Performance Evaluation 58 (2004) 15–23 Traffic conditioner: upper bound for the spacer overflow probability Nathalie Omnès a,∗ , Annie Gravey b , Raymond Marie c a Mitsubishi Electric ITE TCL, 1, allée de Beaulieu, CS 10 806, 35 708 Rennes Cedex 7, France b Département informatique, ENST Bretagne, Technopole de Brest Iroise, B.P. 832, 28 285 Brest Cedex, France c Equipe ARMOR, IRISA, Campus universitaire de Beaulieu, 35 042 Rennes Cedex, France Received 3 December 2002; received in revised form 19 November 2003 Available online 20 July 2004 Abstract The current challenge for telecommunication networks is to offer new types of services. To achieve this, somehow traffic has to be conditioned. A spacer is a token bucket traffic conditioner that reshapes flows according to a periodic profile. Packets are delayed until they can be inserted according to this profile. This short paper concentrates on packet discard by overflow in the spacer. An upper bound for the overflow probability is given, valid even when it is fully loaded. It shows the ratio of discarded packets is of the same order than the ratio of out-of-profile packets. © 2004 Elsevier B.V. All rights reserved. Keywords: Traffic conditioning; Leaky bucket; Analytical model; Upper bound; Loss probability 1. Introduction Although Internet Protocol (IP) is currently widely used, it does not provide a straightforward solution to the applications’ needs. Hence it does not permit to offer all the quality of service guarantees on a large scale, and in particular to real-time services such as distributed games. To overcome this problem, more services should appear in the future. The Internet Engineering Task Force (IETF) has standardized in RFC 2475 (see Ref. [7]) an architecture for Differentiated Services (DiffServ). For the sake of scalability, several types of nodes are distinguished. DiffServ ingress and egress nodes are located on the boundary of a DiffServ domain, while DiffServ interior ∗ Corresponding author. Tel.: +33-223-45-58-34; fax: +33-223-45-58-59. E-mail addresses: omnes@tcl.ite.mee.com (N. Omn` es), annie.gravey@enst-bretagne.fr (A. Gravey), raymond.marie@irisa.fr (R. Marie). 0166-5316/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.peva.2004.05.001