In this paper, we propose the high-level service architecture supporting multimedia multicast. The proposed architecture specifies network-oriented and lightweight communication management, which includes group management, multiparty call control and multicast connection/multiple connections control. Many of the existing approaches handling multimedia multicast applications are dependent on specific transport technologies, such as the Internet and ATM, and lack effective communication management. On the other hand, our approach defines flexible and extensible communication management that can be applied to a variety of multimedia multicast applications, independently of transport technologies. Our architecture supports the separation of control from a terminal, which enables remote control and control mobility, so that a user can use a multicast service in a more various way. The architecture is overlaid above legacy transport networks so that the existing network protocols are used for connection control. This minimizes the modification to a legacy transport network and enhances the practicality of the architecture. In addition, terminal manager and virtual device concepts are introduced that hide the details of physical devices from an application designer. The architecture consists of several service components that effectively interact with each other on a distributed platform. To verify and evaluate our architecture, we have prototyped the high-level service architecture on a CORBA platform and analyzed the architecture using a simulation.

IEEE 802.15.4 is a new standard, uniquely designed for low rate wireless personal area networks (LR-WPANs). It targets ultra-low complexity, cost, and power, for low-data-rate wireless connectivity. However, one of the main problems of this new standard is its insufficient, and inefficient, media access control (MAC) for priority data. This paper introduces an extended contention access period (XCAP) concept for priority packets, also an traffic adaptive contention differentiation utilizing the XCAP (TACDX). The TACDX determines appropriate transmission policy alternatively according to the traffic conditions and type of packet. TACDX achieves not only enhanced transmission for priority packets but it also has a high energy efficiency for the overall network. The proposed TACDX is verified with simulations to measure the performances.

Since the sensor nodes are subject to faults due to the highly-constrained resources and hostile deployment environments, fault management in wireless sensor networks (WSNs) is essential to guarantee the proper operation of networks, especially routing. In contrast to existing fault management methods which mainly aim to be tolerant to faults without considering the fault type, we propose a novel efficient fault-aware routing method where faults are classified and dealt with accordingly. More specifically, we first identify each fault and then try to set up the new routing path according to the fault type. Our proposed method can be easily integrated with any kind of existing routing method. We show that our proposed method outperforms AODV, REAR, and GPSR, which are the representative works of single-path routing, multipath routing and location based routing, in terms of energy efficiency and data delivery ratio.

As the need for underwater communication has recently grown, an acoustic modem has become more necessary for the sensor nodes to perform effective underwater communication. To develop acoustic modems for effective underwater communication, some limitations must be overcome, such as the limited power supply and high cost of commercial acoustic modems. Recently, low-power, low-cost acoustic modems have been developed. However, the data rates of these modems are very slow. The objective of this work is to develop an acoustic modem capable of supporting high data rates. We introduce a coherent acoustic modem that uses waterproof ultrasonic sensors to process acoustic waves. The proposed modem is based on a low-power, low-cost, short-range concept, and it also supports a high data rate as confirmed by underwater experiments. Experimental results show that our modem has the best performance among all recently developed low-power modems.

We define the term sensor node profile (SNP) in IEEE 802.15.4, which considers the transmitting data type as well as a variety of nodal characteristics which are able to manage the channels of each node by using the SNP. Through the use of the SNP the nodes are able to maximize the channel resource usage, which could form the basis of algorithms that can provide the required Quality of Service (QoS).

This paper describes distributed communications based on a new paradigm of middleware platform called the typed bus (TB) platform. While traditional middleware platforms provide the same type of communication paths between distributed objects, the TB platform provides typed buses, which are communication paths differentiated according to application's communication characteristics. Each typed bus represents unique communication type and controls communications between distributed objects according to its type as a hardware system bus constrains communication between hardware components. Distributed communications are achieved via typed buses, which check if the communications are compliant with their types. In this paper we propose the architecture of the TB platform, introduce TB Type Definition Language used to specify a typed bus's type, and describe an implementation of our platform.

