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Appendix D. Glossary
61200275L1-1 TSU IQ+ User Manual D-7
far end
The unit or units not on-site (at the customer's premises or the other end of the
T1 link).
FCS
frame check sequence. The standard 16-bit cyclic redundancy check used for
HDLC and frame relay frames. The FCS detects bit errors occurring in the bits of
the frame between the opening flag and the FCS, and is only effective in detect-
ing errors in frames no larger than 4096 octets. See also CRC.
FDL
facility data link. A 4 kbps data channel provided by 12 of the ESF framing bits.
The FDL can be used by both the carrier and the TSU IQ+ unit for communica-
tion purposes. The TSU IQ+ unit uses the FDL for report requests, clearing error
counters, and activation of the loopbacks.
FECN
forward explicit congestion notification. A bit set by a frame relay network to
notify an interface device (DTE) that congestion avoidance procedures should be
initiated by the receiving device. See also BECN.
file server
In the context of frame relay network supporting LAN-to-LAN communications,
a device connecting a series of workstations within a given LAN. The device
performs error recovery and flow control functions as well as end-to-end
acknowledgment of data during data transfer, thereby significantly reducing
overhead within the frame relay network.
frame-relay-capable interface device
A communications device that performs encapsulation. Frame-relay-capable
routers and bridges are examples of interface devices used to interface the cus-
tomer's equipment to frame relay network. See also interface device and encap-
sulation.
frame relay frame
A variable-length unit of data, in frame-relay format that is transmitted through
a frame relay network as pure data. Contrast with packet.
frame relay network
A telecommunications network based on frame relay technology. Data is multi-
plexed. Contrast with packet switching network.