1.5.1: Network Hardware & Software

Imagine you had a room of standalone machines and someone asks you to make them a network!

What would you need to go out and buy?

Interconnections

To link the computers together in a network, you would need to buy some interconnections.

This might simply be some cable, but you could also use a wireless technology to connect the computers together.

With any interconnections, you need to think about:

- Cost. How much will the interconnections cost?
- Bandwidth. What bandwidth will users of the network need?

Bandwidth is the term used to describe the amount of data transmitted across a network.

Transmitting data such as music or video is a high bandwidth activity.
Transmitting word-processed documents is a low bandwidth activity.

Different interconnections are able to carry different bandwidths.

A network designer needs to identify what users will be using the network for and then select an appropriate connection method.

A coaxial cable (like a tv cable) or a fibre optic cable useful for high bandwidth applications like video streaming.
A wireless interconnection might be selected for a school network,
- so long as the users just wanted to use basic applications such as word processing, databases etc.
If the users wanted good Internet access,
- the wireless solution might be discarded in favour of a cable solution for bandwidth reasons.

- Cable routes. A wireless technology might be preferred in situations where bandwidth isn't an issue and physically laying cables might be a problem,
  - e.g. Where lots of buildings needed to be connected and you don't want to dig up roads!
- Distances also need to be considered.
  - Different interconnections can send signals different distances.
  - It may be necessary to buy some extra equipment called repeaters to boost signals if transmission distances are too large.
- Electrical interference.
  - Both cabled and wireless technologies are subject to electrical interference from any electrical devices
    - because the data itself is electrical in nature.
  - This is not true for fibre optics, which use light pulses to send data rather than electrical signals.
  - In locations where there is a large possibility of electrical interference, fibre optic technology could be considered.
- Security. Wireless technology is insecure. It is relatively easy with the right equipment to 'capture' the data sent in this way.
  - Cables are more secure but can also be tapped into.
  - In both cases, encryption technology should be used if data is that sensitive.
  - Fibre optic technology is difficult to tap into - the light signals degenerate if someone tries to break into the signal.

The bus has terminators at the end of the cable.

Network Cards / Network Adapters

Each computer that is going to be part of a network needs to be actually connected up to the network.

To do this, you will need to buy and fit a Network Interface Card for each computer.

The network card inside a computer:

Provides a means of connecting a computer to a network.
Provides a way of splitting up data that you want to send across a network and then getting that data actually onto the network successfully.
Provides a way of collecting 'packets' of data' addressed to that particular computer from the network.

A connection can be physically made using a cable from the network card to the main network cable.

Networks could also make use of wireless network cards.

These are installed in computers, but do not physically connect to the network, but connect using radio signals.

Another term in use is network adapter.

The meaning of this term has broadened to mean any card that connects a computer to a network.

e.g. You could talk about the thin little card that allows you to connect a laptop to a network (known as a PCMCIA card) as a network adapter, or a card that allows a wireless connection as a network adapter, or a basic network card as a network adapter.

Server

Computers on a client-server network are known as clients.

The clients need a very high-specification computer to organise and manage the communications around the network and to take responsibility for controlling access to the files held centrally.

This high-specification computer is known as a server, and for a quality client-server network, you will need to go out and buy a server.

Although a server is just like a normal computer it does have a huge hard disk compared to the clients. This is because it needs to store everyone's data files as well as store applications centrally.

The server will also have much more RAM than the clients and a very fast processor, to enable it to work as quickly as possible.

The server will usually have some kind of automated back-up hardware, to ensure that users' files are backed-up regularly.

Network Operating System (NOS)

The server on its own is not enough.

Software to allow the server to organise and manage the communications around the network

and to allow the server to take responsibility for controlling access to the files held on its hard disk.

This software is known as the 'Network Operating System', or NOS.

Typically, the NOS controls access to the facilities on the network by making a user log in.

They do this by providing each user with a user ID and a password, which they then have to type in when they want to use the facilities of the network.

Dial-up Internet Connection

If your LAN needs to communicate with other networks via the Internet (so your LAN is part of a WAN), you need some further equipment.

Connections to the Internet can be done in a number of ways.

One way is to set up a 'dial-up connection'.

