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In order to improve the utilization of network bandwidth in multimedia business, a variety of header compression schemes have been proposed. This paper first introduces the background and feasibility of the header compression technology, and then states the principles of three traditional header compression schemes: VJHC, IPHC and CRTP. Since the three traditional header compression schemes can't be used in the wireless networks environment whose bit error rate is very high, this article high lights a robust header compression scheme - ROHC. This article illustrates the states and modes of the compressor and the decompressor in detail, and describes the compression process and the decompression process. Finally, it points o ut the re search direction of header compression schemes.

Compared to html page, the mobile web page has different features. The mobile web page is arranged through some important tags such as , >table>, which are called Gathering Node in this paper. Based on these Gathering Nodes, we proposed a Block Gathering Based Page Segmentation algorithm (BGBPS). The experiment shows that BGBPS algorithm has great effect on semantic segmentation of mobile web page.

The flaws of ARP protocol, the kinds of ARP attack and the major existing defensive technologies are analyzed in details. Due to the cost of existing defensive technologies is too high; therefore, we design and develop a light-weight tool based on Linux platform. It is suitable for most users because it can detect and defend the ARP attacks accompany with very small extra overhead. Moreover, it is convenient for administrators to manage network. Detailed design and some key codes are presented in this article.

Optical access technology has quickly got a worldwide development. Currently, the deployment of equipment and fiber lines in the optical access network require complex manual design. However, because of non-standard artificial design, it is difficult to make the network reasonable, and increasing post-engineering and maintenance difficulties. Based on the partition algorithm in the previous article, this paper presents a new partitioning algorithm for the PON network design, which is a combination of the Ant Colony Optimization algorithm and partitioning algorithm. Compared with other algorithms, the ant colony optimization is more efficient and more accurate. It is very suitable for solving calculating the capacity of the large and complex network. Therefore, we use ant colony optimization for PON network design. By entering the number of nodes, users, service traffic, the unit cost parameters, it can automatically calculate the number and configuration of OLT, which can help to optimize the network layout, and save the network construction costs.

Immersion and interactivity are the main characteristics of virtual reality technology. It gives the user the real world experience beyond the two-dimensional. This article focuses on the key technologies involved and their principles and applications in the process of establishing a dynamically modified to in-depth 3D interactive of Digital Campus System. These technologies include modeling, scene generation technology and interactive technology. Their interaction with the system features and user experience are closely related.

Low-rate Denial-of-Service attacks are stealthier and trickier than traditional DDoS attacks. According to the characteristic of periodicity and short burst in LDoS flows, a detection measure against LDoS attacks based on rate anomalies has been proposed. In the period when the router packet loss-rate is abnormal caused by the attack pulse, the rate of attack flow is large, while in other time the rate of attack flow is close to 0. In the view point of the periods that the packet loss is abnormal, we can find that the attack flow rate is far higher in these periods than the average rate, while the normal flow is lower to the average rate. In this paper, we proposed a measure that observes the flow rate in the periods that the packet loss rate is abnormal, computing the difference of the rate in these periods and the average rate. If it is beyond a certain threshold, treats the flow as a malicious flow and filters the flow with corresponding method.

The Apriori algorithm is a most influential one to excavate association rules. The basic idea of the algorithm is: identify all the frequent itemsets to get association rule. This paper presents the improved Apriori algorithm based on interested items, which mainly construct an ordered interested table and traverse it to excavate frequent itemsets quickly. The paper also by writing c# code achieves the improved algorithm. Confirmed by many experiments, this algorithm is better than traditional algorithms in time consuming.

PIM-SM multicast routing opposed to unicast technology has great advantages in multicast applications, but this routing technology has some flaws in the specific network topology. This article talks about the improvement for PIM-SM which is in the exceptional circumstances. For example, if SPT overlaps some or all of RPT, the DR of the source host will send the redundant data packets and the end-to-end delay among group members will be relatively large. Compared with before, the performance of improved PIM-SM doesn't reduce but also overcome these shortcomings.

Topology-aware application layer multicast takes the real underlying physical network connections into consideration while constructing multicast tree. The aim is to shorten end-to-end data forwarding delay, but it may lead to some end systems with high bandwidth close to the source node need to provide data forwarding service for many sub-nodes, and finally become the bottleneck of the multicast tree. To balance the requirement mentioned above, we propose a more comprehensive problem model MDDLRB (Minimum Delay, Degree-Limited Residual-Balanced) to construct application layer multicast spanning tree. Furthermore, to solve the MDDLRB problem, we present a heuristic algorithm based on delay increment and equilibrium optimization strategy. The simulation results show that the algorithm can get a better system performance.

