Glossary
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Application layer
Layer 7 of the OSI reference network model, supplying
services to application procedures (such as electronic mail or file transfer)
that are outside the OSI model. This layer chooses and determines the avail-
ability of communicating partners along with the resources necessary to
make the connection, coordinates partnering applications, and forms a con-
sensus on procedures for controlling data integrity and error recovery.
See
also: Data Link layer, Network layer, Physical layer, Presentation layer,
Session layer,
and
Transport layer.
ARA
AppleTalk Remote Access: A protocol for Macintosh users estab-
lishing their access to resources and data from a remote AppleTalk location.
area
A logical, rather than physical, set of segments (based on either
CLNS, DECnet, or OSPF) along with their attached devices. Areas are com-
monly connected to others using routers to create a single autonomous
system.
See also: autonomous system.
ARM
Asynchronous Response Mode: An HDLC communication mode
using one primary station and at least one additional station, in which trans-
mission can be initiated from either the primary or one of the secondary units.
ARP
Address Resolution Protocol: Defined in RFC 826, the protocol that
traces IP addresses to MAC addresses.
See also: RARP.
AS
autonomous system: A group of networks under mutual administra-
tion that share the same routing methodology. Autonomous systems are sub-
divided by areas and must be assigned an individual 16-bit number by the
IANA.
See also: area.
AS path prepending
The use of route maps to lengthen the autonomous
system path by adding false ASNs.
ASBR
Autonomous System Boundary Router: An area border router
placed between an OSPF autonomous system and a non-OSPF network
that operates both OSPF and an additional routing protocol, such as RIP.
ASBRs must be located in a non-stub OSPF area.
See also: ABR, non-stub
area,
and
OSPF.
ASCII
American Standard Code for Information Interchange: An 8-bit
code for representing characters, consisting of seven data bits plus one
parity bit.
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