1. 1 The Internet What is the ‘Net’ Is this all just a craze? How does it work?

2. 2 The Internet Looking at …. –What is the ‘Net’? –Protocols –IP and TCP –Domain Name Service and Domain Names –FTP –Email –Video-conferencing

3. 3 The Internet What is the Internet ? “The Internet is a world-wide 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

4. 4 The Internet The Internet is a network of networks

5. 5 The Internet Comprised of nodes which communicate with each other using a specific protocol Internet Node A Node B protocol used to handle communication through Internet

6. 6 Computer Protocol HTTP, FTP, Telnet, IP, etc.. are all protocols What is a protocol? –An agreed set of rules –a standard procedure for regulating data transmission between nodes (computers) why are protocols important? –Internet comprised of networks of networks –each network contains different types of nodes/hosts (Windows, Unix, …)

7. 7 Computer Protocol Networks may be different and thus communicate differently –need a standard !!!!! Protocols set standard message types to enable communication (in various forms) between computers

8. 8 IP (Internet Protocol) IP provides every node connected to the Internet with a unique address –e.g. 167.252.135.277 IP is a standard protocol enabling message passing between nodes All nodes connected to Internet agree on using IP as a standard protocol to enable communication

9. 9 IP Addressing All nodes have a unique address Each address is represented by 32 bits –e.g. 10010011111111001000010000101011 –broken into four bytes separated by a decimal point –e.g. 10010011. 11111100.10000100.00101011 –and converted to decimal –e.g. 147.252.132.43

10. 10 IP Message Format There exists a specific format for messages that nodes send to each other Application data is appended onto the message

11. 11 TCP (Transmission Communication Protocol) It ensures that IP messages are delivered reliably –IP is not a reliable network protocol –TCP adds reliability IP and TCP exist at two separate levels, or layers in the protocol stack

12. 12 TCP (Transmission Communication Protocol) The final message (or packet) is forwarded from node to node over the internet which may exist on different networks Nodes look at the destination address of the packet and forward it

13. 13 DNS (Domain Name Service) We have seen all nodes connected to the Internet have a unique IP Address How does one node connect to another if it doesn’t know the IP Address? DNS resolves this issue Using DNS, every IP Address can be resolved to a name (Hostname as it is referred)

14. 14 DNS (Domain Name Service) IP does not understand what Hostnames are so DNS acts as a form of ‘translator’ DNS translates between IP Addresses and Hostnames We must first look at what Domain Names are

15. 15 Domain Names Any entity connected to the Internet is located using a Domain Name –e.g. www.dit.ie www.dit.ie –represents the Internet address The.ie part is the top-level of the domain and represents an entity located in Ireland –others include.de,.jp.,.com.,.edu The ‘dit’ part of the address (including the top level) is the second level domain and represents the organisation

16. 16 Domain Names There may be other domain levels in an Address. –E.g. www.comp.kst.dit.ie The Left-most level is the server on which the resource resides (in this case is ‘www’) www.dit.ie Top Level Domain Second Level Domain Server

17. 17 DNS (Domain Name Service) DNS is used to resolve hostnames (www.dit.ie) and IP Addresses It is based on a Tree-like, hierarchical structure The root domain is “.” It resides at the top of the tree and various subdomains branch out These subdomains include.com,.ie,.org,..etc. The tree continues to branch with each subdomain in turn containing various subdomains –e.g. www.kst.dit.ie

18. 18 DNS Tree example. (root domain).ie.org.com.edu dit.ietcd.iegoogle.com kst.dit.ieang.dit.ie stanford.eduberkeley.edu cs.stanford.edu

19. 19 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 kst.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 kst.dit.ie name server. –In this way, DNS maintains only the information that is pertinent to that domain

20. 20 DNS (Name Resolution) Requests are made to the name servers in order to resolve names e.g. to find the IP address for home.kst.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 kst.dit.ie domain –Finally a request is made to the kst.dit.ie domain for the address of the server named ‘home’. This IP address is returned and can be used for communication between nodes

21. 21 FTP (File Transfer Protocol) Used to transfer files over the Internet between computers Downloading using FTP –file transfer from remote server to local computer (localhost) Uploading using FTP –file transfer from local computer to remote server

22. 22 FTP (File Transfer Protocol) FTP used to transfer files, applications, etc.. Using FTP –ftp:// –e.g. ftp://www.comp.dit.ie/~mcollins/report.pdf –may require authentication (name & password) –open directly or save to hard drive

23. 23 E-mail E-mail (Electronic mail) –Revolutionised old ‘snail mail’!! Delivers formatted messages over the Internet E-mail address are unique (no two people have the same address) –username@domainname A computer in the domain is used as a Mail server.

24. 24 E-mail Mail server –Gathers incoming email, looks at recipient address and forwards to recipient –Collects outgoing e-mail and sends onto Internet –Incoming e-mail with bad/incorrect addresses are returned to sender, usually with an error message

25. 25 Video-Conferencing aka ‘NetMeeting’ used mainly in business and work environments facilitates visual, audio and text communication together over the Internet usually requires large bandwidth and dedicated channel (e.g. ISDN, ADSL, Fiber Optic connection).

26. 26 Video-Conferencing Uses include –File Transfer –Whiteboard (smartboard) for sharing diagrams and enabling remote editing) –Talk real-time chat with full audio, video and text exchange) –Program sharing Many VC software packages on market

27. 27 Summary We have looked at: –Makeup of Internet –Protocol –IP –TCP –DNS and Domain Names –FTP –E-mail –Video-Conferencing