The hybrid application layer multicast (ALM) has been shown its efficiency by leveraging the conventionally main structures of application layer multicast, tree-based and mesh-based. However, how to select the proper node to construct the overlay and how to establish the connection between any two nodes are still unsolved. Therefore, this paper is to design a novel construction algorithm for the hybrid ALM to resolve the above two issues. Firstly, by carrying out the analysis of nodes' characteristics, all nodes are divided into groups and a node priority is proposed to select the super node within each group. Secondly, by using the selected super node, all nodes are hierarchically controlled and different kinds of connections are carried out in the ALM, where the connection between super node and other nodes is set to be a tree to enhance the efficient utilization of network resource while the connection between other normal nodes is decided to be a mesh to reduce the overhead. Simulation results show that the proposal outperforms other conventional methods.

With the development of recent vehicular communication technologies, distributing multimedia contents in the vehicular communication networks (VCNs) has become more and more popular, to provide conveniences and entertainment services during the time of driving. However, as multimedia contents are changed and updated dynamically, how to keep the consistency between the original and these replicas in VCNs is very important. Therefore, this paper designs a novel algorithm to control the consistency for the VCNs. In our proposal, after the analyses of the status of road-side units, on-board units and local geographical information, we divide all replicas into two groups, where one is necessary for update and the other are not. Then, we compare the cost to update replicas by using wireless and wired connection, and propose a method to make selection between them. The performance of our proposal is tested by simulation experiments. And the results show that our method can reduce the delay successfully.

With the growing use of dynamic content by mobile content distribution systems, how to manage dynamically changing files has become an important issue, since the cached replicas on different mobile sites must be updated if the originals have been changed. Therefore, this paper proposes a priority based selection method to enhance the efficient utilization of network resource and support the client mobility for mobile contents delivery network (M-CDN). On one hand, a consistency priority is calculated by analyzing the characteristics of mobile surrogates. If a given content which has been changed on its original node, only the replicas with the high consistency priority instead of all replicas are updated. On the other hand, an update priority is also proposed. If a replica has been selected for update, the latest version will be sent from the site decided by the update consistency. Simulation results show that the proposed new approach outperforms other conventional methods.

Content Delivery Overlays improves end-user performance by replicating Web contents on a group of geographically distributed sites interconnected over the Internet. However, with the development whereby overlay systems can manage dynamically changing files, an important issue to be resolved is consistency management, which means the cached replicas on different sites must be updated if the originals change. In this paper, based on the analytical formulation of object freshness, Web access distribution and network topology, we derive a novel algorithm as follows: (1) For a given content which has been changed on its original server, only a limited number of its replicas instead of all replicas are updated. (2) After a replica has been selected for update, the latest version will be sent from an algorithm-decided site instead of from its original server. Simulation results verify that the proposed algorithm provides much better consistency management than conventional methods with the reduced the old hit ratio and network traffic.

With the development whereby mobile content distribution systems can manage dynamically changing files, an important issue to be resolved is consistency management, which means the cached replicas on different mobile sites must be updated if the originals change. This paper is to design an integrated consistency-control algorithm for mobile contents delivery network (M-CDN) to enhance the efficient utilization of network resource and support the client mobility. Firstly, by carrying out an analysis of mobile surrogates' characteristics, for a given content which has been changed on its original node, only a limited number of its replicas instead of all replicas are updated. Secondly, if a replica has been selected for update, the latest version will be sent from an algorithm-decided site instead of from its original server. Simulation results show that the proposal outperforms other conventional methods.

IEEE802.11 WLAN (Wireless LAN) has been widely used in enterprise and public space such as air port. In these large WLAN networks, RRM (Radio Resource Management) is necessary for the efficient use of radio resource and also for load balancing among APs (Access Point) Since, in IEEE802.11, STA (Station) has the right to select an AP with which it will associate, AP selection mechanism implemented in STA is important for RRM. This paper proposes an AP selection mechanism, called HRFA (High-Rate First Association) in order to achieve load balancing and the efficient use of radio resource. Furthermore, IEEE802.11e is currently standardizing a MAC protocol to provide QoS (Quality of Service) in MAC layer and support real-time traffic over WLAN. In order for WLAN to be more widely used and to provide QoS in WLAN networks, the functionalities of IEEE802.11e have to be provided in WLAN devices. Our proposed HRFA can be applied to IEEE802.11e WLAN and can be implemented without any modifications in IEEE802.11 and 802.11e standard. Therefore it is useful from implementation-cost and compatibility point of views. Simulation results show that HRFA can efficiently ultilize radio resource and also achieve load balancing in IEEE802.11e WLAN networks.

