Abstract:
A photonic-based distributed network switch that utilizes multiple photonic broadcast stars and separate optical transmitters to improve overall reliability, allow load balancing, and provide failover for the network switch and the network with which the switch is used.

Description:
FIELD 
       [0001]    This disclosure relates to a photonic-based distributed network switch useable in a broadcast-based photonic network. 
       BACKGROUND 
       [0002]      FIGS. 1-3  illustrate a known photonic-based distributed switch  10  that employs a single passive photonic broadcast star  12  and a plurality of independent ports  14  connected to the star.  FIGS. 2 and 3  show one of the ports  14  of the switch  10  as including an external interface channel  16  for interfacing to external host devices  18 , a processor such as a field programmable gate array (FPGA)  20  connected to the interface channel  16  for processing optical data frames and determining which data frames to forward/receive to/from the external channel, a fixed wavelength optical transmitter  22  that outputs an optical signal containing data frames received over the interface channel  16  to the star  12  on one wavelength, and a multi-wavelength optical receiver  24  that receives multiplexed optical data streams from the star  12  and demultiplexes the received data streams. 
         [0003]    In this known switch, the broadcast star is a single point of failure such that if the star  12  fails, the entire switch goes down. 
       SUMMARY 
       [0004]    A photonic-based distributed network switch is described that utilizes multiple photonic broadcast stars to improve overall reliability, allow load balancing, and provide failover for the network switch and the network with which the switch is used. 
         [0005]    To provide load balancing, a processor is provided to determine which broadcast star to route data to. The processor can distribute the data load among the multiple broadcast stars so that each star is functionally operative during use of the switch, instead of a backup star being primarily inoperative and only being used in the event of failure of a first, primary star. However, if one of the multiple stars happens to fail, the processor controls automatic failover so that all data is routed to the remaining operative star(s). 
         [0006]    In one embodiment, a photonic-based distributed network switch includes first and second passive optical stars, and a plurality of independent ports each of which is connected to the first and second passive optical stars. Each port includes an external interface, and a processor connected to the external interface, where the processor includes a plurality of independent processing elements operating in parallel. For each port, first transmit and receive channels connect the first passive optical star to the processor, and second transmit and receive channels connect the second passive optical star to the processor. As used herein, independent processing elements operating in parallel includes, but is not limited to, multi-core processors, FPGAs, ASICs, DSPs and other similar devices. 
         [0007]    In another embodiment, a photonic-based distributed network switch includes first and second passive optical stars, and a plurality of independent ports each of which is connected to the first and second passive optical stars. Each port includes an external interface configured to interface to a plurality of external devices, and a processor connected to the external interface. The processor includes a plurality of independent processing elements operating in parallel. Each port also includes a first multi-wavelength optical receiver connected to the first passive optical star and connected to the processor, and a second multi-wavelength optical receiver connected to the second passive optical star and connected to the processor. In addition, each port also includes a first fixed wavelength optical transmitter connected to the first passive optical star and connected to the processor, and a second fixed wavelength optical transmitter connected to the second passive optical star and connected to the processor. 
     
    
     
