ADTRAN Atlas 550 User Manual page 244

Appendix G. Glossary
DSU
Data Service Unit. A device used with a CSU to support digital communications by converting signals.
(See also CSU.)
DTE
Data terminal equipment. The portion of a data terminal that interfaces to the end-user's equipment.
The main difference between DCE and DTE is that pins 2 and 3 are reversed on the EIA-232.
DTMF dialing
Dual tone multifrequency dialing. The tones used by customer equipment to signal the network.
Dual Nx56/64 Module
(Nx is pronounced "en-by.") One of the ATLAS 550 option modules. The Dual Nx56/64 Module pro-
vides two synchronous V.35 DTE ports, each of which can operate at any rate that is a multiple of 56 or
64 kbps, up to 2.048 Mbps.
Dual T1/PRI Module
One of the ATLAS 550 option modules. The Dual T1/PRI Module provides two channelized T1 or Pri-
mary Rate ISDN (PRI) interfaces. Each interface can operate independently in DS-1 or DSX-1 mode,
and any port can serve as the primary or backup timing source for the entire system.
E1 circuit
European equivalent to the T-1 with a capacity of 2.048 Mbps. An E1 can handle 32 voice channels
with each conversation being digitized at 64 kbps.
ESF
Extended superframe. A method of grouping T1 carrier frames into larger superframes, each contain-
ing 24 consecutive T1 frames.
FECN
Forward Explicit Congestion Notification. Sent to the device receiving data from the frame relay net-
work to indicate that there is congestion in the receive direction. The receiving DTE device should take
action to slow down traffic from the remote end. Compare with BECN.
flash memory
A kind of non-volatile storage device, similar to EEPROM, where erasing can only be done in blocks or
the entire chip.
flash upgrades
Upgrades that can be downloaded into the flash memory.
FRAD
Frame Relay Access Device. Any equipment that provides a connection between a frame relay net-
work and a LAN.
Frame Relay
A subset of the X.25 packet switching protocol that allows for efficient transmission of data by utiliz-
ing many virtual circuits on a single physical interface.
FTP
File Transfer Protocol. The TCP/IP protocol used to log in to a network, list files and directories, and
transfer files.
G-4 ATLAS 550 User Manual 61200305L1-1