Enabling IGMP Snooping on a Vehicle-Mounted AP

Vehicle-mounted multimedia devices on moving trains deliver multimedia information services to passengers in multicast mode. Reliable multicast data transmission ensures smooth delivery of multimedia information services. All vehicle-mounted multimedia devices are added to a multicast group. As the train moves ahead, the active link changes frequently. Only the trackside AP and vehicle-mounted AP are aware of the link change. Other ground devices such as switches connected to trackside APs cannot detect the change and fail to forward multicast data. To resolve the problem, IGMP snooping is enabled on the vehicle-mounted AP and ground devices to generate Layer 2 multicast forwarding entries. After switching the active link to a new trackside AP, the vehicle-mounted AP sends a Report message to the trackside AP. The trackside AP forwards the message to the ground device, which then updates the multicast forwarding table accordingly. To prevent loss of multicast packets during a link handover, the vehicle-mounted AP still receives multicast data from the old trackside AP before the multicast flow is switched to the new trackside AP. After receiving multicast data from the new trackside AP, the vehicle-mounted AP sends a Leave message to the old trackside AP. The old trackside AP forwards the Leave message to the ground device, which then stops sending multicast data to the old trackside AP. This mechanism ensures seamless switching of multicast data.