Envoy ACP/XF Configuration and Management Manual

EnvoyACP/XF Configuration and Management Manual—429232-003
Glossary-1
Glossary
ABM. Asynchronous Balanced Mode. A mode of communications within the ADCCP
protocol in which two combined stations communicate on a point-to-point link. Either or
both stations can issue commands to set up or dissolve the link. During data
transmission, the stations function as peers. This mode is also used by the HDLC
protocol.
ADCCP. Advanced Data Communications Control Procedures. This is the general standard
for bit-synchronous protocols. It includes two major modes of operation—ABM and
NRM. ADCCP-ABM is analogous to HDLC, and ADCCP-NRM is analogous to SDLC.
See also ABM and NRM.
address field. The field immediately following the starting flag in a bit-synchronous frame.
When stations are operating in Normal Response Mode (NRM), this field always
identifies the secondary station that is communicating with the primary station.
Generally, the address field is 1 octet long; however, in extended mode, the address
field can be up to 4 octets long. Extended address fields are not supported by the
SDLC protocol standard.
ASCII. American National Standard Code for Information Interchange. A method of coding
data, consisting of 7 bits for each character plus a parity bit. Designed for synchronous
or asynchronous use, the code has 128 standard characters.
bit-synchronous. A class of serial communications protocols for data-link control. This
class includes ADCCP, HDLC, SDLC, and FRAME protocols. Many wide-area network
(WAN) architectures define a bit-synchronous protocol as the standard link-level
protocol.
CCITT. Comité Consultatif International Télégraphique et Téléphonique (International
Telegraph and Telephone Consultative Committee). A standards-setting group for
international telephone carriers.
CLIP. Communications line interface processor. Part of the LIU within the WAN
concentrator, the CLIP is a programmable process that provides link-level protocol and
a software interface to the host. The CLIP does some of the work that used to be
handled by the host-resident communication processes. CLIP software implements the
specific communications protocols, such as SDLC or HDLC.
control field. The field following the address field in a bit-synchronous frame. It contains bit-
encoded commands and responses and can also contain frame sequence numbers.
The contents of the control field indicate whether the frame has an information,
supervisory, or unnumbered format. Generally, this field is 1 octet long; however, in
extended mode, the control field can be 2 octets long.
CRC. Cyclical redundancy check. A technique for checking the validity of a multiple-byte
block of data. If one CRC does not match the one previously generated, an error exists
somewhere within the block of data. See also frame check sequence.