Optimal Content Location in Multicast Based Overlay Networks with Content Updates

The architecture of overlay networks should support high-performance and high-scalability at low costs. This becomes more crucial when communication, storage costs as well as service latencies grow with the exploding amounts of data exchanged and with the size and span of the overlay network. For that end, multicast methodologies can be used to deliver content from regional servers to end users, as well as for the timely and economical synchronization of content among the distributed servers. Another important architectural problem is the efficient allocation of objects to servers to minimize storage, delivery and update costs. In this work, we suggest a multicast based architecture and address the optimal allocation and replication of dynamic objects that are both consumed and updated. Our model network includes consumers which are served using multicast or unicast transmissions and media sources (that may be also consumers) which update the objects using multicast communication. General costs are associated with distribution (download) and update traffic as well as the storage of objects in the servers. Optimal object allocation algorithms for tree networks are presented with complexities of O(N) and O(N ²) in case of multicast and unicast distribution respectively. To our knowledge, the model of multicast distribution combined with multicast updates has not been analytically dealt before, despite its popularity in the industry.     

Analysis of an admission model in a fourth generation mobile network with triple play traffic

A problem of calculating the quality of the Triple Play service in an LTE mobile network under conditions of unicast and multicast transfer modes is considered. A mathematical model of the resource admission in the LTE network is constructed in the form of a system with explicit losses and three disciplines of servicing the unicast, multicast, and elastic traffics. Approximate methods of calculating the stationary probability distribution of the states of the models with unicast and elastic traffics are discussed. An approximate method based on the calculation of the marginal distribution of the number of users with unicast and multicast traffics is proposed for calculating the average transfer time of the elastic traffic. An exact algorithm for determining the stationary probability distribution of the system’s states that provides a considerable decrease in the dimension of the problem is presented.     

基于应用层组播的流媒体直播系统

应用层组播技术不需要网络层设备的支持，适合用于流媒体服务。在基于单播的流媒体直播系统基础上，设置应用层组播服务器，赋予客户端转发数据的能力，设计符合流媒体特点的应用层组播协议，形成了基于应用层组播的流媒体直播系统。按照该方案开发的原型系统运行状况表明，该设计方案能够稳定地提供流媒体服务。相比于基于单播的流媒体直播系统，采用应用层组播技术可以明显提高系统的用户数量，并保持较好的服务质量。     

Location aware, dependable multicast for mobile ad hoc networks

This paper introduces dynamic source multicast (DSM), a new protocol for multi-hop wireless (i.e., ad hoc) networks for the multicast of a data packet from a source node to a group of mobile nodes in the network. The protocol assumes that, through the use of positioning system devices, each node knows its own geographic location and the current (global) time, and it is able to efficiently spread these measures to all other nodes. When a packet is to be multicast, the source node first locally computes a snapshot of the complete network topology from the collected node measures. A Steiner (i.e., multicast) tree for the addressed multicast group is then computed locally based on the snapshot, rather than maintained in a distributed manner. The resulting Steiner tree is then optimally encoded by using its unique Pr

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u" height="11" width="9">fer sequence and is included in the packet header as in, and extending the length of the header by no more than, the header of packets in source routing (unicast) techniques. We show that all the local computations are executed in polynomial time. More specifically, the time complexity of the local operation of finding a Steiner tree, and the encoding/decoding procedures of the related Prüfer sequence, is proven to be O(n²), where n is the number of nodes in the network. The protocol has been simulated in ad hoc networks with 30 and 60 nodes and with different multicast group sizes. We show that DSM delivers packets to all the nodes in a destination group in more than 90% of the cases. Furthermore, compared to flooding, DSM achieves improvements of up to 50% on multicast completion delay.     

