Introduction to Tandem X.25 Capabilities

Glossary
Glossary–4 065307 Tandem Computers Incorporated
data packet. Packet containing data.
DCE. Data circuit-terminating equipment. In the context of the X.25 standard, the
network is identified as a DCE. X25AM can be configured as either DCE or DTE. The
term DCE is also used to refer to a modem.
destination address. See called address.
device. Physical or logical system component. For X25AM, a line is a device defined in
the CONFTEXT file.
DISC. Disconnect. Link-level frame, used for call disconnection.
DNIC. Data Network Identification Code. The DNIC is part of a CCITT numbering
scheme providing each network with a unique address. The DNIC contains a
three-digit data country code (DCC) and a one-digit network identification (NI) code.
See also X.121.
DSC. See COUP.
D-series system. A system running a D-series version of the Guardian 90 operating
system. A D-series system can have more than 256 concurrent processes in a CPU.
DSR. Data set ready. Signal coming from a modem which usually indicates to the
computer equipment that the modem is powered on.
DTE. Data terminal equipment. The user’s computer system; that is, equipment
connected by data communications equipment (DCE) to telephone company lines or
data circuits. A DTE is usually a terminal or a computer. With X.25AM, the Tandem
system can function as either a DTE or a DCE.
EBCDIC. Extended binary-coded decimal interchange code. Standard method of
coding data, consisting of eight bits of data with no parity bit for each character.
fast select. Optional network facility allowing call setup packets to contain a call user
data field of up to 128 octets.
flow control. Mechanism by which the recipient of incoming data notifies the sender to
stop or start transmitting data depending on the state (full or empty) of the recipient's
incoming data buffer.
frame. Message unit consisting of a sequence of bits bracketed by beginning and
ending flag sequences. It can contain packets.
frame layer. Also called the link level. It is the X.25 protocol description for the link
access procedures for the link between the network and the computers, terminals, or
other devices.
frame relay. A layer-2 protocol providing packet-switching data communications. It
does not include the explicit flow-control procedures provided by X.25.
FRMR. Frame Reject. A response frame indicating the receipt of an invalid frame
format, invalid command, or invalid response.
full duplex. Method of serial communications in which the data flow between two
points can occur in both directions simultaneously.