6100 ADCCP Programming Manual

Glossary
Glossary–6 069225 Tandem Computers Incorporated
SREJ. See Selective Reject (SREJ).
station. An independently controllable configuration of data terminal equipment
(DCE) from or to which messages are transmitted on a data link.
supervisor. The controlling station in a centralized multipoint data link.
supervisory frame. A frame format used to convey READY or BUSY status or to request
retransmission when an error is detected.
switched. A line configuration for circuit-switched networks such as a public
telephone network. Contrast with switched.
synchronous data-link control (SDLC). One of the bit-synchronous communications
protocols. It uses Normal Response Mode (NRM) operation. SDLC is the protocol
used in Systems Network Architecture (SNA) networks.
synchronous. A general class of data communications that includes ADCCP, Bisync,
synchronous data-link control (SDLC), and high-level data-link control (HDLC)
protocols. It is the opposite of asynchronous communications. In synchronous
transmission, the sending and receiving are controlled by timing signals. Also, a flag,
SYN, or other character is used instead of a start-stop bit.
SYSGEN. The system generation program that is run against a CONFTEXT file (which
describes a Guardian 90 system configuration) and that generates a system-
customized version of the Guardian 90 operating system. The SYSGEN program is
usually invoked by the INSTALL program.
U-frame. See unnumbered frame.
unnumbered frame. A frame format used to pass data-link management commands and
responses between the primary and the secondary stations.
unnumbered poll frame. A command frame used to solicit response frames from
secondary stations or a combined station. Secondary or combined station that receives
a UP-frame with the poll bit set respond with a frame that has the final bit set.
Secondary and combined stations respond to a frame without the final bit set with a
UP-frame without the poll bit set whenever they have I-frames or UI frames to send,
accepted but not acknowledged an I-frame, or have an unreported change of condition
or status, or have a status to report.
UP-frame. See unnumbered poll frame.
V.25 bis. A CCITT recommendation for a protocol for setting up a data connection with
a serial modem that has automatic calling capability on the general, switched
telephone network.
V.35. A CCITT recommendation for a wide-band, 48-kbits-per-second modem. V.36
modems, which have electrical interface characteristic equivalent to RS-449, replaces
V.35.
window size. The maximum number of I-frames that can be sent without
acknowledgment.
XID. See exchange identification command.