Security and delay issues in SIP systems

The deployment of multimedia over IP (MoIP), and in particular voice over IP services, requires to solve new security issues they introduce, before completely exploiting the great opportunities they offer to telecommunication market. Furthermore, the implementation of various security measures can cause a marked deterioration in quality of service, which is fundamental to the operation of an MoIP network that meets users' quality expectations. In particular, because of the time‐critical nature of MoIP and its low tolerance for disruption and packet loss, many security measures implemented in traditional data networks are simply not applicable in their current form. This paper presents an analysis of the security options of Session Initiation Protocol‐ (SIP)‐based MoIP architecture aimed at evaluating their impact on delay. In particular, each security option is analyzed in terms of clock cycles needed to perform the related operations. This parameter could be used to estimate the delay introduced by the security mechanisms. Moreover the paper proposes a rigorous definition of five security profiles, which provide different levels of security to a MoIP system. Copyright © 2009 John Wiley & Sons, Ltd.     

下一代通信网络中的SIP语音业务

介绍了最新的基于因特网的语音技术。在该方案设计中采用了融合传统电路交换网和IP网的结构思想,不仅将语音的传输放到了IP网上,更为集成将来的业务,诸如网页、电子邮件、多媒体技术等提供了灵活的结构。其初期目的在于替代传统的企业级电话业务。     

SIP在3G通信网络中的应用研究

在高速移动的条件下方便快捷而又经济地通信,是市场的迫切需求.会话初始化协议(SIP)是能够在第3代移动通信系统(3G)中传输IP(Internet Protocol)多媒体业务的信令协议.它能够融合Internet和移动蜂窝系统.文中简要介绍和分析了SIP,并给出了一种基于该协议的在3G通信网络中的应用方案.     

一种新的SIP泛洪攻击检测方法

IMS(IP multimedia subsystem,IP多媒体子系统)是3G系统中核心网的重要部分,它由SIP提供的会话发起能力建立端到端的会话,并获得所需要的服务质量。针对IMS网络中存在的SIP泛洪攻击,本文在详细分析SIP泛洪攻击原理和实现过程的基础上,提出了一种基于累积和算法的SIP泛洪攻击检测方法。该方法首先对接收到的SIP数据分组中的invite消息的数量进行统计,然后将统计结果输入累积和算法,以检测是否发生SIP消息泛洪攻击,最后通过设置的阈值判决检测结果。实验结果表明,本文提出的方法能够有效地检测IMS网络中的SIP泛洪攻击。     

An Approach for Telecom Operators to Achieve Converged Telecom and Internet Services

This article discusses a possible approach for telecom operators to achieve converged telecom and Internet services. It involves integrally developing telecom networks and Internet businesses through the convergence of their instant news and social networking services. Some background, benefits for telecom operators, and possible challenges are analyzed. A new service convergence approach such as this can also facilitate triple-screen and multi-screen convergence in the future.     

无线语音／多媒体IP传输技术中首标压缩方案的研究

全IP的3G网络代表了移动通信网络发展的趋势。文中探讨了无线语音／多媒体IP传输技术中的首标压缩问题，给出了一种主要针对无线VIP／MIP的基于校验元的首标压缩方案以及相应仿真结果。     

Experimenting with Feature Interaction Management in SIP Environment

This article reports architectural aspects of a solution for detecting and resolving feature interactions (FI) in SIP-based IP telephony architectures. The solution takes into account the special context of SIP that permits end user programmability, which means the possibility for end users to design their own tailored services and personalize them as much as they like. Programmability renders more frequent the so called multi-component FI situations, where the conflicting services reside in different network components. This type of FI is the more complicated one. The authors describe how the different components of the presented SIP architecture operate together in order to run services and avoid this type of interactions. A prototype of the solution has been developed.     

UPnP在多媒体通信穿越FW/NAT中的应用

本文首先分析了多媒体通信面临的FW／NAT(firewall／network address translation,防火墙和地址转换)穿越问题,然后对UPnP技术进行了介绍,包括其基本概念、网络组成、协议栈和工作原理等内容。文中还介绍了UPnP对因特网接入网关的支持,分析了UPnP穿越FW／NNT的原理。最后以SIP为例研究了UPnP在多媒体通信穿越FW／NAT中的应用,提出了SIP穿越FW／NAT的解决方案。     

有线-无线混合IP网络多媒体传输算法研究

提出了一种端到端的在异构的有线．无线混合IP网络上多媒体传输的改进算法WMTA（wireless multimedia transmission algorithm）。通过研究Gilbert无线差错模型仿真环境中包的长度与丢包率的关系,发现包长与丢包率呈线性增长的关系。基于上述观察,算法通过交替发送大小数据包探测随机和拥塞丢包数,并根据两种丢包的程度进行速率控制。针对不同网络状态转换时算法更新慢的缺点,添加了更新因子K,使算法在网络状态转换时能迅速适应当前网络的状态。仿真结果表明,与现有算法相比,WMTA无论是在运行单个流还是存在竞争流情况下,都能够达到更高的吞吐量和带宽利用率,有效地提高了网络中多媒体传输的服务质量（QoS）。     

