IMS中基于LZSS的SIP信令压缩算法研究

3GPP在R5核心网引入了IMS结构，并选择会话初始协议（SIP）作为呼叫/会话的控制信令。但在无线环境下消息过长成为SIP在IMS中的应用瓶颈。在SigComp框架下，对各种压缩算法进行了比较，并根据SIP消息特点选择LZSS算法作为SIP信令压缩的基本算法。为了进一步提高SIP信令的压缩比，提出了LZSS＋Huffman的压缩算法及其实现流程，并对算法的压缩效果进行了仿真分析。     

VoIP系统SIP-QoS代理服务器设计方案

文中以解决VoIP系统的语音质量问题为目标,深入研究了基于SIP的VoIP系统QoS控制技术。参照IMS网络结构,考虑通信业务的QoS要求,研究以SIP为信令协议的VoIP系统如何进行呼叫控制、资源预留和策略决策,融入到SIP用户代理、SIP代理服务器,提出了一个具有QoS能力的SIP代理服务器的设计方案,增加了策略决策功能（PDF）等网络实体,支持QoS的能力得到增强。文中详细讨论了支持QoS的SIP网络的增强能力,具有QoS能力的SIP代理服务器的功能结构,QoS功能模块,以及QoS资源授权和预留决策过程。     

VoIP系统SIP—QoS代理服务器设计方案

文中以解决VoIP系统的语音质量问题为目标,深入研究了基于SIP的VoIP系统QoS控制技术。参照IMS网络结构,考虑通信业务的QoS要求,研究以SIP为信令协议的VoIP系统如何进行呼叫控制、资源预留和策略决策,融人到SIP用户代理、SIP代理服务器,提出了一个具有QoS能力的SIP代理服务器的设计方案,增加了策略决策功能（PDF）等网络实体,支持QoS的能力得到增强。文中详细讨论了支持QoS的siP网络的增强能力,具有QoS能力的SIP代理服务器的功能结构,QoS功能模块,以及QoS资源授权和预留决策过程。     

基于SigComp的会话初始化协议压缩算法

独立媒体服务(IMS)是第三代合作伙伴计划(3GPP)在版本5中提出的支持IP多媒体业务的子系统,而基于文本的SIP消息过大成为其在IMS无线环境应用下的瓶颈,因此采用会话初始化协议（SIP）来建立和维护多媒体会话。在SigComp框架下,将改进后的LZSS算法与算术编码相结合对SIP信令进行压缩。实验表明新的算法有较高的压缩率,对改善IMS的SIP会话建立延时有一定的参考价值。     

基于先到先服务的二维动态优先级信令排队算法

针对信令寻径式交换机的特征,提出对交换机的信令实施一种以先到先服务排队策略为基础,基于信令固定优先级和交换机端口轮转优先级的二维动态优先级排队算法,该算法将不同时刻到达交换机的信令请求按照到达的先后次序进行排队,同一时刻到达交换机的信令请求先按照信令固定优先级进行排队,优先级相同的信令请求按照交换机端口的轮转优先级进行排队,因此这种排队算法称为基于先到先服务的二维动态优先级排队算法,简称TDDP-FCFS(Two Dimensional Dynamic Priority-based First Come First Serve)。然后,使用强占型M/M/1/∞队列对其进行建模,讨论了TDDP-FCFS算法的性能指标以及计算方法,并给出了实际的计算结果。结果表明,TDDP-FCFS排队算法兼顾了信令优先级和交换机的端口优先级,实现简单,且能够很好地满足信令寻径式交换机的调度要求,具有较高 的调度效率。     

基于IMS的交互式语音及视频应答系统的研究

为了使终端用户能更好地体验视频业务带来的生活乐趣,满足终端用户语音视频应答,以视频呼叫控制（VCC）为核心技术,提出了一种基于IMS架构设计的交互式语音及视频应答系统（IVVR）。提出的IVVR系统是一种全新的无线语音及视频应答增值服务,视频电话用户通过拨打指定电话号码,获得所需信息,参与互动式的语音视频服务。不仅保证兼容现有3G/NGN网络,而且能更好地适应通信网络及终端融合的趋势,为通信网络过渡到IMS做好了充分的准备。     

分布式容错SIP协议栈的设计

SIP从20世纪90年起一经使用,就彻底改进了人们使用融合服务彼此进行通信的方式。会话初始协议提供了在网络上无缝透明传递声音、视频、数据和无线服务的框架结构。但SIP应用的可靠性的研究还处于初级阶段。文章阐述一种分布式容错SIP协议栈的实现方式,以方便可靠的SIP网络的设计和构建,从而使得SIP服务的用户得到更好的服务体验。     

