whether frames can be discarded if the network is
congested.
DATA
Control information or encapsulated data goes in this field.
FCS
FCS (FRAME CHECK SEQUENCE) is a checksum used for error detection.
FLAG
This flag field holds the "End of frame" marker.
1.1.2 Connection setup
The carrier gives you a specific DLCI (Data Link Connection Identifier) for each PVC which is a path
number of a portion of the PVC (the DLCI changes for each hop through the network), not the address of the
destination. It is a logical identifier with local significance only.
A management protocol called LMI (Local Management Interface) provides information about the status of
PVC-to-network access devices. It defines management frames for monitoring the integrity of a link and
whether a link is active or not.
The frame-relay network manages congestion by setting bits in frames that warn end devices that there is
congestion on the network. A bit called FECN (forward explicit congestion notification) is set to notify a
receiving system of congestion and a bit called BECN (backward explicit congestion notification) is set to
notify sending devices of congestion. In the latter case, the sending device will temporarily slow down or
stop transmissions.
1.1.3 Standards
The two main groups that create recommendations and standards in the telecommunications field are ITU – T
(International Telecommunication Union – Telecommunications Standardization Sector) and ANSI
(American National Standards Institute). Standards vary slightly for both organizations, so please select the
User's Guide Supplement
Table 1
Frame Relay Format
Description
Prestige 153X Supplement
3
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