Abstract:
A method for providing multi-wavelength switching. The method comprising receiving a plurality of signals through at least one input port, and separating the plurality of said signals into at least one wavelength signal set based on wavelengths, wherein a first wavelength signal set of said at least one wavelength signal sets corresponds to a first wavelength. The method further comprises providing a plurality of output lanes to at least one output port, and determining if two signals from said first wavelength signal set traveling on said first wavelength are scheduled output from an output port during an overlapping time period through said plurality of output lanes. The method further comprises determining if one of said plurality of output lanes is available during said overlapping time period when said two signals are schedule for said output port during the overlapping time period, wherein a first signal of said two signals is routed for output on an available lane if one of said plurality of output lanes of said output port is available.

Description:
RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 60/986,818 filed Nov. 9, 2007. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to optical networks, and, more particularly, to systems used for routing multi-wavelength optical signals. 
     BACKGROUND OF THE INVENTION 
     Over the last decade, the amount of information that is conveyed electronically has increased dramatically. As the need for greater communications bandwidth increases, the importance of efficient use of communications infrastructure increases as well. The emergence of dense-wavelength division multiplexing (DWDM) technology has improved the bandwidth problem by increasing the capacity of an optical fiber. In wavelength division multiplexing (WDM), channels are arranged by a predetermined wavelength interval, and signals are loaded on each channel. Also, a number of channels are optically multiplexed, and the signals are transmitted through an optical fiber. A receiver optically demultiplexes the channels according to their wavelengths and utilizes each channel separately. DWDM is now well established as a principal technology to enable large transport capacities in long-haul communications. 
     However, the increased capacity creates a serious mismatch with current electronic switching technologies that are designed to process individual channels within a DWDM link. In electronic switching, the optical fiber additionally requires a photoelectric converter for converting an optical signal into an electrical signal and an electro-optic converter for converting an electrical signal into an optical signal, which results in an increased cost. While electronic switching routers, such as internet protocol (IP) routers, can be used to switch data using the individual channels within a fiber, this approach implies that tens or hundreds of switch interfaces must be used to terminate a single DWDM fiber with a large number of channels. This could lead to a significant loss of statistical multiplexing efficiency when the parallel channels are used simply as a collection of independent links, rather than as a shared resource. 
     In order to solve such problems, there were several proposed solutions in the related art optical switching technologies, which do not convert the transferred optical signal into the electrical signal but processes the optical signal directly. Optical switching technologies based on wavelength routing (circuit-switching) of a limited pool of wavelengths don&#39;t make efficient use of the transmission medium when data traffic dominates the public network. This is the case today where the increasing demand for bandwidth is largely due to a spectacular growth in IP data traffic. All-optical packet switching would be an optimum transfer mode to handle the flood of optical IP packets to and from the Internet core in the most efficient way. However, a number of packet-switching operations (e.g. ultra fast pulsing, bit and packet synchronization, ultra-high-speed switching, buffering and header processing) cannot be performed optically, on a packet-by-packet basis today. 
     An optical burst switching (OBS) network makes use of both optical and electronic technologies. The electronics provides control of system resources by assigning individual user data bursts to channels of a DWDM fiber, while optical technology is used to switch the user data channels entirely in the optical domain. In the OBS, the length of a data packet can be variable and packet routing can be performed without an optical buffer by setting a path in advance using a control packet. 
     In the OBS network, generally, Internet protocol (IP) packets or data stream of any form inputted in an optical domain are gathered as a data burst in an edge node, and such data bursts are routed by way of a core node depending on their destinations or Quality of Services (QoS) and then sent to the destination nodes. Further, a burst header packet and the data burst are respectively transmitted on different channels and at an offset time. That is, the burst header packet is transmitted earlier than the data burst by the offset time and it reserves a optical path through which the data burst is transferred, so that the data burst can be transmitted through the optical network at a high speed without being buffered. 
     However, in the OBS network, data burst can be lost due to a contention in the optical switch. One optical burst switching scheme uses wavelength conversion to reduce the contention on output channels. Unfortunately, all optical wavelength converters may remain expensive now and in foreseeable future. The need for wavelength converter makes the cost of deploying OBS networks high. 
     In order to remove the wavelength conversion constraints in OBS networks, Time Sliced Optical Burst Switching (TSOBS) replaces switching in the wavelength domain with switching in the time domain. However, although the TSOBS router eliminates the wavelength converters, it uses more optical crossbars than a traditional OBS router, and also makes extensive use of fiber delay lines (FDLs) which are not required for traditional OBS routers. In addition, synchronizing time slots also presents a challenge. 
     Therefore, it is desirable to provide optical switching methods and systems providing multi-wavelength switching without wavelength conversion. The methods and systems discussed herein provide a lower cost option for fiber optic switching. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing and other considerations, the present invention relates to multi-wavelength switching. 
     In accordance with the present invention, there is provided methods to reduce the need for wavelength conversion in optical burst switching networks. The present invention provides statistical multiplexing performance. The present invention provides methods of constructing an optical router using small space switching matrix. The present invention provides methods for incremental deployment of wavelengths. The present invention provides methods for fast and efficient wavelength scheduling. The present invention provides methods for controlling the throughput. The present invention provides methods for controlling the latency. 
     Accordingly, methods for multi-wavelength switching are provided. The method comprises receiving a plurality of signals through at least one input port, and separating the plurality of said signals into at least one wavelength signal set based on wavelengths, wherein a first wavelength signal set of said at least one wavelength signal sets corresponds to a first wavelength. The method further comprises providing a plurality of output lanes to at least one output port, and determining if two signals from said first wavelength signal set traveling on said first wavelength are scheduled output from an output port during an overlapping time period through said plurality of output lanes. The method further comprises determining if one of said plurality of output lanes is available during said overlapping time period when said two signals are schedule for said output port during the overlapping time period, wherein a first signal of said two signals is routed for output on an available lane if one of said plurality of output lanes of said output port is available. 
