Publications of Marvin Sirbu Available on Line

This paper provides a framework for understanding competition and industry structure in the context of Fiber to the Home (FTTH). We present engineering cost models, which indicate that FTTH is a decreasing cost industry, thereby making facilities based competition an unlikely outcome. Non-facilities based competition (or service level competition) in FTTH can happen in data-link layer (or transport) services via unbundled dark fiber (i.e. unbundled network elements) and in higher layer (voice, video and data) services via logical layer unbundling (or open access). FTTH architectures differ in the extent to which they support unbundling and therefore the extent of non-facilities based competition in FTTH depends on the architecture of the shared network over which multiple service providers offer service.

Chuang, J. and Sirbu, M., "Distributed Network Storage with Quality-of-Service Guarantees,"  presented at the Internet Society INET'99 Conference, San Jose, Ca, June, 1999.

This paper envisions a distributed network storage service with Quality-of-Service (QoS) guarantees, and describes its architecture and key mechanisms. When fully realized, this service architecture would be able to support, in one  integrated framework, network storage services ranging from best-effort caching to replication with performance guarantees. Content owners could, through the use of standardized protocols, reserve network storage resources to satisfy their application-specific performance requirements. They would be able to specify either the number and/or placement of the replicas, or higher-level performance goals based on access latency, bandwidth usage or data availability. The network storage provider would then optimally allocate storage resources to meet the service commitments, using leftover capacity for best-effort caching.  This work identifies and discusses key research areas and problems that need to be tackled, including those in service specification, resource mapping, admission control, resource reservation and real-time storage management.

Kawakura, Y., Sirbu, M., Simpson, I., and Tygar, D., "Flexible and Scalable Credential Structures:  NetBill Implementation and Experience,"  submitted to CrypTec '99.  (PDF)  (gzipped Postscript)

In electronic commerce consumers often need to present attributes such as membership in order to benefit from specific pricing or access. A scalable, efficient mechanism for conveying attributes independently from authentication is required. In this paper we describe a system based on a combination of Public Key Kerberos for Distributed Authentication (PKDA) and attribute credentials as a means for solving meeting these requirements. This system is compared to other proposals for distributed authentication and authorization, and is shown to be superior in several respects. The system has been implemented as part of the NetBill micropayment system and has been demonstrated to work well in meeting the stated requirements.

Chuang, J. and Sirbu, M. "Pricing Multicast Communications: A Cost-Based Approach", presented at the Internet Society INET'98 Conference, Geneva, Switzerland, July 21-24 1998. (PDF) (gzipped Postscipt)

Multicast and unicast traffic share and compete for network resources. To facilitate equitable resource allocation between traffic types, the price of multicast relative to unicast should be based on the relative resource consumption. Based on analysis of resource consumption over a wide range of networks, we show that the relative cost of a multicast tree varies as the 0.8 power of the multicast group size. This relationship saturates when all nodes of the network are included in the multicast tree.

Sirbu, M., "Credits and Debits on the Internet," IEEE Spectrum, 34, no.2, February, 1997, pp. 23-29.

Chuang, J. and Sirbu, M., "The Bundling and Unbundling of Information Goods: Economic Incentives for the Network Delivery of Academic Journal Articles," Dec 1996. (Postscript, PDF) Presented at the Conference on Economics of Digital Information and Intellectual Property, Cambridge MA, Jan 23-25 1997.

The digitization of infomation goods requires a total rethinking of their production and marketing economics. An N-good bundling model with multi-dimensional consumer preferences is developed to study the key factors that determine the optimal bundling strategy. Using analytic and empirical methods, mixed bundling is shown to be the dominant strategy.

Sirbu, M. and Chuang, J., Distributed Authentication in Kerberos Using Public Key Cryptography(HTML,1996). Presented at the Internet Society 1997 Symposium on Network and Distributed System Security. Also available in Adobe PDF or PostScript formats.

This paper describes a method for using public key cryptography to mutually authenticate clients and servers and to establish a symmetric session key. The method described here is superior to SSL 3.0 in that it minimizes server state; operates over both UDP and TCP; can be used even through a proxy server; and supports delegation. The technology described in this paper is used in the NetBill system to provide session level authentication and privacy.

Xie, J., Song, M., Sirbu, M. and Wang, Q., Kalman Filter Estimation of New Product Diffusion Models (PDF),  Journal of Marketing Research, 34, 3, August 1997, pp. 378-393.

This paper introduces a new estimation procedure, Augmented Kalman Filter with Continuous State and Discrete Observations (AKF(C-D)), for estimation of diffusion models. This method is directly applicable to any differential diffusion model without imposing constraints on the model structure or the nature of the unknown parameters. It provides a systematic way to incorporate prior knowledge about the likely values of unknown parameters, and updates the estimates when new data become available. The empirical comparisons of AKF(C-D) with five other estimation procedures demonstrate AKF(C-D)'s superior prediction performance. As an extension to the basic AKF(C-D) approach, a parallel-filters procedure is also developed for estimation of diffusion models when there is uncertainty about diffusion model structure or prior distributions of the unknown parameters.

