do not prescribe content of return packets

[gernotheiser]

the client should have freedom to change the contents of data. I suggest the following minimum packet content rule.

Layout: |w[0]|w[1]|...|w[n-2]|w[n-1]|

Content:
w[0]: sequence number
w[1]...w[n-2]: sender-defined
w[n-1]: checksum of w[0]...w[n-2]

[wom-bat]

There is now a 'latency-check' target that enforces w[1] = w[0] + 1

[gernotheiser]

is there still a checksum test?