We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with high speed connection to the Internet. This is achieved by forming a WiMAX-based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a wireless mesh network, routing protocol plays an important role in providing efficient and reliable communications. This paper proposes a routing protocol, called MRPT (MAC-based Routing Protocol for TRITON), that piggybacks routing information on WiMAX mesh MAC control messages. This provides proactiveness and readily available multi-path for traffic from ship to land station. For traffic from land station to ship, the proposed routing protocol uses a bitmap encoding to efficiently inform land station of the constructed routing tree. Simulation results confirm that MRPT outperforms AODV, AOMDV and OLSR in terms of delay and throughput.

Multihop Relay (MR) is defined in IEEE 802.16J for coverage extension and capacity enhancement of the legacy IEEE 802.16e point-to-multi-point (PMP) networks. In MR networks, relay stations (RSs) deployment is crucial in achieving good network performance. In this paper, we explore the optimal RS selection problem. By incorporating highway mobility pattern and the Erceg terrain model, the RS selection can be formulated into a non-linear optimization problem, aiming at finding the optimal RS for achieving the maximal end-to-end capacity for subscriber stations (SSs). Numerical results show that the expected end-to- end capacity for individual SS can be increased by 49.86% by using the optimal RS selection approach.

We envisage extending radio coverage of the existing terrestrial wireless broadband networks to the sea to provide ships with cost-efficient high-speed connection to the Internet. This is achieved by forming a WiMAX based maritime wireless mesh network where ships are network nodes connected to the land station across multiple hops. In such a maritime wireless mesh network, time slot allocation is an important issue as it affects the performance in terms of throughout and delay. This papers proposes a distributed adaptive time slot allocation (DATSA) scheme for WiMAX mesh MAC protocol. DATSA is a distributed scheme that allocates time slots robustly by taking into consideration difference between radio reception range and interference range, and latency in scheduling control messages. DATSA has a method to monitor reception quality of an allocated time slot, in order to detect the effect of topology changes due to ship mobility, etc. Based on the monitoring outcome, the method adaptively changes the time slot allocation if necessary. We have evaluated DATSA through random event simulation using QualNet. The simulation results confirm that DATSA outperforms the original WiMAX mesh MAC protocol that has no adaptive time slot allocation, in terms of throughput, average packet delay, and packet delivery ratio.

Unlike terrestrial networks, the received signal strength in maritime wireless networks are subjected to perturbations due to the sea movement. Surface motions at sea cause variations in antenna heights and orientations of the communicating node (e.g. ships and buoys), thus affecting the received signal strength. In order to minimize such undesirable effects, we carried out a detailed study of the relationship between sea waves and the received signal strength. The effect of antenna gain variations due to tilting of antenna masts were studied by modeling sea waves. The channel path-loss variations were studied using a two-ray path-loss model for the maritime environment. Our analysis showed that the sea wave movements affect both short and longer links. We proposed a simple scheme to avoid the use of unstable links and implemented it on the QualNet network simulator. We carried out IEEE 802.16-based mesh network simulations with sea terrain and path loss models. We observed performance improvements in packet delay and throughput when the stable link selection scheme was used.

This paper details a novel approach of developing a low-cost and high speed maritime ship-to-ship/shore mesh network to complement or replace satellite communications in narrow water channels or traffic lanes close to shorelines. To design the system, we gathered requirements from typical users of the system. We then carried out preliminary studies such as radio channel propagation over sea water, ship movement patterns, ship rocking and its effect on radio transmission and network connectivity to determine the feasibility of using a mesh network for maritime networks. We present the architecture and detail some of our routing and scheduling design considerations that address the unique challenges of the maritime environment and provide us with framework for providing fair and equal opportunity access to users.

We envisage coverage extension of the high bit rate terrestrial communication networks to the ships to reduce the cost in maritime communications. The coverage extension is achieved by forming a mobile wireless mesh network amongst neighboring ships, marine beacons and buoys. The wireless mesh network will be connected to the terrestrial networks across multiple hops via land stations at shore. In such a multi-hop wireless network, routing protocol is important. This paper compares the performance of three existing routing protocols in a maritime communication environment. The three routing protocols are OLSR, AODV and AOMDV. The performance comparison is done via simulation. In the simulation, the wireless mesh network is formed using WiMAX mesh MAC protocol. Also, the random sea surface movement and maritime communication link characteristic are simulated. From the simulation results, we found that OLSR is not as efficient as AODV and AOMDV. Also, compared to AODV, the performance of AOMDV is less affected by sea condition.

Abstract Multicast services have been used to transmit multimedia data to large receiver groups. Only recently have counterpart network services been introduced to provide similar scalability and anonymity in the opposite direction (i.e. messages from a group of senders destined for a common receiver). In this paper, we explore how these many‐to‐one services, specifically the concast service, can be used to improve the scalability and performance of multimedia applications. In particular, we show how such services can be used in both the control and data planes to overcome well‐known scalability problems (e.g. with Real Time Protocol) that are difficult to solve effectively with end‐system approaches alone. We validate our solutions by presenting experimental results taken from prototype video and audio applications we designed and implemented. Our initial results show substantial reductions in congestion‐induced loss using these generic services. Copyright © 2003 John Wiley & Sons, Ltd.

