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Edexcel GCSE Computer Science (1CP2) Exam Questions

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3 questions · 6 marks

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1Explain2 marksProtocols & Layers Swap Remove

Two computers exchange data over a network.

Explain why network protocols are needed for the two computers to communicate.

[2 marks]
Mark scheme

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.

Example answers and how they were marked
Full marks2/2

Devices can understand the data they receive because they follow the same set of rules for communication.

Why: Linked point (1) and reason (1): following the same rules is what lets the devices understand the data.

Some marks1/2

Data is sent in an agreed format.

Why: Point (1) identified, but no linked reason saying what the agreed format achieves.

No marks0/2

Protocols are needed so the connection is faster because more data can be sent at once.

Why: Speed is not a reason protocols are needed, so there is no creditworthy point or linked reason.

2Explain2 marksThe Internet Swap Remove

Every device that connects to the internet is given an IP address.

Explain one reason why every device on the internet needs a unique IP address.

[2 marks]
Mark scheme

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

  • Data/packets are delivered to the correct device (1) because the IP address identifies that device on the internet (1)
  • A reply is sent back to the device that made a request (1) because the sender's IP address is used as the destination address for the reply (1)
  • Routers can forward packets to the right device (1) because each packet's destination IP address matches only one device (1)
  • A device can be contacted by other devices (1) because other devices use its IP address to send data to it (1)

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

Allow 'so the router knows where to send data' only when expanded to say the IP address identifies the destination device / is used by routers to forward the packet to that device.

Do not accept 'so it can connect to the internet' / 'so it can access the internet' without saying how the address is used to identify the device or deliver data to it.

Do not accept 'so the device can be identified' on its own without saying what the identification is used for, e.g. delivering data or returning a reply.

Do not award a mark for restating that an IP address is unique / every device has a different address.

Example answers and how they were marked
Full marks2/2

So that data reaches the correct device. The IP address is how the internet tells one device apart from another, so packets are sent to that device and not to a different one.

Why: Point (1): data reaches the correct device. Reason (1): the IP address identifies/tells devices apart, so packets are sent to that device.

Some marks1/2

So that packets go to the right device, because every device has a different address.

Why: Point (1): packets go to the right device. The reason only restates that every device has a different address, which the mark scheme says does not earn the second mark.

No marks0/2

So it can connect to the internet.

Why: No linked explanation of how the address is used; 'so it can connect to the internet' is not accepted without expansion.

3Explain2 marksAddressing Swap Remove

Routers forward data across the internet.

Explain how a router uses the destination IP address of a packet to send the packet towards its destination.

[2 marks]
Mark scheme

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

  • The router reads/checks the destination (IP) address in the packet (1) so it can forward/send the packet towards that address/destination (1)
  • The router looks up/compares the destination (IP) address (1) to choose the route/next network/next router for the packet (1)
  • The router uses the destination (IP) address to choose/select the outgoing connection/network (1) so the packet is sent one step closer to its destination (1)

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

Do not accept a restatement of the question, such as 'the router uses the IP address to forward the packet', without saying how the address is used, e.g. checking the destination address or choosing the route/next network.

Do not accept answers that say the router gives/adds an IP address to the packet, or that the router uses a MAC address instead of the destination IP address.

Example answers and how they were marked
Full marks2/2

The router checks the destination IP address in the packet and sends the packet out on the route/network that leads towards that address.

Why: Point (1): the router checks the destination IP address; linked reason (1): this is used to send the packet towards that destination.

Some marks1/2

The router checks the destination IP address in the packet.

Why: Point (1): the router checks the destination IP address; no linked reason is given, so only the first mark.

No marks0/2

It adds an IP address to the packet so the packet knows where to go.

Why: Misconception: the router does not add an IP address to the packet; the mark scheme says not to accept this, so no marks.

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