Abstracts of Publications
Aun Haider, Harsha Sirisena and Krzysztof Pawlikowski
Proceedings ICT 2003, Papeete, February 2003.
The paper address issues relating to the choice of queue length indication parameter for packet marking/dropping decsions in RED type algorithms under varying traffic conditions. Modifications to RED are pro-posed by the use of both instantaneous queue size and its EWMA for packet marking/dropping and reducing the effect of EWMA value when queue size is less then minth for a certain number of consecutive packet arrivals. Thus new guidelines for better marking/dropping and faster response of RED type algorithms are derived. The resulting new hybrid algorithm is tested
using ns simulations under different scenarios and it is found to give better utilization of network bandwidth and a lower packet loss rate.
Harsha Sirisena, Aun Haider and Krzysztof Pawlikowski
Proceedings of GLOBECOM 2002, Taipei , November 2002.
One problem with a RED router with fixed param-eter settings is that the buffer queue length varies markedly with the traffic level. In this paper, an algorithm is derived analytically for automatically tuning the key RED parameter maxp to keep the average queue length at the target value despite a varying traf-fic load. A control-theoretic stability analysis is performed to ob-tain guidelines for setting the remaining RED parameters and the adaptation frequency. Simulation results show that the new adap-tive algorithm is faster acting and more accurate than previously proposed heuristic methods.
Sundus Mahmod , Harsha Sirisena and Krzysztof Pawlikowski
Proceedings of ICT 2002, Beijing, June 2002.
Call Admission Control (CAC) policies in mobile cellular wireless networks give priority to handoff requests over new call requests. In the guard channel policy, an integer number of channels are reserved for handoff calls, while the fractional guard channel policy rejects new calls with a probability that varies with the current channel occupancy. The effect of reservations on new and handoff call blocking probabilities has previously been studied for a single service class only. This paper presents reservation policies for a multimedia system with two classes of service having different bandwidth requirements. The results show that a product-form solution can also be used for a fractional guard channel handoff policy using the same assumptions as used for a single class. This analytical solution is validated by means of simulations. Numerical optimization of the policies is also performed. Keywords: Call Admission Control, Mobile Net-works, Multimedia Handoff, Guard Channels.
Carl Cook, Krzysztof Pawlikowski, and Harsha Sirisena
In conventional data communication networks, the basic network components are passive, where routing decisions are made solely on the basis of packet header information. In contrast, active networks allow added computation within the network through user-defined routing and processing instructions, providing the on-demand installation of powerful software-based network services.
As an adaptation of previous active networks, this paper introduces an architecture based entirely in middleware. By utilizing middleware services, the architecture resolves authentication, memory-management, and interconnectivity issues otherwise assumed as inherent, and enables a highly functional multiple-language interface for the deployment of dynamic protocols. After describing the architectural de-sign, an empirical system evaluation is presented with comparisons to both conventional network protocols, and a well-known existing active network architecture. Results indicate performance improvements over the existing architecture, and demonstrate the feasibility of a multiple-language active network infrastructure implemented entirely in middleware.
Keywords—Active Networks, Distributed COM, Dynamic Protocols, IP Routing, Middleware
Gustavo M.T. Da Costa , Harsha R. Sirisena
Proceedings of SPECTS 2002, San Diego, July 2002.
TCP optimization for wireless networks, for dealing with packet losses and disconnections due to fading, shadowing and handoffs, ideally should maintain TCP end-to-end semantics with minimal dependence on intermediate nodes. This paper presents such a mechanism that uses disconnection duration estimates at the receiver, derived from timestamps, to avoid an increase in the retransmission timeout (RTO) estimate at the sender following disconnections. Simulation results are presented to illustrate the problem, and to show that the proposed modification significantly improves performance. Incorporating this into the recently proposed Freeze-TCP scheme, which uses disconnection predictions at the receiver, is shown to increase robustness to packet losses during disconnections.
Harsha Sirisena, Mahbub Hassan and Aun Haider
Proceedings of ICT 2002, Beijing, June 2002.
An optimal decentralized congestion avoidance algorithm for TCP is developed by applying optimal control theory to an abstracted model of a bottlenecked TCP connection. A stochastic model of the cross-tra_c, both TCP and non-TCP, on the bottleneck link is employed and the model's parameters are estimated using an LMS algorithm. The problem is formulated so as to maximize the utilization of the available link capacity while minimizing the probability of bu_er over ow and under ow and ensuring weighted fairness among multiple TCP connections. Discrete-event simulation results are presented that show that the algorithm performs in accordance with theory, thereby supporting the correctness of the abstracted model
Abdulla Firag and Harsha Sirisena
Proceedings of PWC 2002, Singapore, October 2002
This paper presents a fully distributed Multiple Access Control (MAC) scheme that supports service differentiation in a wireless LAN environment. In the scheme, stations use CSMA for channel access, with collisions between stations having different priorities resolved by sending beacons in a predefined manner. The scheme includes an authentication protocol for stations to join a Basic Service Set and notify their priority level. Both analytical and simulation results are presented for evaluating the performance of the MAC scheme in a two priority level scenario involving voice and data traffic. The proposed scheme has a saturation throughput of about 0.84 with 1000 byte data packets, almost independent of the number of stations. The results show that good service differentiation is achieved among different priority traffic, including support for voice traffic with Quality of Service bounds on the packet latency.
