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Revision 0.6.0
Packet Interface
CORDET applications interact with each other by exchanging commands and
reports. Within an application, commands and reports are encapsulated in
components but, when they travel from one application to another (over some
communication channel which is provided by some middleware external to the
applications themselves), they take the form of packets (see section 3.6). A
report or command packet is an ordered sequence of bytes that contains all the
information required to reconstruct a report or command.
Thus, the interface between two CORDET applications is packet-based. More
precisely, an application needs an out-going interface through which it can send
to another application a packet representing a command or a report and it
needs an incoming interface through which it can receive from other applications
packets representing commands or reports.
The CORDET Framework assumes that a middleware is present which offers
physical connections through which two applications can send packets to each
other. A physical connection then is a data channel provided by a middleware
and capable of transporting packets from one application to another application.
A CORDET system (namely a set of CORDET applications connected to each
other by a middleware) builds a set of logical connections on top of the physical connections offered by the middleware. A logical connection allows two
applications A1 and A2 to exchange packets either directly through a physical
connection linking A1 to A2 (in which case the logical connection coincides with
a physical connection) or through a chain of other applications which are linked
to each other and to A1 and A2 by physical connections. This is illustrated in
figure 9.1. The figure shows a CORDET system consisting of four applications
(yellow boxes in the figure). The applications are linked to each other by three
physical connections (black lines in the figure). In this system, the following
kinds of logical connections might, for instance, be defined:
1. A logical connection between applications A and
physical connection C1;
2. A logical connection between applications B and
physical connection C3;
3. A logical connection between applications A and
physical connections C1 and C2 and application
node.
B which is built upon
D which is built upon
C which is built upon
B acting as re-routing
When a packet travels through an application en route to another application,
it is said to be re-routed. Packet re-routing is a function which is defined by
the CORDET Framework and is therefore supported by default by CORDET
Systems. In figure 9.1 a packet travelling along a logical connection from application A to application C is re-routed by application B.
This section specifies the interfaces through which applications send packets to
and receive them from the middleware and it specifies the re-routing logic which
allows applications to exchange packets even in the absence of a direct physical
c
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P&P Software GmbH. All Rights Reserved.
This document is provided with the GPL version of the
C2 Implementation of the CORDET Framework.
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