Coded Speech in Packet-Switched Networks: Models and Experiments

This paper considers the possibility of introducing packetized voice traffic into a packet-switched network. It is well known that the network must assure voice packets sufficient delay characteristics for conversational speech, i.e., low delay between speaker and listener and low delay jitter or variance. To reach these goals, simplified protocols and priority rules for voice handling are proposed and evaluated. A model of a packet switching node structure capable of handling both data and voice is derived for both analytical and simulation approaches. The use of low bit rate voice encoders is considered. The necessity of avoiding the transmission of silent intervals is discussed in relation to the behavior of packet voice receivers. Proposed strategies are compared by means of analytical tools and simulation experiments considering the presence of voice, interactive, and batch data packets.     

Performance analysis of a large interconnected network bydecomposition techniques

A study that models the possible configurations of a proposed packet-transport-equipment (PTE)-based university campus network is reported. The function of these PTEs is to receive/forward data packets from/to remote LANs or workstations. The objective is to determine whether the traffic capacity of the proposed network can handle the projected university workload, how different applications impact network load, and where the potential system bottlenecks are. The modeling approach taken treats the interconnected LANs as a hierarchy with the fiber (backbone) ring as the apex. Both analytical and simulation models are developed, with simulation being preferred as the workloads approach saturation conditions     

基于网络编码的机会网络高效路由算法

针对采用Epidemic机制的机会网络路由算法在数据分组传送阶段存在通信冗余的问题,提出了一种基于网络编码的高效路由算法--NCBER(network-coding-based epidemic routing）。NCBER在传送数据分组的过程中使用主动异或网络编码和多播,并取消了 Request（请求）控制分组,从而减少数据分组的转发次数和控制分组数量,降低网络开销,缩短分组传输时延。理论分析和仿真结果表明,NCBER 算法在网络开销和数据分组端到端时延性能方面优于经典的Epidemic路由算法及其改进算法MRRMR（message redundancy removal of multi-copy routing）,并且使数据传送成功率保持在100%。     

Packet-centric approach to distributed sparse-graph coding in wireless ad hoc networks

In this paper we present a packet-centric approach for distributed coding in decentralized wireless ad hoc networks, for applications in distributed data storage, data persistence and efficient data gathering. We study the setting where each of N network nodes generates an information packet and the goal is to efficiently encode information packets and disseminate produced encoded packets across the network in such fashion that gathering of any subset of slightly more than N encoded packets allows for retrieval of the original information. The process of distributed encoding is performed using packets that randomly walk over the network and sample information packets from network nodes, producing the encoded packets in a simple, elegant, fully decentralized and stateless way. The proposed scheme maintains properties of centralized codes in terms of performance parameters, offering at the same time advantage of robustness to node failures and changes in network topology. We specialize the proposed scheme for several important classes of low-complexity encodable/decodable sparse-graph codes – LDGM, LDPC (IRA), LT, and Raptor codes, evaluating its performance via simulation for various data-gathering scenarios.     

基于网络监听的无接口数据采集初探

以基站告警数据采集为例,论述在没有数据采集接口和数据格式未知的情况下,如何利用网络监听技术,捕获MOTOROLA告警客户端和华为告警客户端与服务器之间的网络通讯数据包,并对数据包内容进行由简到繁的筛选过滤和对比分析,逐步将数据包中有用的信息分离出来,实现数据采集。这种数据采集方法具有无需数据采集接口、无需数据格式资料、实时性高、对原有系统没有任何影响的优点。     

IP交换中流分类的神经网络方法

本文对IP交换机中流的分类问题进行了探讨。首先对现有的X／Y分类器进行了分析,指出其不足之处,然后总结了进行流判断时应考虑的各种因素。之后提出了一种利用Hopfield神经网络进行流分类的方法,并对其参数的选取进行了讨论。仿真结果表明,神经网络分类器可根据网络中流的具体情况,自动调节分类阈值,保证IP交换机利用的VC数基本稳定。与常规X／Y分类器相比,神经网络分类器可利用更少的VC交换更多的数据包。     

