Abstract:
The systems and methods provide an out-of-band time and control signal distribution network that may be employed in conjunction with a large scale area network. The network is capable of installation on the seafloor and comprises a plurality of network nodes being interconnected by fiber optic cable, and each having optical transceivers for coupling to an optical fiber cable having data channels carrying data packets among the plurality of network nodes and having one or more control and time channels for carrying control and time signals, and an out-of-band communications module for coupling to the optical fiber cable to utilize the control and time data signals transmitted separately from the data packets, to provide the distribution of in-band data packets among network nodes and the distribution of out-of-band timing and control signals to said plural network nodes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority to and the benefit of U.S. Provisional Patent Application Ser. No. 60/771,048, filed on Feb. 6, 2006 and entitled “Communication/Power Network Having Out-Of-Band Time And Control Signaling,” the entire contents of which are incorporated herein by reference. 
     
    
     GOVERNMENT CONTRACT  
       [0002]     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. OCE 079720 awarded by the National Science Foundation. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     Today, computer and power network systems are being placed in geographically and environmentally remote locations. For example, there is a growing interest in ocean observatories such as the NEPTUNE regional cabled observatory. These observatories are really large computer and power networks comprising a fiber optic cable that interlinks a number of observatory nodes, each of which is capable of serving scientific equipment such as spectrometers or seismometers. These seafloor observatories may be located many hundreds of kilometers off the coast of the nearest shore station and may be positioned at depths of over 5000 meters. Typically, the observatory has one or more network connections to shore stations through which data collected from the seafloor observatory can be passed onto the Internet and which can serve seafloor instruments with power and control commands.  
         [0004]     Servicing and maintaining the undersea network is a complicated and potentially costly task because complex electronic systems must be placed on the seafloor to aggregate, route, and transfer data along optical fibers, and to provide variable amounts of power to both the infrastructure and scientific instruments. These data and power systems require a high reliability method to provide control and monitoring functions that is independent of the main data network. In addition, there is a scientific requirement to provide synoptic high accuracy time to instruments which cannot be accommodated using standard IP protocols like Network Time Protocol on the main data network. These requirements apply in any data/power network which is remote and difficult to access physically.  
       SUMMARY OF THE INVENTION  
       [0005]     The systems and methods described herein provide for more robust data/power networks and in particular more robust data/power networks of the type that can be deployed at remote and difficult to access locations. In particular, the systems and methods described herein provide an out-of-band time and control signal distribution network that may be employed in conjunction with and separately from a large scale data/power network.  
         [0006]     In one aspect, the systems and methods described herein include a communication network capable of installation on the seafloor. The communication network comprises a plurality of network nodes being interconnected by fiber optic cable. One or more of the plurality of network nodes may include optical transceivers for coupling to an optical fiber cable having data channels carrying data packets among the plurality of network nodes and having one or more control and time channels for carrying control and time signals. The nodes also include an out-of-band communications module for coupling to the optical fiber cable to utilize the control and time data signals transmitted separately from the data packets, to provide the distribution of in-band data packets among network nodes and the distribution of out-of-band timing and control signals to said plural network nodes. In certain embodiments, the network nodes are arranged in an architecture selected from the group consisting of a mesh architecture, a bus architecture, a ring architecture, or a star architecture.  
         [0007]     In certain embodiments, the out-of-band communications module further comprises a control module for regulating the flow of control and time signals across the optical channel. The control module may include a time distribution module for distributing a NIST-traceable time signal corrected for transmission latency among the plural network nodes. In such embodiments, the communication network may also include a means for measuring the transmission latency among the plural network nodes. In certain embodiments, the control module further includes an interface controller for selectively allowing a plurality of data channels internal to the network node to access the optical channel carrying control and time signals among the network nodes. In such embodiments, the control module allows one node at a time to access the control and time signals among all of the network nodes. The module may further include a media access controller for blocking data from being received over a channel in response to detecting data being received on another channel. Additionally and optionally, the communication network may comprise a control circuit for regulating access to a given optical path carrying control and time signals among the network nodes and capable of suppressing multiple repeats of said signal.  
