GB2422061A

GB2422061A - CCTV optical packet data transmission system

Info

Publication number: GB2422061A
Application number: GB0500110A
Authority: GB
Inventors: Alan John Hayes
Original assignee: AMG SYSTEMS Ltd
Current assignee: AMG SYSTEMS Ltd
Priority date: 2005-01-06
Filing date: 2005-01-06
Publication date: 2006-07-12
Also published as: GB0500110D0

Abstract

A closed circuit television (CCTV) system (100) comprising at least one video signal collection node (102) linked to a control node (104) by an optical transmission medium (106), said control node (104) comprising means for receiving an optical signal comprising a real-time video signal from a camera connected to a station (108) associated with the at least one collection node (102) and means for transmitting an optical signal in the form of a packet data signal to the at least one collection node (102), said packet data signal comprising one or more signals associated with the camera station (108).

Description

A System and Method for the Collection of Real-Time Video Signals and the

Distribution of Collected Video Signals and/or Associated Signals.

Field of the Invention.

The present invention concerns a system and method for the collection of real-time video signals and the distribution of the collected video signals and/or associated signals.

Background to the Invention.

The use of optical fibre as the transmission media in closed circuit television (CCIV) security and transport surveillance systems is a relatively recent development fuelled in the 1 990's by the need for the installation of extensive CCTV systems to combat crime, vandalism and terrorism.

Conventionally cameras are linked to monitors over copper cable links using the lowest cost components available. As system size has increased, the distance between cameras and monitors has also increased resulting in an unacceptable degradation of received video signal quality, i.e. received picture quality, for link distances over one hundred to one hundred and fifty metres. This has meant that the use of optical fibre transmission has had to be considered even in this most cost conscious of applications.

CCTV surveillance systems for security and transportation systems employing optical fibre as the transmission media have to date generally transmitted video signals back to a monitoring control room over proprietary optical transmission equipment. The video signal is transmitted as real-time video in a form where it is uncompressed and the optical transmission system does not add any noticeable delay to the video signal being received at the monitoring control room.

The availability of high bandwidth packet data protocol networks such as Ethernet based local area networks (LANs), wide area networks (WANs) and the Internet, for example, has led to a move to transmit CCTV video signals from remote monitoring stations to the monitoring control room over such systems An advantage of such a scheme is the ability to transmit the video signals over existing standards based external packet data networks and the integration of the CCTV network with such external packet data networks.

One disadvantage, however, of this new arrangement is that the high bandwidth real-time video signal has to be compressed in order to be packetised for transmission over the packet data networks. One consequence of compression is that a noticeable delay is introduced into video signals being received at the monitoring control room. This delay is particularly noticeable where functions such as pan, tilt and zoom (PTZ) of the cameras at the remote monitoring stations are controlled from the monitoring control room. This is particularly undesirable where active real-time control of the remotely located cameras is required for security or other purposes.

A further disadvantage is that the use of external packet data networks to convey compressed video signals increases the possibility of unauthorised interception of and interference with the video and associated signals.

Object of the Invention.

It is an object of the invention to mitigate and/or obviate problems associated with existing CCTV systems employing optical fibre as the transmission media.

It is another object of the invention to provide a system for collecting real- time, uncompressed video signals over an optical transmission medium and for distributing the collected video signals and associated signals over a packet data network employing said same optical transmission medium.

It is a further object of the invention to combine the transmission of real- time video signals and packet data signals associated with said real-time video signals onto a single, dedicated optical transmission medium to thereby maximise use of such transmission medium in the most advantageous manner.

It is yet a further object of the invention to provide a secure system for collecting real-time, uncompressed video signals over a dedicated optical transmission medium and for distributing the collected video signals and associated signals over a packet data network hosted by said medium.

Summary of the Invention.

In accordance with a first main aspect, the present invention provides a closed circuit television (CCTV) system comprising at least one video signal collection node linked to a control node by an optical transmission medium, said control node comprising means for receiving an optical signal comprising a real- time video signal from a camera connected to a station associated with the at least one collection node and means for transmitting an optical signal in the form of a packet data signal to the at least one collection node, said packet data signal comprising one or more signals associated with the camera station.