Genetic fingerprinting for copyright protection of multicast media

Generally speaking, comparing to the unicast or broadcast methods, it is more efficient to transmit multimedia data via the multicast method to massive users. However, the ease of delivery of multimedia data may cause the copyright of such multimedia to be easily infringed upon, and the fingerprinting scheme is one of effective means for conquering this problem. Fingerprint embedding process often generates the multimedia contents into many different versions, which have to be transmitted via the unicast method. In this paper, we propose a new genetic fingerprinting scheme for copyright protection of multicast video. In this method, the encryption and decryption keys, which aim at scrambling and descrambling multimedia contents, are first produced with genetic algorithms. Next, multimedia data are then encrypted and multicast to all users. At the same time, a secure channel is employed to unicast a designated decryption key to each user. When a user deploys the designated key to decrypt the received data, a corresponding fingerprint would be embedded into the contents. Once upon the reception of the fingerprinted multimedia content, the embedded fingerprint can be extracted shortly, and the copyright can be confirmed and assured. Experimental results demonstrate that the proposed method can transmit multimedia data to clients effectively and cause only a slight degradation in perceptual quality.     

Overcoming Heterogeneity and Autonomy in Multidatabase Systems

A multidatabase system (MDBS) is a software system for integration of preexisting and independent local database management systems (DBMSs). The transaction management problem in MDBSs consists of designing appropriate software, on top of local DBMSs, such that users can execute transactions that span multiple local DBMSs without jeopardizing database consistency. The difficulty in transaction management in MDBSs arises due to the heterogeneity of the transaction management algorithms used by the local DBMSs, and the desire to preserve their local autonomy. In this paper, we develop a framework for designing fault-tolerant transaction management algorithms for MDBS environments that effectively overcomes the heterogeneity- and autonomy-induced problems. The developed framework builds on our previous work. It uses the approach described in S. Mehrotra et al. (1992, in “Proceedings of ACM–SIGMOD 1992 International Conference on Management of Data, San Diego, CA”) to overcome the problems in ensuring serializability that arise due to heterogeneity of the local concurrency control protocols. Furthermore, it uses a redo approach to recovery for ensuring transaction atomicity (Y. Breitbart et al., 1990, in “Proceedings of ACM–SIGMOD 1990 International Conference on Management of Data, Atlantic City, NJ;” Mehrotra et al., 1992, in “Proceedings of the Eleventh ACM SIGACT–SIGMOD–SIGART Symposium on Principles of Database Systems, San Diego, CA;” and A. Wolski and J. Veijalainen, 1990, in “Proceedings of the International Conference on Databases, Parallel Architectures and Their Applications”, pp. 321–330), that strives to ensure atomicity of transactions without the usage of the 2PC protocol. We reduce the task of ensuring serializability in MDBSs in the presence of failures to solving three independent subproblems, solutions to which together constitute a complete strategy for failure-resilient transaction management in MDBS environments. We develop mechanisms with which each of the three subproblems can be solved without requiring any changes be made to the preexisting software of the local DBMSs and without compromising their autonomy.     

Store-and-Forward Multicast Routing on the Mesh

We study the complexity of routing a set of messages with multiple destinations (multicast routing) on an n-node square mesh under the store-and-forward model. A standard argument proves that time is required to route n messages, where each message is generated by a distinct node and at most c messages are to be delivered to any individual node. The obvious approach of simply replicating each message into the appropriate number of unicast (single-destination) messages and routing these independently does not yield an optimal algorithm. We provide both randomized and deterministic algorithms for multicast routing, which use constant-size buffers at each node. The randomized algorithm attains optimal performance, while the deterministic algorithm is slower by a factor of O( log ² n). We also describe an optimal deterministic algorithm that, however, requires large buffers of size O(c). A preliminary version of this paper appeared in Proceedings of the 13th Annual ACM Symposium on Parallel Algorithms and Architectures, Crete, Greece, 2001. This work was supported, in part, by MIUR under project ALGO-NEXT.     

Quorum-based power-saving multicast protocols in the asynchronous ad hoc network

The asynchronous PS (Power-Saving) unicast protocol was designed for two PS wireless hosts to transmit the unicast message in the ad hoc network even their clocks are asynchronous. However, as regard to transmit a multicast message among more than two PS hosts, the protocol could not guarantee that all PS hosts can wake up at the same time. Some PS hosts may be in the PS mode when the multicast message is transmitted. Thus, the multicast message should be retransmitted again and again until all PS hosts receive the message. It will increase the energy consumption and the usage of the bandwidth. In this paper, we propose quorum-based PS multicast protocols for PS hosts to transmit multicast messages in the asynchronous ad hoc network. In those protocols, PS hosts use quorums to indicate their wakeup patterns. We introduce the rotation m-closure property to guarantee that m different quorums have the intersection even quorums are rotated due to asynchronous clocks. Thus, m PS hosts adopting m quorums satisfying the rotation m-closure property could wake up simultaneously and receive the multicast message even their clocks are asynchronous. We propose two quorum systems named the uniform k-arbiter and the CRT (Chinese Remainder Theorem) quorum system, which satisfy the rotation m-closure property. As shown in our analysis results, our quorum-based PS multicast protocols adopting those quorum systems can save more energy to transmit multicast messages.     