Some end-to-end network services benefit greatly from network support in terms of utility and scalability. However, when such support is provided through service-specific mechanisms, the proliferation of one-off solutions tend to decrease the robustness of the network over time. Programmable routers, on the other hand, offer generic support for a variety of end-to-end services, but face a different set of challenges with respect to performance, scalability, security, and robustness. Ideally, router-based support for end-to-end services should exhibit the kind of generality, simplicity, scalability, and performance that made the Internet Protocol (IP) so successful. In this paper we present a router-based building block called ephemeral state processing (ESP), which is designed to have IP-like characteristics. ESP allows packets to create and manipulate small amounts of temporary state at routers via short, predefined computations. We discuss the issues involved in the design of such a service and describe three broad classes of problems for which ESP enables robust solutions. We also present performance measurements from a network-processor-based implementation.

Multicast services have been used for many years to transmit multimedia data to large receiver groups. However, only recently have counterpart network services been introduced that provide similar scalability and anonymity in the opposite direction (i.e., messages from a group of senders destined for a common receiver). In this paper, we explore how these emerging services, specifically a concast service (many-to-one communication service), can be used to improve the scalability and performance of multimedia applications. In particular, we show how such services can be used in both the control and data planes to overcome well-known scalability problems (e.g., with RTP) that are difficult to solve effectively with end-system approaches alone. We validate our solutions by presenting experimental results taken from prototype video and audio applications we designed and implemented. Our initial results show a reduction of as much as two orders of magnitude in packet loss rates using these generic services.

Concast is a network layer service that provides many-to-one channels: multiple sources send messages toward one destination, and the network delivers a single "merged" copy to that destination. As we have defined it, the service is generic but the relationship between the sent and received messages can be customized for particular applications. We describe the concast service and show how it can be implemented in a back ward-compatible manner in the Internet. We describe its use to solve a problem that has eluded scalable end-system-only solutions: collecting feedback in multicast applications. Our preliminary analysis of concasting effectiveness shows that it provides significant benefits, even with partial deployment. We argue that concast has the characteristics needed for a programmable service to be widely accepted and deployed in the Internet.

Concast is a scalable "inverse-multicast" network service: messages sent from multiple sources toward the same destination are merged into a single message that is delivered to the destination. The mapping from sent messages to received messages is programmable, so the service can be tailored to the needs of specific applications. However the service can also be used as a building block for other generic network services, such as a packet multiplexing service that encapsulates multiple small packets into a single larger packet and then unencapsulates the small packets at their (common) destination. Such a service offers several potential benefits, including reduced packet processing overhead and increased rate-sharing, but must also be carefully designed to avoid problems caused by added packet delays. We show how concast can serve as the basis for a multiplexing service that can be tailored to the needs of the application. We present simulation results showing that the benefits of our multiplexing service vary with delay. We also show that given certain queue-manipulation capabilities, benefits can be achieved with zero added delay.

Layered multicast is a promising technique for broadcasting adaptive-quality TV video to heterogeneous receivers. While several-layered multicast approaches have been proposed, prior work has identified several problems including significant and persistent instability in video quality, arbitrary unfairness with other sessions, low access link utilization due to conservative bandwidth allocation, and problems with receiver synchronization. In this paper we propose a new layered multicast scheme, where we exploit a simple, coarse-grained, two-tier loss differentiation architecture to achieve stable and fair bandwidth allocation for viewers. Despite the simplicity of our loss differentiation model, we show that it achieves most of the benefits of complex and costly priority dropping schemes. In addition, our protocol is receiver-driven and thus retains the incentives to limit bandwidth usage that are not present in existing priority dropping schemes.

The paper describes the design and implementation of a median filter for graphics images on the Motorola AltiVec architecture. The filter utilizes 16-way SIMD parallelism to filter images at rates of 1.15 cycles/pixel for 3/spl times/3 squares and 6.6 cycles/pixel for 5/spl times/5 squares. The median filter is based on a new sorting network which sorts N/sup 2/ numbers (arranged in an N/spl times/N square) by sorting all columns, rows, and diagonal lines in the square. The paper also describes a scheme for efficient testing of the sorting network.

This paper introduces concast, a new network service. Concast is the inverse of multicast: multiple sources send messages toward the same destination, which results in a single message being delivered to the destination. The received message appears to come from the concast group rather than any particular receiver. Different forms of concast service can be defined by varying the mapping from the set of sent messages to the received message. The service is useful for preventing implosion and reducing bandwidth consumption in cases where many senders transmit to the same receiver-for example in aggregating (or suppressing) positive (or negative) acknowledgements. We define the semantics of a simple concast service that is the inverse of multicast, as well as a more general custom concast, which allows users to define certain aspects of the service's semantics. We describe how to implement the service so that it scales approximately as well as IP multicast. We also present results from a simulation study showing that concast provides significant benefits in a layered-video application.