George Hadjipollas

Adaptive congestion protocol: A congestion control protocol with learning capability

There is strong evidence that the current implementation of TCP will perform poorly in future high-speed networks. To address this problem many congestion control protocols have been proposed in literature which, however, fail to satisfy key design requirements of congestion control protocols, as these are outlined in the paper. In this work we develop an adaptive congestion protocol (ACP) which is shown to satisfy all the design requirements and thus outperform previous proposals. Extensive simulations indicate that the protocol is able to guide the network to a stable equilibrium which is characterized by max-min fairness, high-utilization, small queue sizes and no observable packet drops. In addition, it is found to be scalable with respect to changing bandwidths, delays and number of users utilizing the network. The protocol also exhibits nice transient properties such as smooth responses with no oscillations and fast convergence. In realistic traffic scenarios comprising of a small number of long flows and a large number of short flows, ACP outperforms both TCP and XCP, even in the presence of random packet losses. ACP does not require maintenance of per flow states within the network and utilizes an explicit multi-bit feedback signalling scheme. To maintain stability it implements at each link a novel estimation algorithm which estimates the number of flows utilizing the link. Using a simple network model, we show analytically the effectiveness of the estimation algorithm. We use the same model to generate phase portraits which demonstrate that the ACP protocol is stable for all delays.

Fuzzy explicit marking for congestion control in differentiated services networks

This paper presents a new active queue management scheme, fuzzy explicit marking (FEM), implemented within the differentiated services (Diffserv) framework to provide the congestion control using a fuzzy logic control approach. Network congestion control remains a critical and high priority issue. The rapid growth of the Internet and increased demand to use the Internet for time-sensitive voice and video applications necessitate the design and utilization of effective congestion control algorithms, especially for new architectures, such as Diffserv. As a result, a number of researchers are now looking at alternatively schemes to TCP congestion control. RED (random early detection) and its variants are one of these alternatives to provide quality of service (QoS) in TCP/IP Diffserv networks. The proposed fuzzy logic approach for congestion control allows the use of linguistic knowledge to capture the dynamics of nonlinear probability marking functions and offer effective implementation, use of multiple inputs to capture the (dynamic) state of the network more accurately, enable finer tuning for packet marking behaviors (either dropping a packet or setting its ECN - explicit congestion notification - bit) for aggravated flows, and thus provide better QoS to different types of data streams, such as TCP/FTP traffic or TCP/Web-like traffic, whilst maintaining high utilization.

Congestion control in differentiated services networks using fuzzy logic

The provision of quality of service (QoS) in a differentiated services (Diff-Serv) environment requires an adequate differentiation between high-priority/assured and low-priority/best-effort classes of service in the presence of congestion, giving priority/preference to assured-tagged traffic. For this purpose, a new active queue management scheme, implemented within the Diff-Serv framework, is presented that provides congestion control in TCP/IP networks using a fuzzy logic control approach. The proposed fuzzy logic approach for congestion control allows the use of linguistic knowledge to capture the dynamics of nonlinear probability marking functions, uses multiple inputs to capture the dynamic state of the network more accurately, and can offer effective implementation. A simulation study over a wide range of traffic conditions - considering multiple bottleneck links - shows that the fuzzy logic based controller outperforms the random early detection (RED) implementation for Diff-Serv in terms of link utilization, packet losses, and queue fluctuations and delays. Also, the proposed scheme can offer better differentiation among assured and best-effort traffic, thus it can provide better QoS to different types of data streams, such as TCP/FTP traffic or TCP/Web-like traffic, whilst maintaining high utilization.

A new estimation scheme for the effective number of users in internet congestion control

Many congestion control protocols have been recently proposed in order to alleviate the problems encountered by TCP in high-speed networks and wireless links. Protocols utilizing an architecture that is in the same spirit as the ABR service in ATM networks require estimates of the effective number of users utilizing each link in the network to maintain stability in the presence of delays. In this paper, we propose a novel estimation algorithm that is based on online parameter identification techniques and is shown through analysis and simulations to converge to the effective number of users utilizing each link. The algorithm does not require maintenance of per-flow states within the network or additional fields in the packet header, and it is shown to outperform previous proposals that were based on pointwise division in time. The estimation scheme is designed independently from the control functions of the protocols and is thus universal in the sense that it operates effectively in a number of congestion control protocols. It can thus be successfully used in the design of new congestion control protocols. In this paper, to illustrate its universality, we use the proposed estimation scheme to design a representative set of Internet congestion control protocols. Using simulations, we demonstrate that these protocols satisfy key design requirements. They guide the network to a stable equilibrium that is characterized by high network utilization, small queue sizes, and max-min fairness. In addition, they are scalable with respect to changing bandwidths, delays, and number of users, and they generate smooth responses that converge quickly to the desired equilibrium.

