Abstract:
A real-time ring-loop surveillance network system is provided. By using digital communication network, multiple channels of media data and control data are transmitted in a ring-loop. The media data includes any forms of digital audio and video data, which is transmitted through 802.3/802.3u physical layer interface. The media data reaches all the stations in the network at the same time, and the number of the stations in the system depends on the system requirements. The number of the channels depends on the transceiver&#39;s speed. The present invention defines frames to encompass the media data and control data for transmission. The point-to-point delay is less than 0.15 ms. When 32 stations are connected in a ring-loop, the maximum delay is less than 5 ms. A backup mechanism is also included to detect and automatically switch to maintain the normal operation of the surveillance network system. The monitor signals are also encompassed in frames transmitted in the same network.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to a surveillance system, and more specifically to a ring-connected surveillance system with real-time backup monitoring.  
       BACKGROUND OF THE INVENTION  
       [0002]     The surveillance system is widely used in various applications, such as fire detection, police surveillance, coast surveillance, environmental protection, military surveillance, aero-traffic, medical service, and various public safety situations. The modem surveillance system incorporates computers, communication, and satellites to provide a close surveillance and protection. As the price of the hardware reduces in recent years, the surveillance system is also adopted in more business settings, offices, and households. For example, the surveillance system can be set up to monitor the safe, business venue, warehouse, high-priced goods, production line, and so on. The surveillance system can even be set up in the neighborhood to prevent theft, burglary, vandalism, or littering.  
         [0003]     However, most of the conventional surveillance systems use a chain-connected or star-connected master/slave structure. For example, U.S. Patent Application Publication 2003/0050989 A1 disclosed an audio data transmission system using a digital communication network, such as Ethernet, to connect a master module and a plurality of slave modules in a chain or a star topology, as shown in  FIG. 1 . Although this type of topology allows data transmission and system monitoring, it lacks in fault-tolerance. Once a communication segment between two stations is out of order, the communication between these two stations is cut off. Another drawback of such type of topology is that the communication delay is large, especially for the stations at the end of the communication chain. This also affects the system efficiency.  
         [0004]     As the hardware price continues to decrease and the surveillance is more widely adopted in different venues, it is imperative to provide a more effective surveillance system to overcome the above drawbacks.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention has been made to overcome the above-mentioned drawback of conventional surveillance systems that have long delay and no fault-tolerance. The primary object of the present invention is to provide a surveillance network system using a ring-loop digital communication network to transport multiple channels of media data and control signal. With the feature of the Ethernet, the media data and the control signal can be transceived. The data from one station can be transmitted through the transceiver of the Ethernet to the next station, and so on. The stations form a ring loop. Under the ring loop structure, a master/slave relation is formed, and the media data are synchronized on all the stations in the ring. The delay is so small that is it imperceptible to the human senses.  
         [0006]     Another object of the present invention is to provide a surveillance network system with a real-time backup mechanism so that the network system can continue to operate normally even when one link in the ring loop is disconnected. In addition, the network system can provide a real-time warning regarding the disconnection so that the problem can be fixed. Through the backup monitor mechanism, the real-time detection of disconnection and the real-time switching are performed so that surveillance network system can switch to the backup transmission route when detecting a disconnected link, and automatically switch back to the original transmission route when the disconnected link is fixed.  
         [0007]     To achieve the above objects, the present invention provides a real-time surveillance network system having a backup monitor mechanism and using a ring-loop communication network for accommodating the transmission of media data and control signal so that the surveillance network system can switch to the backup transmission route too continue normal operation when a disconnected link in the ring-loop is detected. The real-time surveillance network system includes a ring-loop of cables, such as CAT5, CAT6, or optic fiber, connecting a plurality of surveillance stations. The ring-loop consists of a plurality of point-to-point segments, and each segment is made of a cable connecting two surveillance stations. To improve the fault-tolerance and the transmission efficiency, the present invention uses a dual-ring structure to provide the bi-directional transmission capability between neighboring stations. To enable the point-to-point error surveillance, the present invention also includes a backup monitor mechanism to monitor the operation between two neighboring stations, and the system can switch the transmission direction when an error or disconnection is detected in any segment linking two stations. In this manner, the present invention can be warned and continue normal operation when a disconnected link is detected.  
         [0008]     The present invention is applicable to airport, shopping malls, subway system, football stadium, school campus, or other large area that require to transceiver a large amount of data over a long distance for real-time playing.  