CDMA2000系统的无线网络优化

无线数据优化的目的是提高用户数据传输速率和提高网络系统资源利用率,根据此目的提出语音与数据资源的动态分配管理技术,与静态资源分配算法不同,不是为语音或数据用户预留固定的功率或信道,而是根据实时无线呼叫请求智能地分配扇区资源,使同一载波上语音、数据的比例自如调整,力争做到按需分配,重点保障。采用该技术对CDMA20001X网络的优化后,一方面使网络在承载数据业务时,实现扇区数据吞吐量最大化;另一方面使用户能够更及时地接入到数据业务服务,数据速率高,从而提高用户感受的满意度。     

无线VOIP网络中SIP穿越NAT的设计与实现①

SIP是IETF提出的IP电话信令协议,作为NGN重要协议之一,广泛应用于数据、语音、视频等多媒体通信业务中。但网络中大量NAT的 存在加上SIP本身不支持信令和媒体流的穿越,限制了其在广域网上的应用和发展。对目前主要的NAT穿越方案进行了详细的阐述和比较之后,设计并实现了一种基于STUN协议的NAT穿越方案。该方案目前已成功应用于基于PDA的无线VOIP网络中,并可推广到其它基于SIP协议的终端上,为VOIP业务的推广应用扫清了障碍。     

WiMAX拓展实时轮询调度机制分析

为了提高无线资源的利用率,使WiMAX系统更好地支持语音业务,基于IEEE 802.16e协议的QoS调度体系,提出了针对带有静默压缩语音业务的拓展实时轮询调度机制的具体实现方案.而且通过对方案中关键参数的分析,给出了一种QoS保证方法.方法根据用户时延对数据带宽分配进行补偿,并按照用户负载情况动态地调整轮询请求带宽的分配周期.使用OPNET软件进行了系统级性能评估,结果表明所提出的方法可有效地降低用户上行接入时延和上行丢包率,从而提高了通信质量.     

A Survey of Various Schedulers Used for Fair Bandwidth Allocation in WiMAX: IEEE 802.16

ABSTRACT

Wireless Interoperability for Multiple Access (WiMAX) is one of the emerging fields of high-speed wireless communication that has enormous capabilities due to its range and the connection speed. Like wireless local area networks (LANs), WiMAX networks implement multiple quality of service (QoS) frameworks at the Media Access Control (MAC) level for assured data, voice, and video services. The question of ensuring QoS is basically how to distribute available resources to users in order to satisfy QoS parameters such as latency, jitter and throughput requirements. IEEE 802.16 standard does not have any particular guidelines on scheduling of incoming and outgoing data. This has caught the attention of researchers working on WiMAX. This article discusses the various issues in WiMAX along with a classification of various scheduling approaches based upon the type of scheduler for the sake of better understanding the scheduling problem and analyzing various available theories.     

Application-aware scheduling for VoIP in Wireless Mesh Networks

Wireless Mesh Networks (WMNs) are seen as a means to provide last mile connections in Next Generation Networks (NGNs). Because of their auto-configuration capabilities and the low deployment cost WMNs are considered to be an efficient solution for the support of multiple voice, video and data services in NGNs. This paper looks at the optimal provision of resources in WMNs for Voice over IP (VoIP) traffic, which has strict performance requirements in terms of delay, jitter and packet loss. In WMNs, because of the challenges introduced by wireless multi-hop transmissions and limited resources, providing performance quality for VoIP comparable to the voice quality in the traditional circuit-switched networks is a major challenge.This paper analyses different scheduling mechanisms for TDMA-based access control in mesh networks as specified in the IEEE 802.16-2004 WiMAX standard. The performance of the VoIP applications when different scheduling mechanisms are deployed is analysed on a variety of topologies using ns-2 simulation and mathematical analysis. The paper concludes that on-demand scheduling of VoIP traffic – typically deployed in 802.11-based WMNs – is not able to provide the required VoIP quality in realistic mesh WiMAX network scenarios and is therefore not optimal from a network operator’s point of view. Instead, it is shown, that continuous scheduling is much better suited to serve VoIP traffic. The paper then proposes a new VoIP-aware resource coordination scheme and shows, through simulation, that the new scheme is scalable and provides good quality for VoIP service in a wide range of network scenarios. The results shown in the paper prove that the new scheme is resilient to increasing hop count, increasing number of simultaneous VoIP sessions and the background traffic load in the network. Compared to other resource coordination schemes the VoIP-aware scheduler significantly increases the number of supported calls.     