     Yet another embodiment provides methods for multi-wavelength switching. The method comprises receiving a control signal corresponding to a data signal scheduled to arrive on a first wavelength through at least one input port; providing a plurality of output lanes to at least one output port, supporting at least one output wavelength on said plurality of output lanes, and maintaining status information on said plurality of output lanes for said at least one output wavelength. The method further comprises determining a destination output port for said data signal based on routing information in said control signal, and determining if one of said plurality of output lanes of said destination output port is available for an overlapping time with said data signal. The method further comprises selecting an available lane if one of said plurality of output lanes of said destination output port is available for said overlapping time, and routing said data signal to said selected output lane of said destination output port. 
     Yet another embodiment provides systems for multi-wavelength switching. The system comprises at least one input port, wherein a plurality of input signals are provided through said input port, at least one output port comprising of a plurality of output lanes, and at least one demultiplexer (DMUX), wherein said at least one DMUX separates said plurality of input signals into at least one wavelength signal set based on wavelength, wherein a first wavelength signal set of said at least one wavelength signal set corresponds to a first wavelength. The system further comprises a switch fabric routing said plurality of input signals, and a switch controller coupled to said switch fabric, said switch controller determines if contention is present for said first wavelength signal set, contention arising when two signals from said first wavelength set traveling on said first wavelength are scheduled for output during an overlapping time period through a first output port of said at least one output port, said switch controller determining if one of said plurality of output lanes of said first output port is available during said overlapping time period if contention is present for said first wavelength signal set, and said first signal of said two signals is routed for output on an available lane if one of said plurality of output lanes of said first output port is available. The system further comprises at least one multiplexer (MUX), wherein said at least one MUX combines signals scheduled for output on said plurality of output lanes into a modified signal set, wherein said modified signal sets is output through said first output port. 
     The foregoing has outlined some of the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which: 
         FIG. 1  illustrates an optical burst switching network; 
         FIG. 2  shows an example of transmitting a data burst through an optical burst switching network; 
         FIG. 3  shows the timing relationships between the burst header packet and the data burst; 
         FIG. 4  shows an optical core router; 
         FIG. 5  ( a ) shows an example of routing a set of data bursts through an optical core router without wavelength conversion capability; 
         FIG. 5  ( b ) shows an example of routing a set of data bursts through an optical core router with wavelength conversion capability; 
         FIG. 6  shows a general optical switching matrix; 
         FIG. 7  shows an optical switching matrix using limited range wavelength converter; 
         FIG. 8  ( a ) shows the architecture of a Time Sliced Optical Burst Switching (TSOBS) router; 
         FIG. 8  ( b ) shows the Optical Time Slot Interchanger (OTSI) module in a TSOBS router; 
         FIG. 9  shows a multi-lane optical burst switching network according to the present invention; 
         FIG. 10  shows a multi-lane optical core router; 
         FIG. 11  ( a ) shows multi-lane optical burst switching core network connected with multi-lane edge routers; 
         FIG. 11  ( b ) shows multi-lane optical burst switching core network connected with traditional electronic ingress edge routers; 
         FIG. 11  ( c ) shows multi-lane optical burst switching core network connected with traditional electronic egress edge routers; 
         FIG. 11  ( d ) shows multi-lane optical burst switching core network connected with traditional optical core routers; 
         FIG. 12  shows multi-lane optical core router connected in a ring configuration; 
         FIG. 13  shows multi-lane optical core router connected in a star configuration; 
         FIG. 14  ( a ) shows the multi-lane optical core router and the multi-lane edge router are integral parts of a router; 
         FIG. 14  ( b ) shows the integrated router is connected in a ring configuration. 
         FIG. 15  shows the multi-lane control wavelength and multi-lane data wavelengths; 
         FIG. 16  shows the multi-lane optical core router architecture; 
         FIG. 17  shows the architecture of multi-lane space switching matrix; 
         FIG. 18  ( a ) shows the architecture of the multi-lane switch controller; 
         FIG. 18  ( b ) shows a centralized multi-lane switch controller; 
         FIG. 19  shows the flow chart of the functions in the multi-lane burst header packet input processor; 
         FIG. 20  shows an example block diagram of the multi-lane burst header packet output processor; 
         FIG. 21  shows an example block diagram of the multi-lane scheduler; 
         FIG. 22  is an illustration of multi-lane data wavelength usage; 
         FIG. 23  illustrates multi-lane wavelength grouping; 
         FIG. 24  shows the structure of multi-lane status storage; 
         FIG. 25  ( a ) shows an example of scheduling a multi-lane data burst; 
         FIG. 25  ( b ) shows a multi-lane data burst is scheduled successfully; 
         FIG. 25  ( c ) shows another example of scheduling a multi-lane data burst; 
         FIG. 25  ( d ) shows that a multi-lane data burst is discarded; 
         FIG. 26  ( a ) shows a lane usage map; 
         FIG. 26  ( b ) shows an example of scheduling a multi-lane data burst using the lane usage map; 
         FIG. 26  ( c ) shows that an updated lane usage map after a multi-lane data burst is accepted; 
         FIG. 26  ( d ) shows another example of scheduling a multi-lane data burst using the lane usage map; 
         FIG. 26  ( e ) shows the multi-lane data burst is discarded; 
         FIG. 27  ( a ) shows the points that define the dip in the lane usage map; 
         FIG. 27  ( b ) shows the mini dip table that records a single dip in the lane usage map; 
         FIG. 27  ( c ) shows that the entire lane usage map can be recorded using a series of mini dip tables; 
         FIG. 28  ( a ) shows an example of scheduling a multi-lane data burst using the mini dip tables; and 
         FIG. 28  ( b ) shows only a single mini dip table needs to be accessed to schedule a multi-lane data burst. 
