Analysis of TCP’s Computational Energy Cost for Mobile Computing

1.1 在多道程序和分时环境中，多个用户同时共享一个系统，这种情况导致多种安全问题。

a. 列出此类的问题b.在一个分时机器中，能否确保像在专用机器上一样的安全度？并解释之。

Answer:a.窃取或者复制某用户的程序或数据；没有合理的预算来使用资源（CPU，内存，磁盘空间，外围设备）ｂ．应该不行，因为人类设计的任何保护机制都会不可避免的被另外的人所破译，而且很自信的认为程序本身的实现是正确的是一件困难的事。

1.2 资源的利用问题在各种各样的操作系统中出现。

试例举在下列的环境中哪种资源必须被严格的管理。

（ａ）大型电脑或迷你电脑系统（ｂ）与服务器相联的工作站（ｃ）手持电脑Answer: （ａ）大型电脑或迷你电脑系统：内存和CPU 资源，外存，网络带宽（ｂ）与服务器相联的工作站：内存和 CPU 资源（ｃ）手持电脑：功率消耗，内存资源1.3 在什么情况下一个用户使用一个分时系统比使用一台个人计算机或单用户工作站更好？Answer:当另外使用分时系统的用户较少时，任务十分巨大，硬件速度很快，分时系统有意义。

充分利用该系统可以对用户的问题产生影响。

比起个人电脑，问题可以被更快的解决。

还有一种可能发生的情况是在同一时间有许多另外的用户在同一时间使用资源。

当作业足够小，且能在个人计算机上合理的运行时，以及当个人计算机的性能能够充分的运行程序来达到用户的满意时，个人计算机是最好的，。

1.4 在下面举出的三个功能中，哪个功能在下列两种环境下，(a)手持装置(b)实时系统需要操作系统的支持？(a)批处理程序(b)虚拟存储器(c)分时Answer:对于实时系统来说，操作系统需要以一种公平的方式支持虚拟存储器和分时系统。

对于手持系统，操作系统需要提供虚拟存储器，但是不需要提供分时系统。

批处理程序在两种环境中都是非必需的。

1.5 描述对称多处理（ＳＭＰ）和非对称多处理之间的区别。

多处理系统的三个优点和一个缺点？Answer:ＳＭＰ意味着所以处理器都对等，而且I/O 可以在任何处理器上运行。

比较题1.SRAM and DRAM*RAM is short for random access memory.@Static RAM(SRAM) keeps data in the main memory,without frequent refreshing,for as long as power is supplied to the cicuit. SRAM is very fast but it is much more expensive than DRAM and takes more space than DRAM. Dynamic RAM(DRAM) is the most often used RAM in today's computer.DRAM can hold its data if it is refreshed by special logic called the refresh circuit.It is much cheaper and take much less space than DRAM.2.System software and Application software*What is software?Collection of programs is called software .*What is computer softwar?It is defined as the instructions and associated data , stored in electronic format , that direct the computer to accomplish task.*what is the shareware ?Shareware is copyrighted software marketed under a “try before you buy” policy.@Systemsoftware is the stuff that make your computer work.The application software is generally the computer programs which are used for the purpose of performing special tasks using a computer,it trains the PC‟s brain for higher cognitive functions rather than just keeping the PC alive and connected to the other.*Examples about Application Software:(1)Accounting software(2)Collaboratire software(3)Compilers and Interpreters(4)Computers Games(5)Database(6)Educational software(7)E-mailN and W ANLAN:A LAN is a high-speed data network that covers a relatively small geographic area .It typically connects workstations, personal computer, printers, servers, and other devices.W AN:A W AN connect multiple geopgraphically nearby LANs to one another over great geographic distances. The speed available on a W AN waries depending on the cost of the connections and may be low. W ANs opeate using routers , which can “choose ” the most appropriate path for data to take to reacha network node.4.What's the difference between Software Engneering & System Engneering ?@System Engineernig is concerned with all aspects of computer based systems developmentincluding hardware ,software and process engineering.Software Engineering is part of this more general process.5.CRT & LCD@CRT: Calhoole ray lube displays had a standarditool form factor owing to the required shape of heavriy vacuum tubeLCD;Liquid cryslal Displays have a new seirse of style.Free from the bulky shap of CRT,today's flat panel vendors are letting their imaginations run free with monitors that are colourd and shaped to match a design concept.*Advantage of LCD monitor①LCD monitor consume less power②Do not produce electromagnetic radiation as CTRs do③Are right and slim in size④Do not flickers like CRT’s⑤Full viewable size6.Synchronous & Asynchronous@S:you need two separated cables with every clock pulse one data bit is transfermed.A:transmission clock and data are tranfermed with only one cable.7.RISC & CISC@CISC:Complex Instruction Set ComputerIt is microprocessor designIt is used to transulations are complex to machine understand;It is need large memory area;It is very slow in processRISC:Reduced Instruction Set ComputerIt is advanced microprocessor designIt is reduced the complex Set of CISCIt is need minimem-storageIt is very fast to compare with CISC8.Switch & Router@9.Windows OS and Unix OS@Windows OS：Be easily understood.Unix OS:The UNIX OS was desiged to let a number of programmers access the computer at the same time and share its resources.10.Multitasking & Multiuser@Multitasking：Many computers do just one thing at a time ,as anyone who uses a PC laptop can attest. Try logging onto your company …s network while opening your browser and while opening a word processing program .Chances are the processor will freeze for a few seconds while it sorts out the multiple instructions. Multiuser:The same design which permits multitasking permits multiple users to use the computer .The computer can take the commands of a number of users –determined by the design of the computer – to run programs , access files , and print documents at the same time.11.Multitasking & Parallel processing@Multitasking:A single CPU excutes several programs at onceParallel processing:More than one CPU excutes a single program12.3GPL & 4GPL@3GPL：A 3GPL was no longer a need to work in symbolics.Instead,a pogrammer could use a programming language what resembled more to the natural languages.4GPL ：A fourth generation programming language is a programming language designed with a specific purpose in mind such as the development of commercial business software.Y ou can use to build an application without the third generation progamming language.13.Paraller processing and Compilier interpreter@14.switch RL and swich GPL@pare OSI with TCP/IPSimilarities :(1)both have layers(2)both have application layers(3)both have comparable transport and Network layers(4)packet ---switched technology is assumed(5)networking professional need to know both modelsdifferences :(1)TCP/IP combines presentation and session layer functions into its application layer.(2)TCP/IP combines the OSI data link and physical layers into one layer(3)TCP/IP simpler because it has few layers(4)OSI complex because it has multiple layers(5)TCP/IP have 4 layers , but OSI have 7 layerspilers and Interpreters@Compiler:A compiler is a computer program that translate a computer program written in one computer language into a program written in another computer language.Interpreter:An interpreter is a computer program that excutes other programs.简答题1.Field in AI①Games playing:programming computers to play games such as chess and checkers.②Expert system:programming computers to make decisions I real –life situations.③Natual language:programming computers to understand natural human language.④Neural networks:systems that simulate intelligence by attemping to reproduce the types of physical connections that occur in animal brains.⑤Robotics:programming computers to see and hear and react to other sensory stimuli .2.Write sth about Quanty Computing？@It was proposed in 1970‟s.It is based on quantum physics,b y taking advantages of certain quantum physics properties of atom or nuclei that allow them to work together as quantum bits or qubits to be the computer processor and memory . 3.Nano technologyIt is a field of science atoms is meant to control individual atoms and molecules to create computer chips and other devices that are thousand of times smaller them current technologies permit.4.Explain Register & it's type?@Only register can be directly indexed for input or output of an instruction, as defined by the instruction set.Types:Data register: Used to stored integer numbersAddress register: Hold memory addresses and are used to access memory General purpose register: It store data and addressFloating point register: Used to stored floating point numbers.Constant register : It hold read only values zero or one.Vector register : It hold single instruction and multiple data(SIMD).Special purpose register: It stored internal CPU data like stack pointer or processor status wordsInstruction register: the instruction currently being executed by the processer is stored here.5.10 lines about Data W arehouse & Data marts?@Data warehouse:Data warehouses are computer based information systems that are home for "secondhand"data that originated from either another application or from an external system or source.W arehouse optimize database query and reporting tools because of their ability to analyze data.They are a way for managers and decision makers to extract information quickly and easily in order to answer questions about their business.Data marts:It are smaller than data warehouse and genera lly contain information from a single department of a business or organization.The current trend in data warehousing is to develop a data warehouse with sevral smaller related data mats for specific kinds of queries and reports.6.Multimedia@Multimedia as the name suggests is an integration of various medium of communication which include text,graphics,animation,audio,still omages and motion video in a way that provides the user with a high level of control and interaction.Multimedia can be defined as any contains three or more of the following elements:text,still images,animation,sound,video and/or hypertext navigation.7.TCP/IP@TCP and IP were developed by Department of Defence of USA research project to connect a number of different networks designed by different vendors into a network of networks.It delivered a few basic services that everyone needs like file transfer,electronic mail,remote logon across a very large number of client and sever systems.TCP/IP is composed of layers:IP-is reponsible for moving packet of data from node to node.TCP-is responsible for verifying the correct delivery of data from client to server. Sockets-is a name given to the package of sunroutines that provide access to TCP/IP on most systems.8.What's bus and it's type?A bus is an important subsystem in computer architecture which transfers data or power between computer components inside a computer or butween computers.There are two types of bus:parallel bus and serial bus.Something about I/O Bus？9.Something about I/O System instructions?@There are four I/O buses in the modern PC architecture and each of them has several functions.They may lead to internal and external ports or they lead to other controlling buses,The four buses are:ISAPCI-which is the newer high speed multifunction I/O bus.AGP-which is only used for graphices adapter.USB-which is the new low speed I/O bus to replaces ISA.11.What's Internet?@Internet is consists of computers and router they obey the rules which is definited in the network. It allows users to communicate with their friends,to send message to the internet to shall the message.12.Basic Principles of 4GL includes?@(1)The Principle of Minimum W ork(2)The Principle of MInimum Skill(3)The Principle of avoiding alien syntax and mnemonics(4)The Principle of Minimum Time(5)The Principle of Minimum errors(6)The Principle of Minimum Maintenance(7)The Principle of Minimum Results13.Something about SQL?@SQL is short for`Structured Query Languages,which comprises one of the fundamental building blocks of modern database architecture.SQL defines the methods used to create and manipulate relational database on all major platforms.14.Parallel Bus and Serial Bus?Parallel Bus,which carries data words across multiple wires.Serial Bus,which carries data in bit-serial form.15.Features of Unix?@(1)Multitasking capability(2)Multiuser capability(3)Portability(4)UNIX programs(5)Library of applications software16.Something about 5th Generation Computers?@Fifth generation computing devices are based on artificial intelligence.AI includes the following fields:(1)games playing(2)expert systems:programming computers to make decisions in real-life situations(3)natural language:programming computers to understand natural human languages(4)neural netwoks(5)robotics17.What is an Internetwok?@An internetwork is a collection of individual networks,connected by intermediate networking devices.that functions as a single large network.Internetworking refers to the industy,products,and procedures that meet the challenge of creating and administering internetworks.18.ISO and OSI@ISO stands for International Standardization Organization and OSI System Interconnect Reference Model.The ISO/OSI is one of the most important systems architectures for talking about commucations.ISO/OSI is divided into seven layers,the pupose of each layer is to offer certain services to the higher layers.(画7层图)7 layers:(1)physical layer --- transmitting individual bits from one node to the next(2)data link layer --- data representation(3)network layer --- end to end communication(4)transport layer --- provide services from internet layer to application layer(5)session layer --- communication between hosts(6)presentation(7)application layer --- provide some applicationwork : interconnection between 2 or more computerpurpose of network :(1)sharing the file and applications(2)sharing hardware deviceskinds of network :(1)UK JANET (Joint Academic Network)(2)Europe EARN (European Academic Research Network)(3)USA ARPA net (Advanced Research Projects Agency Network )Application of network:(1)resource sharinghardware (computer resource , disks , prints )software (application software )(2)information sharingeasy accessibility from anywheresearch capability(3)communicationEmail , Message broadcast.Types of network :(1)LAN (Local Area Network) network in small geographical area(2)MAN (Metropolitan Area Network) network in a city(3)W AN (Wide Area Network) spread geographical20.URLS@URL stands for uniform resource locatorA URL is the address of document on the computer简写：(1) IC --- Integrated Circuit(2) PC --- Personal Computer(3) CPU ---Central Processing Unit(4) VDU --- Visual Display Unit(5) PCI --- Peripheral Component Interconnect(6) USB ---Universal Serial Bus(7) GUI --- Graphical User Interface(8) OSI --- Open System Interconnection(9) ISO --- International Standard Organization(10) HTTP --- Hypertext Markup Language(11) TCP --- Transfer Control Protocol / Internet Protocol(12) DNS --- Domain Name System(13) FTP --- File Transfer Protocol(14) UDP --- User Datagram Protocol(15) ARP --- Address Resolution Protoco。

