AccordingtoHolzmann 14], protocol speci?cationscomprise ?veelements: the service the protocol provides toits users; the set of messages that are exchanged between protocol entities; the format of each message; the rules governingm- sage exchange (procedures); and the assumptionsabout the environment in which the protocol is intended tooperate. In protocol standards documents, information related to the operatingenvironment isusually writteninformally andmayoccur in several di?erentplaces 37]. This informal speci?cation style canlead to misunderstandings andpossibly incompatible implementations. In contrast, executableformalmodelsrequireprecisespeci?cations oftheoperating environment. Ofparticularsigni?canceisthecommunicationmediumorchannel over which the protocol operates. Channelscan havedi?erent characteristics depending on the physical media (e. g. optical ?bre, copper, cable orunguided media (radio)) they employ. The characteristics also depend on the levelof the protocol inacomputer protocol architecture. Forexample, the link-leveloperates over a singlemedium, whereas the network, transport andapplication levelsmayoperate over a network, or network of networks such as the Internet, which couldemploy several di?erent physical media. Channels (such as satellite links) can be noisy resulting in bit errors in packets. To correct biterrors in packets, many importantprotocols (such the Internet's TransmissionControl Protocol 27]) use CyclicRedundancy Checks (CRCs) 28] to detect errors. On detectingan error, the receiver discards the packet andrelies on the sender to retransmit itforrecovery, known as Au- maticRepeatreQuest(ARQ) 28]. Thisisachievedbythereceiveracknowledging the receipt of good packets, andby the transmitter maintainingatimer. When the timer expires before an acknowledgementhasbeen received, the transmitter retransmits packets that havebeen sent but are as yet notacknowledged. It may also be possibleforpacketsto be lost due to routers in networks discarding packets when congested

These Transactions publish archival papers in the broad area of Petri nets and other models of concurrency, ranging from theoretical work to tool support and industrial applications. ToPNoC issues are published as LNCS volumes, and hence are widely distributed and indexed. This Journal has its own Editorial Board which selects papers based on a rigorous two stage refereeing process. ToPNoC contains: Revised versions of a selection of the best papers from workshops and tutorials at the annual Petri net conferences; special sections/issues within particular subareas (similar to those published in the Advances in Petri Nets series); other papers invited for publication in ToPNoC; papers submitted directly to ToPNoC by their authors.

This is the first volume of ToPNoC. It contains revised and extended versions of a selection of the best papers from the workshops held at the 28th International Conference on Applications and Theory of Petri Nets and Other Models of Concurrency, which took place in Siedlce, Poland, June 25-29, 2007. The material has been selected and evaluated by the two Workshop and Tutorial Chairs, Wil van der Aalst and Jonathan Billington, in close cooperation with the chairs of the individual workshops.

The 13 papers in this volume cover a wide range of concurrency-related topics, including: teaching concurrency; process languages; process mining; software engineering; state space visualization techniques; timed Petri nets; unfolding techniques and hardware systems. Thus, this volume gives a good overview of the state of the art in concurrency research.

Petri nets offer a mathematically defined technique for the specification, design, analysis, verification and performance evaluation of concurrent distributed systems. They offer not only precise semantics and a theoretical foundation, but also a graphical form that facilitates the understanding of both information and control flow within the same formalism. As an intuitively appealing graphical form of presentation, Petri nets are the model of choice in various applications.
Communications networks, ranging from traditional telecommunication systems to advanced Internet-based information services, are inherently distributed and comprise systems with concurrently operating components. This volume presents a selection of the latest advances in the use of Petri nets for the modeling, analysis and management of communication networks and systems in the broadest sense of these terms.

This book constitutes the refereed proceedings of the 17th International Conference on Application and Theory of Petri Nets, held in Osaka, Japan, in June 1996.
The 26 revised full papers included in the book together with three invited presentations were selected from a total of 78 submissions. The book addresses the current theoretical and applicational aspects of the various types of Petri Nets and competently reflects the state of the art in the area.