Abstract:
A method and apparatus for switching optical signals by selectively routing such signals through a packet switch is disclosed. Depending upon predetermined traffic conditions in data being received and transmitted, the system may be provisioned to provide circuit like optical switching, or a mixture of optical and packet switching. An exemplary growable optical switch architecture is disclosed in the preferred embodiment.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional application Ser. No. 60/234,122, filed on Sep. 21, 2000, and also claims the benefit of the U.S. Provisional Application filed on Nov. 30, 2000, entitled “Optical Flow Networking”, Ser. No. 60/250,246, naming Kai Y. Eng as Inventor. Additionally, this application is a continuation-in-part of U.S. application Ser. No. 09/565,727, filed on May 5, 2000, the disclosure of which is incorporated herein in its entirety by this reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    This invention relates to telecommunications, and more specifically, to an improved method and apparatus for switching and routing optical signals. The preferred embodiment is also directed to an improved technique of routing optical signals such that efficiency is maximized by subjecting certain signals to packet switching technologies, and routing others in the optical domain without such packet switching.  
         BACKGROUND OF THE INVENTION  
         [0003]    Optical communications networks are becoming more and more prevalent in order to facilitate high bandwidth long haul connections among communications nodes in a network. One issue not solved by the present state of the art is the provision of full flexibility in routing options at each of plural nodes in a network. More specifically, typically the optical transport systems represent large “pipes” to convey data at relatively high bit rates, such as 2.5 gigabits per second, or even 10 gigabits per second. The actual packet switching at the nodes is performed by a completely separate computer system known as a packet switch or packet engine.  
           [0004]    Conventionally, the routing industry is completely separate from the optical switching industry, having different vendors and different technologies. There exists little or no standards for the packet switching modules and the optical systems to interoperate.  
           [0005]    The optical portion of long haul communications systems operate by provisioning circuit like connections from specified optical inputs to specified outputs. This provisioning is conventionally accomplished independent of, and without knowledge of, any configuration or provisioning of the packet switching portions of the network.  
           [0006]    Conversely, the packet switching portions of the networks operate by reading addresses in the packet headers, and routing the packets based thereon. However, the packet switching operations are far slower than that of the circuit like optical switching. Moreover, the packet switching operates independently of the circuit switching, and thus, there exists no way to optimize the routing algorithms utilized by the packet switch.  
           [0007]    Additionally, numerous other inefficiencies exist due to the total separation of the optics from the packet switching. For example, there is no way of taking advantage of the fact that certain switching needs may be based more upon optical switching requirements or packet switching requirements. There exists no known technique of taking immediate advantage of changes in the optical topology of the network in setting up packet routing algorithms, since the packet routing algorithms have no knowledge of the optical topology of the network, or of changes in such topology. Similarly, the packet routing algorithms operate to maximize efficiency without accounting for the topology of the optical network and its changes, thereby precluding optimum performance.  
           [0008]    In view of the above, there exists a need in the art for an improved technique of switching signals routed through a data network using optical media and optical switches, as well as packet switches.  
         SUMMARY OF THE INVENTION  
         [0009]    The above and other problems of the prior art are overcome and a technical advance is achieved in accordance with the teachings of the present invention. An optical engine and a packet engine are interconnected in a manner such that incoming optical signals may be switched directly out through the optical engine or processed through the packet engine, depending upon requirements needed to maximize switching efficiency.  
           [0010]    In one exemplary embodiment, an optical engine and a packet switching engine are employed and interconnected. Packets arriving to the packet engine may be switched out of the packet engine or out of the optical engine, and packets arriving in the optical engine may be switched out of the optical engine or out of the packet engine. Additionally, packets arriving in the optical engine may be switched through the packet engine and back out the optical engine.  
           [0011]    In a particular preferred embodiment, three switching modules are used to construct the optical switches in a manner that provides add and drop capability using a modular architecture. This preferred architecture allows a relatively large switch to be built from relatively small components. It also permits the provisioning of a packet switch to be done in a manner that accounts for the static and dynamic properties of the optical network. The architecture allows the full integration of the optical switching portion of a node with the packet switching portion of a node.  