The IEEE 802.11e defines a MAC protocol, which provides EDCA (enhanced distributed channel access) and HCCA (HCF controlled channel access) to support differentiation service over WLAN (wireless LAN). In IEE E802.11e WLAN, real-time application such as VoIP (voice over IP) can have more chance to access the WM (wireless medium) than non real-time application. In addition to QoS support in WLAN, power consumption is a critical issue when WLAN is used in handheld devices. For power saving in the use of real-time applications like VoIP under EDCA, U-APSD (unscheduled automatic power save delivery) was proposed in Y. Chen et al. (2004). In fact, it can save power consumption and works well when it is used for bi-directional voice connections generated at constant bit rate. However, when it is used for real-time applications like ON-OFF traffic, buffering delay at AP (access point) increases. To reduce the buffering delay, this paper proposes two mechanisms. Simulation results show that they can alleviate buffering delay generated at AP

In contrast to conventional P2P systems in wired networks that consist of static peers, mobile P2P are subjected to the limitations of battery power, wireless bandwidth, and the dynamically changed network topology. Challenges arise in how to improve the source discovery and data replication. In this paper, we talk about an integrated searching and prefetching algorithm for the segmented streaming in mobile peer-to-peer (P2P) Networks. Firstly, each stream is divided into several segments and each segment is assigned a priority based on theory analyses. Then, for a given segment, the different number of queries is sent to search it and the length of the query for this segment is also dynamically decided by the segment-priority to avoid the unnecessary overhead. Next, along the path where a stream is sent from the requester node, parts of the nodes on this path are selected to pre-fetch the requested segment to reduce the user delay for the next possible request. Finally, Simulation results show that better performance than the conventional methods can be achieved

Ad hoc networks have recently become a hot topic. In ad hoc networks, battery power is an important resource, since most terminals are battery powered. Terminals consume extra energy when their network interfaces are in the idle state or when they overhear packets not destined for them. They should, therefore, switch off their radio when they do not have to send or receive packets. IEEE802.11 features a power saving mechanism (PSM) in the distributed coordination function (DCF). In PSM for DCF, nodes must stay awake for a fixed time, called the ATIM window (ad-hoc traffic indication map window). If nodes do not have data to send or receive, they enter the doze state except for during the ATIM window. However, ad hoc networks with PSM have larger end-to-end delays to deliver packets and suffer lower throughput than the standard IEEE802.11. To solve this problem, this paper proposes a protocol that reduces delay and achieves high throughput and energy efficiency. Simulation results show that our proposal outperforms other PSMs in terms of throughput, end-to-end delay and energy efficiency.

What we are concerned with in this paper is a shared virtual environment (SVE) on a non-dedicated network like the Internet. Especially, we address haptics on an SVE for the new generation of network applications. The goal of our research Is to build an SVE system in which multiple participants can collaborate using haptics feedback, even though the participants are located around the world. One of the problems for this system is network impairment, and we have examined the effect of constant network delay and packet loss on the haptics collaboration system. In this paper we examine and evaluate the effect of delay jitter on the system when using media synchronization and dead reckoning.

Currently network haptic applications become more effective than ever, various usages are being sought in order to improve efficiency and accuracy of tele-operation and communications among users in shared virtual environments (SVEs). The behavior of haptic communication system under realistic network conditions (delay, jitter, and bandwidth limitation) has recently been studied. Therefore the aim of our research is to develop the network-based haptic interaction system which adapts to realistic network environments including the Internet. In this work, we design and implement a prototype of the system with network tolerance in consideration of various network problems. Experiments using objective and subjective evaluations showed that the system works properly under realistic network conditions.

The paper discusses how the OLVP system, an innovative video-on-demand system, can be used to efficiently support video delivery applications over an asynchronous transfer mode (ATM) network. We show how the OLVP system provided a high quality of service (QoS) to video applications executing over a set of distributed and heterogeneous system resources. System architecture is described. Key functionality, including distributed video storage management, real-time admission control strategy and resource allocation routing mechanism, traffic management and routing algorithms (both in the ATM network and in the OLVP system) are investigated. To illustrate the success of our approach, we provide a performance evaluation based on simulations of the system.

One of the most important techniques introduced into the recent facsimile is redundancy-reduction coding. The CCITT already standardized the coding schemes to be employed in Group 3 and Group 4. There are, however, left for further study the optional non-information-preserving coding scheme for black-and-white pictures and the coding scheme for multilevel and color pictures. Much work has been carried out with respect to these kinds of coding, including pattern-matching coding for black-and-white pictures and various information-preserving and non-information-preserving coding for multilevel and color pictures. The Group 4 apparatus is a new generation facsimile apparatus, which is mainly operated on public switched data networks. This kind of facsimile apparatus features higher resolution and error-free reception, and has the teletex-facsimile mixed mode capability as an option. The most important technical problem in the standardization of the Group 4 facsimile is the communication protocol which has been developed based on the existing teletex protocol. Facsimile communication is carried out not only on general public switched telephone or data networks, but also on specialized networks dedicated to it. Some sorts of communication processing such as speed conversion, automatic appending function, repeated delivery attempt, etc., are incorporated into these networks. The development of facsimile equipment has also shown progress in these few years. For example, a very compact apparatus has been developed using a new contact type imager and a codec built by special-purpose LSIs. The press fax apparatus employing flat-bed scanner and multicolor facsimile apparatus have also been put into market. This paper describes the outline of recent advances in facsimile, including the above-mentioned items.

It is pointed out that the degradation effect due to premodulation filtering in GMSK (Gaussian-filtered minimum shift keying) is largest at the edges of time slots, which instant has been adopted as the sample timing in the conventional coherent detector of GMSK. Then a new coherent detector employing signals sampled at a different timing in a deviated-frequency-locking scheme is presented to achieve a better bit-error-rate performance versus carrier-to-noise ratio.