一种有效的BPSK/QPSK信号调制识别方法

根据不同调制信号相位差分的变化规律,文章提出了基于相位差分峰值幅度比较的BP SK/QPSK调制识别方法。仿真结果验证了调制识别方法的有效性。     

海上毫米波通信技术

随着海上编队从濒海走向远洋,传统的点对点通信向综合信息传输网络化方向的转变势在必行,进而突显了对带宽的渴求。毫米波通信在解决带宽瓶颈、减轻设备载荷等方面有其独特优势。结合工作实践,分析了毫米波通信现状及其在海上实现时的主要技术途径,提出了毫米波通信系统组成模型,为毫米波通信在未来大型海上编队中的应用研究奠定了基础。随着时间的推移与技术的进步,毫米波通信技术在海上通信领域会获得广泛应用。     

过饱和多址系统中部分相干多用户信码/相位最佳联合检测

本文主要研究了过饱和多址系统中低复杂度部分相干多用户信码/相位最佳联合检测的问题.本文首先基于最大后验概率准则从理论上推导出了部分相干多用户信码/相位联合估计子的表达式;然后给出了低复杂度最佳联合检测算法用以计算此估计子,而且该算法适用于具有二维星座的线性调制方式;同时通过计算机仿真分析了该接收机的误码性能及相位提取误差等有关问题,并与相干、非相干解调两种情况作了比较,得出了一些有益的结论.     

An efficient mechanism for dynamic multicast traffic grooming in overlay IP/MPLS over WDM networks

This paper proposes an efficient overlay multicast provisioning (OMP) mechanism for dynamic multicast traffic grooming in overlay IP/MPLS over WDM networks. To facilitate request provisioning, OMP jointly utilizes a data learning (DL) scheme on the IP/MPLS layer for logical link cost estimation, and a lightpath fragmentation (LPF) based method on the WDM layer for improving resource sharing in grooming process. Extensive simulations are carried out to evaluate the performance of OMP mechanism under different traffic loads, with either limited or unlimited port resources. Simulation results demonstrate that OMP significantly outperforms the existing methods. To evaluate the respective influences of the DL scheme and the LPF method on OMP performance, provisioning mechanisms only utilizing either the IP/MPLS layer DL scheme or the WDM layer LPF method are also devised. Comparison results show that both DL and LPF methods help improve OMP blocking performance, and contribution from the DL scheme is more significant when the fixed routing and first-fit wavelength assignment (RWA) strategy is adopted on the WDM layer. Effects of a few other factors, including definition of connection cost to be reported by the WDM layer to the IP/MPLS layer and WDM-layer routing method, on OMP performance are also evaluated.     

An Adaptive Approach to Singular Point Detection in Fingerprint Images

This paper presents a novel algorithm for detection of singular points, the core and delta points, in fingerprint images. The number and location of singular points, are used to classify fingerprint images into five general groups; and therefore to narrow down the search space in large fingerprint databases. Using the proposed directional masks in the first step, we detect the neighborhood of the singular points. In the second stage by implementing the proposed algorithm, an adaptive singular point detection method, is designed to extract the exact location of core and delta points. Usage of the proposed directional masks speeds up the process and the proposed adaptive singular point detection method increases the accuracy of the algorithm.     

一种快速鲁棒的视频序列运动目标检测方法

稀疏表示已经成为运动目标检测的有效方法之一,但其还没有很好地解决目标检测的快速性和鲁棒性.本文基于最大后验概率提出了一种快速鲁棒的运动目标检测模型,并设计了该模型的求解算法.该算法包括两个阶段：在第一阶段利用编码迁移实现稀疏系数的快速求解;在第二阶段基于运动目标的空间连续性结构,利用图切实现目标检测.在多个具有挑战性的图像序列上的实验结果表明,与其他经典运动目标检测算法相比,本文方法在快速性和鲁棒性方面具有较优的性能.     

蒸发冷却空调在通信机房（基站）中的应用探讨

通信机房（基站）的空调系统,要求全年制冷运行,节能潜力大。在通信机房的节能改造过程中,采用蒸发冷却空调进行降温的方式节能效果显著。结合通信机房对空调系统的要求,分析了蒸发冷却空调应用于通信机房（基站）在通风、降温、加湿、净化等方面的优势,并对一通信机房,进行了节能分析。     

基于几何结构的SAR图像无监督变化检测方法

 传统的基于统计特性的SAR图像变化检测方法,易受成像条件的影响而误差很大.本文针对图像内在几何结构,提出了一种无监督SAR图像变化检测算法.通过模糊微分构造描述图像局部特征的近似完整数据集,并充分利用图像局部邻域信息和空间相关性,构造深入描述图像结构化信息的特征矢量空间,最后通过基于模拟退火的K均值(SAKM)聚类算法,实现图像变化区域与非变化区域的分类.实验证明,本文方法不仅能够很好的检测出图像的轮廓变化和图像的区域变化,而且对噪声及配准精度均具有很好的鲁棒性.