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AQA GCSE CS · 3.5.1 to 3.5.2

Computer Networks and Topologies

Section A: 10 multiple choice questions, 10 marks. Section B: 3 written questions, 11 marks. Total 21 marks.

Name

Class

Date

Mark  / 21

Section A

Circle the letter of the correct answer. One mark each.

  1. 1What is the main difference between a LAN and a WAN?1
    1. AA LAN covers one site with hardware the organisation owns, a WAN spans sites using hired infrastructure
    2. BA LAN is wireless and a WAN is wired
    3. CA WAN cannot connect to the internet
    4. DA LAN has fewer than 100 devices
  2. 2In a star topology, what happens if one cable fails?1
    1. AThe switch reroutes traffic through another device
    2. BThe whole network stops
    3. COnly the device on that cable is disconnected
    4. DData collisions increase
  3. 3Why does a bus network slow down as more devices are added?1
    1. AThe backbone cable gets physically longer
    2. BEvery device shares one cable and only one can transmit at a time
    3. CEach device needs its own switch port
    4. DBus networks cannot use fibre optic cable
  4. 4What is the single point of failure in a star network?1
    1. AThe central switch
    2. BThe terminator
    3. CAny one cable
    4. DThe network interface card
  5. 5Which device connects two different networks together?1
    1. AA network interface card
    2. BA switch
    3. CA router
    4. DA wireless access point
  6. 6Why is a wired connection generally more secure than a wireless one?1
    1. ACables cannot carry personal data
    2. BWired connections are always encrypted
    3. CWireless signals cannot be recorded
    4. DAn attacker needs physical access to the cable rather than just being in range
  7. 7What is the purpose of MAC address filtering?1
    1. ATo assign IP addresses automatically
    2. BTo speed up wireless transmission
    3. CTo encrypt data travelling over the network
    4. DTo allow only devices on an approved list to join the network
  8. 8Why is MAC address filtering not a strong security measure on its own?1
    1. AIt only works on wired networks
    2. BA MAC address can be spoofed to imitate an approved device
    3. CIt slows the network down too much
    4. DIt prevents legitimate devices from connecting
  9. 9Which topology needs the least cable?1
    1. AStar
    2. BIt depends on the number of switches
    3. CBus
    4. DBoth need the same amount
  10. 10A school wants to connect twenty fixed desktop computers in one room, and speed and security matter most. Which is the better choice?1
    1. AWired connections in a star topology
    2. BA bus topology using wireless
    3. CWireless with MAC filtering only
    4. DWireless connections through one access point

Section B

Answer in the space provided. The number of marks tells you how many separate points to make.

  1. 1StateState one advantage and one disadvantage of a star topology compared with a bus topology.2
  2. 2ExplainExplain why a bus network becomes slower as more devices are added.3
  3. 3DiscussA company is setting up a network in a listed building where cables cannot be run through the walls. Discuss whether a wireless network would be suitable.6

Mark scheme

Section A

1A2C3B4A5C6D7D8B9C10A

Section B

1 State one advantage and one disadvantage of a star topology compared with a bus topology. 2

One mark for each of the following, to a maximum of 2.

  • An advantage such as each device having a dedicated connection, so it is faster and a cable failure affects one device only
  • A disadvantage such as needing more cable and a switch, so it costs more

Model answer. An advantage is that every device has its own dedicated cable to the switch, so devices do not compete for the medium and a single cable failure disconnects only the device on it. A disadvantage is cost: a star needs a separate cable run for every device plus a central switch, which is considerably more expensive than one shared backbone.

2 Explain why a bus network becomes slower as more devices are added. 3

One mark for each of the following, to a maximum of 3.

  • All devices share a single backbone cable
  • Only one device can transmit successfully at a time
  • More devices means more collisions, and after a collision data must be resent

Model answer. Every device on a bus network is attached to the same backbone cable, so they all share one transmission medium and only one device can be transmitting successfully at any moment. As devices are added, the chance that two of them try to transmit at the same instant rises, and when that happens the signals interfere and both transmissions are lost. Each device then has to wait and send again, which adds further traffic to the same cable, so throughput falls away noticeably once the network becomes busy.

3 A company is setting up a network in a listed building where cables cannot be run through the walls. Discuss whether a wireless network would be suitable. 6

One mark for each of the following, to a maximum of 6.

  • Wireless needs no cabling, so it can be installed without altering the building
  • It allows devices to move around the building
  • Wireless is generally slower and less consistent than a wired connection
  • The signal is weakened by thick walls and by distance from the access point
  • Wireless is less secure by default because the signal travels through the air
  • Reaches a justified conclusion, including measures such as encryption and multiple access points

Model answer. Wireless is the obvious fit for the constraint. No cabling has to be run, so the fabric of a listed building is untouched, installation is quick and cheap, and staff can move around with laptops and tablets rather than being tied to a desk. There are three real costs to weigh. Wireless is generally slower and less consistent than a wired connection, so a task that moves large files will take longer. The signal is weakened by distance and by obstacles, and the thick masonry typical of a listed building is exactly the kind of obstacle that causes dead spots. And the signal travels through the air, so anyone within range can receive it, which makes the network easier to attack than one where an intruder would have to reach a cable. None of those is decisive against wireless here, because the alternative is effectively unavailable. The company should install wireless, but should plan for it properly: several access points positioned to give overlapping coverage rather than one central unit, WPA2 or WPA3 encryption so that intercepted traffic cannot be read, a strong non default password on every access point, and a separate guest network so that visitors never reach company systems. If any single task genuinely needs sustained high bandwidth, a small number of surface mounted cable runs to those specific machines would be a sensible exception.