     
    
    
     For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures. 
     DETAILED DESCRIPTION 
     Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views. 
     Optical Burst Switching (OBS) networks rely on wavelength conversion to provide statistical multiplexing performance. The cost of wavelength converters will remain expensive in foreseeable future, making the cost to deploy OBS network prohibitively high. The methods described in this disclosure provide statistical multiplexing performance without using the expensive wavelength converters. By eliminating the need for wavelength converters, the present invention greatly reduces the cost for OBS deployment. 
       FIG. 1  shows an example of an optical burst switching network  100 . The optical burst switching network  100  includes multiple electronic ingress edge routers  120 , multiple optical core routers  110 , and multiple electronic egress edge routers  130  connected by wavelength division multiplexing (WDM) links  140 . The term WDM as used herein includes both dense wavelength division multiplexing (DWDM) and coarse wavelength division multiplexing. The electronic ingress edge router  120  and the electronic egress edge router  130  perform burst assembly and disassembly functions respectively, and serve as legacy interfaces between the optical core routers  110  and conventional electronic routers. 
       FIG. 2  ( a ) shows an example of routers connected by WDM links. A WDM link  140  includes multiple wavelengths  210 , and represents the total unidirectional transmission capacity (in bits per second) between two adjacent routers. Two adjacent routers are typically connected with a WDM link  140  in each direction. 
     In optical burst switching network  100 , wavelengths  210  in a WDM link  140  is divided into a set of control signals, such as control wavelength  230 , and a set of data signals, such as data wavelengths  240 , as illustrated in  FIG. 2  ( b ). At least one of the wavelengths  210  in a WDM link  140  should be assigned as a control wavelength  230 . A data burst  250  is the basic data transfer block in the optical burst switching network  100 . A data burst  250  can be a single data chunk, or a collection of data packets which are destined for the same destination electronic egress edge router  130 . Other attributes such as quality of service (QoS) requirements may also be considered when forming data bursts  250 . 
     In optical burst switching networks  100 , before a data burst  250  is launched on one of the data wavelengths  240 , a burst header packet  260  is launched on the control wavelength  230 . The burst header packet  260  carries routing information, as well as information specific to the optical burst switching network  100 . Examples of information contained in burst header packet  260  may include: (1) offset time, specifying the time difference between the transmission of the first bit of a burst header packet  260  and the transmission of the first bit of its associated data burst  250 ; (2) burst length or burst duration, specifying the duration of the data burst  250 ; (3) data wavelength identifier, specifying the data wavelength  240  on which the data burst  250  is transmitted; and (4) QoS, specifying the quality of service to be received by the data burst  250 . 
     An important feature of the optical burst switching network  100  is that the data burst  250  and the burst header packet  260  are transmitted and switched separately. The operation of the optical burst switching network  100  is described as follows. When data chunks or data packets arrive at the electronic ingress edge router  120 , they are assembled into data burst  250  based on their destination electronic egress edge router  130  addresses and other attributes such as QoS. Once the data burst  250  is formed, a burst header packet  260  is generated and sent on the control wavelength  230  at an offset time ahead of the data burst  250 . The burst header packet  260  is processed electronically at each optical core router  110 . Based on the information carried in the burst header packet  260 , the optical core router  110  dynamically sets up an optical path shortly before the arrival of the data burst  250 . The data burst  250  is not electronically processed in the optical core router  110 , and is passed to the output specifying the data wavelength  240  as a pure optical signal. This process continues as the data burst  250  traverse the optical burst switching network  100  till it reaches the electronic egress edge router  130 , where the data burst  250  is disassembled back into data chunks or data packets. 
       FIG. 3  shows the relationships between the burst header packets  260  and their associated data bursts  250 . In this example, wavelength  210  w 0  is assigned as the control wavelength  230  to send burst header packets  260 , and wavelength  210  w 1  to w h  are assigned as data wavelengths  240 .  FIG. 3  shows that data burst  1   310  and data burst  2   320  are traveling on data wavelength  240  w 1  and w 2 , respectively, while burst header  1   330  and burst header  2   340  are traveling on control wavelength  230  w 0 .  FIG. 3  also illustrates the offset time between burst header packet  1   330  and data burst  1   310 , and the length (duration) of data burst  1   310 . 
     Optical burst switching processes burst header packets  260  electronically, while providing ingress-egress optical paths in the optical burst switching network  100 . Each burst header packet  260  carries necessary routing and optical burst switching network  100  specific information about the associated data burst  250  such that the data burst  250  can pass through the optical core router  110  as an optical signal. 
       FIG. 4  shows an optical core router  110  connected to WDM links  140 . Incoming WDM links  430  and outgoing WDM links  440  are connected to the input ports  410  and the output ports  420  of the optical core router  110 . The data wavelengths  240  in the WDM links  140  are connected to an optical switching matrix  450  in the optical core router  110 . The control wavelengths  230  are connected to a switch control unit  460 . The burst header packets  260  sent on the control wavelength  230  are converted to electronic signals and processed electronically inside the switch control unit  460 . Based on the information carried in the burst header packets  260  and outgoing WDM link  140  status, the switch control unit  460  sets up and tears down optical paths at appropriate times to allow data bursts traveling on data wavelengths  240  to pass through the optical core router  110  without converting to electronic signals. 
