Administrator's Guide
Appendix D. Definitions of terms
Server
A server can be a program that performs a service on a network or a computer that runs
one or more server programs. One example is a computer that stores files centrally,
which makes it a kind of server, usually called a file server. The program that manages
traffic so that people from the outside can access an organization’s web pages is a server
program.
SIP
SIP, Session Initiation Protocol, is a protocol for creating, maintaining and terminating
various media stream sessions over an IP network. SIP is used to negotiate which me-
dia streams the parts can send and receive, and which parts should be involved in the
exchange. When this is established, the media streams are sent according to their own
protocols (e.g. HTTP). A thorough description of SIP can be found in RFC 2543.
SLIP
SLIP is short for Serial Line IP. This is usually used to send IP packets over modem
connections. See IP.
SLIRP
SLIRP is a program that sends IP packets over serial connections, such a modem con-
nections. SLIRP is run as a user program. SLIRP does not need its own IP address; it
uses the server’s IP address. The program works with both SLIP and PPP clients. See
IP.
SMTP
Simple Mail Transfer Protocol, a protocol for sending e-mail between e-mail servers.
SMTP uses port 25.
SNMP
A protocol used for network monitoring. SNMP uses ports 161 and 162.
Sockets
When two computers connect to each other, they use their IP addresses and port num-
bers. The combination of an IP address and a port number is called a socket. See IP
addresses and Ports.
SSH, Secure SHell
SSH is a system for secure, encrypted connections between two computers over a net-
work. SSH uses one open and one secret key. In contrast to Kerberos, SSH does not use
a central server for security. SSH uses port 22.
SSL
SSL is short for Secure Sockets Layer. The SSL protocol handles establishing of en-
crypted computer connections. Usually HTTP and WWW traffic is sent on SSL. HTTP
on SSL is called HTTPS.
Static Routing
A fixed path for the contact between computers. With a static routing, traffic cannot
be redirected to another path if the connection is broken. This would require dynamic
routing, for example, with RIP.
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