Patent Publication Number: US-6993260-B2

Title: Interconnecting processing units of a stored program controlled system using free space optics

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to U.S. patent application Ser. No. 09/932,704, entitled “Interconnecting Processing Units Of A Stored Program Controlled System Using Time Division Multiplexed Free Space Optics”, filed concurrently herewith and commonly assigned to Lucent Technologies Inc., and incorporated by reference herein, with priority claimed for all commonly disclosed subject matter. 
   This application is also related to U.S. patent application Ser. No. 09/932,705, entitled “Interconnecting Processing Units Of A Stored Program Controlled System Using Wavelength Division Multiplexed Free Space Optics”, filed concurrently herewith and commonly assigned to Lucent Technologies Inc., and incorporated by reference herein, with priority claimed for all commonly disclosed subject matter. 
   This application is also related to U.S. patent application Ser. No. 09/932,706, entitled “Interconnecting Processing Units Of A Stored Program Controlled System Using Space Division Multiplexed Free Space Optics”, filed concurrently herewith and commonly assigned to Lucent Technologies Inc., and incorporated by reference herein, with priority claimed for all commonly disclosed subject matter. 
   This application is also related to U.S. patent application Ser. No. 09/932,707, entitled “Installation Of Processing Units Into A Stored Program Controlled System Wherein The Component Processing Units Are Interconnected Via Free Space Optics”, filed concurrently herewith and commonly assigned to Lucent Technologies Inc., and incorporated by reference herein, with priority claimed for all commonly disclosed subject matter. 
   FIELD OF THE INVENTION 
   This invention relates to the field of stored program controlled systems, including, but not limited to, telephone switching offices, data routers, and robotic machine tools; and, more specifically, this invention describes an optical communication path providing communication among processing units in a stored program controlled system. 
   BACKGROUND OF THE INVENTION 
   The background of the present invention may be summarized in one word: “wires”. Most stored program controlled systems of even minor complexity consist of a plurality of single or limited functionality processing units, each of which is connected to one or more of the other processing units by wires. There are literally millions of miles of interconnecting wires in current use in systems as diverse as stored program controlled telephone and data switching systems, robotic assembly lines, high speed mainframe computers, modem aircraft, local area networks, etc. 
   These wires provide the medium for communication signals among processing units to facilitate functionality of the whole. For example, a signal generated by a processing unit in the cockpit of an airplane is transmitted over a wire to a processing unit in the tail section to manipulate the tail control surfaces. Likewise, in a stored program controlled telephone switching office, a signal to connect a telephone call from one line to another is carried by wires interconnecting the processing units to which the telephone lines are connected. 
   In most stored program control systems, the “interconnecting wires” is a complex array of backplane wiring interconnecting processing units on cards, shelves of cards and cabinets of shelves. Each of these (card, shelf of cards, cabinet of shelves) may be considered a “processing unit”, because cards and shelves of related tasks are usually wired together in functional units, and then generally wired together in a cabinet. Cabinets of large stored program controlled systems are interconnected by bundles of wires (cables). Thus, the interconnecting wires provide communications paths that enable the individual processing units of the stored program controlled system to interact, thus providing the functioning of the whole. 
   A single change in an individual processing unit of a stored program controlled system may cause literally thousands of interconnecting wires to be moved from one processing unit to another, or connected or reconnected in some fashion. These new connections must be carefully planned and executed by skilled craftspeople who make each connection and then test it. One minor error may cause a major malfunction. 
   Further, these wires are bulky and are frequently grouped together into a cable bundle. Such bundling is problematic in and of itself; in that, if one or more wires in the bundle is cut, then some or all of the functionality of the stored program controlled system is lost, and it is difficult to find one damaged wire in a bundle of wires. In a worst case scenario, a single short in a bundle of wires can cause devastating fires, such as the fire in the telephone switching office in Hinsdale, Ill. in May of 1988. This fire caused a nationwide disruption of telephone service that lasted for a few days and interruption of local telephone service that lasted for several months. 
   Over the past decade, some interconnecting wire has been replaced by fiber optical cable. This was an advance in the art, because more signals (higher bandwidth) are carried over a smaller physical cross-section. However, fiber optics has been treated for the most part like another wire: each fiber connects one processing unit to another, the optical signal is converted between optical and electrical signals at each terminus, and the electrical signals are processed in the usual fashion. 
