A Calculus of Communicating Systems with Label Passing—Ten Years After Uffe H. Engberg Mogens Nielsen BRICS ∗ Department of Computer Science † University of Aarhus Ny Munkegade DK-8000 Aarhus C, Denmark Abstract This note is dedicated to Robin Milner. We take the opportunity of looking back on a ten year old report of ours on an extension of CCS with label passing. 1 Preface This note is dedicated to Robin Milner on his 60 th birthday. On this occasion we have taken the opportunity of commenting on a report of ours from 1986, on an extension of Milner’s CCS with label passing [EN86]. The challenging problem of extending CCS with a notion of label (or channel) passing was motivated and formulated by Milner himself already in 1979, before CCS was published. At the time Milner was spending his sabbatical at the University of Aarhus, and in discussions with one of us (Nielsen) we looked upon various ideas for such extensions of CCS, but did not manage to get any of these to work properly. In 1985 Engberg was looking for a subject for his MSc thesis, and we decided to make another attempt at the six year old problem and ideas. At that time, a few attempts had already been made towards calculi with notions of mobility (as it was later called by Milner et al. in [MPW89]), notably the parametric channels by Astesiano and Zucca [AZ84] and the LNET formalism by Kennaway and ∗ Basic Research in Computer Science, Centre of the Danish National Research Foundation. † e-mail address: {engberg,mnielsen}@brics.dk, fax: ++45 89 42 32 55 1