A file is sent across the internet in packets.
Explain why packets from the same file may take different routes.
Mark scheme
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.
Example answers and how they were marked
Each router chooses the best route at the time, so if one route becomes busy or fails, later packets are sent a different way.
Why: Linked point (1) that each router chooses the best route at the time and reason (1) that a busy or failed route means later packets take a different path.
Routers send packets along the least congested route.
Why: States that a router chooses the least congested route (1) but gives no linked reason why this makes the packets from the file take different routes.
Because each packet is given a different IP address so they go to different places.
Why: Misconception named in the mark scheme: all packets from the same file share the same destination IP address, even though their routes can differ.