Simulating soft handover and power control for enhanced UMTS

In this paper we present a soft handover algorithm for wide band CDMA based E-UMTS networks and the associated power control algorithm. The handover and power control algorithms have been developed and implemented in the framework of a system level E-UMTS simulator developed under the 1ST SEACORN project. The paper provides a background on handover design techniques and explains the handover implementation. The soft handover algorithm has been modeled using the guidelines provided in the standards and the literature for W-CDMA intra-frequency handovers. The combination of established handover techniques with enhanced UMTS is a novelty feature of this paper and provides a reference for further performance comparison

A discrete event based simulation environment for enhanced UMTS 3 rd generation networks

This paper presents a new system level simulator that has been developed to evaluate E-UMTS (Enhanced Universal Mobile Telecommunication Systems) 3G Networks. The article describes how the simulator supports different mobility, propagation, and traffic generation models and how this simulation framework can be used to evaluate new protocols, algorithms, or resource management mechanisms. Specific models and performance details for a sample scenario of a business city center are also provided.

Queue Length Based Internet Congestion Control

In this paper we present a new queue length based Internet congestion control protocol which is shown through simulations to work effectively. The control objective is to regulate the queue size at each link so that it tracks a reference queue size chosen by the designer. To achieve the latter, the protocol implements at each link a certainty equivalent proportional controller which utilizes estimates of the effective number of users utilizing the link. These estimates are generated online using a novel estimation algorithm which is based on online parameter identification techniques. The protocol utilizes an explicit multi-bit feedback scheme and does not require maintenance of per flow states within the network. Extensive simulations indicate that the protocol is able to guide the network to a stable equilibrium which is characterized by max-min fairness, high utilization, queue sizes close to the reference value and no observable packet drops. In addition, it is found to be scalable with respect to changing bandwidths, delays and number of users utilizing the network. The protocol also exhibits nice transient properties such as smooth responses with no oscillations and fast convergence.

A simulation tool to evaluate radio resource management algorithms for enhanced UMTS

This paper presents a new system level simulator that has been developed to evaluate radio resource management (RRM) techniques in UMTS (Universal Mobile Telecommunication Systems) and enhanced-UMTS networks. The simulator includes new implementations for the user equipment, node B, radio network controller nodes and can evaluate parameters associated with UMTS or enhanced-UMTS performance, related to the introduction of RRM functions. The RRM functions implemented deal with admission control, packet scheduling, handover control, load control, and power control. The evaluation of RRM mechanisms is supported by the provision of appropriate radio propagation, traffic generation, and mobility models.

Fuzzy logic congestion control in TCP-IP differentiated services networks for quality of service provisioning

In this paper, a new active queue management (AQM) scheme that provides congestion control in TCP/IP networks using a fuzzy logic control approach is presented. The proposed scheme is implemented within the differentiated services (Diff-Serv) framework, providing quality of service (QoS). It is based on the fuzzy explicit marking (FEM) controller proposed to provide congestion control in TCP/IP best-effort networks. The proposed FEM In/Out (FIO) controller is evaluated in a wide range using the NS-2 simulator. The fuzzy control methodology can offer significant improvements on controlling congestion in TCP/IP Diff-Serv networks and providing adequate quality of service.

Enhanced UMTS Cellular Planning for Multiple Traffic Classes in Offices Scenarios

It is shown that enhanced UMTS is an affordable solution for providing the required network quality and to reduce infrastructure investments in offices scenarios. System capacity results are obtained by using a system level simulator which considers traffic characterisation parameters and services usage in detail, among other. Results for the most profitable cell radius are obtained via an optimisation procedure based in economic aspects. A higher number of pico cells (with a smaller radius, around 30-32 m) can be installed in the future, when costs of deploying and maintaining the network decreases, allowing for supporting higher system capacity, and reducing prices. Our approach is based in a detailed services analysis, which represents a worst case situation relatively to the total services approach, because the later does not discriminate results for the different traffic classes. The impact of call blocking, handover failure, end-to-end delay, and delay variation are taken into account