IBM 3745 Series Service Functions page 304

synchronous transmission. Data transmission in
which the sending and receiving instruments are
operating continuously at substantially the same fre-
quency and are maintained, by means of correction,
in a desired phase relationship. Contrast with
asyn-
chronous transmission.
5ystems Network Architecture (5NA). The
description of the logical structure, formats, protocols,
and operational sequences for transmitting informa-
tion through a user application network. The struc-
ture of SNA allows the users to be independent of
specific telecommunication facilities.
time out. The time interval allotted for certain oper-
ations to occur.
token-ring subsystem (TR5S). The part of the con-
troller that controls the data transfers over an IBM
Token-Ring Network.
The TRSS consists of up to four token-ring adapters
(TRAs).
token-ring adapter (TRA). Line adapter for an IBM
Token-Ring Network, composed of one token-ring
multiplexer card (TRM), and two token-ring interface
couplers (TICs).
The TRSS consists of up to four token-ring adapters
(TRAs).
transmission interface. The interface between the
controller and the user application network.
transm~ssion line. The physical means for connecting
two or more DTEs (via DCEs). It can be nonswitched
or switched. Also called
line.
transmission subsystem (T55). The part of the con-
troller that controls the data transfers over low- and
medium-speed, switched and non switched trans-
mission interfaces.
The TSS consists of:
• Up to 32 low-speed scanners (LSSs) associated
with
• LlC units (LlUs), through
• Serial links (SLs).
T55T board. line adapter board for token-ring
adapters
twin. Configuration with two CCUs.
twin-dual. Mode of operation with two CCUs oper-
ating simultaneously in two distinct subareas.
twin-backup. Mode of operation
J
identical to twin-dual
with fallback capability.
twin-standby. Mode of operation with one CCU active
and the other in standby, ready to take over.
two-processor switch (TP5). A feature of the channel
adapter that connects a second channel to the same
adapter.
user application network. A configuration of data
processing products, such as processors, controllers,
and terminals, for the purpose of data processing and
information exchange. This configuration may use
circuit-switched, packet-switched, and leased-circuit
services provided by carriers or the PTT. Also called
user network.
vertical redundancy check (VRC). An odd parity
check performed on each character of a block as the
block is received.
V.24,25,35. EIA/CCITT recommendations on trans-
mission interfaces
X.20 bis, 21, 21 bis, 21 native, 25. CCITT recommen-
dations on transmission interfaces
Glossary
X-13