WLAN基础知识培训胶片介绍.ppt

当发射端希望发送数据时，首先检测介质是否空闲，若是介质为空闲时，送出RTS（Request To Send请求发送），RTS信号包括发射端的地址、接收端的地址、下一笔数据将持续发送的时间等信息，接收端收到RTS信号后，将响应短信号CTS(Clear To Send)，CTS信号上也RTS内记录的持续发送的时间，当发射端收到CTS包后，随即开始发送数据包，接收端收到数据包后，将以包内的CRC(Cyclic Redundancy Check，循环冗余校验)的数值来检验包数据是否正确，若是检验结果正确时，接收端将响应ACK包，告知发射端数据已经被成功地接收。当发射端没有收到接收端的ACK包时，将认为包在传输过程中丢失，而一直重新发送包。 * There are five topics. * * A traditional Access Point is a self-contained, standalone device. It can be set up to provide wireless to a small group of 5 nodes or as one of many access points on a large corporate network. Each access point is an autonomous device. Each access point must be individually configured and managed. Any changed to the network as a whole would have to be applied to each and every access point on the corporate network. This means that using telnet or a web browser, you may have to change 50 or 60 access points in order to implement a small change on the network. These access points are often referred to as Fat Access Points because they have all this intelligence built into the individual unit. Not only is all of the intelligence built into a Fat Access Point, but all of the network and wireless security information is built into this device too. If one of these access points were stolen, a technically savvy thief could gain access to encryption keys. In order to protect the network from a stolen AP, the network administrator would have to enter new security settings on each of the access points that were still part of the corporate network. If fat access points are used in a large enterprise network, an extensive site-survey needs to be performed to determine where each and every access point needs to be installed, along with channel settings and power settings. Any auditing and correction of the access point settings will also need to be performed on an access point by access point basis. There are five topics. * * Wireless security is broken into three key components, each of which can exist individually or as a group. T