无冲突NC-IPRMA协议下的数据--话音综合

提出了一个面向微蜂窝通信的支持数据─话音综合业务的无冲突分组预约多址协议─—NC-IPRMA协议,通过M／M／N／／M．排队模型分析了NC-IPRMA协议的话音子系统性能,通过系统仿真分析了数据一话音综合性能。研究结果表明,在支持数据─话音综合业务方面,NC-IPRMA协议比PRMA和IPRMA协议更高效,这包括更高的信道利用率,更短的数据分组时延和更大的话音终端容量。由于采用排队等待方式接入时隙信道,NC-IPRMA协议彻底消除了以竞争方式接入信道的PRMA协议（及其各种改进方案）存在的重负荷下的不稳定问题。     

无冲突NC—IPRMA协议下的数据——话音综合

提出了一个面向微蜂窝通信的支持数据－－话音综合业务的无冲突分组预约多址协议－－ＮＣ－ＩＰＲＭＡ协议,通过Ｍ／Ｍ／Ｎ∞／Ｍ,排队模型分析了ＮＣ－ＩＰＲＭＡ协议的话音子系统性能,通过系统仿真分析了数据－－话音综合性能。研究结果表明,在支持数据－－话音综合业务方面,ＮＣ－ＩＰＲＭＡ协议比ＰＲＭＡ和ＩＰＲＭＡ协议更高效,这包括更高的认道利用率,更短的数据分组时延和更大的话音终端容量。由于采用排队等待方式接     

Internet电话原理

现在使用的普通电话采用线路交换方式,而In－ternet电话则采取报文交换方式,因此Internet电话通过PSTN时,在Internet与PSTN之间需经过话音同关转换,转换成符合Internet传输的IP数据报文,并遵循TCP／IP协议传输。Internet电话的通信方式分为3种：PC－to－PC、PC－to－Phone和Phone－to－Phone。其结构如图1所示。话音通过PSTN后,需经连接网关（CG）、话音同关（VG）分别与NO．7信令系统（SS7）网和IP网连接。其中CG完成IP协议（如H．323和SIP）和PSTN协议（如ISUP、PRI）之间的互联,SS7网充当其中介物;VG…     

防止局域网业务阻塞的协议

本文介绍了支持话音和数据业务的高速互连局域网（ＬＡＮ）中防止业务阻塞的协议。网络用桥进行互连。协议依靠周期地传送ＭＡＣ控制帧（阻塞通知帧），从桥发往信源站。这些帧有实时桥内数据缓冲区容量和话音排队时延信息。在这些信息基础上，信源站可以封锁向网络发送的数据，因此，当桥超载时分配更多的带宽给话音和数据业务。同时阐述了用仿真法评价协议的性能。仿真结果表明：协议有效地防止了桥的阻塞，改进了话音和数据业务的     

动态多通道卫星话音／数据综合的S－ALOHA性能分析

本文分析了一种新的多通道话音／数据综合ＶＳＡＴ系统的Ｓ－ＡＬＯＨＡ性能，并给出了数值计算结果；从中可看到该协议既能提供较高的吞吐量，又能有效地减小话音时延，并能协调话音和数据之间对性能要求的差异，文中考虑了Ｓ－ＡＬＯＨＡ中分组达到时间抖动的影响．文中还讨论了话音在重负载的条件下可占用数据通道的动态分配方案，并给出了动态分配的算法。     

分组卫星话音／数据综合的混合多址协议性能研究

本文讨论了一种用于分组话音／数据综合的混合多址协议，该协议是固定分配与随机访问的混合，并且赋予话音分组优先传输权，从而保证了无重传话音分组有较小的丢失概率。本文进行了详细的理论分析，并得出了性能比较特性，所得结果认为这是一个兼顾话音／数据综合的较好协议，且具有一定的灵活性。     

动态多通道卫星话音／数据综合的S—ALOHA性能分析

本文分析了一种新的多通道话音／数据综合ＶＳＡＴ系统的Ｓ－ＡＬＯＨＡ性能，并给出了数值计算结果；从中可秆到该协议既能提供较高的吞吐量，又能有效地减小话音时延，并能协调话音和数据这间对性能要求的差异，文中考虑了Ｓ－ＡＬＯＨＡ中分组达到时间抖动的影响。文中还讨论了话音的重负载的条件下可占用数据通道的动态分配方案，并给出了动态分配的算法。     

无冲突话音/数据综合业务分组预约多址(CF-IPRMA)协议及其性能

本文提出了无冲突话音／数据综合业务的ＰＲＭＡ协议：ＣＦ－ＩＰＲＭＡ协议,并利用马尔可夫链模型法,对ＣＦ－ＩＰＲＭＡ协议中的数据通信性能进行了分析;分析结果表明,该协议在保证话音通信质量的前提下,具有较高的数据业务通过率。     

