Rami G. Mukhtar

Active Queue Management for Fair Resource Allocation in Wireless Networks

This paper investigates the interaction between end-to-end flow control and medium access control (MAC)-layer scheduling on wireless links. We consider a wireless network with multiple users receiving information from a common access point; each user suffers fading and a scheduler allocates the channel based on channel quality but is subject to fairness and latency considerations. We show that the fairness property of the scheduler is compromised by the transport-layer flow control of transmission control protocol (TCP) New Reno. We provide a receiver-side control algorithm, CLAMP, that remedies this situation. CLAMP works at a receiver to control a TCP sender by setting the TCP receivers advertised window limit, and this allows the scheduler to allocate bandwidth fairly between the users.

Efficient Internet traffic delivery over wireless networks

The high demand for wireless Internet connectivity has driven the development of highly efficient radio link technologies. However, their performance can be compromised by inadvertent interactions with the higher-layer TCP flow control protocol. Maximizing the performance of wireless links requires that mechanisms operating at every layer of the protocol stack interact efficiently. This article provides a brief tutorial of some of these radio link enhancements. It then outlines how higher-layer flow control protocols should behave, and provides techniques for taming the behavior of TCP, to ensure that the performance of lower-layer enhancements is not compromised.

A model for the performance evaluation of packet transmissions using type-II hybrid ARQ over a correlated error channel

Type-II Hybrid-ARQ (Type-II HARQ) has been shown, under certain circumstances, to increase the efficiency and reduce loss of data transmissions over a wireless channel. However, it is difficult to predict how it will perform when transmission symbol errors are correlated. We present a computationally efficient approach to the performance evaluation of packet transmissions over a wireless link employing Type-II HARQ error mitigation when the physical channel is subject to correlated transmission symbol errors. This provides a tool for static or online optimization of system parameters. We present numerical results for a wide range of channel statistics, illustrating the effect of bit error correlation, bit error rate, and block size on packet latency and loss rate.

CLAMP: differentiated capacity allocation in access networks

The paper presents a solution for providing differentiated capacity allocation in an access network. The system is based on CLAMP (curtailing the large TCP advertised window to maximize performance), an algorithm that can differentiate between flows sharing the same FIFO queue. The system is suitable for access networks, such as those based on DSL and HFC modems and wireless LAN access points. The deployment of CLAMP is completely contained within the access network; no changes to the remainder of the network are required. CLAMP provides the opportunity to enforce local policies on TCP flows that originate from sources distributed globally. The performance of CLAMP is verified by both simulation and analysis.

CLAMP: a system to enhance the performance of wireless access networks

The paper presents an improved version of CLAMP, a system that controls the behavior of TCP to enhance the performance of wireless access points. It only requires modifications to be made to the access network, and is totally compatible with TCP senders. We demonstrate its performance by simulation, and provide insight into the stability of the algorithm via analysis.

A client side measurement scheme for request routing in virtual open content delivery networks

A content delivery network (CDN) routes a clients request to an edge server that can best serve the content at the time. Effective request routing is heavily dependent on up-to-date information of server loads and the network condition. We propose a novel client side measurement scheme that measures both server load, and the network condition, in a single measurement. The scheme is distributed, does not require any modification to the clients, and is compatible with existing client and server software. By experimenting on the existing Internet, we demonstrate that this measurement metric is highly correlated with total page loading time. Combined with request-routing, our measurement method provides an efficient client request redirection system that is totally transparent to the content provider, and facilitates the deployment of virtual open CDNs.

A model for TCP behaviour over cellular radio channels with link layer error recovery

We present a model for characterising the behaviour of the buffer at a base station router when TCP flow control is used in combination with a link layer retransmission protocol over a cellular wireless link. We show how our model can be used to predict packet latency, optimally dimension the buffer, and tune TCP to ensure maximum utilisation of the link, for specific wireless channel conditions. Finally we verify the model with simulation results obtained using the NS-2 simulator.

Analysis of TCP performance over hybrid "fast fixed-to-slow wireless" buffered links

We investigate performance improvements through TCP window size optimisation achievable when TCP Reno is used over a highly heterogeneous network, such as an 802.11b wireless LAN or a GPRS-based internet connection. Initially, our modelling focuses on a constant rate, buffered access link, based on a loss-less wireless channel and with a bandwidth at least one order of magnitude less than its fixed-network continuation into the core. We implement the model guidelines on wireless LAN and GPRS access links, confirming that TCP throughput can be increased by optimising the TCP receiver window size to the link characteristics, and more significantly, that there exists a broad range of near-optimal awnd values.

Efficient macro mobility management for GPRS IP networks

Mobile IP has several inefficiencies, and was not originally designed for situations where both peers are highly mobile. We present a mobility management solution that retains compatibility with existing Internet protocols, whilst increasing the efficiency of communications between two GPRS mobile hosts. Our proposal eradicates triangle routing and minimizes handover latency. We show by numerical analysis that the routing optimization improves the performance of TCP controlled data flows, reducing buffering requirements and minimizing the recovery time after a handover occurs.

Unified web-based network management based on distributed object orientated software agents

This paper presents an architecture that provides a unified web interface to managed network devices that support CORBA, OSI or Internet-based network management protocols. A client gains access to managed devices through a web browser, which is used to issue management operations and receive event notifications. The proposed architecture is compatible with both the OSI Management reference Model and CORBA. The steps required for designing the building blocks of such architecture are identified.