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A <message_spec>
described as being WITH DATA TOUCHING
will force every word in a message to be both read and written
(“touched”). When <message_spec>
describes an outgoing message, the data will be touched before
transmission. When <message_spec>
describes an incoming message, the data will be touched after
reception. In a sense, WITH DATA TOUCHING
presents a more realistic assessment of network performance, as
real applications almost always access the data they send or
receive. It also distinguishes between messaging layers that
implicitly touch data and those that can transmit data without
having to touch it. One would expect the latter to perform better
when the data is not touched, as the former may be paying a penalty
for touching the data. However, either could perform better when
messages are sent WITH DATA TOUCHING
,
because the latter now has to pay the penalty that the former has
already paid.
Another form of data-touching supported by coNCePTuaL is
WITH VERIFICATION
.
This causes the source task to write known, but randomly generated,
data into the message before transmission and the target task to
verify that every bit was correctly received. When a message is
received WITH VERIFICATION
,
the bit_errors
variable (see Predeclared
variables) is updated appropriately.
WITHOUT DATA TOUCHING
and WITHOUT
VERIFICATION
are synonymous. Both explicitly specify the
default behavior of neither touching nor verifying message
contents.