通信类英文文献及翻译
姓名：峻霖班级：通信143班学号：2014101108
附录
一、英文原文：
Detecting Anomaly Traf?c using Flow Data in the
real VoIP network
I. INTRODUCTION
Recently, many SIP[3]/RTP[4]-based VoIP applications and services have appeared and their penetration ratio is gradually increasing due to the free or cheap call charge and the easy subscription method. Thus, some of the subscribers to the PSTN service tend to change their home telephone services to VoIP products. For example, companies in Korea such as LG Dacom, Samsung Net- works, and KT have begun to deploy SIP/RTP-based VoIP services. It is reported that more than ?ve million users have subscribed the commercial VoIP services and 50% of all the users are joined in 2009 in Korea [1]. According to IDC, it is expected that the number of VoIP users in US will increase to 27 millions in 2009 [2]. Hence, as the VoIP service becomes popular, it is not surprising that a lot of VoIP anomaly traf?c has been already known [5]. So, Most commercial service such as VoIP services should provide essential security functions regarding privacy, authentication, integrity and
non-repudiation for preventing malicious traf?c. Particu- larly, most of current SIP/RTP-based VoIP services supply the minimal security function related with authentication. Though secure transport-layer protocols such as Transport Layer Security (TLS) [6] or Secure RTP (SRTP) [7] have been standardized, they have not been fully implemented and deployed in current VoIP applications because of the overheads of implementation and performance. Thus, un-encrypted VoIP packets could be easily sniffed and forged, especially in wireless LANs. In spite of authentication,the authentication keys such as MD5 in the SIP header could be maliciously exploited, because SIP is a text-based protocol and unencrypted SIP packets are easily decoded. Therefore, VoIP services are very vulnerable to attacks exploiting SIP and RTP. We aim at proposing a VoIP anomaly traf?c detection method using the ?ow-based traf?c measurement archi-tecture. We consider three representative VoIP anomalies called CANCEL, BYE Denial of Service (DoS) and RTP ?ooding attacks in this paper, because we found that malicious users in wireless LAN could easily perform these attacks in the real VoIP network. For monitoring VoIP packets, we employ the IETF IP Flow Information eXport (IPFIX) [9] standard that is based on NetFlow v9. This traf?c measurement method provides a ?exible and extensible template structure for various protocols, which is useful for observing SIP/RTP ?ows [10]. In order to capture and export VoIP packets into IPFIX ?ows, we de?ne two additional IPFIX templates for SIP and RTP ?ows. Furthermore, we
add four IPFIX ?elds to observe 802.11 packets which are necessary to detect VoIP source spoo?ng attacks in WLANs.
II. RELATED WORK
[8] proposed a ?ooding detection method by the Hellinger Distance (HD) concept. In [8], they have pre- sented INVITE, SYN and RTP ?ooding detection meth-ods. The HD is the difference value between a training data set and a testing data set. The training data set collected traf?c over n sampling period of duration Δ t.The testing data set collected traf?c next the training data set in the same period. If the HD is close to ‘1’, this testing data set is regarded as anomaly traf?c. For using this method, they assumed that initial training data set did not have any anomaly traf?c. Since this method was based on packet counts, it might not easily extended to detect other anomaly traf?c except ?ooding. On the other hand, [11] has proposed a VoIP anomaly traf?c detection method using Extended Finite State Machine (EFSM). [11] has suggested INVITE ?ooding, BYE DoS anomaly traf?c and media spamming detection methods. However, the state machine required more memory because it had to maintain each ?ow. [13] has presented NetFlow-based VoIP anomaly detection methods for INVITE, REGIS-TER, RTP ?ooding, and REGISTER/INVITE scan. How-ever, the VoIP DoS attacks considered in this paper were not considered. In [14], an IDS approach to detect SIP anomalies was developed, but only simulation results are presented. For monitoring VoIP traf?c, SIPFIX [10] has been proposed as an IPFIX extension. The key ideas of the SIPFIX are application-layer inspection and
SDP analysis for carrying media session information. Yet, this paper presents only the possibility of applying SIPFIX to DoS anomaly traf?c detection and prevention. We described the preliminary idea of detecting VoIP anomaly traf?c in [15]. This paper elaborates BYE DoS anomaly traf?c and RTP ?ooding anomaly traf?c detec-tion method based on IPFIX. Based on [15], we have considered SIP and RTP anomaly traf?c generated in wireless LAN. In this case, it is possible to generate the similiar anomaly traf?c with normal VoIP traf?c, because attackers can easily extract normal user information from unencrypted VoIP packets. In this paper, we have extended the idea with additional SIP detection methods using information of wireless LAN packets. Furthermore, we have shown the real experiment results at the commercial VoIP network.
