Deadline-based connection setup in wavelength-routed WDM networks

Abstract

This article addresses the ubiquitous topic of quality of service (QoS) aware connection provisioning in wavelength-routed WDM optical networks. The impact of the connection setup time of an optical connection has not been adequately addressed in the open literature. As such, this paper presents a novel approach that uses the optical connection setup time as a service differentiator during connection provisioning. The proposed approach utilizes the Earliest Deadline First (EDF) queueing algorithm to achieve deadline-based connection setup management with the deadline being the setup time requirement of an optical connection. The proposed EDF-based approach would allow the network operator to improve the QoS perceived by the end clients. Performance of this novel scheme is analyzed by accurately calculating various parameters, such as the fraction of connections provisioned on-time (i.e. prior to deadline expiration) and the average time it takes to successfully setup a connection. In addition, the presented approach is validated by a simulation that analyzes the performance of the proposed connection setup scheme in the specific context of the National Science Foundation Network (NSFNET). The obtained results show that a deadline-based setup strategy can minimize blocking probability while achieving QoS differentiation.

Introduction

Wavelength Division Multiplexing (WDM) is becoming the de facto technology for driving up the transmission capacity of optical networks and thus enabling optical operators to keep up with the continuous growth of data traffic. WDM multiplexes many non-overlapping WDM channels onto the same optical fiber, where each of these channels can be operated at the peak rate of several gigabits per second. Optical fiber communication is therefore being firmly established as the preferred means of communications for the ever-emerging bandwidth consuming applications and services. However, the perpetual advent of new applications, each having different QoS requirements, aggravated by the need to carry these applications over optical networks, is proving to be the next big challenge for future WDM optical networks. This is especially true since existing optical networks still need to evolve from single service networks to multi-service ones [1], in which different types of services with different QoS requirements can be supported. Hence, the main trend is leaning towards migrating from a plain optical network with static point-to-point connections to a new era of dynamic, wavelength-routed, all-optical WDM optical networks [2].

In a wavelength-routed WDM network, an Optical Cross-Connect (OXC) switches the optical signal on a WDM channel from an input fiber to an output fiber; thus a connection (lightpath) may be established from a source to a destination. In this regard, numerous research efforts [3], [4], [5] have contemplated equipping these networks with a multi-service capability making them provide predictable quality of transport services. Quality of transport is measured by the set of parameters that affect the data flow after the lightpath is established.

However, most of the previous efforts did not consider in their formulations the crucial parameter of connection setup time. Inspired by these observations, this work focuses on the connection setup time parameter that is likely to become a common feature of a customer’s service profile. The authors in [6], [7] presented the connection setup time as a potential service differentiator in Service Level Agreements (SLAs) between optical operators and their customers.

The connection setup time is widely defined as the amount of time separating the instant a lightpath (i.e. a service) setup request is received by the operator and the moment the requested lightpath is established. This paper investigates the impact of the connection setup time on the setup of a connection as a service differentiator. The work is motivated by the need to consider the optical connection setup time as a timely increasing priority indicator (a type of competition-oriented parameter which may be linked to pricing) during the setup process.

Therefore, connection setup time can be viewed as a deadline. A connection setup request arriving at an optical source node A at instant t with a setup time requirement equal to S will be assigned a deadline of $t+S$. If such a setup request cannot be met due to a lack of optical resources, the blocked connection request at A is stored in an Earliest Deadline First queue. In other words, instead of dropping connection requests that cannot be satisfied by the optical network, they will be queued at the entry point of the network in an order consistent with their respective priorities (deadlines).

The proposed approach utilizes an adaptation of the well-known Earliest Deadline First scheduling algorithm aimed at optical connection setup management. More specifically, blocked connection setup requests are inserted into a queue and are then served according to an EDF scheduling discipline, whereby the connection request with the earliest setup time deadline, is served first. The main advantage of this technique is to enforce quality of service differentiation among customers having different connection setup time requirements.

The rest of this paper is structured as follows: in Section 2, the deadline-based connection setup approach is described and its relation to the literature is discussed. Section 3 introduces a mathematical model to compute the success probability of a deadline-driven connection setup request. Numerical results to evaluate the benefits of the proposed approach are presented in Section 4. Section 5 highlights further the merits of the deadline-based setup scheme through a simulation in the context of the National Science Foundation Network (NSFNET). Finally, Section 6 concludes the paper and presents future perspectives for research.