         [0009]     The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention can be understood in more detail by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0011]      FIG. 1  shows a schematic view of a conventional surveillance system;  
         [0012]      FIG. 2  shows a schematic view of an embodiment of the real-time surveillance network system of the present invention;  
         [0013]      FIG. 3  shows a schematic view after ID assigned to the stations of the embodiment in  FIG. 1 ;  
         [0014]      FIG. 4  shows a disconnected link in the embodiment in  FIG. 3 ;  
         [0015]      FIG. 5  shows two disconnected links in the embodiment in  FIG. 3 ;  
         [0016]      FIG. 6  shows a schematic view of the network card of a station according to the present invention;  
         [0017]      FIG. 7  shows a schematic view of the operation of the network card of  FIG. 6  when no backup situation occurring;  
         [0018]      FIG. 8  shows a schematic view of the operation of the network card of  FIG. 6  when the network card used as a bypass station in the backup situation;  
         [0019]      FIG. 9  shows a schematic view of the operation of the network card of  FIG. 6  when the network card used as a stop station in the backup situation;  
         [0020]      FIG. 10  shows a schematic view of the operation of the network card of  FIG. 6  when the network card used as a start station in the backup situation;  
         [0021]      FIG. 11  shows a schematic view of the complete operation of the network card of  FIG. 6 ;  
         [0022]      FIG. 12  shows a schematic view of an FPGA embodiment of the clock reconstitution module;  
         [0023]      FIG. 13  shows a schematic view of a carry frame of the present invention;  
         [0024]      FIG. 14  shows a schematic view of a monitor frame of the present invention; and  
         [0025]      FIG. 15  shows a flowchart of a real-time surveillance network system of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]      FIG. 2  shows a schematic view of an embodiment of a real-time surveillance network system of the present invention. The embodiment includes 8 stations.  FIG. 2  shows the 8 stations are connected in a ring-loop, while the ID of the stations is yet determined. At this point, the backup monitor mechanism on each station checks the connection with the neighboring stations. For example, the second station checks the connection with the first and the third station. All the connections can be monitored through the console of each station or the PC connecting to the surveillance network.  
         [0027]      FIG. 3  shows a schematic view of the embodiment of  FIG. 2  after the control software on the PC assigns the ID to each station in the network system. For example, if the PC is connected to the first station, and the each station is assigned an ID in an increasing order successively, the resulted ID assignment will be as shown in  FIG. 3 . After assign the first station as station  1 , the ID assignment starts from  1 B transmits to  2 A, and assigns the second station as station  2 , and proceeds from  2 B to  3 A, and so on. After the ID assignment, the station with the smallest ID number will be selected as the master, and the remaining stations are slaves, as shown in  FIG. 3 , station  1  is the master, and stations  2 - 8  are slaves.  
         [0028]      FIG. 4  shows a disconnected link is detected in the embodiment of  FIG. 2  after a long duration of operation. As shown in  FIG. 4 , the segment linking  6 B and  7 A is disconnected. Through the backup monitor mechanism, station  6  is assigned as a start station, and station  7  is assigned as a stop station. The remaining stations  1 ,  2 ,  3 ,  4 ,  5 ,  8 , are all assigned as bypass stations. A single disconnected link will not render the network system malfunction. The present invention can tolerate a single point error by re-directing the transmission direction so that the surveillance network system can continue to operate normally. For example, the media data and the control signal from station  6  to station  7  will be routed through stations  5 ,  4 ,  3 ,  2 ,  1 ,  8  so that the transmission can continue. However, only the carry frames will be re-directed for the transmission, the monitor frames are still transmitted using the original direction to detect whether the error on the link is fixed. The carry frames and the monitor frames will be explained later in the description. When the link between  6 B and  7 A is fixed, the surveillance network system will switch back to its original routing direction, marked as no backup state. Therefore, no stations are assigned as start station, stop station, or bypass station after the link  6 B to  7 A is fixed, which is the same as before the error occurred in the link  6 B- 7 A.  
         [0029]      FIG. 5  shows two disconnected links are detected in the embodiment of  FIG. 2  after a long duration of operation. As shown in  FIG. 5 , the segment linking  4 B and  5 A and the segment linking  8 B and  1 A are both disconnected. Through the backup monitor mechanism, station  4  is assigned as a start station, and station  1  is assigned as a stop station. Stations  2 ,  3  are assigned as bypass stations. Stations  1 ,  2 ,  3 ,  4  will form a local network. Station  5  will be assigned as the master of another local network because station  5  has the smallest ID number in the local network. Station  5  is also the stop station, and station  8  is the start station. Stations  6 ,  7  are assigned as bypass stations. As there are two disconnected links, two local networks are formed. If there are more disconnected links, more separated local networks will be formed. Within each local network, the station with a smallest ID number is the master of the local network. When a disconnected link is fixed, for example, link  4 B- 5 A, the two local networks will be merged, and station  5  will be assigned as slave again. In this case, station  1  is the stop station, station  8  is the start station, and the remaining stations  2 ,  3 ,  4 ,  5 ,  6 ,  7  are all assigned as bypass stations, which is similar to the embodiment in  FIG. 4  with one disconnected link.  
