David A. Garbin

Performance modeling of distributed automatic call distribution systems

The number of businesses using Automatic Call Distribution (ACD) systems has grown significantly in the last five years. The industry shows all the signs of continued or greater growth in the foreseeable future. While ACD systems have proliferated they have also evolved from fundamentally local to distributed systems. An ACD manager can no longer optimize his traffic by using inputs from a simple set of queueing tables. The most common system is now a distributed network where subsystems interact with each other and cannot be analyzed in isolation. This paper examines the strengths and weaknesses of queueing models that have been used historically with ACD systems and develops modifications to these models (including agents wrap-up times) that are combined with queueing network theories to construct an original ACD network performance algorithm to work with distributed systems.

An Enhanced Extension to Wilkinson's Equivalent Random Technique with Application to Traffic Engineering

In this paper we present an enhanced extension to Wilkinsons equivalent random technique that allows one to easily compute the different levels of blocking that various streams of traffic see using the same trunk group. This empirical extension is based on a regression analysis and is superior to a similar extension by Katz. An application of our extension to system sizing problems in AUTOVON is presented. Previous sizing methods in the AUTOVON access area did not properly account for the peakedness of overflow traffic and thereby violated desired grades of service. The methods presented here overcome this problem, and yield a lower cost solution using fewer two-way trunks.

Open Source for Enterprise Geographic Information Systems

Enterprises can benefit from an open source geographic information system architecture, but understanding the nature of GIS data and the functions of each open source component is crucial to implementation success.

Modeling the performance of low latency queueing for emergency telecommunications

Event simulation and analytic modeling are used to evaluate the performance of low latency queueing (LLQ), a queueing discipline available in some Internet packet switching routers for integrated services performance assurance. LLQ combines priority queueing with class-based weighted fair queueing (CBWFQ). Priority queueing is used to ensure satisfying tight delay constraints for real-time traffic, whereas CBWFQ is used to ensure acceptable throughput for traffic classes that are less sensitive to delay. Simulations are developed both using a commercial product, OPNET Modeler, and also custom simulators that we developed. Our custom simulators model two different approaches to CBWFQ; and comparisons between the approaches and that of the commercial simulator are conducted. Our computational experiences (central processing unit [CPU] times for model execution and postprocessing) in using the simulators are described. This work is an important first step in the ability to model a proposed enhancement to LLQ which may be beneficial to emergency telecommunications services.

Design and analysis of high availability networks

This study provides an analysis of representative critical service networks based upon research of component failure data. We used IP-SURVIV, a Noblis survivability analysis tool, to assess the availability of three representative critical service networks as components were disabled. Our findings indicate that the generally accepted high availability network topology and routing strategies - dual-homing access nodes and providing a primary and a single alternate route between all backbone node pairs - may result in surprisingly low network availability. We present architecture guidelines which significantly improve network availability. In light of our findings, entities requiring robust, high availability network service should consider reassessing the availability of their networks and also consider implementing both a multi-carrier, 3- connected backbone and a second MPLS backup route to achieve high availability (i.e., ≥ 0.9999).

The Circuit-Switched Network Design and Analysis Model: A Chronology of Its Development and Use

The Defense Information System Agency DISA has managerial and engineering responsibility for a circuit-switched network currently known as the Defense Information System Network---Voice. This network was originally implemented in the 1960s and was known as the Automatic Voice Network. Throughout this time, DISA has used a network design and analysis model to reconfigure the network. This model was developed in the early 1970s, has been continually enhanced, and is used on a weekly basis to engineer and manage the network. Since 1975, it has been used to save the United States U.S. government approximately

Using simulation to evaluate LTE load control for priority users

1,400,000,000.00. In this paper, we present a chronology of its development, enhancement, and use.

Of dual-core networks during rare events

Disasters can cause extraordinary service demand by the public. It is imperative that services supporting disaster response perform with minimal degradation during such events. In order to provide adequate service to special users such as first responders, priority treatment mechanisms have to be developed. Priority treatments have been incorporated for earlier wireless technologies, but have to be established on Long-term Evolution (LTE) / 4G. One of the proposed priority-treatment concepts is Access Class Barring (ACB), which will shed traffic from public users in response to extreme overloads, resulting in priority for special users. However, the degree to which ACB would improve voice call completion is unknown. A discrete-event simulation was performed to model extreme overload situations and predict the performance of ACB under various configurations. The simulation study found that ACB could drastically improve the priority call completion probability in the most extreme overloads while maintaining performance for public traffic.

Measuring resilience in multi-carrier emergency and critical telecommunications systems

Telecommunication networks are evolving to become more reliable, but many networks remain vulnerable to widespread systemic failures. Reliability of individual components has improved and some networks can achieve availabilities on the order of 0.99999. However, the routing technologies used by these networks, like Open Shortest Path First and Border Gateway Protocol can create system-wide vulnerabilities. Some of the vulnerabilities include widespread outages such as earthquakes and floods, unintentional device mis-configurations, and hacker attacks. One of the leading-edge architectures to address system-wide outages is the use of a dual-core backbone, which uses two independent long-haul cores to connect the networks sites. The network is designed to tolerate the failure of a single core and leave the network fully functional. This work presents an OPNET simulation model of a dual-core architecture. This model predicts the restoral time of various network outages for different device configuration options and different topology options.

Using event simulation to evaluate internet protocol enhancements for special services

The ability to provide critical communications, particularly during disasters, is essential for national security and emergency preparedness (NS/EP). The authors present a quantitative study of the resilience of IP-based NS/EP services for the National Communications System (NCS). This analysis builds on a previous study of the survivability of a single carrierpsilas telecommunications network by extending it to a multi-carrier network. The authors quantify the differences in the ability to communicate depending on whether or not the carriers modify their internetwork routing policies to allow use of another carrier for transit by NS/EP traffic. The carrier network topologies used in the analysis are similar to major ISP backbones. The authors used IP-SURVIV, a Noblis network resiliency analysis tool, to analyze the throughput and connectivity of a multi-carrier network topology as network elements are disabled. Numerical results from random failure scenarios show that modifying internetwork routing policies to allow transit routing does improve network survivability, and should be considered for NS/EP traffic. This work also has broader application to resilience analysis of other critical communication systems on multi-carrier IP networks.