III. THE VOIP ANOMALY TRAFFIC DETECTION METHOD
A. CANCEL DoS Anomaly Traf?c Detection
As the SIP INVITE message is not usually encrypted, attackers could extract ?elds necessary to reproduce the forged SIP CANCEL message by snif?ng SIP INVITE packets, especially in wireless LANs. Thus, we cannot tell the difference between the normal SIP CANCEL message and the replicated one, because the faked CANCEL packet includes the normal ?elds inferred from the SIP INVITE message. The attacker will perform the SIP CANCEL DoS attack at the same wireless LAN, because the purpose of the SIP CANCEL attack is to prevent the normal call estab-lishment when a victim is waiting for calls. Therefore, as soon
as the attacker catches a call invitation message for a victim, it will send a SIP CANCEL message, which makes the call establishment failed. We have generated faked SIP CANCEL message using sniffed a SIP INVITE message.Fields in SIP header of this CANCEL message is the same as normal SIP CANCEL message, because the attacker can obtain the SIP header ?eld from unencrypted normal SIP message in wireless LAN environment. Therefore it is impossible to detect the CANCEL DoS anomaly traf?c using SIP headers, we use the different values of the wireless LAN frame. That is, the sequence number in the 802.11 frame will tell the difference between a victim host and an attacker. We look into source MAC address and sequence number in the 802.11 MAC frame including a SIP CANCEL message as shown in Algorithm 1. We compare the source MAC address of SIP CANCEL packets with that of the previously saved SIP INVITE ?ow. If the source MAC address of a SIP CANCEL ?ow is changed, it will be highly probable that the CANCEL packet is generated by a unknown user. However, the source MAC address could be spoofed. Regarding 802.11 source spoo?ng detection, we employ the method in [12] that uses sequence numbers of 802.11 frames. We calculate the gap between n-th and (n-1)-th 802.11 frames. As the sequence number ?eld in a 802.11 MAC header uses 12 bits, it varies from 0 to 4095. When we ?nd that the sequence number gap between a single SIP ?ow is greater than the threshold value of N that will be set from the experiments, we determine that the SIP host address as been spoofed for the anomaly traf?c.