   Therefore, a problem in the art is that processing units in a stored program controlled processing system are interconnected by extensive wiring which is difficult to install, maintain and modify. 
   SUMMARY OF THE INVENTION 
   This problem is solved and a technical advance is achieved in the art by a system and method that uses free space optics to interconnect processing units of a stored program controlled system. Communication signal paths are provided in a stored program controlled system comprising a plurality of units configured to process signals (“processing units”) by a beam line in free space, proximal to each of the plurality of units. The beam line is configured to contain optically encoded communications signals that are transmitted between and among the processing units. Each processing unit includes a probe for receiving optically encoded signals from the beam line, and, advantageously, a probe for injecting optically encoded signals into the beam line. There may be a first terminal unit at a first end of the beam line configured to originate and/or terminate the optically encoded signals and a second terminal unit at the second end of the beam line also configured to originate and/or terminate the optically encoded signals. 
   Each processing unit may comprise a frame, a shelf, or an individual card on a shelf of the stored program controlled system, and each processing unit performs functions related to the stored program controlled system&#39;s intended functionality. Probes are configured to receive or send optically encoded signals in the free space beam line. The probe further comprises supporting circuitry to translate optically encoded signals into and out of electrically encoded signals, and route such signals. 
   The beam line may run above, below, through or adjacent to the processing units and the beam may be encoded in time division multiplexing, spatial division multiplexing or wavelength division multiplexing. The beam line may be formed and directed using routing mirrors, prisms, lenses, gratings and holograms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of this invention may be obtained from a consideration of the specification taken in conjunction with the drawings, in which: 
       FIG. 1  is a perspective view of a free space beam line illustrating the relationship of the beam line and probes according to a general overview of an exemplary embodiment of this invention; 
       FIG. 2  is a cross-sectional view of the free space beam line taken along line  2 -Z of  FIG. 1 ; 
       FIG. 3  is an exemplary embodiment of transmitting and receiving probes of  FIGS. 1 and 2 ; 
       FIG. 4  is another exemplary embodiment of transmitting and receiving probes of  FIGS. 1 and 2 ; 
       FIG. 5  is a block diagram of uni-directional communication along a free space beam line according to one exemplary embodiment of this invention; 
       FIG. 6  is a block diagram of a further exemplary embodiment of this invention having bi-directional probes; 
       FIG. 7  is a block diagram of another exemplary embodiment of this invention wherein each of the processing units may communicate with each other; 
       FIG. 8  is a physical layout of a stored program controlled switching office according to an exemplary embodiment of this invention; 
       FIG. 9  is a block diagram of the exemplary embodiment of  FIG. 8  in which the free space beam line is distributed to each shelf; and 
       FIG. 10  is a block diagram of the exemplary embodiment of  FIG. 8  in which the free space beam line is distributed to each card on each shelf. 
   

   DETAILED DESCRIPTION 
   Turning to  FIG. 1 , a perspective view of a free space beam line  10  according to one exemplary embodiment of this invention is shown. According to this exemplary embodiment, a free space beam line  10  is generated by a transmitter  12  within a transmitting probe  14  which projects optically encoded signals, as will be described below in connection with  FIGS. 3 and 4 . Transmitting probe  14  produces a beam line  10  of desired diameter along the length of its path. 
   A plurality of receivers  16  within receiving probes  18  are distributed throughout beam line  10  along the outer periphery in the form of a spiral or helix, in this exemplary embodiment. Other possible configurations of probes along the beam line will be apparent to one skilled in the art after studying this disclosure. Receiving probes  18  are distributed in a helix in this exemplary embodiment so that there is a minimal amount of shadowing; that is, one receiving probe  18  being in the shadow of a previous receiving probe  18  in beam line  10  causing the probe in the shadow to receive little or none of the optically encoded signals in beam line  10 . 
   Free space beam line  10  may be contained within a reserved volume or conduit  22 , in an enclosure, such as a cylinder or pipe or, alternatively, may be in the open. If the beam line  10  is contained in a conduit, then the interior surface may be coated at the time of manufacture to be optically absorptive or optically reflective depending upon the length of the pipe, the wavelength of the signal generated by the laser within transmitter  12  and loss budget to provide optimal reception of optically encoded signal by the plurality of receiving probes  18  throughout the length of beam line  10 . 
