基于增强响应信任链的SIP安全机制

SIP因自身缺少有力的安全机制而面临很多安全威胁,其中最为突出的威胁是利用响应消息进行的攻击。文中通过扩展SIP协议,提出了一种基于增强响应信任链的SIP安全机制。该安全机制通过请求消息和响应消息提供逐跳实体之间安全认证,有效地阻止了利用响应消息进行的攻击,保证了SIP会话参与者身份的真实性以及通信数据的完整性。     

SIP视频会议中服务器的研究与改进

视频会议系统中会议服务器决定着会议的稳定性、规模和质量.通过研究SIP协议、SIP协议实体和SIP视频会议中服务器的结构等,对现有结构和服务器进行了改进和设计.采用负载均衡方法,提高了系统动态自适应能力,扩大了视频会议的规模.利用SIP消息分发以及优先处理机制,进一步提高了视频会议服务器的消息处理效率,以解决消息并发和消息拥塞的问题,提高系统的可靠性.     

SIP与ISUP的互通

本文讨论了ISUP和SIP映射方法，并在讲述SIP和ISUP的信令配合过程的基础上，分析了消息级别上ISUP和SIP消息间的映射。     

SIP协议栈的研究

本文介绍了会话初始化协议(SIP)的基本内容，提出了基于C 语言的SIP协议栈的设计和实现方案，设计了SIP协议栈的结构、消息的收发和并发处理机制。     

SIP协议在VoIP中的应用

SIP协议是NGN中的重要协议，越来越得到业界的重视。本文简单介绍了VoIP和SIP协议的含义，并从背景、功能、主要消息这几个方面对SIP协议的工作原理进行了介绍，分析了SIP呼叫建立的流程。     

改进的HTTP摘要认证方案的设计与实现

由于现有的认证机制不能有效解决会话初始协议(SIP)消息传送时网络侦听的问题,因此SIP网络传输时存在易遭受异常消息攻击、数据包被侦听、密文被分析等诸多安全威胁.文章经比较分析、研究改进,应用一个并行多进程的SIP非法消息检测流程,扩展了SIP认证头域,引进了密文隐写系统,能有效保证应用层的安全.实验结果验证了该方案的有效性.     

基于SIP的下一代多媒体会议架构技术分析

系统全面地介绍了基于XCON会议模型的SIP会议技术架构，主要实体例如会议策略协议及消息通知机制，以及该技术的发展现状。同时与H．323标准作了比较，分析其优势。     

SIP协议系统模型的形式化研究

通信协议形式化是提高其可靠性和正确性的重要手段.会话初始协议SIP是软交换的一个主要协议,应用形式化方法研究了SIP协议的结构及系统模型,主要从系统级和功能级上使用形式化规格描述语言SDL和消息顺序图MSC对SIP协议主要系统组件进行形式化描述,得到了SIP协议的形式化规范,并应用形式化方法进行了验证.为SIP协议部件库研究开发提供形式化技术基础.     

SIP协议分析及其安全性研究

SIP正逐步取代H.323协议成为VoIP网络的核心信令控制协议.综述了SIP协议的功能、实体、消息结构,分析了SIP面临的主要安全问题,介绍了IPSec,TLS,HTTP摘要认证和S/MIME等目前流行的SIP安全机制,通过比较分析,指出各种安全措施的主要优缺点.最后对SIP安全问题进行了总结,并指出下一步解决SIP安全问题的研究方向.     

SIP信令与媒体流穿透NAT的实现

从会话初始化协议(SIP)消息的特点出发.基于网络地址转换(NAT)和防火墙自身的角度考虑,提出了一种无需扩展SIP协议的应用层解决方案.该方案通过引入UDP对NAT的简单穿透(STUN)协议,获得IP地址和端口的映射绑定关系,修改SIP和会话描述协议(SDP)消息中的内容来保证通信连接,从而实现了对NAT的穿透.     