         [0008]     In certain embodiments, the communication network comprises a serial interface circuit for communicating optical data over the optical channel at a rate of between 50 BAUD (Bits Per Second) and 115,000 BAUD. In such embodiments, the communication network further comprises a base band keying circuit for on/off keying a laser diode to generate data signals for distribution over the optical channel. The laser diode may include a communications laser.  
         [0009]     The network may comprise a power regulator circuit for regulating the power applied to the laser diode. The power regulator circuit may utilize the internal Laser Diode monitor diode to monitor optical power generated by the laser diode using a non-carrier based communications protocol and a feedback loop to regulate the power generated thereby. In certain embodiments, the network comprises a wake-up circuit for causing the device to enter into an active state in response to an incoming signal. The network may also comprise a time distribution system for synchronizing clocks within the network nodes in response to a timing pulse transmitted over the optical channel. In certain embodiments, the communication network comprises a low power sleep mode allowing a control module to turn itself off by timed prearrangement or by lack of incoming signals. The network may have in situ battery power for at least one week.  
         [0010]     In another aspect, the systems and methods described herein include a communication network comprising a master node and a plurality of network nodes arranged into a selected network configuration. The master node may include a data packer generator, control and time distribution circuits for generating control and time signals and a NIST-traceable time source. In certain embodiments, the system includes a steering module to allow operation in mesh, bus, ring, or star architectures and an optical transceiver for transmitting and receiving data as optical signals over an optic channel. The plurality of networks may include an optical transceiver for coupling to an optical channel carrying data packets among the plurality of network nodes and having a control and time channel for carrying control and time signals.  
         [0011]     The plurality of network nodes may also include an out-of-band communications module for coupling to the optical fiber cable to detect the control and time signals transmitted separately from the data packets, to thereby provide the distribution of in-band data packets among network nodes and the distribution of out-of-band time and control signals to said plural network nodes.  
     
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0012]     The foregoing and other objects and advantages of the invention will be appreciated more fully from the following further description thereof, with reference to the accompanying drawings wherein;  
         [0013]      FIG. 1  depicts a functional block diagram of a network having an out-of-band time and control system according to the invention.  
         [0014]      FIG. 2  provides a more detailed depiction of the time distribution system illustrated in  FIG. 1 .  
         [0015]      FIG. 3  provides a block diagram of one node of the system depicted in  FIG. 1 .  
         [0016]      FIGS. 4A and 4B  depict in more detail the opto-electronics and steering board mechanism depicted in  FIG. 3 .  
         [0017]      FIG. 5  is a functional block diagram of one embodiment of a steering board.  
         [0018]      FIGS. 6A and 6B  depict pictorially a process of selecting steering module paths.  
         [0019]      FIGS. 7A and 7B  depict pictorially a system that prevents ring around from occurring in the data network.  
         [0020]      FIG. 8  depicts a system for correcting transmission latency among the nodes of a network.  
         [0021]      FIG. 9  depicts a power regulator circuit for the laser diode.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     The systems and methods described herein include improved systems and methods for operating, monitoring, and diagnosing data/power networks, including network equipment and network devices that are located in remote and difficult to access locations. In particular, the systems and methods described herein provide out-of-band control and time signal distribution systems that allow for access to principle in-band data communication modules and power modules in distributed network nodes, independent of the proper functioning of those principle modules. Additionally, the systems and methods described herein allow for accessing the modules in the network node via their primitive, typically low data rate, access methods and protocols and employ a minimal suite of simple equipment for the out-of-band system. Additionally and optionally, the systems provide for low power consumption permitting operation on auxiliary power such as a battery during malfunction of the power system.  
         [0023]      FIG. 1  depicts one embodiment of a system according to the invention wherein an out-of-band control and time distribution system is provided. In particular,  FIG. 1  depicts a network  10  that comprises a shore master node  12 , and a plurality of slave nodes  14 - 22 . As further shown in  FIG. 1 , the slave nodes may have scientific equipment and devices such as the depicted devices  24  and  28  that couple to node  18 . The depicted shore node  12  and the slave nodes  14 - 22  are interconnected through communication paths that in this embodiment are optical fiber full duplex data communication paths. In the embodiment shown, one fiber pair east and one fiber pair west carry the out-of-band data and time sync concurrently on each fiber. Each fiber may operate independently in half duplex mode, thus the system  10  may be quadruply redundant. An additional “north” fiber pair may be added in case of three-way branching nodes.  
