Beyond TCP-friendliness A New Paradigm for End-to-end Congestion Control
Real-Time Multiplayer Gaming Keeping Everyone on the Same Page Abstract
Real-Time Multiplayer Gaming: Keeping Everyone on the Same PageSean A. PfeiferEmbry-Riddle Aeronautical Universitysarcius@AbstractIn the multiplayer world, whether it is in simulations or games, keeping clients and servers updated with the correct information can be a difficult problem to tackle. In a business where millions of customers rely on your systems to react in a timely fashion, it is important to properly handle latency. One could also take into consideration that even projects such as military simulations must deal with these issues. One of the main issues is dealing with network latency on both the client and server side. Another huge issue should come to mind at the same time: what about people who are attempting to cheat, or misuse the system? In other words, how do we provide a means to deal with the latency issue while preventing these systems from being abused to provide an unfair advantage to certain players? There are a multitude of ways to deal with both issues, with trade offs for each that must be balanced in order to create an acceptable experience.1. IntroductionLatency and cheating issues create major problems when dealing with a multiplayer application that is supposed to be “real-time.” The idea of “real-time” is used in this context to describe applications that have a low tolerance for missed deadlines. In this case, the systems are “soft real-time,” with flexible deadlines focused more on player experience. Many times, fixing one issue can have a negative affect on the other; when clients have more authority and logic, they can operate under high latency, however this usually makes a wide opening for cheaters.In these games, the game environment is usually constantly changing on the server, and thus clients need to be kept properly updated. Many times events occur server-side that require a player to react in a short period of time or face consequences, and in this way the entire system is real-time. Usually, deadlines may be missed and the consequences may only be a slight degradation, however many the response time constraints differ based on the application.It may help to put the problem into perspective if one imagines the applications being described as multiplayer action games, such as the “first-person shooter” or “flight simulation” categories of games. For instance, if a player is defending their base from an enemy scout who is about to open a door to enter, a delay of a fraction of a second for that one player can cause the loss of the game for the whole team. Another good example would be a pilot attempting to land an airplane, and then all of the sudden the controls and instruments stop responding. If these controls and instruments don't respond within a certain period of time, the pilot is very likely to have a harsh landing. When these sorts of things happen, players tend to get very agitated, and if it's a constantly recurring issue, your product sales may suffer. The timing issues also pertain to other games, such as MMORPGs (Massively Multiplayer Online Role-Playing Games), however those applications can arguably be classified as “softer” in regards to latency.2. Latency IssuesOne may argue that the latency problem isn't substantial when taking into account today's high-speed networks. Today's high-speed networks are indeed helpful, however, many people have slow or unreliable broadband connections [1]. Running on a local area network is not feasible for the architecture of the majority of multiplayer games. Because of this, users can expect to experience packet loss, slow connections, and out of order packets, all due to the connections from one end to the other. This may make the problem seem like a simple networking issue, but, as you will see, the issue has a more central role in creating the application itself. On a Local Area Network (LAN), latencies are generally under 10 milliseconds, however, when dealing with the Internet as a whole, latencies can range from 100 milliseconds to 500 milliseconds [2]. Goodconnections are generally around 50 milliseconds [2].As stated before, having latent clients has a different impact on the gameplay of different genres. In general, games that require split-second reaction time, such as combat simulation or first-person shooter games, have smaller tolerance for latency and missed deadlines than others.Figure 2.1: Latency Thresholds per Genre [2]Figure 2.1 is a table that lists the approximate latency thresholds for a few of the major classes of games [2]. This data was collected as part of game latency studies, which illustrated “the effects of latency on performance for player actions with various deadline and precision requirements” [2]. The studies measured performance for certain time-related actions in different game genres, such as accuracy in a shooter game, or time taken to complete a lap in a racing game [2]. The different models presented as part of the figure describe how a player is represented in-game. The “avatar” model describes a game in which a player has a certain character to represent him or her inside of the game. Avatar games may have different perspectives, usually first-person or third-person, which describe whether the camera view is looking from the character's eyes or from outside, looking at the character. The “omnipresent” model is a situation where the player has no visible character, but instead, for instance, an overhead view of the game area and directs other units to certain locations. As you can see, the example genres that you would expect to have high reaction requirements have lower latency thresholds, while those that are a bit slower paced can tolerate more lag-time.Figure 2.2: Latency-Performance Measures in Genres [2]The graph in Figure 2.2 describes the performance in each of the three previously introduced game types [2]. The gray area “is a visual indicator of player tolerances for latency,” and the areas below are generally unacceptable [2]. Of course, these tolerances vary depending on the game and the player, but this graph should give a general idea of the concept [2].Rather than attempting to compensate for this issue by improving the connection – which is out of the hands of the game-developers – we can use techniques to allow “the game to compensate for connection quality” [1]. Two common techniquesare client-side prediction and lag compensation [1]. Each of these techniques has its own drawbacks and “quirks,” but theycan assist in solving the overall problem of unacceptable lag for players. Note that these do not actually reduce the latency ofthe connections, but rather the perceived latency in the game for players.Client-Side PredictionClient-side prediction is a method that attempts to “perform the client's movement locally and just assume, temporarily, thatthe server will accept and acknowledge the client commands directly” [1]. As a game designer, you have to be able to let goof the idea that clients should be “dumb terminals,” and must build more of the actual game logic into the clients [1].However, the client isn't in full control of the simulation – there is still an “authoritative server” running to ensure clients arewithin certain bounds (for example: not instantly teleporting across the map when they have to walk) [1]. With thisauthoritative server, “even if the client simulates different results than the server, the server's results will eventually correctthe client's incorrect simulation” [1]. One potential problem with using this technique is that “this can cause a veryperceptible shift in the player's position due to the fixing up of the prediction error that occurred in the past” [1].To perform this prediction, the client stores a certain number of commands that have been entered by the user, and when thereis lag in the connection, the client uses the last command acknowledged by the server and attempts to simulate using the mostrecent data from the server [1]. In a popular multiplayer game called Half-Life, “minimizing discrepancies between client and server logic is accomplished by sharing the identical movement code” for clients and servers [1]. One issue with thismethod of latency reduction is that clients will likely end up running the same commands repeatedly until they areacknowledged by the server, and deciding when to handle sounds or visual effects based on these commands [1]. This is allfine and nice in attempting to predict one's own movement, but what about predicting the movement of others in the gameworld, so they don't seem to lag about?One of two major methods of determining the location of other objects in the game world is “extrapolation” [1].Extrapolation is performed on the client, and makes an attempt to simulate an object forward in time to predict the nextposition of an object [1]. Using this method, clients can reduce the effect of lag if the extrapolated object has a straight,predictable path. However, in most first-person shooter games, “player movements are not very ballistic, but instead are verynon-deterministic and subject to high jerk” [1]. This possible constant change in player movement makes it unrealistic toapply this method to this circumstance. In order to help fix the large error that can occur in extrapolation, the extrapolationtime can be reduced, effectively reducing how far in the future the object is predicted to be [1]. However, players must stilllead their targets, even with “instant-hit weapons,” because of the latency being experienced [1]. In addition, players mayhave an extremely difficult time hitting opponents that seem to be “'warping' to new spots because of extrapolation errors”[1].The second major method is “interpolation,” which “can be viewed as always moving objects somewhat in the past withrespect to the last valid position received for the object” [1]. In this method, you buffer data in the client, and display the dataafter a certain period of time [1]. This method will help with the visual smoothness of other objects in the game-world,however can make the interaction latency issue worse – the players are not actually being drawn as fast as data is received,but rather drawn, say, 100 milliseconds in the past [1].Lag CompensationAnother common technique for compensating for latent connections is “lag compensation.” Lag compensation can bethought of as “taking a step back in time, on the server, and looking at the state of the world at the exact instant that the userperformed some action” [1]. So, this technique doesn't perform client-side actions, but rather deals with the state of objectson the server. Note that we are completely moving the state of the object back in time, and not simply the location [1]. As aresult, players can run on their own systems without seeming to experience latency [1]. The game design must be modifiedto take this functionality into account; this technique requires servers to store a certain amount of historical data in order toperform the “step back in time”.This may seem like a great remedy for latency, however, like client-side prediction, it has its drawbacks. At times,“inconsistencies that sometimes occur ... are from the points of view of the players being fired upon” [1]. One example ofthese inconsistencies is when a “highly lagged player shoots at a less lagged player and scores a hit, it can appear that thelagged player has somehow 'shot around a corner'” [1]. This sort of issue is not usually as extreme in “normal combatsituations,” however it can still occur at times [1]. In order to attempt to fix this and make it fair, the server should mostlikely only accept commands from a reasonable period of time in the past, otherwise the majority of players could have anunacceptable experience due to a small amount of extremely lagged players.3. CheatingThe previously introduced techniques assist in handling latency-performance issues in multiplayer games, but may interfere