A QUALITY-BASED COST DISTRIBUTION CHARGING SCHEME FOR QoS MULTICAST NETWORKS 1 Antonio Bueno, Ramon Fabregat, Pere Vilà Institut d’Informàtica i Aplicacions (IIiA), Universitat de Girona Avda. Lluís Santaló, s/n, 17071 Girona (SPAIN) E-Mail: {bueno, ramon, perev}@eia.udg.es Phone: +34 972 418 475 Fax: +34 972 418 098 1 This article is supported by Spanish Education Ministry (CICYT) under contract TEL99-0976. Abstract This paper presents a new charging scheme for cost distribution along a point-to-multipoint connection when destination nodes are responsible for the cost. The scheme focus on QoS considerations and a complete range of choices is presented. These choices go from a safe scheme for the network operator to a fair scheme to the customer. The in-between cases are also covered. Specific and general problems, like the incidence of users disconnecting dynamically is also discussed. The aim of this scheme is to encourage the users to disperse the resource demand instead of having a large number of direct connections to the source of the data, which would result in a higher than necessary bandwidth use from the source. This would benefit the overall performance of the network. The implementation of this task must balance between the necessity to offer a competitive service and the risk of not recovering such service cost for the network operator. Along this paper multicast charging will be made without making any reference to any specific category of service. The proposed scheme is also evaluated with the criteria set proposed in the European ATM charging project CANCAN ([CAN-D5] and [CAN-D9]). 1. Introduction Charging for network services is a wide and active subject of study. The main motivations are understanding and/or influencing behaviour, measuring policy compliance, and rational cost allocation/recovery [MIL91]. Charging a point-to-point service is mainly a question of studying the traffic transported, measure it in one way or the other and integrate all this information in a effective but understandable scheme to determine the tariff to be applied to the customer. Not a simple problem but widely studied. In ATM networks charging has been studied by European projects CANCAN and CA$hMAN, mainly for point-to-point services (see [CAN-D5] and [CAN-D9]). Further study for ATM and IP networks has been carried out by European project SUSIE [SUS-D4]. When point-to-multipoint services are the subject of charging (instead of point-to-point services) additional problems appear. It is not only the amount of connections involved but also the nature of these services: some point-to-multipoint services need additional synchronisation, others may have different categories of users and, in general, most of this type of services have also considerable bandwidth requirements. In point-to-point services, it is advisable to include in service description the charge responsible policy [CAN- D9], i.e. who will pay for the service: sender, receiver or both and, in this last case, how. In point-to-multipoint it becomes necessary to know how the charge will be distributed because the many variations that can be found. Multiple users are involved in these services and, sometimes, they are senders and receivers at the same time. Examples of such services are videoconferencing and commercial information retrieving. The three main scenarios for multicast are one-to-many (1-N), many-to-one (N-1) and many-to-many (N-N), as shown in fig. 1. Typical examples are information distribution for 1-N, data collection for N-1 and videoconference for N-N: 1-N N-1 N-N fig. 1 The main subject of discussion in this paper is the 1-N service. The N-1 service is not profitable for this paper due to the unicity of the information sent by each channel. Finally, in this paper, the N-N service will be considered as an aggregate of point-to-multipoint connections. QoS Multi- cast Charging