         [0030]      FIG. 6  shows a schematic view of a network card, including physical layer transmission connection points (Port A, Port B)  601 ,  602 , digital media and control data input  603 , digital media and control data output  604 , digital media data transmission management  605 ,control data transmission management  606 , digital media data receiving management  607 , control data receiving management  608 , frame compose management  609 , frame decompose management  610 , output frame management  611 , receiving frame management  612 , frame source output selections  613 ,  615 , frame input destination selections  614 ,  616 , transmitting media  617 ,  619 , receiving media  618 ,  620 , physical layer transmitting interfaces  621 ,  623 , physical layer receiving interfaces  622 ,  624 , and clock reconstitution module  625 . The master/slave assignment determines which clock will be used, which is also the synchronization mechanism of the entire network system. If a station is a master, the station outputs its own clock. If a station is a slave, the station outputs the reconstituted clock.  
         [0031]      FIG. 7  shows the operation of a network card in a no backup situation. When the system operates in a no backup situation, the digital media data and control data are transmitted at a fixed clock rate of 48 KHz to frame compose management  609 , through output frame management  619 , frame source output selection  615 , transmitting media  619 , to physical layer transmitting interface  623  for transmitting. On the other hand, the frames are received by physical layer receiving interface  622 , through receiving media  618 , frame input destination selection  614 , receiving frame management  612 , to frame decompose management  610  for decomposing into digital media data for digital media data receiving management  606  and control data for control data receiving management  608 . Therefore, when operating in a no backup situation, the communication flows in from physical layer transmission connection point  601 , and out from physical layer transmission connection point  602 . If a station is a master, clock  625 a to clock reconstitution module  625  is not for adjustment reference. Clocks  625   b ,  625   c  are generated by clock reconstitution module  625 . If a station is a slave, clock  625   a  to clock reconstitution module  625  is for adjustment reference, and clocks are the clocks after the adjustment and are synchronized with the 48 KHz of the master.  
         [0032]      FIG. 8  shows the operation of the network card when a station is assigned as a bypass station. When the system detects a disconnected link, a backup situation occurs. When a station is assigned as a bypass station, the receiving flow does not change direction, while a new transmitting direction is added. The frames are received by physical layer transmission connection point  602 , through physical layer receiving interface  624 , through receiving media  620 , frame input destination selection  616 , to frame source output selection  613 , and transferred through transmitting media  617  to physical layer transmitting interface  621 . Basically, the bypass station maintains the same original receiving direction, and the other frames entering from the other direction is, instead of sending to frame decompose management  610  for decomposition, transmitted to transmitting interface  617  for transmission. The clock of the station depends on whether it is a master or a slave. The adjustment pulse of the clock of the bypass station is from receiving media  618 .  
         [0033]      FIG. 9  shows the operation of the network card when a station is assigned as a stop station. When a backup situation occurs and a station is assigned as a stop station, the transmitting flow does not change direction, while receiving direction is changed. The frames enter physical layer transmission connection point  602 , through physical layer receiving interface  624 , through receiving media  620 , frame input destination selection  616 , to receiving frame management  612 , and transferred to frame decompose management  610  for decomposition. The decomposed digital media data is placed into digital media data receiving management  607  with the same original transmission direction. The clock of the station depends on whether it is a master or a slave. The adjustment pulse of the clock of the bypass station is from receiving media  620 .  
         [0034]      FIG. 10  shows the operation of the network card when a station is assigned as a start station. When a backup situation occurs and a station is assigned as a start station, the receiving flow does not change direction, while transmitting direction is changed. The frames are sent from frame compose management  609 , through output frame management  611 , frame source output selection  613 , transmitting media  617 , to physical layer transmitting interface  621 , and reach physical layer transmission connection point  601  for transmitting. The received frames enter through physical layer transmission connection point  601 , through physical layer receiving interface  622 , through receiving media  618 , frame input destination selection  614 , to receiving frame management  612 , and transferred to frame decompose management  610  for decomposition. The clock of the station depends on whether it is a master or a slave. The adjustment pulse of the clock of the bypass station is from receiving media  620 .  
         [0035]      FIG. 11  shows a complete operation of the network card of  FIG. 6 . In addition to the aforementioned carry frame which composing the frames, a monitor frame is also transmitted and received for monitoring the backup state, shown as monitor transmitting management  626 , monitor receiving management  627  in  FIG. 11 . The monitor frames are sent from output frame management  611  to frame source output selection  613  or  615  for transmitting and received from receiving media  618  or  620 , through frame input destination selections  614  or  616 , to frame decompose management  610  for decomposition. The overall operation is clocked by clock reconstitution module  625 , and therefore using the carry frame for clock adjustment. The adjusted clock is sent to frame compose  609 , but also depends on whether the station is a master or a slave station.  