with other aspects of the game. The big question here is “How much authority and information do I want to give the clients?” When dealing with “dumb terminals,” clients simply send the server messages for actions they wish to perform, and the server replies with the reaction.If client-side prediction is done, the issue of cheating seems to be removed, as clients have no authority over decisions that are made. However, cheaters could possibly still abuse the system. One such example would be what's known as a “time-cheat,” giving the cheater an unfair advantage by allowing him or her to “see into the future, giving the cheater additional time to react to the other players' moves” [3]. A cheater using this technique may be hard to detect by players of the game, as it may seem that that the player is simply lagging and has good luck [3]. An example would be a cheater who has low latency, and is receiving data on time, but reports that data has been received late. In this circumstance, the cheater is claiming he or she received data late, and may make decisions based on past data. For instance, the cheater could fire a weapon at the previous position of a player, report that he fired in the past, and score a hit. If a player is able to use past data like this, they could potentially perform flawlessly, ruining the fairness of the game!In order to deal with this, one may employ a few different solutions. One solution would be to simply place anti-cheat software on the client's system, and update your software as new cheats are found. This solution can be an annoyance for players, as an extra, intrusive piece of software is generally frowned upon by gamers. In addition, this solution depends on cheats to occur in the wild where they can be analyzed to be fixed, and only after the cheat has become rampant. This method may be effective enough for some applications, however, may be unacceptable for others. Instead, the communication protocol can be modified to prevent certain kinds of time-cheats, using a protocol like the “sliding pipeline protocol” [3]. With this protocol, whose details are described in [3], it is guaranteed that “no cheater sees moves for a frame to which it has not yet committed a move and ... that no cheater may continually decide on a move with more recent information than a fair player had” [3]. In general, the game designer must take into account the fact that there will be players attempting to cheat in this way, and can adjust, on the fly, the amount of time the server will “look into the past” based on the latency of all users [3].As expected, issues can also occur when clients are running their own simulations of the game-world. When clients simulate the world they may be given more information than a client is normally allowed to see. For example, if a wall is in front of a player, that player usually cannot see what is on the other side, and so will not be informed of it. A common cheat would be to abuse this system to enable the player to see the locations of other players or objects – to see through walls. One of the only ways to prevent cheating in this instance is to install anti-cheat programs (such as Valve Anti-Cheat) that attempt to detect known cheats.When running simulations, clients must also be kept in check to prevent impossible or unfair actions. As noted before, there must be an authoritative server that checks on the actions of each client. A simple instance of this would be when a cheating client claims they have raced six laps around a race track, when in reality the race had just started. The client would report this, and the server would have to verify that the client's position had moved a valid amount, or else it should reject the claim made by the client. Without proper checking by the authoritative server, clients can get away with performing impossible feats.All in all, the latency issue must be dealt with while keeping the possibility of cheaters in mind – unless, of course, you don't care about cheaters!4. ConclusionsLatency issues in games are still very real today, even if the majority of players have high-speed connections. The trick in dealing with these issues lies in determining what type of technique to use for a specific system. Each of the techniques presented in this paper have their own quirks and downfalls, and each is very different in implementation. As each technique is deeply rooted in the functionality of the client and/or the server, the team must decide what combination of methods will be used during design. In addition to dealing with the latency issue, the team may or may not decide to take into account how cheaters will attempt to abuse the system – each method of latency reduction may introduce different possibilities for cheating. Again, the idea isn't to reduce the actual lag-time between client and server, but make “users find [the game's] performance acceptable in terms of the perceptual effect of its inevitable inconsistencies” [4]. Ultimately, the goal of the game designers when dealing with latency should be to make the game playable as well as fair.5. References[1]Bernier, Yahn, Latency Compensating Methods in Client/Server In-game Protocol Design and Optimization, Valve,[Cited 2007, October 4], Available HTTP: http://www.resourcecode.de/stuff/clientsideprediction.pdf.[2]Claypool, Mark, Claypool, Kajal, On Latency and Player Actions in Online Games, July 8, 2006, [Cited 2007,October 4], Available HTTP: ftp:///pub/techreports/pdf/06-13.pdf.[3]Cronin, Eric, Filstrup, Burton, Jamin, Sugih, Cheat-Proofing Dead Reckoned Multiplayer Games (ExtendedAbstract), University of Michigan, [Cited 2007, October 4], Available HTTP:/games/papers/adcog03-cheat.pdf.[4]Brun, Jeremy, Safaei, Farzad, Bousted, Paul, Managing Latency and Fairness in Networked Games, [Cited 2007,October 4], Available HTTP: /ft_gateway.cfm?id=1167861&type=pdf.。
CUBIC A New TCP-Friendly HighSpeedTCP Variant
CUBIC:一种新型高速TCP变种协议一、概述CUBIC是一种TCP（Transmission Control Protocol）拥塞控制协议，顾名思义，CUBIC可以理解为将传统TCP协议中的线性滑动窗口协议升级为三次的。
这样一来，使得拥塞控制协议具有更大的可扩展性，尤其适合用在高速和长距离链路上。
同时，CUBIC算法对于不同链路上的公平带宽分配以及窗口增减策略都有改进。
CUBIC是一个已在Linux系统上实现的拥塞控制协议，所以其重要性自然不言而喻。
二、问题的提出随着Internet的发展，网络中出现了越来越多的高速和长距离链路，这些链路的特点是时延带宽积（BDP）很大，也就是说，这些链路所能容纳的总数据量很大。
传统TCP协议，例如TCP-Reno、TCP-NewReno、TCP-SACK中，每过一个RTT（Round Trip Times），窗口增加一个单位，这使得TCP的数据传输速度缓慢，远不能充分利用网络带宽。
这里，作者举了一个例子来说明传统TCP协议不能充分利用网络带宽：假设网络带宽是10Gbps，RTT是100ms，数据包是固定的1250字节，则此网络所能容纳的数据包总量是：（10*109*0.1）/（1250*8）=105个数据包。
假设窗口从50000开始增长，也需要50000个RTT才能达到网路的满负荷，如果一个TCP流在此之前结束（显然往往如此），则未充分利用带宽。
三、BIC-TCP的优点针对上述问题，很多TCP变种协议被提出，BIC-TCP是其中的一个佼佼者。
BIC-TCP使用一种二分搜索算法：假如上次发生TCP丢包时的窗口大小为max，上个未发生丢包的RTT的窗口大小为min，BIC-TCP中的窗口首先增长到max和min的中点mid。
窗口大小超过mid后，若未发生丢包，表明网络还能容纳更多的数据包，则BIC-TCP算法将mid设为新的min，再次开始二分搜索。
这种算法的合理之处是可想而知的：如果网络状况没有发生剧变，当前链路的容量必然是位于上次丢包发生后的最大和最小之间。
单位招聘考试PTN专业(试卷编号161)
单位招聘考试PTN专业(试卷编号161)1.[单选题]R860设备最大支持本地会话的ID为（）A)1200B)1800C)1000答案:B解析:2.[单选题]当前SPN网络中，ISIS协议一般使用（）层次A)1) LEVEL1B)2) LEVEL2C)3) LEVEL 1/2答案:B解析:3.[单选题]SPE从NPE学到核心网路由后，不再向其他UPE和SPE发布，只向UPE发布一条（）A)默认路由B)明细路由C)黑洞路由答案:A解析:4.[单选题]烽火CiTRANS R865设备共有（）槽位，其中业务槽位（）个A)32/24B)32/26C)30/24D)30/26答案:A解析:5.[单选题]U31服务器对应的SQL Server默认的用户名是A)RootB)ZTEC)adminD)sa答案:D解析:：SNMPB)读团体名：fiber-RO读写团体名：fiber-RW安全名：fiberhome组名：onlye访问控制列表名称：SNMPC)用户组名：NMS用户名：fiberhome访问控制列表名：SNMPD)以上说法均不正确答案:C解析:7.[单选题]OAM测试，做的一条百兆业务，测试环回帧功能时，设置完成后，需要在源站的哪个盘上点右键进行“状态监视”A)上话业务的ESJ1盘B)XCUJ1盘C)XSJ1盘D)NMUJ1盘答案:B解析:8.[单选题]对于CES业务，当AC侧需要加载保护时，如果加载的是1+1保护，那么主备AC端口会受到2份完全一样的报文，此时该如何转发？（）A)与传统网络一样，同样进行仿真转发，再还原B)对与两份完全一样的报文，在备用AC端口进行丢弃C)对与两份完全一样的报文，在接入侧设备进行选收D)对与两份完全一样的报文，在接入侧设备进行并收，透传给基站答案:B解析:9.[单选题]下面评估内容不属于结构评估的是A)超大环和超长链B)成环率C)超大汇聚节点D)双归保护结构答案:D解析:10.[单选题]PTN640设备在配置1:1保护时，LSP标签值正向与反向（ ）A)可以相同；B)一定相同；C)一定不同；D)没有要求。
IGMP协议
IGMP协议概述The Internet Group Management Protocol(IGMP)is a network‑layer protocol used by hosts and ad‑jacent routers on an Internet Protocol(IP)network to report their multicast group memberships.It is an essential component of IP multicast,which enables efficient delivery of data to multiple hosts simultaneously.BackgroundIn traditional IP networks,data packets are typically sent to a unicast address,which means they are delivered to a specific destination host.However,in scenarios where data needs to be sent to multiple recipients simultaneously,such as multimedia streaming or real‑time collaboration applications,the unicast approach becomes inefficient and resource‑consuming.This is where multicast comes into play.What is Multicast?Multicast is a communication method that allows a single sender to transmit data packets to a group of receivers.Instead of sending separate copies of the data to each receiver,the sender multicasts the data once,and it is then replicated and delivered only to the members of the multicast group who have expressed interest in receiving the data.Role of IGMPIGMP plays a crucial role in enabling hosts to join and leave multicast groups dynamically.It allows routers to learn which hosts are interested in receiving multicast traffic for specific groups and effi‑ciently forward the data only to those interested hosts.How IGMP Works1.Host Joins a Multicast Group:When a host wants to receive multicast traffic for a specific group,it sends an IGMP join message to its local router,indicating its interest in joining the group. 2.Router Membership Query:Routers periodically send IGMP membership queries on the networkto discover which hosts belong to multicast groups.These queries elicit IGMP membership re‑ports from the hosts.3.Host Membership Reports:Upon receiving a query,hosts respond with IGMP membership re‑ports,indicating the multicast groups they are interested in.4.Router Forwarding:Routers maintain a list of active multicast groups and their associated hosts.They use this information to forward multicast traffic only to the hosts that have joined the re‑spective groups.Benefits and ApplicationsIGMP enables efficient distribution of multicast traffic,reducing network congestion and bandwidth consumption.It finds applications in various scenarios,including:•Video streaming and IPTV•Online gaming and interactive applications•Software‑defined networking(SDN)•Content delivery networks(CDNs)•Collaborative tools and virtual classroomsSecurity and LimitationsWhile IGMP facilitates multicast communication,it’s important to consider security aspects and im‑plement appropriate measures to prevent unauthorized access or malicious activities.Additionally, IGMP has some limitations,such as scalability challenges in large networks and potential issues with router performance under heavy multicast traffic.In conclusion,IGMP is a critical protocol for managing multicast group memberships in IP networks. By allowing hosts to join and leave multicast groups dynamically,IGMP enables efficient and scalable delivery of multicast traffic,catering to various applications and improving network performance. IGMP协议的工作原理IGMP（Internet Group Management Protocol）是一种网络层协议，用于在Internet协议（IP）网络上的主机和相邻路由器之间报告它们的组播组成员关系。
计算机网络课后题答案第九章【精选】
第九章无线网络9-01．无线局域网都由哪几部分组成？无线局域网中的固定基础设施对网络的性能有何影响？接入点AP 是否就是无线局域网中的固定基础设施？答：无线局域网由无线网卡、无线接入点(AP)、计算机和有关设备组成，采用单元结构，将整个系统分成许多单元，每个单元称为一个基本服务组。
所谓“固定基础设施”是指预先建立起来的、能够覆盖一定地理范围的一批固定基站。
直接影响无线局域网的性能。
接入点AP 是星形拓扑的中心点，它不是固定基础设施。
9-02．Wi-Fi 与无线局域网WLAN 是否为同义词？请简单说明一下。
答：Wi-Fi 在许多文献中与无线局域网WLAN 是同义词。
802.11 是个相当复杂的标准。
但简单的来说，802.11 是无线以太网的标准，它是使用星形拓扑，其中心叫做接入点AP(Access Point)，在MAC 层使用CSMA/CA 协议。
凡使用802.11系列协议的局域网又称为Wi-Fi(Wireless-Fidelity,意思是“无线保真度”)。
因此，在许多文献中，Wi-Fi 几乎成为了无线局域网WLAN 的同义词。
9-03 服务集标示符SSID 与基本服务集标示符BSSID 有什么区别？答：SSID（Service Set Identifier）AP 唯一的ID 码，用来区分不同的网络，最多可以有32 个字符，无线终端和AP 的SSID 必须相同方可通信。
无线网卡设置了不同的SSID 就可以进入不同网络，SSID 通常由AP 广播出来，通过XP 自带的扫描功能可以相看当前区域内的SSID。
出于安全考虑可以不广播SSID，此时用户就要手工设置SSID 才能进入相应的网络。
简单说，SSID 就是一个局域网的名称，只有设置为名称相同SSID 的值的电脑才能互相通信。
BSS 是一种特殊的Ad-hoc LAN 的应用，一个无线网络至少由一个连接到有线网络的AP 和若干无线工作站组成，这种配置称为一个基本服务装置BSS (Basic Service Set)。
TR-143
