Netopia 435 Reference Manual page 115

6-2 Netopia ISDN Router Reference Guide
AppleTalk is a protocol set for local area networks developed by
Apple Computer. While initially applied to the LocalTalk cabling
system for connecting Macintosh computers and LaserWriters, it
has been expanded to use other cabling systems, such as Ethernet,
as well as the dial-up telephone networks and packet switching
systems. LocalTalk was originally known as the AppleTalk Personal
Network system.
Each computer or peripheral device (printer, fax, file server)
connected to a network is called a node and has a unique node
address, which can be any number from 1 to 254. Whenever you
open the Chooser or any application that communicates with other
computers on your network, your application compiles a list of all
node names and addresses. All you see are the names---for
example, "Paul'sMac," "TechSportsWriter," or "2nd Floor Apple-
Share"--but your application also knows the node addresses of all
these devices.
When you send information, commands, or requests to a printer,
server, or another workstation, your application formats the
information into units known as packets. It then attaches the
correct address to the packets and sends them to the AppleTalk
software on your computer, which forwards the packets across the
network. Packets also include a return address, so the receiver will
know where to reply.
If the cabling of your network were a street system, then a node
address would correspond to a building's street address. Node
addresses are not permanent. Each AppleTalk device determines its
node address at startup. Although a Macintosh that is starting up
will try to use its previous address, the address will often be
different every time you restart. This dynamic node addressing
scheme prevents conflicts when devices are moved between
networks and simplifies the administrative tasks of a network. If you
have only one network, the node address alone is all the
information AppleTalk needs to send a packet from one computer to
another.
However, networks can be connected together through routers,
such as the Netopia ISDN Router, into an internetwork (often
shortened to internet). Because devices on different networks can
have duplicate node numbers, AppleTalk tells them apart according
to an additional part of their addresses: the network number.