     In optical burst switching network  100 , data bursts  250  are generally launched without pre-established lightpaths. Lightpaths are set up on-the-fly as data burst  250  approaches the optical core router  110 . Contention occurs when two bursts traveling on the same wavelength compete for the same output port. When contention cannot be resolved, one of the contenting bursts has to be dropped, despite the fact that it has consumed upstream network resources. Therefore, burst loss probability is a key performance measure in optical burst switching network  100 . Contention can be greatly reduced by converting one of the incoming bursts to a different wavelength. Therefore, wavelength conversion is generally required to achieve acceptable performance in optical burst switching networks  100 . 
     In the example illustrated in  FIG. 5  ( a ), data burst  3   530  and data burst  4   540  destined for the same output port are coming on data wavelength  240  w 1  from two different input ports. In  FIG. 5  ( a ), the optical core router  110  does not have wavelength conversion capability. Since data burst  3   530  and data burst  4   540  overlap in time and are on the same data wavelength  240 , only data burst  3  is routed successfully, and data burst  4  has to be discarded. 
     In  FIG. 5  ( b ), the optical core router  110  has wavelength conversion capability. In this case, data burst  4   540  is converted to data wavelength  240  w 2 . Both data burst  3   530  and data burst  4   540  are routed successfully. 
     As we can see, wavelength conversion reduces the burst loss probability, which is the key performance measure of optical burst switching network. In order to reduce the burst loss probability, traditional optical burst switching networks  100  rely on wavelength conversion for contention resolution. When two bursts competing for the same output port  420  at an optical core router  110 , one of the bursts  250  needs be converted to a different wavelength so that both bursts can be carried on the outgoing WDM link  140  successfully. Because dense wavelength division multiplexing (DWDM) technology allows each fiber to carry tens or hundreds of wavelengths, a burst can be statistically multiplexed onto any of the data wavelengths  240  on the outgoing WDM link  140 , achieving low burst loss probability. 
     However, as the technology stands now, the price for wavelength converters remains high. This becomes one of the major obstacles that prevent optical burst switching network  100  from widespread deployment. 
     DWDM technology allows for expansion in transmission link capacity. For example, optical link capacity can be easily increased from 10 Gb/s to 1 Terabits/s by lighting up 100 wavelengths over the same fiber, assuming each wavelength channel is at 10 Gb/s. With the current technology, it is feasible to support more than 256 wavelength channels per fiber. Unfortunately, this technology trend has several negative implications on the optical router designs. 
     1) A large number of wavelengths may require large switching matrix. If an optical core router  110  has d input ports  410  and d output ports  420 , each of which is connected to a WDM link  140  with M data wavelengths  240 , the size of the optical switching matrix  450  is N=d×M. For example, if d=8 and M=256, the size of the optical switching matrix  450  is 2048×2048. This has a serious implication on the implementation of optical core routers  110 . For example, it is more difficult to realize large optical switching matrix  450  because of technology constraints such as insertion loss. The largest switching matrix available today is 1024×1024. In addition, large switching matrix is much more expensive than small switching matrix, which can drive the cost of optical core routers  110  even higher. 
     2) Adding additional wavelengths to an existing system may require replacement of an existing switching matrix in the optical core router  110 . As we can see from the calculation above, the size of the optical switching matrix  450  is directly related to the number of data wavelengths  240  per input port  410 . For example, a 32×32 optical switching matrix  450  is needed if d=8 and M=4. If we want to use 16 data wavelengths  230  instead, we need to replace the existing optical switching matrix  450  with a 128×128 optical switching matrix  450 . Since a large optical switching matrix  450  is much more expensive, there is little incentive for network service providers to provision a large optical switching matrix  450  in the optical core router  110  for future wavelength expansion. This basically limits the expandability of optical core routers  110 . 
     An optical switching matrix  450  in the optical core router  110  is able to switch data burst  250  from an incoming WDM link  430  to an outgoing WDM link  440 . The cost of constructing an optical core router  110  is mostly determined by the cost for the optical switching matrix  450 . Several optical switching architectures have been proposed for OBS networks  100  in order to reduce the cost of the optical switching matrix  450 . 
       FIG. 6  shows a general structure of optical switching matrix  450 . The optical demultiplexer (DMUX)  610  separates wavelengths coming from the optical fiber  600 . Input wavelengths are converted to free output wavelengths using tunable wavelength converters (TWC)  620 . A nonblocking space switch  630  connects the input wavelengths to the desired outputs as well as the appropriate output buffers that are realized using fiber delay lines (FDLs)  640 . The multiwavelength bandpass filter  650  combines the wavelengths onto the outgoing optical fiber  600 . 
     A rearrangably nonblocking switch design using Arrayed Waveguide Grating (AWG)  710  router and limited range wavelength converters (LWC)  720  is shown in  FIG. 7 . The dark dots in the figure represent LWCs  720 . The construction uses twice as many wavelength converters as the structure shown in  FIG. 6 . However, in this design, the less expensive limited range wavelength converters  720  instead of full-range tunable wavelength converters  620  can be used. 
     The above mentioned architectures rely on wavelength converters. Unfortunately, wavelength converter is the largest single cost component in an optical core router  110 . 
     In order to remove the need for costly wavelength conversion, Time Sliced Optical Burst Switching (TSOBS) was proposed as a variant of optical burst switching by replacing switching in the wavelength domain with switching in the time domain. In TSOBS, data wavelengths  240  consist of a repeating frame structure, which is further divided into time slots of fixed length. A data burst  250  can occupy one time slot in each of the successive frames. By allowing time slot shifting, TSOBS provides statistical multiplexing performance without using wavelength conversions. 
