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Title: The local area π-calculus
Author: Chothia, Tom
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2004
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All computers on the Internet are connected, but not all connections are equal. Hosts are grouped into islands of local communication. It is the agreed conventions and shared knowledge that connect these islands, just as much as the wires and switches that run between them. The power and limitation of these conventions and shared knowledge and hence their effectiveness can be investigated by an appropriate calculus. In this thesis I describe a development of the π-calculus that is particularly well suited to express such systems. The process calculus, which I call the local area calculus or lαπ, extends the π-calculus so that a channel name can have within its scope several disjoint local areas. Such a channel name may be used for communication within an area or it may be sent between areas, but it cannot itself be used to transmit information from one area to another. Areas are arranged in a hierarchy of levels which distinguish, for example, between a single application, a machine, or a whole network. I present a semantics for this calculus that relies on several side-conditions which are essentially runtime level checks. I show that a suitable type system can provide enough static information to make most of these checks unnecessary. I examine the descriptive power of the lαπ -calculus by comparing it to the π-calculus. I find that, perhaps surprisingly, local area communication can be encoded into the π -calculus with conditional matching. The encoding works by replacing communication inside an area with communication on a new channel created just for that area. This is analogous to replacing direct communication between two points with a system that broadcasts packets over a background ether. I show a. form of operational correspondence between the behaviour of a process in lαπ and its π -calculus translation. One of my aims in developing this calculus is to provide a convenient and expressive framework with which to examine convention-laden, distributed sys­tems. I offer evidence that the calculus has achieved this by way of an extended case study. I present a model of Internet communication based on sockets and TCP over IP and then extend this system with Network Address Translation. I then give a model of the File Transfer Protocol that uses TCP/IP to commu­nicate between networks. Traces of the model show that FTP, run in its normal mode, will fail when the client is using Network Address Translation, whereas an alternative mode of FTP will succeed. Moreover a normal run of the model over NAT fails in the same way as the real life system would, demonstrating that the model can identify this failure and correctly highlight the reasons behind it.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available