| |
|
H |
| Half
duplex |
 |
Data
transmission that can occur in two directions over
a single line, but only
one direction at a time. Contrast full duplex. |
| Hardware
address |
|
See
Network Address |
| HDLC |
|
High-Speed Data Link Control, A protocol defined by
the International Standards Organization and used in
X.25 communications; specifies an encapsulation method
for data on synchronous serial data links. Various
manufacturers have proprietary versions of HDLC, including
IBM's SDLC. |
| HDSL |
|
High bit-rate Digital Subscriber Line |
| Header |
|
The initial part of a data packet or frame containing
identifying information such as the source of the data,
its destination, and length. |
| Heartbeat |
|
Ethernet
defined SQE signal quality test function. |
| HEC |
|
Header Error Control |
| Hertz
(Hz) |
|
A
frequency unit equal to one cycle per second. |
| Hierarchical
routing |
|
Routing
based on a hierarchical addressing system. IP routing
algorithms use IP addresses, for example, which contain
network numbers, host numbers, and frequently, subnet
numbers. |
| HLM |
|
Heterogeneous LAN Management, Management of LANs that
contain dissimilar devices running different protocols
and different applications. |
| Hop |
|
A unit that equates to the passage of a packet through
one router. |
| |
|
|
| Hop
count |
|
A
routing metric used to measure the distance between
a source and a destination. |
| Host |
|
Generally
a node on a network that can be used interactively,
i.e., logged into, like a computer. |
| Host
table |
|
A
list of TCP/IP hosts on the network along with their
IP addresses. |
| HPF |
|
High
Pass Filter |
| HSCSD |
|
High Speed Circuit Switched Data |
| HSSI |
|
High-Speed Serial Interface, A de facto standard for
high-speed serial ocmmunications at up to 52 Mbps over
WAN links. Used for the physical connection between
a router and a DSU. |
| HTML |
|
Hyper Text Mark-up Language |
| HTTP |
|
Hyper Text Transfer Protocol |
| Hub |
|
Common name for a repeater. Strictly, it is a non-retiming
device. |
| |
|
|