7.1 NOTATION.......................................................................................................... 23 7.2 DOWNLOAD PROFILE ......................................................................................... 23 7.3 DOWNLOADTCP PROFILE.................................................................................. 23 7.4 UPLOAD PROFILE ............................................................................................... 24 7.5 UPLOADTCP PROFILE........................................................................................ 24 7.6 UDPECHO PROFILE ........................................................................................... 25 7.7 UDPECHOPLUS PROFILE ................................................................................... 25
基于TCPN的复杂航班推出问题的建模与仿真
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图 １ 共用 同一 中间机坪 滑行道 的推 出问题 示意图 （） ６ 该模 型只考虑管制 员在处理 两个相继 入库航
（ ）Ｅ是 弧表 达式 （ｒ ｅｐｅｓ ｎｆｎｔ ｎ ， ５ ａ ｘｒｓ ｏ ｃｏ ） 是定 ｃ ｉ ｕ ｉ 义 在有向连接弧 Ａ上时间或非时间的表达式 ；
2021年IMS题库
IMS试题库一、填空题1.属于会话控制层网元有 CSCF 、 BGCF 、MGCF 、MRFC 、I-BCF2.IMS系统中，顾客私有标记为 IMPI ，顾客公有标记为 IMPU ；私有标记重要用于鉴权和认证；公有标记重要用于在业务呼喊时作为对外可寻址标记；3.DNS负责从 URL地址到 IP地址转换，ENUM负责从 E.164号码到 URL地址转换。
4.在IMS2.0中，使用ATCA平台IMS CORE产品整个软件安装重要涉及：各单板底层软件安装、 OMU软件安装和LMT安装、 GTAS SAM安装、 HSS数据库连接配备和运营准备、 ICG软件安装、 SMU和SAM客户端安装、各网元配备和加载。
5.SDP合同中，o行描述会话所有者关于参数，m行描述会话媒体信息6.PSI含义是公共服务标记7.SIP 合同响应消息中，1××代表暂时响应，2××代表成功，3××代表重定向，4××代表客户端错误，5××代表服务端错误，6××代表全局错误。
8.划分VLAN重要作用是隔离广播域，抑制广播报文、分隔不同顾客,提高网络安全性。
9.VRRP意思为虚拟路由器冗余合同，其在组网中重要作用是通过VRRP合同来实现路由器之间冗余和倒换，提高IP承载网可靠性，同步对端设备只看到一种虚拟路由器。
10.PE 是指服务提供商骨干网边沿路由器，CE是指直接与服务提供商相连顾客设备。
11.CSCF产品重要基本进程有： SCU 、CDB 、DPU 、BSU 。
二、判断题（对的打“√”，错误打“×”。
）1.3GPP R5版本定位于提供IP实时多媒体业务，核心网在PS基本上增长了IP多媒体域（IMS〕，IMS重要功能在控制层面，承载通过PS域。
（T）2.OMA组织重要是制定IMS系统架构方面关于规范。
（F）3.在运营商内设立各种HSS状况下，I-CSCF在登记注册及事务建立过程中通过SLF获得顾客签约数据所在HSS域名，SLF可与HSS合设。
RKS-G4028系列28G端口（带802.3bt PoE选项）全Gigabit模块管理以太网交换机
RKS-G4028Series28G-port (with 802.3bt PoE option)full Gigabit modular managed EthernetswitchesFeatures and Benefits•Meets a wide range of demands from Fast Ethernet to full Gigabit industrialnetworks (up to 28Gigabit ports)•Modular interfaces for flexible connector type combinations •Support for IEEE 802.3bt PoE for up to 90W output per port •High EMC immunity compliant with IEC 61850-3and IEEE 1613•Hardware-based IEEE 1588PTP for high-precision time synchronization •Turbo Ring and Turbo Chain (recovery time <20ms @250switches)1,andSTP/RSTP/MSTP for network redundancy•-40to 75°C operating temperature range•Supports MXstudio for easy,visualized industrial network management •Developed according to the IEC 62443-4-1and compliant with the IEC62443-4-2industrial cybersecurity standardsCertificationsIntroductionThe RKS-G4028Series is designed to meet the rigorous demands of mission-critical applications for industry and business,such as power substation automation systems (IEC 61850-3,IEEE 1613),railway applications (EN 50121-4),and factory automation systems.The RKS-G4028Series’Gigabit and Fast Ethernet backbone,redundant ring,and 24VDC,48VDC,or 110/220VDC/VAC dual isolated redundant power supplies increase the reliability of your communications and save on wiring costs.The modular design of the RKS-G4028Series also makes network planning easy,and allows greater flexibility by letting you install up to 28Gigabit ports with various connector types.Additional Features and Benefits•Layer 3switching functionality to move data and information across networks (L3models only)•IEEE 1588v2PTP (Precision Time Protocol)for network time synchronization•Command line interface (CLI)for quickly configuring major managed functions•IGMP snooping and GMRP for filtering multicast traffic•Port-based VLAN,IEEE 802.1Q VLAN,and GVRP to ease network planning•QoS (IEEE 802.1p/1Q and TOS/DiffServ)to increase determinism •IEEE 802.3ad,LACP for optimum bandwidth utilization •Line-swap fast recovery•TACACS+,IEEE 802.1X,SNMPv3,HTTPS,and SSH to enhance network security•SNMPv1/v2c/v3for different levels of network management •RMON for proactive and efficient network monitoring•Bandwidth management prevents unpredictable network status with “Lock port”to restrict access to authorized MAC addresses •Port mirroring for online debugging•Automatic warning by exception through email and relay output •Automatic recovery of connected device’s IP addresses•Configurable by web browser,Telnet/serial console,CLI,Windows utility,and ABC-02-USB automatic backup configuratorSpecificationsInput/Output InterfaceAlarm Contact Channels1relay output with current carrying capacity of 2A @24VDC1.If the port link speed is 1Gigabit or higher,the recovery time is <50ms.Ethernet Interface10/100/1000BaseT(X)Ports(RJ45connector)RKS-G4028-4GT models:4RKS-G4028-L3-4GT models:4100/1000BaseSFP Slots RKS-G4028-4GS models:4RKS-G4028-L3-4GS models:4RKS-G4028-PoE-4GS models:4RKS-G4028-L3-PoE-4GS models:4Module There are3module slots on the ers can select different types of modules toinsert into the switch.The modules that can be selected include8-port/6-port moduleswith10/100/1000BaseT(X),10/100BaseT(X),100/1000BaseSFP,or100BaseFX(SC/STconnector)interfaces.Refer to Expansion Modules in the Accessories section for a full list of supportedinterface modules.Standards IEEE802.1D-2004for Spanning Tree ProtocolIEEE802.1p for Class of ServiceIEEE802.1Q for VLAN TaggingIEEE802.1s for Multiple Spanning Tree ProtocolIEEE802.1w for Rapid Spanning Tree ProtocolIEEE802.1X for authenticationIEEE802.3for10BaseTIEEE802.3ab for1000BaseT(X)IEEE802.3ad for Port Trunk with LACPIEEE802.3u for100BaseT(X)and100BaseFXIEEE802.3x for flow controlIEEE802.3z for1000BaseSX/LX/LHX/ZXIEEE802.3bt for Power over EthernetEthernet Software FeaturesManagement IPv4/IPv6Note:IPv6is available for L2models only.Flow controlBack Pressure Flow ControlDHCP Server/ClientARPRARPLLDPLinkup DelaySMTPSNMP TrapSNMP InformSNMPv1/v2c/v3RMONTFTPSFTPHTTPHTTPSTelnetSyslogPrivate MIBFiber checkDHCP Relay Agent(Option82)Port Mirroring(SPAN,RSPAN)Filter GMRPGVRPGARP802.1QIGMP Snooping v1/v2/v3IGMP QuerierRedundancy Protocols STPRSTPTurbo Ring v2Turbo ChainRing CouplingDual-HomingMRPLink AggregationNetwork Loop ProtectionMSTPRouting Redundancy L3models:VRRPSecurity Broadcast storm protectionRate LimitAccess control listStatic port lockSticky MACHTTPS/SSLSSHRADIUSTACACS+Login and password policySecure bootMAC authentication bypassTrust access controlDynamic ARP InspectionDHCP SnoopingIP Source GuardTime Management SNTPIEEE1588v2PTP(hardware-based)Supported power profiles:IEEE1588Default2008,IEC61850-9-3-2016,IEEE C37.238-2017NTP Server/ClientNTP AuthenticationProtocols IPv4/IPv6Note:IPv6is available for L2models only.TCP/IPUDPICMPARPRARPTFTPDNSNTP ClientDHCP ServerDHCP Client802.1XQoSHTTPSHTTPEtherNet/IPModbus TCPTelnetSMTPSNMPv1/v2c/v3RMONSyslogUnicast Routing L3models:OSPF,Static RouteMIB P-BRIDGE MIBQ-BRIDGE MIBIEEE8021-SPANNING-TREE-MIBIEEE8021-PAE-MIBIEEE8023-LAG-MIBLLDP-EXT-DOT1-MIBLLDP-EXT-DOT3-MIBSNMPv2-MIBRMON MIB Groups1,2,3,9Power Substation MMS1588PTP Power Profile IEC61850-9-31588PTP Power Profile C37.238-2017Switch PropertiesIGMP Groups1024Jumbo Frame Size9.6KBMAC Table Size16KMax.No.of VLANs256Packet Buffer Size 1.5MbitsPriority Queues8VLAN ID Range VID1to4094USB InterfaceStorage Port USB Type AMicroSD InterfaceStorage Port MicroSD cardSerial InterfaceConsole Port RS-232(RJ45)Power ParametersTotal PoE Power Budget PoE models:300WMax.PoE Power Output per Port PoE models:IEEE802.3af:15.4WIEEE802.3at:30WIEEE802.3bt:90WInput Voltage RKS-G4028-LV models:24/48VDCRKS-G4028-2LV models:24/48VDC(redundant power supplies)RKS-G4028-HV models:110/220VAC,110/220VDCRKS-G4028-2HV models:110/220VAC,110/220VDC(redundant power supplies)PoE models:48VDC(for the PoE system)Operating Voltage RKS-G4028-LV/2LV models:18to72VDCRKS-G4028-HV/2HV models:88to300VDC,85to264VACPoE models:46to57VDC(for the PoE system)Overload Current Protection SupportedReverse Polarity Protection SupportedInput Current RKS-G4028-LV/2LV models:Max.2.53A@24VDCMax.1.25A@48VDCRKS-G4028-HV/2HV models:Max.0.55A@110VDCMax.0.29A@220VDCMax.1.01A@110VACMax.0.62A@220VACEPS(PoE models only):Max.7.50A@48VDCPower Consumption(Max.)RKS-G4028-LV/2LV models:Max.60.72W@24VDCMax.60W@48VDCRKS-G4028-HV/2HV models:Max.60.5W@110VDCMax.63.8W@220VDCMax.62.2W@110VACMax.64.1W@220VACNote:These are the maximum power consumption ratings for the device with themaximum number of modules installed.Physical CharacteristicsIP Rating IP30Dimensions440x44x300mm(17.32x1.37x11.81in)Weight RKS-G4028-LV/HV models:4900g(10.80lb)RKS-G4028-2LV/2HV models:5200g(11.46lb)RKS-G4028-PoE-LV/HV models:5000g(11.02lb)RKS-G4028-PoE-2LV/2HV models:5300g(11.68lb)Installation Rack mountingEnvironmental LimitsOperating Temperature-40to75°C(-40to167°F)Storage Temperature(package included)-40to85°C(-40to185°F)Ambient Relative Humidity5to95%(non-condensing)Standards and CertificationsSafety EN62368-1UL62368-1UL61010EMC EN55032/35EMI CISPR32,FCC Part15B Class ATraffic Control NEMA TS2EMS IEC61000-4-2ESD:Contact:8kV;Air:15kVIEC61000-4-3RS:80MHz to1GHz:35V/mIEC61000-4-4EFT:Power:4kV;Signal:4kVIEC61000-4-5Surge:Power:4kV;Signal:4kVIEC61000-4-6CS:10VIEC61000-4-8PFMFIEC61000-4-11DIPsPower Substation IEC61850-3IEEE1613Railway EN50121-4Freefall IEC60068-2-32Shock IEC60068-2-27Vibration IEC60068-2-6MTBFTime RKS-G4028-4GT-HV models:572,888hoursRKS-G4028-4GT-2HV models:518,894hoursRKS-G4028-4GS-HV models:529,925hoursRKS-G4028-4GS-2HV models:483,436hoursRKS-G4028-4GT-LV models:548,589hoursRKS-G4028-4GT-2LV models:479,574hoursRKS-G4028-4GS-LV models:508,639hoursRKS-G4028-4GS-2LV models:449,160hoursRKS-G4028-PoE-4GS-HV models:508,190hoursRKS-G4028-PoE-4GS-2HV models:465,282hoursRKS-G4028-PoE-4GS-LV models:488,598hoursRKS-G4028-PoE-4GS-2LV models:433,472hoursStandards Telcordia(Bellcore),GBWarrantyWarranty Period5yearsDetails See /warrantyPackage ContentsDevice1x RKS-G4028Series switchInstallation Kit2x rack-mounting ear4x protective caps for unused SFP ports(for RKS-G4028-GS models only)8x round stickers for module screwsDocumentation1x quick installation guide1x warranty cardNote 1.Only the RKS-G4028-PoE Series and RKS-G4028-L3-PoE models support PoEfunctionality with RM-G4000-8GPoE and/or RM-G4000-8PoE modules.2.Power over Ethernet requires the48VDC external power supply(46to57VDC).3.The48VDC external power supply,SFP modules,and modules from the RM-G4000Module Series need to be purchased separately for use with this product.DimensionsOrdering InformationModel Name Max.No.ofPortsPoE Support L3Functionality Input VoltageRedundantPower SuppliesExternal PowerSupplyOperatingTemp.RKS-G4028-4GT-HV-T28––110/220VAC/VDC––-40to75°CRKS-G4028-4GT-2HV-T28––110/220VAC/VDC✓–-40to75°CRKS-G4028-4GS-HV-T28––110/220VAC/VDC––-40to75°CRKS-G4028-4GS-2HV-T28––110/220VAC/VDC✓–-40to75°CRKS-G4028-4GT-LV-T28––24/48VDC––-40to75°C RKS-G4028-4GT-2LV-T28––24/48VDC✓–-40to75°C RKS-G4028-4GS-LV-T28––24/48VDC––-40to75°C RKS-G4028-4GS-2LV-T28––24/48VDC✓–-40to75°CRKS-G4028-L3-4GT-HV-T 28–✓110/220VAC/VDC––-40to75°CRKS-G4028-L3-4GT-2HV-T 28–✓110/220VAC/VDC✓–-40to75°CRKS-G4028-L3-4GS-HV-T 28–✓110/220VAC/VDC––-40to75°CRKS-G4028-L3-4GS-2HV-T 28–✓110/220VAC/VDC✓–-40to75°CRKS-G4028-L3-4GT-LV-T28–✓24/48VDC––-40to75°CRKS-G4028-L3-4GT-2LV-T28–✓24/48VDC✓–-40to75°CRKS-G4028-L3-4GS-LV-T28–✓24/48VDC––-40to75°CRKS-G4028-L3-4GS-2LV-T28–✓24/48VDC✓–-40to75°CRKS-G4028-PoE-4GS-HV-T 28✓–110/220VAC/VDC–✓-40to75°CRKS-G4028-PoE-4GS-2HV-T 28✓–110/220VAC/VDC✓✓-40to75°CRKS-G4028-PoE-4GS-LV-T28✓–24/48VDC–✓-40to75°CRKS-G4028-PoE-4GS-2LV-T28✓–24/48VDC✓✓-40to75°CRKS-G4028-L3-PoE-4GS-HV-T 28✓✓110/220VAC/VDC–✓-40to75°CRKS-G4028-L3-PoE-4GS-2HV-T 28✓✓110/220VAC/VDC✓✓-40to75°CRKS-G4028-L3-PoE-4GS-LV-T28✓✓24/48VDC–✓-40to75°CRKS-G4028-L3-PoE-4GS-2LV-T28✓✓24/48VDC✓✓-40to75°C Accessories(sold separately)Expansion ModulesRM-G4000-8TX Fast Ethernet module with810/100BaseT(X)portsRM-G4000-8SFP Fast Ethernet module with8100BaseSFP slotsRM-G4000-8PoE Fast Ethernet module with810/100BaseT(X)IEEE802.3bt PoE portsRM-G4000-8GTX Gigabit Ethernet module with810/100/1000BaseT(X)portsRM-G4000-8GSFP Gigabit Ethernet module with8100/1000BaseSFP slotsRM-G4000-8GPoE Gigabit Ethernet module with810/100/1000BaseT(X)IEEE802.3bt PoE portsRM-G4000-6MSC Fast Ethernet module with6multi-mode100BaseFX ports with