Chapter 3

 Help you understand what kind of communication media is available to run a network and how they effect bandwidth including: ◦ Cables ◦ Optical and ◦ Wireless

 In the previous lesson we looked at what bandwidth was and how bottlenecks can effect performance.  We also looked at the importance of choosing the right bandwidth speed for your needs.  Once you have decided on your needs you need to think about the kinds of communications media you require and the hardware to support it.

 It is important to consider the type of interconnection when building a network.  Factors to consider include: ◦ The predicted bandwidth. ◦ The environment. ◦ The distance between clients. ◦ The level of security needed. ◦ The cost of the interconnection.  Computers can be connected to a network through different media. Sample media include: ◦ Twisted pair. ◦ Coaxial cable. ◦ Fibre optics. ◦ Wireless connections.

 Many networks use this cable.  It is light, flexible and cheap and has been around a long time which means network engineers are familiar with it.  Used extensively at home to connect computers to the telephone system.  Consists of pairs of conductors covered in insulation material and then twisted together.  Within one cable you might have 4 pairs but there are different designs, each with their or characteristics.  Twisting the wire reduces the effects of electrical interference at minimal costs.  You can further reduce this electrical interference by covering the cables in silver foil.

 Many people have debated the ups and downs of UTP over STP (Shielded Twisted Pair) and these discussions can be found on the net.  It is important to note that the bandwidth of UTP is slower then coaxial and fibre optic cable and you need repeaters more often with UTP also. ◦ i.e. It has more resistance and a higher level of data degradation over longer distances.

 Made up of a central conducting core wrapped in protection within a cable.  Wrapped around the installation is a think metal sheath that provides the electrical interference protection.  Finally, the cable has an outer covering.  It is the cable of choice when connecting a television to an aerial.  It is heavier and less flexible compared to a UTP and also more expensive too.  Cable lengths can be longer than UTP but still not as long as fibre optic cables.  You need less repeaters than a UTP too and is mechanically strong and has a high level of resistance to electrical interference.

 Consists of glass cores surrounded in protective material.  Signals are sent via light sources. As signals are not electrical they do not suffer from electrical interference.  Also, the cables do not suffer from the effects of moisture as they are non-metallic (like most cables).  The cables are extremely brittle compared to metallic cables and need to be well protected.

 They are high bandwidth compared to UTP cables and are often used for networks were video conferencing is needed.  The cost of these cables are relatively cheap compared to metallic ones but they require specialists to install them which makes them expensive overall.  Often used as the backbone for LAN networks to connect servers to switches and located in places where there are clusters of computers. ◦ After the switches UTP and coaxial cables tend to be used.  The bandwidth is so impressive that speeds of up to 1Gbit/sec is easily reached.

 Note: the angle of the acceptance cone. If the cable is bent too much the light will not be able to travel through it.

 Complete this table:

 We now have the ability to connect up networks without the need for wires.  Data can be fired using lasers across a network or use radio signals to send information across a LAN.  Lasers are useful for connecting two building together. You must have a clear line between the equipment that sends and receives the equipment or else the signals will get blocked.  A school might use wireless technology if they have no space for a fixed computer room. They may use laptops with wireless technology to allow for a roaming classroom.  Also, it can allow teachers to take electronic registers and work in areas of the school away from noisy pupils!  You need wireless access points which relay information from the main server. They can often be seen attached to walls.

 Draw backs include low bandwidth which means generic software will work fine but high bandwidth applications such as video conferencing is sometimes impossible.  Electrical interference is a big problem and also it is potentially more insecure.  Signals are easily intercepted and if data has not been encrypted then it is easily viewed.  Companies wanting to send data over large distances should look at satellite technology, cellular technology and microwave technology.

 A widely used design for baseband LANs, which can work at 10Mbps, 100Mbps and 1Gbps.  Works by connecting stations together using coaxial cables.  Ethernets make use of data collision avoidance and detection strategies.  As traffic increases on an Ethernet data collisions become more likely. This is because each station is broadcasting information to other stations. ◦ The more stations the more traffic.  When a computer sends out data it waits for a reply. If it does not receive a reply it assumes the data packet was lost.  In the event of a collision data packets will be sent out again.

 Look again at switches and what they do.  Switches can be used to split large networks into segments to reduce traffic.  Also, stations can be given temporary communication links using a switch.

1. Describe how wireless networks can be used to improve the speed and delivery of medical care at the scene of an emergency, perhaps in an ambulance. 2. Describe the use and the technology behind the wireless network used to deliver education to children in remote parts of the Australian outback. You will need to research this.

1. Discuss the problem of balancing ‘over engineering’ with ‘future proofing’ in a new network. 2. Use the Internet and define the term Wi-Fi. Describe its benefits in the business environment. 3. What is UTP and list the reasons why it is commonly used for LANs. 4. Discuss in what circumstances a company might select a.Coaxial Cable or b.Fibre Optics for its network. 5. Define Ethernet.

1. Explain what is meant by ‘collision avoidance’ and ‘collision detection’. 2. How does an Ethernet deal with data collision? 3. What is meant by a ‘switched Ethernet LAN’? 4. Why do communications slow down when there are many users connected to a LAN? 5. Describe how a switch can reduce the number of collisions in a LAN and therefore improve communications.