TRUNK RESERVATION ANALYSIS OF TELUS' EDMONTON TELECOMMUNICATION NETWORK

INFOR, Aug 2003 by Sim, Thaddeus

ABSTRACT

Following deregulation of the Canadian telecommunications industry in the early 1990's, telecommunication companies have experienced an increase in the demand on their networks. In this paper, we describe a proof-of-concept study of implementing a control mechanism called trunk reservation in TELUS' Edmonton network. Trunk reservation limits the number of inefficient multi-link calls connected in the network when it approaches operational capacity, hence allowing more calls to connect via their direct paths. To find the optimal trunk reservation parameters for the Edmonton network, we use fixed-point approximations of a birth-death process to formulate the problem, which we solve using simulated annealing. Our results indeed show that trunk reservation decreases the amount of multi-link calls in the network. We also show that our network with non-uniform trunk reservation parameters performs better than networks where the number of reserved trunks is determined using a "one size fits all" approach.

Keywords: Telecommunications, trunk reservation, alternate-routing, simulated annealing.

RESUME

Suite a la dere glementation de l'industrie canadienne de telecommunications au debut des annees 90, les compagnies de telecommunication ont connu une augmentation de la demande sur leurs reseaux. Dans cet article nous decrivons une etude sur l'application d'un mecanisme de commande appele la reservation de tronc dans le reseau TELUS d'Edmonton. La reservation de tronc limite le nombre d'appels inefficaces sur un reseau multi-liens proche de sa capacite operationnelle, permettant ainsi a plus d'appels de se relier par des chemins directs. Afin de determiner les parametres optimaux de reservation de tronc pour le reseau d'Edmonton, nous avons formule le probleme a l'aide de la methode « naissance-mort par approximation a points fixes » et resolu ce dernier a l'aide de la methode du recuit simule. Les resultats obtenus montrent en effet que la reservation de tronc diminue la quantite d'appels sur un reseau multi-liens. Ils montrent egalement qu'un reseau comme le notre, avec des parametres de reservation de tronc non-uniformes, est plus performant que les reseaux ou le nombre de troncs reserves est determine par la methode « une meme taille pour tous » .

Mots-cles : Telecommunications, reservation de tronc, routage alternatif, recuit simule.

Reed. Apr. 2002, Rev. Feb.-June 2003, Ace. June 2003

1. INTRODUCTION

In the early 1990's, the Canadian Radio-Television and Telecommunications Commission (CRTC) deregulated telecommunication services in Canada, allowing for competition in the telecommunications industry. Cheaper telephone services have resulted in increased demand and subsequently, increased loads on telecommunication networks. Rapid adoption of dial-up Internet services in the late 1990s have further fuelled the demand increase. Moreover, the profile of call durations have also changed to include longer duration telephone calls, a result of cheaper calling costs and dial-up Internet usage.

TELUS, the leading telecommunications service provider in Western Canada, anticipates that their existing circuit-switched telecommunication networks (networks where a telephone call occupies a phone line for the entire duration of the call) in Western Canada will be operating at capacity in the near future due to this increase in demand. The CRTC requires that all telecommunication service providers maintain a minimum grade of service of ROl: a service level where at most one out of every 100 telephone calls is blocked. With the demand increase and the need to satisfy the ROl service-level constraint, TELUS will have to make a decision on capital expenditures regarding their existing networks in the near future.

While TELUS explores long-term strategic options for their telecommunication networks, they also require some short-term solutions to increasing their network capacities without any immediate significant capital expenditure outlays. One project completed for TELUS under this framework is a proof-of-concept study of implementing a control mechanism in their telecommunication networks called trunk reservation.

Before describing trunk reservation and its benefits in telecommunication networks, we first introduce some terminology. A telecommunication network consists of switches (nodes) and trunk groups (arcs). A trunk group is a collection of trunks connecting similar pairs of switches. A path is a set of distinct trunk groups that form a connection between the origin and destination switches of a call. A route is an ordered collection of paths connecting the same pair of origindestination switches, specifying the paths used for routing calls between the pair in the order that seizure of the paths is attempted (Akinpelu, 1984). A routing system with several alternate paths per route is called an alternate routing system.

Table 1 shows a portion of a routing table with the route for the origin-destination switch pair 1-5. This route consists of three paths, with the "Route Index" column identifying the order of paths a call will attempt. The first path of a route is usually the direct path (if the trunk group exists) between the origin-destination switches. all subsequent paths in the route (route index 2 and higher) are multi-link paths, which consist of two or more trunk groups. If a call cannot connect on its first path because all the trunks in the trunk group are occupied, the call is not blocked but it overflows onto its second path (route index 2). In Table 1, the second path connects calls from switches 1 to 5 through the trunk group connecting switches 1 and 4, followed by the trunk group connecting switches 4 and 5. If at least one of the trunk groups comprising the second path is fully occupied, the call again overflows onto its next alternate path. A call is blocked only when it overflows from its final alternate path, and the caller receives a network busy tone.