Key words: priority, quality of service, collision resolution beacon, authentication protocol
Sean Lin , Harsha Sirisena
Proceedings of ICT 2002, Beijing , June 2002.
With the advent of Internet Protocol version 6 that will gradually replace the current IPv4, there is a growing need for suitable transition mechanisms. IPv4-only and IPv6-only nodes cannot communicate with each other due to different and incompatible headers, and hence various IPv4 to IPv6 transition mechanisms have been proposed. This paper presents such a device, xNAPT, which works by translating between IPv4 and IPv6 headers and allocating an IPv4 address to the IPv6 node for IPv4 communication, and allocating an IPv6 address to the IPv4 node for IPv6 communication. Translation is determined through the use of DNS records. Static mappings are also possible. Performance evaluation results using Netperf carried out on an implementation of xNAPT in an Allied Telesyn® router are presented
Rezvan, M, Pawlikowski, K and Sirisena, H.,
Telecommunication Systems, Feb. 2001.
A reservation scheme, named Dynamic Hybrid Partitioning, is proposed for the Medium Access Control (MAC) protocol of wireless ATM (WATM) networks operating in Time Division Duplex (TDD) mode. The goal is to improve the performance of the real-time Variable Bit Rate (VBR) voice traffic in networks with mixed voice/data traffic. In most proposed MAC protocols for WATM networks, the reservation phase treats all traffic equally, whether delay-sensitive or not. Hence delay-sensitive VBR traffic sources have to compete for reservation each time they wake up from idle mode. This causes large and variable channel access delays, and increases the delay and delay variation (jitter) experienced by ATM cells of VBR traffic. In the proposed scheme, the reservation phase of the MAC protocol is dynamically divided into a contention-free partition for delay-sensitive idle VBR traffic, and a contention partition for other traffic. Adaptive algorithms dynamically adjust the partition sizes to minimize the channel bandwidth overhead. Simulation results show that the delay performance of delay-sensitive VBR traffic is improved while minimizing the overhead.
Felix Hartanto, GMD FOKUS Kaiserin-Augusta-Allee 31 D-10589 Berlin, Germany.
Harsha R. Sirisena
IEEE LANMAN'99 Post-Conference Proc. 2001
Considering the limited bandwidth of the wireless link, it is important that the error control mechanism in wireless networks be spectrally efficient. Towards this end, we develop a hybrid error control architecture which takes into account the use of hierarchical video coding. Additionally, the architecture also includes a module which estimates the packet error rate and round trip time observed by the receiver and adjusts the level of redundancy used based on the estimate. By choosing different options in the architecture, we get different error control schemes.
In this paper, we investigate the performance of five different error control schemes, namely ARQ, pure FEC, hybrid FEC/ARQ, hybrid FEC/ARQ with priority-dependent redundancy, and adaptive hybrid FEC/ARQ with priority-dependent redundancy. We evaluate the performance of these schemes using MPEG-2 video traces. The results show that pure FEC offers the worst overall performance. The ARQ scheme offers the best performance under low bit error rate and short round trip time, while the priority-aware hybrid FEC/ARQ with or without FEC adaptation offers the best performance under other conditions.
Hassan, M. and Sirisena, H.
Proc. ICC 2001, Helsinki, June 2001.
The design of explicit rate-based congestion control for computer networks is treated as a stochastic optimal control problem. The performance index is chosen to achieve the twin objectives of minimising queue length fluctuations and fully utilising the available bandwidth. Simple, explicit optimal control schemes are obtained for both a LAN scenario, where round-trip delay is negligible, and a WAN scenario. The optimal controller found is of the proportional plus feedforward type. An adaptive scheme is proposed where the auto-regressive parameters of the traffic, needed for gain calculations, are estimated by n LMS algorithm. Discrete event simulations are carried out to verify the fluid-flow models used in developing the controllers, to compare their performance against that of PI controllers proposed previously, and to study the effect of self-similar traffic and two key results are obtained. First, queue-length fluctuations, and hence potentially packet losses, are much smaller for the optimal feedforward controller than for the PI controller. Second, in contrast to uncontrolled queues, the queue length variance decreases with increasing Hurst parameter for self-similar traffic.
Ostring, S., Sirisena, H. and Hudson, I.
