Specification, Quantification and Provision of Quality of Service and Congestion Control for New Communication Services

Edmundo Monteiro*, Fernando Boavida*, Gonçalo Quadros*, Vasco Freitas**

Universidade de Coimbra*
Departamento de Engenharia Informática
P-3030 Coimbra, Portugal

Tel: +351 239 7000000
Fax: +351 239 701266
e-mail: edmundo (at) dei.uc.pt

Universidade do Minho **
Departamento de Informática
P-4700-320 Braga, Portugal

Tel.: +351 253 604465
Fax.: +351 253 678954
e-mail: vf (at) di.uminho.pt


Reservationless computer communication networks based on the best effort paradigm are no longer capable of providing the quality of service necessary for the new generation of computer communication services, such as voice, video and multimedia services. These new services and their users have very different communication needs, and must not be treated equal by the communication system.

Quality of service (QoS) specification on a per communication service basis, and quality of service guarantee by reservation-oriented communication systems are the key solutions for the support of new age information systems. QoS specification requires service characterization based on a set of QoS parameters that, on one hand, is rich enough to accommodate service and traffic dynamics and, on the other hand, is simple and flexible enough to allow the implementation of an efficient reservation policy. QoS guarantee by reservation-oriented communication systems can only be achieved by the deployment of new congestion control functions that can prevent service degradation and - based on a quantification scheme - be used to evaluate the network in terms of QoS performance and available capability.

Traditionally, congestion control functions were focused on the communication system itself. It is now evident that new congestion control functions must be focused on communication services, as the network may be in a congestion level that is perfectly adequate for a broad range of services and totally inadequate for other services. Thus, the congestion must be evaluated from the user (or service) point of view, in addition to the network point of view.

In this paper, the authors propose a Quality of Service Framework that provides the basis for QoS specification, quantification and guarantee, and thus constitutes a fundamental tool to the definition and establishment of new generation computer communication services. Firstly, a new congestion definition is proposed, focusing the effects of the communication system on the behavior of communication services. In line with the proposed definition, a model for QoS specification and characterization is presented. Secondly, a metric for the continuous evaluation of the congestion level of individual communication services is given. The metric is based on the deviation of traffic parameters from the values specified during the QoS negotiation phase. From individual service evaluation, an algorithm for the calculation of partial and global communication system congestion is then proposed. Finally, a multidimensional framework for congestion control characterization is presented, in which each dimension identifies a different view - or plane - of the problem.