1. A property of a communication system (network) such that
the output data stream delivered is the exact bit sequence presented to the
input of the system without any restriction or exception.
2. A property of a communication system such that the output data stream
delivered provides an output bit sequence functionally equivalent to the input
bit sequence, from which the exact input bit sequence can be derived.
The second definition implies that the communication system provides protocol
translation between input and output devices whereas the first definition
implies that there is a compensating translation. The second definition cannot
be implemented in all cases since there are functions that are supported by some
terminal devices but have no equivalent in others.