Abstract—Enabling video transport over ad hoc networks is more challenging than over other wireless networks. The wireless links in an ad hoc network are highly error prone and can go down frequently because of node mobility, interference, channel fading, and the lack of infrastructure. However, the mesh topology of ad hoc networks implies that it is possible to establish multiple paths between a source and a destination. Indeed, multipath transport provides an extra degree of freedom in designing error resilient video coding and transport schemes. In this paper, we propose to combine multistream coding with multipath transport, to show that, in addition to traditional error control techniques, path diversity provides an effective means to combat transmission error in ad hoc networks. The schemes that we have examined are: 1) feedback based reference picture selection; 2) layered coding with selective automatic repeat request; and 3) multiple description motion compensation coding. All these techniques are based on the motion compensated prediction technique found in modern video coding standards. We studied the performance of these three schemes via extensive simulations using both Markov channel models and OPNET Modeler. To further validate the viability and performance advantages of these schemes, we implemented an ad hoc multiple path video streaming testbed using notebook computers and IEEE 802.11b cards. The results show that great improvement in video quality can be achieved over the standard schemes with limited additional cost. Each of these three video coding/transport techniques is best suited for a particular environment, depending on the availability of a feedback channel, the end-to-end delay constraint, and the error characteristics of the paths. Index Terms—Ad hoc networks, error resilience, IEEE 802.11, multipath transport, video transport, wireless networks.

Abstract. Multipath routing schemes distribute traffic among multiple paths instead of routing all the traffic along a single path. Two key questions that arise in multipath routing are how many paths are needed and how to select these paths. Clearly, the number and the quality of the paths selected dictate the performance of a multipath routing scheme. We address these issues in the context of the proportional routing paradigm where the traffic is proportioned among a few “good” paths instead of routing it all along the “best ” path. We propose a hybrid approach that uses both globally exchanged link state metrics — to identify a set of good paths, and locally collected path state metrics — for proportioning traffic among the selected paths. We compare the performance of our approach with that of global optimal proportioning and show that the proposed approach yields near-optimal performance using only a few paths. We also demonstrate that the proposed scheme yields much higher throughput with much smaller overhead compared to other schemes based on link state updates. 1

Localized Quality of Service (QoS) routing was recently proposed as an alternative to the QoS routing algorithms that use global network state information to make routing decisions. In localized QoS routing, each router maintains a predetermined set of candidate paths for each of the destinations. For a connection request, a router decides the path for the request based on the information maintained locally at the router. Hence, localized QoS routing does not use any global network state information in the routing process and avoids the problems associated with the maintenance of the global network state information. To achieve good routing performance, localized QoS routing must select the predetermined set of candidate paths between the source and the destination e#ectively. This paper studies path selection methods for localized QoS routing. Five path selection heuristics, namely breadth-first search path selection, per-pair shortest path selection, global path selection, hybrid per-pair/global path selection, and per-pair path selection with global tuning, are proposed and their performance is evaluated through simulation. We conclude that path selection methods can greatly a#ect the performance of localized QoS routing and that an e#ective path selection algorithm must consider various factors, including path length and load balancing in the whole network. 1

Novel routing paradigms based on policies, quality of service (QoS) requirements, and packet content have been proposed for the Internet over the last decade. Constraint-based routing algorithms select a routing path satisfying constraints which are either administrativeoriented (policy routing), or service-oriented (QoS routing). The routes, in addition to satisfying constraints, are selected to reduce costs, balance network load, or increase security. In this paper, we discuss several constraint-based routing approaches and explain their requirements, complexity, and recent research proposals. In addition, we illustrate how these approaches can be integrated with Internet label switching and QoS architectures. We also discuss examples of application-level routing techniques used in today's Internet.

