Design And Implementation Of WiFi Multicast Reliability Assurance Mechanism In Classroom Scenarios

WiFi is a widely used wireless LAN technology at present.With the promotion of new teaching mode and the rapid popularity of portable mobile terminals,there is often a multi-screen display scene from the teacher's host to a large number of students' mobile terminals in the multimedia smart classroom,and for this "point-to-multipoint" scenario,the use of multicast technology can improve the transmission efficiency.There is a practical need to provide multicast services in WiFi networks.The 802.11 protocol used in WiFi technology only provides reliability services for unicast at the MAC layer,but lacks reliability support for multicast,and existing WiFi multicast reliability solutions perform multicast to unicast at the wireless router.multicast to unicast,and the next hop data is distributed in the form of unicast.When the number of users is large,this solution will take up a lot of wireless channel resources to send duplicate data,which may lead to serious congestion in the wireless channel and make it difficult to meet the video playback needs of a large number of student terminals with limited bandwidth resources.In the smart classroom,students usually use Windows operating system,but students studying computer and other related majors may prefer to use Linux operating system.At the same time,the reliability solution based on the MAC layer of the receiver needs to make changes to the NIC driver,however,commercial NICs usually do not support changes,and the system and NIC versatility of the device is a problem that has yet to be solved.In this thesis,we design and implement the reliability assurance mechanism of WiFi multicast transmission in smart classroom scenario to provide technical support for the project "Multicast retransmission of WLAN video service in education scenario",and the main work is as follows(1)To address the problem of large number of student terminals,we propose a hybrid multicast-unicast delivery mechanism for WiFi networks,which backs up the sent multicast data in the middle layer of wireless routers and retransmits the lost data from multicast to unicast,replacing the group multicast to unicast for all users with a directed,small amount of multicast to unicast,ensuring the balance between reliability and bandwidth resource consumption in WiFi multicast.(2)To address the diversification of mobile terminals,we design multicast-to-unicast merged reception synchronization submission and packet loss feedback schemes based on the WFP framework for Windows terminals and the Netfilter framework for Linux terminals,respectively,both of which are implemented based on the network layer without changes to the MAC layer and are applicable to any wireless NICs produced by different manufacturers.(3)To address the problem of high false frame rate in wireless networks,a highly efficient adaptive feedback frame format is designed,in which the receiver sends feedback on false frames and adjusts the feedback mode independently according to the false frame rate,so that one feedback can carry the maximum amount of incorrectly received information to reduce the number of feedbacks.(4)The proposed WiFi multicast transmission reliability assurance mechanism is implemented,a test scenario is built to verify the functionality,and a performance test is conducted to show that the proposed scheme achieves a balance between reliability and bandwidth resource consumption in multi-user WiFi multicast.