access list --List kept by routers to control access to or from the router for a number of services (for example, to prevent packets with a certain IP address from leaving a particular interface on the router).
CMNS --Connection Mode Network Service. Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring).
CUG --closed user group. A collection of DTE devices for which the network controls access between members and between members and nonmembers. A DTE may subscribe to zero, one, or more CUGs. A DTE that does not subscribe to a CUG is referred to as being in the open part of the network.
DCE --data communications equipment. Devices and connections of a communications network that make up the network end of the user-to-network interface. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal used to synchronize data transmission between DCE and DTE devices. Modems and interface cards are examples of DCE.
DTE --data terminal equipment. Device at the user end of a user-network interface that serves as a data source, destination, or both. DTE connects to a data network through a DCE device (for example, a modem) and typically uses clocking signals generated by the DCE. DTE includes such devices as computers, protocol translators, and multiplexers.
HDLC-- high-level data link control. Bit-oriented synchronous data link layer protocol developed by ISO. HDLC specifies a data encapsulation method on synchronous serial links using frame characters and checksums.
LAPB --Link Access Procedure, Balanced. Data link layer protocol in the X.25 protocol stack. LAPB is a bit-oriented protocol derived from high-level data link control (HDLC).
PVC --permanent virtual circuit. Virtual circuit that is permanently established.
SVC --switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is complete.
X.25 --ITU-T standard that defines how connections between DTE and DCE are maintained for remote terminal access and computer communications in PDNs. X.25 specifies LAPB, a data-link-layer protocol, and PLP, a network-layer protocol.
X.25 profile --Bundled X.25 and LAPB commands that can be applied to specific connections.
XOT --X.25 over TCP.