SC connectorsRM-G4000-6MST Fast Ethernet module with6multi-mode100BaseFX ports with ST connectorsRM-G4000-6SSC Fast Ethernet module with6single-mode100BaseFX ports with SC connectorsRM-G4000-4MSC2TX Fast Ethernet module with4multi-mode100BaseFX ports with SC connectors,210/100BaseT(X)portsRM-G4000-4MST2TX Fast Ethernet module with4multi-mode100BaseFX ports with ST connectors,210/100BaseT(X)portsRM-G4000-4SSC2TX Fast Ethernet module with4single-mode100BaseFX ports with SC connectors,210/100BaseT(X)portsRM-G4000-2MSC4TX Fast Ethernet module with2multi-mode100BaseFX ports with SC connectors,410/100BaseT(X)portsRM-G4000-2MST4TX Fast Ethernet module with2multi-mode100BaseFX ports with ST connectors,410/100BaseT(X)portsRM-G4000-2SSC4TX Fast Ethernet module with2single-mode100BaseFX ports with SC connectors,410/100BaseT(X)portsStorage KitsABC-02-USB Configuration backup and restoration tool,firmware upgrade,and log file storage tool for managedEthernet switches and routers,0to60°C operating temperatureABC-02-USB-T Configuration backup and restoration tool,firmware upgrade,and log file storage tool for managedEthernet switches and routers,-40to75°C operating temperatureABC-03-microSD-T MicroSD-based configuration backup and restoration tool,firmware upgrades,and log file storage toolfor managed Ethernet switches and WLAN products,-40to85°C operating temperatureSFP ModulesSFP-1FELLC-T SFP module with1100Base single-mode with LC connector for80km transmission,-40to85°Coperating temperatureSFP-1FEMLC-T SFP module with1100Base multi-mode,LC connector for2/4km transmission,-40to85°C operatingtemperatureSFP-1FESLC-T SFP module with1100Base single-mode with LC connector for40km transmission,-40to85°Coperating temperatureSFP-1G10ALC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for10km transmission;TX1310nm,RX1550nm,0to60°C operating temperatureSFP-1G10BLC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for10km transmission;TX1550nm,RX1310nm,0to60°C operating temperatureSFP-1G20ALC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for20km transmission;TX1310nm,RX1550nm,0to60°C operating temperatureSFP-1G20BLC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for20km transmission;TX1550nm,RX1310nm,0to60°C operating temperatureSFP-1G40ALC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for40km transmission;TX1310nm,RX1550nm,0to60°C operating temperatureSFP-1G40BLC WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for40km transmission;TX1550nm,RX1310nm,0to60°C operating temperatureSFP-1G10ALC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for10km transmission;TX1310nm,RX1550nm,-40to85°C operating temperatureSFP-1G10BLC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for10km transmission;TX1550nm,RX1310nm,-40to85°C operating temperatureSFP-1G20ALC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for20km transmission;TX1310nm,RX1550nm,-40to85°C operating temperatureSFP-1G20BLC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for20km transmission;TX1550nm,RX1310nm,-40to85°C operating temperatureSFP-1G40ALC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for40km transmission;TX1310nm,RX1550nm,-40to85°C operating temperatureSFP-1G40BLC-T WDM-type(BiDi)SFP module with11000BaseSFP port with LC connector for40km transmission;TX1550nm,RX1310nm,-40to85°C operating temperatureSFP-1GEZXLC SFP module with11000BaseEZX port with LC connector for110km transmission,0to60°C operatingtemperatureSFP-1GEZXLC-120SFP module with11000BaseEZX port with LC connector for120km transmission,0to60°C operatingtemperatureSFP-1GLHLC SFP module with11000BaseLH port with LC connector for30km transmission,0to60°C operatingtemperatureSFP-1GLHXLC SFP module with11000BaseLHX port with LC connector for40km transmission,0to60°C operatingtemperatureSFP-1GLSXLC SFP module with11000BaseLSX port with LC connector for1km/2km transmission,0to60°Coperating temperatureSFP-1GLXLC SFP module with11000BaseLX port with LC connector for10km transmission,0to60°C operatingtemperatureSFP-1GSXLC SFP module with11000BaseSX port with LC connector for300m/550m transmission,0to60°Coperating temperatureSFP-1GZXLC SFP module with11000BaseZX port with LC connector for80km transmission,0to60°C operatingtemperatureSFP-1GLHLC-T SFP module with11000BaseLH port with LC connector for30km transmission,-40to85°C operatingtemperatureSFP-1GLHXLC-T SFP module with11000BaseLHX port with LC connector for40km transmission,-40to85°Coperating temperatureSFP-1GLSXLC-T SFP module with11000BaseLSX port with LC connector for1km/2km transmission,-40to85°Coperating temperatureSFP-1GLXLC-T SFP module with11000BaseLX port with LC connector for10km transmission,-40to85°C operatingtemperatureSFP-1GSXLC-T SFP module with11000BaseSX port with LC connector for300m/550m transmission,-40to85°Coperating temperatureSFP-1GZXLC-T SFP module with11000BaseZX port with LC connector for80km transmission,-40to85°C operatingtemperatureSFP-1GTXRJ45-T SFP module with11000BaseT port with RJ45connector for100m transmission,-40to75°C operatingtemperatureSoftwareMXview-100MXview license for100nodesMXview-50MXview license for50nodesMXview-250MXview license for250nodesMXview-500MXview license for500nodesMXview-1000MXview license for1000nodesMXview-2000MXview license for2000nodesMXview Upgrade-50MXview license expansion for50nodes©Moxa Inc.All rights reserved.Updated June14,2023.This document and any portion thereof may not be reproduced or used in any manner whatsoever without the express written permission of Moxa Inc.Product specifications subject to change without notice.Visit our website for the most up-to-date product information.。
UDC3200类型数字控制器选型指南（PDF文件）说明书
51-51-16U-80Issue 17Page 1 of 3UDC3200 Universal Digital ControllerModel Selection GuideInstructionsSelect the desired key number. The arrow to the right marks the selection available.Make the desired selections from Tables I through VI using the column below the proper arrow. A dot ( ) denotes availability.Key Number----_ _ _ _ _- _KEY NUMBER - UDC3200 Single Loop ControllerIf ApplicableSelection Stocking P/NDigital Controller for use with 90 to 250Vac Power DC3200 Digital Controller for use with 24Vac/dc PowerDC3201TABLE I - Specify Control Output and/or AlarmsTABLE II - Communications and Software Selections0 _ _ _1 _ _ _2 _ _ _3 _ _ _ _ 0 _ __ A _ __ B _ __ C _ _No Selection_ _ 0 __ _ _ RInfrared interfaceInfrared Interface Included (Can be used with a Pocket PC)Software SelectionsStandard Functions, Includes Accutune Math OptionSet Point Programming (1 Program, 12 Segments) Set Point Programming Plus Math Reserved Solid State Relay (1 Amp) Plus Alarm 1 (5 Amp Form C Relay)_ A Open Collector Plus Alarm 1 (5 Amp Form C Relay)_ TCommunicationsNoneAuxiliary Output/Digital Inputs (1 Aux and 1 DI or 2 DI)RS-485 Modbus Plus Auxiliary Output/Digital Inputs10 Base-T Ethernet (Modbus RTU) Plus Auxiliary Output/Digital Inputs T _Dual 2 Amp Relays (Both are Form A) (Heat/Cool Applications)R _Output #2 and Alarm#1 or Alarms 1 and 2No Additional Outputs or Alarms _ 0One Alarm Relay Only_ B E-M Relay (5 Amp Form C) Plus Alarm 1 (5 Amp Form C Relay)_ E DescriptionAvailabilityOutput #1Current Output (4 to 20ma, 0 to 20 ma) C _Electro Mechanical Relay (5 Amp Form C)E _Solid State Relay (1 Amp)A _Open Collector transistor output_ _ _ _ _ __ __ _ _ __ _ __ _IIIIIIIVVVIUDC3200 ControllerNew! Easy To Use UDC3200 1/4 DIN Single Loop ControllerThe UDC3200 Controller packs new powerful features while retaining all the simplicity and flexibility of the industry standard UDC3300 Controller. Many new optional features include: - Enhanced Display- Built-in infrared communications port for configuring with a Pocket PC or Laptop - PC Based Configuration Tools - Ethernet Communications - Two Analog Inputs- Accutune III, Fast/Slow, Heat/Cool - Thermocouple Health Monitoring51-51-16U-80Issue 17Page 2 of 3ORDERING INSTRUCTIONS: These are provide as guidance for ordering such as those listed1. Part numbers are provided to facilitate Distributor Stock.2. Orders may be placed either by model selection or by part number.3. Part numbers are shown within the model selection tables to assist with compatibility information.4. Orders placed by model selection are systematically protected against incompatibility.5. Compatibility assessment is the responsibility of the purchaser for orders placed by part number.6. Items labeled as N/A are not available via the stocking program and must be ordered by model selection.AvailabilitySection 5Page: UDC-79Page 1 of 3UDC3200Supplemental Universal Digital Controller Accessories & Kits。
RCNA试题多选
1、一个TCP/IP的B类地址默认子网掩码是A、255.255.0.0B、/8C、255.255.255.0D、/24E、/16F、255.0.0.0标准答案： AE2、下列哪些是RIP路由协议的特点?A、距离向量B、每60秒一次路由更新C、管理代价120D、支持负载均衡标准答案： ACD3、静态路由配置命令ip route包含下列哪些参数：A、目的网段及掩码B、本地接口C、下一跳路由器的IP地址D、下一跳路由器的MAC地址标准答案： ABC4、 FTP使用的端口号为：A、20B、21C、23D、110标准答案： AB5、RIP第二版与RIP第一版相比，做了什么改进：A、增加了接口验证，提高了可靠性B、采用组播方式进行路由更新，而不是广播方式C、最大跳数（hop）增加到255D、支持变长子网掩码（VLSM）标准答案： ABD6、下列哪些属于R2624的合法命令行模式?A、用户模式B、特权模式C、全局配置模式D、接口配置模式E、VLAN配置模式标准答案： ABCD7、面向连接的网络服务主要包括哪几个工作阶段?A、呼叫建立B、数据传输C、负载均衡D、呼叫终止标准答案： ABD8、 PPP支持哪些网络层协议?A、IPB、IPXC、RIPD、FTP标准答案： AB9、下列哪些路由协议属于链路状态路由协议？A、RIPv1B、IS-ISC、OSPFD、RIPv2E、静态路由标准答案： BC10、以下哪些设备可以隔离广播？A、HubB、RepeaterC、RouterD、BridgeE、Switch标准答案： CDE11、如何在R2624路由器上测试到达目的端的路径?A、tracertB、pathpingC、tracerouteD、ping的扩展形式标准答案： CD12、假设你是学校的网络管理员，原来有三个VLAN，现在增加了一个科室，要创建一个新的VLAN，名字为DIAOYAN。
请问以下哪个叙述是正确的？A、VLAN必须创建B、必须指定VLAN名C、VLAN必须配置一个IP地址D、把连接该科室的计算机所在的端口指定到新创建的VLAN中标准答案： AD13、下列条件中，能用作扩展ACL决定报文是转发或还是丢弃的匹配条件有：A、源主机IPB、目标主机IPC、协议类型D、协议端口号标准答案： ABCD14、R2624使用动态RIP协议，可能会存在什么问题?A、路由环路B、收敛慢C、网络小，RIP最大只能15跳D、网络小，RIP最大只能256跳标准答案： AC15、S2126G交换机如何将当前运行的配置参数保存?A、writeB、copy run starC、write memoryD、copy vlan flash标准答案： ABC16、以下属于生成树协议的有？A、IEEE802.1wB、IEEE802.1sC、IEEE802.1pD、IEEE802.1d标准答案： ABD17、下列哪些属于分组交换广域网接入技术的协议?A、Frame-RelayB、ISDNC、X.25D、DDNE、ADSL标准答案： AC18、路由协议分为___和___两种路由协议?A、距离向量B、链路状态C、路由状态D、交换状态标准答案： AB19、当两台路由器通过V.35线点到点连接，配置好后用ping来测试直连的对端接口，发现不通，请问可能是哪种故障？A、线插反B、DCE端未设置时钟速率C、封装不匹配D、设置访问列表禁止了ICMP标准答案： ABCD20、 TCP/IP协议的网络层次并不是按OSI参考模型来划分的，相对应于OSI 的七层网络模型，TCP/IP没有定义A、应用层B、表示层C、会话层D、传输层E、网络层F、数据链路层G、物理层标准答案： BCF21、下列哪些访问列表范围符合IP范围？A、1-99B、100-199C、800-899D、900-999标准答案： AB22、在路由器上面有以下一些配置，则以下答案正确的是：access-list 1 permit 192.168.1.32 0.0.0.224 interface fasterethnet0 ip access-group 1 outA、源地址为192.168.1.42 的数据报允许进入局域网f0内B、源地址为192.168.1.42 的数据报不允许进入局域网f0内C、源地址为192.168.1.72 的数据报允许进入局域网f0内D、源地址为192.168.1.72 的数据报不允许进入局域网f0内标准答案： AD23、下列哪些属于分组交换广域网接入技术的实例?A、F-RB、ISDNC、X.25D、DDNE、ADSLF、PSTN标准答案： ACF24、以下属于TCP/IP协议的有：A、FTPB、TELNETC、FRAMERELAYD、HTTPE、POP3F、PPPG、TCPH、UDPI、DNS标准答案： ABDEGHI25、以下哪些选项中是TCP数据段所具有而UDP所没有的？A、源端口号B、目的端口号C、顺序号D、应答号E、滑动窗口大小F、上层数据标准答案： CDE26、下面对使用交换技术的二层交换机的描述哪些是正确的A、通过辨别MAC地址进行数据转发B、通过辨别IP地址进行转发C、交换机能够通过硬件进行数据的转发D、交换机能够建立MAC地址与端口的映射表标准答案： ACD27、下列哪些属于UDP著名的应用?A、RIPB、TFTPC、FTPD、DNS标准答案： ABD28、下列哪些数据链路层协议支持上层多协议?A、SLIPB、EthernetC、PPPD、ISO HDLC标准答案： BC54、以下哪些地址不能用在互联网上?A、172.16.20.5B、10.103.202.1C、202.103.101.1D、192.168.1.1标准答案： ABD29、在RSTP中,Discarding状态端口都有哪些角色?A、ListeningB、backupC、LearningD、alternate标准答案： BD30、 CSMA/CD使用下面哪两种技术控制冲突？A、节点在发送前播发一个警告信息B、节点发送信号前先监视线路是否空闲C、如果节点监测到冲突就会停止发送，退避一个随机的时间D、节点边发边听，如果有另一信号干扰发送，则停止发送标准答案： BC31、下列哪些用于距离向量路由选择协议解决路由环路的方法?A、水平分割B、路由毒化C、逆向毒化D、倒记时E、触发更新标准答案： ADE32、静态路由缺省的管理代价为:A、10B、0C、100D、1标准答案： BD33、 IEEE802.1Q数据帧主要的控制信息有:A、VIDB、协议标识C、BPDUD、类型标识标准答案： AB34、请问通常配置Star-S2126G交换机可以采用的方法有？A、Console线命令行方式B、Console线菜单方式C、TelnetD、Aux方式远程拨入E、WEB方式标准答案： ABCE35、以下哪几种为典型的广域网链路封装类型A、ARPAB、FDDIC、帧中继D、PPPE、TOKEN-RING标准答案： CD36、下列哪些IP地址可以被用来作为多播地址？A、255.255.255.255B、250.10.23.34C、240.67.98.101D、235.115.52.32E、230.98.34.1F、225.23.42.2G、220.197.45.34H、215.56.87.9标准答案： DEF37、下列哪些IP地址可以被用来进行多点传输？A、255.255.255.255B、250.10.23.34C、240.67.98.101D、235.115.52.32E、230.98.34.1F、225.23.42.2G、220.197.45.34H、215.56.87.9标准答案： DEF38、交换机的功能有?A、路径选择B、转发过滤C、报文的分出与连组D、地址学习功能标准答案： BD39、为什么要使用路由选择协议？A、从一个网络向另一个网络发送数据B、保证数据使用最佳的路径C、加快网络数据的传输D、方便进行数据配置标准答案： AB40、下列哪些属于RFC1918指定的私有地址?A、10.1.2.1B、202.106.9.10C、192.108.3.5D、172.30.10.9标准答案： AD41、访问列表分为哪两类A、标准访问列表B、高级访问列表C、低级访问列表D、扩展访问列表标准答案： AD42、以下哪些协议属于TCP/IP协议栈？A、IPB、UDPC、HttpsD、802.1qE、SNMP标准答案： ABCE43、锐捷S2126G/50G支持的二层协议包括？A、IEEE802.1sB、IEEE802.3adC、IEEE802.3xD、IEEE802.1x标准答案： ABD44、如果局域网互联采用Star-S2126G，则PC与交换机之间可采用哪种线连接？A、EIA/TIA 568B直通线B、EIA/TIA 568A直通线C、反转线D、交叉线标准答案： ABD45、RIP路由协议是一种什么样的协议?A、距离向量路由协议B、链路状态路由协议C、内部网关协议D、外部网关协议标准答案： AC46、以下对交换机工作方式描述正确的是?A、使用半双工方式工作B、可以使用全双工方式工作C、使用全双工方式工作时要进行回路和冲突检测D、使用半双工方式工作时要进行回路和冲突检测标准答案： BD47、说出两个距离向量路由协议有？A、RIPV1/V2B、IGRP和EIGRPC、OSPFD、IS-IS标准答案： AB48、下列哪个应用是基于ICMP实现的?A、pingB、tracertC、nslookupD、traceroute标准答案： ABD49、请选出使用静态路由的好处？A、减少了路由器的日常开销B、可以控制路由选择C、支持变长子网掩码（VLSM）D、在小型互连网很容易配置标准答案： ABD50、校园网设计中常采用三层结构，它们是哪三层?A、核心层B、分布层C、控制层D、接入层标准答案： ABD51、以下对存储转发描述正确的是?A、收到数据后不进行任何处理，立即发送B、收到数据帧头后检测到目标MAC地址，立即发送C、收到整个数据后进行CRC校验，确认数据正确性后再发送D、发送延时较小E、发送延时较大标准答案： CE52、关于VLAN下面说法正确的是?A、隔离广播域B、相互间通信要通过三层设备C、可以限制网上的计算机互相访问的权限D、只能在同一交换机上的主机进行逻辑分组标准答案： ABC53、出现交换环路的网络中会存在什么问题?A、广播风暴B、多帧复制C、MAC地址表不稳定D、广播流量过大标准答案： ABCD54、下列哪些接口用于连接WAN?A、serialB、asyncC、briD、consoleE、aux标准答案： ABCE55、下列哪些属于常见的DTE与DCE之间的连接标准?A、EIA/TIA-232B、Frame-RelayC、DDND、V.35标准答案： AD56、请简述RIP协议为什么不适合在大型网络环境下使用?A、跳数限制为15跳B、是为小型网络设计的C、覆盖面积太少D、无法给网络进行加密E、极大的限制网络的大小标准答案： ABE57、相对于RIP ver1，RIP ver2增加了那些新的特性？A、提供组播路由更新B、鉴别C、支持变长子网掩码D、安全授权E、错误分析标准答案： ABC58、LAN中定义VLAN的好处有?A、广播控制B、网络监控C、安全性D、流量管理标准答案： AC59、静态路由和动态路由的区别？A、人工指定的B、人工选择最优路径C、多条路由的自动选路D、路由自动切换标准答案： AB60、技术部经理要求你在路由器上做以下权限控制：允许所有的TCP服务除了FTPt以外。