           [0012]    The foregoing and other advantages and features of the present invention will become clearer upon review of the following drawings and detailed description of the preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 shows a high level functional diagram of a combination of optical engine packet engine node in accordance with the present invention;  
         [0014]    [0014]FIG. 2 shows a slightly more detailed diagram of the optical engine utilizing multi-channel DWDM inputs and outputs;  
         [0015]    [0015]FIG. 3 shows an additional embodiment of the invention utilizing signal channels inputs and outputs;  
         [0016]    [0016]FIG. 4 depicts a conceptual diagram of the interconnection of the packet engine and optical engine;  
         [0017]    [0017]FIG. 5 depicts a modularly built optical switching architecture; and  
         [0018]    [0018]FIG. 6 depicts one of the modules of the arrangement of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 depicts a functional block diagram of an exemplary embodiment of the present invention. The arrangement of FIG. 1 includes plural optical transceivers  101 - 103 , an optical engine  104  and a packet switching engine, or simply a packet engine,  105 . Inputs and outputs  106  and  107 , respectively, connect packet engine  105  to the two other nodes of a packet switching network that also perform packet switching. Optical engine  104  takes inputs and provides outputs from and to an optical network as indicated by input/output lines (“I/O”)  110 - 115 .  
         [0020]    A provisioning computer  120  is connected to both a packet engine  105  and optical engine  104  in order to provide provisioning for both the packet engine and optical engine. Notably, the preferred embodiment uses the same provisioning computer, and even the same software, for setting up and provisioning the optical portions of the network, as well as for the packet switching portions of the network. By having a common provisioning computer and/or software, the provisioning can be done in a manner that optimizes each of the optical and packet engine&#39;s provisioning.  
         [0021]    The computer  155  provisions the optical engine  104  and packet engine  105  by setting and/or resetting switching that cause inputs to be directed to prescribed outputs. In the case of the optical engine  104 , for example, the provisioning may cause mirrors to either activate or deactivate. In the case of the packet engine  105 , the provisioning is arranged to cause outputs destined for a specified “next hop” in the packet network to exit the packet engine out of a specified output. The setting and resetting of switches as part of the provisioning is known to those of skill in the art and will not be discussed in great detail herein.  
         [0022]    As is known to those of skill in the art, the optical engine typically operates as a cross connect, accepting data on one or more inputs at one or more wavelengths, and transmitting such data out of 1 or more outputs on the same or different wavelength. Thus, for example, optical engine  104  may comprise input wavelengths  1 - 3 , output wavelengths  4 - 6 , and a switching matrix that can take each input and transmit it out onto a different output. Typically, optical engine  104  may also reshape and regenerate the optical signals so that any degradation due to transmission and switching is removed. Thus, the optical signals exiting from the optical engine are “clean”, i.e. with very high signal to noise ratios.  
         [0023]    [0023]FIG. 2 depicts a block diagram of optical engine  104  of FIG. 1. FIG. 2 intended to be an exemplary embodiment showing one implementation of the concepts described herein, and is not intended to limit the scope of the present invention. Many of the subcomponents of the system are readily available and known to those of skill in the art, and thus, they will not be described in great detail hereafter.  
         [0024]    Optical engine  104  is connected to the packet engine  105  of FIG. 1 through lines  121  and  120  as shown in FIGS. 1 and 2. Each of the lines  120 - 121  may actually be plural lines, as indicated in FIG. 1. Lines  120  and  121  facilitate the exchange of data between packet engine  105  and optical engine  104 . The optical engine comprises optical multiplexors  205  and  206  for receiving and transmitting data to and from an optical transport network. Each transceiver comprises a multiplexing portion  208  for receiving information from plural channels and transmits the information as one optical signal in the 1550 nanometer (nm) region. Conversely, the receiving portion includes a demultiplexer  210 , which demultiplexes signals received in the 1550 nm range as shown, and demultiplexes them into plural outputs. These wavelengths are by way of example, and not limitation.  
         [0025]    Notably, the switching matrix  215  may receive as input a signal generated from the receipt of optical signals as well as signals received from the packet engine. The output of switching matrix  215  may be transmitted directly to the optical network such as over line  217 , or may be transmitted to the packet engine, such as over line  218 .  