     The overall TSOBS router  800  architecture is shown in  FIG. 8  ( a ). The synchronizer (SYNC)  810  at each input synchronizes the incoming frame boundaries to local timing reference by using variable delay lines. The Optical Time Slot Interchanger (OTSI)  820  provides the required time domain switching for all data wavelengths  240 . The OTSI  820  also separates the data wavelengths  240  and forwards them to corresponding optical crossbars  830 . The optical crossbars  830  provide space switching to the individual data wavelengths  240 , respectively. The outputs from the optical crossbars  830  are fed into a set of passive optical multiplexers  730 , which combines the wavelengths on the output fiber  600 . The OTSI  820  is the key building block of the TSOBS router  800 .  FIG. 8  ( b ) shows a high level design of the OTSI  820 . Each OTSI  820  uses a set of optical demultiplexers  610 , optical crossbars  830 , Fiber Delay Lines (FDLs)  640  and optical multiplexers  730  for shifting in time slots. 
     Note that in a TSOBS router  800 , optical crossbars  830  are used in both the OTSI  820  and the top level TSOBS router  800  architecture. In addition, in order to provide nonblocking performance, N fiber delay lines  640  are needed for each data wavelength  240 , where N is the number of time slots in a frame. Although the TSOBS router  800  eliminates the tunable wavelength converters  620 , it uses more optical crossbars  830  than a traditional OBS router, and also makes extensive use of FDLs  640  which are not required for traditional OBS core routers  110 . In addition, synchronizing time slots also presents a challenge. 
     Traditional OBS networks  100  use wavelength conversion to resolve output contentions. Although this approach provides efficient statistical multiplexing performance, the cost for wavelength converters  620  in the optical core routers  110  has become the major cost in deploying OBS networks  100 . 
     In the present disclosure, several embodiments of systems and methods for providing improved multi-wavelength optical switching are discussed herein. The embodiments provide statistical multiplexing performance without the need to use wavelength converters  620 . The signaling protocol used by the embodiments is compatible with the one used in traditional OBS networks  100 . Therefore, routers in these embodiments can easily interface with traditional OBS optical core routers  110  without additional overhead. 
     The improved multi-wavelength optical switching reduces the burst loss due to output channel contention by providing statistical multiplexing performance and reduce the cost of constructing an OBS router. The improved switching provides an OBS router architecture using a plurality of optical space switching matrix with small number of optical crosspoints. The improved switching allows incremental deployment of wavelengths, efficient control over the wavelength channels, and fast scheduling of wavelength channels. Further, the improved switching uses wavelengths efficiently, allows control of the transmission latency, and allows control of the transmission throughput. 
     In the several embodiments discussed herein, the improved multi-lane optical switching may be discussed with reference to a Multi-Lane Optical Burst Switching (ML-OBS) network  900 . However, the features of the embodiments discussed herein may be applied to any form multi-lane optical switching. The scope of the specifications and claims are in no way limited to the particular configurations discussed herein, except as specifically recited in the claims. 
     In a multi-lane optical burst switching (ML-OBS) core network  900  shown in  FIG. 9 , two adjacent multi-lane optical core routers  910  are connected by a multi-lane WDM link  920  in each direction. A multi-lane WDM link  920  comprises of a plurality of WDM lanes  930 , each of which is an optical fiber  600  that carries at least one of a plurality of wavelengths  210 . The multi-lane WDM link  920  can be constructed using one or multiple multi-fiber optical cables, or a collection of individual optical fibers  600 . 
     As shown in  FIG. 10 , an incoming multi-lane WDM link  920  is connected to a multi-lane input port  1010  of a multi-lane optical core router  910 . An incoming data wavelength  240  to the multi-lane optical core router  910  can be switched onto any of the WDM lanes  930  in the desired multi-lane output port  1020  of the multi-lane optical core router  910  without the need for wavelength conversion. By engineering the size of the lanes  930  properly, desired statistical multiplexing performance can be achieved without encountering the need for wavelength conversion. 
     In a preferred embodiment, the multi-lane core network  900  is connected to multi-lane edge routers  1110  using multi-lane WDM links  920  as illustrated in  FIG. 11  ( a ). 
     In another embodiment shown in  FIG. 11  ( b ), a multi-lane input port  1010  of a multi-lane optical core router  910  is connected to at least one of a plurality of traditional OBS electronic ingress edge routers  120  using WDM links  140 . 
     In another embodiment shown in  FIG. 11  ( c ), a multi-lane output port  1020  of a multi-lane optical core router  910  is connected to at least one of a plurality of traditional OBS electronic egress edge routers  130  using WDM links  140 . 
     In another embodiment shown in  FIG. 11  ( d ), a multi-lane optical core router  910  is connected to at least one of a plurality of traditional OBS optical core routers  110  using WDM links  140 . 
     In another embodiment shown in  FIG. 12 , multi-lane optical core routers  910  are connected in a ring structure using multi-lane WDM links  920 . 
     In another embodiment shown in  FIG. 13 , the multi-lane optical core routers  910  are connected to multi-lane edge routers  1110  in a star structure. 
     In another embodiment shown in  FIG. 14  ( a ), multi-lane optical core router  910  and multi-lane edge router  1110  are integral parts of a multi-lane router  1410 . 
     In another embodiment shown in  FIG. 14  ( b ), integrated multi-lane routers  1410  are connected in ring structure using multi-lane WDM links  920 . 
     ML-OBS core network  900  can use any specifically designed protocols, or use the preferred embodiment described as follows. 