Computations on Nondeterministic Cellular Automata

This work concerns the trade-offs between the dimension and the time and space complexity of computations on nondeterministic cellular automata. We assume that the space complexity is the diameter of area in space involved in computation. It is proved that (1) every nondeterministic cellular automata (NCA) of dimensionr, computing a predicatePwith time complexityT(n) and space complexityS(n) can be simulated byr-dimensional NCA with time and space complexityO(T^1/(r+1)S^r/(r+1)) and byr+1 dimensional NCA with time and space complexityO(T^1/2+S), whereTandSare functions constructible in time, (2) for any predicatePand integerr>1 if is a fastestr-dimensional NCA computingPwith time complexityT(n) and space complexityS(n), thenT=O(S), and (3) ifT_{r, P}is the time complexity of a fastestr-dimensional NCA computing predicatePthenT_r+1,P=O((T_{r, P})^1−r/(r+1)2),T_r+1,P=O((T_{r, P})^1+2/r).Similar problems for deterministic cellular automata (CA) are discussed.     

Multicast Pull Scheduling: When Fairness Is Fine

Abstract. We investigate server scheduling policies to minimize average user perceived latency in pull-based client-server systems (systems where multiple clients request data from a server) where the server answers requests on a multicast/ broadcast channel. We first show that there is no O(1) -competitive algorithm for this problem. We then give a method to convert any nonclairvoyant unicast scheduling algorithm A to nonclairvoyant multicast scheduling algorithm B . We show that if A works well, when jobs can have parallel and sequential phases, then B works well if it is given twice the resources. More formally, if A is an s -speed c -approximation unicast algorithm, then its counterpart algorithm B is a 2s -speed c -approximation multicast algorithm. It is already known [5] that Equi-partition, which devotes an equal amount of processing power to each job, is a (2 + ε) -speed O(1 + 1/ε) -approximation algorithm for unicast scheduling of such jobs. Hence, it follows that the algorithm {BEQUI}, which broadcasts all requested files at a rate proportional to the number of outstanding requests for that file, is a (4 + ε) -speed O(1 + 1/ε) -approximation algorithm. We give another algorithm BEQUI-EDF and show that BEQUI-EDF is also a (4 + ε) -speed O(1 + 1/ε) -approximation algorithm. However, BEQUI-EDF has the advantage that the maximum number of preemptions is linear in the number of requests, and the advantage that no preemptions occur if the data items have unit size.     

Using AVL trees for fault-tolerant group key management

In this paper we describe an efficient algorithm for the management of group keys for group communication systems. Our algorithm is based on the notion of key graphs, previously used for managing keys in large Internet-protocol multicast groups. The standard protocol requires a centralized key server that has knowledge of the full key graph. Our protocol does not delegate this role to any one process. Rather, members enlist in a collaborative effort to create the group key graph. The key graph contains n keys, of which each member learns log₂n of them. We show how to balance the key graph, a result that is applicable to the centralized protocol. We also show how to optimize our distributed protocol, and provide a performance study of its capabilities. Published online: 26 October 2001     

Hardware supported multicast in fat-tree-based InfiniBand networks

The multicast operation is a very commonly used operation in parallel applications. It can be used to implement many collective communication operations as well. Therefore, its performance will affect parallel applications and collective communication operations. With the hardware supported multicast of the InfiniBand Architecture (IBA), in this paper, we propose a cyclic multicast scheme for fat-tree-based (m-port n-tree) InfiniBand networks. The basic concept of the proposed cyclic multicast scheme is to find the union sets of the output ports of switches in the paths between the source processing node and each destination processing node in a multicast group. Based on the union sets and the path selection scheme, the forwarding table for a given multicast group can be constructed. We implement the proposed multicast scheme along with the OpenSM multicast scheme and the unicast scheme on an m-port n-tree InfiniBand network simulator. Several one-to-many, many-to-many, many-to-all, and all-to-many multicast cases are simulated. The simulation results show that the proposed multicast scheme outperforms the unicast scheme for all simulated cases. For one-to-many case, the performance of the cyclic multicast scheme is the same as that of the OpenSM multicast scheme. For many-to-many and all-to-many cases, the cyclic multicast scheme outperforms the OpenSM multicast scheme. For many-to-all case, the performance of the cyclic multicast scheme is a little better than that of the OpenSM multicast scheme.

