Internet中的主机管理与域名系统

Internet连接了全球成千上万的计算机，我们浏览的信息就存储在这些计算机上。当我们要从自己的计算机浏览其他计算机时，Internet是如何区别和定位每一台计算机的呢？为了唯一地确定Internet上的每台主机，TCP／IP协议为网络上的每一台主机都分配了一个32位长的二进制地址，这个地址称为IP地址。由于8位二进制的数可以表示十进制0-255之间的数，所以为了便于人们识别，这个32位的IP地址，一律写成4个十进制0-255之间的数字字段，中间用半用的句点隔开，即人们常说的千点分十进制表示方法。如“202.196.237.133”’。IP地址是Internet…     

IPv6导致网络应用不畅

目前使用的IP协议,其学名为IPv4,地址长度32位。互联网的快速发展,使得IP地址日益枯竭,从而催生了下一代IP协议IPv6。IPv6地址长度是128位,可有效解决IP地址短缺和网络安全等问题。近几年推出的操作系统,基本都支持IPv4和IPv6。     

校园网IP地址防盗用策略

IP地址盗用是网络管理中一个亟待解决的问题,它严重影响了合法用户的权益,影响了网络的正常运转。防范IP地址盗用变得越来越重要。给出了一个新的IP地址防盗用的方法,较好解决了这个问题。     

我国国家域名.CN进入IPv6时代

目前的互联网协议为IPv4，其地址为32位编码，可提供的IP地址大约为40多亿个．已经分配了70％，预计2005年将全部分配完毕。而且由美国掌握绝对控制权，美国一个大学拥有的IP地址就几乎等于全中国的IP地址，中国的公众网被迫大量地使用转换地址，严重影响了互联网本身的效益及安全。IPv6的地址是128位编码，能产生2^128个IP地址，     

网关绑定引发网络故障

面对大型企业中在用的数千台终端，如何在保证网络畅通的前提下防止各终端地址互不冲突，是每个企业网管都必须面对的难题。通常，划分VLAN、分配静态IP地址、启用IP-MAC地址绑定，这些措施基本都能保证地址资源的合理规范使用了。     

局域网内IP地址盗用的防范措施

IP地址的盗用给网络管理带来安全隐患，针对常见的IP地址盗用方法，分析IP地址盗用原理，提出有效的防范措施。     

水利部动图卫星广播系统(下)

四、关键技术 1.卫星IP广播 IP多播是指IP报文向一个“主机组”的传送，这个主机组由一个单独的IP地址标识，也称为“组播地址”。除了目的地址部分，组播报文与普通报文没有区别，网络尽力传送组播报文但是并不保证一定送达。     

多媒体业务NAT／防火墙穿越

计算机网络、电信网络和有线电视网．这三网正在走向融合的基于IP技术的下一代网络(NGN)．导致了对IP地址资源需求的迅速增加．超出了最初预期和设计的32bit(IPv4地址长度)。解决地址资源短缺的思路大致有两类：(1)“开源”，即使用地址长度更大的下一代IP协议——IPv6。(2)节流．即尽量提高对现有IPv4地址资源的利用率．比如动态分配IP地址．使用网络地址翻译(NAT)技术等。     

ZXB10多业务路由交换机VPN业务的实现

MPLS VPN的基本工作方式是采用第三层技术，服务提供商为每个MPLS VPN分配一个路由标识符(RD)，该标识符在SP的网络中是独一无二的。转发表中包括一个独一无二的VPN IP地址，由RD和用户的IP地址组合而成。VPN转发表中包括与VPNIP相对应的标签，通过这个标签将数据传送到相应的地点。即用标签代替IP地址，用户可以保持他们的专用地址结构，无需进行网络地址转换即可传送数据。     

IP地址的小常识

连接到互联网上的每台计算机都有唯一一个号码标识,这个号码标识被称为IP地址。IP是Internet Protocol(网际协议)的英文缩写。每个IP地址都是由两部分组成的:网络号和主机号。网络号标识一个物理的网络,同一个网络上所有主机需要同一个网络号,该号在互联网中是唯一的。这就像是个人身份证号中前6位是表示地域信息,居于同一地域的人这6位号码都相同的道理一样。主机号用来确定连接在物理网络中的每台主机或服务器。对于同一个网络号,主机号码唯一,不允许重复,这就像是身份证号码中后几位表示个人出生日期的数字。由网络号和主机号组成的IP地址具体而唯一地     

NOVEL BIPHASE CODE——INTEGRATED SIDELOBE SUPPRESSION CODE

A kind of novel binary phase code named sidelobe suppression code is proposed in this paper.It is defined to be the code whose corresponding optimal sidelobe suppression filter outputs the minimum sidelobes.It is shown that there do exist sidelobe suppression codes better than the conventional optimal codes-Barker codes.For example,the sidelobe suppression code of length 11 with filter of length 39 has better sidelobe level up to 17dB than that of Barker code with the same code length and filter length.     