         [0024]     The system  10  may be a master/slave communication system. In such an embodiment, the master node may be the shore node  12  that is placed on shore and that solicits data streams from the slave nodes  14 - 22  or from slave devices that are connected to the nodes  14 - 22 . In such an embodiment, the nodes cannot initiate communications but will respond to commands or requests for communication and data from the master node  12 . The master node may have a terminal to provide an operator with an input device into which they can type a node address prior to entering lines of data. The master node  12  can transmit the data to the adjacent nodes and they in turn will relay the data to the next adjacent nodes. This process continues until the data has reached all of the nodes. Each node has a unique address. Only the node with the respective address will respond. When it does, after solicitation by the master, the process above is reversed and the response is relayed back to the master node. A steering module on each node prevents it from transmitting when it is in the process of relaying data. If the data arrive at a node in the process (state) of relaying data from another node or another fiber, it ignores the received data for a period of time known as the “quiescence time”. When a node receives one or more frames of data containing the address of the node (node address), the frame is further broken down. A sub-address identifies the device within the node, such as a router, for which the data are destined. A cross-bar switch (shown in  FIG. 3 ) interprets the address and connects the received data stream from the SAIL module (shown in  FIG. 4A ) to the designated equipment. A shore station will also send out periodic, such as 15 minute, timing sync updates which are processed by the nodes in the network  10 .  
         [0025]     In particular,  FIG. 1  depicts pictorially the transmission of a data signal from a shore master node  12  to device  2  ( 28 ) attached to node  03  ( 18 ). As shown, the transmitted signal addressed to #ND03/DV2 is transmitted from the shore master node  12  to the node  14 , forwarded to node  16  and forwarded to node  18 , which compares the address in the packet to the address used by node  18 .  FIG. 1  further shows that node  14  sends the data packet to both node  16  and node  20 . Node  20  forwards the message on to node  22 , and node  22  terminates transmission of that signal when it receives the similar signal from node  18 .  
         [0026]     The network  10  depicted in  FIG. 1  is a type of network that may be deployed at a remote location, and for the purpose of illustration the network  10  will be described hereinafter as a network employed as part of a seafloor observatory network of the type used for scientific exploration. Such networks may be deployed in oceans or lakes at depths of 100 to 5000 or more meters below the surface. The distance between nodes may range from hundreds of meters to hundreds of kilometers. In the embodiment depicted in  FIG. 1 , the node  10  includes a shore node  12  that acts as the master node for the network  10 . In optional embodiments, the shore node  12  may be absent and the network  10  may work from an alternate master node or may have a master node that is disposed on the ocean floor but providing for coupling or data transmission to a shipboard terminal or network node. In any case, it will be apparent to those of skill in the art that  FIG. 1  merely depicts an illustrative embodiment of a network of the type that may use an out-of-band time and control signal distribution system, and that this depicted network is merely one example and that other examples of networks having other architectures, topologies and equipment may be realized without departing from the scope hereof.  
         [0027]     For an undersea network, each of the nodes, or at least a portion of the nodes, in the network  10  may be undersea nodes having watertight housings of the type capable of withstanding substantial hydrostatic pressure. In one embodiment, the watertight housings may be formed from suitable waterproof or water impermeable material. In particular, the water proof material may be formed from fine polyester/nylon blends, rubber or plastic, hydrophobic material or other non-porous materials and may include suitable sealants. The watertight housings may include at least one layer of NEOPRENE® or GORETEX®. In other embodiments, the watertight housings may formed by coating a layer of waterproof material on a non-waterproof material. The watertight housings may also have one or more layers of material that may be impermeable to other liquids and gases. The watertight housings may also have of one or more layers of material that may be resistant to high temperature and pressure (e.g., high-temperature and high pressure at ocean depths of greater than 300 m). In other embodiments, the watertight housings may comprise of one or more layers of material that may be resistant to corrosive and abrasive substances. In still other embodiments, the watertight housings may comprise of one or more layers of material that may be resistant to abuse from wildlife. In certain embodiments, a portion of the watertight housings may be formed from a material that allows the signal to be transmitted, to pass through. As an example, for optical communication, a portion of the watertight housing may be formed from a transparent material to allow light rays to pass through. The watertight housing substantially prevents environmental damage to the node and its various internal components including the sensitive electronic circuits therein. Similarly, watertight cabling may be used to interconnect the nodes. The watertight cabling may be of the type used with undersea telecommunication networks. The housings and cabling may be disposed on the seafloor. In the depicted embodiment, the cabling includes fiber optic elements as well as copper wire.  
