Fritz! Fon WLAN 7390 Installation, Configuration And Operation page 183

Glossary
Outside dialing
prefix
Public IP
address
Port
FRITZ!Box Fon WLAN 7390
own public IP address in all outgoing data packets. The
router saves all necessary information in a table so that in-
coming data packets can then be assigned to the correct
network device.
The outside dialing prefix is the digit dialed at an exten-
sion line to obtain an outside line. Generally this is "0".
A public IP address is an IP address valid in the Internet.
Every computer or router participating in the Internet must
have a uniquely assigned public IP address. This address
is usually negotiated dynamically with the Internet Service
Provider when a connection to the Internet is dialed. The
Internet Service Provider assigns the negotiated IP ad-
dress to the computer or router for the duration of an Inter-
net session.
So that a single network connection on a computer can be
used by multiple applications to exchange data with re-
mote sites at the same time, a computer administers what
are known as ports for the IP-based protocols TCP and
UDP. Ports substantiate the point of access for the data
packets delivered via the IP Internet protocol. While the IP
address determines the destination computer quite gen-
erally, the port addresses the communication interface
provided by an application for a certain communication
procedure.
The Internet protocol allots 16 bits for the specification of
the port number. Thus a total of 65,535 different port
numbers can be specified. Ports up to port number 1,024
are reserved for special system applications and typical
Internet applications. These include, for instance, the port
numbers 21 for FTP (File Transfer Protocol), 25 for SMTP
(Simple Mail Transfer Protocol), 53 for DNS (Domain Name
Service) and 80 for HTTP (Hypertext Transfer Protocol).
Ports are primarily of interest to users for their role in pro-
tecting an Internet connection from external attacks. Most
firewalls offer the possibility of preventing data traffic on
certain ports. This means that certain port numbers can
be blocked to prevent data from being delivered to system
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