Modeling dialup internet access: an examination of user-to-modem ratios, blocking probability, and capacity planning in a modem pool

Abstract

In the near future, dialup connections will remain as one of the most popular methods of remote access to the Internet as well as to enterprise networks. The dimensioning of modem pools to support this type of access is of particular importance to commercial Internet service providers as well as to universities that maintain their own modem pools to support access by faculty, staff, and students. The primary contribution of this paper is to analyze how network administrators may decrease the probability of blocking for access to the pool by imposing session limits restricting the maximum duration of the online session. Session limits may provide a viable alternative to improving network performance without necessarily adding capacity to the pool. Blocking probability is examined under a number of different scenarios to assess potential improvements in the quality of service by imposing session limitations during peak-period operations. Scope and purpose The dimensioning of modem pools to support dialup access by subscribers is an important problem facing both Internet service providers (ISP) and academic institutions that support this type of access. This paper focuses on the use of computer simulation to address modem pool performance using blocking probability as a proxy for level of service during peak periods of operation. The parameter estimates for network traffic are based on historical session log data from large university-based ISP. The paper begins with a brief discussion of traffic variables and examines the underlying distributions associated with each variable. A simulation model is constructed using OPNET Technologies network modeling tool, OPNET Modeler TM. The results of the various simulations are presented and discussed in detail. Long-range capacity planning in dialup environments is critical despite the fact that network-related research has shifted away from dialup issues and focused on more cutting-edge issues. Although dialup network access remains the most heavily utilized consumer-based access method in the world, few providers seem to be considering issues such as the level of service provided to customers and how they may be able to improve service. We examine the issue of service quality in terms of the probability of blocking. Once a benchmark blocking probability is calculated for the modem pool, we investigate how the implementation of innovative management strategies, such as imposing session limits, may impact blocking vs. the traditional approach of simply adding capacity. The paper seeks to provide readers with some indication as to the level of service associated with various user-to-modem ratios and how different combinations of session limits and capacity may improve service.