16

CHAPTER 1. THE INTERNET

mainframe computers).

The 80s saw the rapid prolifieration of PC's and workstations combined

into small local area networks (LANs) and these LANs came to be added to the

ARPANET in greater numbers, resulting in a rapid growth of the internet. Also,

in 1985, the NSFNET was formed by the National Science Foundation with the

stipulation that a university could connect to this network only if it provided ac 

cess to all scholars at the institution, not just the science departments. Another

important development during the 1980's was the connection of networks into a

single internet all using the TCP/IP protocol for communication. The 90's saw

the birth of the World Wide Web and the rapid expansion of the internet both

in terms of size and in terms of its use by the general population.

1.2

Internet Addressing: domain names and IP

addresses

The internet currently consists of about 100 million servers although this number

grows every month (and actually oscillates minute by minute for reasons that

will become clear). Each computer on the internet has a unique identification

number called its IP address (for Internet Protocol). An IP number consists

of a sequence of four numbers in the range 0 255. For example, a typical IP

address at Brandeis in 2002 is 129.64.2.10, where the numbers in the IP address

are separated by periods by convention. This is the dotted decimal form of an

IP address.

IP addresses are actually stored on the computer and transmitted as 32 bit

long binary numbers. Please read the appendix on binary numbers to learn

about binary numbers and how they are used to represent decimal numbers.

Most computers on the internet also have an identifying name known as a

domain name. For example, the domain name for the main Brandeis web server

is www.brandeis.edu and its IP address is 129.64.99.138. The relationship

between domain names and IP addresses is available on the net from computers

known as domain name servers.

The internet actually consists of a large number of networks which are seam 

lessly interconnected. For example, the Local Area Network (LAN) at Brandeis

University consists of a few thousand computers. These computers are all di 

rectly connected to the internet and have IP addresses of the form

129.64.xxx.yyy

where xxx and yyy are numbers in the range 0 255. Conversely, any IP address

of this form refers to the Brandeis LAN. Thus, the Brandeis LAN can expand

to include up to 256 x 256 = 65536 computers which can all be simultaneously

directly connected to the internet. This method of allocating IP addresses in

blocks is widely used today.