LDoS attacks are a new type of denial of service attacks put forward by Kuzmanovic. According to several experiments, it is very effective in degrading the normal TCP senders throughput. XCP is a feedback-based congestion control protocol; it supplies feedback which is acquired through the use of a congestion header on each sent packet from the network to the sender on the maximum rate for injecting data into the network. In this paper, we studied the TCP protocol with explicit congestion control and found it has some characteristic in defending LDoS attacks, which give us a new idea to prevent LDoS attacks.

The fault detection mechanism of existing topology-aware ALM protocol is very simple which greatly weakens its performance. So it needs a more efficient mechanism to ensure the robustness and QoS of ALM. We propose a novel fault detection mechanism named REW (Reverse-inhibition Early Warning) which can send warning message before the buffer data are consumed away to avoid the termination of service. It can reduce the number of repetitive and wrong warning through reverse-inhibition strategy at the same time. The simulation results show that REW fault detection mechanism can reduce disconnection delay caused by multicast members' fault with low maintain and control overhead.

In contrast to traditional brute-force attacks, RoQ (Reduction of Quality) attacks are periodic, stealthy, yet potent, which exploit the vulnerability of adaptation mechanisms to undermine certain services. As the application-level peer-to-peer (p2p) protocols depend on a recovery-adjustment process to maintain global consistency of routing information when peers join and leave the systems, we propose a novel breed of RoQ attacks in structured p2p systems: (1) We induce a general model for RoQ attacks, and then derive in structured p2p networks a new attack form that RoQ attackers periodically create concurrent failure through manipulation of massive nodes, degrading the system performance repeatedly. (2) We explore the impacts of RoQ attacks on Chord with detailed analysis and theoretical estimations, and confirm them by simulation results on p2psim, including successful lookup ratio and lookup latency. Moreover, we also discuss the detection and defense against such attacks and the improvements of protocols for attack tolerance.

LDoS (Low-rate Denial of Service) attack is periodic, stealthy, and with high efficiency, which has become a great threat to the network security. Previous researches about LDoS attack mainly focus on its impact on wired networks. However, our analysis shows that such attack could also be launched in Ad-hoc network, and as a completely distinct MAC layer protocol is adopted in this environment, the form and effect of the attack could be different and need re-evaluation. This paper presents a study of LDoS attack in Ad-hoc network: (1) We investigate the differences of attack form brought by the medium reservation mechanism and CSMA/CA of 802.11b, and find that decreasing the period of LDoS attack into a smaller time scale would achieve a higher attack efficiency; (2) We show that the attack effect differs from that in wired networks, and the attacker's location has an impact on it; (3) We verify our findings by simulation experiments in NS-2; (4) Detection and defense methods are explored to counter against such attack.

Grid resource monitoring system should take charge of watching a large amount of heterogeneous resources and their usage state. The paper analyzes the disadvantages of the current grid resource monitoring framework, then proposes a new monitoring model GMF-BMA and discusses the communication among middle layer, infrastructure layer and sensor layer in details. A prototype implementation of the model based on Grasshopper mobile agent platform is also described. Experiments reveal that the framework can reduce the additional overhead produced by grid resource monitoring.

UDDI acts a very important role in the web service. It can be used to publish and lookup services. Most of the current UDDI models are centralized so that the performance will decrease if there are too many services to be registered or queried. In this paper, an interoperable model of distributed UDDI is proposed. The model divides whole UDDI servers into there types: root server, super domain server and normal server. The simulation results show that the model can get better lookup performance.

We have presented a resource discovery algorithm with probe feedback mechanism (RDPF) in grid computing formerly. The algorithm chooses different path to send request messages and corresponding response messages. A feedback mechanism is added in response message to rediscovery requested resource if the resource can't be found in forwarding path. The experiment indicates that the algorithm can improve the success ratio of resources discovery and need not to increase the extra system cost. But the algorithm treats the grid as a full-distributed environment where every node has the same level. In fact, the real grid is composed of many different Autonomous Systems. We can use the layer character to optimize the performance. The paper presents a resource discovery algorithm with probe feedback mechanism in multi-domain grid (RDPF_MG) as an alternative to the existing resource discovery algorithm with probe feedback mechanism in order to be compatible with different grid environments.

In this paper, we propose an improved architecture that supports exact MSBN belief updating using iterative message passing. Compared with recursive inference algorithms, iterative message passing is more robust in a multiagent environment where agents often have to face unreliable communication channels. Our method improves the overall time efficiency of existing iterative methods by avoiding repeated multiplications during message computation. Furthermore, in the proposed method, agents integrate incoming messages as batch at pre-determined intervals. We show that after enough message passings, an agentpsilas local belief will converge to the correct result.

