Administrator's Guide
Appendix D. Definitions of terms
PPP
PPP is short for Point-to-Point Protocol. This is usually used to send IP packets over
modem connections. See also IP.
Protocols
Protocols are sets of rules for how programs communicate with each other. For exam-
ple, a web server can use the protocols HTTP and HTTPS.
Proxy
Proxies are devices through which web pages, FTP files, and so on can be retrieved for
a local network. This can be good to combine with a cache memory, which will store
pages and files once fetched from the Internet site. When another user wants to look at
a page already in the cache, it acts as a web server, sending the cached page instead of
fetching a new copy through the Internet.
In your web browser, specify a computer and cache/proxy to be used to store this infor-
mation.
Relay
When the local network is connected to the Internet through a firewall, all types of
services are usually blocked. It is as if the network is not connected to the Internet.
Relays can then be set up to allow certain services, such as the WWW, to pass through
under controlled circumstances. Think of it as a giant stone wall with a gate and a
specialized gate keeper. The gate keeper only lets certain visitors pass. To allow others
to pass through, you set up another gate with another specialized gate keeper.
Request-URI
A Request-URI is used by the SIP protocol to indicate where a SIP request should be
sent. The Request-URI can contain a username, a SIP domain or an IP address. It also
contains the sip/sips parameter (sips if the request should be sent encrypted all the way,
sip if not) and the SIP version (usually SIP/2.0).
RFC
An RFC (Request For Comments) is a document which standardizes some aspect of
the Internet traffic. RFC:s are available at http://rfc.dotsrc.org/rfc-url.sgml.
RIP
RIP is a protocol that manages dynamic routing. Dynamic routing means that the path
for traffic can be changed. RIP selects the path that goes through the least number of
routers, but does not consider the bandwidth or load on the network. RIP is only used
in local networks. Fixed paths for traffic are called static routing.
Router
A router is a machine that is used to connect several smaller and larger networks. Often,
a router is used to connect a local network to the Internet. This router only lets traffic
to the Internet out; all other traffic remains on the local network. A router can also be
called a gateway.
Routing
A routing is a path for the traffic between different computers.
354