Preferably, the optical transmission medium comprises a single, dedicated optical fibre linking the at least one collection node to the control node.

The one or more signals may comprise the packet data signal comprises any one or a combination of a camera function control signal, a telephony signal and/or a compressed video signal.

Preferably, the at least one collection node has means for transmitting a first optical signal comprising the real-time video signal from the camera connected to the station associated with the at least one collection node and a second optical signal in the form of a packet data signal comprising one or more signals associated with the camera station and means for receiving as a third optical signal the packet data signal transmitted by the control node.

The one or more signals comprising the packet data signal transmitted by the at least one collection node may comprise a telephony signal.

Preferably, the packet data signal(s) comprises a packet data protocol signal and may comprise an Internet Protocol (IP) signal.

Preferably, the control node includes a packet data protocol device for encoding and/or encapsulating the one or more signals associated with the camera station to be transmitted to the at least one collection node, said packet data protocol device encoding and/or encapsulating said one or more signals with respective destination addresses. The packet data protocol device may comprise an Ethernet router.

Preferably, the control node includes a de-multiplexer for receiving the optical signal comprising the real-time video signal from the camera connected to the station associated with the at least one collection node and another optical signal comprising the packet data signal transmitted by the at least one collection node, said de-multiplexer being arranged to wavelength division de- multiplex said optical signals to separate said signals according to their respective different optical wavelengths. The de-multiplexer may be arranged to receive a plurality of optical signals from a plurality of collection nodes, said plurality of optical signals comprising a plurality of respective real-time video signals from cameras associated with said collection nodes and another optical signal comprising a packet data signal, said de-multiplexer separating said optical signals according to their respective different optical wavelengths, said packet data signal comprising signals generated by camera stations associated with said plurality of collection nodes.

Preferably, each collection node includes a packet data protocol device for recovering the one or more signals associated with its camera station transmitted by the control node. The packet data protocol device of each collection node may comprise an Ethernet router.

Preferably, each collection node includes a multiplexer for combining the optical signal comprising the real-time video signal from the camera connected to the station associated with the collection node and another optical signal comprising the packet data signal transmitted by the collection node, said multiplexer being arranged to wavelength division multiplex said optical signals for transmission over the optical transmission medium in respective different optical wavelengths.

The control node may comprise a CCTV monitoring control room and the at least one collection node may comprise a remote monitoring station.

In accordance with a second main aspect, the present invention provides a method of transmitting signals in a closed circuit television (CCTV) system comprising at least one video signal collection node linked to a control node by an optical transmission medium, said method comprising the steps of receiving at the control node an optical signal comprising a real-time video signal from a camera connected to a station associated with the at least one collection node and transmitting from said control node an optical signal in the form of a packet data signal to the at least one collection node, said packet data signal comprising one or more signals associated with the camera station.

Further aspects and features of the present invention will be apparent from the appended claims and following description.

Brief description of the drawings.

A description of the present invention will follow with reference to the accompanying drawings, of which: Figure 1 is a prior art CCTV optical transmission system; Figure 2 is another prior art CCIV optical transmission system; Figure 3 is yet another prior art CCIV optical transmission system; Figure 4 is schematic diagram of a first embodiment of a CCTV optical transmission system in accordance with the present invention; Figure 5 is a more detailed schematic diagram of the CCIV optical transmission of figure 4; and Figure 6 is a schematic diagram of a second embodiment of a CCIV optical transmission system in accordance with the present invention.

Detailed description of a preferred embodiment.

The foregoing and further features of the present invention will be more readily understood from the following description of preferred embodiments, by way of example thereof.

Referring firstly to figure 1, illustrated is a prior art CCIV optical transmission system The system 10 comprises a camera 12 at a remote monitoring station 14 connected by an optical fibre transmission medium 16 to a monitoring control room 18. The sole purpose of the optical fibre transmission medium 16 is to transfer in optical form electrical signals from the camera 12 to the monitoring control room 18 without degradation in the transmitted signal quality. As such, the optical transmission medium 16 is transparent to the system user.