In a ZigBee network, a finite address space is allocated to every potential parent device and a device may disallow a join request once this address space is exhausted. When a new node (child) requests to a coordinator (parent) to join a ZigBee network, the coordinator checks its address space. If it has sufficient address space, the coordinator accepts the new node as its child in the ZigBee network. If the new node has router capability (JoinAsRouter), it becomes a router in the ZigBee network. However, this association procedure makes ZigBee networks inefficient for routing, because the coordinator checks only the maximum and current numbers of child nodes. In the worst case, the network will be arranged so that the router nodes are crowded in the network. Therefore, we propose the KMCD-IME (Keeping the Maximum Communication Distance and Initial Mutual Exclusion among router nodes) algorithm with two additional conditions when a new node joins the ZigBee network. The first condition maintains the maximum communication distance between the new node and the would-be parent node. The second condition is the Initial Mutual Exclusion among router nodes. The router nodes are evenly spread across the network by KMCD-IME and an effective routing topology is formed. Therefore, the KMCD-IME algorithm extends the lifetime of the ZigBee network.

An energy-efficient clustering scheme to maximize the network lifetime is presented in IEEE 802.15.4 networks. In the proposed clustering scheme, even though the cluster is divided into several sub-clusters in order to decrease data redundancies, the sub-CH does not transmit the beacon frame due to the problem of beacon collision. Our clustering scheme also allows the CH to control the size of the sub-cluster according to the residual energy of the sub-CH. The performance of the proposed scheme is verified by simulations that demonstrate how our scheme provides a better network lifetime than the conventional scheme.

Currently, there are various routing methods that consider the energy in a wireless sensor environment. The algorithm we consider is a low-rate wireless personal area network, viz., 802.15.4, and ZigBee routing network. Considering, the overall organization of the network energy efficiency, we suggest a logical position exchange (LPE) algorithm between specified nodes. Logical positioning means connecting high sub-networks and low sub-networks based on the neighbor nodes information of the address ID, and depth in the ZigBee tree topology network. When one of the nodes of the tree topology network, which is responsible for connecting multiple low sub-networks and high sub-networks, has difficulty performing its important roles in the network, because of energy exhaustion, it exchanges essential information and entrusts logical positioning to another node that is capable of it. A partial change in the logical topology enhances the energy efficiency in the network.

Time synchronization is of paramount importance in wireless sensor networks (WSNs) due to the inherent distributed characteristics of WSNs. Border surveillance WSNs, especially, require a highly secure and accurate time synchronization scheme to detect and track intruders. In this paper, we propose a Secure and Efficient Time synchronization scheme for Border surveillance WSNs (SETB) which meets the requirements of border surveillance WSNs while minimizing the resource usage. To accomplish this goal, we first define the performance and security requirements for time synchronization in border surveillance WSNs in detail. Then, we build our time synchronization scheme optimized for these requirements. By utilizing both heterogeneous WSNs and one-way key chains, SETB satisfies the requirements with much less overhead than existing schemes. Additionally, we introduce on-demand time synchronization, which implies that time synchronization is conducted only when an intruder enters the WSN, in order to reduce energy consumption. Finally, we propose a method of deploying time-source nodes to keep the synchronization error within the requirement. Our analysis shows that SETB not only satisfies the performance and security requirements, but also is highly efficient in terms of communication and computation overhead, thus minimizing energy consumption.

In this paper, we analyze two representative tree-based RFID anti-collision algorithms: the Query Tree protocol and the Binary Search algorithm. Based on the advantages and disadvantages of the two algorithms, we propose and evaluate two optimized anti-collision algorithms: the Optimized Binary Search, which performs better than the Query Tree Protocol with the same tag-side overhead, and the Optimized Binary Search with Multiple Collision Bits Resolution algorithm, which performs the best with an acceptable increase in tag-side processing overhead.

The new generation of telemedicine systems enables healthcare service providers to monitor patients not only in the hospital but also when they are at home. In order to efficiently exploit these systems, human information collected from end devices must be sent to the medical center through reliable data transmission. In this paper, we propose an adaptive relay transmission scheme to improve the reliability of data transmission for wireless body area networks. In our proposal, relay nodes that have successfully decoded a packet from the source node are selected as relay nodes in which the best relay with the highest channel gain is selected to forward the failed packet instead of the source node. The scheme addresses both the data collision problem and the inefficient relay selection in relay transmission. Our experimental results show that the proposed scheme provides a better performance than previous works in terms of the packet delivery ratio and end-to-end delay.

An Energy-efficient Flexible Beacon Scheduling (EFBS) mechanism is proposed to solve the beacon collision problem in cluster-tree healthcare systems. In EFBS, after clustering, BAN Coordinators perform power control. Then they are divided into groups and each group is assigned one contention-free time-slot. The duration of the beacon-only period is flexible. According to the simulation results, EFBS provides better performance than other beacon scheduling approaches.

