History of the Internet

1. History of the Internet • Mid 1960’s During the Cold War – need for bomb proof communications system. • Government Agency and few Universities • Emergency military communications system operated by Department of Defense’s Advanced Reserarch Project Agency (ARPA) – ARPANET • Eventually all Universities with defense related projects connected to ARPANET • Military pipeline to communication tool for scientists ARPA transferred to National Science Foundation. • Years later businesses began using the internet and the administrative responsiblilities were again transferred. • No one party operates the internet, but there are several entities that oversee the system and the protocols involved

2. A Basic Guide to the Internet What is the Internet? Network of Networks Computers communicate over the internet using TCP/IP (Transmission Control Protcol / Internet Protocol) Client / Server Architecture Funding the Internet Funded through Agencies ( National Science Foundation, Government agencies pay for some high speed backbones)

3. Who Runs the Internet – overseen by a variety of groups to establish standardss • Internet Society (A private nonprofit organisation) • IETF (Internet Engineering Task Force) TCP/IP • W3C (World Wide Web Consortium) MIT • Private Companies oversee the registering of Internet Domains.

4. Underlying Architecture of the Internet We are going to look at the following Architectures • How computers send data across the internet • How TCP/IP works • How Internet Addresses and Domain Names Work • How Routers Work How Computers send data across the Internet • TCP/IP • Hubs • Bridges • Gateways • Repeaters • Routers

5. How Computers Send Data • TCP – breaks the data into packet • Computer sends those packets – local Network, Internet Service Provider (ISP), or On-Line Service • Packets then travel through many levels of networks, computers, and communication lines before reaching their final destination. • Variety of Hardware transmits the data between various networks. Five most important pieces of hardware are: • Hubs usesd to link groups of computers to one another and lets computers communicate with each other. • Bridges Links one LAN with another LAN • Gateways like Bridges but allow communication between different types of networks • Repeaters - when data travels over long distance the signal sending the data can weaken over long distances, repeaters are used to amplify the data at interval • Routers come into play when data being sent between two different networks, examine packets for destination and select the quickest route taking into account traffic on the internet.

6. How TCP/IP Works • The Internet is a packet switched network • Messages broken into a number of packets + data to help the packet find its way through the Internet (TCP) • Series of switchs called routers (IP) ensures that the packages arrive at their correct destination • Packets are sent over many different routes at the same time • Hardware restriction – data broken into packets of 1,500 bytes each. • Packet given header with order of packet & checksum (based on the amount of data in packet) • Each packet is put into separate IP envelopes, which contains addressing information telling the Internet where to send the packet • IP envelopes contain headers that contain informations • Senders Address • Destination Address • Amount of time packet should be kept

7. As packets sent across Internet Routers examine IP envelope destination addresses and determine the most efficient route for sending each packet. (Packets can arrive out of order) • Packets arrive at their destination and TCP calculates the checksum for each packet (error checking) • When all noncorrupt packets arrive at their destination TCP assembles them into their original form • Winsock software (TCP/IP stack or Socket) serves as an intermediary between the Internet and PC • Two ways to connect to the Internet and use the TCP/IP protocol • Direct connection (via LAN, cable modem, DSL line – needs a network card & hardware driver) • Dialing connection (Modem) • Serial Line Internet Protocol (SLIP) • Point-to-Point Protocol (PPP)

8. Sample Internet Connections The basic idea of communication via the internet is to have two remote sites or computers connected together via a network or transmission line

9. Internet Addresses and Domain Names The Heart of the Internet work is the Domain Name System (DNS), the way in which computers can contact each other and do things such as e-mail or display web pages. If a user wants to contact a specific location – e.g. visit Web pages they type in the address (URL) – www.computing.dcu.ie while numbers are convenient for machines, they are not for human beings, therefore humans use names for addresses and TCP/IP uses it DNS (Domain Name System) application (Name Servers) to provide name-to-address translation. The DNS translates the plain english address into a series of numbers called an IP address, 136.2.6.11.XXX An IP address marks the location on the internet similar to a house number and street address. All computers connected to the Internet must have an IP address.