In this prior art arrangement, the optical transmission medium 16 comprises a single optical fibre 20.

The camera 12 is connected to an electrical to optical converter (transmitter) 22 which takes the analogue signal voltage outputted by the camera 12 and converts it into a light signal that varies in proportion to the camera output signal. The light signal is generated by a light emitting diode (LED) or laser transmitter 24, for example, which is designed to couple a maximum of the generated light into the optical fibre 20. The optical fibre 20 serves to guide the light from the LED or transmitting laser 24 with a minimum of loss to the monitoring control room 18.

At the monitoring control room 18, light transmitted along the optical fibre 20 is received by an optical to electrical converter (receiver) 26. This unit takes the optical signal and converts it to an electrical signal in a semiconductor detector 28 such as a photodiode or avalanche photodiode, for example. Signal processing circuitry 30 regenerates the video output signal. The signal processing may include automatic gain control, for example. The outputted regenerated video signal is passed to a monitor 32 where the video images being transmitted from the remote monitoring station 14 may be viewed in real- time by an operator. The regenerated video signal may also be recorded on a suitable recording medium such as a video tape or digital video disc 34, for example, for subsequent replaying.

The prior art system as illustrated in figure 1 is particularly applicable to a CCTV installation where the camera 12 is fixed to view a specific scene, i.e. there is no requirement to remotely control movement of the camera 12. In this arrangement, since the fibre optic link 20 is only required to transmit a video signal from the camera 12 to the monitor 32, only a single optical fibre 20 is required for each camera to monitor path.

Figure 2 illustrates another prior art CCTV optical transmission system in which an operator in the monitoring control room is able to remotely control movement of the camera. In the following description of this prior art arrangement, like numerals to those employed in the description of figure 1 will be used to denote like parts.

In this prior art arrangement, a return control signal for effecting PTZ movements of the camera 12 must be transmitted from the monitoring control room 18 to the remote monitoring station 14 on a second optical fibre 38. The control signal is converted from an electrical to optical signal by a transmitter 42 in the monitoring control room and then injected into the second optical fibre 38.

At the remote monitoring station 14, the control signal is converted to an electrical signal by a receiver 44 and then passed to a controller 46 associated with the camera 12 which effects movement of motors 48 or the like to change any of the pan, tilt and/or zoom functions of the camera 12.

In some systems, a return signal from the camera 12 is required to confirm camera movement. In these cases, the return signal is carried on a channel encoded by the transmitter 22 into the real-time video signal transmitted from the camera 12 to the monitor 32.

It is also known to provide two-way audio links between the monitoring control room 18 and the remote monitoring stations 14. This is also particularly true of video assisted help point and door entry installations. Again optical transmitter and receiver units are provided to enable this facility.

It is possible to provide all of these video, control and audio functions over a single optical fibre using multiplexing techniques such as wave division multiplexing (WDM) where each signal is allocated a different wavelength (colour) of light source to transmit light. The multiplexed signals can then be transmitted bi-directionally on the single fibre. This prior art arrangement is better illustrated by figure 3. In the following description of the arrangement of figure 3, like numerals to those employed in the descriptions of figures 1 and 2 will be used to denote like parts.

In the prior art arrangement of figure 3, the remote monitoring station 14 includes, in addition to the camera 12, a telephony unit 50 for two- way audio communication with the monitoring control room 18 and a monitor 52 for displaying a video image from at least one other remote monitoring station The video signal from said other remote station is relayed to the remote station 14 via the monitoring control room 18.

The analogue video signal from the camera 12 is converted as before to an optical signal by a transmitter 22. The transmitter 22 is controlled to effect the conversion to a first selected wavelength (light colour) which is input to a wavelength division multiplexer (WDM) 56. An outgoing signal from the telephony unit 50 is also converted to optical form by a respective transmitter 54 and also inputted to the WDM 56. The transmitter 54 is controlled to effect the conversion to a second, different light colour. The WDM 56 multiplexes the video and audio optical signals and injects these into the optical fibre 20 for transmission to the monitoring control room 18. Other remote stations perform the same function but utilising different pairs of light colours.

