--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).
--Connection Mode Network Service. Extends local X.25 switching to a variety of media (Ethernet, FDDI, Token Ring).
--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.
--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.
--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.
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.
--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).
--permanent virtual circuit. Virtual circuit that is permanently established.
--switched virtual circuit. Virtual circuit that is dynamically established on demand and is torn down when transmission is
--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.
--Bundled X.25 and LAPB commands that can be applied to specific connections.
--X.25 over TCP.