       FIG. 15  shows the multi-lane control wavelength  1530  and multi-lane data wavelengths. Ingress multi-lane edge router  1110  receives data packets or chunks of data from incoming interfaces. Based on the destination multi-lane edge router  1110  address, and possibly along with the QoS level, data are assembled into a multi-lane data burst  1510 . For each assembled multi-lane data burst  1510 , a multi-lane burst header packet  1520  is generated and forwarded on a multi-lane control wavelength  1530  at an offset time ahead of its associated multi-lane data burst  1510 . The multi-lane control wavelengths can be wavelengths in a separate optical fiber  600 , or one or several wavelengths  210  in the WDM lanes  930 . The multi-lane burst header packet  1520  carries information common to traditional OBS network  100  such as routing information, burst duration, and offset time. In addition, the multi-lane burst header packet  1520  also carries multi-lane optical burst switching network  900  specific information such as the lane identifier (ID). A multi-lane data burst  1510  can be transmitted on at least one wavelength  210  on at least one of a plurality of lanes  930 . 
     In one embodiment, a multi-lane data burst  1510  is transmitted on a single data wavelength  1540  on a single WDM lane  930 . In this case, the multi-lane burst header packet  1520  includes information about the lane ID and the wavelength ID of its associated multi-lane data burst  1510 . 
     In another embodiment, a multi-lane data burst  1510  is transmitted on multiple multi-lane data wavelengths  1540  on a single WDM lane  930 . In this case, the multi-lane burst header packet  1520  includes information about the lane ID, and the wavelength range if the wavelength IDs are consecutive, or individual wavelength IDs otherwise. 
     In another embodiment, a multi-lane data burst  1510  is transmitted on the same multi-lane data wavelength  1540  on multiple lanes  930 . In this case, the multi-lane burst header packet  1520  includes information about the wavelength ID, the lane ID range if the lane IDs are consecutive, or individual lane IDs otherwise. 
     In another embodiment, a multi-lane data burst  1510  is transmitted on multiple data wavelengths  210  on multiple WDM lanes  930 . In this case, the multi-lane burst header packet  1520  includes information about the wavelength range if the wavelength IDs are consecutive, or individual wavelength IDs otherwise, and the lane ID range if the lane IDs are consecutive, or individual lane IDs otherwise. 
     The assignment of the lane IDs and the wavelength IDs can be based on different criteria such as random select, throughput requirement, latency requirement, and destinations. The assignment of the lane IDs and wavelength IDs can be centralized or decentralized. 
       FIG. 16  shows an example block diagram of a multi-lane optical core router  910  according to the present invention. The multi-lane optical core router  910  includes a multi-lane space switching matrix  1610  and a multi-lane switch controller  1620 . The multi-lane space switching matrix  1610  separates the multi-lane control wavelengths  1530  from multi-lane data wavelengths  1540 , sends/receives the multi-lane control wavelengths  1530  to/from the multi-lane switch controller  1620 , and routes optical signals according to the configuration commands from the multi-lane switch controller  1620 . 
     There are many ways to construct the multi-lane space switching matrix  1610 , as long as an incoming wavelength on an incoming lane can be switched to an outgoing lane on the same wavelength.  FIG. 17  shows the preferred embodiment which uses separate optical switching planes  1710  for each individual wavelength. In this embodiment, at the input of the multi-lane optical core router  910 , each lane  930  in the multi-lane WDM link  920  is fed into an optical demultiplexer  610 . The optical demultiplexer  610  separates the wavelengths and sends the individual wavelengths to their corresponding optical switching planes  1710 . The outputs from the optical switching planes  1710  are then combined onto the lanes  930  on the outgoing multi-lane WDM link  920 . Note that in this embodiment, each wavelength is switched separately. Therefore, we can use small parallel optical switching planes  1710 , rather than a large switching matrix. This further reduces the integration cost. Additional optical switching planes  1710  can be incrementally installed to support more wavelengths. Most importantly, the optical switching matrix  1610  does not need wavelength converters, making the cost of constructing a multi-lane optical core router  910  a fraction of what is needed to build a traditional OBS optical core router  110 . 
       FIG. 18  ( a ) shows a first embodiment  1800  of the multi-lane switch controller  1620  according to the present invention. The multi-lane switch controller  1620  includes multiple optical to electrical (O/E) converters  1810 , multiple multi-lane burst header packet input processors  1820 , a switch  1830  (e.g. a cross-bar switch, a shared memory switch, or any other suitable switch), multiple multi-lane burst header packet output processors  1840 , and multiple electrical to optical (E/O) converters  1850 . 
       FIG. 18  ( b ) show another embodiment  1860  of the multi-lane switch controller  1620  where a centralized multi-lane burst header packet processor  1870  is used. The functions in the multi-lane burst header packet processors  1870  include all necessary burst header packet processing described in the distributed version. While the following descriptions discussed herein are focused on the distributed version illustrated in  FIG. 18  ( a ), the scope of the specifications and the claims are in no way limited to the specific embodiments discussed herein. 
     When a multi-lane burst header packet  1520  traveling on the multi-lane control wavelength  1530  enters the multi-lane switch controller  1620 , it first enters an O/E converter  1810  and undergoes an optical to electronic conversion. Next the multi-lane burst header packet  1520  enters the multi-lane burst header packet input processor  1820 . 
     The input processor flow chart  1900  shown in  FIG. 19  describes the main functions performed in the multi-lane burst header packet input processor  1820 . The multi-lane burst header packet input processor  1820  first record the arrival time of the multi-lane burst header packet  1520  to the multi-lane switch controller  1620 . The arrival time, along with the offset time carried in the multi-lane burst header packet  1520 , is used to compute the multi-lane data burst  1510  arrival time. The input port  410 , the WDM lane  930  and the multi-lane control wavelength  1530  that the multi-lane burst header packet  1520  arrives on is also recorded. This information is used to configure the multi-lane space switching matrix  1610 , as well as to compensate for the discrepancy between the traveling time of the multi-lane burst header packet  1520  and the multi-lane data burst  1510 . 
     The multi-lane burst header packet input processor  1820  then extracts information from the multi-lane burst header packet  1520  about the associated multi-lane burst. Some example fields include the wavelength ID, the lane ID, the offset time, the burst length and QoS parameters. 