相互依存网络边攻击下的相继故障研究在当今的信息时代，网络已成为人们日常生活和工作中不可或缺的一部分。

网络的发展也使得世界变得更加紧密，各个国家、地区和人们通过网络来实现交流和合作。

对于我们每个人来说，网络的安全至关重要。

然而，人们不断创造新的技术，网络也不断发展，这也为网络的安全问题带来了新的挑战。

而相互依存网络边攻击下的相继故障，也是网络安全问题中的一个热点。

相互依存网络是指一个网络系统中，不同网络间的依存性和相互支持性。

这种网络系统是由多个网络构成的，它们之间没有互相独立的联系，而是相互依存、相互支持的。

例如，我们使用的电力和通信服务就是由多个网络构成的相互依存网络。

相互依存网络的攻击会影响到其他网络甚至整个系统的运行，其故障具有“连锁式”传递特性，可能导致整个网络系统崩溃。

在相互依存网络边攻击下的相继故障研究中，人们通过研究网络攻击行为和网络系统的特性，来寻找可能造成网络故障的源头并预测可能的故障传播路径。

研究表明，在网络系统中，每个节点都相互连接，节点之间的关系构成了网络的拓扑结构，如果网络中存在重要节点被攻击或发生故障，可能导致整个网络的瘫痪。

通过对网络系统中节点的“重要程度”进行分析和评估，可以有效地预测网络故障的发生。

研究表明，在相互依存网络中，有些节点虽然并不是整个系统中最重要的节点，但是在某些情况下却可能对整个网络产生重要影响。

例如，在电力系统中，变压器之间的连接节点可能导致整个电力系统的瘫痪。

而在金融系统中，银行的相互交易关系也可能引起整个系统的崩溃。

为了应对相互依存网络边攻击下的相继故障，需要采取有效的防御措施。

一方面，网络中的每个节点都应该得到保护和维护，特别是系统中的重要节点。

另一方面，应建立完善的网络安全保障机制，加强网络安全监控，避免网络攻击和故障的发生。

总之，相互依存网络边攻击下的相继故障研究是网络安全领域的一个重要研究方向，它是对网络系统的安全性能和可靠性的考验。

Energy-aware routing Aggregating traffic flows over a subset of the network devices and links Allowing other links and interconnection devices to be switched off
Adapative link rate(cont.)
Sleeping mode Consider two state of operation
a sleeping (or idle) mode a fully working mode
The difficulty is to find the desired compromise between system reactivity
Energy-Aware Application(Cont.)
Kernel-Level Network Stack
Modify the TCP protocol Introduce explicit signaling at the transport layer via a specific option (TCP SLEEP) in the TCP header In which case the other party will buffer data received from the application instead of sending it right away Enhance the energy efficiency of existing implementations Examine the energy consumption induced by the computational load of TCP Exploit some functionalities provided by the NIC

高性能计算（High-performance computing）是一种需要大量计算资源的计算方法，通常用于解决复杂的科学、工程和商业问题。

然而，为了确保计算任务能够高效地执行，我们需要对其资源需求进行分析和优化。

本文将讨论如何分析高性能计算任务的资源需求，以帮助读者更好地规划和管理计算任务。

一、任务特性分析在进行资源需求分析之前，首先需要对计算任务的特性进行分析。

不同类型的计算任务对计算资源的需求可能会有很大的差异。

例如，有些任务可能需要大量的内存和存储来处理大规模的数据集，而另一些任务可能主要需要大量的计算核心来处理复杂的计算模型。

因此，我们需要了解计算任务的类型、数据量、计算量以及运行时间等特性。

二、性能指标测量与分析在分析任务的资源需求之前，我们首先需要了解任务的性能指标。

将任务的执行时间作为性能指标是一种常用的方法。

我们可以通过测量任务的实际执行时间来了解任务对计算资源的需求。

为了准确测量性能指标，我们还需要考虑许多其他因素，如系统的负载情况、网络带宽和延迟、数据传输速度等。

这些因素可能对任务的性能产生显著影响，因此需要进行详细的分析。

三、资源需求分析现在我们已经了解了任务的特性和性能指标，可以开始进行资源需求分析了。

在分析资源需求时，我们通常需要考虑以下几个关键因素：1. CPU资源需求：根据任务的计算量，我们可以估算出所需的CPU核心数。

通常情况下，计算密集型任务需要更多的核心来处理大量的计算操作。

2. 内存需求：某些任务可能需要较大的内存空间来存储和处理数据。

我们需要根据任务要求来评估所需的内存大小。

3. 存储需求：对于处理大规模数据集的任务，我们需要足够的存储空间来存储数据。

此外，还需要考虑数据的读取和写入速度，以确保任务的正常执行。

4. 网络需求：某些任务可能需要高带宽和低延迟的网络环境。

我们需要评估任务对网络资源的需求，并选择合适的网络配置。

5. 并行性分析：许多任务可以通过并行计算来提高处理能力。

2022年职业考证-软考-网络工程师考试预测题精选专练VII（附带答案）第1套一.综合题(共25题)1.单选题在SNMPv3安全模块中的加密部分，为了防止报文内容的泄露，使用DES算法对数据进行加密，其密钥长度为（）。