The network is connected to a modem and the modem is connected to a phone line.
T0 use the web, WWW, the network dials up a phone number and makes a connection to the ISP (see below).
You can then send or receive data.
When you have finished, you disconnect the connection.
The modem turns the digital signals of the LAN into the 'analogue' signals of the phone line,
Lastly, it reconverts the analogue signals received back into digital signals for the network.

Modems have limited bandwidth and the connection to the Internet is not permanent.

In addition, if you are using an office phone line for your dial-up connection then that line cannot be used for anything else, such as making a phone call or sending a FAX. Of course, you could always go to the expense of having another phone line put in.

Leased line Internet connections using ISDN and ADSL.

An alternative to a dial-up connection is a leased line connection.

In this type of connection,

You pay a fixed fee for a permanent Internet connection.
You have access to the Internet 24 hours a day.
You do not need to dial-up a phone number because you are always connected!

Modems used in dial-up connections work at speeds of up to 56 Kbytes.

While this may be fine for light Internet use, leased lines give much higher bandwidths and this may be necessary if there is heavy use in the office by a lot of people or use involving large multimedia files.

Another way to connect up to a network using a leased line is to rent an ISDN connection.

This type of connection is much faster than a modem, at a 128 Kbps - its higher bandwidth is far more suitable for communications that involve multimedia. Dial-up connections make use of the public phone lines, which are analogue in nature.

You need a modem to convert the digital signals of a computer into the analogue ones the phone line uses.

ISDN connections make use of a purely digital network.

You don't therefore need a modem although you do need a special piece of equipment called an adapter.

ADSL

Schools and homes are increasingly signing up for leased lines in the shape of ADSL instead.

This type of connection will typically gives between 2 Mbyte and 50 Mbyte download speed.

It is a permanent connection so you never need to dial-up an ISP.

ADSL can also use the existing phone line and phone calls can still be made and received whilst using the Internet!!

One slight problem is that there is not ADSL coverage over 100% of the UK yet so if your business happens to be in an area not covered, you will have to look for an alternative connection method, possibly using the more expensive satellite technology.

The infrastructure is already in place for this because of the widespread use of satellite TV.

ISP Account

If you want to connect a network to the Internet then you need an Internet Service Provider (ISP) account.

This is a company that acts as a door to the Internet.

You sign up with an ISP for a fixed monthly or annual fee and they then allow you to access the Internet through them.

You need an ISP for both dial-up connections and leased lines.

Practice Questions 1

TASK 1 - Define 'network'.
TASK 2 - Explain the difference between a LAN and a WAN.
TASK 3 - Outline some of the things you can do with a network that you can't do with standalone machines.
TASK 4 - Do some research. Find out what an 'Intranet' is.
TASK 5 - A company has 15 standalone machines.
- Summarise what you would need to buy to create a LAN.
- TASK 6 - What is meant by 'bandwidth'?
TASK 7 - Suggest four different types of interconnections that could be used to create a network.
TASK 8 - Outline any advantages that fibre optic technology has over coaxial cables.
- Can you suggest any disadvantages?
TASK 9 - What causes 'electrical interference' and how could a network designer reduce the effects of it on a network?
TASK 10 - What is meant by 'data encryption'?
- TASK 11 - Do some research. What is a 'peer-to-peer network'?
- Compare a client-server network to a peer-to-peer network.
TASK 12 - What is a Network Operating System responsible for?
TASK 13 - Do some research.
- What exactly is ISDN and ADSL?
- Why might they be considered when connecting a network to the Internet rather than a modem?
- What hardware and software do you need for ISDN, and for ADSL?
TASK 14 - An office has a small network. It wants to connect the network to the Internet.
- Compare and contrast a dial-up connection with a leased line.
TASK 15 - A small office has decided to use a dial-up connection for Internet access. It has drawn up a shortlist of 4 ISPs.
- Suggest criteria that could be used to compare the different companies.

Network Topologies

Computers that are going to be connected together can be connected in different ways.

The way that the computers on a network are connected together is known as the topology of the network.

A network topology is a logical representation of how the hardware devices on a network connect.

Bus networks

A bus network is one where the stations are connected to a main communications cable, called a bus.