Handling Mobility Management and QoS Aspects in All-IP Networks

It is well-known that all-IP networks will be more dynamic and should be more flexible than current networks. Deploying these networks requires, however, overcoming many challenges. One of the main challenges is how to provide Quality of Service (QoS) guarantees in such highly dynamic mobile environments. Addressing this challenge is the main focus of this paper, which provides an insight into how mobility management and QoS solutions can be coupled with each other. Moreover, the paper describes in detail the QoS-aware Mobile IP Fast Authentication Protocol (QoMIFA), which is capable of handling mobility management and simultaneously reserving resources, thus, satisfying the requirements of all-IP mobile communication networks. The paper evaluates also the performance of QoMIFA compared to the well-known Simple QoS signaling protocol (Simple QoS) by means of simulation studies modeled in the network simulator 2 (ns2). The evaluation comprises the investigation of the impact of the network load on both protocols. Our simulation results show that QoMIFA is capable of achieving fast and smooth handoffs in addition to its capability of reserving resources very quickly. With respect to the time required to reserve resources for uplink traffic, QoMIFA is up to 80% faster than Simple QoS. If the resources are reserved for downlink traffic, QoMIFA performs up to 93% better. Considering the number of dropped packets per handoff, QoMIFA reduces the packets lost per handoff by 22% up to 76% on uplink and by 55% up to 93% on downlink as compared to Simple QoS. A main advantage of QoMIFA is that it minimizes the packets sent as best-effort (without QoS guarantees) after handoffs. QoMIFA reduces the best-effort packets transmitted on downlink by approximately 94% compared to Simple QoS and eliminates these packets on uplink.     

Learning automata routeing in connection-oriented networks

Learning automata are used at the source nodes of a connection-oriented network to dynamically route newly arriving virtual calls to their destination. First, two new learning automata are introduced. Then, these two learning automata, as well as the well-known L Learning automaton and the deterministic shortest-path algorithms are used in a simulation program to route virtual calls. The more frequent the updating and the more recent network state information used, the better the performance. In the sequence, the virtual link length is developed as a function of both the number of packets and the number of virtual calls at the network link. This virtual link length is used in the learning automata routeing algorithm and is shown via simulation to be superior to the minimum packet delay or shortest-queue-type link length, usually used in real networks. Thus, in connection-oriented networks, not only the packet but also the virtual call traffic characteristics should be used in the routeing decisions. Furthermore, when the network state information is out-of-date, or when there are few virtual calls and each one carries a large number of packets, then the virtual link length should be based more on the number of virtual calls than on the number of packets at this link. On the other hand, when the network state information is current and there are many virtual calls and each one carries a small number of packets, then the virtual link length should be based more on the number of packets than on the number of virtual calls at this link.     

A novel approach for mitigating gray hole attack in MANET

Mobile ad hoc network (MANET) is defined as the category of wireless network that is capable of operating without any fixed infrastructure. The main assumption considered in this network is that all nodes are trusted nodes but in real scenario, some nodes can be malicious node and therefore can perform selective dropping of data packets instead of forwarding the data packets to the destination node. These malicious nodes behave normally during route discovery phase and afterwards drop fractions of the data packets routed through them. Such type of attack is known as smart gray hole attack which is variation of sequence number based gray hole attack. In this paper, we have launched smart gray hole attack and proposed a new mechanism for mitigating the impact of smart gray hole attack. Mitigating Gray hole Attack Mechanism (MGAM) uses several special nodes called as G-IDS (gray hole-intrusion detection system) nodes which are deployed in MANETs for detecting and preventing smart gray hole attack. G-IDS nodes overhear the transmission of its neighbouring nodes and when it detects that the node is dropping the data packets which are greater than threshold value then it broadcast the ALERT message in the network notifying about the identity of malicious node. The identified malicious is then blocked from further its participation by dropping the request and reply packet. In order to validate the effectiveness of our proposed mechanism, NS-2.35 simulator is used. The simulation results show that the proposed mechanism performs slightly well as compared with the existing scheme under smart gray hole attack.     

Minimum energy hierarchical dynamic source routing for Mobile Ad Hoc Networks

In this paper, Minimum Energy Dynamic Source Routing (MEDSR) and Hierarchical Minimum Energy Dynamic Source Routing (HMEDSR) protocols for Mobile Ad Hoc Networks (MANET) are proposed. The objective of MEDSR protocol is to reduce energy consumption in MANET while maintaining connectivity in the network. The objective of HMEDSR is to reduce the overhead of MEDSR. The overall result is that energy spent in transmitting overhead packets is reduced. This reduction allows more energy in transmitting data packets. The Dynamic Source Routing (DSR) protocol is modified to implement both MEDSR and HMEDSR protocols, and these implementations are tested with a network simulator (Network Simulator (NS-2)). The simulation results show that both MEDSR and HMEDSR protocols reduce energy consumption per data packet by 25% compared to DSR, but HMESDR further reduces energy consumption by 12% compared to MEDSR by controlling overhead packets.     