Routing protocols are an essential part of the efficient design of mobile ad hoc networks (MANETs). Existing routing protocols such as DSR, AODV, and TORA are based on a best effort strategy [18][19]. However, in order for MANETs to be practical for more demanding real time applications such as multimedia, providing a certain needed level of quality of service becomes an essential component in the communication protocol design [2][11][21][22]. QoS routing protocols provide the capability of finding a path between two nodes which satisfies the application layer’s minimum bandwidth requirements. Previous papers addressed this issue for different communication environments such as TDMA (Time Division Multiple Access) [7][8][12][13] and CDMA (Code Division Multiple Access)-over-TDMA [3][14][15]. While most of these models are generally more practical and less expensive, they impose on the designer the constraint of the hidden terminal and exposed terminal problems. The paper by Liao and Tseng [12] addressed these issues and provided a TDMA-based bandwidth reservation protocol for QoS routing in MANETs. However, this protocol does not account for the race condition which can become more significant with increased node mobility, network density and higher traffic loads. This race condition is also a limitation of other QoS routing protocols [7][8]. This paper addresses this issue and provides a protocol which enables the network to cope with this and other related problems such as parallel reservation. We also provide increased optimizations which significantly enhance the throughput and efficiency of the QoS routing protocol.

In large networks, maintaining precise global network state information is almost impossible. Many factors, including non-negligible propagation delay, infrequent link state update due to overhead concerns, link state update policy, resource reservation, and hierarchical topology aggregation, have impacts on the precision of the global network state information. To achieve efficient Quality of Service (QoS) routing, a practical routing algorithm must be able to make effective routing decisions in the presence of imprecise global network state information. In this paper, we compare five QoS routing algorithms that were proposed to tolerate imprecise global network state information, safety-based routing, randomized routing, multi-path routing, localized routing, and static multi-path routing. The performance of these routing algorithms are evaluated under three different link state update policies, the timer based policy, the threshold based policy and the class based policy. The strengths and limitations of each scheme are identified.

Recent work on differentiated services in the Internet has defined new notions of QoS that apply to aggregates of traffic in networks with coarse spatial granularity. Most proposals for differentiated services involve traffic control algorithms for aggregate service levels, packet marking and policing, and preferential treatment of marked packets in the network core. The issue of routing for enhancing aggregate QoS has not received a lot of attention. This study investigates the potential benefit of using alternate routing strategies in support of differentiated services. We propose a traffic control scheme, called Simple Alternate Routing (SAR), wherein portions of marked packet flows can be assigned to alternate paths through a Service Provider Network (SPN) in response to congestion feedback information. The scheme is simple, requiring only minor changes to the SPN border routers so that alternately routed packets can be tunneled via conventional paths to an intermediate bo...

In this paper we study several issues in the design of localized QoS routing schemes, schemes that make local 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 locally collected link-level QoS state information, and the other using locally collected path-level QoS state 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. Using these localized routing QoS models we also investigate the impact of the granularity of local QoS state information on their stability and adaptivity. Through our study, we demonstrate that an appropriately designed localized QoS routing scheme that makes routing decisions solely based on local information can potentially achieve such global objectives as a stable network system with good (i.e., near-optimal) overall system performance. 1

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.

Abstract — We propose a routing and load-balancing approach with the primary goal of being robust to sudden topological changes and significant traffic matrix variations. The proposed method load-balances traffic over several routes in an adaptive way based on its local view of the load in the network. The focus is on robustness and simplicity, rather than optimality, and so it does not rely on a given traffic matrix, nor it is tuned to a specific topology. Instead, we aim to achieve a satisfactory routing under a wide range of traffic and topology scenarios based on each node’s independent operation. The scheme avoids the instability risks of previous load-responsive routing schemes, it does not load the control plane with congestion-related signaling, and it can be implemented on top of existing routing protocols. In this paper, we present the proposed scheme, discuss how it aims to meet the objectives of robustness and load-responsiveness, and evaluate its performance under diverse traffic loads and topological changes with flow-level simulations. I.