Yonatan Levy

VoIP reliability: a service provider's perspective

Voice over IP services offer important revenue-generating opportunities, as well as many technical challenges in providing high-quality services. Users have come to expect highly available telecommunications services with high-quality voice. Service providers need reliable high-performance networks to meet user expectations, and must be able to guarantee performance and reliability to their customers. In converged voice and data networks, the network infrastructure must deliver very high quality and availability for some customer needs, while also providing low-cost high-capacity bandwidth for other needs. The use of quality of service mechanisms to provide prioritization for various traffic types is a key element needed for voice and data network convergence. However, it is not sufficient if the underlying networks are unreliable. The focus of this article is to address the reliability aspects of VoIP services, including the underlying IP networks.

Global mobility management by replicated databases in personal communication networks

This paper explores the use of replicated databases for management of customer data (e.g., mobility data, call routing logic) in global, intelligent, and wireless networks. We propose and analyze two, full and partial, data replication schemes-which are compatible with industry protocol standards-and compare them with the traditional, centralized database scheme. By identifying a set of key teletraffic and mobility parameters, we develop a modeling framework based on queueing models and apply it to assess the relative performance and merits of these schemes. The paper also addresses some implementation issues. Numerical results reveal that the full replication scheme outperforms the centralized one over a wide range of the parameters considered in this study. Furthermore, if some customer data-such as location data for highly mobile customers in wireless networks-change frequently, and if each call launches multiple queries into the databases, the partial replication scheme offers further performance improvement. In general, however, the choice of the database design would depend on the specific characteristics of the service and user behavior under consideration.

Advanced routing solutions for toll-free customers: Algorithm design and performance

This paper describes algorithms that are at the core of recent offerings in the ATT (2) address diverse goals such as geographic preferences and constraints, least cost routing, performance thresholds, and service objectives; and (3) allow user control within a structured algorithmic framework. We provide examples of simulation predictions of performance and efficiency improvements as well as results of field experience by customers.

Call routing to distributed queues: Is FIFO really better than MED?

New services providing automatic call distribution in the network have been one of the most hotly contested areas in the USA telecommunications arena in recent years. This has been fueled by increasing demand from large corporations for intelligent network routing that will keep their geographically distributed telemarketing/service centers operating with maximum efficiency. This paper compares two basic strategies for a network call distributor: a centralized FIFO queue and a distributed queueing strategy called Minimum‐Expected‐Delay (MED). According to MED, a central controller routes each arrival to the node that minimizes its expected delay (waiting time). Our main result qualifies the conventional wisdom that perceives FIFO as optimal. We show that the waiting time under FIFO is not stochastically smaller than that under MED. Furthermore, we prove that the waiting time distribution functions intersect at a single point. Numerical experiments suggest that, for certain performance criteria and over a range of parameters of interest, MED can actually outperform FIFO.

Managing performance using weighted round-robin

IP networks will evolve from todays best-effort Internet into multi-class networks supporting quality of service requirements of diverse applications. This paper addresses one of the challenges of these new IP networks: how to set control parameters to deliver differentiated performance. We study this problem in a simplified setup of a single link and a weighted round robin queueing discipline. After giving an exact formulation of the problem, we apply an approximation of the waiting times to gain insight into the feasible performance and behavior of service limits as a function of the traffic parameters. The methodology is illustrated with several numerical examples.

Admission control for VoIP calls with heterogeneous codecs

As VoIP services proliferate due to rapid advances in technology and market demands, service providers are aggressively looking for better ways to offer VoIP services to customers including support of different codec technologies via a single network access point. This service flexibility introduces major traffic engineering challenges, especially when supporting a mix of data and voice services. In order to guarantee individual sources call blocking probability, intelligence must be added to the call admission process. To tackle the issue, we propose an intelligent call blocking algorithm that is guided by a pre-defined blocking targets.

Data replication schemes for global networks

This paper explores the use of replicated databases for management of customer data (e.g., mobility data, call routing logic) in global, intelligent and wireless networks. We propose and analyze two, full and partial, data replication schemes — which are compatible with industry protocol standards — and compare them with the traditional, centralized database scheme. By identifying a set of key teletraffic and mobility parameters, we develop a modeling framework based on queueing models, and apply it to assess the relative performance of these schemes. Our results reveal that the full replication scheme outperforms the centralized one over a wide range of parameters. Furthermore, if customers update some of their data frequently (such as location data for highly mobile customers in wireless networks) and each call launches multiple queries into the databases, the partial replication scheme offers further performance improvement.

A Simple Fair Cell Discarding Algorithm on Per-VC Queueing Bases

In this paper we propose a simple Fair Cell Discarding (FCD) algorithm with virtual per-VC queueing. The main objective of FCD algorithm is to redistribute the cell losses according to each connection’s QoS requirement. In case the buffer is full, the newly arrived cell is not automatically discarded but rather a cell from a sub-queue U which is selected according to a fairness criterion which is defined by connections mean arrival rates and their QoS (Quality of Service) such as CLR. (Cell Loss Ratio) requirements. Extensive analytical analysis and simulations have been conducted to evaluate FCD algorithm’s property and to validate its effectiveness under various traffic and switch configurations. Our study reveals that a very simple approach like FCD can actually differentiate connections with different traffic characteristics and QoS requirements; and satisfy their specified QoS as long as a minimum amount of resources (bandwidth and total buffer space) is allocated for guaranteeing the aggregate QoS/CLR requirement of all active connections.