H
HA
Host Attach. In
ExtremeXOS software, HA is part of ESRP that allows you to connect active hosts directly to an
ESRP switch; it allows configured ports to continue Layer 2
forwarding regardless of their ESRP status.
half-duplex
This is the communication mode in which a device can either send or receive data, but
not simultaneously. (Devices at 1 Gbps or higher do not run in half-duplex mode; they run only
in full-duplex mode.)
heartbeat
message
A
UDP data packet used to monitor a data connection, polling to see
if the connection is still alive.
In general terms, a heartbeat is a signal emitted at
regular intervals by software to demonstrate that it is still alive. In networking, a
heartbeat is the signal emitted by a Level 2 Ethernet transceiver at the end of every packet
to show that the collision-detection circuit is still connected.
hitless failover
In the Extreme Networks
implementation on modular switches and SummitStacks, hitless failover means that designated
configurations survive a change of primacy between the two MSMs (modular switchtes) or
master/backup nodes (SummitStacks) with all details intact. Thus, those features run
seamlessly during and after control of the system changes from one MSM or node to
another.
host
- A computer (usually containing data) that is accessed by a user working on a remote
terminal, connected by modems and telephone lines.
- A computer that is connected to a TCP/IP network, including the Internet. Each host has
a unique IP address.
HTTP
Hypertext Transfer
Protocol is the set of rules for transferring files (text, graphic images, sound, video, and
other multimedia files) on the World Wide Web. A Web browser makes use of HTTP. HTTP is an
application protocol that runs on top of the TCP/IP suite of protocols. (RFC 2616: Hypertext
Transfer Protocol -- HTTP/1.1)
HTTPS
Hypertext Transfer
Protocol over Secure Socket Layer, or HTTP over SSL, is a web protocol that encrypts and
decrypts user page requests as well as the pages that are returned by the Web server. HTTPS
uses Secure Socket Layer (SSL) as a sublayer under its regular HTTP application layering.
(HTTPS uses port 443 instead of HTTP port 80 in its interactions with the lower layer,
TCP/IP.) SSL uses a 40-bit key size for the RC4 stream encryption algorithm, which is
considered an adequate degree of encryption for commercial exchange.