Sirbu, M. and Chuang, J., Public-Key Based Ticket Granting Service in Kerberos (ASCII), 1996

This document formally defines extensions to the Kerberos protocol specification (RFC 1510, "The Kerberos Network Authentication Service (V5)", September 1993) to provide a method for supporting ticket-granting services based on public-key cryptographic algorithms. These extensions eliminate the need for a client to contact a centralized Ticket Granting Service in order to establish a secure and authenticated session ticket for use with a kerberized server. Technology based on this proposal is used in the NetBill system for efficient symmetric key based session level security while avoiding the TGS bottleneck.

Omoigui, N., Sirbu, M., Eldering, C. and Himayat, N., Comparing Integrated Broadband Architectures from an Economic and Public Policy Perspective in Telecommunications and Internet Policy, Brock, G., ed. (Lawrence Erlbaum: Washington, DC, 1996).

This paper compares the installed first cost of various architectures for providing integrated broadband services to residences. The capital costs of the various alternatives are developed from a detailed engineering layout model which computes the total component requirements and installation costs for the various alternatives starting from component level prices. A number of conclusions relevant to the regulation of cable and LEC provision of broadband services are derived from the analysis.

Qiong Wang, Marvin A. Sirbu, and Jon M. Peha, An Optimal pricing Model for Cell-Switching Integrated-Services Networks, Journal of Electronic Publishing, May, 1996. A revised version will appear as "Optimal Pricing for Integrated-Services Networks with Guaranteed Quality of Service,"in Internet Economics , J. Bailey & L. McKnight ed., MIT Press, 1997.

This paper develops an optimal pricing model and an iterative solution technique for ATM integrated services networks provding both predictive guaranteed services and "best effort" services.

Sirbu, M. and Tygar, J.D., NetBill: An Internet Commerce System Optimized for Network Delivered Services (HTML, 1995), Proceedings of the IEEE CompCon, March, 1995.

This is an HTML version of the most current paper describing the Netbill system. A postscript version is available (1.1 MB).

Cox, B., Tygar, D. and Sirbu, M., NetBill Security and Transaction Protocol (HTML, 1995)

This paper appears in Proceedings of the First USENIX Workshop on Electronic Commerce. The full paper is also available in PostScript, PDF, or ASCII text. The PostScript or PDF versions are preferred, as they include the graphics, face changes, and special characters that are absent in the other versions.

Camp, L.J., Sirbu, M., Tygar, J.D.Token and Notational Money in Electronic Commerce

This paper was prepared for the Usenix Workshop on Electronic Commerce; NY, NY, July 11-12, 1995 (a previous version was presented at the Telecommunications Policy Research Conference; Oct. 1-3, 1994; Solomons Island, MA). The paper reviews several proposed electronic commerce protocols from both a technical and legal perspective. Includes a review of U.S. legislation governing privacy and anonymity in commercial transactions.

Selgado, H., Sirbu, M., and Peha, J., "Spectrum Sharing Through Dynamic Channel Assignment for Open Access to Personal Communications Services" Proceeings of the IEEE International Communications Conference, 1995.

Rather than auction exclusive access to blocks of spectrum for cellular services, this paper considers allowing multiple operators to share a single block of spectrum through Dynamic Channel Assignment. Using DCA, operators claim unused channels as necessary to service calls, and release them for other operators to use as calls complete. A simulation analysis shows that such a scheme is as effective in using bandwidth as dedicated assignments to individual operators.

Xie, J. and Sirbu, M., "Price Competition and Compatibility in the Presence of Positive Demand Externalities," Management Science, 41, 5, May, 1995, pp. 909-926

This paper examines the dynamic pricing behaviors of an incumbent and a later entrant, with special attention to the impacts of demand externalities, compatibility, and competition on prices and profits. We assume a durable good with sales determined by a Bass diffusion model influenced by comparative product pricing. We model optimal pricing as a differential game with the optimal price trajectory established as Nash open-loop controls.

Yuan, Y., Roehrig, S. and Sirbu, M., Service Models, Operational Decisions and Architecture of Digital Libraries Proceedings of DL95, June 1995.

This paper examines an economic model of publishers, electronic distributors and consumers similar to what is emerging on the World Wide Web. Issues addressed include optimal pricing, and optimal replication of distribution sites.

Electronic Commerce Presentation to the Conference on "News Industries & Journalism/Preparing for 2010", Sponsored by New Directions for News, Univeristy of Missouri, June, 1995.

A slide presentation reviewing information markets and payment systems on the Internet.

Technology and Infrastructure, in A National Information Network: Changing Our Lives in the 21st Century, Annual Review of the Institute for Information Studies (IIS: Queenstown, Md., 1992)

This chapter summarizes emerging trends in telecommunications technology and their implications for a National Information Infrastructure.