问题1选项A.56B.64C.120D.128【答案】A【解析】DES算法：加密前，对明文进行分组，每组64位数据，对每一个64位的数据进行加密，产生一组64位的密文，最后把各组的密文串接起来，得出整个密文，其中密钥为64位（实际56位，有8位用于校验）。

2.单选题下面的IP地址中，能够作为主机地址的是（）问题1选项A.168.254.0.243/30B.10.20.30.40/29C.172.16.18.0/22D.192.168.11.191/26【答案】C【解析】主机地址的主机位非全0和非全1C选项的IP地址转换为二进制表示后，满足此条件。

3.案例题阅读以下说明，回答问题1至问题4，将解答填入答题纸对应的解答栏内。

【说明】某企业网络拓扑图如图1-1所示。

该网络可以实现的网络功能有:1.汇聚层交换机A与交换机B采用VRRP技术组网；2.用防火墙实现内外网地址转换和访问策略控制；3.对汇聚层交换机、接入层交换机（各车间部署的交换机）进行VLAN划分。

图1-1【问题1】(6分)为图1-1中的防火墙划分安全域，接口①应配置为(1)区域，接口②应配置为(2)区域，接口③应配置为(3)区域。

【问题2】 (4分)VRRP技术实现(4)功能，交换机A与交换机B之间的连接线称为(5)线，其作用是(6).【问题3】(6分)图1-1中PC1的网关地址是(7)；在核心交换机上配置与防火墙互通的默认路由，其目标地址应是(8)；若禁止PC1访问财务服务器，应在核心交换机上采取(9)措施实现。

【问题4】 (4分)【答案】【问题1】(6分)（1）非信任（2）信任（3）DMZ【问题2】(4分)（4）冗余备份、容错（5）心跳线（6）传递VRRP协议报文【问题3】(6分)（7）192.168.20.1（8）0.0.0.0（9）ACL【问题4】(4分)（10）堆叠（11）级联（12）堆叠（13）级联【解析】【问题1】(6分)为图1-1中的防火墙划分安全域，接口①应配置为非信任区域，接口②应配置为信任区域，接口③应配置为DMZ区域（因为有对外提供服务的公共服务器）。

2024年国家电网招聘之电网计算机练习题(二)及答案单选题（共45题）1、IPv6地址由多少比特组成？_____A.32B.48C.64D.128【答案】 D2、与 HAVING 子句一起使用的子句是（）。

A.GROUP BYB.ORDER BYC.JOIND.WHERE【答案】 A3、BGP runs over a reliable transport （请作答此空）. This eliminates the need to implement explicit update fragmentation, retransmission, acknowledgement, and （）. Any authentication scheme used by the transport protocol may be used in addition to BGP's own （）mechanisms. The error notification mechanism used in BGP （）that the transport protocol support s a “graceful” close, i.e., that all outstanding data will be delivered （）the connection is closed.A.protocolB.movingC.machineD.gateway【答案】 A4、设有广义表D(a，b，D)，其长度为3，深度为()A.∞B.3C.2D.5【答案】 A5、在 OSI 环境中，不同开放系统对等实体之间的通信，需要（N）实体向相邻的上一层（N+1）实体提供一种能力，这种能力称为（）。

A.（N）协议B.（N）服务C.（N）用户D.（N）功能【答案】 B6、设数组 Data[0..m]作为循环队列 SQ 的存储空间，front 为队头指针，rear 为队尾指针，则执行出队操作的语句为（）。

算力英语作文Computing power, or "hash power" as it is commonly referred to in the world of cryptocurrency, plays a crucial role in ensuring the security and functionality of blockchain networks. 算力在加密货币世界中通常被称为“哈希率”，在确保区块链网络的安全和功能性方面发挥着至关重要的作用。

The concept of computing power refers to the amount of computational resources dedicated to maintaining and securing a blockchain network. 算力的概念指的是用于维护和保护区块链网络的计算资源的数量。

From a technical perspective, computing power is measured in hash rate, which represents the number of hash calculations that a computer or network can perform in a given period of time. 从技术角度来看，算力是以哈希率来衡量的，它代表了计算机或网络在一定时间内可以执行的哈希计算数量。

The higher the hash rate, the more computational power a network possesses, thereby increasing its security and efficiency. 哈希率越高，网络的计算能力就越大，从而提高了其安全性和效率。

In the context of blockchain networks, computing power is essential for the process of validating and confirming transactions, as well asfor securing the network against potential attacks. 在区块链网络中，算力对于验证和确认交易的过程以及保护网络免受潜在攻击至关重要。

中国地质大学智慧树知到“计算机科学与技术”《计算机安全》网课测试题答案（图片大小可自由调整）第1卷一.综合考核(共15题)1.下面哪项与VPN安全技术无关()。

A.加密技术B.隧道技术C.包过滤技术D.QoS技术2.下列有关DES说法，不正确的是()。

A.设计DESS盒的目的是保证输入与输出之间的非线性变换B.DES算法设计中不存在弱密钥C.目前已经有针对DES的线性密码分析和差分密码分析方法D.DES是基于Feistel密码结构设计的3.防火墙有()基本功能。

A.过滤、远程管理、NAT技术、代理B.MAC与IP地址的绑定、流量控制和统计分析C.流量计费、VPN、限制同时上网人数、限制使用时间D.限制特定使用者才能发送E-mail，限制FTP只能下载文件不能上传文件、阻塞JavActiveX控件4.PKI提供的核心服务包括()。

A.认证B.完整性C.密钥管理D.简单机密性5.注册中心是PKI的核心执行机构，是PKI的主要组成部分。

()T.对F.错6.解毒过程是根据病毒类型对感染对象的修改，并按照病毒的感染特性所进行的恢复，恢复过程可能破坏未被病毒修改的内容。

()T.对F.错7.在PKI信任模型中，()模型中，每个用户自己决定信任哪些证书。

A.认证中心的严格层次结构模型B.分布式信任结构模型C.Web模型D.以用户为中心的信任模型8.TEMPEST技术的主要目的是()。

A.减少计算机中信息的外泄B.保护计算机网络设备C.保护计算机信息系统免雷击和静电的危害D.防盗和防毁9.非对称密码算法简化密钥管理，可实现数字签名。

()T.对F.错10.嗅探器检测的PING方法就是向可疑主机发送包含错误IP地址和MAC地址。

() T.对F.错11.拒绝服务攻击的后果是()。

A.信息不可用B.应用程序不可用C.系统宕机D.阻止通信12.下列选项中属于网络安全的问题是()。

A.散布谣言B.拒绝服务C.黑客恶意访问D.计算机病毒13.从协议层次模型的角度看，防火墙应覆盖网络层，传输层与()。

Jeanette Wing has concluded that computational concepts are deeply embedded into everyday thinking in many fields . Computation is everywhere.
HPM&S
相关学科发展背景
这一理念试图将计算机科学由最初的数值计算工具、仿真与可视化技 术以及后来基于网络、面向多学科的e-Science平台，变成普遍适用于 自然和社会领域的通用思维模式。
HPM&S
Computational Social Science 计算社会科学
Computational Social Science
Nobel Physics Laureate Ken Wilson was among the first to say that computation had become a third leg of science, joining the traditions of theory and experiment.
HPM&S
《Science》2009年2月发表的一篇关于计算社会科学的文 章《ComputationalSocial Science》，该文由美国11个大 学及研究机构的共15名研究人员共同编写。
文章从计算社会科学的数据获取、研究方法、制约因素、 人才培养4个方面，描述了计算社会科学的发展、讨论了社 会科学研究的特点等。
HPM&S
Natural information processes.: nature long ago learned how to encode information about organisms in DNA and then to generate new organisms from DNA through its own computational methods.

