可靠多播传输协议研究

战术通信网需要多播技术以支持多种组播应用,如情形感知、任务协作等。无线通信可为战术通信网组播通信提供支持,但其可靠性不高,不能直接应用,必须加以控制。为此,研究了一种利用IP多播路由和转发服务提供端到端可靠数据传输协议,即面向否定确认的可靠多播协议(NORM)。深入分析了NORM协议的反馈确认、拥塞控制、包级FEC等关键技术。在结论与展望中,提出了这一领域的难点和对今后工作的展望。     

Reliable concurrent multicast from bursty sources

This paper presents a protocol and design for concurrent and reliable group multicast (many-to-many) from bursty data sources in general networks. In a group multicast, any node can be a multicast source and multiple nodes may start to multicast simultaneously, i.e., an asynchronous access to the network. The reliable multicast protocol presented is window based with a combined sender and receiver initiation of the recovery protocol. In reliable multicasting the necessary requirement is to ensure that data is received correctly by all the active members of the multicast group. The approach taken is to combine the multicast operation with the internal flow control. As a result, it is possible to provide: (1) congestion-free multicast routing with a single and immediate acknowledgment message to the sender. Furthermore, in every multicast, (2) a node can access all the capacity allocated to its group with no delay, however, if several nodes are active in the same group, then the capacity will be shared fairly. In addition, (3) each sender in the multicast group uses a single timer, and (4) a node can become active or inactive in a transparent fashion, i.e., there is no need to explicitly notify the members of the group. A multiple criteria optimization study of the bandwidth allocation to each multicast group is presented. The optimization problem has two min-max objective functions: (1) for delay, which is caused by the number of links needed to connect the group, and (2) for congestion, which is caused by sharing a link among multiple multicast groups. The bandwidth allocation among multicast groups sharing the same link are further optimized using the max-min fairness criterion     

TCP-Peachtree: a multicast transport protocol for satellite IP networks

In this paper, a reliable multicast transport protocol TCP-Peachtree is proposed for satellite Internet protocol (IP) networks. In addition to the acknowledgment implosion and scalability problems in terrestrial wirelined networks, satellite multicasting has additional problems, i.e., different multicast topology, different type of congestion control problems, and low bandwidth feedback link. In TCP-Peachtree, the modified B+ tree logical hierarchical structure is used to form dynamic multicast groups. Local error recovery and acknowledgment (ACK) aggregations are performed within each subgroup and also via logical subgroups. In order to avoid the overall performance degradation caused by some worst receivers, a local relay scheme is designed. Two new algorithms, jump start and quick recovery, which are based on the usage of a type of low-priority segments called NIL segments, are proposed for congestion control. NIL segments are used to probe the availability of network resources and also for error recovery. The delayed selective acknowledgment (SACK) scheme is adopted to address the bandwidth asymmetry problems and a hold state is developed to address persistent fades. The simulation results show that the congestion control algorithms of TCP-Peachtree outperform the TCP-NewReno when combined with our hierarchical groups and improve the throughput performance during rain fades. It is also shown that TCP-Peachtree achieves fairness and is very highly scalability.     

On max-min fair congestion control for multicast ABR service in ATM

In the ATM Forum activities, considerable efforts have focused on the congestion control of point-to-point available bit rate (ABR) service. We present a novel approach that extends existing point-to-point (unicast) congestion control protocols to a point-to-multipoint (multicast) environment. In particular, we establish a unified framework to derive a multicast congestion control protocol for an ABR service from a given rate-based unicast protocol. We generalize a known necessary and sufficient condition on the max-min fairness of unicast rate allocation for a multicast service. Using this condition, we show that the resulting multicast protocol derived using our framework preserves the fairness characteristics of the underlying unicast protocol. The practical significance of our approach is illustrated by extending a standard congestion control mechanism for an ABR service to a multicast environment. The performance of the resulting multicast protocol is examined using benchmark network configurations suggested by the traffic management subworking group at the ATM Forum, and simulation results are presented to substantiate our claims     

Modeling and analysis of TCP-like multicast congestion control in hybrid terrestrial/satellite IP networks

Given their broadcast nature, satellite communications are one natural engineering choice for multicast service deployment. In this paper, the throughput performance of transmission control protocol (TCP)-like multicast congestion control is analyzed in hybrid terrestrial/satellite networks. With this objective, an analytical framework based on Markov chains is introduced. The major advantage of the proposed analytical model is its scalability in that the number of states of the Markov chain modeling the system is independent of the number of receivers in the multicast session. This is a very important feature as simulation is unfeasible for large numbers of receivers. The framework is used to evaluate the impact of the long propagation delays, high bit-error rates, and channel asymmetry characterizing hybrid terrestrial/satellite communications. The performance results show that in certain cases, it is more convenient to divide the receivers in an appropriate number of groups and establish a different multicast session toward each of the above groups. Also, the convenience of an acknowledgment (ACK) flow reconstructor is shown.     