         [0028]     In this out-of-band control and time distribution system  10  one fiber optic pair referred to as fiber pair east and one fiber optic pair referred to as fiber pair west carry the out-of-band data and the time sync signals concurrently on each fiber. Each fiber may operate independently in half duplex mode, thus providing a system that is quadruply redundant. In optional embodiments where a sub-sea node is to provide an additional branch, a north fiber pair may be added as needed. Node  14  is an example of a node have east, west and north fibers and has a branch that extends between node  14  and node  16  and a branch that extends between node  14  and node  20 . In other embodiments additional branches may be employed. The number of branches, and fiber pairs that connect to a node will depend upon the application and architecture employed.  
         [0029]     The optical fibers can carry the clock signal between the nodes. As shown in  FIG. 2 , the shore node  12  can have a synchronization board  30  that will couple to a GPS clock  32 . The GPS clock  32  can act as a master clock that generates an accurate signal which the clock synchronization board  30  can use to generate the clock sync update signal. The next clock signal as shown in  FIG. 2  is delivered across the OBC fiber to a clock sync update board  34  in the sub-sea node  14 . The clock sync update logic board  34  is capable of adjusting the clock sync signal to take into consideration the latency that arises from the transfer of the sync signal across the multiple meters that make up the OBC fiber run. For example, a typical optical distance delay, neglecting electronic delay, is about 2×10 5  meters round trip at 2×10 8  m/sec [2×10 5 ÷2×10 8 ] which equals about 1 millisecond per round trip. The clock sync logic board  34  can adjust the clock sync signal to take into consideration the distance delay and can pass the adjusted signal to the crystal clock  38 . The crystal clock  38  can be a normal conventional crystal clock of the type that is commonly used in a network node or a server station for generating a clock signal. The crystal clock  38  may be adjustable so that the latency adjusted sync pulse generated by the clock sync board  34  can adjust the crystal clock so that the one pulse per second generated by crystal clock  38  is synchronized and adjusted for latency to the clock signal being used by shore node  12 .  
         [0030]     As shown in  FIG. 2  the one pulse per second clock signal may, optionally, be passed to a network time protocol (NTP) server  40 . The NTP server  40  may deliver the clock signal appropriate for the instrument  42 . As also shown in  FIG. 2  the crystal clock  38  may have a connection to the instrument  42  as well. In this way the instrument  42  receives the one pulse per second signal for the purpose of correcting any on board clock skew or any clock inaccuracies that arise within the instrument  42 .  
         [0031]     In one embodiment, to meet the stringent jitter requirement, a low speed optical system is provided which employs direct on/off modulation of a communications laser. This is shown in  FIG. 9 . Use of commercially available optical transceivers which employ a continuous wave carrier may cause jitter. Further, commercial equipment commonly maintains a carrier wave during an idle mode which consumes auxiliary power and is therefore undesirable. In one embodiment, the system employs a laser transmitter that uses direct on/off modulation to generate the timing signal.  
         [0032]     Turning to  FIG. 3  one embodiment of the out-of-band control (OBC) module is shown as a functional block diagram in  FIG. 3 . In particular,  FIG. 3  shows an OBC module  41  that includes an OBC telemetry module  43  and OBC/time-and-control sub-assembly  44 . The OBC telemetry module  43  includes four opto-electronic converter boards  48   a  and  48   b  and  50   a  and  50   b . The OBC time-and-control sub-assembly  44  includes two OBC steering boards  52 , a time distribution board  58  that couples to a oscillator  54  and to an arbitration module  64 , and also includes a SAIL serial converter board  60  and a cross bar switch  68 , as well as a communication node controller  70 .  