   Conduit  22  includes, in this exemplary embodiment, a first terminal unit  24  and a second terminal unit  26 . First terminal unit  24  includes a transmitting probe  14  and second terminal unit  26  includes a receiving probe  18 , in this exemplary embodiment. First terminal unit  24  originates optical beam line  12  and second terminal unit  26  terminates the portion of optical beam line  12  passing beyond the other probes  18 . As will be discussed further, below, first terminal unit  24  and/or second terminal unit  26  may include both transmitters and receivers, and may be interconnected to recycle the encoded signal. 
     FIG. 2  illustrates a view looking down a cross-section of free space beam line  10  taken along line  2 — 2  of  FIG. 1 . Conduit  22  includes a plurality of receiving probes  18  around its inner edge. In the illustration of  FIG. 2 , the laser of transmitter  12  ( FIG. 1 ) focuses beam line  10  to encompass the interior circumference of conduit  22  whereby each probe  18  receives the encoded optical signal. Second terminal unit  26  is illustrated herein as comprising a receiving probe  18 . (Second terminal unit may also include a transmitter  12 , not shown.) Alternatively, second terminal unit  26  may comprise an end cap. An end cap may be absorptive in order to stop the beam line  10  or may be reflective (i.e., a mirror or retroreflector) to recycle beam line  10  in the opposite direction. 
   Turning now to  FIG. 3 , exemplary embodiments of a transmitting probe  14  and a receiving probe  18  are shown. In this exemplary embodiment, transmitting probe  14  includes a transmitter  12  comprising a laser  30  (i.e., a laser diode  32  and a feedback photodetector  34 , as known in the art), which converts electronically encoded signals into free space optical beam line  10 . Free space optical beam line  10  is projected through a concave lense  36  and a convex lense  38  (which form a reverse Galilean telescope, as is known in the art). A laser driver  40  feeds electrically encoded signals to, and receives feedback from, laser  30 , as known in the art. Feedback amplifier  42  regulates the input to laser  30 . Laser  30  and laser driver  40  are both known to those skilled in the art. Laser  30  and laser driver  40  are illustrated herein as two separate units, but may be one unit. 
   Free space beam line  10  is received at a receiving probe  18  at a receiver  16 , which includes a convex lense  44  that focuses beam line  10  on a photodetector  46 . Photodetector  46  receives a portion of beam line  10  and generates an electrical signal in response thereto. The electrical signal is fed into a receiver circuit  48  comprising a trans-impedance amplifier (TIA)  50 , clock recovery circuit  52  and decision circuit  54 . Receiver  16  and receiver circuit  48  are well known in the art. Receiver  16  and receiver circuit  48  are illustrated herein as two separate units, with receiver circuit  48  contained within a signal receiver  55 . However, these two units may be one unit, as is known in the art. 
   Laser  30  is driven by an electrical signal from signal generator  56 . Signal generator  56  comprises laser driver  40 , protocol handler  58  and multiplexer  60 . Multiplexer receives multiple inputs  62  from one or more processing units, which are multiplexed according to a predetermined algorithm (many algorithms for multiplexing are known in the art and are thus not discussed here). Signals are then passed to protocol handler  58 . Protocol handler  58  encapsulates the signals with the protocol used by the beam line  10 . Such protocols are described in U.S. patent applications Ser. Nos. 09/932,704, 09/932,705 and 09/932,706 which are incorporated by reference, above. The signal generated by protocol handler  58  is fed into laser driver  40 , which controls laser  30 . 
   When a signal is received by photodetector  46 , it is delivered to signal receiver  55 , which comprises receiver circuit  48 , protocol handler  64  and demultiplexer/router  66 . The received signal is decoded in receiver circuit  48 , as known in the art. The receiver circuit  48  is connected to a protocol handler  64  which de-encapsulates the signal received according to the protocol used by protocol handler  58 . Protocol handler  64  passes the signal to a demultiplexer and router  66  which demultiplexes the signal and then sends signals  68  to the receiving processing unit or units. Demultiplexing and routing algorithms are well known in the art, and are thus not further described. 