At the monitoring control room 18, received multiplexed video and audio light signals are de-multiplexed by a wave division de-multiplexer 58 to recover the individual light colours which are each converted by respective receivers 26 to electrical form. The recovered electrical signals are then passed to a system controller 62 for signal processing as appropriate. Recovered video signals are passed by the system controller 62 to respective monitors 32 and the audio signals to respective telephony units 64.

The system controller 62 has one or more work stations 66 connected thereto to enable operators to send control signals to the cameras 12 of the remote monitoring stations 14 to effect movement of such cameras 12. The operators may also relay a recovered video signal from one remote station to another for display on a monitor 52 thereof. Control, audio and relayed video signals transmitted from the system controller 62 to the remote stations 14 are each converted by respective transmitters 60 into selected, different light colours prior to being inputted to a WDM 68 at the monitoring control room 18.

The WDM 68 multiplexes the optical signals and injects them onto the optical fibre 20. At each remote station, a wave division de-multiplexer 70 of that station tuned to the selected, different wavelengths corresponding to its camera controller 46, telephony unit 50 and monitor 52, de-multiplexes said light colours to retrieve the signals whereupon they are converted to electrical form by respective receivers 72 prior to being conveyed to their respective units.

Thus, it can be seen that, in the prior art arrangement of figure 3, it is possible to link a plurality of remote stations 14 to a monitoring control room 18 via a single optical fibre 20 through the use of wavelength division multiplexing/de-multiplexing. However, whilst WDM maximises the use of the installed fibre, it does so at the expense of more expensive transmitters and receivers Also, the number of transmitters and receivers required at each remote monitoring station 14 and the monitoring control room 18 is directly proportional to the number of light colours required for the different signals being injected into the optical fibre 20 and thus the cost of implementing this arrangement is costly.

Figures 4 and 5 illustrate a first embodiment of a CCTV optical transmission system in accordance with the present invention. Referring firstly to figure 4, the system 100 comprises a plurality of video signal collection nodes 102 connected to a control node 104 by a single dedicated optical fibre 106.

The collection nodes 102 and the control node 104 are arranged in a ring on the fibre 106. It will be appreciated, however, that the collection nodes 102 may be linked to the control node 104 in a spur arrangement or a branch arrangement, there being only a single dedicated optical fibre 106 between any collection node 102 and the control node 104.

Each collection node 102 comprises means for transmitting a first optical signal comprising a real-time video signal from an associated camera connected to a remote camera station (Not shown) and a second optical signal in the form of a packet data signal comprising one or more signals associated with the camera station onto the optical fibre 106 and means for receiving a third optical signal comprising a packet data signal transmitted on the optical fibre 106 from the collection node 104. Conversely, the control node 104 has means for receiving at least one first optical signal comprising a real-time video signal and at least one second optical signal comprising a packet data signal from the optical fibre 106 and means for transmitting a third optical signal in the form of a packet data signal comprising signals relating to one or more camera stations.

Each collection node 102 may comprise a remote monitoring station 108 or may be connected to such a station by a hardwired or wireless link 110 The control node 104 may comprise a monitoring control room 112 or may be connected to such a room by a hardwired or wireless link 114.

Referring now to figure 5, the system 100 comprises at least one remote monitoring station 108 linked to the monitoring control room 112 by the dedicated single optical fibre 106. Whilst only one remote monitoring station 108 is illustrated, it will be understood that the system 100 may include a p'urality of such stations 108 arranged in a ring as illustrated by figure 4.

The remote monitoring station 108 comprises a collection node part 102 and a local area network (LAN) part 114 each delimited by respective dotted lines in the figure for the sake of convenience. Whilst the link 110 between the collection node part 102 and the LAN 114 is shown as being hard wired, it will be appreciated that the link could be a wireless link. It will also be appreciated that the remote monitoring station may be arranged in accordance with any suitable packet data network including, for example, an asynchronous transfer mode (ATM) network or a token ring network or any IEEE8O2.3 compliant network.