Improved heuristics for multicast routing in wireless mesh networks

Multicast is a communication technique that allows a source to transmit data to a set of recipients in an efficient manner. Therefore, the primary objective of a multicast routing protocol would be to minimize number of transmissions to conserve bandwidth. The problem of computing multicast trees with minimal bandwidth consumption is similar to Steiner tree problem and has shown to be NP-complete. So, heuristic based algorithms are suitable to approximate such bandwidth optimal trees. This paper proposes a multicast routing protocol based on minimum number of transmission trees using an heuristic approach. The simulation results show that the proposed algorithm offers better performance over existing protocols, even in the worst-case scenario when the set of multicast receivers are sparsely distributed across the network.     

Efficient cross-layer protocol for bandwidth-satisfied multicast in multi-rate MANETs

Since the multi-rate enhancements have been implemented in 802.11 wireless networks, QoS-constrained multicast protocols for multimedia communication should be adapted to exploit them fully. This work proposes a multicast protocol for data rate selection and bandwidth-satisfied multicast tree determination with an efficient cross-layer design based on the integration of PHY and MAC layers into the network layer. To use bandwidth efficiently and increase network capacity (which is the number of multicast flows supported by the network), we aim to select the combination of data rates and a multicast tree whose total amount of bandwidth consumption to the network is minimal in order to maximize the network capacity. The performance of the proposed protocol is compared with two existing protocols. Simulation results indicate that the proposed protocol has the ability to admit more multicast flows.     

Reliable Multicast in Multi-Access Wireless LANs

Multicast is an efficient paradigm for transmitting data from a sender to a group of receivers. In this paper, we focus on multicast in single channel multi-access wireless local area networks (LANs) comprising several small cells. In such a system, a receiver cannot correctly receive a packet if two or more packets are sent to it at the same time, because the packets collide. Therefore, one has to ensure that only one node sends at a time. We look at two important issues. First, we consider the problem of the sender acquiring the multi-access channel for multicast transmission. Second, for reliable multicast in each cell of the wireless LAN, we examine ARQ-based approaches. The second issue is important because the wireless link error rates can be very high.We present a new approach to overcome the problem of feedback collision in single channel multi-access wireless LANs, both for the purpose of acquiring the channel and for reliability. Our approach involves the election of one of the multicast group members (receivers) as a leader or representative for the purpose of sending feedback to the sender. For reliable multicast, on erroneous reception of a packet, the leader does not send an acknowledgment, prompting a retransmission. On erroneous reception of the packet at receivers other than the leader, our protocol allows negative acknowledgments from these receivers to collide with the acknowledgment from the leader, thus destroying the acknowledgment and prompting the sender to retransmit the packet.Using analytical models, we demonstrate that the leader-based protocol exhibits higher throughput in comparison to two other protocols which use traditional delayed feedback-based probabilistic methods. Last, we present a simple scheme for leader election.     

On acknowledgement schemes of sliding window flow control

An investigation is conducted of two acknowledgment schemes for sliding window flow control in packet communications: the delayed acknowledgment (D-ACK) scheme and the window acknowledgment (W-ACK) scheme. It is shown that the acknowledgment scheme of the link layer of the X.25 protocol can be modeled by the D-ACK scheme and that of the packet layer by the W-ACK scheme. The efficiencies of these acknowledgment schemes are shown by the mean number of acknowledgment control frames generated for the transmission of a single information frame, the transmission blocking probability, and the mean transmission time of data frames. Numerical and simulation results showing that the D-ACK scheme with an appropriately selected value of predetermined waiting time is better than the W-ACK scheme are presented     

Group Communication Using Modular Protocol Stacks

Today's distributed systems consist of many different components, making the efficient management of such systems an extremely difficult task. Group communication should provide a potential solution to make the management process more flexible. It is possible to build a group communication system based on traditional distributed technology such as CORBA (Common Object Request Broker Architecture), but efficiency is poor due to lack of support for multicast and the overhead of building groups in current commercially available products. Multicast is a key part of a future group communication architecture and although reliability is not yet supported there are workarounds which provide a solution. This paper discusses the design and implementation of reliable IP multicast protocols for group communication. One important aspect of this work is the modularisation of the protocol blocks, and the design of a modular protocol, which can be used in conjunction with other similar protocol blocks to build a communication stack for group communications, is described in detail.     