         [0026]    As a result of the foregoing, the system can be viewed conceptually as shown in FIG. 4. As shown therein, inputs may arrive to the optical engine and be transmitted through the packet engine and back out the optical engine, such as indicated by path  401 . Other inputs may be received via the optical engine and transmitted directly through the optical engine, without being sent through the packet engine, such as indicated by path  402 . Still further inputs may be received via the packet engine and sent out the optical engine, such as indicated by path  403 . Finally, inputs may arrive in packet form via the packet engine  105  and be transmitted out of the packet engine such as shown at path  404 .  
         [0027]    All signals passing from an input to an output of packet engine  105  are routed by examining the packet header and choosing an output to convey the packet to the next packet switch and the packet switching engine, in accordance with any of a variety of well known routing and packet switching algorithms. All signals passing from an input to an output of the optical engine are conveyed in a circuit switching manner from an input to an output, and may exit on a different wavelength than that on which it arrived.  
         [0028]    In view of the foregoing, it can be appreciated in various mixtures of packet and circuit switching are made feasible by the techniques of the present invention. For example, returning to FIG. 1, the input to optical transceiver  101  from optical engine  104  may comprise the combination of signals received originally in optical engine  104  from packet engine  105 , with signals originally received through optical transceiver  103  from the optical network and routed through packet engine  105 . Accordingly, the designer may “mix and match” any of the desired manners of provisioning either the optical engine or the packet engine.  
         [0029]    One manner in which this mix and match can be taken advantage of is in the determination of whether to route arriving optical signals through the packet engine  104  or directly back out the optical engine  105 . For example, consider an arriving bit stream from the optical network that is conveyed from line  115  of FIG. 1 through optical transceiver  103 . If the arrival rate of the data is such that it nearly maximizes the capacity of an inbound and an outbound channel, than greater efficiency can be achieved by avoiding any packet switching. The following example is illustrative.  
         [0030]    Suppose that the bit stream represents data arriving at an average rate of 2.4 gb/s, and that the line  115  over which the data arrives is provisioned to be an optical line at 2.5 gb/s. Further, consider a situation wherein all of such 2.4 gb/s of arriving data is to be sent to a specific next node over output line  110 . In such a case, it is not worthwhile to send the arriving data through the packet engine  105 . This is because nearly all of the capacity of both the inbound link  115  and the outbound link  110  will be used for the single optical provisioned connection. For example, 2.4/2.5, or approximately 96 percent of the capacity of outbound link  110  will be used by the incoming data from line  115 . If all of the data incoming from line  115  where sent through the packet engine  105 , such procedure could at best cram an additional 4 percent onto the outgoing line  110 . However, the benefit of getting an additional four percent may, and likely would, be outweighed by the additional load and latency created as a result of the fact that all data arriving on line  115  would have to be conveyed to and processed by the packet switch.  
         [0031]    In accordance with the teachings of the present invention, the provisioning software may be set to recognize when a predetermined percentage of the optical bandwidth of any incoming line is utilized for a specific single optical output. The predetermined percentage maybe set be a user, and can be changed through a simple data input technique such as a graphical user interface. (GUI).  
         [0032]    When the user or software recognizes that the percentage of data arriving on a single predetermined input is destined for a single predetermined output, the optical provisioning will be configured to avoid transmitting packets arriving on the input through the packet engine. This optical provisioning could even happen automatically, by providing a capacity monitor for the lines. When the preset condition is recognized, the optical provisioning is changed. Elimination of routing of packets through the packet engine  105  under certain circumstances creates a slight inefficiency in the sense that no further capacity of the outbound line  110  can be used. Thus, it is only filled to 96 percent capacity in the example given. However, reduced latency and increased speed are achieved.  
         [0033]    Alternatively, the avoidance of packet switching can be done in advance by the user, rather than automatically be the switching system. More specifically, if the user knows that a certain percentage of the traffic arriving on a particular input is destined for an output, than the system can be provisioned to avoid the packet switching when it is preprovisioned.  
