Glossary
561
Group of Four
Used by Cisco Local Management Interface on Frame Relay
networks to manage the permanent virtual circuits (PVCs). See also: PVC.
guard band
The unused frequency area found between two communica-
tions channels, furnishing the space necessary to avoid interference between
the two.
half duplex
The capacity to transfer data in only one direction at a time
between a sending unit and receiving unit. See also: full duplex.
handshake
Any series of transmissions exchanged between two or more
devices on a network to ensure synchronized operations.
H channel
High-speed channel: A full-duplex, ISDN primary rate channel
operating at a speed of 384Kbps. See also: B, D, and E channels.
HDLC
High-Level Data Link Control: Using frame characters, including
checksums, HDLC designates a method for data encapsulation on synchro-
nous serial links and is the default encapsulation for Cisco routers. HDLC is
a bit-oriented synchronous data-link layer protocol created by ISO and
derived from SDLC. However, most HDLC vendor implementations
(including Cisco's) are proprietary. See also: SDLC.
helper address
The unicast address specified, which instructs the Cisco
router to change the client's local broadcast request for a service into a
directed unicast to the server.
hierarchical addressing
Any addressing plan employing a logical chain of
commands to determine location. IP addresses are made up of a hierarchy of
network numbers, subnet numbers, and host numbers to direct packets to
the appropriate destination.
hierarchical network
A multi-segment network configuration providing
only one path through intermediate segments between source segments and
destination segments.
hierarchy
See: hierarchical network.
HIP
HSSI Interface Processor: An interface processor used on Cisco 7000
series routers, providing one HSSI port that supports connections to ATM,
SMDS, Frame Relay, or private lines at speeds up to T3 or E3.
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com