B. BYE DoS Anomaly Traf?c Detection
In commercial VoIP applications, SIP BYE messages use the same authentication ?eld is included in the SIP IN-VITE message for security and accounting purposes. How-ever, attackers can reproduce BYE DoS packets through snif?ng normal SIP INVITE packets in wireless LANs.The faked SIP BYE message is same with the normal SIP BYE. Therefore, it is dif?cult to detect the BYE DoS anomaly traf?c using only SIP header information.After snif?ng SIP INVITE message, the attacker at the same or different subnets could terminate the normal in- progress call, because it could succeed in generating a BYE message to the SIP proxy server. In the SIP BYE attack, it is dif?cult to distinguish from the normal call termination procedure. That is, we apply the timestamp of RTP traf?c for detecting the SIP BYE attack. Generally, after normal call termination, the bi-directional RTP ?ow is terminated in a bref space of time. However, if the call termination procedure is anomaly, we can observe that a directional RTP media ?ow is still ongoing, whereas an attacked directional RTP ?ow is broken. Therefore, in order to detect the SIP BYE attack, we decide that we watch a directional RTP ?ow for a long time threshold of N sec after SIP BYE message. The threshold of N is also set from the experiments.Algorithm 2 explains the procedure to detect BYE DoS anomal traf?c using captured timestamp of the RTP packet. We maintain SIP session information between clients with INVITE and OK messages including the same Call-ID and 4-tuple (source/destination IP Address and port number) of the BYE
packet. We set a time threshold value by adding Nsec to the timestamp value of the BYE message. The reason why we use the captured timestamp is that a few RTP packets are observed under 0.5 second. If RTP traf?c is observed after the time threshold, this will be considered as a BYE DoS attack, because the VoIP session will be terminated with normal BYE messages. C. RTP Anomaly Traf?c Detection Algorithm 3 describes an RTP ?ooding detection method that uses SSRC and sequence numbers of the RTP header. During a single RTP session, typically, the same SSRC value is maintained. If SSRC is changed, it is highly probable that anomaly has occurred. In addition, if there is a big sequence number gap between RTP packets, we determine that anomaly RTP traf?c has happened. As inspecting every sequence number for a packet is dif?cult, we calculate the sequence number gap using the ?rst, last, maximum and minimum sequence numbers. In the RTP header, the sequence number ?eld uses 16 bits from 0 to 65535. When we observe a wide sequence number gap in our algorithm, we consider it as an RTP ?ooding attack.
IV. PERFORMANCE EVALUATION
A. Experiment Environment
In order to detect VoIP anomaly traf?c, we established an experimental environment as ?gure 1. In this envi-ronment, we employed two VoIP phones with wireless LANs, one attacker, a wireless access router and an IPFIX ?ow collector. For the realistic performance evaluation, we directly used one of the working VoIP networks deployed in Korea where an 11-digit telephone number (070-XXXX-XXXX) has been assigned to a SIP phone.With wireless SIP phones supporting 802.11, we could make calls to/from the PSTN or cellular phones. In the wireless access router, we used two wireless LAN cards- one is to support the AP service, and the other is to monitor 802.11 packets. Moreover, in order to observe VoIP packets in the wireless access router, we modi?ed nProbe [16], that is an open IPFIX ?ow generator, to create and export IPFIX ?ows related with SIP, RTP, and 802.11 information. As the IPFIX collector, we have modi?ed libip?x so that it could provide the IPFIX ?ow decoding function for SIP, RTP, and 802.11 templates. We used MySQL for the ?ow DB.
B. Experimental Results
In order to evaluate our proposed algorithms, we gen-erated 1,946 VoIP calls with two commercial SIP phones and a VoIP anomaly traf?c generator. Table I shows our experimental results with precision, recall, and F-score that is the harmonic mean of precision and recall. In CANCEL DoS anomaly traf?c detection, our algorithm represented a few false negative cases, which was related with the gap threshold of the sequence number in 802.11 MAC header. The average of the F-score value for detecting the SIP CANCEL anomaly is 97.69%.For BYE anomaly tests, we generated 755 BYE mes-sages including 118 BYE DoS anomalies in the exper-iment. The proposed BYE DoS anomaly traf?c detec-tion algorithm found 112 anomalies with the F-score of 96.13%. If an RTP ?ow is terminated before the threshold, we regard the anomaly ?ow as a normal one. In this algorithm, we extract RTP session information from INVITE and OK or session description messages using the same Call-ID of BYE message. It is possible not to capture those packet, resulting in a few false-negative cases. The RTP ?ooding anomaly traf?c detection experiment for 810 RTP sessions resulted in the F score of 98%.The reason of false-positive cases was related with the sequence number in RTP header. If the sequence number of anomaly traf?c is overlapped with the range of the normal traf?c, our algorithm will consider it as normal traf?c.
