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96 APPENDIX A: NETWORKING PRIMER
How does a LAN connect
to a WAN?
You can connect a LAN to a WAN via a number of devices such as a router or a
bridge that can place a call to the remote LAN using an analog telephone line.
Routers and bridges are devices that link networks. A bridge sends every bit of
information across the WAN while a router is considered a more sophisticated
device because of its ability to route only the desired bits of information across the
WAN. Routers are also capable of monitoring the integrity of the data and
transmission path.
What is a LAN Modem? A LAN Modem is a hybrid device which combines the dial-up capabilities of a
standard modem and an Ethernet hub. This eliminates the computer COM port
speed bottleneck associated with serial port based modems (the LAN runs at 10
Mbps) while providing local networking between the attached computers on the
LAN. Even with this sophisticated functionality, a LAN Modem is easy to install and
use and presents an ideal solution for small networks.
What is a POTS
connection?
POTS stands for “Plain Old Telephone Service” and refers to a basic telephone
connection without any added features or functions. A POTS line is used to
connect analog devices, such as a telephone, fax machine, or your 56K LAN
Modem to the public telephone network.
How do different
devices communicate
with each other?
Once the computers are physically connected in a network, they must run some
type of standard communications software that allows different types of
computers to communicate with each other. Transmission Control
Protocol/Internet Protocol (TCP/IP) is becoming the most common software used
to accomplish this.
What is TCP/IP? TCP/IP is a standardized communications protocol that works across LANs and
WANs, allowing different devices to communicate with each other. As its name
indicates, TCP/IP has two main components; TCP and IP. TCP manages the transfer
of data and corrects any errors that occur during transmission, ensuring that data
is reliably transferred. IP is responsible for routing the data in packets from one
location to another across a network. It then uses the source and destination
information contained within each data packet to determine the proper routing
and destinations for each packet of information.
Note that TCP/IP encompasses more than the two protocols which define its
name. It provides additional functions comprises various software applications that
allow various network services such as remote file transfer (FTP), remote login
(Telnet), as well as email Simple Mail Transfer Protocol (SMTP) and Post Office
Protocol (POP) 3.
What is an IP Address? An IP address is a 32 bit address used by TCP/IP to uniquely identify the location of
a device on a network. Note that the IP address does not refer to the device itself.
If, for example, you relocate a PC to another area of the same network, you may
need a new IP address.
The structure of this 32-bit address varies depending upon the size of the network
on which the device is located. From largest to smallest, network types are
referred to as Class A, Class B, Class C, and Class D. Within each class, a certain
number of bits identifies the class, the network and the local address. For
example, in a Class C network the first three bits (110) identify the network type