The LAN 114 includes a camera 116, a controller 118 for effecting PTZ functions of the camera in response to received control signals and optionally a telephony unit or system 120 and a monitor 122.

The collection node 102 comprises a multiplexer 124 for multiplexing a real-time video signal from the camera 116 with a packet data signal derived from any of the controller 118, telephony unit 120 and/or monitor 122. The multiplexer 124 has associated therewith means 126 for converting electrical signals to optical signals for injection into the optical fibre 106. The multiplexer 124 may operate in the electrical domain with its output being converted to optical form for transmission to the monitoring control room 112 over the optical fibre 106. Preferably, the multiplexer 124 comprises a wave division multiplexer (WDM) 124 and the means 126 comprise respective transmitters 128 for the real-time video signal and the packet data signal to convert them into optical form of respective selected different wavelengths (light colours) prior to being multiplexed in the WDM 124. Whilst the transmitters 128 are shown as being separate devices to the WDM 124, it will be appreciated that the transmitters 128 may integrated into the WDM 124. The collection node 102 also includes a packet data protocol device 130 for encapsulating and/or encoding signals from any of the controller 118, telephony unit 120 and/or monitor 122 into the packet data signal. The packet data protocol device 130 is arranged to also receive a packet data signal from the optical fibre 106. This signal is provided by the monitoring control room 112 and may comprise a packet data encapsulated control signal for effecting movement of the camera 116, an audio signal and/or a compressed video signal. Associated with the packet data protocol device is a receiver 132 for converting the received packet data signal from optical to electrical form. Whilst the receiver 132 is shown as being a separate device to the packet data protocol device 130, it will be appreciated that said receiver 132 could be integrated with said device 130 It will also be appreciated that the WDM 124, transmitters 128, packet data protocol device 130 and receiver 132 may be integrated as a single device which couples the LAN 114 to the optical fibre 106.

The packet data protocol device 130 comprises any device capable of receiving at least one input signal such as a control signal, for example, and encoding and/or encapsulating said signal into a packet data stream in accordance with a packet data protocol. The device may, for example, comprise an asynchronous transfer mode (ATM) multiplexer or switch for encapsulating the received signal or signals into an ATM cell stream.

Preferably, however, the device 130 comprises an Ethernet router operating the Internet Protocol (IP) as the packet data protocol. Consequently, the audio signal input to such device 130 could be encapsulated as a Voice over IP (V0IP) data stream. The telephony unit 120 may comprise an IP telephony unit.

The monitoring control room 112 comprises a control node part 140 and a LAN part 142. The link 144 between the control node 140 and the LAN 142 may be hard wired as illustrated or may comprise a wireless link.

The control node 140 comprises a de-multiplexer 146 for de-multiplexing the optical signals from the one or more remote monitoring stations 108 to recover the respective real-time video signals and packet data signals from said stations 108. Recovered optical signals are then converted to electrical form by respective receivers 147. It will be seen that the demultiplexer 146 recovers a separate optical signal for each of the one or more (three in this example) stations 108 but only a single optical signal comprising the packet data signals from said one or more stations. It will be appreciated that, in order to recover the separate real-time video signals from the stations 108, each station 108 transmit its respective real-time video signal in a selected, different optical wavelength. However, the packet data signals from the stations 108 can be transmitted using the same wavelength at each station. Whilst the de- multiplexer 146 is illustrated as being a wave division de-multiplexer, it will be appreciated that the de-multiplexer could be an electrical domain de-multiplexer with associated optical to electrical signal conversion means.

The control node 140 also includes a packet data protocol device 148 for receiving from the de-multiplexer 146 the recovered packet data signal from the one or more stations 108. Preferably, the packet data protocol device 148 comprises an Ethernet router which delivers signals from the one or stations 108 encoded in the packet data signal to monitoring control room devices in accordance with destination addresses encoded within such signals in a manner that will be familiar to a skilled artisan. The Ethernet router 148 is also arranged to receive signals from any of a plurality of telephony units 150, any of a plurality of computer work stations 152, any of a plurality of monitors 154 and/or a system controller 156. These signals are encoded and/or encapsulated in an lP packet stream that is converted to an optical form by a transmitter 158 prior to being injected into the optical fibre 106 for transmission to the one or more stations 108.