V. CONCLUSIONS
We have proposed a ?ow-based anomaly traf?c detec-tion method against SIP and RTP-based anomaly traf?c in this paper. We presented VoIP anomaly traf?c detection methods with ?ow data on the wireless access router. We used the IETF IPFIX standard to monitor SIP/RTP ?ows passing through wireless access routers, because its template architecture is easily extensible to several protocols. For this purpose, we de?ned two new IPFIX templates for SIP and RTP traf?c and four new IPFIX ?elds for 802.11 traf?c. Using these IPFIX ?ow templates,we proposed CANCEL/BYE DoS and RTP ?ooding traf?c detection algorithms. From experimental results on the working VoIP network in Korea, we showed that our method is able to detect three representative VoIP attacks on SIP phones. In CANCEL/BYE DoS anomaly traf?c
detection method, we employed threshold values about time and sequence number gap for class?cation of normal and abnormal VoIP packets. This paper has not been mentioned the test result about suitable threshold values. For the future work, we will show the experimental result about evaluation of the threshold values for our detection method.
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Advantages of Managed Code Microsoft intermediate language shares with Java byte code the idea that it is a low-level language witha simple syntax , which can be very quickly translated intonative machine code. Having this well-defined universal syntax for code has significant advantages. Platform independence First, it means that the same file containing byte code instructions can be placed on any platform; atruntime the final stage of compilation can then be easily accomplished so that the code will run on thatparticular platform. In other words, by compiling to IL we obtain platform independence for .NET, inmuch the same way as compiling to Java byte code gives Java platform independence. Performance improvement IL is actually a bit more ambitious than Java bytecode. IL is always Just-In-Time compiled (known as JIT), whereas Java byte code was ofteninterpreted. One of the disadvantages of Java was that, on execution, the process of translating from Javabyte code to native executable resulted in a loss of performance. Instead of compiling the entire application in one go (which could lead to a slow start-up time), the JITcompiler simply compiles each portion of code as it is called (just-in-time). When code has been compiled.once, the resultant native executable is stored until the application exits, so that it does not need to berecompiled the next time that portion of code is run. Microsoft argues that this process is more efficientthan compiling the entire application code at the start, because of the likelihood that large portions of anyapplication code will not actually be executed in any given run. Using the JIT compiler, such code willnever be compiled.
计算机专业英语翻译
国家计算机教育认证 计算机英语 计算机英语词汇对译 蒙阴高新电脑学校 资料整理：孙波 IT CFAC gaoxindiannaoxuexiao
2010年9月1日
?PC personal computer 个人计算机 ?IBM International Business Machine 美国国际商用机器公司的公司简称，是最早推出的个人 计算机品牌。 ?Intel 美国英特尔公司，以生产CPU芯片著称。 ?Pentium Intel公司生产的586 CPU芯片,中文译名为“奔腾”。 ?Address地址 ?Agents代理 ?Analog signals模拟信号 ?Applets程序 ?Asynchronous communications port异步通信端口 ?Attachment附件 ?Access time存取时间 ?access存取 ?accuracy准确性 ?ad network cookies广告网络信息记录软件 ?Add-ons 插件 ?Active-matrix主动矩阵 ?Adapter cards适配卡 ?Advanced application高级应用 ?Analytical graph分析图表 ?Analyze分析 ?Animations动画 ?Application software 应用软件 ?Arithmetic operations算术运算 ?Audio-output device音频输出设备 ?Basic application基础程序 ?Binary coding schemes二进制译码方案 ?Binary system二进制系统 ?Bit比特 ?Browser浏览器 ?Bus line总线 ?Backup tape cartridge units备份磁带盒单元 ?Business-to-consumer企业对消费者 ?Bar code条形码 ?Bar code reader条形码读卡器 ?Bus总线 ?Bandwidth带宽 ?Bluetooth蓝牙 ?Broadband宽带 ?Business-to-business企业对企业电子商务 ?cookies-cutter programs信息记录截取程序 ?cookies信息记录程序