Effect of microwave annealing on SOI MOSFETs: Post-metal annealing with low thermal budget

We investigate the effect of microwave irradiation (MWI) on silicon-on-insulator (SOI) based MOSFETs. The MWI technique is used for post-metal annealing (PMA) in air ambient, and compared with conventional thermal annealing in a forming gas ambient. This type of annealing not only constitutes a low cost, short time, low temperature, vacuum-free alternative to conventional post-metal annealing methods, but it also allows much lower thermal budgets, which, in turn, minimizes dopant motion, redistribution, and diffusion. The MWI treated MOSFETs showed superior electrical characteristics in terms of field effect mobility, on-off ratio, subthreshold swing, interface trap density, stability, and hot carrier effect immunity. Therefore, MWI technology is expected to become a promising annealing method for silicon-based processes, with low cost and low thermal budget.     

Microwave breast imaging: 3-D forward scattering simulation

Active microwave imaging (MWI) is emerging as a promising technique for the detection of biomedical anomalies such as breast cancer because of the high electrical contrasts between malignant tumors and normal tissue. Previously, we have developed fast two-dimensional forward and inverse scattering algorithms for MWI systems. In this paper, we report the full three-dimensional (3-D) forward scattering simulation in order to account for 3-D effects and to provide a fast solver in future 3-D nonlinear inverse scattering methods. The 3-D fast forward method is based on the stabilized biconjugate-gradient fast Fourier transform (BCGS-FFT) algorithm. The method has been validated for various MWI measurement scenarios. Using this fast simulation method, we demonstrate the importance of accounting for 3-D effects in MWI, and we compare numerical results with the measurements from an experimental prototype.     

PLASMA DENSITY MEASUREMENTS OF CONFINED CAPACITIVELY COUPLED PLASMA BY MICROWAVE INTERFEROMETER AND ION ENERGY DISTRIBUTION FUNCTION METHODS

Measurements of hydrogen plasma density are made in a symmetric single frequency confined capacitively coupled plasma (C-CCP) RF system. Comparison is made between density measured by microwave interferometer (MWI) and electrode wall ion density gathered from Ion Energy Distribution Function (IEDF) responses. Ion number density at electrode wall is obtained by two methods as IEDF integration method and IEDF splitting method. Both methods were compared with MWI and a linear relation is obtained between both methods and MWI. It is demonstrated that electrode wall surface density obtained by IEDF splitting and IEDF integral methods are about 50,000 times less than the bulk plasma density, and integral method reads more data than splitting method. The three different measurement results are compared and they are in good qualitative agreement; the deviation in ratio of bulk plasma density measured by MWI to number density at the electrode wall resolved from ion energy distribution function is greatest at highest pressure or electrode voltages/powers. The reasons for deviations are explained by analysis of the potential drop across the presheath decreases with respect to increased applied power.     

SEM observation of the insect prepared by microwave irradiation

The ptilinum of the fly and the compound eye are among the most fragile organs encountered during conventional procedures of morphological sample fixation. In order to identify a fixative suitable for preparing such samples for scanning electron microscopy, we examined various fixation conditions using microwave irradiation (MWI). The conditions examined were: (i) fixatives; (ii) temperature; (iii) concentration; (iv) duration; (v) dehydration; and (vi) substitution. The identified optimal conditions were 5% glutaraldehyde with MWI (350 W, 5 min). The MWI was continued until the maximal temperature of 75 degrees C was attained, followed by intermittent irradiation to maintain a temperature of 75 degrees C. After irradiation, the sample was left at room temperature for 24 h in the fixative and then dehydrated in increasing concentrations of ethanol. Each step in the ethanol series lasted for 24 h. The final absolute ethanol step included three solution changes, with each incubation lasting 1 h. A subsequent stepwise substitution of t-butyl alcohol for ethanol was conducted by reducing the ratio of 100% ethanol to t-butyl alcohol from 2:1 to 1:1 and then 1:2 (24 h each). The substitution was completed by three solution changes using 100% t-butyl alcohol, 30 min each. The best results were obtained by freeze-drying samples using t-butyl alcohol. The use of MWI improved fixative permeation, which occurred at a uniform rate throughout the sample. Comparison with temperature in a water bath at 75 degrees C indicated that the fixation effect of MWI was due to its heat generation in addition to some unknown mechanism.     

