DT266/3 Internet Application Development

1. DT266/3 Internet Application Development The Internet

2. Internet • “The Internet is a worldwide system of computer networks, a network of networks in which users at any one computer can, if they have permission, get information from any other computer” • http://www.whatis.com

3. Internet • "Internet" refers to the global information system that – (i) is logically linked together by a globally unique address space based on the Internet Protocol (IP) or its subsequent extensions/follow-ons;(ii) is able to support communications using the Transmission Control Protocol/Internet Protocol (TCP/IP) suite or its subsequent extensions/follow-ons, and/or other IP-compatible protocols; and(iii) provides, uses or makes accessible, either publicly or privately, high level services layered on the communications and related infrastructure described herein. • Federal Networking Council (1995)

4. So what is it? • The Internet is a network…

5. So what is it? • …of networks...

6. So what is it? • …comprised of nodes, each of whom cancommunicate with eachother using a standard set of rules... NODE B NODE A INTERNET TCP/IP

7. TCP/IP • Transmission Control Protocol/Internet Protocol • Carries information around the Internet for us • Hold on… • What is a protocol? • Why do we need it?

8. Protocol • The forms of ceremony and etiquette observed by diplomats and heads of state. • A code of correct conduct: safety protocols; academic protocol. • http://www.dictionary.com • …what they’re really saying is that a protocol is… • an agreed set of rules • or, in computer science • A standard procedure for regulating data transmission between computers. • http://www.dictionary.com

9. Protocol • Why is it so important for the Internet • Consider postal system... • Internet is comprised of networks of networks • Each network contains different types of nodes/hosts • Unix • Windows • Each network is (possibly) a different type • speaks a different language • Need a common standard

10. TCP/IP • IP • Internet Protocol • Gives every node connected to the Internet a unique address • Provides a standard message type for nodes to send messages between eachother • This protocol is agreed by all nodes connected to the Internet to allow them to communicate in the same language

11. IP - Internat Addressing • All nodes have a unique address • Each address is represented by 32 bits • e.g. 10010011111111001000010000101011 • broken into four parts separated by a decimal point • e.g. 10010011. 11111100.10000100.00101011 • and converted to decimal • e.g. 147.252.132.43

12. IP – Message Format • There exists a specific format for messages that nodes send to eachother • Application data is appended onto the message

13. TCP • TCP is the transmission control protocol • It ensures that IP messages are delivered • IP and TCP exist at two separate levels, or layers in the protocol stack

14. Protocol Stack Application Layer Transport Layer Network Layer • Application, such as web browser wishes to send a message. • Puts together its message using its own protocol (HTTP - we will meet this again later) and hands it down to transport layer APP

15. Protocol Stack Application Layer Transport Layer Network Layer • Transport layer receives message and wraps it up using its own protocol - TCP • Resulting message is handed down to Network Layer. TRANS APP

16. Protocol Stack Application Layer Transport Layer Network Layer • Network Layer receives message and wraps it up using its own protocol, IP and sends it across the network, i.e. over the Internet, with the IP address of its destination NW TRANS APP INTERNET

17. Protocol Stack • The final message, called an IP packet, is sent from node to node, using a process called routing (outside the syllabus of this course). • Each node looks at the destination address and forwards the message onwards. • When the node reaches the destination the encapsulation process we just witnessed is reversed.

18. Protocol Stack Application Layer Transport Layer Network Layer • Destination network layer receives message after it was routed across the Internet. • NW Layer removes the contents and passes it up to the Transport Layer NW TRANS APP INTERNET

19. Protocol Stack Application Layer Transport Layer Network Layer • Transport layer looks at message. Then sends an acknowledgement back to the sending node. This is a confirmation that the message was sent. • It then removes the contents of its packet and hands it up to the application layer TRANS APP

20. Protocol Stack Application Layer Transport Layer Network Layer • The application layer has now received the message that was sent to it by the other application, somewhere else on the Internet. • This layering concept is very common, and is core to computer networking. • It separates functions and protocols i.e. NW Layer handles routing and addressing, TR Layer handles errors and lost packages, APP Layer uses the information. APP

21. TCP/IP and OSI • The example we have just seen is quite simplified. • There are two separate protocol stacks • OSI Protocol Stack • TCP/IP protocol stack. • OSI has seven layers • TCP/IP has five layers • Our example illustrated the functionality of the three layers most important to us, as Internet Developers. • You may like to take a look at “James Bond and the seven layer reference model”.

22. Internet Addressing - DNS • So… • All nodes/hosts on the Internet have a unique address? • Yes, we just saw that! • And if I want to talk to another node I need to know it’s address? • Well, not quite? • Huh? • Well, most hosts have names as well. Host names! • I see, so does IP understand these names as well. • No, but we have a translator to switch between names and addresses. DNS, the Domain Name Service. • WOW! How does it work? ??? !!!