         [0033]     Turning to the OBC, telemetry module  43  couples the node to the fiber cables that carry both the in-band and out-of-band signals. The in-band fiber pairs of which there are at least two, one west and one east, come inward on fiber pairs  72  and  74  and they couple to the optics and the switches device  76 . The optics and switches device  76  couples to Ethernet connections  78  that connect to communication node controller  70 . In this way in-band data and control signals can be sent through the optical fibers and can couple into the node through the optical switches  76  and the communication node controller  70 . Through the in-band data interface, high-speed data transmission can occur across the network system and during typical operations the majority of data collected by the instruments can be transferred among the nodes and to the shore node  12 . The telemetry module  43  also services the out-of-band control and time signals and interfaces the node to the fibers carrying that out-of-band time and control data. As shown in  FIG. 3 , the telemetry module  43  couples to the OBC fiber pairs  46 , both the east and the west that carry the OBC signals across the network. The OBC fiber pair west couples to two converter boards, converter board  48   a  and converter board  48   b . Each of the converter boards  48   a  and  48   b  couple to an OBC steering board  52  that interfaces the telemetry module  43  with the OBC time-and-control sub-assembly  44 . The OBC fiber pair east couples to the opto-electronic converter  50   a  and the opto-electronic converter  50   b . Again these opto-electronic converter boards interface to respective ones of the OBC steering boards  52  in the OBC time-and-control sub-assembly  44 .  
         [0034]     Consequently, each OBC steering board  52  couples to an opto-electronic converter that interfaces with one fiber in a west pair and one fiber in an east pair. The redundant OBC steering modules  52  as well as the other components provide redundant paths for the OBC time and control data to enter into the node or to be delivered from the node. This provides fault redundancy that increases the reliability of the node. For purposes of clarity the remaining description of the OBC time-and-control sub-assembly  44  will be done with reference to the OBC steering board  52  that couples to the Bus A  62  on the left side of the cross bar switch  68 . In particular, the OBC steering module  52  couples to a Bus A  62  that allows for bi-directional signal distribution between the time distribution card  58  and the SAIL serial converter board  60 .  
         [0035]     The OBC steering module  52  is depicted in more detail in  FIGS. 4A and 4B  as are the opto-electronic converters for the west and east going fibers. The opto-electronic converter boards  48   a  include an optical circulator or splitter/coupler  80  that couples to the optical fiber carrying a 1550 nm optical signal. The circulator  80  couples to the optical receiver  82  and to the optical transmitter  84  thereby providing bi-directional data communication signals through the circulator  80 . As further shown in  FIG. 4A , the receiver outputs a TTL level signal to Section A (east) of the steering module  52 . The steering module  52  regulates data flow in and out of the respective node, regulating data flow such that only one section transmits data at a time. Data enters from a line into that line&#39;s section, such as Section A, Section B, Section C and so on, and is then relayed out of the steering module  52  via the remaining sections. During this process, the receive is blocked on the remaining sections to prevent them from attempting to relay data. When the Section A is transmitting it sends out data through Ports B, C and D. Ports B, C, and D cannot receive and relay other transmissions during this time. A time-out circuit prevents monopolization by Section A. The opto-electronic converters  48   a  and  48   b  transform a half-duplex optical signal on a single fiber into a square wave at CMOS levels. The CMOS level signal is transmitted from the receivers to the appropriate section in the steering board  52  and similarly when the respective sections of the steering board  52  are to transmit data, the sections transmit CMOS level signals to the optical transmitters  84  in the opto-electronic converter boards  48   a  and  48   b.    
         [0036]      FIG. 5  depicts a functional block diagram of the steering boards and in particular illustrates that each Section A, B, C and D employs a similar control circuit. For the purpose of clarity the following description will discuss the circuit of Section A, but it will be apparent that the circuits associated with Sections B, C and D are constructed and operate similarly.  
