1 12Lecture 15 The Internet Overview  Internet / Intranet  TCP/IP  IP address  IP address Classes  Calculating the IP address  Domain Names

2 Lecture 15 The Internet l The Internet is a WAN which spans the entire planet l The word Internet comes from the term internetworking, which implies communication among networks l It started as a United States government project, sponsored by the Advanced Research Projects Agency (ARPA), and was originally called the ARPANET l The Internet grew quickly throughout the 1980s and 90s l Less than 600 computers were connected to the Internet in 1983; now there are over 10 million

3 Lecture 15 TCP/IP l A protocol is a set of rules that determine how things communicate with each other l The software which manages Internet communication follows a suite of protocols called TCP/IP l The Internet Protocol (IP) determines the format of the information as it is transferred l The Transmission Control Protocol (TCP) dictates how messages are reassembled and handles lost information

4 Lecture 15 IP and Internet Addresses l Each computer on the Internet has a unique IP address, such as: l 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 )

5 12Lecture 15 Structure of The Internet T he 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

6 12Lecture 15 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: 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

7 12Lecture 15 Network ID and Host ID Network IDHost ID  bit  W. X. Y. Z

8 12Lecture 15 ClassIP addressNetwork ID Host ID Aw.x.y.zW8W8 x.y.z 24 bit Bw.x.y.zw.x 16 bit y.z 16 bit Cw.x.y.zw.x.y 24 bit Z 8 bit Converting IP Addresses from Binary to Decimal

9 12Lecture 15 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.

10 12Lecture 15 IP classes l Class C Classs 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 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.

11 12Lecture 15 ClassMost significant bit MINMAXNumber bit Network Number of networks Number of hosts per network A ,777, B , , C ,097, The network ID cannot be 127. This ID is reserved for loopback and diagnostic funcitons Calculating the IP class

12 12Lecture 15 examples Examples Write the address class ===  class A network number is lSlS

13 Lecture 15 Domain Names l The last section (the suffix) of each domain name usually indicates the type of organization: educomorgnet - educational institution - commercial business - non-profit organization - network-based organization Sometimes the suffix indicates the country: New suffix categories are being considered ukaucase - United Kingdom - Australia - Canada - Sweden

14 Lecture 15 Domain Names l A domain name can have several parts l Unique domain names mean that multiple sites can have individual computers with the same local name l When used, an Internet address is translated to an IP address by software called the Domain Name System (DNS) l There is no one-to-one correspondence between the sections of an IP address and the sections of an Internet address

15 Lecture 15 The World-Wide Web l The World-Wide Web allows many different types of information to be accessed using a common interface l A browser is a program which accesses and presents information »text, graphics, sound, audio, video, executable programs l A Web document usually contains links to other Web documents, creating a hypermedia environment l The term Web comes from the fact that information is not organized in a linear fashion

16 Lecture 15 The World-Wide Web l Web documents are often defined using the HyperText Markup Language (HTML) l Information on the Web is found using a Uniform Resource Locator (URL): ftp://java.sun.com/applets/animation.zip l A URL indicates a protocol (http), a domain, and possibly specific documents