In use, the camera 116 of the remote monitoring station 108 outputs a real-time video signal. This signal is converted by a transmitter 128 to an optical form at a first selected wavelength which comprises one input to the WDM 124. Audio signals from the IP telephony unit 120, for example, together with any signals from the camera controller 118 and/or monitor 122 are encoded and multiplexed into an IP packet stream by the Ethernet router 130 prior to being converted to optical form at a second selected wavelength as a second input to the WDM 124. The two different wavelength inputs to the WDM 124 are then multiplexed and injected into the optical fibre 106 for transmission to the monitoring control room 112.

Each of the remote monitoring stations injects a multiplexed optical signal into the optical fibre using a different, respective wavelength for its real- time video signal but may use the same wavelength as other stations 108 for its packet data signal The Ethernet routers of the respective remote stations 108 may use collision detection techniques, for example, to prevent the optically encoded packet data signals from the various stations 108 interfering with each other It will also be appreciated that any other suitable means of processing the packet data signals from the remote stations 108 may be employed.

At the monitoring control room 112, the received multiplexed optical signals from the one or more stations 108 are de-multiplexed by the WDM de- multiplexer 146 to recover the respective light colours for the real-time video signals and the single optical signal comprising the packet data signal(s). The recovered light colours are separately converted to electrical form by the receivers 147. The recovered real-time video signals are passed to the system controller 156 for transfer to respective monitors 154 for display. It will be appreciated that the monitoring control room may include only one monitor 154 for display ofthe recovered real-time video signals and that a human operator may select which of the recovered signals to view at any one time through a selection inputted via one of the computer work stations 152. One or more video recording units 170 may be provided for recording the real-time video signals for subsequent replay.

The recovered packet data signal is passed to the Ethernet router 148 where signals addressed to respective ones of the telephony units 150, computer work stations 152, system controller 156 and/or monitors 154 are distributed by said router 148 to said devices according to destination addresses encoded within said signals.

Signals from any of the telephony units 150, computer work stations 152, system controller 156 and/or monitors 154 such as camera PTZ control signals, IP telephony signals and relayed compressed video signals can be sent to any of the stations 108 via the Ethernet router 148 which encodes said signals into an IP data stream. The IP data stream is converted to optical form at a selected wavelength and injected into the optical fibre, It will be noted that only a single light colour is required for transmitting the control signals etc to one or more of the stations 108. It will also be appreciated that any video signals relayed to the one or more stations 108 by the monitoring control room 112 are compressed by the Ethernet router 148 prior to transmission. Consequently, relayed video signals do not require the bandwidth (number of light colours) necessary for transmitting real-time video signals. The relayed video signals will suffer some delay introduced by the compression of the signal and encapsulation into IP but this is acceptable where said signals are being relayed to other stations 108 for information purposes without the requirement for real-time interaction with said signals at said stations.

Signals such as camera PTZ control signals are low bandwidth signals and need not be compressed prior to being encapsulated into an IP packet stream. Consequently, such signals do not suffer noticeable delay in their transmission and are suitable for effecting real-time control of the cameras.

Thus, the system of the present invention enables real-time video signals to be collected at a monitoring control room, compressed versions of said video signals to be relayed to remote monitoring stations, control signals to be transmitted to the stations for real-time control of cameras at said remote stations and audio (telephony) signals to be transmitted bi-directionally between the control room and the stations on a single dedicated optical fibre through a combination of multiplexing/demultiplexing of real-time video signals and 1 5 packet data signals.

The embodiment of figures 4 and 5 reduces the number of WDM multiplexers and de-multiplexers required and significantly reduces the number of optical transmitters and receivers required compared with the prior art arrangements thus significantly reducing the cost of the system.

