Envoy ACP/XF Configuration and Management Manual

Glossary
EnvoyACP/XF Configuration and Management Manual—429232-003
Glossary-3
information frame
information frame. A frame format used to pass data between two stations.
IOP. Input output process. EnvoyACP/XF is considered an IOP. It is an input-output process
controlling a bit-synchronous communications line.
MCW. Message control word. The first 2 bytes (one word) of the application buffer, used by
EnvoyACP/XF to build the control and address fields of the frame.
modulo. Refers to the maximum number of frames that can be transmitted before an
acknowledgment is received; it is the maximum number of frames that can be handled
by the link-level sequence numbers. Because the link-level sequence numbers are
contained in the control field, the size of the modulo is determined by the size of the
control field. With standard 1-octet control fields, the maximum is modulo-8. With
extended control fields, the maximum is modulo-128. See also window.
multidrop. Same as multipoint.
multipoint. A data-link configuration in which one station is designated as the supervisor
and controls all communications over the link. The other stations are designated as
tributaries.
nonswitched. A line configuration that provides a permanent path between two stations.
This path can be either a privately owned cable or a dedicated path leased from a
common carrier.
NRM. Normal Response Mode. A mode of communications within the ADCCP protocol in
which a secondary station can transmit data only after a request from the primary
station. This mode of operation is also used by SDLC.
octet. A term that applies to the bit-synchronous frame format, equivalent to 8 bits or 1 byte.
page. Contains 1,024 words of contiguous data or 2048 bytes.
point-to-point. A data-link configuration between two stations. This configuration may exist
between a primary and a secondary station or between two combined stations.
primary. In an SDLC or ADCCP-NRM configuration, the primary station initiates a data
transfer and is in control during the exchange of messages. It notifies each secondary
link station when it can transmit data and when it should expect to receive data. See
also secondary.
RR. Receiver ready. A type of SDLC or ADCCP-NRM frame. This is one of the supervisory
frames.
RS-232. An industry standard for serial data transmission. It describes pin assignments (for
a 25-pin connector), signal functions, and electrical characteristics. RS-232C is the
current standard.