Mesh wave impedance concept in FDTD technique

A new mesh wave impedance (MWI) that characterises the properties of waves travelling along the along the mesh according to the FDTD technique is defined and the formulas are derived in plane wave and two-dimensional cases. The MWI depends on the parameters of both the medium (μ, ϵ) and the mesh (cell size Δ, time step Δt), as well as the frequency. The wave reflection coefficient that occurs at the interface of two meshes with different mesh wave impedances have been obtained. Numerical examples have verified the mesh wave impedance concept and the reflection coefficient formula     

Rapid microwave-assisted synthesis of silver decorated-reduced graphene oxide nanoparticles with enhanced photocatalytic activity under visible light

A facile, fast, and scalable microwave irradiation (MWI) method for the synthesis of Ag nanoparticles (Ag NPs) dispersed on graphene sheets has been developed. The reduction of graphene oxide takes place in ethanol solution within 2 min of MWI without any additional reducing agent or complicated treatment. The morphology and microstructure of the as-prepared hybrid were characterized by Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) images. The result showed the Ag NPs with an average size of 5–10 nm decorated on the rGO sheets. X-ray powder diffraction (XRD) determined that the crystallographic structure of Ag is face-centered cubic and there was a strong interaction between Ag NPs and rGO sheets. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) showed that GO had been reduced to rGO in our hybrid. Moreover, visible photocatalytic activity of the rGO–Ag nanocomposites was tested using Rhodamine B (RhB) as the model contaminant. This result indicates that rGO–Ag nanocomposites display distinctly enhanced photocatalytic activities. The investigation gave a promise to the development of original yet highly efficient graphene-based photocatalysts that utilize visible light as an energy source.     

基于虚拟机的VPN综合实验设计

虚拟专用网络(VPN)指的是在公用网络上建立专用网络的技术,可以基于PPTP、L2TP/IPSec或者SSTP隧道来建立。传统VPN实验是基于PPTP协议的。文中设计了更广泛的VPN实验:基于L2TP over IPSecs协议和SSTP协议。而基于虚拟机平台的实验具有更方便、更经济的优点。此外,该实验还涉及到了Windows平台上各种安全设置,如活动目录、DNS服务器、DHCP服务器、防火墙、证书颁发中心CA等,具有很强的综合性。     

下一代电信网络的核心--软交换技术

如何建设下一代电信网络,是电信运营商极为关注的课题.文中系统论述了下一代网络的核心技术、组网结构、所具有的功能,并对softswitch中使用的有关协议进行了较为详细的说明和比较.     

A Real Time Transport Scheme for Wireless Multimedia Communications

In wireless communications systems, a mobile station is typically equipped with limited processing capability and buffer space for transmitting and receiving. The radio link is usually found to be noisy and its propagation delay is sometimes non-negligible as compared with the packet transmission delay. And because of the necessity of flow control and packet retransmission upon error, the delay and throughput performance cannot satisfy the need of a particular traffic type, i.e., real-time multimedia. This paper presents a scheme suitable for the above condition, called the Burst-oriented Transfer with Time-bounded Retransmission (BTTR). The present scheme uses a large transmission window for sending/receiving a burst of time-sensitive data and, within this window, another smaller observation window is repeatedly used for error status feedback via the backward channel. There is time limitation on each retransmission such that the burst of data can be received in a timely manner, however, with some degradation on the packet loss rate. An analysis is given in terms of the expectations of delay, throughput, and packet drop rate. A comparison with an error-free link protocol will also be given. The result shows that the proposed scheme can meet the delay and throughput requirement under reasonable packet drop rate.     

An efficient energy consumption model using data aggregation for wireless sensor network

Wireless sensor networks (WSNs) have become increasingly important in recent years. Small and low-power sensor nodes make up these sensor networks. A random distribution of nodes is made throughout an unmanaged target region. One of WSN's key challenges is its limited and irreplaceable energy supply. In most situations, sensor nodes cannot be replaced since they operate in a hostile physical environment. The act of gathering and aggregating usable data from different sensor nodes situated to perceive almost the same attribute of the occurrence is known as data aggregation. The mathematical model is used in this research study to generate cluster-based data aggregation, which is an effective technique to increase energy usage by minimising the number of data transfers. The proposed mathematical model-based data aggregation (MM-DA) attains a 97% packet delivery ratio with minimal energy consumption. The MM-DA outperforms other existing approaches in terms of packet delivery ratio (PDR), energy consumption (EC), network lifetime and control overhead.