1. The Internet Salihu Ibrahim Dasuki (PhD) CSC102 INTRODUCTION TO COMPUTER SCIENCE

2.  Aim ◦ Introduce the Internet – with an “I”  Purpose ◦ To understand how the Internet is organised, how messages are addressed, and introduce some examples of Internet applications CSC102 INTRODUCTION TO COMPUTER SCIENCE

3.  The Internet is a collection of connected networks  The networks are maintained by organizations called Internet Service Providers (ISPs)  The system of ISP networks can be classified in a hierarchy CSC102 INTRODUCTION TO COMPUTER SCIENCE

5.  Tier-1 ISPs ◦ Consist of high-speed, high capacity, international WANs – they form the backbone of the Internet  Tier-2 ISPs ◦ More regional, less capable than Tier-1 ISPs  Tier-1 and Tier-2 ISP networks are essentially networks of Routers CSC102 INTRODUCTION TO COMPUTER SCIENCE

6.  Tier-1 ISPs ◦ Consist of high-speed, high capacity, international WANs – they form the backbone of the Internet  Tier-2 ISPs ◦ More regional, less capable than Tier-1 ISPs  Tier-1 and Tier-2 ISP networks are essentially networks of Routers CSC102 INTRODUCTION TO COMPUTER SCIENCE

8.  Access IPs are essentially independent internets operated by a single organization to provide Internet access to individual users ◦ E.g. Baze University will have its own internet  The devices that individual users connect to Access ISPs are known as end systems ◦ E.g. Computers, telephones, televisions CSC102 INTRODUCTION TO COMPUTER SCIENCE

9.  In the Internet, each end-system is identified by a unique address called its IP address  IP stands for Internet Protocol  Originally the IP address was 32 bits in length, giving ◦ 4,294,967,296 unique addresses  It is being converted now to 64 bits, to give ◦ 18,446,744,073,709,551,616 unique addresses CSC102 INTRODUCTION TO COMPUTER SCIENCE

10.  IP addresses are usually written in dotted decimal notation  Each byte is represented in decimal notation  E.g. 10000101 is 133, 10110001 is 177, 11001111 is 207 and 11000000 is 192   The address 11000000110011111011000110000101 is 192.207.177.133 CSC102 INTRODUCTION TO COMPUTER SCIENCE

11.  Binary or dotted decimal notion are not easy for humans to work with!  So an alternative addressing system is available, based on the concept of a domain  A domain is a region of the Internet operated by a single authority, but not necessarily a geographic region. E.g.: ◦ a company, a university, a club, a government agency, etc. CSC102 INTRODUCTION TO COMPUTER SCIENCE

12.  Each domain must be registered with ICANN  ICANN is the Internet Corporation for Assigning Names and Numbers ◦ www.icann.org  Handled by companies called ‘registrars’  As part of registration process, the domain is assigned a domain name, a mnemonic name used to identify the domain CSC102 INTRODUCTION TO COMPUTER SCIENCE

13.  Each domain must be registered with ICANN  ICANN is the Internet Corporation for Assigning Names and Numbers ◦ www.icann.org  Handled by companies called ‘registrars’  As part of registration process, the domain is assigned a domain name, a mnemonic name used to identify the domain CSC102 INTRODUCTION TO COMPUTER SCIENCE

14.  aun.edu.ng is the domain name of American University of Nigeria  bbc.co.uk is the domain name of the BBC  microsoft.com is the domain name of Microsoft  Note the ‘.com’, ‘.ng’, ‘.uk’, and ‘.edu’ CSC102 INTRODUCTION TO COMPUTER SCIENCE

15.  Top-level Domains (TLDs)  The suffix (e.g..com) reflects the domain’s classification: .com – commercial .org – non-profit organisation .edu – educational organisation .gov – U.S. government institutions .info – unrestricted use .net – originally intended for ISPs .us,.uk,.ng, etc. – country-level TLDs CSC102 INTRODUCTION TO COMPUTER SCIENCE

16.  Top-level Domains (TLDs)  The suffix (e.g..com) reflects the domain’s classification: .com – commercial .org – non-profit organisation .edu – educational organisation .gov – U.S. government institutions .info – unrestricted use .net – originally intended for ISPs .us,.uk,.ng, etc. – country-level TLDs CSC102 INTRODUCTION TO COMPUTER SCIENCE

17.  Top-level Domains (TLDs)  The suffix (e.g..com) reflects the domain’s classification: .com – commercial .org – non-profit organisation .edu – educational organisation .gov – U.S. government institutions .info – unrestricted use .net – originally intended for ISPs .us,.uk,.ng, etc. – country-level TLDs CSC102 INTRODUCTION TO COMPUTER SCIENCE

18.  Domain names are converted to IP addresses by means of name servers – directories that provide address translation to clients  Collectively, the set of name servers on the Internet are called the domain name system (DNS)  The process of using DNS to find an IP address is referred to as DNS lookup CSC102 INTRODUCTION TO COMPUTER SCIENCE

19.  An executing computer program is a process  A process can be stand-alone, a client or a server  A client requests services from other processes  A server provides services for other processes CSC102 INTRODUCTION TO COMPUTER SCIENCE

20.  Clients can connect to servers to request services  Clients and servers can be on separate computers located anywhere on the Internet  DNS lookup is an example – DNS directories are spread out across the Internet CSC102 INTRODUCTION TO COMPUTER SCIENCE

21.  There are many “Internet” applications  Electronic Mail (email) – uses mail servers to distribute electronic mail messages  Voice over IP (VoIP) – Internet telephone  Internet radio – listen to home radio stations streamed on the Internet while on travel  And many others CSC102 INTRODUCTION TO COMPUTER SCIENCE

22.  Computers distributed (i.e. Spread out) across the Internet can work together to solve computational problems and provide computer services  Three types – ◦ Cluster Computing – many computers work together to mimic a more powerful computer ◦ Grid Computing – enables millions of computers to work on complex mathematical and scientific problems ◦ Cloud Computing – large numbers of shared computers can be offered to clients as computing and storage resources CSC102 INTRODUCTION TO COMPUTER SCIENCE

23.  The Internet is an example of an internet – a network of networks  The Internet is maintained by Internet Service Providers (ISPs)  Each device on the Internet has a unique IP address  The Internet offers the possibility of a wide range of applications, many based on the client/server model CSC102 INTRODUCTION TO COMPUTER SCIENCE