Chart图表
Chassis支架
Chip芯片
Clarity清晰度
Closed architecture封闭式体系结构
Column列
Combination key结合键
computer competency计算机能力
connectivity连接，结点
Fiber-optic cable光纤电缆
File compression文件压缩
File decompression文件解压缩
filter过滤
firewall防火墙
firewall防火墙
Fixed disk固定硬盘
Flash memory闪存
Flexible disk可折叠磁盘
cynic愤世嫉俗者
D
Database数据库
database files数据库文件
Database manager数据库管理
Data bus数据总线
Data projector数码放映机
Desktop system unit台式电脑系统单元
Destination file目标文件
ergonomics人类工程学
ethics道德规范
External modem外置调制解调器
extranet企业外部网
F
Fax machine传真机
Field域
Find搜索
FireWire port port火线端口
Firmware固件
Flash RAM闪存
Broadband宽带
Business-to-business企业对企业电子商务
Business-to-consumer企业对消费者

计算机专业英语单选题1.A ＿＿D＿ copy is a copy of a current file made in order to protect against loss or damage.备份拷贝是为了防止丢失或损坏而制作的当前文件的副本。

A.softmost commonly used tool in the design phase is the ＿＿＿＿D＿＿＿＿.在设计阶段最常用的工具是结构图chart chart chart3.＿＿＿＿A＿＿＿＿ refers to the parts of the computer that you can see and touch.硬件指的是你能看到和触摸到的电脑的各个部分A.Hardware4.if we want to retrieve data from the database with SQL,we should use the comand of D如果我们想用SQL从数据库中检索数据，我们应该使用comandA.ins＿ert ＿ate ＿ete ＿ectof the following is not the stages of programming?A下面哪个不是编程的阶段A.Print the program. the program. the program. a program.will become increasingly __B__ throughout every aspect of our lives.多媒体将在我们生活的各个方面变得越来越普遍A.precisethrough the Internet, the_C___ performs the reverse function.通过Internet进行通信，数据通信设备（DCE）执行反向功能。

A.CRT station controller (STACO) communications equipment (DCE)languages must first be translated into a(n) ＿＿＿＿C＿＿＿language before they can be understood and processed by a computer高级语言必须首先被翻译成（n）机器语言，然后才能被计算机理解和处理。

基于性能计数事件的计算机功耗估算模型I. IntroductionIn recent years, large-scale data centers have emerged as critical infrastructure to support the growing demands of cloud computing, big data analytics, and artificial intelligence. Efficiently managing the power consumption of data centers has become an important issue because power consumption accounts for a significant portion of the operational costs, environmental impacts, and system reliability. In order to optimize the power consumption of data centers, it is essential to develop accurate andefficient models for estimating the power consumption of computer systems.One approach that has gained significant attention is the use of performance counter events, which are hardware level events that monitor the performance of a computer system by counting the number of specific hardware operations performed. These events are often used by system administrators and developers to diagnose performance issues and optimize workloads. In recent years, researchers have also developed models that use performance counter events to estimate the power consumption of computer systems.This paper provides an overview of the use of performance counter events for estimating computer power consumption. Specifically, we review existing research on performance counter models and discuss their advantages and limitations. We also identify future research directions forimproving the accuracy and efficiency of these models.II. BackgroundPerformance counter events are hardware level eventsthat are used to measure the performance of a computer system. These events are often used to diagnose performance issuesand optimize workloads by monitoring the usage of system resources such as the CPU, memory, network, and storage.These events are available on most modern processors,including Intel x86, ARM, and IBM Power architectures, andare accessible through various software tools such as perf, PAPI, and Intel VTune.There are two types of performance counters: fixed-function and programmable counters. Fixed-function countersare predefined by the hardware and are dedicated to specific tasks, such as measuring the number of instructions executedor cache misses. Programmable counters, on the other hand,can be programmed by the user to monitor specific events of interest. These events can include cache misses, TLB misses, branch mispredictions, and memory bandwidth utilization.Performance counter events can be used to estimate the power consumption of a computer system by correlating the number of events with the power consumption of specific components, such as the CPU, memory, or disk. The basic ideais that the power consumption of a component is proportionalto the number of hardware events associated with that component. By measuring the number of events associated with each component, it is possible to estimate the power consumption of the entire system.III. Performance Counter ModelsThere have been several models proposed for estimatingthe power consumption of computer systems using performancecounter events. These models can be broadly classified into two categories: regression-based and sampling-based models.Regression-based models use linear or non-linear regression techniques to model the relationship between the performance counter events and the power consumption of a computer system. These models require a training dataset of performance counter values and corresponding power consumption values. The model is then used to estimate the power consumption of new workloads based on their performance counter values.Sampling-based models use statistical techniques to estimate the power consumption of a computer system by sampling the performance counter events at regular intervals. These models do not require a training dataset and can be applied to any workload.One of the earliest models for estimating power consumption using performance counter events is the Power-Efficiency Profile (PEP) model proposed by Ghose et al. in 2006. This model uses linear regression to model the relationship between the number of hardware events and the power consumption of a computer system. The PEP model has been used in several studies to estimate the power consumption of different workloads, such as web servers, scientific computing, and database systems.Another popular model is the PowerPack model proposed by Wang et al. in 2013. This model uses non-linear regression to model the relationship between the performance counter events and the power consumption of a computer system. The PowerPack model uses multiple regression models to estimate the power consumption of different components, such as the CPU, memory, and disk. The PowerPack model has been used in severalstudies to estimate the power consumption of different workloads, such as web servers, scientific computing, and database systems.Sampling-based models have also been proposed for estimating power consumption. One such model is the PowerSleuth model proposed by Kharya et al. in 2014. This model uses statistical techniques such as mean, standard deviation, and quantiles to estimate the power consumption of a computer system. The PowerSleuth model has been used in several studies to estimate the power consumption ofdifferent workloads, such as web applications and database systems.IV. Advantages and LimitationsOne major advantage of performance counter models is that they do not require external sensors or meters to measure power consumption. This makes them easier to deploy and less expensive. Additionally, performance counter models can be used to estimate the power consumption of different workloads and systems without requiring detailed system specifications.One limitation of performance counter models is that they require a significant amount of data to accurately model the relationship between the performance counter events and power consumption. This data is often obtained through extensive profiling of the system, which can be time-consuming and resource-intensive. Additionally, many of the existing models depend on specific operating systems or hardware architectures, which can limit their applicability to other environments.Another limitation is that performance counter models can be sensitive to the workload and environment in whichthey are used. For example, a model trained on one workload may not accurately estimate the power consumption of another workload with different hardware utilization patterns. This can limit the generalizability of these models.V. Future Research DirectionsThere are several research directions for improving the accuracy and efficiency of performance counter models. One approach is to develop models that can adapt to different workloads and environments. This could involve developing models that can dynamically adjust their parameters based on the characteristics of the workload and environment or developing models that can be trained on a wider variety of workloads and environments.Another approach is to integrate performance counter models with power management systems. This could involve using performance counter models to estimate the power consumption of different components and using this information to dynamically adjust the power states of these components to optimize power consumption. This could improve the energy efficiency of computer systems without sacrificing performance.Finally, there is a need for more research on the accuracy and reliability of performance counter models. This could involve comparing the estimates generated by these models with actual power consumption measurements to determine the accuracy of these models. Additionally, thereis a need for more research on the impact of different performance counter events on power consumption and how this impact varies with different workloads and environments.VI. ConclusionPerformance counter events are a powerful tool formonitoring the performance of computer systems. They can also be used to estimate the power consumption of these systems. Several models have been proposed for estimating power consumption using performance counter events, including regression-based and sampling-based models. These models have several advantages, such as not requiring external sensors or detailed system specifications. However, they also have limitations, such as requiring extensive profiling to obtain accurate data and being sensitive to the workload and environment in which they are used. Future researchdirections include developing models that can adapt to different workloads and environments, integrating performance counter models with power management systems, and improving the accuracy and reliability of these models.。