未来的家英文作文一等奖
未来的家英文作文一等奖In the future, homes will be equipped with advanced technology that can respond to voice commands andanticipate our needs. For example, the lights will automatically adjust to the time of day and our preferences, and the temperature will be regulated based on our body temperature and movement.The design of future homes will prioritizesustainability and eco-friendliness. Solar panels,rainwater harvesting systems, and energy-efficient appliances will be standard features in every household.The architecture will also incorporate natural elements to create a harmonious blend between indoor and outdoor spaces.Entertainment and leisure will be seamlessly integrated into the home environment. Virtual reality rooms,interactive walls, and holographic displays will offer endless possibilities for immersive experiences. Smart furniture will be able to transform and adapt to differentactivities, making the living space versatile and dynamic.Health and wellness will be central to the design of future homes. From air and water purification systems to integrated workout areas and relaxation pods, every aspect of the home will be tailored to promote physical and mental well-being. Personalized healthcare devices and monitoring systems will also be readily available.The concept of privacy will be redefined in future homes. With the advancement of biometric security systems and AI-powered surveillance, residents will have unprecedented control over who can access their living spaces. At the same time, interconnectedness and shared spaces will foster a sense of community and collaboration among neighbors.In conclusion, the future of homes will be defined by a seamless integration of technology, sustainability, entertainment, health, and community. The traditional boundaries between indoor and outdoor, private and public, will be blurred, creating a new paradigm for living spaces.。
对未来汽车描述英文作文
对未来汽车描述英文作文Title: A Glimpse into the Future of Automobiles。
The future of automobiles is a captivating realm where innovation and technology converge to redefine the way we commute, interact, and perceive transportation. In this essay, we will delve into the potential advancements that await us, painting a vivid picture of what our roads might look like in the years to come.Firstly, let's discuss the propulsion systems of future vehicles. While internal combustion engines have long been the norm, we are witnessing a paradigm shift towards electric propulsion. Electric vehicles (EVs) are becoming increasingly prevalent, offering a cleaner and more sustainable alternative to traditional gasoline-powered cars. With advancements in battery technology, range anxiety is gradually becoming a thing of the past, as EVs can now travel considerable distances on a single charge. Moreover, the integration of renewable energy sources, suchas solar panels, into the design of vehicles further enhances their eco-friendliness and reduces dependency on conventional power grids.Furthermore, the concept of autonomous driving is poised to revolutionize the automotive industry. Self-driving cars equipped with sophisticated sensors, cameras, and artificial intelligence algorithms are on the brink of becoming mainstream. These vehicles promise not only increased safety on the roads but also greater convenience for commuters. Imagine a future where you can relax, work, or socialize while your car autonomously navigates through traffic, communicates with other vehicles, and adapts to changing road conditions in real-time. The implications of autonomous driving extend beyond individual convenience, potentially reshaping urban planning, reducing traffic congestion, and optimizing transportation systems on a large scale.In addition to propulsion and autonomy, the design and functionality of future cars are undergoing significant transformations. The emphasis on aerodynamics, lightweightmaterials, and energy efficiency is driving the evolution of sleek, futuristic vehicle designs. Interior spaces are being reimagined as versatile environments that seamlessly integrate connectivity, entertainment, and productivity features. Augmented reality windshields, interactive dashboard displays, and advanced infotainment systems are just a glimpse of the immersive technologies that will redefine the driving experience.Moreover, the concept of car ownership itself is evolving in the face of emerging trends such as ride-sharing, carpooling, and mobility-as-a-service (MaaS) platforms. The rise of shared mobility solutions and on-demand transportation services is challenging traditional ownership models, fostering a culture of access over ownership. In this shared mobility ecosystem, fleets of autonomous vehicles could be dynamically deployed to meet the evolving needs of users, optimizing resourceutilization and reducing overall vehicle ownership and congestion levels.As we peer into the future of automobiles, it becomesevident that we are on the cusp of a transportation revolution. From electric propulsion and autonomous driving to innovative designs and shared mobility solutions, the possibilities are both exhilarating and transformative. While the road ahead may be paved with challenges and uncertainties, one thing is certain: the future of automobiles promises to be nothing short of extraordinary. So buckle up and prepare for an exhilarating journey into the unknown realms of automotive innovation.。
高中英语作文《创新才能进步》
High school is a vibrant melting pot of ideas and aspirations, a time when we're nurtured to think beyond conventional wisdom and challenge the status quo. One concept that stands tall as a beacon of potential and progress is the significance of innovation. It isn't merely about inventing something novel; it's about delving into uncharted territories, questioning established norms, and devising groundbreaking solutions to problems that have long eluded solution.I recall a particularly enlightening project in our high school science class where we were tasked with addressing the perennial issue of water conservation. While most classmates opted for traditional approaches such as repairing leaks and promoting water-efficient handwashing habits, I felt compelled to embark on a path less traveled. My research led me to discover the concept of rainwater harvesting, a method that was relatively uncommon at the time but held promise of transforming how we manage this vital resource.The notion of capturing rainwater and repurposing it for irrigation or sanitation needs struck me as a stroke of genius. It was an embodiment of innovation in its purest form: not just generating something new but reimagining a solution that could alleviate a pressing environmental challenge. When I presented my findings to my peers, while some expressed doubt, there were also those who recognized the revolutionary potential of my proposal.In the realm of business, innovation serves as the lifeblood of success. Think of companies like Apple, which have consistently defied expectations by introducing game-changing products. The iPhone wasn't just a phone; it was a paradigm shift that reshaped the mobile technology landscape. Similarly, the MacBook wasn't merely a laptop; it was a symbol of a new era in personal computing, embodying sleek design and user-friendliness. Apple's ability to innovate has been pivotal to its enduring dominance in the tech industry.However, innovation extends far beyond the creation of new gadgets or services. It was during the COVID-19 pandemic that the true essence of innovation shone through. Restaurants, faced with the unprecedented challenge of dining restrictions, swiftly innovated by introducing contactless delivery and takeaway options, ensuring their survival. Businesses transitioned to remote work models, leveraging technology to maintain productivity and continuity. These instances illustrate how innovation can be a savior in times of crisis.Furthermore, innovation is the cornerstone of societal advancement. It fuels breakthroughs in technology, medicine, and education, propelling humanity towards a more prosperous and sustainable future. Without the spirit of innovation, we wouldn't have witnessed the advent of life-saving vaccines, the development of cutting-edge communication tools, or the emergence of efficient transportation systems. It is the relentless pursuit ofinnovation that propels us forward on the path of progress and development.In essence, innovation is the catalyst for transformation. It urges us to challenge the status quo, to explore uncharted territories, and to devise novel solutions to persistent challenges. Whether we are students grappling with real-world problems, entrepreneurs striving to disrupt industries, or citizens contributing to the betterment of society, the spirit of innovation should guide our actions. Let us embrace innovation, foster a culture of creativity, and together, we can make a significant impact on the world around us.。
绿色城市健康生活的英语作文开头