A hybrid multicast–unicast assignment approach for data distribution management in HLA

The main focus of data distribution management (DDM) in HLA is to reduce the amount of data received by federates in large-scale distributed simulations. The use of limited multicast resources plays a key role in the performance of DDM. In order to improve the performance of DDM by using communication protocol effectively, a hybrid multicast–unicast data transmission problem and its formal definition are presented, and then a hybrid multicast–unicast assignment approach is proposed. The approach uses a new adaptive communication protocol selection (ACPS) strategy to utilize the advantages of multicast and unicast, avoid their disadvantages, and consider the inter-relationship between connections. It includes the ACPS static assignment algorithm and the ACPS dynamic assignment algorithm, according to the difference between the static connections and the dynamic connections. In our approach, a concept of distance is presented to measure the inter-relationship between connections for multicast and the message redundancy for unicast, which is the core of the two algorithms in order to gather the connections to a multicast group or to balance the use of unicast and multicast for best performance. As a result, our algorithms can more effectively decide whether a new connection should use unicast or multicast communication, and whether adjusting previous assignment result can further improve the performance. In addition, a control mechanism is introduced to deal with connection changes during the dynamic assignment. The experiment results indicate that our algorithms can utilize the multicast and unicast communication resources effectively, as well as can achieve better performance than existing methods in the real running environment.     

基于集成FEC的可靠多目广播及性能评价

对点对点通信，数据的传输常使用自动重复求技术，而前向纠错多用于半可靠实时传输。然而，ＡＲＱ用于多目广播的性能不佳。     

Mutual anonymous overlay multicast

Multicast services are demanded by a variety of applications. Many applications require anonymity during their communication. However, there has been very little work on anonymous multicasting and such services are not available yet. Due to the fundamental differences between multicast and unicast, the solutions proposed for anonymity in unicast communications cannot be directly applied to multicast applications. In this paper we define the anonymous multicast system, and propose a mutual anonymous multicast (MAM) protocol including the design of a unicast mutual anonymity protocol and construction and optimization of an anonymous multicast tree. MAM is self-organizing and completely distributed. We define the attack model in an anonymous multicast system and analyze the anonymity degree. We also evaluate the performance of MAM by comprehensive simulations.     

Configurable active multicast congestion control

A multicast congestion control and avoidance scheme is indispensable for group-based applications to fairly share and efficiently use network resources with unicast applications and maintain the stability of the Internet. It is difficult for the traditional pure “end-to-end” solution to address both TCP-friendliness and inter-receiver fairness [T. Jiang, M.H. Ammar, E.W. Zegura, Inter-receiver fairness: a novel performance measure for multicast ABR sessions, in: Proceedings of ACM SIGMETRICS’98; T. Jiang, E.W. Zegura, M. Ammar, Inter-receiver fair multicast communication over the Internet, in: Proceedings of NOSSDAV’99] by using only one multicast group. In this paper, we present a novel active multicast congestion control scheme (AMCC). Significantly different from the popular end-to-end congestion control approach, AMCC is a router-assisted window-based hierarchical one. With flexible configuration of parameters and effective use of network resources such as buffers at the active routers, AMCC cannot only behave as a TCP-friendly single-rate congestion control scheme, but also have the benefits of a multi-rate congestion control scheme to achieve inter-receiver fairness by limiting the effect of congestion on a specific link to a small region. In addition, when it is used with reliable multicast applications, AMCC has the special mechanisms to regulate repair packets, which are not specifically addressed by the previous work. We implement and evaluate our protocol in NS2 [http://www.isi.edu/nsnam/ns/].     

