A Cautionary Perspective on Cross Layer

Recently, in an effort to improve the performance of wireless networks, there has been increased interest in protocols which rely on interactions between different layers. However such cross layer design can run at cross purposes with sound and longer term architectural principles, and can lead to various negative consequences. This motivates us to step back and re-examine holistically the issue of cross layer design and its architectural ramifications

Truthful prioritization for dynamic bandwidth sharing

We design a protocol for dynamic prioritization of data on shared routers such as untethered 3G/4G devices. The mechanism prioritizes bandwidth in favor of users with the highest value, and is incentive compatible, so that users can simply report their true values for network access. A revenue pooling mechanism also aligns incentives for sellers, so that they will choose to use prioritization methods that retain the incentive properties on the buy-side. In this way, the design allows for an open architecture. In addition to revenue pooling, the technical contribution is to identify a class of stochastic demand models and a prioritization scheme that provides allocation monotonicity. Simulation results confirm efficiency gains from dynamic prioritization relative to prior methods, as well as the effectiveness of revenue pooling.Engineering and Applied Science

Experimental investigations into TCP performance over wireless multihop networks

The results of an extensive experimental study of the performance of the TCP protocol over wireless multi-hop ad hoc networks are presented. The investigations are performed in a real indoor environment over a network of laptops equipped with off-the-shelf IEEE 802.11b wireless cards. The cards were partially covered with copper tape to reduce their range, which enabled creation of manageable topologies. Several tools were written and assembled to make the entire process of experimentation including topology setup, traffic generation, trace collection, and archival and analysis of data repeatable, reliable and as automated as possible. The experimental observations are subjected to a thorough statistical analysis. The final result of the study is a recommendation of some TCP and IEEE 802.11 parameters that are best for TCP performance over wireless multi-hop networks. The most critical of these include setting a destination dependent clamp on the sender congestion window and disabling the RTC-CTS handshake. The methods and techniques used, as well as the support tools developed, and statistical analysis, may be of larger interest in wireless network experimentation

PROTOCOLS AND ARCHITECTURE FOR WIRELESS AD HOC NETWORKS

The subject of this dissertation is ad hoc wireless networks. In such networks packets are relayed over multiple hops to reach their destination. In order to operate ad hoc networks several protocols, for media access control, power control, routing, and transport are needed. This dissertation is concerned with the development and evaluation of such protocols, and the associated architecture of the protocol stack. We take a holistic approach to the problems in ad hoc networks. Transmission power control is important because of the fundamental nature of the wireless network that it is interference limited. Transmission power control has the potential to increase a network’s traffic carrying capacity, reduce energy consumption, and reduce the end-to-end delay. We start by postulating general design principles for power control based on the effect of transmit power on various performance metrics. These are used to design a set of protocols which attempt to optimize different performance metrics, as all the metrics cannot be simultaneously optimized in general. Some of these protocols have been implemented in the Linux kernel in an architecturally appropriate manner. Extensive testing was not possible due to the limitations of the current generation of hardware, and so performance results obtained throug

System services for ad-hoc routing: Architecture, implementation and experiences

This work explores several system issues regarding the design and implementation of routing protocols for ad-hoc wireless networks. We examine the routing architecture in current operating systems and find it insufficient on several counts, especially for supporting on-demand or reactive routing protocols. Examples include lack of mechanisms for queuing outstanding packets awaiting route discovery and mechanisms for communicating route usage information from kernel to userspace. We propose an architecture and a generic API for any operating system to augment the current routing architecture. Implementing the API may normally require kernel modifications, but we provide an implementation for Linux using only the standard Linux 2.4 kernel facilities. The API is provided as a shared user-space library called the Ad-hoc Support Library (ASL), which uses a small loadable kernel module. To prove the viability of our framework, we provide a full-fledged implementation of the AODV protocol using ASL, and a design for the DSR protocol. Through this study, we also reinforce our belief that it is profoundly important to consider system issues in ad-hoc routing protocol design.

Principles and protocols for power control in wireless ad hoc networks

Abstract—Transmit power control is a prototypical example of a cross-layer design problem. The transmit power level affects signal quality and, thus, impacts the physical layer, determines the neighboring nodes that can hear the packet and, thus, the network layer affects interference which causes congestion and, thus, affects the transport layer. It is also key to several performance measures such as throughput, delay, and energy consumption. The challenge is to determine where in the architecture the power control problem is to be situated, to determine the appropriate power level by studying its impact on several performance issues, to provide a solution which deals properly with the multiple effects of transmit power control, and finally, to provide a software architecture for realizing the solution. We distill some basic principles on power control, which inform the subsequent design process. We then detail the design of a sequence of increasingly complex protocols, which address the multidimensional ramifications of the power control problem. Many of these protocols have been implemented, and may be the only implementations for power control in a real system. It is hoped that the approach in this paper may also be of use in other topical problems in cross-layer design. Index Terms—Design principles, Linux implementation, power control