     The multi-lane data burst arrival time T_ba can be calculated as follows: T_ba=T_ha+Offset−T_adjust, where T_ha is the recorded multi-lane burst header packet arrival time, Offset is the offset field carried in the multi-lane burst header packet  1520 , and T_adjust is the traveling time difference between the multi-lane burst header packet  1520  and the multi-lane data burst  1510  due to the difference in the length of the optical fibers  600  in different WDM lanes  930 , the difference in propagation speed on difference wavelengths, and any additional delay that the multi-lane burst header packet  1520  experiences in circuitry before the arrival time is recorded. If input fiber delay lines (FDLs)  640  are installed at the input port of the multi-lane optical core routers, the additional fiber delay as well as any other delay that the multi-lane data, burst  1510  experiences before it reaches the multi-lane space switching matrix  1610  should also be included in T_adjust. T_adjust can be negative in value. 
     The multi-lane burst header packet input processor  1820  then does a route lookup and burst classification according to the routing information carried in the multi-lane burst header packet  1520 . The results from the route lookup determine which output port  420  the multi-lane data burst  1510  needs to be forwarded to. In the distributed control scheme shown in  FIG. 18  ( a ), each multi-lane burst header packet output processors  1840  manages the multi-lane resources for a particular output port  420 . In this case, the multi-lane burst header packet  1520  needs to be sent to the corresponding multi-lane burst header packet output processors  1840  for further processing. The multi-lane burst header packet  1520  is then placed in a queue waiting to be transferred across the switch  1830  to the desired multi-lane burst header packet output processors  1840 . 
     The multi-lane burst header packet output processor  1840  handles multi-lane burst scheduling and configuration of the multi-lane space switching matrix  1610 . An example block diagram of the multi-lane burst header packet output processor  1840  is shown in  FIG. 20 . 
     When a multi-lane burst header packet  1520  is received from the switch  1830  by the multi-lane burst header packet output processor  1840 , it first enters the pre-processor  2010 . The pre-processor  2010  extracts the multi-lane data burst  1510  information from the header packet  1520 , and stores the entire packet  1520  in the multi-lane burst header packet memory  2050 . 
     The extracted multi-lane data burst  1510  information is used to generate a multi-lane burst scheduling request which is forwarded to the multi-lane scheduler  2020 . The multi-lane scheduler  2020  allocate an available lane  930  on the wavelength that the multi-lane data burst  1510  is arriving on, and generates a multi-lane switch configuration request to the multi-lane switch configuration controller  2040 . The multi-lane switch configuration controller  2040  uses the information in the configuration request, such as the incoming lane ID, incoming wavelength, input port, outgoing lane ID, outgoing wavelength, time to connect, and time to disconnect, to set up and tear down an optical path in the multi-lane space switch matrix  1610 . The post-processor  2030  reads the multi-lane burst header packet  1520  from the packet memory  2050 , modifies the corresponding fields such as the offset, outgoing lane, or the like, and sends the updated multi-lane burst header packet  1520  to the E/O converter  1850 . 
       FIG. 21  shows an example block diagram of the multi-lane scheduler  2020 . When a multi-lane burst scheduling request is received by the multi-lane scheduler  2020 , it is first placed in a request queue  2110 . Based on different objectives, the requests in the request queue can be maintained in the order that the requests arrive (FIFO order), the order that the multi-lane data burst  1510  arrive, some particular orders that support Quality-of-Service (QoS), or any other suitable order. The request queue  2110  is then accessed by the multi-lane scheduling module  2120 . The multi-lane scheduling module  2120  uses the multi-lane data burst  1510  information in the scheduling request to select an outgoing lane to send the multi-lane data burst  1510 . The multi-lane status storage  2130  contains information about the wavelength usage in each lane, and is used by the multi-lane scheduling module  2120  to schedule the incoming multi-lane data bursts  1510 . 
       FIG. 22  is an illustration of multi-lane data wavelength usage. The durations occupied by the scheduled bursts  2210  are not available for new burst scheduling requests. 
     Since managing a large number of wavelengths and lanes is a challenge, the present invention takes advantage of the intrinsic characteristics of the multi-lane space switching matrix  1610  and partitions the wavelengths into smaller groups according to the wavelengths. 
       FIG. 23  shows the result of the wavelength grouping. According to the present invention, the same wavelengths from different lanes are placed into the same wavelength group  2310 . The lane status of each wavelength group  2310  is recorded in the multi-lane wavelength status storage  2410  as shown in  FIG. 24 . 
     The reason for such partitioning is explained as follows. When the multi-lane space switching matrix  1610  is not equipped with wavelength converters, an incoming multi-lane data burst  1510  can only be switched to any of the lanes  930  on the same wavelength as the one which the burst  1510  is arriving on. To find a proper lane for the incoming burst  1510 , the multi-lane scheduling module only needs to search for an idle lane on that particular wavelength for the duration of the multi-lane data burst  1510 . If such lane  930  is found, the burst  1510  is scheduled to be transmitted on that lane  930 . If no lane  930  is available, then the burst  1510  may have been discarded or may require wavelength converters  620  and/or fiber delay lines  640  to shift the wavelength or time domain. The present invention focus on embodiments that do not use wavelength converters  620  and/or fiber delay lines  640 . However, it should be noted that the present invention does not forbid the use of such components. 
     As shown in  FIG. 24 , the multi-lane status storage  2130  is organized as a set of multi-lane wavelength status storages  2410 , each of which contains the lane  930  status of a particular multi-lane data wavelength  1540 . The multi-lane wavelength status storage  2410  can be implemented using SRAM, DRAM, SDRAM or flip-flops. If the multi-lane data burst  1510  is transmitted on a single multi-lane data wavelength  1540 , only the multi-lane wavelength status storage  2410  of that particular wavelength needs to be accessed. If the multi-lane data burst  1510  spans across multiple wavelengths  1540 , then a subset of the multi-lane wavelength status storages  2410  needs to be accessed. 
