??? Cancellation feature enables prior requests from the client to be cancelled later
by the client.
??? Commands feature ensures that response messages from the server match with
respect to the particular commands being requested by the client.
??? Setup feature is a handshake between the client and the server that activates the
protocol.
Advanced Topics 225
Only a subset of the information that is present in the concrete messages of the protocol
is relevant for modeling these protocol features. Therefore, concrete messages
of the protocol are mapped to the abstract actions of the model program as follows.
Each message has a particular command field that indicates the operation requested
by the client or responded by the server. For this protocol it is natural to map the kind
of the message, that is, whether it is a request or a response message, together with
the command field of the message to one action symbol. This is because there are
only a couple of dozen commands in total and different features are very naturally
related to different groups of commands.Without loss of generality, we suppose that
the commands are Setup, Work, and Cancel. The corresponding action symbols are
as follows:
??? ReqSetup and ReqWork are action symbols that represent requests from the client
to execute the commands Setup and Work, respectively. A setup (work) request
is an action ReqSetup(m,c) (ReqWork(m,c)), where m is a message ID and c is a
number of requested credits.
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