计算机系统与网络安全技术_电子科技大学中国大学mooc课后章节答案期末考试题库2023年1.以下关于TCP/IP协议族的说法不正确的是（）答案:TCP/IP协议族中的TCP协议在设计之初考虑到了安全问题2.以下关于跨站点脚本攻击（Cross-Site Scripting Attack）的说法不正确的是（）答案:如果用户输入不能用来生成静态内容，则跨站点脚本攻击无法实现3.整数29的欧拉函数等于（）答案:284.下列关于RSA加密算法正确的说法是（）RSA是非对称加密算法5.下列关于网络地址转换（NAT）正确的说法是（）答案:NAT和防火墙能协同工作6.以下关于蜜罐（Honeypot）说法不正确的是（）答案:蜜罐技术可以用来阻止网络攻击的发生7.以下关于Windows NT操作系统中安全标识SID（security identification）的说法正确的是（）答案:SID可以作为用户或群组拥有访问权限的标志8.以下关于Windows操作系统注册表的说法正确的是（）程序和系统的配置参数一般都存放在注册表中9.关于病毒和蠕虫的说法正确的是（）答案:病毒需要依附于驻留文件来进行复制，而蠕虫不使用驻留文件也可在系统之间进行自我复制10.NP问题的含义是（）答案:非确定性图灵机上能够在多项式时间内得到处理的问题11.下面关于TCP协议的说法中，不正确的是（）答案:TCP是非面向连接的协议12.以下关于身份认证的说法不正确的有（）答案:身份认证有单向和双向认证之分，且可以简单地重复两次单向认证来实现双向认证13.以下关于链路加密的说法不正确的是（）答案:链路加密中每个用户可以选择自己的加密密钥14.按照加密和解密密钥是否相同，密码算法可分为（）答案:对称密码算法和非对称密码算法15.后三位数字是（）答案:40116.以下关于IPSec说法正确的是（）答案:IPSec属于网络层的安全解决方案17.以下关于入侵检测系统（IDS）的说法正确的是（）答案:入侵检测系统可分为主机入侵检测系统和网络入侵检测系统18.以下不属于ISO 7498-2和ITU-T X.800规定的安全服务的有（）答案:加密（Encryption）19.以下关于UDP协议的说法不正确的是（）答案:UDP是面向连接的协议20.以下关于安全漏洞的说法不正确的有（）答案:软件是产生安全漏洞的唯一原因21.下列哪项不是动态路由选择协议（）答案:CDP22.OSI关于7层通信协议模型从下到上依次为（）答案:应用层表示层会话层传输层网络层链路层物理层23.按照每次处理数据块的长度不同，密码算法可分为（）答案:分组密码算法和序列密码算法24.下列关于DES加密算法的说法中正确的是（）答案:DES的中文意思是数据加密标准25.下列哪些方法可以防止重放攻击（）答案:时戳机制26.下列关于数字签名说法正确的是（）答案:数字签名不可改变27.已知明文攻击是指（）答案:攻击者Oscar拥有具有明文串x和相应的密文y28.为了使用RSA加密算法，Alice选择了两个素数：pa＝17，pb＝11，以及随机数ea＝7作为自己的公钥，则Alice的私钥是（）答案:2329.RFC 1321中以下关于MD5的说法正确的有（）答案:MD5的输入可以为任意长，但是其输出是128位30.美国国家标准学会（ANSI）制订的FIPS PUB 180和180-1中关于SHA-1说法正确的有（）答案:SHA-1的输入不能为任意长，但其输出是160位31.以下关于IPSec中的密钥管理说法正确的有（）答案:互联网络安全关联和密钥管理协议（IAKMP）是IPSec密钥管理的框架32.以下关于入侵检测系统的说法正确的是（）答案:入侵检测系统分为主机入侵检测和网络入侵检测33.以下关于计算机犯罪（Computer Crime）说法最正确的是（）答案:行为人通过计算机操作所实施的危害计算机信息系统（包括内存数据及程序）安全以及其他严重危害社会的并应当处以刑罚的行为34.目前，得到许多国家认可的信息安全管理标准是（）答案:BS779935.MD5常用与数据（）保护答案:机密36.拒绝服务攻击的后果是（）答案:以上都是37.下列设备中属于物理层的设备是（）答案:中继器38.ARP的功能是（）答案:由目标的IP地址求目标的MAC地址39.以下哪项不是公钥密码体制的特点（）答案:保密通信双方需共享密钥40.包过滤发生在哪一层（）答案:网络层41.屏蔽子网结构过滤防火墙中，堡垒主机位于（）答案:周边网络42.在某单位的网络安全方案中，采用隔离网闸实现物理隔离其中，网络物理隔离的基本思想是（）答案:内外网隔开，但分时对一存储设备进行写和读，间接实现信息交换43.NAT(网络地址转换)的功能是什么（）答案:实现私有IP地址与公共IP地址的相互转换44.在网络中分配IP地址可以采用静态地址或动态地址方案。

X X X X 学院计算机专业英语班级计科学号12姓名日期2015-12-Security of Computer Network System Abstract: This paper discussed the secure and dependable problem about the computer network system. On some aspects: the importance of network security basic theory function and the method of solving a problem etc. Good views for solving the problem are put forward. It strengthens people’s consciousness on network security.Key words: Computer network Virtual private network Encryption techniques FirewallIntroduction: Along with the computer network technology development the network security and the reliability have become the question of common interest by all users. The people all hoped their own network system can move reliably not external intruder disturbance and destruction .Therefore solves the network security and the reliable problem carefully is a guarantee the network normal operation’s premise and safeguard.First: the importance of the network security. With the information developing fast today the computer network obtained the widespread application but along with the network information transmission capacity growing faster some organizations and departments benefit the speed up with the service operation in the network while the data has also suffered to extent attack and destruction. The aggressor may intercept the information in the network steals the user’s password the database information also may tamper with the database content the forge users status denies own signature. And what is more the aggressor may delete the database content the destroy node releases computer virus and so on. This cause data security and own benefit have received the serious threat. According to American FBI US Federal Bureau of Investigation invest the network security creates the economic loss surpasses 17 billion dollars every year.75 corporation report finance loss is because the computer system security problem creates. More than 50 safe threat come from inside. But only 59 loss could be possible estimate. In China the economic loss amount in view of financial domain and the banknegotiable securities computer system security problems creates has reached as high as several hundred million Yuan also sometimes occurs in view of other profession network security threat. Thus it can be seen regardless of is the mean attack or unconscious disoperation will all be able to bring the inestimable loss to the system. Therefore the computer network must have the enough strong security measure. Regardless of is in the local area network or in WAN the network security measure should be Omni-directional in view of each kind of different threat and the vulnerability so that it can guarantee the network information’s secrecy the integrity and the usability.Second: Network security rationale. International Standardization Organization ISO once suggested the computer security the definition was: “The computer system must protect its hardware the data not accidentally or reveals intentionally the change and the destruction.”In order to help the computer user discrimination and the solution computer network security problem the American Department of Defense announced “the orange peel book”orange book official name is “credible computer system standard appraisal criterion”has carried on the stipulation to the multiuser computer system security rank division. The orange peel book from low to high divides into the computer security four kinds of seven levels: D1 C1 C2 B1 B2 B3 A1.Above allD1 level does not have the lowest safety margin rank C1 and the C2 level has the lowest safety margin rank B1 and the B2 level has the medium safekeeping of security ability rank B3 and A1 belongs to the highest security rating. In the network concrete design process it should act according to each technology standard the equipment type the performance requirement as well as the funds which in the network overall plan proposed and so on the overall evaluation determines one quite reasonably the performance high network security rank thus realization network security and reliability.Third: The network security should have function. In order to adapt the information technology development well the computer network application system must have following function: 1 Access control: Through to the specificwebpage the service establishment access control system in arrives the overwhelming majority attack impediment in front of the attack goal. 2 Inspects the security loophole: Through to security loophole cyclical inspection even if attacks may get the attack goal also may cause the overwhelming majority attack to be invalid. 3 Attack monitoring: Through to specific webpage service establishment attack monitoring system but real-time examines the overwhelming majority attack and adopts the response the motion for example separation network connection recording attack process pursuit attack source and so on. 4 Encryption Communication: Encrypts on own initiative the communication may enable the aggressor to understand the revision sensitive information. 5 Authentication: The good authentication system may prevent the aggressor pretends the validated user. 6 Backup and restoration: The good backup and restores the mechanism may causes the losses when the attack as soon as possible restores the data and the system service. 7 Multi-layered Defense: The aggressor after breaks through the first defense line delays or blocks it to reach the attack goal. 8 Sets up the safe monitoring center: Provides the security system management the monitoring the protection and the emergency case service for the information system.Fourth: The network system safety comprehensive solution measures. If want to realize the network security function we should carry on the Omni-directional guarding to the network system and thus formulate the quite reasonable network security architecture. Below on the network system security problem proposes some guard measure. Physics safe may divide into two aspects: One is the artificial harm to the network the other is the network to the users. Most common thing is the constructor who did not understand to the buried cable clearly thus lead to the destruction of electric cable this kind of situation may through standing symbolized the sign guards against Has not used the structure wiring the network to be able to appear the user frequently to the electric cable damage this needs to use the structure wiring to install the network as far as possible Artificial or naturaldisaster influence when to consider the plan. The access control security the access control distinguishes and confirms the user limits the user in the already activity and the resources scope which is authorized. The network access control safe may consider from following several aspects. 1 password: The network security system most outer layer defense line is network users registering in the registration process the system would inspect the user to register the name and the password validity only then the legitimate user can enter the system. 2 The network resources’host the attribute and the visit jurisdiction: The network resources mainly include the resources which shared files the shared printer network users and so on that all the network users can use. The resources were the host to manifest the different user to the resources subordinate relations such as builder modifier and group member and so on. The resources attribute expressed itself deposit and withdrawal characteristics as can read by who write or the execution and so on. The visit jurisdiction mainly manifests in the user to the network resources available degree in using assigns the network resources to be the host the attribute and the visit jurisdiction may effectively in the application cascade control network system security. 3 Network security surveillance: The network surveillance is generally called for “the network management”its function mainly is carries on the dynamic surveillance to the entire network movement and handles each kind of event promptly. May understand simply through the network surveillance discovers and solves in the network security problem such as the localization network fault point seizes the IP embezzler the control network visit scope and so on. 4 Audit and track: Network audit and track which is including the network aspect resources use network breakdown and system keeping. It composed generally by two parts: One the recording event soon each kind of event entirely records in the document. Two carries on the analysis and the statistics to. Data transmission security, transmission security requirements to protect the information on the network is transmitted to prevent the passive and active violations. The security of data transmission can take the following measures: (1)encryption and digital signature: digital signature is the receiver of data used to confirm the sender of the data is true and correct. (2) firewall: firewall (Firewall) is a security measure that is widely used in Internet. It can be used to set up a series of components in different network or network security domain. It can detect, limit and change the data flow of the firewall, and detect the information, structure and running status of the network as far as possible, so as to realize the network security. (3) Username or Password certification: the authentication method is the most commonly used as an authentication method for the operating system, telnet (remote login), rlogin (remote login), but the process is not encrypted, that is, password is easy to be monitored and decryption. (4) authentication using the algorithm: radius (Remote Authentication Dial protocol, OSPF (open routing protocol), SNMP Security Protocol use shared Security Key (key), and the abstract algorithm (MD5) certification, but abstract algorithm is an irreversible process, therefore, in the authentication process, by the information cannot be calculated Security Key shared, so the sensitive information in the network transmission. The algorithm is mainly used on the market are mainly MD5 and SHA - 1. (5) authentication and encryption based on PKI: using PKI (public key system). This method has a high security level, which is integrated with the technology of the algorithm, asymmetric encryption, symmetric encryption, digital signature, and so on. This authentication method is currently used in the fields of email, application server access, customer authentication, firewall authentication, etc.. This kind of authentication method is very safe, but it involves a relatively heavy certificate management task. (6) virtual private network (VPN) technology: VPN technology mainly provides two-way communication in the public security, the transparent encryption scheme to ensure data integrity and confidentiality.In summary, for the security of computer network transmission, we must do the following. First, we should strictly limit access to the Internet users of the system information and resources, this function can be achieved by setting the Net Screen firewall on the access server. Second, we should strengthen the identityauthentication of Internet users, using RADIUS and other special authentication server. On the one hand, it can achieve the unified management of Internet users account; on the other hand, in the process of identity verification using encryption means to avoid the possibility of leakage of the account. Third: The use of encryption technology in the process of data transmission, to prevent data theft. One way is to use for Business Security PGP to encrypt data. Another approach is to use the VPN technology provided by Net Screen firewall. VPN in the provision of network data encryption, but also provides a single user of the encryption software, that is, the use of software encryption technology to ensure the security of data transmission.浅析计算机网络安全摘要：针对计算机网络系统存在的安全性和可靠性问题，本文从网络安全的重要性、理论基础、具备功能以及解决措施等方面提出一些见解，并且进行了详细的阐述，以使广大用户在计算机网络方面提高安全防范意识。

