Bruce S. Northcote

Geometric equilibrium distributions for queues with interactive batch departures

Gelenbe et al. [1, 2] consider single server Jackson networks of queues which contain both positive and negative customers. A negative customer arriving to a nonempty queue causes the number of customers in that queue to decrease by one, and has no effect on an empty queue, whereas a positive customer arriving at a queue will always increase the queue length by one. Gelenbe et al. show that a geometric product form equilibrium distribution prevails for this network. Applications for these types of networks can be found in systems incorporating resource allocations and in the modelling of decision making algorithms, neural networks and communications protocols.In this paper we extend the results of [1, 2] by allowing customer arrivals to the network, or the transfer between queues of a single positive customer in the network to trigger the creation of a batch of negative customers at the destination queue. This causes the length of the queue to decrease by the size of the created batch or the size of the queue, whichever is the smallest. The probability of creating a batch of negative customers of a particular size due to the transfer of a positive customer can depend on both the source and destination queue.We give a criterion for the validity of a geometric product form equilibrium distribution for these extended networks. When such a distribution holds it satisfies partial balance equations which are enforced by the boundaries of the state space. Furthermore it will be shown that these partial balance equations relate to traffic equations for the throughputs of the individual queues.

Triggered batch movement in queueing networks

A product form equilibrium distribution is derived for a class of queueing networks, in either discrete or continuous time, in which multiple customers arrive simultaneously, multiple customers complete service simultaneously, and any event occurring in the network can force/trigger the release of multiple customers to be routed through the network.

Methodology for implementing scalable test configurations in ATM switches

In performance testing of ATM switches and networks of switches a variety of connection configurations is needed. In most of the cases, these configurations require one traffic generator and/or analyzer for each switch port. Since this equipment is rather expensive, it is desirable to define scalable configurations that can be used with a limited number of generators. In this paper we present a methodology for the implementation of scalable connection configurations. The methodology is simple and offers a general solution to generate scalable connection configurations. Several examples of scalable configurations illustrate the methodology. The application of this methodology helps users to repeat easily performance tests under the same traffic load conditions.

Dimensioning Telstra's WCDMA (3G) network

Loss models can be used to determine engineered capacity of circuit-switched telecommunications systems. They readily model the multi-service, multi-resource nature of call admission control (CAC) schemes for such systems, including service prioritization via the use of resource reservation. Third generation wireless networks (3G) are incredibly complex with regard to system resources and supported services. In particular, the 3G radio environment is subject to interference and fading. Recognizing that communications systems are engineered to a nominal “time consistent busy hour”, we seek a method for capturing the behavior of the 3G radio environment over such a time period, and incorporating it into a modified loss model for determining capacity. We present a novel methodology to derive environmental parameters that can be used to characterize the radio environment as it affects individual cells in the network. Consequently we have developed a 3G radio access network (RAN) and transport network (TN) dimensioning tool for Telstra that, on a per cell and hourly basis, estimates spare capacity based on target grades of service (GoS). These incorporate loss probabilities for all services, and throughput requirements for high speed downlink packet access (HSDPA) services. This integrated network management tool calculates each resources utilization at various envelope boundary points to determine the active resource constraints, thereby allowing Telstra engineers to most effectively apply capacity expansions to the RAN & TN.

An investigation of CCS tandem overload control issues

In this paper we analyze issues associated with overloads in tandem switching systems in common channel signaling (CCS) networks. In particular, we examine the need for, and effectiveness of, automatic congestion control (ACC), a CCS mechanism which allows switching systems to inform originating exchanges of overloaded processing resources and thereby control call rates to congested nodes. We demonstrate the critical need for end-offices and tandem switching systems to implement some form of ACC if network performance is to be maintained during congestion in tandem exchanges. In addition, we find that the presently defined ACC should be expanded to allow more levels of congestion to be reported to originating nodes, so that a more effective, finer grained control is produced.

A comparison of CCS tandem overload controls

In this paper we analyse issues associated with overloads in tandem switching systems in Common Channel Signalling (CCS) networks. In particular, we examine the need for, and effectiveness of, Automatic Congestion Control (ACC), a CCS mechanism which allows a congested switching system to inform adjacent CCS nodes of its level of overload, and subsequently controls the rate at which traffic is sent to the congested node. We demonstrate the critical need for end-offices and tandem switching systems to implement some form of ACC if network performance is to be maintained during congestion, especially in tandem exchanges. In addition, we find that the presently defined ACC should be expanded to allow more levels of congestion to be reported to adjacent nodes, so that a more effective, finer grained control is produced.