Award up to two marks for a linked explanation such as:
- Each router chooses the best route at the time (1) so when a route becomes busy/congested or fails, later packets are forwarded along a different path (1)
- Routers forward each packet separately (1) so the path a packet takes depends on the traffic conditions when that packet arrives (1)
- A router may send a packet to a different next router (1) if its routing table shows a better/less congested route for that packet (1)
- Traffic on the internet changes (1) so no single path is kept for the file and each packet can use whichever route is best when it is sent (1)
For both marks, the expansion must follow/associate with the statement.
Allow reference to a routing table, or to how a router decides the route, as part of the linked reason.
Do not accept 'the packets have different IP addresses' because all packets from the same file have the same destination IP address, even though their routes can differ.
Do not accept 'the internet is busy' or 'there is a lot of traffic' on its own without linking this to the router choosing a different route.
Do not accept 'different routers send the packets' on its own without a reason why a different router/route is chosen.
Do not accept an answer that only says the packets take different routes without explaining why.