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.