       FIG. 25  ( a ) shows an example of scheduling data burst B 1   2510  that arrival on wavelength W 1 . In this case, only the wavelength group for W 1  needs to be accessed. Since Lane  1   2520  is available for the duration of the data burst B 1   2510 , B 1   2510  is scheduled on Lane  1   2520  of wavelength W 1  as shown in  FIG. 25  ( b ). 
       FIG. 25  ( c ) shows an example of scheduling data burst B 2   2530  that arrival on wavelength W 1 . Since no lane is available for the duration of B 2   2530 , B 2   2530  is discarded as shown in  FIG. 25  ( d ). 
     The present invention uses a novel way of managing the lane status information to allow fast efficient burst scheduling. Instead of managing individual lane status, the present invention keeps track of an aggregated lane usage map  2610  for each wavelength group  2310  as illustrated in  FIG. 26  ( a ). The lane usage map  2610  represents the total number of lane in use for any time instance in each wavelength group  2310 . The lane usage map includes a set of dips  2620 , which are consecutive regions where the lane usage is below the maximum number lanes  930  in the wavelength group  2310 . 
     The lane usage map  2610  can be used to efficiently determine if an incoming burst can be scheduled or not, and which lane  120  should be assigned to the multi-lane data burst  1510 .  FIG. 26  ( b ) shows an example of scheduling data burst B 3   2630 . Since the entire data burst B 3   2630  fits the opening of the dip, B 3   2630  can be scheduled. In this case, Lane  1  is picked as shown in  FIG. 26  ( c ). The lane usage map  2610  is updated accordingly. 
       FIG. 26  ( d ) is another example of scheduling data burst B 4   2640 . Since the duration of B 4   2640  does not fit in the opening of the dip  2620 , no lane  930  can accommodate B 4   2640 . Therefore, B 4   2640  is discarded as shown in  FIG. 26  ( e ). 
     The dip  2620  is characterized by the beginning time and ending time of the lane usage level as shown in  FIG. 27  ( a ).  FIG. 27  ( b ) shows an example data structure of a mini dip table  2710  which can record the information about a single dip  2620 .  FIG. 27  ( c ) illustrates how a complete lane usage map  2610  can be recorded using a set of mini dip tables  2710 . 
       FIG. 28(   a ) illustrates that data burst B 5   2810  needs to be scheduled using the lane usage map. As shown in  FIG. 28  ( b ) since the beginning time of B 5   2810  falls into dip C  2830 , only mini dip table C  2820  needs to be accessed to determine if B 5   2810  can be scheduled, and if yes, which lane  930  can be assigned to burst B 5   2810 . 
     Note that the lane usage map is stored in some storage elements such as SRAM, DRAM, SDRAM, flip flop, or the like. The storage elements are accessed by some triggering events such as a match in the wavelengths, a match in time duration, a clock, and/or some other external events. When a burst is scheduled on the lane, the lane usage map  2610  is updated by updating at least one of the mini dip tables  2710 . When a new dip  2620  is created, an additional mini dip table  2710  is needed to record the information about the dip  2620 . When a dip  2620  becomes too small to be useful (such as fitting a minimum size burst), the mini dip table  2710  that represents such dip  2620  can be recycled. The mini dip table  2710  can be statically or dynamically managed. For fast access to the mini dip table  2710 , some indexing mechanisms can be used. One embodiment of the indexing mechanism is a tree structure. Another embodiment of the indexing mechanism is to use summary bits. The pointer to the storage location is calculated based on some triggering event such as a scheduling request, the transmission request, a clock, or external events. The calculated pointer is used to read some storage locations to make a decision. The decision may also trigger some events that cause a second pointer to be calculated. The second pointer is used to access and possibly modify data in some storage locations. The storage locations are dynamically managed and can be reconfigured for new use. Since the data stored in the storage locations represent are time sensitive, old data entries that represent past time are of no use, and, therefore, are recycled into the free entry list. 
     The above discussion of the invention is directed to multi-lane optical burst switching network. It should be noted, however, the invention is applicable to other types of networks, including traditional optical burst switching network, reconfigurable wavelength routed network, optical packet switching network, and electronically switched packet networks. The multi-lane optical space switching matrix  1610  can be replaced with a electrically switched crossbar switch. The invention discussed above, including the separate switching planes for each wavelength, allows more switching planes to be incrementally deployed to allow for more wavelengths as demand increases. The methods for wavelength grouping and the lane usage map are applicable to other systems that allow for subgroup partitioning such as routers using limited range wavelength converters  720 , and DRAM banks. Although the burst scheduling method disclosed in the invention is designed for scheduling within a wavelength group, it is directly applicable to the burst scheduling problem in traditional optical burst switching network. The present invention is also applicable to Wide Area Network (WAN), Virtual Private Network (VPN), cloud computing, storage area network, optical backplane, multi-processor, and blade server communication. The present invention is also applicable to systems that require resource allocation. 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
     From the foregoing detailed description of specific embodiments of the invention, it should be apparent that a system for optical switching that is novel has been disclosed. Although specific embodiments of the invention have been disclosed herein in some detail, this has been done solely for the purposes of describing various features and aspects of the invention, and is not intended to be limiting with respect to the scope of the invention. It is contemplated that various substitutions, alterations, and/or modifications, including but not limited to those implementation variations which may have been suggested herein, may be made to the disclosed embodiments without departing from the spirit and scope of the invention as defined by the appended claims which follow.