Networks and Communication

Connection is the whole problem

Networks look like a long list of words to memorise: LAN, WAN, star, bus, protocol, TCP, IP, layers. Learned as a list they blur together. Learned as answers to one question, they lock into place. A network is nothing more than computers connected so they can share data and resources, such as files, a printer, or a route to the internet. That is the whole idea. Everything else in the topic is solving a problem that the connecting creates. Problem one: how do you arrange the devices? The layout of a network is its topology. In a star, every device has its own cable to a central switch, so one broken cable loses only that one device. Other arrangements trade cost against how well they cope with a failure. Arrangement is the first thing connection forces you to decide. Problem two: how do different machines agree on what the bits mean? A protocol is a set of rules for communicating. TCP and IP are the rules that run the internet, HTTP and HTTPS carry web pages, and SMTP sends email. Without an agreed protocol, connected machines still cannot understand each other. Problem three: how do you keep something this complicated manageable? You split the job into layers, where each layer does one thing and can be designed or changed without disturbing the others. That is how a system this large stays workable. Scale it up and you have the internet, which is a network of networks, joined by routers, all speaking the same core protocols. Carry one question through everything that follows: what problem of connecting computers does this solve, the arrangement, the agreement, or the dividing of the job?

Words for networks

Five terms, each defined by what it is. They are the frame for the whole topic.

Tap the two connection problems

Tap the TWO statements that describe a problem created by connecting computers, rather than an unrelated fact.

• The devices have to be arranged so that one broken cable does not take the whole network down
• Different machines have to agree on rules so they can understand what each other sends
• A computer case can be made in many different colours
• A keyboard usually has more than one hundred keys

Which network is this

A company connects its offices in three different cities so they can share data. What kind of network is that?

• A WAN, a wide area network, because it covers a large geographical area and links sites that are far apart
• A LAN, because all the computers belong to one company
• A star, because the offices connect together
• A protocol, because they share data

Local against wide

Two kinds of network, told apart by the area they cover and who owns them.

Match each term to what it means

Two that follow from connection

Select the TWO statements that follow from a network being about solving the problems connection creates.

• A star topology is chosen partly because one broken cable then loses only one device, not the whole network
• Two machines can only communicate if they follow the same protocol
• Adding more cables always makes a single computer run faster on its own
• Splitting the job into layers makes a network harder to manage

How the internet fits together

A way to hold the bigger picture, and to answer questions about it. The internet is a network of networks. Your device joins a local network, that local network joins others, and routers pass data between them until it reaches the network the destination is on. No single machine holds the whole internet; it is many networks cooperating. Routers direct the traffic. A router works out where to send data next so that it moves across the networks toward its destination, one hop at a time. Protocols do the agreeing. TCP and IP together break data into pieces, address them, send them across the networks, and reassemble them at the far end. HTTP and HTTPS then carry web pages on top of that. Layers keep it manageable. The job is split into layers, each doing one thing, such as addressing, or moving data across a link. A change to one layer does not force a change to the others, which is why the internet could grow so large. So an answer names the level it is working at. Say whether you are talking about the arrangement, the protocol, or the layer, rather than mixing them. Two habits cost marks. The first is confusing a network type, by size, with a topology, an arrangement. The second is treating a protocol as a piece of hardware rather than a set of rules.

Order how a message crosses the internet

Put these stages of a message travelling across the internet into a sensible order.

• The data is split into pieces and each is given an address
• The pieces leave the device onto its local network
• Routers pass the pieces from network to network toward the destination
• The pieces arrive on the destination network
• The pieces are reassembled into the original data

Build the networking rule

This is the idea the whole topic rests on. Assemble it.

The networks quick-fire

Five questions on networks and how they connect. Three lives.

One web page, delivered

Here is the whole topic working together on one everyday action: opening a web page. The devices and steps are described in general terms, with no invented numbers. You type an address and your device asks for the page. The request does not go straight to the far computer. First it joins your local network, the small network in your home or school, which may be arranged as a star with every device on its own cable to a central switch. That is the topology at work. Next the request has to travel. The protocols take over: the data is broken into addressed pieces by TCP and IP, so that each piece knows where it is going. Your local network hands the pieces to a router, and routers pass them from network to network, hop by hop, across the internet, which is simply all these networks joined together. The pieces arrive on the network of the computer that holds the page, the server. There the pieces are reassembled, the server sends the page back the same way, and HTTPS carries it so your browser can display it. Notice how every part of the topic had a job. The topology arranged your local devices. The protocols agreed how the data was addressed and carried. The layers let addressing and moving be handled separately. And the internet was the networks cooperating. One action, and it used the whole topic. That is the map to carry into any network question: name which of those jobs the question is really asking about.

Complete the network facts

Two or more computers connected so they can share data and resources form a _____. A network that covers one small area such as a building is a _____. A set of rules for how devices communicate, such as TCP/IP, is a _____. The internet is a global network of networks joined together.

Three networks to plan

Three situations. In each case pick the network choice that fits, and see why.

• A school wants every computer in one building to share files and a printer quickly, using its own equipment. What does it need?
• A business wants an office layout where one broken cable does not disconnect every machine. Which topology helps?
• Two computers made by different companies cannot exchange data even though they are connected. What is most likely missing?

Explain how a network works

A student in the year below has learned the network words as a list and mixes them up. Explain how the parts of a network fit together so the words make sense.

• Explain what a network is and why computers are connected
• Explain the difference between a LAN and a WAN
• Explain what a topology is, using the star as an example of why arrangement matters
• Explain what a protocol is and why two machines need the same one
• Explain why a network is split into layers
• Finish with the one question to ask of any part of the topic