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Every computer that is connected to the internet is part of a network, even the one in our home.
For example, we may use a modem and dial a local number to connect to an Internet Service

Provider (ISP). At work, a computer may be part of a Local Area Network (LAN), but it most likely
still connects to the internet using an ISP that the company has contracted with. When it connects
to the ISP, it becomes part of their network. The ISP may then connect to a larger network and
become part of their network. The internet is simply a network of networks.
Most large communication companies have their own dedicated backbones connecting various
regions. In each region, the company has a Point of Presence (POP). The POP is a place for local
users to access the company’s network, often through a local phone number or dedicated line. The
amazing thing here is that there is no overall controlling network. Instead, there are several high-
level networks connecting to each other through Network Access Points or NAPs.

Fig. 8.4(b): POP and NAP

Gateway: Gateway is a device that connects dissimilar networks. A backbone is a central
interconnecting structure that connects one or more networks just like the trunk of a tree.

At the source computer the message to be sent is broken down into small parts called packets. Each
packet is given a serial number, e.g., 1, 2, 3. All these packets are sent to the destination computer.
The destination computer receives the packets in random order (10 may come before 1). The
packets are reassembled in the order of their number and message is restored.

How it functions smoothly: Every computer connected to the internet uses the same set of rules
for communication. A set of rules is called protocol. Communication protocol used by internet is
TCP/IP. The TCP (Transmission Control Protocol) part is responsible for dividing the message
into packets on the source computer and reassembling them at the destination computer. The IP
(Internet Protocol) is responsible for handling the address of the destination computer so that the
packet is sent to its proper destination.
8.4.1 Elementary Terminology of Networks

1. Nodes (Workstations): The term node refers to computers that are attached to a network and
are seeking to share resources.
2. Server: A computer that facilitates the sharing of data, software and hardware resources on
the network. Computer Networks
3. Network Interface Unit (NIU) (MAC Address): A network interface unit is an interpreter that
helps in establishing communication between the server and the client.
8.5