Multicast transport protocols: a survey and taxonomy

Network support for multicast has triggered the development of group communication applications such as multipoint data dissemination and multiparty conferencing tools. To support these applications, several multicast transport protocols have been proposed and implemented. Multicast transport protocols have been an area of active research for the past couple of years. This article summarizes the activities in this work-in-progress area by surveying several multicast transport protocols. It also presents a taxonomy to classify the surveyed protocols according to several distinct features, discusses the rationale behind the protocol's design decisions, and presents some current research-issues in multicast protocol design     

Ad hoc mobile multicast routing using the concept of long‐lived routes

Mobile ad hoc networks are recognized by their abilities to form, sustain, and deform networks on‐the‐fly without the need for any pre‐established and fixed infrastructures. This wireless multi‐hop technology requires adaptive networking protocols with low control overhead and low power consumption to operate efficiently. Existing research so far are mainly concerned with unicast routing for ad hoc mobile networks. There is a growing interest in supporting multicast communication in an ad hoc mobile environment. In this paper, the associativity‐based ad hoc multicast (ABAM) routing protocol is proposed. The concept of association stability is utilized during multicast tree discovery, selection, and reconfiguration. This allows routes that are long‐lived to be selected, thereby reducing the frequency of route reconstructions. ABAM employs a localized route reconstruction strategy in response to migrations by source, receiver, and tree nodes. It can repair an affected subtree via a single route reconstruction operation. ABAM is robust since the repair can be triggered by a node in the tree or by the migrated node itself. ABAM is also capable of handling multicast group dynamics when mobile hosts decide to join and leave an existing multicast group. Our simulation results reveal that under different mobility scenarios and multicast group size, ABAM has low communication overhead and yields better throughput performance. Copyright © 2001 John Wiley & Sons, Ltd.     

Performance evaluation of the MoM mobile multicast protocol

This paper presents a performance study of a mobile multicast protocol called MoM, which is designed to support IP multicast for mobile hosts in an IP internetwork. The protocol uses the basic unicast routing capability of IETF Mobile IP, and leverages existing IP multicast to provide multicast services for mobile hosts as well. A key feature of the MoM protocol is the use of designated multicast service providers (DMSPs) to improve the scalability of mobile multicast. Discrete-event simulation is used in the performance evaluation of the protocol. The performance study focuses on the scalability, routing efficiency, fairness, and overhead of the MoM protocol, as well as on DMSP selection policies and the deliverability of multicast messages. The simulation results suggest distinct performance advantages for the MoM protocol over other approaches for mobile multicast, such as bi-directional tunnelling, particularly as the number of mobile group members increases. Furthermore, even simple policies for choosing a DMSP from possible candidates provide reasonable tradeoffs between handoff rates, routing efficiency, deliverability of messages, and protocol overhead. This revised version was published online in June 2006 with corrections to the Cover Date.     

一种适用于动态/移动环境的新的组播协议

组播协议由于能够有效的利用网络带宽并降低服务器的负担因而受到广泛的关注.其中的共享树组播协议由于具有良好的扩展性而得到更多的支持,然而目前的共享树组播协议在动态移动环境中的性能很差,一些改进协议(单核移动协议)虽然可以很好的提高原有协议的性能但是所需要的额外开销很大.针对这种情况,本文提出了一种新的共享树组播协议-动态多核协议,该协议能够根据组播成员的分布动态的渐进的调整组播树的形状,从而能够在低开销的情况下为移动用户提供良好的性能.计算机仿真和数学分析都表明动态多核协议要明显优于共享树组播协议和单核移动协议.     

An Efficient Multicast Routing Protocol in Wireless Mobile Networks

Providing multicast service to mobile hosts in wireless mobile networking environments is difficult due to frequent changes of mobile host location and group membership. If a conventional multicast routing protocol is used in wireless mobile networks, several problems may be experienced since existing multicast routing protocols assume static hosts when they construct the multicast delivery tree. To overcome the problems, several multicast routing protocols for mobile hosts have been proposed. Although the protocols solve several problems inherent in multicast routing proposals for static hosts, they still have problems such as non-optimal delivery path, datagram duplication, overheads resulting from frequent reconstruction of a multicast tree, etc. In this paper, we summarize these problems of multicast routing protocols and propose an efficient multicast routing protocol based on IEFT mobile IP in wireless mobile networks. The proposed protocol introduces a multicast agent, where a mobile host receives a tunneled multicast datagram from a multicast agent located in a network close to it or directly from the multicast router in the current network. While receiving a tunneled multicast datagram from a remote multicast agent, the local multicast agent may start multicast join process, which makes the multicast delivery route optimal. The proposed protocol reduces data delivery path length and decreases the amount of duplicate copies of multicast datagrams. We examined and compared the performance of the proposed protocol and existing protocols by simulation under various environments and we got an improved performance over the existing proposals.     

