Design And Implementation Of A Smooth Roaming System For Mobile Terminal

With the popularity of a variety of smart phones and tablet PCs,wireless local area network(WLAN)into the explosive growth stage,the number of wireless LAN users at home and abroad are increasing rapidly,and the biggest advantage of using wireless LAN is the mobile terminal is not affected by the location of the physical medium,Terminals in WLAN coverage range,the terminal can move,and how to ensure the mobile terminal business is not interrupt-ed during the move,become a hot research issues application of wireless local area network technology.Today,the mobility of WLAN technology promotes the Informationization construction of hospital,greatly improving efficiency of the mobile wireless rounds such as inhealth care,health care service,and the Ministry of health hospital accreditation standards also strongly recommended the use of new technology such as electronic medical records.Uninterrupted,high-performance requirements for mobile health care,wireless LAN roaming technology bring new challenges.Handover mechanism of traditional mobile terminal need to reexecute the search,connection,authentication,key negotiation process,which will not only result in the terminal handover process of packet loss and reduce network reliability,long delay will cause a certain time of business interruption,which can't satisfy the requirements of medical roaming mobile terminal roaming.In the process of WLAN roaming,certification time is too long lead to packet loss and even business interruption and other issues,in order to solve this problem,this article through the analysis of traditional user roaming mechanism,puts forward a new kind of wireless local area network(LAN)smooth roaming the overall solutionFirst of all,this thesis added Supervisory AP in the traditional AC+AP architecture.Supervisory AP retains some of the functions of AP and increase the functions of AC,Supervisory AP is used to control the terminal connection,roaming switch and small AP management.Supervisory AP increased to promote the overall network capacity and reduce the AC load.Secondly,this thesis presents a new user association mechanism.The traditional user access mechanism provides the same public BSSID for each terminal,the BSSID changes before and after the roaming switch.In this thesis,in the process of user access,small AP provides a unique BSSID for each terminal,BSSTD around the roaming switch has not changed,so that Users can feel-free roaming.Thirdly,this thesis improves the traditional roaming decision condition.In the traditional roaming decision mechanism,when the RSST value of the terminal is lower than the threshold value,the roaming switch can be carried out,and then the AP with the maximum signal intensity indication value is selected as the target AP.This thesis improves the roaming decision condition,setting a threshold value,without affecting the business case for the terminal to select the optimal AP switch,and prevent ping-pong effect.Finally,in the process of roaming handoff,the storage and forwarding mechanism and cache mechanism are used to realize roaming low latency and no packet loss.The performance experiments of the system throughput can reach 150Mbps,roaming delay of handover process between 20ms-30ms,packet loss rate is close to zero,indicating that these techniques effectively accelerate the switching speed,can meet the needs of high performance roaming without packet loss,has a certain reference value for practical application.