ADTRAN T1 ESF CSU ACE User Manual page 76

Appendix D. Glossary
DSU loopback
A telco initiated test which loops the DSU back to the telco and is used to test the
DDS circuit as well as the DSU/CSU.
DTE
data terminal equipment. The end-user terminal or computer that plugs into the
termination point (DCE) of a communications circuit. The main difference
between the DCE and the DTE is that pins two and three are reversed.
encapsulation
A process by which an interface device places an end device's protocol-specific
frames inside a frame rely frame. The network accepts only frames formatted
specifically for frame relay; therefore interface devices acting as interfaces to a
frame relay network must perform encapsulation. See also interface device or
frame relay capable interface device.
end device
The ultimate source or destination of data flowing through a frame relay net-
work sometimes referred to as DTE. As a source device, it sends data to an inter-
face device for encapsulation in a frame relay frame. As a destination device, it
receives de-encapsulated data (i.e., the frame relay frame is stripped off, leaving
only the user's data) from the interface device.
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 kbit/s non-disruptive management channel provided in
ESF framing mode. This data link conforms to ANSI T1.403 and AT&T TR 54016
specifications.
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 initi-
ated by the receiving device. See also BECN.
D-4 T1 ESF CSU ACE User Manual 61203025L1-1