Edexcel GCSE Computer Science (1CP2) Exam Questions

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

• The receiver can put the packets back into the correct order (1) because packets may arrive out of order/take different routes (1)
• The receiver can see if a packet is missing (1) because the sequence of numbers shows a gap (1)
• The receiver knows when the whole file has arrived (1) because the total number of packets/last packet number is known (1)

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

Allow 'so the packets can be put back in the correct order/reassembled' for the first mark, but the second mark needs the reason, i.e. packets may arrive out of order/take different routes.

Do not accept 'so the packets can be identified' without stating what the number is used for, e.g. reordering or spotting a missing packet.

Do not accept 'so the router knows where to send it' - the router uses the destination IP address, not the packet number.

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.

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

• A LAN covers a small geographical area (1) because all the charity's computers are in one building/on one site (1)
• The charity can use its own cabling/equipment (1) so it does not need to rent leased lines from a telecoms provider (1)
• The charity owns the infrastructure (1) so it avoids the cost of leased lines/external connections that a WAN needs (1)
• The devices are close together (1) so the LAN can use short, high-speed cabling (1)

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

Do not accept 'it is faster/better/cheaper' on its own without a linked reason (e.g. short distance, own cabling, no leased lines).

Allow 'the LAN is private/secure' only with a linked reason such as the charity controls its own equipment.

Do not accept 'a LAN is local' or 'a WAN is too far/expensive' without a linked reason about the small area or leased lines.

Do not accept 'the computers are in one building/on one site' on its own because it repeats the stem; it must be linked to a reason such as a LAN covering a small geographical area.

Do not accept 'stronger Wi-Fi/signal' as a reason.

Do not accept 'can share files/printers' on its own because this is a reason for any network, not for choosing a LAN over a WAN.