绿色城市健康生活的英语作文开头Title: Embracing Green Cities for a Healthy LifestyleIn the midst of a rapidly urbanizing world, the concept of a green city has emerged as a beacon of hope for a healthier and more sustainable lifestyle. A green city, by definition, is one that prioritizes environmental preservation, ecological balance, and the well-being of its residents through sustainable urban planning and practices. It is a vision that is not just rooted in aesthetics but also in the deep-seated understanding that our cities and our health are interconnected. The heartbeat of a green city lies in its vibrant green spaces. These are not just areas of lush greenery but also havens of tranquility, where the hustle and bustle of urban life give way to the soothing sounds of nature. Parks, gardens, and open spaces not only provide a refuge for the mind but also serve as natural lungs, purifying the air and mitigating the effects of urban pollution. They encourage physical activities like walking, jogging, and cycling, thereby promoting a healthier lifestyle among city residents.Moreover, a green city promotes the use of renewable energy sources like solar and wind power, reducing dependency on fossil fuels and their associated emissions. This shift not only contributes to climate change mitigation but also ensures a reliable and sustainable energy supply for the city. The integration of green building practices, such as the use of sustainable materials and energy-efficient designs, further enhances the environmental friendliness of the urban landscape.The green city paradigm also extends to transportation systems. It advocates for the development of public transportation networks that are efficient, accessible, and environmentally friendly. Cycling infrastructure and pedestrian-friendly streets encourage alternative modes of transportation, reducing the carbon footprint of the city while promoting active living.The health benefits of living in a green city are numerous and far-reaching. The availability of green spaces and the promotion of physical activities contribute to improved cardiovascular health, reduced stress levels, and enhanced mental well-being. The cleaner air and water quality also lead to fewer respiratory and gastrointestinal illnesses, improving the overall health of the population. Furthermore, a green city fosters a sense of community and belonging among its residents. The shared appreciation for the environment and the commitment to sustainable living create a stronger social bond that goes beyond the mere physical infrastructure of the city. This sense of community encourages people to take ownership of their surroundings, participate in local initiatives, and contribute to the overall well-being of the city.However, achieving the vision of a green city requires a concerted effort from all stakeholders. Governments need to prioritize sustainable urban planning and invest in green infrastructure. Industries and businesses must adopt environmentallyresponsible practices and innovate to reduce their carbon footprint. And individuals, too, have a crucial role to play by making sustainable choices in their daily lives, such as reducing waste, conserving energy, and supporting local, organic produce. In conclusion, the green city is not just a dream but a feasible and necessary reality for our future. It offers a path to a healthier, happier, and more sustainable way of life. As we continue to urbanize, it is imperative that we embrace the principles of green cities and integrate them into the fabric of our urban landscapes. Only then can we truly enjoy the benefits of urbanization without compromising the health and well-being of our planet and its inhabitants.The journey towards a green city is challenging but rewarding. It requires a holistic approach that considers the environment, society, and economy in tandem. With the right policies, infrastructure, and public support, we can create cities that are not just green but also vibrant, inclusive, and resilient. Let us stride forward, embracing the green city as a blueprint for our healthy and sustainable future. This vision of a green city is not without precedence. Many cities across the globe have already embarked on this journey, demonstrating that it is indeed possible to balance urban development with environmental protection. From the rooftop gardens of Singapore to the bike-friendly streets of Copenhagen, these cities offer inspiration and hope for what we can achieve if we are committed to the cause.In the end, the green city is not just a physical space but a way of life. It is a reflection of our values and aspirations, a testament to our commitment to a healthier and more sustainable future. Let us work together, across borders and generations, to bring this vision to life and create a world where every city is a green city, and every life is a healthy one.。
水杯的细致描绘作文英语
水杯的细致描绘作文英语Title: A Detailed Description of a Water Bottle。
Introduction:In our daily lives, among the plethora of objects we encounter, there exists a humble yet indispensable item the water bottle. This unassuming vessel serves as a conduitfor hydration, accompanying us through our various endeavors, be it a strenuous workout session, a leisurely stroll in the park, or a hectic day at work or school. In this essay, we shall embark on a detailed exploration of the intricacies of a water bottle, unraveling its design, functionality, and significance in our lives.Body:1. Material Composition and Design: The typical water bottle is crafted from a diverse range of materials, including plastic, glass, stainless steel, or even eco-friendly alternatives like bamboo or silicone. Each material bestows unique characteristics upon the bottle, influencing factors such as durability, weight, and eco-friendliness. The design of the water bottle varies widely, from sleek and minimalist to bold and vibrant, catering to diverse aesthetic preferences. Furthermore, ergonomic considerations often dictate the shape and size of the bottle, ensuring ease of handling and portability.2. Structural Components: A water bottle comprises several integral components, each contributing to its functionality. The body of the bottle, typicallycylindrical or flask-shaped, serves as the primaryreservoir for holding water. The presence of a cap or lid, often equipped with a sealing mechanism, prevents leakage and contamination, preserving the purity of the water within. Some advanced bottles feature additional elements such as straws, flip-open lids, or even built-in filtration systems, enhancing user convenience and utility.3. Functional Attributes: Beyond its basic function of containing water, the modern water bottle boasts a plethoraof functional attributes designed to augment user experience. Many bottles are insulated, capable of maintaining the temperature of the liquid inside, whether hot or cold, for extended periods. This feature proves invaluable for individuals seeking to enjoy their preferred beverages at optimal temperatures, irrespective of environmental conditions. Furthermore, the advent of smart water bottles equipped with integrated sensors and connectivity capabilities enables users to track their hydration levels and receive reminders to drink water, promoting health and well-being.4. Environmental Implications: In recent years, heightened awareness of environmental sustainability has spurred a paradigm shift in consumer preferences towards eco-friendly water bottle options. Reusable bottles, constructed from recyclable materials and designed forlong-term use, have emerged as a sustainable alternative to single-use plastic bottles, which contribute significantly to pollution and environmental degradation. By embracing reusable bottles, individuals can mitigate their ecological footprint and contribute to the preservation of ourplanet's precious resources.5. Cultural and Symbolic Significance: Beyond its utilitarian function, the water bottle holds cultural and symbolic significance in various contexts worldwide. In some cultures, the act of sharing a drink from a communal water vessel symbolizes camaraderie and hospitality, fostering bonds of kinship and solidarity. Moreover, the water bottle has become emblematic of the broader wellness movement, embodying the ideals of health, vitality, andself-care embraced by individuals seeking to lead balanced lifestyles.Conclusion:In conclusion, the water bottle transcends its humble origins to emerge as a multifaceted artifact emblematic of human ingenuity, necessity, and cultural symbolism. Through its diverse material compositions, innovative designs, and functional attributes, the water bottle not only fulfills our basic hydration needs but also reflects broadersocietal values and aspirations. As we navigate thecomplexities of the modern world, let us cherish the humble water bottle as a testament to our quest for convenience, sustainability, and well-being.。
2022年职业考证-软考-系统架构设计师考试全真模拟易错、难点剖析B卷(带答案)第76期
2022年职业考证-软考-系统架构设计师考试全真模拟易错、难点剖析B卷（带答案）一.综合题(共15题)1.单选题SYN Flooding攻击的原理是（）。
问题1选项A.利用TCP三次握手，恶意造成大量TCP半连接，耗尽服务器资源，导致系统拒绝服务B.操作系统在实现TCP/IP协议栈时，不能很好地处理TCP报文的序列号紊乱问题，导致系统崩溃C.操作系统在实现TCP/IP协议栈时，不能很好地处理IP分片包的重叠情况，导致系统崩溃D.操作系统协议栈在处理IP分片时，对于重组后超大的IP数据包不能很好地处理，导致缓存溢出而系统崩溃【答案】A【解析】本题考查的是SYN Flooding攻击原理相关内容。
SYN Flood攻击利用TCP三次握手的一个漏洞向目标计算机发动攻击。
攻击者向目标计算机发送TCP连接请求（SYN报文），然后对于目标返回的SYN-ACK报文不作回应。
目标计算机如果没有收到攻击者的ACK 回应，就会一直等待，形成半连接，直到连接超时才释放。
攻击者利用这种方式发送大量TCP SYN报文，让目标计算机上生成大量的半连接，迫使其大量资源浪费在这些半连接上。
目标计算机一旦资源耗尽，就会出现速度极慢、正常的用户不能接入等情况。
攻击者还可以伪造SYN报文，其源地址是伪造的或者不存在的地址，向目标计算机发起攻击。
SYN Flooding攻击与TCP报文的处理过程没有很大的关系。
BCD选项错误，A选项正确。
2.单选题下面关于Kerberos认证的说法中，错误的是（）。
问题1选项A.Kerberos 是在开放的网络中为用户提供身份认证的一种方式B.系统中的用户要相互访问必须首先向CA申请票据C.KDC中保存着所有用户的账号和密码D.Kerberos 使用时间戳来防止重放攻击【答案】B【解析】本题考查的是数字证书相关应用。
Kerberos 是一种网络认证协议，其设计目标是通过密钥系统为客户机、服务器应用程序提供强大的认证服务。
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5
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()。
TCP_Wrappers
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Beyond TCP-Friendliness:A New Paradigm for End-to-End Congestion ControlA.Legout,and E.W.BiersackInstitut EURECOMB.P.193,06904Sophia Antipolis,FRANCElegout,erbi@eurecom.frOctober28,1999Eurecom Technical ReportAbstractWith the success of the Internet comes the deployment of an increasing number of applications that do not use TCP as a transport protocol.These applications can often improve their own performance by not being“TCP-friendly”and severely penalizing TCP streams.Also,designing these new applications to be“TCP-friendly”is often a difficult task.For these reasons,we propose a new paradigm for end-to-end congestion control(the FS paradigm)that relies on a Fair Scheduler network and assumes only selfish and non-collaborative end users.Theflow isolation property of the FS paradigm is commonly agreed by the network community, however the lack of formalism of the FS paradigm hides fundamental properties.We rigorously define the properties of an ideal congestion control protocol and show that the FS paradigm allows to devise end-to-end congestion control protocols that meet almost all the properties of an ideal congestion control protocol.The FS paradigm is fully compatible with the TCPflows.Moreover,we show that the incremental deployment of the FS paradigm is feasible per ISP and leads to immediate benefits for the TCPflows since their mean bandwidth is increased by up to25%.Our main contribution is the formal statement of the congestion control problem as a whole that allows to rigorously prove the validity of the FS paradigm.Keywords:Congestion Control,Scheduling,Paradigm,Multicast,Unicast.1IntroductionCongestion Control has been a central research topic since the early days of computer networks.Naglefirst identified the problems of congestion in the Internet[1].Thefirst fundamental turning point in Internet congestion control took place at the end of the eighties.Nagle proposed a strategy based on the round robin scheduling[2],whereas Jacobson proposed a strategy based on Slow Start(SS)and Congestion Avoidance(CA)[3].Each of these solutions has its drawbacks.Nagle’ssolution has a high computation complexity and requires modifications to the routers.Jacobson’s solution requires the collaboration of all the end users1.The low performance of the routers and the small size of the Internet community at that time led to the adoption of Jacobson’s proposal.SS and CA mechanisms were put in TCP.Ten years later,the Internet still uses Jacobson’s mechanisms in a somewhat improved form[4].We define the notion of Paradigm for Congestion Control as a model used to devise congestion control protocols that have the same set of properties.Practically,when one devises a congestion control protocol with a paradigm,one has the guarantee that this protocol will be compatible2with all the other congestion control protocols devised with the same paradigm,at the expense of some constraints enforced by the paradigm.This notion of paradigm is not obvious in the Internet.A TCP-friendly paradigm was implicitly defined.However this paradigm was introduced after TCP,when new applications that can not use TCP had already appeared.As TCP relies heavily on the collaboration of all the end users–collaboration is in the sense of the common mecha-nism used to achieve congestion control–the TCP-friendly paradigm was introduced(see[5],[6])to devise congestion control protocols compatible to TCP.A TCP-friendlyflow has to adapt its throughput according to the equation3:(1)where,is a constant,is the size of the packets used for the connection,is the round trip time,and is the loss rate experienced by the connection.To compute this,one needs to measure the loss rate and the.The throughput for a TCP-friendlyflow heavily decreases with the loss rate.However,this behavior does notfit to many applications’requirements.For instance,audio and video applications are loss-tolerant and the degree of loss tolerance can be managed with FEC[8].These multimedia applications can tolerate a significant loss rate without a significant decrease in the quality perceived by the end users.The multicastflows suffer from TCP-friendliness since a source-based congestion control scheme for multicastflows has to adapt its sending rate to the worst receiver(in the sense of the loss rate),to follow the TCP-friendly paradigm.A receiver-based multicast congestion control scheme can be TCP-friendly but at the expense of a large granularity in the choice of the layer bandwidth[9][10].The TCP-friendly paradigm relies on the collaboration of all the users,which can not be longer assumed given the current size of the Internet[6].This paradigm requires that all the applications use the same congestion control mechanism based on Eq.