A Localized Adaptive Proportioning Approach to QoS Routing

In QoS routing, paths for flows are selected based on knowledge of resource availability at network nodes and the QoS requirements of flows. Several QoS routing schemes have been proposed that differ in the way they gather information about the network state and select paths based on this information. We broadly categorize these schemes into best path routing and proportional routing. The best path routing schemes gather global network state information and always select the best path for an incoming I-low,based on this global view. It has been shown that best path routing schemes require frequent exchange of network state, imposing both communication overhead on the network and processing overheads on the core routers. On the other hand, proportional routing schemes proportion incoming flows among a set of candidate paths. We have shown that it is possible to compute near-optimal proportions using only locally collected information. Furthermore, a few good candidate paths can be selected using infrequently exchanged global information and thus with minimal communication overhead. We describe these schemes in detail and demonstrate that proportional routing schemes can achieve higher throughput with lower overhead than best path routing schemes

On Localized Control in QoS Routing

In this note, we study several issues in the design of localized quality-of-service (QoS) routing schemes that make routing decisions based on locally collected QoS state information (i.e., there is no network-wide information exchange among routers). In particular, we investigate the granularity of local QoS state information and its impact on the design of localized QoS routing schemes from a theoretical perspective. We develop two theoretical models for studying localized proportional routing: one using the link-level information and the other using path-level information. We compare the performance of these localized proportional routing models with that of a global optimal proportional model that has knowledge of the global network QoS state. We demonstrate that using only coarser-grain path-level information it is possible to obtain near-optimal proportions. We then discuss the issues involved in implementation of localized proportional routing and present some practical schemes that are simple and easy to implement

Towards Mapping of Underwater Structures by a Team of Autonomous Underwater Vehicles

In this paper, we discuss how to effectively map an underwater structure with a team of robots considering the specific challenges posed by the underwater environment. The overarching goal of this work is to produce high-definition, accurate, photorealistic representation of underwater structures. Due to the many limitations of vision underwater, operating at a distance from the structure results in degraded images that lack details, while operating close to the structure increases the accumulated uncertainty due to the limited viewing area which causes drifting. We propose a multi-robot mapping framework that utilizes two types of robots: proximal observers which map close to the structure and distal observers which provide localization for proximal observers and bird’s-eye-view situational awareness. The paper presents the fundamental components and related current results from real shipwrecks and simulations necessary to enable the proposed framework, including robust state estimation, real-time 3D mapping, and active perception navigation strategies for the two types of robots. Then, the paper outlines interesting research directions and plans to have a completely integrated framework that allows robots to map in harsh environments.acceptedVersio

Localized Approach to Providing Quality-of-Service

The exponential growth of Internet brings to focus the need to control such large networks. It is desirable to find simple local rules and strategies that can produce coherent and purposeful global behavior. The need for such mechanisms arises in a variety of settings. In quality-of-service based routing, paths for flows are selected basedupon the knowledge of resource availability at network nodes and the QoS requirements of flows. The best-path routing schemes gather global network state information and always select the best path for an incoming flow based on this global view. On the other hand, the proportional routing schemes proportion incoming flows among multiple candidate paths. We show that near-optimal proportions can be obtained using only locally collected information and a few good candidate paths can be selected using infrequently exchanged global information. We demonstrate that proportional routing schemes achieve higher throughput with lower overhead than best-path routing schemes. Video delivery for full quality playback requires a certain amount of network bandwidth and client buffer. But when these resources are limited, a naive video transmission may cause packet drops at the network and frame drops at the client, resulting in wastage of resources. To avoid this, a server may need to preemptively discard frames locally taking advantage of application-specific information. We first formulate the optimal selective frame discard problem and then present several efficient heuristic algorithms. We also develop adaptive selective layer discard algorithms for providing smoother quality playback of a layered video. Distributed dynamic channel assignment algorithms run at each base station in a wireless cellular network attempt to reduce the network-wide call blocking and call dropping probabilities while making assignment decisions based on neighborhood information only. They may also reassign channels being used by calls in progress to make room for another call. We propose two channel selection strategies based on localpacking for compact packing of channels. We also present a reassignment based call admission control scheme that dynamically adjusts the number of guard channels reserved for handoffs based on reassignment frequency in the neighborhood

Failure Insensitive Routing for Ensuring Service Availability

Abstract. Intra-domain routing protocols employed in the Internet route around failed links by having routers detect adjacent link failures, exchange link state changes, and recompute their routing tables. Due to several delays in detection, propagation and recomputation, it may take tens of seconds to minutes after a link failure to resume forwarding of packets to the affected destinations. This discontinuity in destination reachability adversely affects the quality of continuous media applications such as Voice over IP. Moreover, the resulting service unavailability for even a short duration could be catastrophic in the world of e-commerce. Though careful tuning of the various parameters of the routing protocols can accelerate convergence, it may cause instability when the majority of the failures are transient. To improve the failure resiliency without jeopardizing the routing stability, we propose a local rerouting based approach called failure insensitive routing. Under this approach, upon a link failure, adjacent router suppresses global updating and instead initiates local rerouting. All other routers infer potential link failures from the packet’s incoming interface, precompute interface specific forwarding tables and route around failed links without explicit link state updates. We demonstrate that the proposed approach provides higher service availability than the existing routing schemes.

On the Efficacy of Opportunistic Routing

Abstract—Traditional routing schemes select the best path for each destination and forward a packet to the corresponding next hop. While such best-path routing schemes are considered well-suited for networks with reliable point-to-point links, they are not necessarily ideal for wireless networks with lossy broadcast links. Consequently, opportunistic routing schemes that exploit the broadcast nature of wireless transmissions and dynamically select a next-hop per-packet based on loss conditions at that instant are being actively explored. It is generally accepted that opportunistic routing performs substantially better than best-path routing for wireless mesh networks. In this paper, we analyze the efficacy of opportunistic routing. We define a new metric EAX that captures the expected number of any-path transmissions needed to successfully deliver a packet between two nodes under opportunistic routing. Based on EAX, we develop a candidate selection and prioritization method corresponding to an ideal opportunistic routing scheme. We then conduct an off-line comparison of best-path routing and opportunistic routing using our EAX metric and MIT Roofnet trace. We observe that while opportunistic routing offers better performance than bestpath routing, the gain is not as high as commonly believed. I

Disruption-tolerant content-aware video streaming

Communication between a pair of nodes in the network may get disrupted due to failures of links/nodes resulting in zero effective bandwidth between them during the recovery period. It has been observed that such disruptions are not too uncommon and may last from tens of seconds to minutes. Even an occasional such disruption can drastically degrade the viewing experience of a participant in a video streaming session particularly when a sequence of frames central to the story are lost during the disruption. The conventional approach of prefetching video frames and patching lost ones with retransmissions is not always viable when disruptions are localized and experienced only by a few among many receivers. Error spreading approaches that distribute the losses across the video work well only when the disruptions are quite short. As a better alternative, we propose a disruption-tolerant content-aware video streaming approach that combines the techniques of content summarization and error spreading to enhance viewers experience even when the disruptions are long. We introduce the notion of “substitutable content summary frames ” and provide a method to select these frames and also their transmission order to mitigate the impact of a disruption. In the event of a disruption, the already received summary frames are played by the client during disruption and near normal playback is resumed after the disruption. We evaluate our approach and demonstrate that it provides acceptable viewing experience with minimal startup latency and client buffer