Recently, application-layer multicast (ALM) has emerged as a means to solve most of the problems of IP-based multicast. Topology-aware approach of ALM is more attractive because it exploits underlying network topology data to construct multicast overlay networks. In this paper, a novel overlay network construction mechanism called balanced multi-domain topology-aware grouping (BMTAG) is introduced. BMTAG adopts a special node (domain monitor) to be the parent of all other nodes in the same domain. The mechanism can not only save the time used to discover the topology and execute the path matching algorithm but also lower the depth of the multicast tree. Building a multicast tree with balanced traffic to avoid the bottleneck is another purpose of BMTAG. Simulation results show that BMTAG can get higher performance than TAG especially when the group size is large or the percentage of domain nodes is high.

Application-layer multicast (ALM) can easily address most of the problems of IP-based multicast such as forwarding state scalability, full router dependence and so on. The topology-aware approach of ALM is more attractive because it exploits underlying network topology data to construct multicast overlay networks. In this paper, a more efficient mechanism of overlay construction called subnet topology-aware grouping (STAG) is introduced. Under this mechanism, new node who wants to join the multicast tree will broadcast a JOIN message in the subnet firstly or at the same time when it sends a JOIN message to source member. It can save the time used to discover topology information and execute the path matching algorithm if there are some multicast members in the same subnet. Simulation results show that new nodes of STAG can acquire multicast service more quickly with similar or less overhead when the group size is large or the percentage of subnet nodes is high.

Generating precise network topologies is an important issue for the purpose of simulating and evaluating networking applications. Recent research results reveal that the topology of Internet is neither a purely random network nor a hierarchical structure, but similar to complex networks obeying power law distributions. Under this condition, a practical degree-driven method is widely used for generating network topologies with prescribed degree sequence. To import random features, additional random transformations are required to perform upon the generated graph. In this paper, we propose a connectivity-prior algorithm to create a connected graph and develop a simple but efficient method to perform randomization operations to transform the generated graph. During the creating and transforming process, the graph is kept connected. We made experiments with the latest degree sequence data of the actually Internet topologies. The results show that our method works more efficiently.

Application-layer multicast (ALM) can solve most of the problems of IP-based multicast. Topology-aware approach of ALM is more attractive because it exploits underlying network topology data to construct multicast overlay networks. In this paper, a novel mechanism of overlay construction called Multi-domain Topology-Aware Grouping (MTAG) is introduced. MTAG manages nodes in the same domain by a special node named domain manager. It can save the time used to discover topology information and execute the path matching algorithm if there are some multicast members in the same domain. The mechanism can lower the depth of the multicast tree too. Simulation results show that nodes can acquire multicast service more quickly when the group size is large or the percentage of subnet nodes is high.

In advance reservation environment, failure discovery strategy is very important to keep the normal running of whole system. One job?s overtime (exceeding its booked time) may lead to a serious of jobs? abnormal termination in co-allocation environment. So there should be some strategies to solve this problem. In this paper, a novel overtimetolerance strategy is introduced. The strategy can tolerate active job exceeding its booking time and redirect transparently later inactive jobs to other resources. The architecture of implementing our strategy is described in this paper too. Simulation shows our overtime-tolerance strategy can decrease the abnormal termination ratio and improve the system throughput.

Resource discovery is a challenging problem in grid computing because computational resources are large-scale geographically distributed. Traditional decentralized resource discovery algorithms often focus on the searching method in forwarding direction. Response message is just used to report the matching node or matching failure. In this paper, a new resource discovery algorithm is introduced. Under this mechanism, request message and corresponding response message may choose different path to destination node. So we add probe feedback mechanism in response message to rediscovery requested resource if the resource can?t be found in forwarding path. It provides more chances to satisfy the request. Furthermore, if advance reservation is supported by environment, response message can return the node which can provide matching resource firstly in near future if there are still no suitable resources in rediscovery period. Simulation shows that it can improve the performance of resource discovery especially when the job size is large and turn-around time is not very important to users.

The problem of resource management and scheduling has always been the main challenge in grid. Grid economy is looked on as a good solution for obtaining better performance than other methods for resource management in dynamic grid environments. But, the decision making about resources selection with portfolio optimization has been paid little attention to in grid economy. This paper introduced the concept and methods with portfolio optimization in grid economy. Keywords: Grid Economy, Portfolio Optimization, Linear Programming, Max-Min Portfolio

The paper is concerned with block data transmission methods employing adaptive MLSE in a digital receiver. A new scheme of short-block transmission SBED-ADMLSE is proposed to overcome the effect of error propagation on the performance of the conventional long-block transmission method LB-ADMLSE that uses decision data directly to assist adaptive channel estimation. Performance comparison between SBED-ADMLSE and LB-ADMLSE with the same transmission efficiency is performed by the simulations of 4-QAM transmission at a symbol rate of 25 kbaud with a three-path Rayleigh fading channel model. Simulation results demonstrate the effectiveness of the new scheme under severe channel environments. Error propagation is overcome by SBED-ADMLSE. The new scheme can provide superior performance at fading rates up to 30 Hz without diversity operation. With the aid of two-branch diversity, it can be advantageous at fading rates up to 70 Hz. >