Helping First Responders

Video system facilitates needs of police and transit administrators

Managers of the Shanghai Metro System were very concerned about what could happen if there was an accident. With so many people using the underground rail system, responding to a calamity and getting the injured rescued could be a major problem.

There are many challenges in creating such as system. First of all, because the system is so vital, it needs to stay in either semi-automatic or full-automatic mode all the time. Thus, the video system itself must be monitored continually to ensure that all aspects of it are running in real-time and that recorded video is available to the surveillance center as well as the police at all times.

Adding to the challenge, a huge number of cameras are deployed. To date, the system uses more than 1,000 cameras and approximately 60 networked matrix switchers. Another problem is that as trains go over the rails, they create electromagnetic interruptions that can impact the video cameras and other surveillance devices. These factors presented a tough challenge for the transmission design.

Meeting the Challenge in a City of 19 Million

In a metro system, camera positioning is paramount. If the person on the video can’t be recognized, the system is of no value as a deterrent. Therefore, in any one visit to a Shanghai metro station, a passenger will be viewed by four different cameras, all from the front, and will appear in six different surveillance images.

For instance, both the entrances and exits of metro stations have fixed cameras, each capable of viewing a person from the front as he or she enters a ticket-check station. In each of the metro halls, an integrated high-speed dome camera surveys the entire facility. Secluded corners have additional fixed cameras so that these areas are not out of sight to the surveillance system. Cameras also are on the platforms to give rail system administrators an overview of passenger flow and help train drivers make sure that all passengers are on or off the train before the train is put into motion.

To understand how the system works, it helps to visualize the flow of video. The video from the camera is transmitted to a video equalizer in the train station’s control room. Once equalized, it is transmitted to a video distributor where functional icons are overlaid on the video image. From there, the video goes to the matrix switcher and DVR, respectively. One channel of the DVR is looped back to the matrix so that the matrix can call up the video being recorded in the DVR. Three keyboards, installed in the train control room, the security room and the maintenance room are used to run their own individual applications. For instance, the train control room is most interested in traffic flow while the security room concerns itself with safety and criminal concerns. Each is connected to the RS232 port of the matrix, and each has its own priorities.

The control center and each station are connected by an Ethernet network, used solely by the video surveillance system, to offset the aforementioned problems of electromagnetism. A matrix in any one of the metro stations uploads eight channels of images through eight video coders. Eight video decoders in the control center then take the images collected from the front matrix and transmit them to the central control matrix. All matrixes also are connected via Ethernet, each provided with its own IP address.

The central control keyboard also is connected into the Ethernet network instead of the central control matrix. Its control signal is transmitted from a keyboard to the video management server. Once the server translates the codes collected from the keyboard, it identifies the priority of the keyboard and transmits the corresponding control demand that controls each station, central matrix and codec to perform image switching and PTZ operation for the domes in each station.

Control and Priority Levels

Although complex, the system is easy for operators to run. For instance, control center operators can call up and control video in each station via one of the keyboards connected to the Ethernet network. However, they can’t do anything solely at will because control procedures and priorities are managed uniformly by a sole management server within the network.

For example, if the central operator wants to call up video from a specific station, codes are transmitted to the server, which makes a judgment and sends out commands to ask the station video matrix to switch the desired video to a specific video coder. Simultaneously, it asks a specific video decoder to decode the coder address of that station. The decoded image is then transmitted to the central matrix. There, the server sends its commands to the central matrix, asking it to output the image uploaded by the decoder onto a chosen monitor.

Likewise, the control signals for the domes are identified by the server, comparing their priority with other keyboards, including the keyboards within the network and the keyboards in each station. At this point, the server transmits the control command into the matrixes in each station.

Each keyboard can set up 20 priority levels to any camera. They do not need to be the same; each camera can have different priority levels. Priority levels are further customized to the needs of each metro station.

Within a single station, cameras are divided into two groups. The first group, situated at the entrances and exits, are for the police. Obviously, their control priority is determined by the police.

The second group, comprised of the metro station domes that survey the operation in general and passenger flow in particular, is subject to the needs of the metro transit authorities. As part of a total system, there is a crossed priority among the two groups and, depending on circumstances, one group can have priority over another.

To do all of this, the system must meet three requirements.

  • The matrix must be able to change the original keyboard setting priority for a camera. As previously noted, each keyboard can provide up to 20 different priorities for each camera.
  • The video surveillance server needs to identify the priority comparison of the fixed cameras set up by the different keyboards in the control center. As the keyboards in the control center send out code to the server through IP, the server identifies the different keyboards by their IP addresses, which provides the server with each camera’s priority level. At that point, the server transmits the control commands collected from the keyboards to the corresponding device.
  • Although the server can compare priorities among the keyboards by their differing IP addresses, it is still difficult to compare the priorities of the IP keyboard and that of a keyboard used in a metro station. That’s because the server cannot get the data from the station keyboard. Thus, another change needs to be made to the matrix. Once the station keyboard controls its front end camera, the matrix promptly uploads the current dome’s priority—controlled by the station keyboard—onto the central server via IP. The server then backs-up the collected data in its database. When and if necessary, the backup data is read for priority comparisons.

Classic Matrix

The Shanghai Metro Transit System leverages Infinova’s classic use of an Ethernet matrix for metro surveillance systems, yielding easy connection, simple system expansion, strong compatibility and reliability.

As an example, although of different protocols and brands, the matrixes and DVRs are integrated. By using a server, internal and external ports are unified, enabling easier system expansion within the transit system—such as the surveillance connection between stations— and externally—such as from a metro station to the police—simply by using the server to exchange information.

The matrix system can collect alarm information from every alarm—fire control or theft alerts—and all video loss alarm information for transmission on to the central management server. When the central management server receives such alarms, it can pop up the alarm information window, discharge the alarm bells and flicker the alarm light. This capability can be provided to other devices in the network, as well.

The central management server also collects standard clock signals and calibrates the time for the video matrix switchers, DVR, character overlapping device, client end and other devices within the LAN to ensure the entire surveillance system is synchronized.

The matrix main control keyboard is provided with a network-control DVR function by entering the corresponding hotkey that switches the keyboard to function as the control network DVR. As a result, central users can control any DVR within the network directly through the matrix keyboard, calling up recorded files from remote sites to simplify both real-time surveillance and evidence collection. Compared to systems that can only control the local DVR via RS 485, RS 232 or other ports, controlling DVRs as the Shanghai Metro System does makes much more sense.

System expansion is simplified. By merely adding one network matrix and video coder, then adding the corresponding IP address and channel connection mode into the central server, expansion is complete. This lets the central keyboard send out code to the server. Once the server identifies its priority and transmits the control code to the matrix, it is able to control the newly added matrix switch and control front-end pan and tilt rotation.

Matrix network integration also is simplified. Due to the control server, other surveillance systems, such as the Shanghai police’s system, can get access to the system easily via a seamless connection. For instance, the police video system only has to transmit control commands to the transit system’s management server, where they are translated, identified and then sent to the appropriate matrix to call up the desired video. Plus, all is done in Windows, avoiding the need for the police, or others, to have any other systems or software. They only need to provide the appropriate protocol to get access.

As a result, Shanghai authorities are able to pinpoint any accidents and determine their severity to ensure the right numbers of first responders get to the right place as quickly as possible. The transit authorities can determine if they need to run more or less train cars in relation to passenger needs, and the police are provided with evidence that will help them capture wrongdoers and get them prosecuted and convicted.

This article originally appeared in the March 2012 issue of Security Today.


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