(1).This paradigm does not extend to the new applications being deployed across the Internet. Companies start to use non-TCP-friendly congestion control schemes4,as they observe better performance for audio and video applications than with TCP-friendly schemes.However the benefit due to non-TCP-friendly schemes is a transitory effect and an increasing use of non-TCP-friendly schemes may lead to a congestion collapse in the Internet.Indeed,at.4Here congestion control may be a misleading expression,since theflows are often constant bit rate.the present time,most of the users access the Internet at56Kbps or less.However,with the deployment of xDSL most of the users will have,in a few years,an Internet access at more than1Mbps.It is easy to imagine the disastrous effect of hundred of thousands unresponsiveflows at1Mbps crossing the Internet.It is commonly agreed that router support can help congestion control.However there are several fears about router support.The end-to-end argument[11]is one of the major theoretical foundations of the Internet,adding functionality inside the routers must not violate this principle.As TCP is the main congestion control protocol used in the Internet, router support must,at least,not penalize TCPflows(this can be related to the end-to-end argument,see[12]).Moreover it is not clear which kind of router support is desirable;router support can range from simple buffer management to active networking.One of the major reasons the research community distrusts network support is the lack of a clear statement about the use of network support for congestion control.One simple way to use network support for congestion control is to change the scheduling discipline inside the routers.PGPS-like scheduling[13]is well known for itsflow isolation property.This property sounds suitable for congestion control.However,the research community does neither agree on the utility of this scheduling discipline for congestion control(even if itsflow isolation property is appreciated)nor on the way to use this scheduling discipline.We strongly believe that the lack of consensus is due to a fuzzy understanding about which properties a congestion control protocol should have and how a PGPS network(i.e.a network where each node implements a PGPS-like scheduler)can enforce these properties.The aim of this paper is to shed some light onto these questions.A user acts selfishly if he only tries to maximize its own satisfaction without taking into account the other users (Shenker gives a good discussion about the selfishness hypothesis in[14]).The TCP-friendly paradigm is based on cooperative and selfish users.We base our new paradigm called Fair Scheduler(FS)paradigm on non-cooperative and selfish users.We formally define the properties of an ideal congestion control protocol(see section2.2)and show that almost all these properties are verified with the FS paradigm when we assume a network support that simply consist in having a Fair Scheduler in the routers(see section2.3).We define a Fair Scheduler to be a Packet Generalized Processor Sharing scheduler with longest queue drop buffer management(see[13],[15],[16],and[17]for some examples).In particular,a Fair Scheduler must guarantee max-min fairness and delay bounds.Our study shows that simply changing the scheduling allows to use the FS paradigm for congestion control while outperforming the TCP-friendly paradigm. Indeed,the FS paradigm provides a basis for devising congestion control protocols tailored to the application needs. We do not introduce a new congestion control protocol,but a model(a paradigm)to devise efficient congestion control protocols.We do not want to replace or modify TCP.Instead,we propose an alternative to the TCP-friendly paradigm to devise new congestion control protocols compatible with TCP.Important to us is that the FS paradigm does not violate the end to end argument,due to the network support.The weak network support that consists in changing the scheduling is of broad utility–we show that the FS scheduling significantly improves the performances of the TCP connections–and consequently does not violate the end-to-end argument[12].We can note that one part of our results are implicitly addressed in previous work(in particular[18]and[14]),we are making the step from an implicit definition of the problemsand an explicit statement of the problem introducing a formalism that constitutes an indisputable contribution.We expect this study will stimulate new interest for this FS paradigm,fully compatible with TCP congestion control,that allows to devise end-to-end congestion control protocols that meet almost all the properties of an ideal congestion control protocol.In section2we define the FS paradigm for end-to-end congestion control.In section3,we study the practical aspects of the deployment of the FS paradigm in the Internet.Section4compares the FS paradigm and the TCP-friendly paradigm.Section5addresses the related work,while section6summarizes ourfindings and concludes the paper.2The FS ParadigmWe formally define the FS paradigm in three steps.First,we define the notion of congestion.This definition is a slight modification of the Keshav’s definition[18].Second,we formulate six properties that an ideal congestion control protocol must meet.These properties are abstractly defined,i.e.independent of any mechanism(for instance we talk about fairness but not about scheduling and buffer management,which are two mechanisms that influence fairness).Third,we define the FS paradigm for congestion control.We show that almost all the properties of an ideal congestion control protocols are met by a congestion control protocol based on the FS paradigm.We note that all the aspects of congestion control–from the definition of congestion to the definition of a paradigm to devise new congestion control protocols–are addressed with the same formalism.This formalism allows us to have a consistent study of the congestion control problem.2.1Definition of CongestionThefirst point to clarify when we talk about congestion control is the definition of congestion.Congestion is a notion related to both user’s satisfaction and network load.If we only take into account the user’s satisfaction,we can imagine a scenario,where the user’s satisfaction decreases due to jealousy(for instance)and not due to any modifications in the quality of the service a user receives(for instance,user A learns that user B has a better service,and is no more satisfied with his own service).This can not be considered as congestion.If we only take into account the network load,congestion is only related to network performance,which can be a definition of congestion(for instance it is the definition in TCP), but we claim that we must take into account the user’s satisfaction.We always have to keep in mind that a network exists to satisfy users.Our definition of congestion is:Definition1A network is said to be congested from the perspective of user i,if the satisfaction of i decreases due to a modification of the characteristics of his network connection5.A similar definition wasfirst introduced by Keshav(for a discussion of this definition see[18]).Keshav’s initial definition is:“A network is said to be congested from the perspective of user if the satisfaction of decreases due toS 23R R R 1Figure 1:Example for the definition of congestionan increase in network load”.Our only one point of disagreement with Keshav is about the influence of network load.He says that only an increase in network load that results in a loss of satisfaction is a signal of congestion,whereas we claim that a modification (increase or decrease)in network load with a decrease of satisfaction is a signal of congestion.We give an example to illustrate our view.Let the scheduling be WFQ [13],let the link capacity be 1for all the links,and let the receiver’s satisfaction depend linearly on the bandwidth received.The flow(senderand receiver )has a weight of 1,the flow (sender and receiver )has a weight of 2,the flow (sender and receiver )has a weight of 1.In a first time the three sources have data to send,the satisfaction of is and satisfaction of isand the satisfaction of becomes6The interested reader can refer to [14]for formal definitions.verifies these properties.Here,the only one assumption we make is the selfish behavior of the users.So these properties remain very general.The six properties are:Stability Given each user is acting selfishly,we want the scheme to converge to a Nash equilibrium.At Nash equilibrium, nobody can increase its own satisfaction.So this equilibrium makes sense from the point of congestion control stability.Since more than one Nash equilibrium can lead to oscillation among these equilibria,the existence and the uniqueness of a Nash equilibrium are the conditions of stability.Efficiency Nash equilibrium does not mean efficiency.A desired property for the Nash equilibrium is to be Pareto opti-mal.In this case,nobody can have a higher satisfaction with another distribution of the network resources without decreasing the satisfaction of another user.The convergence time of the scheme towards the Nash equilibrium is another important parameter for efficiency.The faster convergence is,the more efficient it is.A fast convergence towards a Nash equilibrium that leads to a Pareto optimal distribution of the network resources is the condition of efficiency.Fairness It is perhaps the most delicate part of congestion control.Many criteria for fairness exist,but there is no criterion agreed on by the whole networking community.We use max-min fairness(see[19])7.We make a fundamental remark on this fairness property.If we consider for all the users a utility function that is linearly dependent on the bandwidth received,max-min fairness is equivalent to pareto optimality.If a user does not have a utility function that depends linearly on the bandwidth received he will not be able to achieve its fair share(in the sense of max-min fairness).Therefore max-min fairness defines/imposes an upper bound on the distribution of the bandwidth: If every user wants as much bandwidth as he can have,nobody will have more than its max-min share.But if some users are willing to collaborate8they can achieve another kind of fairness and in particular proportional fairness[20].Robustness against misbehaving users.We suppose that all the users act selfishly,and as there is no restriction on the utility functions,the behavior of the users can be very aggressive.Such a user must not decrease the satisfaction of the other users.Moreover,he should not significantly modify the convergence speed of the scheme towards a Nash equilibrium(see the efficiency property).Globally,the scheme must be robust against malicious,misbehaving,and greedy users.Scalability The Internet evolves rapidly with respect to bandwidth and size.Moreover inter-LAN,trans-MAN,and trans-WAN connections coexist.A congestion scheme must scale on many axes:from an inter-LAN connection toa trans-WAN connection,from a28.8Kbyte/s