Layer 7 of the OSI Reference 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 availability of
communicating partners along with the resources necessary to make the con-
nection, coordinates partnering applications, and forms a consensus on pro-
cedures for controlling data integrity and error recovery.
AppleTalk Remote Access: A protocol for Macintosh users estab-
lishing their access to resources and data from a remote AppleTalk location.
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.
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
Address Resolution Protocol: Defined in RFC 826, the protocol that
traces IP addresses to MAC addresses. See also: RARP.
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,
American Standard Code for Information Interchange: An 8-bit
code for representing characters, consisting of seven data bits plus one parity bit.
Application-Specific Integrated Circuits: Used in Layer 2 switches
to make filtering decisions. The ASIC looks in the filter table of MAC
addresses and determines which port the destination hardware address of a
received hardware address is destined for. The frame will be allowed to
traverse only that one segment. If the hardware address is unknown, the
frame is forwarded out all ports.
Copyright ©2001 SYBEX , Inc., Alameda, CA