To solve the RFID reader collision problem, a Multi-dimensional Channel Management (MCM) mechanism is proposed. A reader selects an idle channel which has the maximum distance with the used channels. A backoff scheme is used before channel acquisition. The simulation results show MCM has better performance than other mechanisms.

In this paper, MWAN (Mobile Wireless Ad hoc Networks with internet connection) is considered, which is a solution for many tasks owing to its ease of use, and practicality. Recently, MWAN is required to support large data like multimedia data transfer and it is transferred through several relay nodes. There are 2 problems that cause difficulties for large data transfer through a mobile network. First one is rerouting delay by handoff and second one is network congestion caused by handoff. Also, faulty data transfer caused by handoff delay makes extra load and causes some problems for MWAN. To solve these problems and get network reliability, we propose a new multipath routing scheme that can provide solution for seamless connection while handoff. In the proposed scheme, our MWAN can support multiple paths for data transfer, maintain end-to-end connection while handoff and get new route quickly. The performance of the proposed scheme is evaluated and compared with other multipath routing scheme to show the improvement.

This paper proposes a new ad hoc routing protocol using route redundancy as one of route selection criteria. It is important to provide redundancy for the route from source to destination in mobile ad hoc networks that are susceptible to failure. Route redundancy implies the relative possibility that redundant paths will exist on a route to be built up. Our proposal aims to establish a route that contains more redundant paths toward a destination node by involving intermediate nodes with relatively more adjacent nodes in a possible route. Our approach can localize the effects of route failures, and reduce control traffic overhead and route reconfiguration time by enhancing the reachability to the destination node without source-initiated route rediscoveries at route failures. We show the route setup procedure considering link redundancy and the route reconfiguration procedures employing redundant path information at the intermediate nodes. Further, this paper presents a new route maintenance protocol. Most of existing ad hoc routing protocols re-initiate a route query procedure when a destination node moves away and a route failure occurs. However, our scheme makes the destination node find a neighbor node that knows the way to the source node and establish a partial route to the neighbor node. If the destination node can find any and connect to it, the route will be recovered. This produces less control overhead than a source-initiated route discovery. We show the performance of our routing schemes through simulations using the Network Simulator 2 (ns-2).

Recently, IEEE 802.15.4 has been standardized for WSNs (Wireless Sensor Networks). This paper proposes an enhanced CCA scheme which involves the data transmission device sending a notifyBusyChannel (nBC) signal in the backoff period when the Channel Using Quotient (CUQ) exceeds 0.5. The CUQ stands for the rate of channel utilization in the previous slot duration. In a single CCA operation, the device nodes are made aware of the busy status of the channel by the nBC signal. We implement the ECCA scheme in a hardware chip for a performance evaluation. The results show that the proposed scheme has short queuing times and less energy consumption than IEEE 802.15.4 CCA. And the scheme is compatible with conventional IEEE 802.15.4 devices.

A network of sensors can be used to obtain state based data from the area in which they are deployed. To reduce costs, the data sent via intermediate sensors to a sink are often aggregated. In this letter, we introduce Self-Construction of Aggregation Tree (SCAT) scheme which uses a novel data aggregation scheme utilizing the knowledge of the mobile node and the infrastructure (static node tree) in gathering the data from the mobile node. The static nodes can construct a near- optimal aggregation tree by themselves, using the knowledge of the mobile node, which is a process similar to forming the centralized aggregation tree.

As the network speed becomes faster and requirements about various services are increased, a number of groups are currently developing technologies aimed at evolving and enhancing the capabilities of existing network. A Next-Generation Network (NGN) is defined as a hybrid telecommunications network that employs new distributed processing techniques to provide all types of services. By integrating the Intelligent Network (IN) technology and the Mobile Agent (MA) technology we can support service flexibility and service portability in NGN. In this paper, we propose a caching-based mobile agent model for NGN and analyze the performance of this model. The mobile agent technology increases the service portability and the caching strategy does the service reusability. Each Physical Entity (PE) has MAs within their repository through the caching strategy and processes service requests from users without the control of the central system such as Service Control Point (SCP). Therefore, we can decrease the total network load and the response time for user requests.

In this paper, we define a wireless sensor network with multiple types of sensors as a wireless heterogeneous sensor network (WHSN), and propose an efficient query dissemination scheme (EDT) in the WHSN. The EDT based on total dominant pruning can forward queries to only the nodes with data requested by the user, thereby reducing unnecessary packet transmission. We show that the EDT is suitable for the WHSN environment through a variety of simulations.