10. DHCP Server Two types of IP address exist • Static IP Addresses • Dynamic IP Addresses Dynamic IP Addresses DHCPDISCOVER DHCPOFFER DHCPREQUEST DHCPPACK

11. Domains can be organised in Hierarchy • Major Domains and minor domains • www.computing.dcu.ie • .ie is the major domain • .dcu is the Dublin City University Domain • .computing is the computer applications server • Some Common Major Domain Names in the United States are: .edu for educational institution, usually a university .com for a commercial business .gov for a government department or agency .mil for a military unit .org for a non-profit organisation Following introduced to reduce the load on .com domain not all are in use yet as they officially registered. .areo for aviation industry .info for general use .biz for business .coop for cooperatives .museum for museums .name for individuals .pro for professionals

12. As networks in other countries were connected to the Internet, they were assigned their own domain names • ie Ireland • ca Canada • au Australia • uk United Kingdom • de Germany In total there are more than 250 top-level domain names The IP address is a 32 bit number but is now being expanded to 128 bit number to allow for more IP addresses to be accommodated. Since networks vary in size, there are four different address formats or classes to consider when applying to NIC for a network number: Class A addresses are for large networks with many devices. Class B addresses are for medium-sized networks. Class C addresses are for small networks (fewer than 256 devices).

13. The IP address is usually made up of two parts, 1st part identifies the network, the 2nd the node (host or actual computer). An IP address is expressed as four decimal numbers (octets), each representing eight bits, separated by periods. The first few bits of each IP address indicate which of the address class formats it is using. The address structures look like this: 130.5.5.25 Each of the decimal digits represents a string of four binary digits. Thus, the above IP address really is this string of 0s and 1s: 10000010.00000101.00000101.00011001 Class A 0Network (7 bits values 1-126)Local address (24 bits, 3 remaining octets used to identify host) Class B 10Network (14 bits first octet 128-191 + second octet used to identify network)Local address (16 bits, 2 octets used to identify host) Class C 110Network (21 bits, first octet 192-223, 1st , 2nd and 3rd octet identify network)Local address (8 bits, 1 octet identifies host)

14. URL (Uniform Resource Locator) URLs uniquely identify each file on the web by specifying its name, what server it is on, and where it resides in the server’s directory structure and how the page can be accessed. http://www.compapp.dcu.ie/NT_Software/index.html • The http:// tells the browser which protocol to use to access the web page. In this case the protocol is “hypertext transfer protocol”. This protocol is the set of rules by which a HTML document is transferred over. • Next www.comapp.dcu.ie is the name of the Internet host at which the resource is located. • Following this you specify a path to a particular directory, in this case you start at the root directory and go down one level to the NT_Software directory. • Finally index.html is the file holding the page you seek.

15. Protocols that may appear in URL’s Much of the power of browsers is that they are multiprotocol. That is, they can retrieve and render information from a variety of servers and sources.

16. How Routers Work Routers are traffic cops of the Internet. They ensure that data gets to its final destination via the most efficient route. • Routers check the IP envelopes for the destination address • Calculate the best route and then send the package on its way • Router send packet to another router closer to its final destination, this router in turns forwards the package on to a router closer to the final destination. • Each router has to consider factors such as • Traffic congestion • Number of hops (IP packets carry a segment that holds the max hop count)

17. Routers have two or more physical ports • Input port (routing process run, routing table) • Output port (results from the routing process defines with output port the routes the packets should follow) • Input queue (holding area for input port, queue capacity exceeded – lost data) Routing Table • Static – simplier and specifies specific paths for packets • Dynamic – packets can have multiple routes to their final destination (table changes as network conditions change). Two broad type of routing protocols exist • Interior (Gateway Routing Information Protocol (IGRP)) • Exterior (Exterior Gateway Protocol (EGP))