PRMA/TDD多址协议下的数据┐话音综合

本文提出了一个在ＰＲＭＡ／ＴＤＤ多址协议下的数据－话音综合方案，该方案以动态边界分离话音和数据业务。动态边界的位置由话音子系统的业务负荷确定，使系统在保证话音业务质量的前提下，让数据业务获得最大带宽。通过马尔可夫链建模，推导出了数据业务最大化公式，并进行了计算机系统仿真。分析结果表明，与ＰＲＭＡ数－话综合方案相比，该方案可使系统性能明显提高。动态边界也使话音业务子系统独立于数据业务子系统，因此，数据业务的突发性和潜在不稳定性不会影响话音业务。     

帧中继上的话音业务──ACTnetworks.Inc的解决方案

帧中继上的话音业务──ＡＣＴｎｅｔｗｏｒｋｓ．Ｉｎｃ的解决方案中国矿业大学北京研究生部毕立波，陈晓钟ＡＣＴｎｅｔｗｏｒｋｓ．Ｉｎｃ关于帧中继上的话音解决方案典型地，一个帧中继接入设备（ＦＲＡＤ）只支持数据协议。但是，ＡＣＴ的ＳＤＭ－ＦＰ和ＳＤＭ－ＪＦ...     

Performance evaluation of a reservation TDMA protocol forvoice/data transmission in microcellular systems

This paper deals with a random reservation TDMA protocol able to support constant bit rate services as well as variable bit rate services. In particular, voice communications and data transmissions are considered. Voice terminals have a higher priority assigned than data terminals in accessing the shared channel. A suitable analytical approach is proposed in order to evaluate the data and voice subsystem performance. Comparisons to the well known PRMA scheme are also given in order to highlight the superior performance of the proposed approach in terms of maximum data load and overall throughput     

基于ARM技术的单兵扩频网络电台设计

设计了基于ARM技术的具有较高传输速率和扩频增益的全数字化单兵网络电台。核心处理器充分考虑了多任务和实时性的要求,采用ARM处理器及嵌入式操作系统uC/OS-II,扩频基带处理器选用扩频处理增益和集成度较高的AMIS-50050芯片,话音采用高压缩比的AMBE压缩算法,语音质量高,组网遵循Ad hoc组网协议。该电台的设计满足单兵对数据、话音、图像传输和系统组网的要求,并具有高性能、高集成度、抗干扰、抗截获、体积小和功耗低的特点。     

Performance evaluation of a CDMA protocol for voice and dataintegration in personal communication networks

Future wireless personal communication networks (PCN's) will require voice and data service integration on the radio link. The multiaccess capability of the code-division multiple-access (CDMA) technique has been widely investigated in the recent literature. The aim of this paper is to propose a CDMA-based protocol for joint voice and data transmissions in PCN's. The performance of such a protocol has been derived by means of an analytical approach both in terms of voice packet dropping probability and mean data packet delay. Voice traffic has been modeled as having alternated talkspurts and silences, with generation of voice packets at constant rate during talkspurts and no packet generation during silence gaps. A general arrival process is assumed for the data traffic. However, numerical results are derived in the case of a Poisson process. Simulation results are given to validate our analytical predictions. The main result derived here is that the proposed CDMA-based protocol efficiently handles both voice and data traffic. In particular, it is shown that the performance of the voice subsystem is independent of the data traffic     

Intelligent MBWIMA/UMTS protocol using cascade fuzzy logic control for UTRA TDD mode

An intelligent medium-access-control (MAC) protocol based on cascade fuzzy-logic-control (CFLC), consisting of a fuzzy V/sub max/ (maximum number of voice/video slots) control and a fuzzy data-rate control for universal mobile telecommunications system (UMTS) terrestrial radio access time-division duplex (UTRA TDD) mode is presented. Voice, data, and video are integrated for transmission using CFLC-based movable-boundary wireless multiple access (MBWIMA) in the UMTS protocol. The performance of the CFLC-based MBWIMA/UMTS protocol with data-rate control is optimized by using the CFLC to generate the proper maximum number of voice/video slots and a suitable data rate. Simulation results demonstrate that the data-packet delay for the CFLC-based MBWIMA/UMTS protocol with data-rate control is less than that for the CFLC-based MBWIMA/UMTS protocol without data-rate control. The CFLC-based MBWIMA/UMTS protocol with data-rate control can greatly improve both the voice-video dropping probability and the data-packet delay of the MBWIMA/UMTS and general packet-radio system/UMTS protocols at the expense of a small decrease in the data-packet throughput. Voice-activity detector, single cell, and multicell environments are also considered.     

