Accessing the World Wide Web from Home

Many students access the World Wide Web from home

Here is how it works, in terms of standards

2Accessing the WWW from Home

A Common and Important Situation– Must be understood

– Good way of introducing networking concepts

3The Internet

The Internet is a Worldwide Group of Networks– Not a single network

– Individual networks on the Internet are called subnets

4The Internet

Messages are Broken into Small Packets for Transmission, as Noted Earlier– More efficient than sending long messages

Message Packets

5The Internet

Routers– Connect the Internet’s individual networks (subnets)– Cooperate to give an end-to-end route for each packet

Routers

Route

6The Internet

Hosts– Any computer attached to the Internet is a host– Webservers are host– Desktop and notebook PCs are hosts too

Host

Host

7The Internet

Network deliver messages based on network addresses– The Internet has two addressing systems for hosts

IP addresses Host names

Host

Host

8The Internet

Host IP addresses– Strings of 32 ones and zeros– Usually represented by four number segments

separated by dots: dotted decimal notation– For example, 128.171.17.13– Official addresses for hosts

127.18.47.145127.47.17.47

9The Internet

Dotted Decimal Notation

– IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101

– To convert this to dotted decimal notation, first, divide them into four bytes (also called octets)

10000000 10101010 00010001 00001101

– Both octets and bytes are collections of eight bits

10The Internet

Dotted Decimal Notation

– Convert each binary (Base 2) octet into decimal (Base 10)

10000000 is 128 10101011 is 171 00010001 is 17 00001101 is 13

11

The Internet

Value(2N) Bit Decimal

128 1 128

64 0 0

32 1 32

16 0 0

8 0 0

4 0 0

2 1 2

1 1 1

163

Position(N)

7

6

5

4

3

2

1

0

Binary10100011

=Decimal163

Note: Starts with 0

12The Internet

Why dotted decimal notation?

– Strings of 32 bits are very difficult to memorize

– Dotted decimal representations of IP addresses are (somewhat) easier to remember

– So dotted decimal notation is merely a mnemonic device for representing IP addresses

13The Internet

Host Names– The other network addressing system on the Internet

– Easy to remember www.microsoft.com voyager.cba.hawaii.edu Two or more text “labels” separated by dots No relationship between segments and labels

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14The Internet

Host Names– Like nicknames

Not official addresses Each host must have an IP address But only some hosts have host names If you give it a host name, your browser must look

up IP address of host (Chapter 3 discusses how)

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