modem to a155Mbit/s line.Feasibility This property contains all the technical requirements.We restrict ourself to the Internet architecture.The Internet connects a wide range of hardware and software systems,thus a congestion control protocol must cope with this heterogeneity.On the other hand,a congestion control protocol has to be simple enough to be efficiently implemented.To be accepted as an international standard,a protocol needs to be extensively studied,the simplicity of the protocol will favor this process.We believe that these properties are necessary and sufficient properties of an ideal congestion control protocol.Indeed these properties cover all the aspects of a congestion control protocol,from the theoretical notion of efficiency to the practical aspect of feasibility.However,it is not clear how we can devise a congestion control protocol that meets all these properties.In the next section we establish the FS paradigm that allows to devise congestion control protocols that assure almost all of congestion control properties.2.3Definition and Validity of the FS ParadigmA paradigm for congestion control is a model used to devise new congestion control protocols.A paradigm makes assumptions and under these assumptions we can devise compatible congestion control protocols;compatible means that the protocols have a same set of properties.Therefore,to define a new paradigm,we must clearly express the assumption made and the properties enforced by the paradigm.To be viable in the Internet the paradigm must be compliant with the end-to-end argument[11].Mainly the congestion control protocols devised with the paradigm have to be end-to-end and should not have to rely on specific network support.These issues are addressed in this section.For simplicity things we make a distinction between the assumption that involves the network support–we call that the Network Part of the paradigm(NP)–and the assumptions that involve the end systems–we call that the End System Part of the paradigm(ESP).The assumptions required for our new paradigm are:For the NP of the paradigm we assume a Fair Scheduler network,i.e.a network where every router implements a Fair Scheduler;For the ESP,the end users are assumed to be selfish and non-collaborative.We call this paradigm the Fair Scheduler(FS)paradigm9.We can note that the FS paradigm,unlike the TCP-friendly paradigm,does not make any assumptions on the mechanism used at the end systems.The FS paradigm guarantees full freedom when devising a congestion control protocol.This property of the paradigm is appealing but may lead to a high heterogeneity of the congestion control mechanisms used.Therefore,one can have a legitimate fear about the set ofproperties enforced by the FS paradigm.If the FS paradigm enforces less properties than the TCP-friendly paradigm,the FS paradigm does not make sense.In fact we show,in the following,that our simple FS paradigm enforces almost all the properties of an ideal congestion control protocol and consequently outperforms the TCP-friendly paradigm.Stability Under the NP and ESP hypothesis,the existence and uniqueness of a Nash equilibrium is assured(see[14]).The congestion control protocols devised with the FS paradigm therefore meet the condition of stability.Efficiency Under the NP and ESP hypothesis,even a simple optimization algorithm(like a hill climbing algorithm) converges fast to the Nash equilibrium.However,the Nash equilibrium is not Pareto optimal in the general case.If all the users have the same utility function,the Nash equilibrium is Pareto optimal.One can point out that ideal efficiency can be achieved with full collaboration of the users(see[14]).However,it is contrary to the ESP assumptions.The congestion control scheme devised with our new paradigm does not have necessarily ideal efficiency.Fairness Every fair scheduler achieves max-min fairness.Moreover,as a Fair Scheduler is implemented in every network node,everyflow achieves its max-min fairness rate on the long term average(see[21]).Our NP assumption enforces fairness.Robustness Using a Fair Scheduler enforces that the network is protected against malicious,misbehaving,and greedy users(see[16]).We can note that one user opening multiple connections can increase its share of the bottleneck, however in practice,the number of connections that a single user can open is limited.Therefore,we do not expect this multiple connections effect to be a significant weakness of the robustness property.Scalability According to the ESP assumption,the only one constraint of the end-to-end protocol designer must consider are selfish and non-collaborative end users.Unlike the TCP-friendly paradigm the designer has a greatflexibility to devise scalable end-to-end congestion control protocols with the FS paradigm.Feasibility A fair scheduler(HPFQ[17])can be implemented today in Gigabit routers(see[22]).So the practical application of the NP assumption is no longer an issue(see section3.2for a discussion on the practical deployment of Fair Schedulers in the Internet).We see that the FS paradigm does not allow to devise an ideal efficient congestion control protocol,because the Nash equilibrium can not be guaranteed to be Pareto optimal.The simple case that consists in considering the user satisfaction of everyone as the same linear function of the bandwidth received leads to ideal efficiency(as every user has the same utility function).However,in the general case ideal efficiency is not achieved.According to the NP assumption, every network node implements a Fair Scheduler,so we can manage the tradeoff among the three main performance parameters:bandwidth,delay,and loss(see[13]).This tradeoff can not be made with the TCP-friendly paradigm,therefore our paradigm leads to a significantly higher efficiency(in the sense of the satisfaction of end users)than the TCP-friendly paradigm.We have given the assumptions made and the properties enforced by the FS paradigm.The NP contains only the Fair Scheduler assumption.As this mechanism is of broad utility–we will show in section3.1that a Fair Scheduler has a great impact on TCPflows–it does not violate the end-to-end argument[12].The issue related to the practical introduction of the paradigm are studied in section3.The FS paradigm,like the TCP-friendly paradigm,applies for both unicast and multicast since the paradigm does not make any assumption on the transmission mode.Moreover,the FS paradigm enforces properties of great benefits for multicastflows.For instance,the efficiency property leads,with the FS paradigm,to a tradeoff between the performance parameters bandwidth,delay,and loss.Whereas the FS paradigm guarantees that this tradeoff can be made end-to-end,it is not the purpose of this paper to address the end-to-end protocol design to achieve this tradeoff.In conclusion,we have defined a simple paradigm for end-to-end congestion control,called FS paradigm,that relies on a Fair Scheduler network and only makes the assumption that the end users are selfish and non-collaborative.We can note that the FS paradigm is less restrictive than the TCP-friendly paradigm,as it does not make any assumptions on the mechanism used at the end users.Whereas the benefits of the FS paradigm with respect toflow isolation are commonly agreed on by the research community,its benefits for congestion control has been less clear since the congestion control properties are often not clearly defined.We showed that the FS paradigm allows to devise end-to-end congestion control protocols that meets almost all the properties of an ideal congestion control protocol.The remarkable point is that simply using Fair Schedulers allows to devise end-to-end congestion control protocols that are tailored to the application needs (due to the greatflexibility when devising the congestion control protocol and due to the tradeoff among the performance parameters)while being a nearly ideal congestion control protocol.We applied with success the FS paradigm to devise a new multicast congestion control protocol(see[23]).This protocol is based on cumulative layers and outperforms all the other protocols based on cumulative layers.In summary our protocol converges to the optimal link utilization in the order of one RTT and follows this optimal rate with no loss induced.Moreover,and as theoretically guaranteed by the FS paradigm,our protocol is fair with the TCPflows.3Practical Aspects of the FS ParadigmIn the previous sections we defined the FS paradigm.Now we investigate the practical issues that come with the intro-duction of such a paradigm in the Internet.3.1Behavior of TCP with the FS ParadigmIn this section,we evaluate the impact of the NP assumption of the FS paradigm on the today’s Internet.A central question if we want to deploy the FS paradigm in the today’s Internet is:As the NP assumption requires modificationsin the network nodes,how will the use of a Fair Scheduler affect the TCP behavior and performance?Suter shows the benefits of a fair scheduler on TCPflows[24].While his results are very promising,they are based on simulations for a very simple topology.We decided to explore the influence of the NP hypothesis on TCP with simulations on a large topology.The generation of realistic network topologies is a subject of active research[25,26,27,28].It is commonly agreed that hierarchical topologies better represent a real Internetwork than doflat topologies.We use tiers([26])to create hierarchical topologies consisting of three levels:WAN,MAN,and LAN that aim to model the structure of the Inter-net topology[26]and call this Random Topology RT.For details about the network generation with tiers and the parameters used the reader is referred to Appendix A.The Network Simulator ns[29]is commonly agreed to be the best simulator for the study of Internet protocols.We use ns with the topology generated by tiers.All the parameters of the topology are defined in Appendix A.The queue length is50packets for both FIFO and FQ scheduling(the shared buffer is50packets large).The buffer management used with FIFO scheduling is drop tail,and the buffer management used with FQ is longest queue drop with tail drop. The TCPflows are simulated using the ns implementation of TCP Reno,with packets of1000bytes size and a maximum window of5000packets(large enough not to bias the simulations).The TCP sources have always a packet to send.The unresponsiveflows are simulated with UDP connections and CBR sources with a10Mbit/s throughput.We study two different scenarios:TCPflows only.We add from to TCPflows randomly distributed on the topology RT(i.e.the source and the receiver of aflow are randomly distributed among the LANs of RT).We do for each configuration of unicast flows an experiment with FIFO scheduling and an experiment with FQ scheduling.These experiments show the impact of the NP assumption on unicastflows.All the simulations are repeatedfive times and the average is taken over thefive repetitions.All the plots are with95%confidence intervals.TCP and unresponsiveflows.For this simulation we consider a unicast environment consisting of TCPflows randomly distributed on the topology RT.We add from to CBRflows randomly distributed on the topology RT.This simulation shows the impact of fully unresponsiveflows(the CBRflows send at10Mbit/s,the bandwidth of the LANs)with FIFO scheduling(as used in today’s Internet),and with FQ scheduling(as suggested by the FS paradigm).All the simulations are repeatedfive times and the average is taken over thefive repetitions.All the plots are with95%confidence intervals.We choose a simulated time of50seconds,large enough to obtain significant results.All the TCPflows start randomly within thefirst simulated second.All the unresponsiveflows start randomly between the forth and thefifth simulated second.We compute the mean bandwidth for all TCP and all unresponsiveflows,.In section3.1.1, we do additional simulations with a simulated time of200seconds to study the behavior of a TCPflow throughout the time(seefigure3).。