Click and code [automatic code generation]

Automatic code generation already plays a valuable role in embedded development. Engineers are turning to advanced software tools that generate code automatically, both during the prototyping stage of the project and when production code is required. At the prototyping stage, automatic code generation can greatly accelerate the development process, allowing many different algorithms to be tried in a shorter period. Furthermore, because there is no significant time penalty for trying alternative solutions, automatic code generation tools positively encourage innovation, eliminating the temptation to re-use previously developed code in compromised solutions. The specification that previously would have been handed to a software engineer for hand coding is now used as an 'executable specification'. In addition to forming the basis for code generation this specification can be used to develop test procedures, that can be applied both in simulation and on the real product. A further advantage of this approach is that algorithm developers can test their ideas without having to wait until the associated code is ready for downloading to a target processor. This not only benefits the algorithm designer, but also frees the software engineer from the routine coding of algorithms, allowing greater effort to be devoted to more challenging issues     

码多普勒对扩频码捕获性能的影响

为了评价高动态场景中码多普勒对捕获的影响,定量分析码多普勒对相关峰值的影响具有指导意义。引入一种有效的求解码相关结果的方法——图解法,采用此方法推导了当存在码多普勒时码相关结果,详细推导了当码搜索步进不连续时码多普勒对相关峰的影响。通过Matlab仿真了码搜索步进为连续和不连续时码多普勒对相关峰值的影响,证明前述推导是正确的。计算结果表明,当码搜索步进为二分之一码片,相关时间内码多普勒引起的码误差超过四分之一码片时将对相关峰值造成影响。     

一种基于分段CRC码级联Hash极化码的设计

极化码作为一种线性分组码，具有较低的编码复杂度和确定的构造，但当其为中短码长时，性能会有所降低。提出一种基于分段循环冗余校验（cyclic redundancy check，CRC）码级联Hash极化码的设计方法，该方法在原有Hash极化码（Hash-Polar）的基础上，采用CRC分段校验进行双校验，分段CRC码在译码过程中能辅助路径度量，即对译码路径进行修饰，以此提高路径选择的可靠性，提高性能；另外，分段校验是将校验码分散地添加到输入的信息序列中，译码时对于CRC不通过的情况，可提前终止译码路径以省去不必要的译码计算量。最后，译码结束时，Hash校验码对修饰后的L条路径进行校验，选出最佳译码路径。仿真结果表明，所提出的设计方法比 CRC 辅助的 Hash 极化码（Hash-CRC-Polar）误码性能更优异。在高斯信道下，当码长为 128 bit、码率为 1/2、误码率为 10^-3时，所提出的基于分段 CRC 校验码的 Hash 极化码比Hash-CRC-Polar获得了约0.25 dB的增益。     

Performance comparison of systematic polar code and non-systematic polar code

Polar code in channel coding schemes is a research hotspot in 5G communication field.Polar code is susceptible to error propagation under successive cancellation decoding,and the performance of the code at short and medium block lengths is not ideal.For the problems,the performance difference between systematic polar code and non-systematic polar code was studied under various simulation conditions.Simulation results demonstrate that systematic polar code has advantage over non-systematic polar code in bit error rate performance,and the former are more robust against error propagation than the latter under successive cancellation decoding.The above results are considerable importance from the theoretical values in 5G communication and performance optimization of polar code.     

Random code chaining

A new technique of random code chaining (RCC) is proposed to make block ciphers more secure in resisting ciphertext searching and authenticity threats. Furthermore, the technique is very suitable for file encryption. With this technique, it is possible to make a modification in encrypted files by re-enciphering only one block message     

Making unbreakable code

A product is on the way that relies on the quantum properties of photons to keep out eavesdroppers. All of them. The battle between codemakers and codebreakers is centuries old, but at the start of the 21st century, could it finally be drawing to a close? Physicists are putting the finishing touches to a method of encrypting messages that is more secure than anything that has gone before. Unlike the ciphers of the past, this new method has the potential to be absolutely unbreakable, not just practically unbreakable, but theoretically unbreakable. Mathematicians believe they can prove it. Central to the technique are the strange laws of quantum mechanics. Already experimental messages encrypted using quantum mechanics are being sent over tens of kilometers of optical fibers and received securely. Researchers are confident that it will not be long before ultra-secret messages are routinely transmitted in this way. But while quantum cryptography may be perfect in theory, practical considerations introduce security loopholes that an eavesdropper can exploit. The seriousness of these is still unclear, and physicists believe they can plug most of the holes with more efficient equipment. Still, enough cracks remain to maintain a healthy interest among cryptographers     

Data security-bad code

A tutorial on viruses, worms, bacteria, and other computer diseases is presented. It describes how experts classify the various forms of malicious code at work today, the ways in which they hide and work their mischief, and a few of the infamous incidents-such as the attack on the Internet network, in the fall of 1988, of a worm program that devoured massive amounts of CPU time-that have gained international notoriety. Some of the basic forms of prevention and cure are discussed