     FIG. 4  illustrates an exemplary embodiment of a transmitting probe  14  and a receiving probe  18  according to another aspect of this invention. In this exemplary embodiment, the electronics are remote from the optical beam line. Transmitting probe  14  in this exemplary embodiment includes a transmitter  12  comprising a laser element  30 , as described above in connection with  FIG. 3 , which changes electrical signals delivered from laser driver  40  into an optically encoded signal. Optionally, this optically encoded signal is fed into lense  80 , which projects the signal through light guide  82  (i.e., optical fiber) in this exemplary embodiment. One skilled in the art will appreciate that some applications will not require lense  80 . Fiber optic conduit  82  projects the optically encoded signal through lenses  36  and  38  (the reverse Galilean telescope as described above) which forms free space beam line  10 . 
   Receiving probe  18  includes a receiver  16 , a lense  306  that focuses light from beam line  10  onto fiber optic conduit  86 . Fiber optic conduit  86  transmits the optical signal through lense  88  onto photodetector  46 . Photodetector  46  sends an electrical signal through receiver circuit  48 , protocol handler  64  and demultiplexer/router  66 , as described above. The signals are delivered to their respective processing unit or units via lines  68 . 
     FIG. 5  is a block diagram of a stored program controlled system  100  in a basic implementation of an exemplary embodiment of this invention. Stored program controlled system  100  may comprise, in this exemplary embodiment, a unidirectional local area network. In the stored program controlled system  100 , a first processing unit  102  comprises a controller which distributes signals to a plurality of processing units  104 ,  106 ,  108  and  110 . Processing units  104 ,  106 ,  108  and  110  receive signals from controller  102  via receiving probes  18  (as described above) and perform their respective functions on received signals. 
   In this one-way communication system, processing unit (controller)  102  passes commands to processing units  104 ,  106 ,  108  and  110  without expecting responses from any of the processing units. Controller  102  generates signals to control processing units  104 ,  106 ,  108  and  110  and encodes the signals into a form that can be translated into optical signals (as discussed above in connection with FIG&#39;s.  3  and  4 ). Controller  102  is connected to a transmitting probe  14  in a first terminal unit  24  in this exemplary embodiment. 
   A free space beam line  10  is thus formed containing the optically encoded signals for processing units  104 ,  106 ,  108  and  110 . The exemplary embodiment of  FIG. 5  includes a conduit  22 . Conduit  22  includes an end cap  112  (instead of a second terminal unit) which may be coated with light absorptive or alternatively reflective material, depending upon which direction the receiving probes  18  are facing. 
   According to this invention, the entirety of free space beam line  10  is filled with optically encoded signals as it exits terminal unit  24 . In this embodiment, each probe receives the optically encoded signal directly. Alternatively, lenses  36  and  38  in transmitter  12  ( FIG. 3 ) of transmitting probe  14  may focus the beam line  10  so that it does not completely fill conduit  22  until it hits end cap  112 . End cap  112  comprises reflective surface in this exemplary embodiment, which provides a full beam line  10  throughout conduit  22 . Considerations of signal strength, beam divergence, bit rate, distance between processing units  104 ,  106 ,  108  and  110 , signal to noise ratio, etc. must be taken into account to determine which method (direct or reflective) of transmission is preferable in a given application. 
   Turning now to  FIG. 6 , an exemplary embodiment of this invention using bi-directional probes is shown generally at  120 . In this exemplary embodiment, processing unit (controller)  122  communicates with a plurality of processing units  124 ,  126 ,  128 , and  130 . As in the previous exemplary embodiments, controller  122  communicates with a first terminal unit  24 , which includes a transmitting probe  14  that produces free space beam line  10 . Beam line  10  is, in this exemplary embodiment, unenclosed. 
   Each processing unit  124 ,  126 ,  128  and  130  has an associated receiving probe  18  for receiving signals from controller  122 . Additionally, each processing unit  124 ,  126 ,  128  and  130  includes a transmitting probe  14  to transmit return signals to receiving probe  16  in terminal unit  24 . The received signals are delivered to controller  122 , which then processes these signals for further control of the stored program controlled unit, creating a full-duplex channel. 
