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GLOSSARY
Protocol
PSTN
Public Network
Quasi-Random Signal
(QRS) Test Patten
Red Alarm Signal
Request To Send
RS-232-C
RTS
Severely Errored
Framing Event
Severely Errored
Second
Simplex
Slave CSU
SNA
Space
Start Bit
Start-Stop
Transmission
Stop Bit
B-8
Formal set of rules governing the format, timing, sequencing, and error control
of exchanged messages on a data network; may also include facilities for man-
aging a communications link and/or contention resolution; a protocol may be
oriented toward data transfer over an interface, between two logical units directly
connected, or on an end-to-end basis between two end users over a large and com-
plex network.
Public switched telephone network; the dial-up phone network.
Generically, a network established and operated by communications common
carriers or telecommunications administrations for the provision of circuit-
switched, packet- switched, and leased-line circuits to the public.
An irregular pattern of bits used to test and measure network jitter, as defined in
AT&T PUB 62411.
A Red alarm signal is a locally detected failure. In response to receiving a Red
alarm from one side, the CSU transmits a Yellow alarm to the other side.
A signal to the sending modem that the terminal is ready to transmit; part of mo-
dem handshaking.
An EIA-specified physical interface. See EIA/TIA-232-E.
Request To Send.
This is the occurrence of two or more frame synchronization bit error events
within a 3-ms period.
A severely ES is a second with 320 or more ESF error events. Severely ESs are
also processed to derive failed signal states.
One-way data transmission, with no capability for changing direction.
A DataComm 551 option that prevents configuration of the CSU through the
Supervisory terminal. A slave CSU displays a warning message when the user at-
tempts to configure it or start a Self-Test or a loopback, although it does not prevent
these tests.
Systems Network Architecture. In IBM networks, the layered logical structure,
formats, protocols, and procedures that govern information transmission.
One of the two possible conditions of an information element (bit), an open line in
a neutral circuit.
In asynchronous transmission, the first element in each character that prepares
the receiving device to recognize the incoming information elements.
Asynchronous transmission for a group of data elements that are preceded by a
start signal and followed by a stop signal; reference employed primarily by IBM
for asynchronous transmission.
In asynchronous transmission, the last transmitted element in each character,
which permits the receiver to come to an idle condition before accepting another
character.
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