Specifications for communication
Communication systems we will study implement one of a few specifications
Messages are sent and received through a channel
The channel state is derived from the messages that have been sent
Ideally the state is the sequence of messages that have been sent and not yet delivered, but for weaker specifications the state is different
A message may be acknowledged
None of the specs allows for messages to be corrupted in transit
- It's easy to convert a corrupted message into a lost message, by attaching a sufficiently good checksum to each message, and discarding any message with an incorrect checksum