To ensure data integrity, the information needs to be protected from
unauthorised manipulation while it is being transmitted. To ensure
that this happens, every item of communication received has to
match the information originally sent. Therefore erratic mathematical
value functions (hash functions) are used to calculate checksums
(hash values). These are encrypted and sent as a digital signature
with the message. The recipient, in turn, checks the signature before
opening the packet. If the signature and, thus, the content of the
data packet has changed, the packet is discarded. The hash al-
gorithms used most frequently are Message Digest Version 5 (MD5)
and Secure Hash Algorithm (SHA1).
High Data Rate Digital Subscriber Line. See DSL.
A network's subscribers use heartbeats to signal that they are ready
to receive.
A telephone call is put on hold without breaking the connection
(inquiry/brokering). A distinction is drawn between holding the con-
nection in the PBX (holding in the system) and holding in the switch-
board or by the SIP provider.
With hold for enquiry, the phone call with the first party is held while
one conducts a second call.
Hop is the term for the connection from one network node to the
next.
A host is a computer system that provides its services to the net-
work.
The domain name of a host. See DNS.
A host route is the name for the route to a single host.
A hotspot is a public internet access point via WLAN or wired Ether-
net.
High Speed Downlink Packet Access (HSDPA, 3.5G, 3G+ or UMTS
broadband) is a data transmission method in the UMTS mobile com-
munications standard.
The HyperText Transfer Protocol (HTTP) is a protocol for transmit-
ting HTML pages (web pages) between server and client. By default
it uses port 80.
The HyperText Transfer Protocol Secure (HTTPS) is a protocol
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Glossary
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