基于云的大数据的节能策略摘要:由于大数据的巨大潜力,许多行业都对大数据产生了兴趣。

大数据需要大的计算能力和分布式存储来处理数据问题,云可以为大数据提供弹性的按需计算能力和存储。

云数据中心可以作为大数据的基础设施层。

随着大数据量的高速增长,云数据中心也在不断扩大。

他们消耗了大量的能源,不断地为大数据提供基础设施。

本文的目的不是要广泛地覆盖大数据,而是要利用虚拟化技术有效地利用云数据中心,从而节省能源。

关键词:数据中心、云计算、虚拟化、二进制打包问题、虚拟机迁移。

简介根据美国国家标准和技术研究所的数据,美国大数据主要由大量的数据集组成,主要集中在体积、种类、速度和可变性等方面,这需要一个可伸缩的体系结构来进行有效的存储、操作和分析[1]。

大数据是超越常规数据库的典型存储、数据分析技术、处理和计算能力的数据集。

它与四种复杂性相关联,通常被称为四种Vs:体积、种类、速度和准确性。

云计算可以为大数据系统提供基础设施,以满足基础设施的成本效益、弹性等需求。

云计算的一项重要技术是虚拟化,它可以在单个物理机器上复用许多不同的虚拟机,同时为每个虚拟机提供单独的框架。

据国际数据公司(IDC)报道,从2005年到2020年[2],全球数据量将增加300倍,即从130eb到40000 eb。

这些巨大的数据存储在消耗巨大电力的数据中心。

由美国国家资源保护委员会(National resources Defense Council of US)公布的数据显示,美国数据中心的能耗数据显示,从2013年到2020年的7年内,数据中心的能源消耗可能会增加约53%[3]。