       DRAWINGS 
         [0008]      FIG. 1  illustrates a known photonic-based distributed network switch. 
           [0009]      FIG. 2  illustrates the operational concept of each of the ports and the passive optical broadcast star of the photonic-based distributed network switch of  FIG. 1 . 
           [0010]      FIG. 3  illustrates the construction of one of the ports of the photonic-based distributed network switch of  FIG. 1 . 
           [0011]      FIG. 4  illustrates a photonic-based distributed network switch that employs a plurality of passive optical broadcast stars. 
           [0012]      FIG. 5  illustrates the construction of one of the ports in the photonic-based distributed network switch of  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring to  FIGS. 1-3  showing the known switch  10 , the ports  14  are connected to and in communication with the passive broadcast star  12  to route data frames to and receive data frames from the star  12 . The term data frame is used herein to refer generally to a discrete flow of data and the term is also intended to encompass a data packet. The data frames to and from the star  12  are optically formed data frames that are multiplexed in a data frame stream. The ports  14  connect the switch  10  to the external devices  18 , such as computers. 
         [0014]    Data signals to and from the external devices  18  are in the form of digital signals, while the data frames in the switch  10  are in the form of analog optical signals. The conversion to/from digital signals from/to optical signals can occur in the ports  14  using suitable conversion techniques. 
         [0015]    With reference to  FIGS. 1 and 2 , the passive optical broadcast star  12  is a passive device that contains only passive optical components and no electronics. The broadcast star  12  replicates all data frames received from a respective port  14  on a one-way incoming transmit channel  26  from a respective port  14  onto multiple one-way outgoing receive channels  28  to the other ports. There is one channel  26  going to the star  12  from each port  14 , and P channels from the star  12  to each port, with P being the total number of ports. A similar construction to that shown in  FIGS. 2 and 3  is used for each port. The broadcast star  12  allows each port  14  to see all data frames for all ports  14 . Therefore, any data frame that comes into for example port  2 , is automatically received by the ports  1 ,  3  and  4  via the star  12 . 
         [0016]    The ports  14  include the interfaces and logic that actively process and forward data frames to and from the switch  10  and connect the switch to the external devices  18 . The external channel  16  is a two-way channel that connects each port  14  to the external devices. The ports  14  operate independently of one another, with each port including the switching and protocol processing logic needed to perform network address resolution and data frame processing and forwarding. 
         [0017]    In each port, the transmitter  22  outputs a single-wavelength optical signal on the one-way incoming channel  26  to the star  12 , with the signal including the data frames received from the external devices  18  via the channel  16 . The optical receiver  24  receives all traffic from the star  12  over the one-way outgoing channels  28  on a multiplexed data stream. The receiver  24  demultiplexes the data stream and routes the data to the processor  20  which processes all received traffic and selects data frames to be forwarded to the external devices  18  via the external channel  16 . 
         [0018]    The external devices  18  are connected to the ports  14  via conventional interface and protocol technology, such as Ethernet.  FIG. 1  illustrates three external devices (for example computers A, B, C) connected to port  1 , two external devices (for example computers D and E) connected to port  2 , two external devices (for example computers F and G) connected to port  3 , and three external devices (for example computers H, I and J) connected to port  4 . 
         [0019]    A problem with the switch  10  configuration is that the broadcast star  12  forms a single point of failure such that if the star fails, the entire switch goes down. 
         [0020]    With reference to  FIGS. 4-5 , an improved photonic-based distributed network switch  30  is illustrated. The switch includes first and second passive optical stars  32 ,  34 , and a plurality of independent ports  36  each of which is connected to the first and second passive optical stars. A plurality of external network-enabled devices  38  are connected to each port. The devices  38  can be any network-enabled devices including, but not limited to, computers, network routers, network switches, storage units, printers, sensor systems, plotters, and wireless access points. 
         [0021]    The details of one of the ports  36  are illustrated in  FIG. 5 , it being understood that each port  36  is configured as shown in  FIG. 5 . The port  36  includes an external interface  40  for connecting the port to the external devices  38 . A processor  42  is connected to the external interface  40 . The processor  42  can be any type of processing element(s) that includes a plurality of independent processing elements operating in parallel. For example, the processor  42  can be a multi-core FPGA. 
         [0022]    The processor  42  processes data frames and determines which data frames to forward to the external interface  40  for routing to the external devices  38 . In addition, the processor is configured to determine which star  32 ,  34  to transmit data frames to, and to control automatic failover if one star  32 ,  34  fails. 
         [0023]    First transmit and receive channels  44 ,  46  connect the first passive optical star  32  to the processor  42 , and second transmit and receive channels  48 ,  50  connect the second passive optical star  34  to the processor. The first and second transmit and receive channels each comprise a fixed wavelength optical transmitter  52 ,  54  in the port and a multi-wavelength optical receiver  56 ,  58  in the port. 
         [0024]    The optical transmitters  52 ,  54  receive multiplexed optical signals from the processor  42  and transmit the signals to their respective stars  32 ,  34 . The transmitters  52 ,  54  can have the same data transmission speed or differing data transmission speeds. In addition, the transmitters  52 ,  54  can have respective individual data transmission speeds that differ from a data transmission speed of the external interface  40 , or they can each have the same transmission speed as the interface  40 . In one exemplary embodiment, the individual transmission speeds of the transmitters  52 ,  54  is each less than the transmission speed of the interface  40 , but have a combined transmission speed that equals the transmission speed of the external interface. For example, if the interface  40  has a transmission speed of, for example 10 Gbps, each of the transmitters  52 ,  54  can have a transmission speed of 5 Gbps. 
         [0025]    The use of the two transmitters  52 ,  54 , together with the processor  42  having independent processing elements operating in parallel, permits load balancing. Load balancing refers to the simultaneous use of each star  32 ,  34  rather than exclusively using one star and using the other star solely as a standby or back-up. The processor  42  is programmed to determine which data, how much data and by which route, to transmit to the stars  32 ,  34 . The processor  42  can employ any criteria for selecting the data to be transmitted and which transmission route to use. For example, the processor  42  can simply alternate between the transmitters  52 ,  54 . In another example, the processor  42  can route data to the transmitters  52 ,  54  based on how busy the stars  32 ,  34  are. For example, if the star  32  is overly busy, the processor routes data through the transmitter  54  to go to the second star  34 . In case of failure of one of the star  32 ,  34 , the processor  42  also controls failover detection and corrective action so that all data flows to the remaining functioning star. 
         [0026]    Therefore, the use of the two stars  32 ,  34  not only provides redundancy in case of failure of one of the stars, but actively using the two stars  32 ,  34  also improves performance of the switch  30 . 
         [0027]    The multi-wavelength optical receivers  56 ,  58  receive multiplexed optical data frame signals from the respective stars  32 ,  34 , demultiplex the signals into separate data frames, and send the data frames to the processor  42 . 
         [0028]    The examples disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.