(完整word版)单片机外文文献翻译
中文资料原文 单片机 单片机也被称为微控制器（Microcontroller Unit），常用英文字母的缩写MCU表示单片机，它最早是被用在工业控制领域。单片机由芯片内仅有CPU的专用处理器发展而来。最早的设计理念是通过将大量外围设备和CPU集成在一个芯片中，使计算机系统更小，更容易集成进复杂的而对体积要求严格的控制设备当中。INTEL的Z80是最早按照这种思想设计出的处理器，从此以后，单片机和专用处理器的发展便分道扬镳。 早期的单片机都是8位或4位的。其中最成功的是INTEL的8031，因为简单可靠而性能不错获得了很大的好评。此后在8031上发展出了MCS51系列单片机系统。基于这一系统的单片机系统直到现在还在广泛使用。随着工业控制领域要求的提高，开始出现了16位单片机，但因为性价比不理想并未得到很广泛的应用。90年代后随着消费电子产品大发展，单片机技术得到了巨大提高。随着INTEL i960系列特别是后来的ARM系列的广泛应用，32位单片机迅速取代16位单片机的高端地位，并且进入主流市场。而传统的8位单片机的性能也得到了飞速提高，处理能力比起80年代提高了数百倍。目前，高端的32位单片机主频已经超过300MHz，性能直追90年代中期的专用处理器，而普通的型号出厂价格跌落至1美元，最高端[1]的型号也只有10美元。当代单片机系统已经不再只在裸机环境下开发和使用，大量专用的嵌入式操作系统被广泛应用在全系列的单片机上。而在作为掌上电脑和手机核心处理的高端单片机甚至可以直接使用专用的Windows和Linux操作系统。 单片机比专用处理器更适合应用于嵌入式系统，因此它得到了最多的应用。事实上单片机是世界上数量最多的计算机。现代人类生活中所用的几乎每件电子和机械产品中都会集成有单片机。手机、电话、计算器、家用电器、电子玩具、掌上电脑以及鼠标等电脑配件中都配有1-2部单片机。而个人电脑中也会有为数不少的单片机在工作。汽车上一般配备40多部单片机，复杂的工业控制系统上甚至可能有数百台单片机在同时工作！单片机的数量不仅远超过PC机和其他计算的总和，甚至比人类的数量还要多。 单片机又称单片微控制器,它不是完成某一个逻辑功能的芯片,而是把一个计算机系统集成到一个芯片上。相当于一个微型的计算机，和计算机相比，单片机只缺少了I/O设备。概括的讲：一块芯片就成了一台计算机。它的体积小、质量轻、价格便宜、为学习、应用和开发提供了便利条件。同时，学习使用单片机是了解计算机原理与结构的最佳选择。
夹具设计英文文献
A review and analysis of current computer-aided fixture design approaches Iain Boyle, Yiming Rong, David C. Brown Keywords: Computer-aided fixture design Fixture design Fixture planning Fixture verification Setup planning Unit design ABSTRACT A key characteristic of the modern market place is the consumer demand for variety. To respond effectively to this demand, manufacturers need to ensure that their manufacturing practices are sufficiently flexible to allow them to achieve rapid product development. Fixturing, which involves using fixtures to secure work pieces during machining so that they can be transformed into parts that meet required design specifications, is a significant contributing factor towards achieving manufacturing flexibility. To enable flexible fixturing, considerable levels of research effort have been devoted to supporting the process of fixture design through the development of computer-aided fixture design (CAFD) tools and approaches. This paper contains a review of these research efforts. Over seventy-five CAFD tools and approaches are reviewed in terms of the fixture design phases they support and the underlying technology upon which they are based. The primary conclusion of the review is that while significant advances have been made in supporting fixture design, there are primarily two research issues that require further effort. The first of these is that current CAFD research is segmented in nature and there remains a need to provide more cohesive fixture design support. Secondly, a greater focus is required on supporting the detailed design of a fixture’s physical structure. 2010 Elsevier Ltd. All rights reserved. Contents 1. Introduction (2) 2. Fixture design (2) 3. Current CAFD approaches (4) 3.1 Setup planning (4) 3.1.1 Approaches to setup planning (4) 3.2 Fixture planning (4) 3.2.1 Approaches to defining the fixturing requirement (6) 3.2.2 Approaches to non-optimized layout planning (6) 3.2.3 Approaches to layout planning optimization (6) 3.3 Unit design (7) 3.3.1 Approaches to conceptual unit design (7)