无线Ad hoc网络中基于节点位置的功率控制算法

为了降低无线Ad hoc网络中节点的能量消耗,该文提出了一种基于节点位置的功率控制算法(PCAP)。PCAP算法通过分析节点间的位置关系,建立节点的优化邻居集合,并对路由层报文、MAC层控制报文和其它数据类报文使用不同的功率控制策略。PCAP算法在保证网络连接性的同时能降低网络能量消耗,计算机仿真表明,PCAP算法在MAC层的吞吐量、MAC层丢包、端到端时延等方面取得较好的性能表现。     

Optimization of multipath transmission path scheduling based on forward delay in vehicular heterogeneous network

In order to solve the problem that the data packets were out of order at the receiving end in the multipath transmission,which greatly reduced the transmission performance,an optimization algorithm was proposed for multipath transmission path scheduling based on forward delay in the vehicle heterogeneous network.The main idea of the proposed algorithm was to schedule data packets through a concurrent path according to the forward delay and throughput difference estimated by the sender.A simulation experiment was carried out on NS-3.The simulation results show that compared with the previous algorithm,the proposed algorithm has better performance than other algorithms in reorder-buffer-occupancy density (RBD) and throughput.The problem of out-of-order data packets at the receiving end is significantly reduced,and the total system throughput and network utilization have been improved.     

基于相遇节点跨层感知的机会网络高效低时延路由算法

针对基于epidemic机制的机会网络路由算法未能及时感知相遇节点以及在数据分组交换过程中存在冗余的问题,提出了一种采用跨层感知相遇节点思路的机会网络高效低时延路由算法——ERCES（epidemic routing based on cross-layer encountered-node sensing）,通过在物理层、MAC层和网络层之间的跨层信息共享与协同,实现相遇节点及时感知,并且采用节点相遇后立即广播新数据分组、收到SV（summary vector）分组后优先发送目的节点为对方的数据分组、动态自适应发送HELLO分组、借助SV删除节点缓存中已到达目的节点的分组等新机制,减少控制和存储开销,降低分组时延。理论分析验证了ERCES算法的有效性,仿真结果表明：与经典的Epidemic Routing算法及其多个改进相比,ERCES算法的控制开销和存储开销分别减少8.2%和2.1%以上,数据分组平均端到端时延至少降低了11.3%。     

Throughput analysis of two-hop wireless networks with network coding

A Two-hop Wireless Network (TWN) is the basic topology structure that provides network coding opportunity for improving throughput. Network coding on a homogeneous TWN, in which all the data flows have the same packet size and all the links have the same transmission rate, has been extensively investigated. In this paper, network coding on more practical heterogeneous TWNs, featured by various packet sizes and transmission rates, is studied. Based on the Markov model, the throughput of the proposed network coding scheme, together with the throughput gain, is derived, which matches the simulation results very well. Numerical analyses indicate that, encoding the packets with close size and close transmission rate and enlarging buffer size at the relay node help in improving the throughput gain.     

Doped fountain coding for minimum delay data collection in circular networks

This paper studies decentralized, Fountain and network-coding based strategies for facilitating data collection in circular wireless sensor networks, which rely on the stochastic diversity of data storage. The goal is to allow for a reduced delay collection by a data collector who accesses the network at a random position and random time. Data dissemination is performed by a set of relays which form a circular route to exchange source packets. The storage nodes within the transmission range of the routeiquests relays linearly combine and store overheard relay transmissions using random decentralized strategies. An intelligent data collector first collects a minimum set of coded packets from a subset of storage nodes in its proximity, which might be sufficient for recovering the original packets and, by using a message-passing decoder, attempts recovering all original source packets from this set. Whenever the decoder stalls, the source packet which restarts decoding is polled/doped from its original source node. The random-walk-based analysis of the decoding/doping process furnishes the collection delay analysis with a prediction on the number of required doped packets. The number of doped packets can be surprisingly small when employed with an Ideal Soliton code degree distribution and, hence, the doping strategy may have the least collection delay when the density of source nodes is sufficiently large. Furthermore, we demonstrate that network coding makes dissemination more efficient at the expense of a larger collection delay. Not surprisingly, a circular network allows for a significantly more (analytically and otherwise) tractable strategies relative to a network whose model is a random geometric graph.     

Are priorities useful in an 802.5 token ring?