IEEE Trans. Communications, 2001.
Long-range dependence is regarded as a fundamental property of network traffic. Using an original approach, this property is incorporated in a traffic control mechanism for elastic connections, which can adapt to the instantaneous network load in a differentiated services-type framework. In this scenario, the network makes predictions of bandwidth requirements of the high priority traffic and returns feedback information to the elastic source. We include a prediction compensation algorithm which compensates for larger prediction errors for connections with longer round-trip delay, and analyse the performance of this algorithm. Thus, the specific topology involved in traffic control for differentiated services has been harnessed, together with long-range dependence, to improve network performance, counteracting the undesired characteristics of self-similarity. Other aspects of the rate-based control algorithm are considered, including its robustness to the particular self-similar model used for the background traffic and the use of on-line estimates of traffic parameters, including the mean, variance and Hurst parameter, in an adaptive version of the algorithm.
Ostring, S. and Sirisena, H.
Proc. ICC 2001, Helsinki, June 2001.
Predicting traffic requirements is a fundamental objective of network management algorithms, regardless of whether the algorithm explicitly states that a predictor is used. Considering the abundant evidence that traffic is long-range dependent (LRD), together with the property that the history of long-range dependent processes has significant impact on the present value of the process, it is natural to assume that predicting LRD traffic is rather rewarding. Indeed, there is significant performance gain in using the correlation structure as the Hurst parameter increases, but we show in this paper that this is primarily due to the utilization of the specific short-term correlations that occur within the structure of traffic, rather than storing a long history of the traffic and utilizing the long-term correlations that exist between the future traffic level and this stored history.
De Silva, P and Sirisena, H.
Proc. IEEE ICCCN 2001, Scottsdale AZ, October 2001
Mobile IP is an IETF RFC that supports transparent host migration on the Internet. In the transition to IP-based cellular networks, it is widely agreed that Mobile IP provides an elegant solution for inter-domain, or macro-mobility management, but lacks critical aspects of mobility management needed within cellular networks. The shortcomings have led to the recent emergence of micro-mobility management protocols. This paper presents an IP-based mobility management protocol, ì-Mobile IP, based on two enhancements, proactive handoff and paging support, to an Internet Draft proposal Regional Registrations. A signaling cost analysis is used to justify the need for such enhancements. We show through simulations the protocol's suitability for supporting real-time communications.
Sven A.M. Ostring, Harsha Sirisena, and Irene Hudson
Proc. EMAC 2000, Melbourne, Sept, 2000, 235-238.
Traffic management is an important part of successfully engineering a network, so that the use of network resources is optimised and congestion situations are avoided. Currently, the concept of providing assured Quality of Service (QoS) is of significant interest, where network services are being designed to support applications, such as video communications, which have very stringent bounds on the delay. There are also other applications, such as file transfers and electronic mail, that can accommodate variable delays, but which are affected more seriously by data loss. This is the motivation for the development of a differentiated service framework in ATM and IP networks, and appropriate traffic management algorithms are required to support these services.
To effectively manage traffic, the nature of the traffic must be well-understood. Traditional Poissonian traffic models do not capture the nature of many emerging classes of traffic, like video and multi-media traffic. Indeed, there is significant evidence that self-similarity is a fundamental characteristic of a wide range of traffic, including Ethernet, VBR video, WWW and signalling traffic, and the behaviour of this type of traffic as it flows through a network is fundamentally different from Poissonian traffic. Due to the burstiness and long-range dependence of self-similar traffic, queues build up to much higher levels and losses are more significant.
The purpose of this paper is to review the concepts of self-similarity necessary for network traffic modelling, and to survey methods of self-similar traffic management which have been presented in the literature together with our own work in this area.
Hassan, M., Sirisena, H. and Atiquzzaman, M.
Computer Communications, Vol. 22, pp. 1296-1306, 1999.
Available bit rate (ABR) is an emerging asynchronous transfer mode (ATM)-based telecommunication service, which dynamically allocates bandwidth to the users according to the available bandwidth in the network. However, research shows that ABR-based connections suffer from congestion at LAN-ATM gateway when ATM network abruptly reduces the bandwidth available to the gateway. Gateway congestion may result in high packet loss. This paper proposes a gateway congestion control mechanism, which controls the rate of outgoing enterprise traffic according to the available bandwidth at the gateway. Our analysis shows how to achieve a stable system and keep the packet loss below a desired threshold. Analytical results are validated by simulation.
Justin Macfarlane, Krzysztof Pawlikowski, Harsha Sirisena
Proc. Second Int. Conf.on Information, Communications and Signal Processing (ICICS'99), Singapore,
pp. #137, Dec. 1999.