Also, by employing a single optical fibre dedicated to the system rather than sending compressed video signals and control signals, for example, over existing external packet data networks, the arrangement of the first embodiment in accordance with the invention provides a high level of security since the dedicated optical fibre does not radiate electromagnetic signals in the manner of coaxial cables, for example, and the optical signal content of the fibre is difficult to access, i.e. tap, for unauthorised parties.

Figure 6 illustrates a second embodiment of a CCIV optical transmission system in accordance with the present invention. The system 200 is generally the same as that of the first embodiment with the exception that the plurality of collection nodes 202 are arranged in a spur arrangement with respect to the control node 204 on the single, dedicated optical fibre 206. The structure of the collection and control nodes is as illustrated with respect to the first embodiment in figure 5.

Claims

Claims.

1 A closed circuit television (CCIV) system comprising at least one video signal collection node linked to a control node by an optical transmission medium, said control node comprising means for receiving an optical signal comprising a real-time video signal from a camera connected to a station associated with the at least one collection node and means for transmitting an optical signal in the form of a packet data signal to the at least one collection node, said packet data signal comprising one or more signals associated with the camera station.

2. A CCIV system as claimed in claim 1, wherein the optical transmission medium comprises a single, dedicated optical fibre linking the at least one collection node to the control node.

3. A CCIV system as claimed in claim 1 or 2, wherein the one or more signals comprising the packet data signal comprises any one or a combination of a camera function control signal, a telephony signal and/or a compressed video signal

4. A CCIV system as claimed in any of claims 1 to 3, wherein the at least one collection node has means for transmitting a first optical signal comprising the real-time video signal from the camera connected to the station associated with the at least one collection node and a second optical signal in the form of a packet data signal comprising one or more signals associated with the camera station and means for receiving as a third optical signal the packet data signal transmitted by the control node.

5. A CCIV system as claimed in claim 4, wherein the one or more signals comprising the packet data signal transmitted by the at least one collection node comprises a telephony signal.

6 A CCTV system as claimed in any of claims 1 to 5, wherein the packet data signal(s) comprises a packet data protocol signal.

7 A CCTV system as claimed in claim 6, wherein the packet data protocol signal comprises an Internet Protocol (IP) signal.

8. A CCTV system as claimed in claim 6 or 7, wherein the control node includes a packet data protocol device for encoding and/or encapsulating the one or more signals associated with the camera station to be transmitted to the at least one collection node, said packet data protocol device encoding and/or encapsulating said one or more signals with respective destination addresses.

9. A CCTV system as claimed in claim 8, wherein the packet data protocol device comprises an Ethernet router.

10. A CCIV device as claimed in any of claims 6 to 9, wherein the control node includes a de-multiplexer for receiving the optical signal comprising the real-time video signal from the camera connected to the station associated with the at least one collection node and another optical signal comprising the packet data signal transmitted by the at least one collection node, said de- multiplexer being arranged to wavelength division de-multiplex said optical signals to separate said signals according to their respective different optical wavelengths.

11. A CCIV system as claimed in claim 10, wherein the de-multiplexer is arranged to receive a plurality of optical signals from a plurality of collection nodes, said plurality of optical signals comprising a plurality of respective real- time video signals from cameras associated with said collection nodes and another optical signal comprising a packet data signal, said de- multiplexer separating said optical signals according to their respective different optical wavelengths, said packet data signal comprising signals generated by camera stations associated with said plurality of collection nodes.

12. A CCTV system as claimed in any of claims 6 to 11, wherein each collection node includes a packet data protocol device for recovering the one or more signals associated with its camera station transmitted by the control node

13. A CCTV system as claimed in claim 12, wherein the packet data protocol device comprises an Ethernet router.

14. A CCTV device as claimed in claim 12 or 13, wherein each collection node includes a multiplexer for combining the optical signal comprising the real- time video signal from the camera connected to the station associated with the collection node and another optical signal comprising the packet data signal transmitted by the collection node, said multiplexer being arranged to wavelength division multiplex said optical signals for transmission over the optical transmission medium in respective different optical wavelengths.

15. A CCIV system as claimed in any of claims 1 to 14, wherein the control node comprises a CCIV monitoring control room and the at least one collection node comprises a remote monitoring station.