根据对一些数据中心的一项调查发现,从可用的计算能力来看,服务器只使用了10%到30%,个人计算机的平均容量利用率低于5%[4]。

除此之外,即使在空闲状态服务器中也使用了超过70%的最高功率[5]。

表一美国数据中心能耗[3]为解决能源消耗高、服务器利用率低的问题,必须消除资源利用效率低下的问题。

A Peer-to-Peer Spatial Cloaking Algorithm for AnonymousLocation-based Services∗Chi-Yin Chow Department of Computer Science and Engineering University of Minnesota Minneapolis,MN cchow@ Mohamed F.MokbelDepartment of ComputerScience and EngineeringUniversity of MinnesotaMinneapolis,MNmokbel@Xuan LiuIBM Thomas J.WatsonResearch CenterHawthorne,NYxuanliu@ABSTRACTThis paper tackles a major privacy threat in current location-based services where users have to report their ex-act locations to the database server in order to obtain their desired services.For example,a mobile user asking about her nearest restaurant has to report her exact location.With untrusted service providers,reporting private location in-formation may lead to several privacy threats.In this pa-per,we present a peer-to-peer(P2P)spatial cloaking algo-rithm in which mobile and stationary users can entertain location-based services without revealing their exact loca-tion information.The main idea is that before requesting any location-based service,the mobile user will form a group from her peers via single-hop communication and/or multi-hop routing.Then,the spatial cloaked area is computed as the region that covers the entire group of peers.Two modes of operations are supported within the proposed P2P spa-tial cloaking algorithm,namely,the on-demand mode and the proactive mode.Experimental results show that the P2P spatial cloaking algorithm operated in the on-demand mode has lower communication cost and better quality of services than the proactive mode,but the on-demand incurs longer response time.Categories and Subject Descriptors:H.2.8[Database Applications]:Spatial databases and GISGeneral Terms:Algorithms and Experimentation. Keywords:Mobile computing,location-based services,lo-cation privacy and spatial cloaking.1.INTRODUCTIONThe emergence of state-of-the-art location-detection de-vices,e.g.,cellular phones,global positioning system(GPS) devices,and radio-frequency identification(RFID)chips re-sults in a location-dependent information access paradigm,∗This work is supported in part by the Grants-in-Aid of Re-search,Artistry,and Scholarship,University of Minnesota. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on thefirst page.To copy otherwise,to republish,to post on servers or to redistribute to lists,requires prior specific permission and/or a fee.ACM-GIS’06,November10-11,2006,Arlington,Virginia,USA. Copyright2006ACM1-59593-529-0/06/0011...$5.00.known as location-based services(LBS)[30].In LBS,mobile users have the ability to issue location-based queries to the location-based database server.Examples of such queries include“where is my nearest gas station”,“what are the restaurants within one mile of my location”,and“what is the traffic condition within ten minutes of my route”.To get the precise answer of these queries,the user has to pro-vide her exact location information to the database server. With untrustworthy servers,adversaries may access sensi-tive information about specific individuals based on their location information and issued queries.For example,an adversary may check a user’s habit and interest by knowing the places she visits and the time of each visit,or someone can track the locations of his ex-friends.In fact,in many cases,GPS devices have been used in stalking personal lo-cations[12,39].To tackle this major privacy concern,three centralized privacy-preserving frameworks are proposed for LBS[13,14,31],in which a trusted third party is used as a middleware to blur user locations into spatial regions to achieve k-anonymity,i.e.,a user is indistinguishable among other k−1users.The centralized privacy-preserving frame-work possesses the following shortcomings:1)The central-ized trusted third party could be the system bottleneck or single point of failure.2)Since the centralized third party has the complete knowledge of the location information and queries of all users,it may pose a serious privacy threat when the third party is attacked by adversaries.In this paper,we propose a peer-to-peer(P2P)spatial cloaking algorithm.Mobile users adopting the P2P spatial cloaking algorithm can protect their privacy without seeking help from any centralized third party.Other than the short-comings of the centralized approach,our work is also moti-vated by the following facts:1)The computation power and storage capacity of most mobile devices have been improv-ing at a fast pace.2)P2P communication technologies,such as IEEE802.11and Bluetooth,have been widely deployed.3)Many new applications based on P2P information shar-ing have rapidly taken shape,e.g.,cooperative information access[9,32]and P2P spatio-temporal query processing[20, 24].Figure1gives an illustrative example of P2P spatial cloak-ing.The mobile user A wants tofind her nearest gas station while beingfive anonymous,i.e.,the user is indistinguish-able amongfive users.Thus,the mobile user A has to look around andfind other four peers to collaborate as a group. In this example,the four peers are B,C,D,and E.Then, the mobile user A cloaks her exact location into a spatialA B CDEBase Stationregion that covers the entire group of mobile users A ,B ,C ,D ,and E .The mobile user A randomly selects one of the mobile users within the group as an agent .In the ex-ample given in Figure 1,the mobile user D is selected as an agent.Then,the mobile user A sends her query (i.e.,what is the nearest gas station)along with her cloaked spa-tial region to the agent.The agent forwards the query to the location-based database server through a base station.Since the location-based database server processes the query based on the cloaked spatial region,it can only give a list of candidate answers that includes the actual answers and some false positives.After the agent receives the candidate answers,it forwards the candidate answers to the mobile user A .Finally,the mobile user A gets the actual answer by filtering out all the false positives.The proposed P2P spatial cloaking algorithm can operate in two modes:on-demand and proactive .In the on-demand mode,mobile clients execute the cloaking algorithm when they need to access information from the location-based database server.On the other side,in the proactive mode,mobile clients periodically look around to find the desired number of peers.Thus,they can cloak their exact locations into spatial regions whenever they want to retrieve informa-tion from the location-based database server.In general,the contributions of this paper can be summarized as follows:1.We introduce a distributed system architecture for pro-viding anonymous location-based services (LBS)for mobile users.2.We propose the first P2P spatial cloaking algorithm for mobile users to entertain high quality location-based services without compromising their privacy.3.We provide experimental evidence that our proposed algorithm is efficient in terms of the response time,is scalable to large numbers of mobile clients,and is effective as it provides high-quality services for mobile clients without the need of exact location information.The rest of this paper is organized as follows.Section 2highlights the related work.The system model of the P2P spatial cloaking algorithm is presented in Section 3.The P2P spatial cloaking algorithm is described in Section 4.Section 5discusses the integration of the P2P spatial cloak-ing algorithm with privacy-aware location-based database servers.Section 6depicts the experimental evaluation of the P2P spatial cloaking algorithm.Finally,Section 7con-cludes this paper.2.RELATED WORKThe k -anonymity model [37,38]has been widely used in maintaining privacy in databases [5,26,27,28].The main idea is to have each tuple in the table as k -anonymous,i.e.,indistinguishable among other k −1tuples.Although we aim for the similar k -anonymity model for the P2P spatial cloaking algorithm,none of these techniques can be applied to protect user privacy for LBS,mainly for the following four reasons:1)These techniques preserve the privacy of the stored data.In our model,we aim not to store the data at all.Instead,we store perturbed versions of the data.Thus,data privacy is managed before storing the data.2)These approaches protect the data not the queries.In anonymous LBS,we aim to protect the user who issues the query to the location-based database server.For example,a mobile user who wants to ask about her nearest gas station needs to pro-tect her location while the location information of the gas station is not protected.3)These approaches guarantee the k -anonymity for a snapshot of the database.In LBS,the user location is continuously changing.Such dynamic be-havior calls for continuous maintenance of the k -anonymity model.(4)These approaches assume a unified k -anonymity requirement for all the stored records.In our P2P spatial cloaking algorithm,k -anonymity is a user-specified privacy requirement which may have a different value for each user.Motivated by the privacy threats of location-detection de-vices [1,4,6,40],several research efforts are dedicated to protect the locations of mobile users (e.g.,false dummies [23],landmark objects [18],and location perturbation [10,13,14]).The most closed approaches to ours are two centralized spatial cloaking algorithms,namely,the spatio-temporal cloaking [14]and the CliqueCloak algorithm [13],and one decentralized privacy-preserving algorithm [23].The spatio-temporal cloaking algorithm [14]assumes that all users have the same k -anonymity requirements.Furthermore,it lacks the scalability because it deals with each single request of each user individually.The CliqueCloak algorithm [13]as-sumes a different k -anonymity requirement for each user.However,since it has large computation overhead,it is lim-ited to a small k -anonymity requirement,i.e.,k is from 5to 10.A decentralized privacy-preserving algorithm is proposed for LBS [23].The main idea is that the mobile client sends a set of false locations,called dummies ,along with its true location to the location-based database server.However,the disadvantages of using dummies are threefold.First,the user has to generate realistic dummies to pre-vent the adversary from guessing its true location.Second,the location-based database server wastes a lot of resources to process the dummies.Finally,the adversary may esti-mate the user location by using cellular positioning tech-niques [34],e.g.,the time-of-arrival (TOA),the time differ-ence of arrival (TDOA)and the direction of arrival (DOA).Although several existing distributed group formation al-gorithms can be used to find peers in a mobile environment,they are not designed for privacy preserving in LBS.Some algorithms are limited to only finding the neighboring peers,e.g.,lowest-ID [11],largest-connectivity (degree)[33]and mobility-based clustering algorithms [2,25].When a mo-bile user with a strict privacy requirement,i.e.,the value of k −1is larger than the number of neighboring peers,it has to enlist other peers for help via multi-hop routing.Other algorithms do not have this limitation,but they are designed for grouping stable mobile clients together to facil-Location-based Database ServerDatabase ServerDatabase ServerFigure 2:The system architectureitate efficient data replica allocation,e.g.,dynamic connec-tivity based group algorithm [16]and mobility-based clus-tering algorithm,called DRAM [19].Our work is different from these approaches in that we propose a P2P spatial cloaking algorithm that is dedicated for mobile users to dis-cover other k −1peers via single-hop communication and/or via multi-hop routing,in order to preserve user privacy in LBS.3.SYSTEM MODELFigure 2depicts the system architecture for the pro-posed P2P spatial cloaking algorithm which contains two main components:mobile clients and location-based data-base server .Each mobile client has its own privacy profile that specifies its desired level of privacy.A privacy profile includes two parameters,k and A min ,k indicates that the user wants to be k -anonymous,i.e.,indistinguishable among k users,while A min specifies the minimum resolution of the cloaked spatial region.The larger the value of k and A min ,the more strict privacy requirements a user needs.Mobile users have the ability to change their privacy profile at any time.Our employed privacy profile matches the privacy re-quirements of mobiles users as depicted by several social science studies (e.g.,see [4,15,17,22,29]).In this architecture,each mobile user is equipped with two wireless network interface cards;one of them is dedicated to communicate with the location-based database server through the base station,while the other one is devoted to the communication with other peers.A similar multi-interface technique has been used to implement IP multi-homing for stream control transmission protocol (SCTP),in which a machine is installed with multiple network in-terface cards,and each assigned a different IP address [36].Similarly,in mobile P2P cooperation environment,mobile users have a network connection to access information from the server,e.g.,through a wireless modem or a base station,and the mobile users also have the ability to communicate with other peers via a wireless LAN,e.g.,IEEE 802.11or Bluetooth [9,24,32].Furthermore,each mobile client is equipped with a positioning device, e.g.,GPS or sensor-based local positioning systems,to determine its current lo-cation information.4.P2P SPATIAL CLOAKINGIn this section,we present the data structure and the P2P spatial cloaking algorithm.Then,we describe two operation modes of the algorithm:on-demand