A-LevelComputer ScienceCommunication and internet technologies9618/12 · Oct/Nov 2023 · Q711 Marks

A Local Area Network (LAN) contains four devices: • a router • two laptop computers • a server.

(a)The server has the IP address 192.168.3.2 Explain why this is not an IPv6 address.[2]
(b)(i)The LAN is set up as a star topology. Draw a diagram of the topology of the LAN.[2]
(b)(ii)Explain how data is transmitted between the two laptops in the LAN.[2]
(b)(iii)Subnetting can be used to separate a network into logical segments. Describe two other reasons why subnetting is used in a network. 1 2[4]
(c)State three tasks performed by devices to deal with collisions when using the Carrier Sense Multiple Access/Collision Detection (CSMA/CD) protocol in a network. 1 2 3[3]
(d)The following incomplete table contains types of IP addresses and their descriptions. Complete the table by writing the missing types of IP addresses and the missing descriptions. Type of IP address Description an IP address that is assigned to a device to allow direct access on the internet static IP address dynamic IP address an IP address used for internal LAN communication only[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[2] (a) Only has four groups of digits // IPv6 has eight groups Uses dotted notation instead of colons Because it is a 32 bit / 4 byte address // IPv6 is 128 bits / 16 bytes
[2] (b)(i) 1 mark for server only connected to router 1 mark for two laptop computers connected only to router [Diagram showing Server, Router, Laptop 1, Laptop 2 with Router as central hub]
[2] (b)(ii) The data from the sending laptop is transmitted to the router. The data has address of recipient. The router determines recipient's destination address by using a routing table. The router transmits data directly / only to recipient.
[4] (b)(iii) To improve the security of the LAN: so that a compromised device does not expose the whole network, so that devices do not receive unintended data, so not all devices can access all segments. To make the network management easier: because faults can be isolated more efficiently, by appropriate example. To make the network easier to expand // For better control of network growth: by allowing for greater range of IP addresses to be available. To improve network performance: To reduce network congestion, by localising network communications // by dividing data between segments, so that devices are not flooded with data, because data sent between devices on the same subnet stays within the subnet.
[3] (c) To monitor the communications channel. To send data only when there is no data being transmitted / the line is quiet / idle. To detect a collision and then stop transmissions of further data // transmit a jamming signal. To calculate a random wait time / back-off time, then retransmit the data after that random wait time. Increase random time if multiple collisions.
[4] (d) Type of IP address: public IP address Description: an IP address that is fixed / doesn't change each time a device re-joins a LAN / network Type of IP address: private IP address Description: an IP address that may be refreshed / changed each time a device re-joins a LAN / network