   Turning now to  FIG. 7 , a further exemplary embodiment of this invention is shown. In this exemplary embodiment, free space beam line  10  is unidirectional, i.e., signals flow in the direction from uni-directional first terminal unit  132  to second unidirectional terminal unit  134  and are then recirculated, as will be described further below. Free space beam line  10  is enclosed in conduit  22 . In this exemplary embodiment, a processing unit controller  136  and processing unit  138 ,  140 ,  142  and  144  are each connected to a respective transmitting probe  14 . Processing units  138 ,  140 ,  142  and  144  are connected to respective receiving probes  18 . Terminal  134  uses terminal receiving proble  135 . 
   In the exemplary embodiment of  FIG. 7 , processing unit or controller  136  originates electrical control signals for processing units  138 ,  140 ,  142  and  144  and communicates such signals to router  146 . Router  146  comprises a conventional router as is known in the art. Router  146  communicates signals for processing units  138 ,  140 ,  142  and  144  to a signal generator  56  (as described above in connection with  FIG. 3 ). Transmitter  14  in unidirectional first terminal unit  132  optically encodes the signals, and transmits optical beam line  10 . Receiving probes  18  receive the optically encoded signals and convey them to their respective processing unit  138 ,  140 ,  142  and  144 . Each processing unit  138 ,  140 ,  142  and  144  may send feedback or other information to controller  136  by injecting signals into free space beam line  10 , which are all received at terminal receiving probe  135  in unidirectional second terminal unit  134 . The signals are then fed back to router  146  where they may be farther circulated in beam line  10  or delivered to controller  136 . 
   Systems using many of the embodiments of this invention (i.e.,  FIG. 7 ) must include features to prevent messages from recirculating in free space beam line  10 . If these features are not included, infinite feedback loops are possible, where a single message is continuously relayed between two endpoints and/or probes, quickly absorbing all available bandwidth. To prevent this, a means to break these loops is provided. Router  146  is programmed (or programmed in conjunction with the probes or endpoints) to detect addresses that lead to looping and not forward those messages back into the beam line. Alternately, the optical characteristics of the beam line, transmitters and receivers are controlled to prevent messages from a given source from circulating indefinitely. 
     FIG. 8  presents a block diagram of one exemplary embodiment of a stored program controlled system which uses a free space optical beam line  10  to interconnect its processing units. In this exemplary embodiment, the stored program controlled system comprises a telephone switching system  200 , such as a 5ESS® Switch or 7R/E Switch manufactured by Lucent Technologies. There are a plurality of processing units  202 ,  204 ,  206 ,  208 ,  210  and  212 . Processing units  202 ,  204 ,  206 ,  208 ,  210  and  212  comprise “frames” as are known in the art. Each frame comprises a plurality of shelves  214  and on each shelf is one or more cards  216  (also called “boards” in the art). Each card  216  performs one or more predefined functions, as is known in the art. 
   In the exemplary embodiment of a 5ESS® Switch, frame  202  comprises a communications module (CM) which effects communication among the other frames in the system. Frame  204  comprises an administration module (AM) which provides overall control of the system and human-machine interface. Frames  206 ,  208 ,  210  and  212  comprise switch modules (SMs), which support a plurality of line and/or trunk units (or some combination thereof) and effect connections of telephone or data calls. All of the processing units (frames  202 ,  204 ,  206 ,  208 ,  210  and  212 ) communicate with each other (generally through CM  202 ) in order to switch telephone calls. 
   Currently, frames such as  202 ,  204 ,  206 ,  208 ,  210  and  212  are interconnected by a plurality of wire buses and/or optical fiber carried in overhead trays or under raised floors. Wiring a new office or even adding a new frame may cause the installation team to revisit the entire wiring of the system in order to ensure proper functionality of the whole stored program controlled system  200  when connected. This invention is intended to replace the current industry standard of wiring between and among frames in central switching offices. This invention eliminates the probability of accidental damage to cabling, decreases new installation and upgrade time. The following exemplary embodiment of this invention is described in the context of such a central switching office. It is, however, clear to one skilled in the art how to implement and use this invention in other applications after a review of this patent application. 
