A Coloured Petri Net Approach to Formalising and Analysing the Resource Reservation Protocol

The goal of the Resource Reservation Protocol (RSVP) is to support the provision of the Quality of Service required for emerging Internet applications (such as video conferencing) that require a level of performance not guaranteed by the Internet. RSVP attempts to provide performance guarantees by establishing resource reservations (such as the number of buffers and bandwidth allocation) within routers and host computers of the Internet. Currently, Internet protocols are not formally specified when they are developed. Instead they are described in a narrative way in documents called Request for Comments (RFCs). This is the case for RSVP. To increase confidence in RSVP we have formalised and analysed its narrative specification using Coloured Petri Nets (CPNs). This paper demonstrates how CPNs can be used for modelling and analysing RSVP. Among the several beneficial features of CPNs are: graphical facilities for specification; support for different levels of abstraction; hierarchical structuring mechanisms; and verification and validation methods, such as querying the state space to investigate properties, and language equivalence to check the consistency of different levels of abstraction. Coloured Petri Nets are supported by a number of computer tools including Design/CPN. Design/CPN supports the construction and maintenance of CPN models and their simulation and analysis using state spaces. These facilities allow us to create a model that provides a clear, unambiguous and precise definition of RSVP, and to analyse the protocol for functional correctness. The paper concentrates on the approach and the tools used in this investigation.