16. A method of transmitting signals in a closed circuit television (CCTV) system comprising at least one video signal collection node linked to a control node by an optical transmission medium, said method comprising the steps of receiving at the control node an optical signal comprising a real-time video signal from a camera connected to a station associated with the at least one collection node and transmitting from said control node an optical signal in the form of a packet data signal to the at least one collection node, said packet data signal comprising one or more signals associated with the camera station.

17. A method as claimed in claim 16, wherein the optical transmission medium comprises a single, dedicated optical fibre linking the at least one collection node to the control node.

18 A method as claimed in claim 16 or 17, wherein the one or more signals comprising the packet data signal comprises any one or a combination of a camera function control signal, a telephony signal and/or a compressed video signal.

19. A method as claimed in any of claims 16 to 18, wherein the at least one collection node is arranged to transmit a first optical signal comprising the real- time video signal from the camera connected to the station associated with the at least one collection node and a second optical signal in the form of a packet data signal comprising one or more signals associated with the camera station and to receive as a third optical signal the packet data signal transmitted by the control node.

20. A method claimed in claim 19, wherein the one or more signals comprising the packet data signal transmitted by the at least one collection node comprises a telephony signal.

21. A method as claimed in any of claims 16 to 20, wherein the packet data signal(s) comprises a packet data protocol signal.

22. A method as claimed in claim 21, wherein the packet data protocol signal comprises an Internet Protocol (IP) signal.

23. A method as claimed in claim 21 or 22, wherein the control node is arranged to encode and/or encapsulate the one or more signals associated with the camera station into a packet data protocol signal to be transmitted to the at least one collection node, said control node being arranged to encode and/or encapsulate said one or more signals with respective destination addresses.

24. A method as claimed in claim 23, wherein the control node uses an Ethernet router for the encoding and/or encapsulation of said one or more signals.

25. A method as claimed in any of claims 21 to 24, wherein the control node is arranged to de-multipiex the optical signal comprising the realtime video signal from the camera connected to the station associated with the at least one collection node and another optical signal comprising the packet data signal transmitted by the at least one collection node, said control node being arranged to wavelength division de-multiplex said optical signals to separate said signals according to their respective different optical wavelengths.

26 A method as claimed in claim 25, wherein the control node is arranged to receive a plurality of optical signals from a plurality of collection nodes, said plurality of optical signals comprising a plurality of respective real-time video signals from cameras associated with said collection nodes and another optical signal comprising a packet data signal, said packet data signal comprising signals generated by camera stations associated with said plurality of collection nodes, and to demultiplex said optical signal to separate said optical signals according to their respective different optical wavelengths.

27. A method as claimed in any of claims 21 to 16, wherein each collection node is arranged to recovering the one or more packet data protocol signals associated with its camera station transmitted by the control node.

28. A method as claimed in claim 27, wherein each collection node is arranged to use an Ethernet router to recover its respective packet data protocol signals.

29. A method as claimed in claim 27 or 28, wherein each collection node is arranged to combine the optical signal comprising the real-time video signal from the camera connected to the station associated with the collection node and another optical signal comprising the packet data signal from that collection node by wavelength division multiplexing said signals as respective different optical wavelengths.

30. A method as claimed in any of claims 16 to 29, wherein the control node is provided as a CCTV monitoring control room and the at least one collection node is provided as a remote monitoring station.

31 A control node for a CCTV system as claimed in any of claims 1 to 15.

I

32 A control node as claimed in claim 31, wherein it comprises a monitoring control room.

33 A video signal collection node for a CCTV system as claimed in any of claims ito 15.

34. A collection node as claimed in claim 31, wherein it comprises a remote monitoring station.

35. A method substantially as hereinbefore described with respect to figures 4 to 6 of the drawings.

36. A CCIV system substantially as hereinbefore described with respect to figures 4 to 6 of the drawings.

37. A control node substantially as hereinbefore described with respect to figures 4 to 6 of the drawings.

38. A video signal collection node substantially as hereinbefore described with respect to figures 4 to 6 of the drawings.