         [0037]     Specifically,  FIG. 5  illustrates that data come in on line  100   a  to the transmit over run time out block  104   a . This may be a monostable vibrator circuit that, after a set period of time, blocks any further transmission of A. The signal from the transit over-run time out block  104   a  is transmitted to the transmit over-ride logic  110   a  which generates the signal A  114   a . Also shown in the Figure are the “has the floor” control signals for sections B, C and D, which feed into the flip-flop  108   a . Flip flop  108   a  also receives the “A trying to transmit” signal from circuit  104   a . The flip-flop  108   a  generates, according to the flip flop state, an A has the floor (A, H &amp; F) signal  118   a  that connects to the flip-flops of sections B, C and D. A transmitter  112   a  receives output signals from Sections B, C and D to transmit over the A channel.  
         [0038]     The operation of the steering board, such as the steering board depicted in  FIG. 5 , is depicted by two  FIGS. 6A and 6B  that show the operation of the steering boards in the network. Generally,  FIGS. 6A and 6B  show that data are received on one branch of the node and relayed through to the other branches. During this time, the receivers on the other branches of the node are blocked to prevent them from relaying information back through the transmitting branch. In particular,  FIG. 6A  shows a node having three branches depicted as  132   a ,  132   b  and  132   c . Each of the branches  132   a  through  132   c  is bi-directional and therefore can both receive and transmit data. In the depicted embodiment, the transmission and reception paths are shown as separate for each branch. However, in other embodiments, various modulation techniques may be employed to allow a single physical transmission medium to carry both the data being transmitted and received by the node  130 .  FIG. 6A  shows that data are being received along branch  132   a . This is shown by the darkened arrow coming into node  130 . As further shown in  FIG. 6A , at the time data are being received at branch  132   a , node  130  under the control of the steering board retransmits the incoming signal on channel A on channel  132   b  and channel  132   c . At the same time, the steering board blocks any incoming signals on the input side of channels  132   b  and  132   c  to prevent a data collision caused by the simultaneous or near simultaneous input of data into the node on two different or three different channels.  FIG. 6B  illustrates a similar operation of the steering board, but in this case data are incoming on channel  132   b  and it is the incoming sides of channels  132   a  and  132   c  that are blocked while the outgoing paths of channels  132   a  and  132   c  are employed to retransmit the signal incoming on channel  132   b.    
         [0039]      FIGS. 7A and 7B  depict two functional block diagrams that show data flow occurring between nodes within a network.  FIGS. 7A and 7B  depict through the data flow diagrams the operation of the network node to prevent “ring around”. Ring around may occur when a network is configured to broadcast a signal from node to node. If the propagation of the signal continues through the network even after the appropriate node has received and processed the signal, this event is called ring around. Ring around can be problematic as, in certain case, the signal propagates through the network for an indeterminate amount of time. Ring around can result from multiple signals as well as one signal, and the result can be an increase in the amount of data collisions that occur within the network. In the embodiment depicted in  FIG. 1 , the regional observatory being used with the network covers several thousand kilometers. As such, the repeating of an optical signal from node to node is required. As discussed above, the steering board as shown in  FIGS. 6A and 6B  acts as a cut through device which electrically regenerates a signal and sends it out to another transceiver or multiple transceivers to broadcast the signal to different nodes in the network. In the embodiment depicted in  FIG. 1 , the network has a mesh architecture. Consequently, the regenerated propagation of a signal through the mesh is subject to “ring around” or “singing”, a phenomenon wherein the signal which is propagated and repeated from node to node returns to the original sender and is erroneously retransmitted. The design of the steering boards includes a time out feature which stops all node receivers when they are transmitting and for a period of time after that. This allows the cascading signal to quiesce before it is accidentally retransmitted through the mesh network.  
         [0040]     Turning to  FIG. 7A , the node  140  is shown as comprising three functional block elements, a steering module  142 , an addressable module  144  and two optoelectronic boards  146   a  and  146   b . In  FIG. 7 , the node  140  needs to send data which it received via its C channel through addressable board  144 . This might be data that have been solicited from the shore via the master station, or information received via a piece of test equipment coupled to the node. In any case, node  140  checks that its lines are not busy, and then starts a transmission relaying the data from C to lines A and B through cards  146   a  and  146   b  respectively. The data begin to travel around the network in both directions (East and West).  
