1 The Internet and Networked Multimedia

2 The Internet  An interconnected set of networks  A gigantic collection of millions of computers, all linked together on a computer network  A home computer is usually linked to the Internet using a normal phone line and a modem that talks to an Internet Service Provider (ISP)  freeserve  msnfreeweb

3 The Internet  A computer in a business or university has a Network Interface Card (NIC) that directly connects it to a Local Area Network (LAN) inside the business  The business then connects its LAN to an ISP using a high speed phone line or optical cable

4 The Internet

5 JANET  The University is connected to the Joint Academic Network (JANET) via the LEarning Network South East (LENSE)  LENSE is a 622Mbit network connecting higher education sites in the south east  Sussex’s connection to LENSE is 155Mbit  JANET (superJANET 4) is a 2.4 – 20Gbit network backbone connecting academic LANs

6 LENSE

7 JANET

8 Development of the Internet  Originally developed by the U.S. Department of Defence  Development started in 1969 with the Advanced Research Projects Agency ARPAnet  Enabled communication between geographically dispersed research centres funded by ARPA

9 Development of the Internet  ARPAnet was the first Wide Area Network (WAN)  Electronic mail was soon introduced using the Simple Mail Transfer Protocol (SMTP)  With the developments of other networks such as MILNET a protocol was required to enable these networks to be linked

10 Development of the Internet  In the early 1980’s the current versions of the core Internet protocols TCP and IP were introduced  In the late 1980’s the Domain Name System (DNS) was introduced  In 1992 The Centre for European Nuclear Research (CERN) released the first version of the World Wide Web software

11 Growth of the Internet

12 Key Properties of the Internet  Interoperable - any computer connected to the internet can communicate with any other computer connected to the internet - due to standardised protocols  Global - based on standardised and universal connectivity, using software that can be distributed throughout the Internet

13 Key Properties of the Internet  Easy to use - World Wide Web has made highly functional multimedia content easily available to users worldwide  Low cost - the cost of the network is shared across all users. A provider of information does not need to pay for the distribution system other than its own connection to the network

14 Design Principles of the Internet  The main problem for the internet is how to build a system that can handle communication between two computers which may:  have any type of operating system  be connected using any type of physical medium

15 Design Principles of the Internet  To complicate matters:  no connected system has any knowledge about the other systems  and there is no way of knowing the location of that system what kind of software it uses what kind of hardware platform it runs on

16 Design Principles of the Internet  The main principles can be split into 5 concepts :  Interoperability  Uniform naming and addressing  Layering  Simplicity  End-to-end protocols

17 Interoperability  Independent implementations of internet protocols work together  Systems can be assembled using client and server computers and software from different vendors  Buyers and sellers are not required to update simultaneously and from the same vendor to conduct commerce

18 Uniform Naming and Addressing  The IP layer offers a uniform 32 bit addressing structure to each computer connected to the network  Every device connected to the Internet MUST have an IP address, whether it be a host, web server, name server or fridge

19 Uniform Naming and Addressing  The Domain Name Servers (DNS) offer a uniform way of translating IP addresses to human-readable names  The DNS system is a database – the biggest distributed database on the planet and no other database on the planet gets this many requests

20 Domain Name Servers (DNS)  DNS has to cope with 5 major problems:  There are billions of IP addresses currently in use  There are many billions of requests made to domain name servers every day  Domain names and IP addresses change daily  New domain names get created daily  Millions of people do the work to change and add domain names and IP addresses every day

21 Domain Names  The.COM,.UK and.NET portions of domain names are called the top-level domain or first- level domain  There are several hundred top-level domain names  Within every top-level domain there is a huge list of second-level domains. For example, in the COM first-level domain there are:  microsoft  ford  plus millions of others...