Scalable feedback for large groups

We investigate the scalability of feedback in multicast communication and propose a new method of probabilistic feedback based on exponentially distributed timers. By analysis and simulation for up to 10⁶ receivers, we show that feedback implosion is avoided while feedback latency is low. The mechanism is robust against the loss of feedback messages and works well in case of homogeneous and heterogeneous delays. We apply the feedback mechanism to reliable multicast and compare it to existing timer-based feedback schemes. Our mechanism achieves lower negative acknowledgment character (NAK) latency for the same performance in terms of NAK suppression. No topological information of the network is used, and data delivery is the only support required from the network. The mechanism adapts to a dynamic number of receivers and leads to a stable performance for implosion avoidance and feedback latency     

Multicasting to multiple groups over broadcast channels

Multicasting is a communication mode in which a given source communicates with a subset of the entire network user population. Previous work in this area concentrated on the multicast problem of a single source that always communicates with the same destination group. In this paper we investigate a more natural case of multicast communication where a single source communicates with several different destination groups. Specially, we focus on the design and analysis of multicast data link protocols for this environment. Straightforward implementations of such protocols are inappropriate in the case of a large destination population, as a source will have to store a large amount of state information even if it maintains only a single variable per destination. In most typical applications, though. The total destination population is large, the number of destinations that any given source is in conversation with, is typically small. We propose a framework for adapting protocols so that memory requirement does not grow with the total destination population but depends upon the number of destinations actually in communication with the source. The savings in memory are achieved by slightly increasing the amount of communication. We address the performance of such a protocol in an environment of a broadcast channel. We analyze several strategies and control techniques and demonstrate the tradeoff between throughput and the amount of memory     

Intelligent Internal Stealthy Attack and its Countermeasure for Multicast Routing Protocol in MANET

Multicast communication of mobile ad hoc networks is vulnerable to internal attacks due to its routing structure and high scalability of its participants. Though existing intrusion detection systems (IDSs) act smartly to defend against attack strategies, adversaries also accordingly update their attacking plans intelligently so as to intervene in successful defending schemes. In our work, we present a novel indirect internal stealthy attack on a tree‐based multicast routing protocol. Such an indirect stealthy attack intelligently makes neighbor nodes drop their routing‐layer unicast control packets instead of processing or forwarding them. The adversary targets the collision avoidance mechanism of the Medium Access Control (MAC) protocol to indirectly affect the routing layer process. Simulation results show the success of this attacking strategy over the existing “stealthy attack in wireless ad hoc networks: detection and countermeasure (SADEC)” detection system. We design a cross‐layer automata‐based stealthy attack on multicast routing protocols (SAMRP) attacker detection system to identify and isolate the proposed attacker. NS‐2 simulation and analytical results show the efficient performance, against an indirect internal stealthy attack, of SAMRP over the existing SADEC and BLM attacker detection systems.     

A scalable multicast routing protocol for building shortest path trees

Scalability is a great concern in the design of multicast routing protocols for the global Internet. Building shortest path trees (SPT) is currently one of the most widely used approaches to supporting multicast routing because of the simplicity and low per‐destination cost of such trees. However, the construction of an SPT typically involves high protocol overhead, which leads to the scalability problem as the number of concurrent multicast sessions increases. In this paper, we present a destination‐initiated shortest path tree (DSPT) routing protocol. The design objective is to effectively reduce the protocol overhead associated with SPT constructions for providing scalable multicast. To achieve this objective, we introduce destination‐initiated joining operations in constructing SPTs. With DSPT, each router receiving a request to join a specific multicast group makes a local decision on selecting its parent node through which it connects to the existing tree. A source‐rooted SPT is built as a result of such collaborative operations at nodes. DSPT requires only limited routing information at routers. Analytical results demonstrate that DSPT scales well with respect to computation, storage and communication overhead when the number of concurrent multicast requests is large. Simulation experiments are also conducted to verify the correctness of the theoretically deduced analytical results. Copyright © 2006 John Wiley & Sons, Ltd.