         [0036]      FIG. 12  shows an FPGA embodiment of the clock reconstitution module of the present invention, including an output  628 , a receiving frame  629 , an input  630 , a state (master or slave) input  631 , a sample phase counter  632 , a phase detection comparison  633 , an adjust clock  634 , a selector  635 , a frequency multiplier  636  and a frequency divider  637 . Clock reconstitution module  625  is responsible for synchronization on the trigger by the received frame. As shown in  FIG. 12 , frame  629  triggers phase detection comparison  633 , and phase detection comparison  633  samples the value in the sample phase counter  632  for comparison, and the comparison result is used by adjust clock  634  for adjusting the clock. Adjust clock  634  adjusts the clock according to the four times of the target frequency. The adjusted frequencies are used by selector  635  and sample phase counter  632 . Depending on state input  631 , the frequency for output  628  is selected. The frequency of input  630  is twice of that of output  628 . The frequencies output from frequency multiplier  636  and frequency divider  736  are supplied to adjust clock  634  and selector  635 .  
         [0037]      FIG. 13  shows the carry frame, consisting of media data and control data, transmitted at the fixed 1/48 KHz. The carry frame is structured to include a PRE field for clock synchronization adjustment in the physical layer, an SFD field for the starting of the frame, a T/L field for the type and the length of the frame excluding the PRE, SFD and CRC fields, a UCD field for system control data, an MD for media data, and a CRC for the CRC value of the entire frame ranging from T/L field to MD field.  
         [0038]      FIG. 14  shows the monitor frame, including detection control commands, transmitted at the fixed 48 KHz. The monitor frame is structured to include a PRE field for clock synchronization adjustment in the physical layer, an SFD field for the starting of the frame, a T/L field for the type and the length of the frame excluding the PRE, SFD and CRC fields, an MCD field for system monitor data, and a CRC for the CRC value of the entire frame ranging from T/L field to MD field.  
         [0039]      FIG. 15  shows a flowchart of the real-time surveillance network system of the present invention. The flowchart is executed by each station in the surveillance network system. When the system starts, it enters step  650  for initialization of system variables and hardware parameters. Step  651  is to check the state of the link at a fixed interval. At the end of the fixed interval, step  652  is executed to send the inquiry frame; otherwise, step  653  is executed to check the link state. If the state of the link is unchanged, step  651  will be executed repeatedly until the state changes, which leads to step  654  to check all the system variables. Step  655  is to check whether the ID of the station is the smallest number in the network. If so, step  657  is taken to set the station as the master; otherwise, step  656  is to set the station as a slave station. The slave station waits for the notification from the master station, enters the media mode (step  670 ), and then returns to step  651 . After a station is set as a master station, the station takes step  658  to calculate the number of the stations in the network, and step  659  to determine whether all the check code of the stations are the same. If not, take step  660  to send an occur message to all the station; otherwise, take step  661  to send notification to all the stations to enter the media mode. Step  662  is to check whether both port A and port B are disconnected. If so, take step  665  to show the disconnection state; otherwise, take step  663  to check whether port A is disconnected. If so, take step  666  to set the station as a stop station; otherwise, take step  664  to check whether port B is disconnected. If so, take step  667  to set this station as a start station; otherwise set this station as a bypass station. Step  669  follows steps  665 ,  666 ,  667 ,  668  to set the network state register so that the network can switch to operate normally, and returns to step  651  for further monitoring. Step  670  is to wait for the notification from the master station and enters the media mode.  
         [0040]      FIG. 15  shows that when a link is disconnected in the network system, the detection and the switch to activate the backup mechanism can be performed in real-time to achieve high efficiency.  
         [0041]     It is worth noticing that the transmission media can be either UTP or optic fiber. If UTP is used, the transmission range can reach 100-150 meters. On the other hand, if a multimode optic fiber is used with the ST connector, the transmission range can be as high as 2000 meters.  
         [0042]     Because the surveillance network system only uses the physical layer characteristics of the Ethernet, the frames can be defined to achieve the maximum transmission efficiency of the Ethernet. For example, if the audio data is 32-bit and the sampling rate is 48 KHz, forty-nine 32-bit channels with control and system monitor data can be accommodated in the network. In addition, the system can be controlled by PC software and backup monitor mechanism. In other words, the media and control data is placed inside the carry frame and the monitor signal is placed inside the monitor frame so that the two different types of frames can be transmitted within the same network.  
         [0043]     Although the present invention has been described with reference to the preferred embodiments, it will be understood that the invention is not limited to the details described thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.