The IEEE standard 802.5 token ring protocol defines eight packet priorities. The intent is that high-priority packets should be delivered prior to low-priority packets. A series of simulations shows that this expected behavior occurs when there are very few network stations, very short data packets (but still long relative to ring latency), very short token hold times, and very high network loads. In the general case, priorities did not markedly influence packet delivery time. Use of the priority system generally resulted in more overhead and longer average packet delays than when all packets were carried as a single priority. The features of the protocol operation that are the cause of this increased delay and lack of priority discrimination are described mathematically     

Efficient data dissemination for Wi-Fi peer-to-peer networks by unicasting among Wi-Fi P2P groups

Recently, the Wi-Fi peer-to-peer (Wi-Fi P2P) technology is discussed to be able to support communications in infrastructure-less network scenarios. In many of such application scenarios, disseminating data (or information) to all network devices is an important issue. According to the Wi-Fi P2P specification, a device can communicate with other devices after joining a Wi-Fi P2P group. A Wi-Fi P2P group is a star network (rooted at a group owner). The group owner can disseminate data to all network devices by broadcasting. However, the Wi-Fi P2P broadcasting mechanism cannot guarantee successful delivery of packets. In order to disseminate data reliably, a possible solution is to disseminate packets to network devices by unicasting. But, by this manner, the group owner will run out of its energy quickly and the time needed to disseminate data to network devices will be lengthened. To consider the above factors, in this paper, we formally define a Wi-Fi P2P data dissemination (WPDD) problem, and prove that this problem is NP-complete. Instead of using one Wi-Fi P2P group to connect all network devices, we propose to divide devices into multiple groups. We then propose a tree-based dissemination scheme and a ring-based data dissemination scheme to achieve data dissemination among groups. The proposed schemes can be compatible with the Wi-Fi P2P specification. We evaluate the performance and effectiveness of the proposed schemes by simulation programs and prototyping implementations.     

High-throughput multicast routing metrics in wireless mesh networks

The stationary nature of nodes in a mesh network has shifted the main design goal of routing protocols from maintaining connectivity between source and destination nodes to finding high-throughput paths between them. Numerous link-quality-based routing metrics have been proposed for choosing high-throughput routing paths in recent years. In this paper, we study routing metrics for high-throughput tree or mesh construction in multicast protocols. We show that there is a fundamental difference between unicast and multicast routing in how data packets are transmitted at the link layer, and accordingly how the routing metrics for unicast routing should be adapted for high-throughput multicast routing. We propose a low-overhead adaptive online algorithm to incorporate link-quality metrics to a representative multicast routing protocol. We then study the performance improvement achieved by using different link-quality-based routing metrics via extensive simulation and experiments on a mesh-network testbed, using ODMRP as a representative multicast protocol.Our extensive simulation studies show that: (1) ODMRP equipped with any of the link-quality-based routing metrics can achieve higher throughput than the original ODMRP. In particular, under a tree topology, on average, ODMRP enhanced with link-quality routing metrics achieve up to 34% higher throughput than the original ODMRP under low multicast sending rate; (2) the improvement reduces to 21% under high multicast sending rate due to higher interference experienced by the data packets from the probe packets; (3) heavily penalizing lossy links is an effective way in the link-quality metric design to avoid low-throughput paths; and (4) the path redundancy from a mesh data dissemination topology in mesh-based multicast protocols provides another degree of robustness to link characteristics and reduces the additional throughput gain achieved by using link-quality-based routing metrics. Finally, our experiments on an eight-node testbed show that on average, ODMRP using SPP and PP achieves 14% and 17% higher throughput over ODMRP, respectively, validating the simulation results.     

机会网络中一种低缓存占用的Epidemic 路由算法

由于机会网络中节点的缓存空间有限,容易导致数据分组丢失和时延增加。针对部分数据分组已经到达目的节点,但是该类分组仍在网络中其它节点存储、传输问题,提出一种低缓存占用的Epidemic路由算法(RBER)。该算法通过SV运算进行节点缓存清理,从而避免这类冗余数据分组对缓存的占用。理论分析和仿真结果表明,该机制能够降低网络开销、数据分组的发送和缓存占用。     

一种基于信任模型的安全度量及安全路由算法设计

针对网络路由的攻击普遍且后果严重。目前的研究大多是采用数字签名,消息验证和入侵检测等机制来提高路由控制信息的安全,基本没有考虑机密应用数据的路由安全问题。该文通过分析通信实体的安全机制和安全威胁来测量链路和节点的信任度,建立节点间的信任关系,并基于该信任模型定义和量化一种新的安全度量SM(Security Metric),提出以SM为选路标准的安全路由算法SMRA(Security Metric based Routing Algorithm)。仿真表明,网络存在攻击时,SMRA算法比OSPF算法有更好的包传输率和路由安全性能。