and proactive .4.1Data StructureThe entire system area is divided into grid.The mobile client communicates with each other to discover other k −1peers,in order to achieve the k -anonymity requirement.TheAlgorithm 1P2P Spatial Cloaking:Request Originator m 1:Function P2PCloaking-Originator (h ,k )2://Phase 1:Peer searching phase 3:The hop distance h is set to h4:The set of discovered peers T is set to {∅},and the number ofdiscovered peers k =|T |=05:while k <k −1do6:Broadcast a FORM GROUP request with the parameter h (Al-gorithm 2gives the response of each peer p that receives this request)7:T is the set of peers that respond back to m by executingAlgorithm 28:k =|T |;9:if k <k −1then 10:if T =T then 11:Suspend the request 12:end if 13:h ←h +1;14:T ←T ;15:end if 16:end while17://Phase 2:Location adjustment phase 18:for all T i ∈T do19:|mT i .p |←the greatest possible distance between m and T i .pby considering the timestamp of T i .p ’s reply and maximum speed20:end for21://Phase 3:Spatial cloaking phase22:Form a group with k −1peers having the smallest |mp |23:h ←the largest hop distance h p of the selected k −1peers 24:Determine a grid area A that covers the entire group 25:if A <A min then26:Extend the area of A till it covers A min 27:end if28:Randomly select a mobile client of the group as an agent 29:Forward the query and A to the agentmobile client can thus blur its exact location into a cloaked spatial region that is the minimum grid area covering the k −1peers and itself,and satisfies A min as well.The grid area is represented by the ID of the left-bottom and right-top cells,i.e.,(l,b )and (r,t ).In addition,each mobile client maintains a parameter h that is the required hop distance of the last peer searching.The initial value of h is equal to one.4.2AlgorithmFigure 3gives a running example for the P2P spatial cloaking algorithm.There are 15mobile clients,m 1to m 15,represented as solid circles.m 8is the request originator,other black circles represent the mobile clients received the request from m 8.The dotted circles represent the commu-nication range of the mobile client,and the arrow represents the movement direction.Algorithms 1and 2give the pseudo code for the request originator (denoted as m )and the re-quest receivers (denoted as p ),respectively.In general,the algorithm consists of the following three phases:Phase 1:Peer searching phase .The request origina-tor m wants to retrieve information from the location-based database server.m first sets h to h ,a set of discovered peers T to {∅}and the number of discovered peers k to zero,i.e.,|T |.(Lines 3to 4in Algorithm 1).Then,m broadcasts a FORM GROUP request along with a message sequence ID and the hop distance h to its neighboring peers (Line 6in Algorithm 1).m listens to the network and waits for the reply from its neighboring peers.Algorithm 2describes how a peer p responds to the FORM GROUP request along with a hop distance h and aFigure3:P2P spatial cloaking algorithm.Algorithm2P2P Spatial Cloaking:Request Receiver p1:Function P2PCloaking-Receiver(h)2://Let r be the request forwarder3:if the request is duplicate then4:Reply r with an ACK message5:return;6:end if7:h p←1;8:if h=1then9:Send the tuple T=<p,(x p,y p),v maxp ,t p,h p>to r10:else11:h←h−1;12:Broadcast a FORM GROUP request with the parameter h 13:T p is the set of peers that respond back to p14:for all T i∈T p do15:T i.h p←T i.h p+1;16:end for17:T p←T p∪{<p,(x p,y p),v maxp ,t p,h p>};18:Send T p back to r19:end ifmessage sequence ID from another peer(denoted as r)that is either the request originator or the forwarder of the re-quest.First,p checks if it is a duplicate request based on the message sequence ID.If it is a duplicate request,it sim-ply replies r with an ACK message without processing the request.Otherwise,p processes the request based on the value of h:Case1:h= 1.p turns in a tuple that contains its ID,current location,maximum movement speed,a timestamp and a hop distance(it is set to one),i.e.,< p,(x p,y p),v max p,t p,h p>,to r(Line9in Algorithm2). Case2:h> 1.p decrements h and broadcasts the FORM GROUP request with the updated h and the origi-nal message sequence ID to its neighboring peers.p keeps listening to the network,until it collects the replies from all its neighboring peers.After that,p increments the h p of each collected tuple,and then it appends its own tuple to the collected tuples T p.Finally,it sends T p back to r (Lines11to18in Algorithm2).After m collects the tuples T from its neighboring peers, if m cannotfind other k−1peers with a hop distance of h,it increments h and re-broadcasts the FORM GROUP request along with a new message sequence ID and h.m repeatedly increments h till itfinds other k−1peers(Lines6to14in Algorithm1).However,if mfinds the same set of peers in two consecutive broadcasts,i.e.,with hop distances h and h+1,there are not enough connected peers for m.Thus, m has to relax its privacy profile,i.e.,use a smaller value of k,or to be suspended for a period of time(Line11in Algorithm1).Figures3(a)and3(b)depict single-hop and multi-hop peer searching in our running example,respectively.In Fig-ure3(a),the request originator,m8,(e.g.,k=5)canfind k−1peers via single-hop communication,so m8sets h=1. Since h=1,its neighboring peers,m5,m6,m7,m9,m10, and m11,will not further broadcast the FORM GROUP re-quest.On the other hand,in Figure3(b),m8does not connect to k−1peers directly,so it has to set h>1.Thus, its neighboring peers,m7,m10,and m11,will broadcast the FORM GROUP request along with a decremented hop dis-tance,i.e.,h=h−1,and the original message sequence ID to their neighboring peers.Phase2:Location adjustment phase.Since the peer keeps moving,we have to capture the movement between the time when the peer sends its tuple and the current time. For each received tuple from a peer p,the request originator, m,determines the greatest possible distance between them by an equation,|mp |=|mp|+(t c−t p)×v max p,where |mp|is the Euclidean distance between m and p at time t p,i.e.,|mp|=(x m−x p)2+(y m−y p)2,t c is the currenttime,t p is the timestamp of the tuple and v maxpis the maximum speed of p(Lines18to20in Algorithm1).In this paper,a conservative approach is used to determine the distance,because we assume that the peer will move with the maximum speed in any direction.If p gives its movement direction,m has the ability to determine a more precise distance between them.Figure3(c)illustrates that,for each discovered peer,the circle represents the largest region where the peer can lo-cate at time t c.The greatest possible distance between the request originator m8and its discovered peer,m5,m6,m7, m9,m10,or m11is represented by a dotted line.For exam-ple,the distance of the line m8m 11is the greatest possible distance between m8and m11at time t c,i.e.,|m8m 11|. Phase3:Spatial cloaking phase.In this phase,the request originator,m,forms a virtual group with the k−1 nearest peers,based on the greatest possible distance be-tween them(Line22in Algorithm1).To adapt to the dynamic network topology and k-anonymity requirement, m sets h to the largest value of h p of the selected k−1 peers(Line15in Algorithm1).Then,m determines the minimum grid area A covering the entire group(Line24in Algorithm1).If the area of A is less than A min,m extends A,until it satisfies A min(Lines25to27in Algorithm1). Figure3(c)gives the k−1nearest peers,m6,m7,m10,and m11to the request originator,m8.For example,the privacy profile of m8is(k=5,A min=20cells),and the required cloaked spatial region of m8is represented by a bold rectan-gle,as depicted in Figure3(d).To issue the query to the location-based database server anonymously,m randomly selects a mobile client in the group as an agent(Line28in Algorithm1).Then,m sendsthe query along with the cloaked spatial region,i.e.,A,to the agent(Line29in Algorithm1).The agent forwards thequery to the location-based database server.After the serverprocesses the query with respect to the cloaked spatial re-gion,it sends a list of candidate answers back to the agent.The agent forwards the candidate answer to m,and then mfilters out the false positives from the candidate answers. 4.3Modes of OperationsThe P2P spatial cloaking algorithm can operate in twomodes,on-demand and proactive.The on-demand mode:The mobile client only executesthe algorithm when it needs to retrieve information from the location-based database server.The algorithm operatedin the on-demand mode generally incurs less communica-tion overhead than the proactive mode,because the mobileclient only executes the algorithm when necessary.However,it suffers from a longer response time than the algorithm op-erated in the proactive mode.The proactive mode:The mobile client adopting theproactive mode periodically executes the algorithm in back-ground.The mobile client can cloak its location into a spa-tial region immediately,once it wants to communicate withthe location-based database server.The proactive mode pro-vides a better response time than the on-demand mode,but it generally incurs higher communication overhead and giveslower quality of service than the on-demand mode.5.ANONYMOUS LOCATION-BASEDSERVICESHaving the spatial cloaked region as an output form Algo-rithm1,the mobile user m sends her request to the location-based server through an agent p that is randomly selected.Existing location-based database servers can support onlyexact point locations rather than cloaked regions.In or-der to be able to work with a spatial region,location-basedservers need to be equipped with a privacy-aware queryprocessor(e.g.,see[29,31]).The main idea of the privacy-aware query processor is to return a list of candidate answerrather than the exact query answer.Then,the mobile user m willfilter the candidate list to eliminate its false positives andfind its exact answer.The tighter the spatial cloaked re-gion,the lower is the size of the candidate answer,and hencethe better is the performance of the privacy-aware query processor.However,tight cloaked regions may represent re-laxed privacy constrained.Thus,a trade-offbetween the user privacy and the quality of service can be achieved[31]. Figure4(a)depicts such scenario by showing the data stored at the server side.There are32target objects,i.e., gas stations,T1to T32represented as black circles,the shaded area represents the spatial cloaked area of the mo-bile client who issued the query.For clarification,the actual mobile client location is plotted in Figure4(a)as a black square inside the cloaked area.However,such information is neither stored at the server side nor revealed to the server. The privacy-aware query processor determines a range that includes all target objects that are possibly contributing to the answer given that the actual location of the mobile client could be anywhere within the shaded area.The range is rep-resented as a bold rectangle,as depicted in Figure4(b).The server sends a list of candidate answers,i.e.,T8,T12,T13, T16,T17,T21,and T22,back to the agent.The agent next for-(a)Server Side(b)Client SideFigure4:Anonymous location-based services wards the candidate answers to the requesting mobile client either through single-hop communication or through multi-hop routing.Finally,the mobile client can get the actualanswer,i.e.,T13,byfiltering out the false positives from thecandidate answers.The algorithmic details of the privacy-aware query proces-sor is beyond the scope of this paper.Interested readers are referred to[31]for more details.6.EXPERIMENTAL RESULTSIn this section,we evaluate and compare the scalabilityand efficiency of the P2P spatial cloaking algorithm in boththe on-demand and proactive modes with respect to the av-erage response time per query,the average number of mes-sages per query,and the size of the returned candidate an-swers from the location-based database server.The queryresponse time in the on-demand mode is defined as the timeelapsed between a mobile client starting to search k−1peersand receiving the candidate answers from the agent.On theother hand,the query response time in the proactive mode is defined as the time elapsed between a mobile client startingto forward its query along with the cloaked spatial regionto the agent and receiving the candidate answers from theagent.The simulation model is implemented in C++usingCSIM[35].In all the experiments in this section,we consider an in-dividual random walk model that is based on“random way-point”model[7,8].At the beginning,the mobile clientsare randomly distributed in a spatial space of1,000×1,000square meters,in which a uniform grid structure of100×100cells is constructed.Each mobile client randomly chooses itsown destination in the space with a randomly determined speed s from a uniform distribution U(v min,v max).When the mobile client reaches the destination,it comes to a stand-still for one second to determine its next destination.Afterthat,the mobile client moves towards its new destinationwith another speed.All the mobile clients repeat this move-ment behavior during the simulation.The time interval be-tween two consecutive queries generated by a mobile client follows an exponential distribution with a mean of ten sec-onds.All the experiments consider one half-duplex wirelesschannel for a mobile client to communicate with its peers with a total bandwidth of2Mbps and a transmission range of250meters.When a mobile client wants to communicate with other peers or the location-based database server,it has to wait if the requested channel is busy.In the simulated mobile environment,there is a centralized location-based database server,and one wireless communication channel between the location-based database server and the mobile。