12Lecture 15 1

The Internet

Overview Internet / Intranet TCP/IP IP address IP address Classes Calculating the IP address

Domain Names

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The Internet

The Internet is a WAN which spans the entire planet

The word Internet comes from the term internetworking, which implies communication among networks

It started as a United States government project, sponsored by the Advanced Research Projects Agency (ARPA), and was originally called the ARPANET

The Internet grew quickly throughout the 1980s and 90s

Less than 600 computers were connected to the Internet in 1983; now there are over 10 million

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TCP/IP

A protocol is a set of rules that determine how things communicate with each other

The software which manages Internet communication follows a suite of protocols called TCP/IP

The Internet Protocol (IP) determines the format of the information as it is transferred

The Transmission Control Protocol (TCP) dictates how messages are reassembled and handles lost information

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IP and Internet Addresses

Each computer on the Internet has a unique IP address, such as: 204.192.116.2

Most computers also have a unique Internet name, which is also referred to as an Internet address:

renoir.villanova.edu

kant.breakaway.com

The first part indicates a particular computer (renoir) The rest is the domain name, indicating the organization

(villanova.edu)

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Structure of The InternetThe Internet is a global IP internetwork - any Internet connected host can (in principle) send IP packets to any other. A hardware device which interconnects two networks is formally called an IP Gateway, or more commonly a router. A router has two (or more) IP addresses - one for each of the networks to which it is connected. Datagrams navigate zero or more (sometimes many) routers, interconnecting the individual networks which together make up the Internet:

                                                              

IP Address

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IP Addresses

The IP protocol provides the basic host-to-host delivery service for TCP/IP. Fundamental to this is the concept of a global internet addressing scheme. In IP, every computer has a unique internet host address. This is a 32 bit, or 4 byte, binary number.

Internet addresses are written (for human consumption) as a dotted sequence of the form:

aa.bb.cc.dd where aa, bb, etc, are the decimal values (ranging from 0 to 255) of the 4 bytes which make up the internet address, for example:

149.144.21.60 This is called the "Common Internet Address Notation" The 32 bit internet address consists of 2 parts, the network part and the host part. The network part must be the same for all hosts connected to the same network. In this context, a network usually means something like a single Ethernet LAN.

The host part must be a number unique to that specific network.

IP Address continue

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Network ID and Host ID

Network ID Host ID

------------------- 32 bit-----------------------

10000011 01101011 00000011 00011000

131. 107. 3 .24

W . X . Y . Z

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Class IP address Network ID

Host ID

A w.x.y.z W8

x.y.z

24 bit

B w.x.y.z w.x16 bit

y.z

16 bit

C w.x.y.z w.x.y24 bit

Z8 bit

Converting IP Addresses from Binary to Decimal

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IP classes

Class A

Class A ddress are assigned to networks with a very large number of hosts. The high-order bit in a class A address is always set to zero. The next 7 bits(completing the first octet) complete the network ID. The remaining 24 bits( the last three octets)represent the host ID. This alows for 126 networks and aprroximately 17 million hosts per network.

Class B

Class B addresses are assigned to medium-sized to large sized network. The two hih-order bits in a class B address are always set to binary 10. The next 14 bits(last two octests)represent the host ID. This allows for 16,384 networks and approximately 65,000 hosts per network.

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IP classes Class CClasss C addresses are used for small LANs. The three high-order

bits in a class C address are always set to binary 110. The next 21 bits(completing the first three octets) complete the network ID. The remaining 8 bits( last octet) represent the host ID. This allows for approximately 2 million networks and 254 hosts per network

Class D Class D addresses are used for multicast group usage. A multicast

group can contain one or more hosts, or none at all. The four high order bit in a class D address are always set to binary 1110. The remaining bits designate the specific group in which the client participates. There are no network or host bits in the multicast operations. Packets are passed to a selected subset of hosts on a network.

Only those hosts registered for the multicast address accept the packet.

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Class Most significant bit

MIN MAX Number bit

Network

Number of networks

Number of hosts per network

A 0 0 1268

8 12627

16,777,214224

B 10 128 19116

16 16,384214

65,534216

C 110 192 22324

24 2,097,152221

254

28

The network ID cannot be 127. This ID is reserved for loopback and diagnostic funcitons

Calculating the IP class

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examples

Examples

Write the address class.

80.1.1.100=== class A network number is 80

135.98.0.0

200.135.80.10

S

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Domain Names

The last section (the suffix) of each domain name usually indicates the type of organization:

edueducomcomorgorgnetnet

- educational institution- educational institution- commercial business- commercial business- non-profit organization- non-profit organization- network-based organization- network-based organization

Sometimes the suffixSometimes the suffixindicates the country:indicates the country:

New suffix categoriesNew suffix categoriesare being consideredare being consideredukuk

auaucacasese

- United Kingdom- United Kingdom- Australia- Australia- Canada- Canada- Sweden- Sweden

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Domain Names

A domain name can have several parts

Unique domain names mean that multiple sites can have individual computers with the same local name

When used, an Internet address is translated to an IP address by software called the Domain Name System (DNS)

There is no one-to-one correspondence between the sections of an IP address and the sections of an Internet address

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The World-Wide Web

The World-Wide Web allows many different types of information to be accessed using a common interface

A browser is a program which accesses and presents information» text, graphics, sound, audio, video, executable programs

A Web document usually contains links to other Web documents, creating a hypermedia environment

The term Web comes from the fact that information is not organized in a linear fashion

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The World-Wide Web

Web documents are often defined using the HyperText Markup Language (HTML)

Information on the Web is found using a Uniform Resource Locator (URL):

http://www.lycos.com

http://www.villanova.edu/webinfo/domains.html

ftp://java.sun.com/applets/animation.zip

A URL indicates a protocol (http), a domain, and possibly specific documents