Abstract Many medium access control protocols have been proposed for optical wavelength division multiplexing local area networks with a star topology. These protocols range from those based on the concept of fixed-assignment of communication subchannels, such as TDMA (Time Division Multiple Access); random-access to communication subchannels, such as DT-WDMA (Dynamic Time-Wavelength Division Multiple Access); of hybrid protocols incorporating both fixed-assignment and reservation rules, such as HTDM (Hybrid TDM).
This paper proposes and evaluates a novel hybrid protocol of fixed-assignment and random-access called “WTDMA with lightpath trespassing”. This protocol combines the most desirable aspects of fixed-assignment and random-access protocols, while limiting their drawbacks. The performance of the protocol is analysed by stochastic simulation. The obtained results show the addition of trespassing lowers the mean packet delay, and with collision avoidance, also increases throughput. These results justify the introduction of the WTDMA with trespassing protocol, and indicate the situations where its use is advantageous.
Andy Cheng-yu Wu Harsha R. Sirisena
Proc. Second Int. Conf. on Information,Communications and Signal Processing (ICICS'99), Singapore, paper #030, Dec. 1999.
The buffer performance of a Multi Protocol Label Switching (MPLS) capable ATM switch, called an ATM Label Switch Router (ATM-LSR), is analysed. A new mathematical model that permits a source peak rate less than the link rate is considered. Computational efficiency is achieved by decreasing the model's complexity by one-tuple. The model is validated via simulation for theoretical traffic with a geometric packet length distribution. The effect of a more realistic wide-area IP traffic model on the buffer performance of both non VC-merging and VC-merging MPLS is also investigated by means of simulation. The results clarify results in the previous study by Widjaja and Elwalid. Moreover, some interesting findings of the simulation studies, which seem counter-intuitive, are explained.
Sven Ostring Harsha Sirisena Irene Hudson
Proc. IEEE International Communications Conf., Vancouver, June 1999, pp.129-134.
This paper presents an ABR control scheme (ABR2-DP) which maximises the utilisation of information available about the network traffic. Firstly, it takes into account the long-range dependence of the self-similar background network traffic, and utilises it for more accurate multi-step predictions of the explicit rate (ER). Secondly, predictions are compensated for in the ER calculations for connections with smaller delay. Hence, the available bandwidth is distributed both in temporal and spatial dimensions. The scheme allows a reduction in buffer requirements and queueing delay. Performance results are presented and compared with a previously proposed scheme which uses digital filtering.
Hartanto, F. and Sirisena, H.R.
Proc. IEEE Workshop on Local and Metropolitan Area Networks, Banff, Canada, May 1998.
Broadband wireless access systems are emerging as a new and growing area of telecommunications which provides a seamless communication between wired and wireless broadband networks. Some of the key enabling technologies, such as adaptive antennas, video compression, microwave and infrared technologies, have been presented in recent years. However, the application of these technologies in a public wireless environment has yet to be tested.
Considering the potential delay in implementing the technologies, this paper describes an alternative scheme for providing broadband wireless access which can be used in existing cellular or wireless data networks. The scheme is based on the idea of inverse multiplexing, which allows aggregation of multiple wireless information channels to create a single higher rate information channel [3, 4]. As an example, we consider the application of inverse multiplexing in an existing Cellular Digital Packet Data (CDPD) network, where the scheme can be used to aggregate number N of 19.2 kbps CDPD channel to create an N x 19.2kbps channel.
The performance improvement offered by the inverse multiplexing scheme is demonstrated using simulation where four channel allocation methods are considered. The results show that the scheme can offer significant reduction in the transmission time and blocking probability for data calls, which in turn leads to higher channel utilisation. The percentage reduction in the transmission time increases with increasing data message/file size. This means that the scheme is more suited for applications which transmit/receive large amounts of data, such as video conferencing, large file transfer, remote database access by field personnel, and transmission of medical images by flying doctors. These applications are very common in a fixed wireless environment, where a wireless network infrastructure, e.g. D-AMPS IS-136 on which CDPD is overlaid, is used to provide the subscriber loop. Therefore, in such an environment the inverse multiplexing scheme as described here can be used to provide a fast and flexible wireless subscriber loop.
F. Hartanto, W. Kreutzer, K. Pawlikowski and H. Sirisena.
Int. J. on Computers and Electrical Eng, 1996, vol.22, no.6, 367-381. C
DESC + + (Discrete Event Simulation package using C + +) has been developed as an object-oriented tool for quantitative simulation studies of communication protocols and architectures of telecommunication networks. The main issue of such performance studies is to secure proper statistical accuracy of the final simulation results. In DESC + + this problem has been solved by automating analysis of simulation output data, aimed at stopping simulation when the estimates reach the required level of precision. The package consists of various object classes. While some of them are responsible for on-line output data analysis, others allow simulation programs of telecommunication networks to be easily developed by re-using existing (sub)models. We discuss main design and implementational issues of DESC + + and illustrate them by an example.