ence model network layer. Contrast with
bridge
and
gateway
.
SSDLC. Synchronous Data Link Control.
Simple Network Management Protocol (SNMP).
(1) An IP network management protocol that is used to
monitor routers and attached networks. (2) A
TCP/IP-based protocol for exchanging network manage-
ment information and outlining the structure for commu-
nications among network devices. SNMP is an
application layer protocol. Information on devices
managed is defined and stored in the application’s Man-
agement Information Base (MIB).
SIMM. Single in-line memory module.
SNA. Systems Network Architecture.
SNMP. Simple Network Management Protocol.
Synchronous Data Link Control (SDLC). A discipline
conforming to subsets of the Advanced Data Communi-
cation Control Procedures (ADCCP) of the American
National Standards Institute (ANSI) and High-level Data
Link Control (HDLC) of the International Organization
for Standardization, for managing synchronous, code-
transparent, serial-by-bit information transfer over a link
connection. Transmission exchanges may be duplex or
half-duplex over switched or nonswitched links. The
configuration of the link connection may be point-to-
point, multipoint, or loop. (I)
system unit. (1) A part of a computer that contains
the processing unit and devices, such as disk and
diskette drives. (2) In an IBM personal computer, the
unit that contains the processor circuitry, read-only
memory (ROM), random access memory (RAM), and
the I/O channel. It can have one or two diskette drives.
Systems Network Architecture (SNA). The
description of the logical structure, formats, protocols,
and operational sequences for transmitting information
units through, and controlling the configuration and
operation of, networks.
Note: The layered structure of SNA allows the ultimate
origins and destinations of information, that is, the end
users, to be independent of and unaffected by the spe-
cific SNA network services and facilities used for infor-
mation exchange.
TTCP. Transmission Control Protocol.
TCP/IP. Transmission Control Protocol/Internet Pro-
tocol.
telephone twisted pair. One or more twisted pairs of
copper wire in the unshielded voice-grade cable com-
monly used to connect a telephone to its wall jack.
Also referred to as
unshielded twisted pair
(UTP).
terminal. In data communication, a device, usually
equipped with a keyboard and display device, capable
of sending and receiving information.
throughput. (1) A measure of the amount of work
performed by a computer system over a given period of
time, for example, number of jobs per day. (I) (A) (2) A
measure of the amount of information transmitted over
a network in a given period of time. For example, a
network’s data transfer rate is usually measured in bits
per second.
token. (1) In a local area network, the symbol of
authority passed successively from one data station to
another to indicate the station temporarily in control of
the transmission medium. Each data station has an
opportunity to acquire and use the token to control the
medium. A token is a particular message or bit pattern
that signifies permission to transmit. (T) (2) In LANs, a
sequence of bits passed from one device to another
along the transmission medium. When the token has
data appended to it, it becomes a frame.
token ring. (1) According to IEEE 802.5, network
technology that controls media access by passing a
token (special packet or frame) between media-attached
stations. (2) A FDDI or IEEE 802.5 network with a ring
topology that passes tokens from one attaching ring
station (node) to another. (3) See also
local area
network (LAN)
.
trace. (1) A record of the execution of a computer
program. It exhibits the sequences in which the
instructions were executed. (A) (2) For data links, a
record of the frames and bytes transmitted or received.
Transmission Control Protocol (TCP). (1) A commu-
nications protocol used in Internet and in any network
that follows the U.S. Department of Defense standards
for inter-network protocol. TCP provides a reliable host-
to-host protocol between hosts in packet-switched com-
munications networks and in interconnected systems of
such networks. It assumes that the Internet protocol is
the underlying protocol. (2) A transport protocol in the
Internet suite of protocols that provides reliable,
connection-oriented, full-duplex data stream service.
X-6 2210 Service and Maintenance