A Bus Network

This set-up is very simple to implement compared to alternative topologies because

very little cable is needed. If the main cable breaks, however, then the whole network stops working and it can be difficult to pinpoint where exactly the fault is. When a message needs to be sent, the workstation checks to see if the line is busy with another message.
The cable can only carry one message at a time.
If the cable isn't busy then a station can put its message on the cable.
If there is a message on the cable then it waits until it is free.

This simple method avoids most ‘collisions’. This is when;

two messages are put on the network cable at exactly the same time, which results in corrupted messages.

Collisions are possible because two stations can see at exactly the same time that the cable is free and at exactly that same time, can put their own messages on the cable!

Fortunately, stations can also detect when these collisions have occurred.

When they do detect a collision, the stations involved are asked to re-send their messages.

Ring Networks

A ring network is like a bus network with the ends connected together!

A Ring Network.

This gives a better performance than a bus network, but is not as fast as a star network. There is a security problem with both bus and ring networks. When a message is sent, it is put on the cable. All stations can read all the messages on the cable and this means that someone who has access to the network with the right software can 'grab' packets of information that they are not entitled to! Ring networks use a sytem of sending messages called Token passing

Star Networks

A star network is one in which the server is in the middle, and cables run from the server to each workstation.

A Star Network.

This kind of network is very secure because all of the communications go from one station to the target station via the server and other stations cannot 'grab' the communication. Security can be managed from one central point - the server. This kind of network takes up a lot of cable compared to a bus network, for example, and this can be expensive. In this kind of network, the server polls each station to see if it has anything to send. Polling is when the server goes from one station to the next in turn, checking if it needs to be serviced.

If the server finds a station that needs to send a message, for example, then it will deal with it.

Mesh Networks

Most organistaions use a combination of several different topologies.

Not all parts of the system need the same reliability

Practice Questions 2

TASK 16 - Draw up a table that summarises the pros and cons of the three types of network discussed above.
TASK 17 - What is meant by the two terms 'collision avoidance' and 'collision detection'?
TASK 18 - Do some research. Find out what other people have to say about these three topologies.

Advantages of networks compared to standalone machines.

The advantages of a network compared to standalone machines are:

Computers that are connected together can communicate with each other. Standalone machines can't.
Users on a network can easily share resources such as printers, scanners and modems. This means that a company doesn't have to buy so much equipment and users do not waste time moving files to different machines so they can use a piece of equipment that is only available on a particular PC.
Users on a network can share data. For example, a team might be working on a project. They can all access and work on the same files easily without having first to back them up on floppy disks, for example, and then transport them to the next team member and then reload the files.
New software need only be added once. It can then be distributed to all other PCs automatically.
When data files are backed up they only need to be backed-up once, centrally, at the server. With standalone machines, you would have to back up the files on every machine. This would be very time-consuming!
Users can retrieve and work on files from any machine on a network. If one machine is being used or breaks down, you simply move to a different machine!
Networks can be managed. This means a network manager is able through the network software to control who can access the network, when they can access it, and what files and software and hardware they are allowed to use. An audit trail of each user can be built up so that projects can be more efficiently costed, for example, by keeping track of what printouts are done in connection with what project. Users, knowing that their activities are being monitored, will also be encouraged to stay on-task and not waste the organisation's time!

Disadvantages of networks compared to standalone machines.

The disadvantages of a network compared to standalone machines are:

1. It costs more money to build a network than it does standalone machines. This is because you have to buy network cards, interconnections, a server and a Network Operating System.
2. There is an additional support cost that is not insignificant. Networks are more complicated than sets of standalone machines. They need specialist knowledge to set them up and maintain them as well as time to maintain them. To do this, you would need to employ somebody with network management skills.
3. Networks have machines in different locations, each of which potentially could be used to gain access to the server's hard disk and the data stored on it. This is a security headache and the need to protect data on a network from hackers adds an extra degree of complexity to a network that doesn't exist with standalone machines.
4. If the server on a client-server network goes down, the whole network will be out of action. It is also possible for one faulty machine on a network to cause other machines on the network to stop working. In addition, if the cables on a network fail, problems on either individual machines or on the whole network may occur.

Practice Questions 3

TASK 19 - A travel agent with 10 standalone PCs in its building is considering converting them into a network.
- Summarise the pros and cons of this idea.
TASK 20 - Investigate what a Network Manager does.

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