Failure scenarios for Reliable UDP?

Question

What could be good list of failure scenaros for testing a reliable udp layer? I have thought of the below cases: - Drop Data packets - Drop ACK, NAK Packets - Send packets in out of sequence. - Drop intial hand shaking packets - Drop close / shutdown packets - Duplicate packets

Please help in identifying other cases that reliable udp needs to handle?

Thanks, Sunil

Answer 1

Have you tried intentionally corrupting packets in transit?

Also, have you considered a scenario where only one-way communication is possible? In this case, the sending host thinks that the send failed, but the receiving end successfully processes the message. For instance:

1. host A sends a message to host B
2. B successfully receives message and replies with ACK
3. ACK gets dropped in the network
4. A waits for timeout and re-sends message (repeats steps 1-3)
5. host A exceeds retry count and thinks the send failed, but host B has in fact processed the message

Answer 2

I have thought UDP is a connectionless and unreliable protocol and that is does not require and specific transport handshake between hosts. And hence there is no such thing as a reliable UDP protocol.

Answer 3

The list you've given sounds pretty good. Also think about:

• Very delayed packets (where most packets come through fine, but one or two are delayed by several minutes);
• Very delayed duplicates (where the original came through quickly, but the duplicate arrived after several minutes delay);
• Silent dropping of all packets above a certain size (both unidirectional and bidirectional cases);
• Highly variable delays;
• Sequence number wrapping tests.