无线Mesh 网络低干扰组播

不同于无线传感器网络和移动Ad Hoc网络,无线Mesh网络中的组播主要侧重于提高吞吐量,而干扰是影响吞吐量的重要因素。在构建组播拓扑时,传统的方法主要考虑最小价值或最短路径,而通过减少干扰来提高组播性能的研究较少,且它们的干扰计算方法都采用单播的思想,并不适合于组播。例如,当n个接收节点同时从一个节点接收数据时,在组播中这n个接收节点之间不存在干扰,而在单播中认为存在干扰。因此,提出了组播冲突图来计算组播干扰,给出组播树干扰的定义。可以发现,求最小干扰组播扰树是NP完全问题,然后提出基于万有引力的启发式算法构建具有较小干扰的组播树。为了适用于多信道的情况,提出了满足不同干扰范围的多跳信道分配算法。最后,仿真结果显示,与MCM相比,所提出的算法无论是在单天线单信道还是多天线多信道下,都能取得较高的吞吐量和较低的延迟。     

Designing Fast Converging Cost Sharing Methods for Multicast Transmissions

We study a multicast game in non-cooperative directed networks in which a source sends the same message or service to a set of r receiving users and the cost of the used links is divided among the receivers according to a given cost sharing method. By following the approach recently proposed by Chen et al. (Proceedings of the 19th Annual ACM-SIAM Symposium on Discrete Algorithms (SODA), pp. 854–863, 2008), we analyze the performances of a family of methods satisfying certain desiderata, namely, weak and strong budget-balance, fairness and separability. We show that any fair method may require an arbitrary number of selfish moves in order to converge to a pure Nash equilibrium, hence we focus on the solutions obtained after one round of selfish moves. We evaluate their quality according to two global social functions: the overall cost of the solution and the maximum shared cost of users. The only method satisfying all the properties is the well-known Shapley value for which we show an approximation ratio of the solutions reached after a one round walk equal to Θ(r ²). We then prove that relaxing the strong budget balance and separability properties (we call feasible any method satisfying weak budget balance and fairness) leads to improved performances since we determine a feasible method achieving an approximation ratio of the solutions reached after a one round walk equal to O(r). This bound is asymptotically optimal since we also show that any method satisfying weak budget balance cannot achieve an approximation ratio of the solutions reached after a one round walk smaller than r. Finally, we prove the NP-hardness of computing the sequence of moves leading to the best possible global performance and extend most of the results to undirected networks.     

Improved Key Management Technique for Secure Multicasting over IP

Multicast communication is going to be the communication paradigm of all future networks. Secure multicasting is a very vital problem in today’s networks. In secure multicasting, the group members share a common key called the group key. Whenever the group members change, the group key must be changed. Therefore, many multicast security problems are abstracted into key management and distribution problems. The problem of distributing cryptographic keys to the group members in an optimum way that minimizes the communication and storage overheads are the important objectives of a secure multicast problem. In this paper, an efficient key management technique is proposed that minimizes the number of message exchanges and the number of keys stored. Existing key management methods have O(N) and O(log N) overheads. The proposed method shows further improvement. The model has been simulated and the results show improvements to existing approaches.G. Padmavathi has been a member of Computer Science Department, Avinashilingam Deemed University, and Coimbatore, India, for 18 years. She has contributed 20 papers at national level and 5 papers at international level. She has four publications in the areas of Fault Tolerant Real Time Systems, Cryptography and Network Security.S. Annadurai, Principal of Government Engineering College, Tirunelveli, Tamil Nadu, India, is a reputed educationalist. He has more than 150 publications at national and international level, and is an expert committee member for government and membership in many professional organizations. His research interests include Image Processing, Soft Computing and Network Security.     

A study of adaptive forward error correction for wireless collaborative computing

This paper addresses the problem of reliably multicasting Web resources across wireless local area networks (WLANs) in support of collaborative computing applications. An adaptive forward error correction (FEC) protocol is described, which adjusts the level of redundancy in the data stream in response to packet loss conditions. The proposed protocol is intended for use on a proxy server that supports mobile users on a WLAN. The software architecture of the proxy service and the operation of the adaptive FEC protocol are described. The performance of the protocol is evaluated using both experimentation on a mobile computing testbed as well as simulation. The results of the performance study show that the protocol can quickly accommodate worsening channel characteristics in order to reduce delay and increase throughput for reliable multicast channels.