The Internet

KS3 Curriculum A pupil should understand the principles underlying how data is transported on the Internet. An end-to-end understanding of what happens when a user requests a web page in a browser, including: Browser and server exchange messages over the network
 What is in the messages [http request, and HTML]
 How data is transported on the Internet Packets and packet switching Simple protocols: an agreed language for two computers to talk to each other. [Radio protocols “over”, “out”; ack/nack; ethernet protocol: first use of shared medium, with backoff.]

Communications Protocols Imagine you are trying to communicate with someone in a crowded room full of people talking You say “Hello, shall we meet later at the racecourse, have you got any wellies?” You friend hears “Hello, shall we meet later at, have you got any”

Communications Protocols How do you know the message is for you? How do you know who to reply to? How do you know you have heard the whole message? Are there missing words? How do you know if the message requires a response? How do you know the response has been received?

Radio protocols We need to develop some rules about how to communicate so that we are sure the right person has received the whole message and has confirmed receipt. Radio protocols for voice communication

Internet Protocol What challenges do we have when sending data over the internet? Large files Routing Reliability – what happens if a 0 or 1 goes missing?

Internet protocol All computers connected to the internet have an IP address (e.g. 212.58.244.69) Data that is sent is split into packets A route is decided for each packet Packets are reassembled by the receiving computer Missing packets can be resent

TCP/IP TCP/IP defines the rule computers must follow to communicate with each other over the internet. TCP/IP stands for Transmission Control Protocol / Internet Protocol. TCP/IP defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them.

Packet switching Tablets of Stone In an ancient city there are a number of very important Governors. These Governors each live in different houses all over the city.   The Governors often want to communicate, they need to send and receive messages all over the city. Governors are identified by their house number and they all have access to a group of messengers whose job it is to deliver the messages. The only way to send messages is by writing them on large rectangular stone tablets which the messengers carry to their destination. The stone tablets are of a fixed size and can only fit 6 pieces of information on them. One piece of information can be one word or one number. Messages are often split over a number of tablets, and as these tablets are very heavy they can only be carried one at a time.

Packet switching Packet switching video Packet switching means each packet can take a different route to its destination, avoiding congestion. The packets leave your computer and are sent through the network. A  machine called a 'Router' works out which is the next fastest connection and sends each packet on its way.  During the course of its journey, a packet will travel through many routers, possibly in many different countries.

Packet switching

Tracert

Advantages of Packet Switching It makes very efficient use of the network - no tied-up lines (not like a telephone). It can easily get around broken bits of the network.

Disadvantages of Packet Switching A packet is usually 512 bytes. If for example the data package itself is only 600 bytes long, then two packets of 512 bytes need to be used. All packets have equal priority which can be a problem for time-critical information such as an emergency signal. Would you pay more, if you could make your packets have priority over someone else's packets? How much would you pay?