X terminal
Terminal that allows a user simultaneous access to several different applications and resources in a multivendor environment through implementation of X Windows. See also X Window System
X Window System
Distributed, network-transparent, device-independent, multitasking windowing and graphics system originally developed by MIT for [...]

WAN
wide-area network. Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay, SMDS, and X.25 are examples ofWANs. Compare with LAN and MAN.
WDM
wavelength division multiplexing. Multiple optical wavelengths can share the same [...]

V.24
ITU-T standard for a physical layer interface between DTE and DCE. V.24 is essentially the same as the EIA/TIA-232 standard. See also EIA/TIA-232.
V.25bis
ITU-T specification describing procedures for call setup and tear down over the DTE-DCE interface in a PSDN.
V.32
ITU-T standard serial line protocol [...]

U interface
The interface between the telco and the user, also known as the local digital subscriber line (DSL) loop.
UDP
User Datagram Protocol. Connectionless transport layer protocol in the TCP/IP protocol stack. UDP is a simple protocol that exchanges datagrams without [...]

T.120
ITU standard that describes data conferencing. H.323 provides for the capability to establish T.120 data sessions inside an existing H.323 session.
T.30
Describes the overall procedure for establishing and managing communication between two fax machines.
T.38
Defines procedures for real-time Group 3 facsimile communication over IP networks.
T1
Digital [...]