   According to one exemplary embodiment of this invention, a free space optical beam line  10  provides interconnection of the frames  202 ,  204 ,  206 ,  208 ,  210  and  212 . Signals are carried on one or more optical wavelengths as is known in the art. There may also be a pilot beam  218  in the visible light wavelengths in order to aid craft personnel to align probes  14  &amp;  18  of the processing units and other optical components. 
   In this exemplary embodiment, each processing unit  202 ,  204 ,  206 ,  208 ,  210  and  212  includes a transmitting probe  14  and a receiving probe  18  positioned in beam line  10  in order to send and receive, respectively, signals in system  200 . Each transmitting probe  14  and each receiving probe  18  may, advantageously, be bi-directional. It is within the scope of one skilled in the art to make the transmitting and receiving probes of FIG&#39;s.  3  and  4  transmit/receive in both directions after reading this specification. Transmitting probe  14  and receiving probe  18  on frame  202  comprise a first terminal unit  24  and transmitting probe  14  and receiving probe  18  on frame  208  comprise a second terminal unit  26 . The probes  14  and  18  in first terminal unit  24  and second terminal unit  26  may be uni-directional. 
   Each transmitting probe  14  is connected to a signal generator  56  and each receiving probe  18  is connected to a signal receiver  55 . Signal generator  56  and signal receiver  55  may be separate cards  216  as illustrated, may be one integrated card, or may both be integrated with other functionality of its respective shelf  214  and/or frame  202 ,  204 ,  206 ,  208 ,  210  or  212 . 
   Additionally, first terminal unit  24  may be connected to second terminal unit  26  by way of a connector  220 . Routers  222  and  224  are illustrated herein as connecting connector  220  to first terminal unit  24  and second terminal unit  26 , respectively. Ordinary routers  222  and  224  may route selected messages between terminal units  24  and  26 , and to prevent endless looping of messages. Connector  220  may comprise another free space optical conduit like beam line  10 , or may comprise a fiber optic or electrical link as is known in the art. 
   Free space beam line  10  may be manipulated by turning mirrors  226 , prisms or the like (not shown but well known in the art) to provide, for example, a continuous beam line  10  through multiple rows of processing units (or floor levels, etc.). Beam line  10  is illustrated as running above the processing units in  FIG. 1 . Beam line  10  may also run under a raised floor, or in a space or conduit otherwise adjacent to or through the processing units. 
   Turning now to  FIG. 9 , another exemplary embodiment of this invention is shown, wherein “processing units” are defined at one level below a frame. In this exemplary embodiment, free space beam line  10  is shown, as described above. Each frame, for example, frame  204 , comprises a plurality of shelves  214 , here shown as  214 A–D. In this exemplary embodiment, a turning mirror  226  is set in main beam line  10  to turn main free space beam line  10  into frame-level free space beam lines  228 . In this exemplary embodiment, transmitting probes  14  and receiving probes  18  send and receive optical signals for each shelf  214 A–D. End cards  230  on each shelf  214 A–D comprise signal generators  56  and signal receivers  55  (not shown) as described above in connection with  FIG. 3 . Mirrors  226  may be partially reflective so as to turn a portion of the signal beams and allow another portion to pass through, as is known in the art. 
   Turning now to  FIG. 10 , another exemplary embodiment is shown, wherein a “processing unit” is now defined as a card  215 . Turning mirrors  226  are again used to turn main free space beam line  10  into frame free space beam lines  228 . Each shelf  214 A– 214 D includes a pair of additional card level turning mirrors  240  in beam lines  228 , respectively. Card level turning mirrors  240  provide card free space beam lines  242 . There may be one or more card level beam lines  242  per shelf  214 . In this exemplary embodiment, there are two free space beam lines  242  per shelf. Each shelf  214  then includes at least one card  216  equipped with a transmitting and/or receiving probes  14  and  18  (as illustrated in  FIG. 3 ) and the supporting signal generator and signal receiver. 
   Frame probe  249  is used for frame-level communication and control functions. For example, power control, temperature sensing and alarm annunciation may be communicated to a central control by frame probe  249 . 
   It is to be understood that the above-described embodiments are merely illustrative principles of the invention and that many variations may be devised by those skilled in the art without departing from the scope of this invention. It is, therefore, intended that such variations be included within the scope of the following claims.