         [0041]      FIG. 7B  shows the state of the network sometime later. At this point the signal broadcast from node  140  has propagated through nodes  150  and  160  and  170  and  180 . Nodes  180  and  170  are now in a race to deliver the signal to node  190 .  FIG. 7B  shows, arbitrarily, that node  190  receives data first from its A channel which couples to node  170 . Upon receipt of data from node  170 , node  190  raises the “A has the floor” state (Ahtf), causing node  190  to ignore any data being received on its B or C channels, while simultaneously relaying the data it has received on its A channel through its B and C transmission lines. Further shown in  FIG. 7B  is that a collision of data occurs on that portion of the network between node  180  and  190 . In particular, node  190 , having received data from node  160 , proceeds to transmit the data outward along the C channel and the B channel. The B channel distributes the data to node  180 . However, in this case node  180 , which was racing with node  170 , will, for a period of time set by the timeout circuit, maintain a block on its received line on the A channel. This prevents node  190  from successfully delivering or transmitting the data signal originally broadcast from node  140  to node  180  which would in turn cause the signal to be routed through node  150  back to node  140 . Instead, the block on the input channel for node  180  effectively blocks the singing of the transmitted signal, allowing the lines to quiesce with no further passing of data around the network.  
         [0042]     Turning now to  FIG. 8 , one example of a system for correcting transmission latency among the nodes in the network is depicted. Specifically, there is a time distribution module that is responsible for maintaining a 1 pulse per second signal to science equipment within a jitter tolerance of about 1 microsecond. This time distribution module also updates an NTP clock to a tolerance of about 1 ms. In one embodiment, there is a crystal oscillator located in the module and that crystal oscillator provides the basic clock used by the module. Periodically, updates are received from the shore station to synch the clock with the shore master clock. Logic in the time module accounts for transmission latency when applying updates. In one practice, the transmission latency or propagation delay is accounted for by using a channel to measure the total propagation delay from a shore GPS referenced clock to an individual node. To this end, a time mark is periodically sent so that local clocks at each node can keep time slaved to the GPS reference clock that might be shore side. Each clock is appropriately offset, each with its particular delay value, so that they are truly synoptic. In one embodiment, the system uses CMOS logic to provide only gate and propagation delay variations which may be accounted for as they do not introduce jitter into the clock signal. Other embodiments may be used and realized without departing from the scope of the invention. But in either case, the systems work to maintain a signal that can be propagated as a time signal between the different nodes and that will provide a time signal that adjusts for and accounts for the latency that can arise when transmitting a signal over the many kilometers that separate the different nodes in the observatory network. One embodiment of the clock synchronization update logic is depicted in  FIG. 2  that shows the sub sea node  14  as having a clock synchronization logic block  34  that is capable of accounting for any propagation delay or distance delay that arises from the transfer of the clock signal from the shore node  12  to the sub sea node  14 .  
         [0043]     Turning to  FIG. 9 , one system for on/off keying of a laser source is depicted. The on/off keying of the laser diode allows for omitting a constant carrier on the laser diode. By removing this constant carrier, the amount of power consumed by the laser diode is substantially reduced. However, by removing the constant carrier, the feedback mechanism normally employed for laser power regulation is removed. To address this, a configuration of an op-amp in the circuit was established. This circuit allows power regulation without a constant carrier.  FIG. 9  depicts the power regulator circuit that may be used for the laser diode that is being on/off keyed. In the depicted circuit, feedback control is provided to regulate laser power. This allows for power regulation for the depicted system that does not employ a constant carrier.  
         [0044]     Those skilled in the art will know or be able to ascertain using no more than routine experimentation, many equivalents to the embodiments and practices described herein.  
         [0045]     Accordingly, it will be understood that the invention is not to be limited to the embodiments disclosed herein, but is to be understood from the following claims, which are to be interpreted as broadly as allowed under the law.