         [0034]    Another condition that helps efficiency by avoiding the packet switching is a condition in which most traffic arriving on lines other than the input line  115  is NOT destined from a particular output. When this condition occurs, the packet switching can be avoided even when most of the capacity of an outgoing optical line is NOT used up. Consider for example, a condition wherein it is known in advance that no data from input lines  115  and  113  is destined for output line  110 , and that the only data destined for output line  110  comes from input line  111 . In such a case, there is no need to transmit data from input line  111  through packet engine  105 . Instead, all such data can be optically switched from input line  111  to output line  110 , even though the amount of such data may be far less than the capacity of the output line  110 . This is because no significant inefficiency occurs due to the fact that even though most of the capacity of output line  110  is not used, the unused capacity would not be used even if the data were routed through packet engine  105 . Accordingly, latency is reduced and overall efficiency is increased.  
         [0035]    In general then, the technique of the present invention may provision the optical and packet engines, either in advance or during operation thereof, in such a manner that upon a predetermined condition in such traffic, the traffic is switched directly through the optical engine as opposed to through the packet engine. In a preferred embodiment, that predetermined condition includes whether or not a prescribed percentage of such traffic or more from a single input is destined for a particular output, or whether traffic from plural outputs is not destined for a particular output. Other conditions may be utilized as well.  
         [0036]    [0036]FIG. 3 shows a slightly different embodiment of the present invention wherein the input and output channels are not multiplexed and demultiplexed as shown in FIG. 2. Instead, each of the plurality of inputs and outputs arrives on a separate line and is fed into the optical switching matrix for processing as previously described with respect to FIG. 2.  
         [0037]    With regard to the teachings of the present invention, the use of multixplexing and demultiplexing, or the use of separated lines without such multiplexing and demultiplexing, is not critical to the operation of the present invention.  
         [0038]    [0038]FIG. 5 shows an exemplary implementation for use in a preferred exemplary embodiment, the arrangement of FIG. 5 optical switching arrangement used within the optical engine of the present invention. The three port cross bar switches  501  and  502  are coupled with a two port cross bar switch  503 . This creates an optical switching arrangement with 16 inputs and 16 outputs, wherein half of each of the inputs and outputs are to and from the optical network, and remaining half are connected through the packet engine as shown in FIG. 1.  
         [0039]    The provisioning of the optical engine includes configuring each of the optical crossbar switches  501 - 503  to direct desired inputs and outputs as indicated conceptually in FIG. 5. More specifically, referring to crossbar switch  501 , the crossbar switch  501  includes 8 inputs and 16 outputs, wherein each of the inputs  501  maybe provisioned for conveying to one of outputs  510  or  511 . Crossbar switch  503  has only 2 ports, the 8 inputs arriving on lines  511  being capable of conveyance to any one of outputs  512 . Moreover, data arriving at cross bar switch  502  on any of lines  512  or input lines  520  may be conveyed to a desired one of output ports  522 .  
         [0040]    As a result of the foregoing arrangement, the three crossbar switches  501  through  503  comprise an optical switching arrangement which accepts  8  optical inputs and transmits 8 optical outputs  522 . However, the arrangement also accepts  8  inputs from a packet switch and outputs 8 outputs  510  to a packet switch. Thus, the resulting system is an optical switching arrangement which receives 16 inputs  508  and  520 , and transmits 16 outputs  510  and  522 , with a limitation that portions of the inputs and outputs must be optical or packets as shown. The foregoing architecture not only allows modular growth, but it permits the provisioning of both the optical and packet portions in one integrated application.  
         [0041]    [0041]FIG. 6 shows the provisioning of the optical switching arrangements of FIG. 5. As indicated in FIG. 6, a mirror  601  may be activated to switch the signal or may be passive such as mirrors  602 - 603  so that the optical signal passes through. In crossbar switch  503 , an input  533  would pass through all mirrors in its path until reaching one which is activated to deflect the signal downward out path  512 . Additionally, reference to FIG. 4, can be appreciated at any of the signals arriving may be passed through the optical engine or switched to the packet engine by appropriate provisioning of the optical arrangement via activating and deactivating the desired mirrors.  
         [0042]    In accordance with the above technique, larger switches may be grown in a modular fashion from smaller optical switching arrangements. The arrangement shown FIG. 5 maybe arranged in a hierarchy to build larger switches from the same size switching components.  
         [0043]    While the above describes the preferred embodiment of the invention, various modifications or additions will be apparent to those of skill in the art. Such modifications and additions are intended to be covered by the following claims.