22 Domain Names  The left-most word, like www, encarta or cyril, is the host name ames.central.sussex.ac.uk  It specifies the name of a specific machine or several machines which deal with requests to that host name  A given domain can, potentially, contain millions of host names as long as they are all unique within that domain

23 Domain Names  All of the names in a given domain need to be unique  Nominet is the central authority that keeps track of.UK top-level domains  Network Solutions is the domain registering authority for.COM  Sussex Uni and EIT have several of their own domain name servers and maintain the machines that implement their part of the DNS system

24 Domain Name Servers (DNS)  Every domain has a domain name server somewhere that handles its requests, and there is a person maintaining the records in that DNS  The DNS system is completely distributed throughout the world on millions of machines administered by millions of people, yet it behaves like a single, integrated database!

25 The DNS Process  When a request comes in, the name server can do one of four things with it:  It can answer the request with an IP address because it already knows the IP address for the domain  It can contact another name server and try to find the IP address for the name requested. It may have to do this multiple times  It can say, "I don't know the IP address for the domain you requested, but here's the IP address for a name server that knows more than I do"  It can return an error message because the requested domain name is invalid or does not exist

26 The DNS Process

27 The DNS Look-up Process  The name server would start its search for an IP address by contacting one of the root name servers  The root servers know the IP address for all of the name servers that handle the top-level domains and returns the appropriate IP address for that name server  E.g. the.UK name server if we are trying to find the IP number for  Your name server then sends a query to the UK name server asking it if it knows the IP address for

28 The DNS Look-up Process  The name server for the UK domain returns the IP addresses for the name servers handling the banq.co.uk domain  Your name server then contacts the name server for banq.co.uk and asks if it knows the IP address for  It actually does, so it returns the IP address to your name server, which returns it to the browser, which can then contact the server for to get a web page

29 IP Addresses  The four numbers in an IP address are called octets, because they are a byte long when viewed in binary form, giving a possible 256 values for each number  The octets are used to create classes of IP addresses that can be assigned to a particular business, government or other entity based on size and need

30 IP Addresses  The octets are split into two sections:  Net - contains the first octet. It is used to identify the network that a computer belongs to  Host - identifies the actual computer on the network. The Host section always contains the last octet Net or host information depending on class

31 IP Addresses  There are five IP classes plus certain special addresses:  Class A – Class E  Network Identification  Loopback  Broadcast

32 Class A IP Addresses  This class is for very large networks, such as a major international company might have  IP addresses with a first octet from 1 to 126 are part of this class  The other three octets are used to identify each host. Thus, there are 126 Class A networks each with 16,777,214 possible hosts  Class A networks account for half of the total available IP addresses

33 Class B IP Addresses  Used for medium-sized networks such as sussex.ac.uk –  IP addresses with a first octet from 128 to 191 are part of this class. Class B addresses also include the second octet as part of the Net identifier  The other two octets are used to identify each host. This means that there are 16,384 (2 14 ) Class B networks each with 65,534 possible hosts  Class B networks make up a quarter of the total available IP addresses

34 Class C IP Addresses  Used for small to mid-size businesses  IP addresses with a first octet from 192 to 223 are part of this class  Class C addresses also include the second and third octets as part of the Net identifier. The last octet is used to identify each host. This means that there are 2,097,152 (2 21 ) Class C networks each with 254 hosts  Class C networks make up an eighth of the total available IP addresses

35 Class D IP Addresses  Used for multicasts  Class D is slightly different from the first three classes. Its first 3 bit values are 1, and fourth bit value of 0 (224 – 239) 1110xxxx  The other 28 bits are used to identify the group of computers the multicast message is intended for

36 Class E IP Addresses  Used for experimental purposes only  Similar to Class D, but with it’s first 4 bit values set to 1 ( ) 1111xxxx  The other 28 bits are used to identify the group of computers the message is intended for

37 Special IP Addresses  There are several special IP addresses which are not assigned to specific hosts  An all zero host refers to the network itself  E.g refers to the network

38 Special IP Addresses  The IP address is used as the loopback address  This means that it is used by the host computer to send a message back to itself. It is commonly used for troubleshooting and network testing  Broadcast - Messages that are intended for all computers on a network are sent as broadcasts. These messages always use the IP address

39 Fin