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The NAT technology enables connection from local networks to the Internet using
a single IP address. All hosts within the local network can access the Internet di-
rectly as if they were on a public network (certain limitations are applied). Services
running on local hosts can be mapped to the public IP address.
Network adapter
The equipment that connects hosts to a traffic medium. It can be represented by
an Ethernet adapter, TokenRing adapter, by a modem, etc. Network adapters are
used by hosts to send and receive packets. They are also referred to throughout
this document as a network interface.
P2P network
Peer-to-Peer (P2P) networks are world-wide distributed systems, where each node
can represent both a client and a server. These networks are used for sharing of
big volumes of data (this sharing is mostly illegal). DirectConnect and Kazaa are
the most popular ones.
Packet
Basic data unit transmitted via computer networks. Packets consist of a header
which include essential data (i.e. source and destination IP address, protocol type,
etc.) and of the data body,. Data transmitted via networks is divided into small
segments, or packets. If an error is detected in any packet or a packet is lost, it is
not necessary to repeat the entire transmission process, only the particular packet
will be re-sent.
POP3
Post Office Protocol is a protocol that enables users to download messages from
a server to their local computer. It is suitable for clients who don’t have a perma-
nent connection to the Internet.
Port
16-bit number (1-65535) used by TCP and UDP for application (services) identifica-
tion on a given computer. More than one application can be run at a host simulta-
neously (e.g. WWW server, mail client, FTP client, etc.). Each application is identified
by a port number. Ports 1-1023 are reserved and used by well known services (e.g.
80 = WWW). Ports above 1023 can be freely used by any application.
PPTP
Microsoft’s proprietary protocol used for design of virtual private networks (see
chapters concerning VPN).
Private IP addresses
Local networks which do not belong to the Internet (private networks) use reserved
ranges of IP addresses (private addresses). These addresses cannot be used in