An embedded fuzzy expert system for adaptive WFQ scheduling of IEEE 802.16 networks

WiMAX is a futuristic technology which provides simultaneous support for web, video, and voice applications. WiMAX networks are best suitable to real time traffic however the quantity of non real time and best effort traffic cannot be neglected. Distribution of resources in such heterogeneous applications is therefore a challenging task. There are many schedulers available for WiMAX but adaptive and adequate schedulers are still in growing stage of development. This paper introduces a novel method using which a system is developed based on concepts of fuzzy logic to schedule traffic in WiMAX networks. The proposed fuzzy expert system simplifies fair allocation of resources to real as well as non real time traffic. The implementation is based on changing the weights of the queues serving real and non- real time traffic adaptively. New weights will be calculated for each bandwidth request made to base station and these weights will in turn decide amount of bandwidth allocated to different traffic classes. The weights are calculated based on three parameters that are amount of real time and non real time traffic in queues, change in throughput requirement for non real time flows and latency requirement of real time input data. Results obtained by virtue of simulations justify the significance of the proposed method.     

多业务通信系统中切换方案的研究

在无线移动通信系统中要想获得连续的通信就必须有切换技术的支撑,切换方案是否优良决定着信号的业务流量以及服务质量。因此,本文主要讨论在多业务系统中,非强占优先切换方案和抢占优先的切换方案。     

A Quality-Driven Cross-Layer Solution for MPEG Video Streaming Over WiMAX Networks

Extensive efforts have been focused on deploying broadband wireless networks. Providing mobile users with high speed network connectivity will let them run various multimedia applications on their wireless devices. Satisfying users with different quality-of-service requirements while optimizing resource allocation is a challenging problem. In this paper, we discuss the challenges and possible solutions for transmitting MPEG video streams over WiMAX networks. We will briefly describe the MPEG traffic model suggested by the WiMAX Forum. A cross-layer solution for enhancing the performance of WiMAX networks with respect to MPEG video streaming applications is explained. Our solution uses the characteristics of MPEG traffic to give priority to the more important frames and protect them against dropping. Besides, it is simple and compatible with the IEEE 802.16 standards and thus easily deployable. It is shown that the proposed solutions will improve the video quality over WiMAX networks.     

Highest Urgency First (HUF): A latency and modulation aware bandwidth allocation algorithm for WiMAX base stations

The mobile WiMAX systems based on IEEE 802.16e-2005 provide high data rate for mobile wireless networks. However, the link quality is frequently unstable owing to mobility and air interference and therefore impacts the latency requirement of real-time applications. In the WiMAX standard, the modulation/coding scheme and the boundary of uplink/downlink sub-frames could be adjusted subject to channel quality and the traffic volume, respectively. This provides us a chance to design a MAC-layer uplink/downlink bandwidth allocation algorithm that is QoS/PHY-aware.This work takes into account the adaptive modulation and coding scheme (MCS), uplink and downlink traffic volume, and QoS parameters of all five defined service classes to design a bandwidth allocation algorithm that calculates the slot allocation in two phases. The first phase decides the boundary of uplink and downlink sub-frames by satisfying requests with pending latency violation and proportionating according to traffic volume, while the second phase allocates slots to mobile stations considering urgency, priority and fairness. Simulation results show our algorithm achieves zero latency violation and higher system throughput compared to existing non-QoS/PHY-aware or less-QoS/PHY-aware approaches.     

Priority-based rate control for service differentiation and congestion control in wireless multimedia sensor networks

In wireless multimedia sensor networks (WMSNs) a sensor node may have different types of sensor which gather different kinds of data. To support quality of service (QoS) requirements for multimedia applications having a reliable and fair transport protocol is necessary. One of the main objectives of the transport layer in WMSNs is congestion control. We observe that the information provided may have different levels of importance and argue that sensor networks should be willing to spend more resources in disseminating packets carrying more important information. Some applications of WMSNs may need to send real time traffic toward the sink node. This real time traffic requires low latency and high reliability so that immediate remedial and defensive actions can be taken when needed. Therefore, similar to wired networks, service differentiation in wireless sensor networks is also an important issue. We present a priority-based rate control mechanism for congestion control and service differentiation in WMSNs. We distinguish high priority real time traffic from low priority non-real time traffic, and service the input traffic based on its priority. Simulation results confirm the superior performance of the proposed model with respect to delays, delay variation and loss probability.     

支持QoS的IEEE 802.11的分布协调功能(DCF)算法

IEEE802．11是一种无线局域网标准，它采用CSMA／CA算法，有两种工作模式——DCF和PCF。当无线站点工作于DCF模式时，可以方便地构建自组网络.DCF模式是一种随机的无线信道共享方式，不能保障语音、视频等实时业务。本文按照各种业务的服务需求，在DCF中引入并行优先级队列，使这些队列接入信道的参数DIFS和CW与各种类型应用相对应，从而在MAC层中实现服务区分。     

在WLAN实现VoIP的新兴多路访问协议

VoIP是一种在延时、抖动和丢包率上对WLAN系统要求很严格的实时应用。对于CSMA/CA而言,如果语音和数据传输同时存在的话,想要语音质量满足通话要求,就要在CSMA/CA上增加优先级控制。文章提出了一种新兴的多路访问控制协议,这个协议使基于自治分布式控制的无线局域网能够满足VoIP的要求。