Edexcel GCSE Computer Science (1CP2) Exam Questions

• B Latency (1)
• The only correct answer is B. The correct answer is latency.
• A is not correct because bandwidth is the capacity of a connection, not a measure of time
• C is not correct because range is the maximum distance a signal can travel, not a measure of time
• D is not correct because speed is the rate at which data is transferred, not a delay

Award one mark for any of the following up to a maximum of two marks:

• Files/data download/upload more quickly (1)
• More employees can use the connection at the same time without it slowing down (1)
• Web pages/streamed video load more quickly with less buffering (1)
• Video calls/conferencing run at a higher quality (1)
• Updates/backups can be completed in less time (1)

Allow 'multiple users' or 'more devices' for the shared-use point

Allow 'video streams more quickly' or 'less buffering' on their own

Do not accept lower latency, as a higher bandwidth does not reduce latency

Do not accept 'more data can be transferred per second' or 'a bigger bandwidth', as these repeat what bandwidth is

Do not accept 'more reliable' on its own, as a higher bandwidth does not make a wired connection more reliable

Award up to two marks for a linked description such as:

• Provides the protocols used by applications (1) so a web browser can use HTTP/HTTPS or an email client can use SMTP/IMAP (1)
• Prepares/creates the data produced by the application (1) and passes it down to the transport layer (1)
• Selects the correct protocol for the application being used (1) so the receiving application can understand the data (1)

Do not accept responses about routing packets/IP addresses; these relate to the internet layer.

Do not accept naming a protocol without describing the purpose of the application layer.

Do not accept generic statements that the layer 'sends data' or 'connects to the network' without a linked development.

Award one mark for any of the following up to a maximum of two marks:

• It is a 32-bit number/address (1)
• It is made up of four 8-bit numbers/bytes/octets (1)
• Each of the four parts is a number in the range 0 to 255 (1)
• The four parts are separated by dots/full stops (1)

Award a maximum of one mark for describing the four parts, whether they are described as 8-bit numbers/bytes/octets or as numbers in the range 0 to 255.

Do not accept 'it has four numbers' on its own, with no reference to 8 bits/bytes/octets or to the range 0 to 255.

Do not accept 'decimal point', 'separated by commas', 'separated by colons' or 'a 32-digit number'.

Do not accept responses that describe IPv6 (128-bit/hexadecimal) addresses.

Award up to two marks for a linked description such as:

• Interference from other devices corrupts the wireless signal (1) so the data has to be resent, which increases the delay (1)
• Devices on a wireless network take turns to use the same channel/frequency (1) so a device may have to wait for the channel to be free before it can transmit, which adds to the delay (1)
• Data on a wireless connection must pass through the access point to reach the wired network (1) so the extra processing/conversion at the access point adds a delay (1)

Do not accept responses that only state that a wireless connection is slower/less reliable than a wired connection, without explaining how this adds latency.

Do not accept 'data is sent through the air' on its own, as this does not explain why latency is higher.

Do not accept responses about bandwidth or speed on their own.

Award up to two marks for a linked explanation such as:

• Data/packets are delivered to the correct/intended device (1) because the destination IP address identifies that device, so a duplicate address would mean packets could be delivered to the wrong device (1)
• Replies are sent back to the device that requested the data (1) because the sender's IP address identifies that device, so a duplicate address would mean the reply could be sent to the wrong device (1)
• The device can be identified separately from other devices (1) so packets are not delivered to a different device that has the same address (1)

For both marks, the expansion must follow/associate with the statement.

Award one mark for a valid point and a second mark only for a linked reason explaining why a duplicate address would cause a problem.

Do not accept 'it is unique'/'it has its own address' as a point, as this repeats the question.

Do not accept 'so it can connect to the internet' or 'so it can be found' on its own without a link to data/packets being delivered to the correct device.

Allow 'data' for 'packets'.

Award up to two marks for a linked explanation such as:

• The time taken (to transmit the file) is reduced (1) because the compressed file is smaller/has fewer bits to send (1)
• The file is sent in less time (1) because fewer bits need to be sent at the same transmission rate (1)
• The time taken is halved (1) if compression halves the file size, because the number of bits sent each second stays the same (1)
• The time taken is reduced (1) because the smaller file takes fewer seconds to send at the same number of bits per second (1)

For both marks, the expansion must follow/associate with the statement.

Allow the two parts in the reverse order, e.g. 'the compressed file has fewer bits (1) so it takes less time to send at the same rate (1)'.

Allow 'quicker/faster to send' where it means less time, but not where it means a higher transmission rate.

Do not accept 'the file is smaller/compression reduces the file size' on its own without saying that the time taken is reduced.

Do not accept 'the transmission rate/speed increases' because the transmission rate stays the same.

Award up to two marks for a linked explanation such as:

• Devices (can) understand/interpret the data they receive (1) because they follow the same set of rules for communication (1)
• Data is sent in an agreed format/structure (1) so the receiving device can interpret/understand it correctly (1)
• Devices (can) connect/communicate successfully (1) because they agree how the data is transmitted, such as the type of signal used (1)
• Errors (can) be detected/handled (1) because both devices follow the same rules for checking the data (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'so devices can talk/communicate with each other' or 'so they can understand each other' without saying they follow the same rules/agreed format.

Do not accept an answer that only states protocols are a set of rules, without saying what this allows (e.g. the data can be understood/interpreted).

Do not accept a faster connection/speed as a reason why protocols are needed.

Do not accept naming a protocol (e.g. TCP/IP, HTTP, Wi-Fi) without an explanation of why it is needed.

Do not accept a description of what a protocol does (e.g. 'TCP splits data into packets') without saying why this is needed.

Award up to two marks for a linked explanation such as:

• Splits the data/file into packets (1) so each packet can be sent separately across the network (1)
• Adds a packet/sequence number to each packet (1) so the packets can be put back into the correct order at the destination (1)
• Detects lost/missing packets (1) so they can be requested/resent (1)
• Creates a connection between the two computers/hosts (1) before the file is sent (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'segments' for 'packets' (TCP divides the data into segments, which become packets at the internet layer).

Do not accept 'sends the data/file' on its own without saying what the transport layer does to the data.

Do not accept naming TCP or a port number on its own without expansion.

Do not accept routing/addressing packets using IP addresses, which is the internet layer.

Indicative content

The role of the central device

• All computers and the printer connect separately to a central switch.
• The central device receives a packet from the sending device and forwards it only to the destination device.
• Each device has its own cable to the central switch, or a wireless connection to a central access point.

Benefits

• If one computer's cable or connection fails, the other computers are not affected, so the school's network stays available.
• Data transfer is fast because each device has a dedicated connection and data is sent directly to the destination.
• It is easy to add a new computer by connecting it to a free port on the central switch.
• It is easy to manage and find faults because each device has its own connection to the central switch.

Drawbacks

• If the central switch fails, the whole network goes down.
• More cable is needed than in a bus topology because every device needs its own cable to the central switch.
• The number of devices is limited by the number of ports on the central switch.
• The central switch and the extra cabling add cost to the school's network.

Levels

• Level 0 (0 marks): No rewardable content.
• Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
• Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
• Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Level 3 responses must cover the role of the central device and at least one benefit and one drawback applied to the school.

Do not accept 'server' as the central device; accept switch, hub or wireless access point.