System Overview
The subway PIS network system uses the Ethernet network built by the system itself to provide a network channel to the PIS. This channel is used to transmit various data information, video information, and control information from the center to each station and subway vehicle.

The subway passenger information system needs to transmit real-time dynamic multimedia information such as travel instructions, service hours, train arrival time, train schedules, manager announcements, government announcements, travel reference, stock information, media news, live events, and advertisements; Provide emergency emergency evacuation alerts in abnormal situations such as fire, obstruction and terrorist attacks. At the same time, the video information is collected by the monitor of each train, and is transmitted wirelessly to the control center in a manner of IP-encapsulating the video. The entire network must be a converged wired and wireless network that supports voice, data, and video, has good QoS support for services, supports multicast communications, and requires the stability and reliability required for operations.

Based on our extensive experience in integration over the years, especially leading technologies in industrial Ethernet switches, we provide a perfect network solution for subway passenger information systems.

Introduction
The subway PIS network system provides the required network platform for data transmission. The applications that need to be supported include the following types:
•The control center broadcasts multimedia information such as audio and video to each train.
•The real-time monitoring information in the vehicle sent back to the control center by each train;
•Other control data, etc.。

The network system uses the Gigabit Ethernet network and wireless network constructed by the system itself to provide a network channel to the passenger information system. The channel is used to transmit various data information, video information and control information from the center to each station and the subway vehicle.

Solution
The network system uses the Ethernet network and the wireless network constructed by the system itself to provide a network channel for the passenger information system. The channel is used to transmit various data information, video information and control information from the center to each station and the subway vehicle.

The network system is divided into two parts: wired network and wireless network.

Wired network equipment mainly includes: control center Ethernet core switches, center-level Ethernet switches, station Ethernet switches, firewalls, and routers. In the control center, each station, depot, and parking lot, Ethernet switch devices are installed and connected through the channels provided by the transmission system. The channel capacity is considered to be not less than 800M, which constitutes a wired transmission path for passenger information system information.

The wireless network is an extension of the cable network and provides ground and train communications. It mainly includes wireless controllers installed in the control center, optical cables in tunnels along the way, and wireless access point devices. The wireless controller is connected to the station passenger information Ethernet switch through the control center passenger information core switch, and the station passenger information Ethernet switch and the wireless access point beside the track are connected through a single mode fiber. At both ends of the platform, AP devices are connected to the passenger information Ethernet switch of this station.

Topology scheme
The subway PIS network system consists of a three-tier network structure, namely control center subsystems, network subsystems (300M radio access network and station network systems of Metro 802.11n), and onboard subsystems (train 1000M Ethernet LAN and wireless vehicle terminals). .The train passes 300M wireless access to the orbital side AP, the orbital side AP accesses the station switch through 1000M Ethernet Ethernet, and the station switch accesses the backbone network through 1000M Ethernet.

Each station platform and track edge are equipped with 2.4GHz wireless access points (APs) complying with the 802.11 standard. They receive signals from the subsystem control center via Ethernet laid in the trackside. Train terminals rely on wireless networks and Ethernet communication technology receives real-time information sent from the AP corresponding to the location of the train, and realizes real-time transmission and playback of the video signal. At the same time, due to the bidirectional nature of wireless information transmission, wireless video systems can also upload real-time passenger information and monitoring information on trains to the station control room and subsystem control center in a timely manner.

The wireless video transmission system mainly involves the radio access points AP and antenna deployment along the edge of the track, seamless switching under high-speed movement, and interconnection with higher-level switch devices and digital multimedia data transmission with the media distribution center.