23. Domain Names • A domain name locates an organisation or other entity on the Internet • www.ireland.com • This represents the Internet address for ireland.com and a particular host server called www. • The com part is the top level domain and represents the type of organisation • Other top level domains include .ie, .edu, .org, .de • The ‘ireland’ part with the top level domain is called the second level domain, and identifies the organisation • Further sub levels may be added, with the left-most part representing the server, in that domain.

24. Domain Names Server Second level domain www.ireland.com • Altogether this name uniquely represents a host • But as we’ve seen, an IP address does this as well • Lets look at DNS, the service which maps human readable host names to machine usable IP addresses Top Level domain

25. DNS • DNS is a hierarchical database • meaning the data is structured in a tree, much like the directory structure of a UNIX or Windows file system. • The root domain, ".", is at the top, and various subdomains branch out from the root. • On the Internet, for example, the first branches coming out of the root are the top-level domains such as .com and .ie • Under each of these top-level domains are more branches containing other domains, such as cisco.com, ireland.com, and dit.ie under the .ie domain. Each of these domains may, in turn, have their own subdomains, such as comp.dit.ie under the dit domain and sales.cisco.com under the cisco.com domain

26. DNS Tree (incomplete) . (root domain) .ie .edu .com .org cisco.com dit.ie tcd.ie ireland.com ietf.org ieee.org comp.dit.ie sales.cisco.com www.sales.cisco.com home.comp.dit.ie

27. DNS - Name Servers • Each domain (and sub-domain) has its own name server, a server which contains the host name information about the hosts and sub-domains within its domain. • The dit.ie domain, for example, has a name server that stores address information about all of the hosts and subdomains in the dit.ie domain. • However, authority for a subdomain, such as comp.dit.ie, can be passed to a name server that has authority for that subdomain. • When a name resolution request comes to the dit.ie name server, it just passes the request off to the comp.dit.ie name server. • In this way, DNS is truly distributed across the Internet, with each domain maintaining only the information that is pertinent to that domain

28. DNS – Name Resolution • Requests are made to the name servers in order to resolve names • e.g. to find the IP address for home.comp.dit.ie the following steps take place • A DNS server would ask the root server for the address of the name server for the .ie domain • The DNS server then can contact the .ie name server and asks this server for the number of the name server for the dit.ie domain • In turn, the DNS server then contacts the dit.ie name server and asks for the address of the name server for comp.dit.ie domain • Finally a request is made to the comp.dit.ie domain for the address of the server named ‘home’. This IP address is returned and can be used for communication between nodes.

29. Organisations • Internet Society (ISOC) • http://www.isoc.org/ • Internet Engineering Task Force (IETF) • http://www.ietf.org/ • Internet Architecture Board (IAB) • http://www.iab.org/

30. History of Internet • The Internet was originally proposed by an American body known as ARPA (Advanced Research Projects Agency). • It was originally conceived as a way of testing the viability of networking. • During the later stages of its life ARPA became more defence-oriented and was renamed DARPA (Defense Advanced Research Projects Agency) and oversaw the first implementation of a network originally known as ARPAnet. • The network was commissioned in 1971.

31. History of Internet • In the early days of the network there was a perceived need for users at one computer to log into another computer. • The protocol that was used in the original ARPAnet, the 1822 protocol, was inadequate for this and another protocol, NCP, was devised and implemented. • By 1973 it became clear that NCP was inadequate to handle the volume of data that was being generated. • In 1974 two researchers, Vincent Cerf and Robert Kahn, suggested that because of the growing use of networking and the inadequacy of current protocols a new set of protocols needed to be devised.

32. History of Internet • The radical suggestion that they made was that the protocols should be independent of any hardware. • This set of protocols that was developed was known as TCP/IP and, by the early 1980s, had supplanted NCP as the protocol set of choice for American networking. • As networking spread in the USA more and more non-military organisations joined the ARPAnet; in the initial stages these were mainly universities. • This lead to the splitting of the ARPAnet into two networks: MILnet which was devoted to military networking and ARPAnet which became a civilian network.

33. History of Internet • As ARPAnet was transformed into a civilian network it was renamed the Internet. • ARPAnet went into decline when the United States Government Office of Advanced Scientific Computing instigated a high-speed network of supercomputers known as NSFNET; it was eventually retired in 1990. • Ref:Distributed Applications and E Commerce, Darrell Ince

34. Summary • Overview of the Internet • Protocols • TCP/IP • Domain Names • Host Names • Domain Name Service • Internet Organisations • History of Internet

35. Reference • Internet Protocols • http://info.acm.org/crossroads/xrds1-1/tcpjmy.html • DNS • http://www.cisco.com/univercd/cc/td/doc/product/iaabu/cddm/cddm111/adguide/dns.htm • http://www.whatis.com/ • http://www.ietf.org/ • http://www.isc.org/