Security Challenge and Defense in VoIP Infrastructures

Voice over Internet protocol (VoIP) has become a popular alternative to traditional public-switched telephone network (PSTN) networks that provides advantages of low cost and flexible advanced ldquodigitalrdquo features. The flexibility of the VoIP system and the convergence of voice and data networks brings with it additional security risks. These are in addition to the common security concerns faced by the underlying IP data network facilities that a VoIP system relies on. The result being that the VoIP network further complicates the security assurance mission faced by enterprises employing this technology. It is time to document various security issues that a VoIP infrastructure may face and analyze the challenges and solutions that may guide future research and development efforts. In this paper, we examine and investigate the concerns and requirements of VoIP security. After a thorough review of security issues and defense mechanisms, we focus on attacks and countermeasures unique to VoIP systems that are essential for current and future VoIP implantations. Then, we analyze two popular industry best practices for securing VoIP networks and conclude this paper with further discussion on future research directions. This paper aims to direct future research efforts and to offer helpful guidelines for practitioners.     

Hierarchy schedule-sensing protocol for CDMA wireless data-centric networks with multiple packet collision and capture effect

This paper focuses on performance analysis of a CDMA wireless data network based on hierarchy schedule-sensing (HSS) protocol, in which a common-code permission frame beacon is used to schedule request transmissions to avoid packet collisions. To further reduce scheduling delay, hierarchical group-based coding is adopted in the scheme. The performance of such a network is evaluated considering packet collisions with and without packet capture effect using a two-dimensional Markovian chain model. In particular, this paper will study the impact of multiple packet-collision effect on network performance with the help of the average packet-collision rate derived explicitly in the paper. The obtained results show that, despite its low implementation complexity, the HSS protocol is a fairly robust medium-access control protocol featuring uniformly high throughput and short delay even under very high traffic load, which especially suits data-centric wireless networks with relatively small coverage area and great node density.     

Hybrid routing and load balancing protocol for wireless sensor network

In wireless sensor network, when the nodes are mobile, the network structure keeps on changing dynamically, that is, new nodes enter the network and old members exit the network. As a result, the path from one node to the other varies from time to time. In addition, if the load on a particular part of the network is high, then the nodes will not be capable of transmitting the data. Thus, data delivery at the destination will be unsuccessful. Moreover, the part of the network involved in transmitting the data should not be overloaded. To overcome these issues, a hybrid routing protocol and load balancing technique is discussed in this paper for the mobile data collectors in which the path from source to destination is ensured before data transmission. The hybrid routing protocol that combines the reactive and proactive approach is used to enhance gradient based routing protocol for low power and lossy networks. This protocol can efficiently handle the movement of multiple sinks. Finally, load balancing is applied over the multiple mobile elements to balance the load of sensor nodes. Simulation results show that this protocol can increase the packet delivery ratio and residual energy with reduced delay and packet drop.     

VMcMAC: Voice Call Support over Wireless Multi-Channel MAC Protocol

This paper presents a new scheme to support voice calls over a wireless multi-channel MAC protocol (VMcMAC). We increase the voice capacity of wireless networks by reducing protocol overhead and interference between voice traffic and data traffic. Voice calls are allocated to specific reserved channels in a distributed TDMA fashion. Each voice node visits the voice channel with a fixed frequency and then transmits a voice frame without sending control messages. Simulation results show a significant improvement in the voice capacity of wireless ad-hoc networks     

An opportunistic cross‐layer architecture for voice in multi‐hop wireless LANs

We propose an opportunistic cross‐layer architecture for adaptive support of Voice over IP in multi‐hop wireless LANs. As opposed to providing high call quality, we target emergencies where it is important to communicate, even if at low quality, no matter the harshness of the network conditions. With the importance of delay on voice quality in mind, we select adaptation parameters that control the ratio of real‐time traffic load to available bandwidth. This is achieved in two ways: minimizing the load and maximizing the bandwidth. The PHY/MAC interaction improves the use of the spectral resources by opportunistically exploiting rate‐control and packet bursts, while the MAC/application interaction controls the demand per source through voice compression. The objective is to maximize the number of calls admitted that satisfy the end‐to‐end delay budget. The performance of the protocol is studied extensively in the ns‐2 network simulator. Results indicate that call quality degrades as load increases and overlonger paths, and a larger packet size improves performance. For long paths having low‐quality channels, forward error correction, header compression, and relaxing the delay budget of the system are required to maintain call admission and quality. The proposed adaptive protocol achieves high performance improvements over the traditional, non‐adaptive approach. Copyright © 2008 John Wiley & Sons, Ltd.     

FLC-Based MBWIMA/UMTS Protocol for Multimedia Services in UTRA TDD Mode

An intelligent medium access control (MAC) protocol based on fuzzy logic control (FLC) is proposed and compared with a general packet radio system in UMTS (GPRS/UMTS), priority scheme and the movable boundary wireless integrated multiple access in UMTS (MBWIMA/UMTS) protocols. The integrated video/voice/data services of UMTS in UTRA TDD mode have different transmission properties. By fuzzy logic control, the resources of the wireless communication can be intelligent assigned for different types of mediums. The voice-video dropping probability and data packet delay are input to FLC to optimally select the maximum number of voice/video slots. Voice activity detector (VAD) and multiple access interference in single cell are also considered in the simulations.