Patent Abstract:
The invention provides an apparatus and method for transparently transporting four plesiochronous Gigabit Ethernet, Fibre Channel or other packet-based data signals over a network. Multiple plesiochronous Gigabit Ethernet data streams are aggregated onto an independent clock source at an ingress circuit through the use of transparent IDLE character insertion. The independent clock is selected such that the output data rate is greater than the composite input data rate of all the plesiochronous data streams. The signals are encapsulated with forward error correction and mapped to a reciprocal FEC interface prior to transport. An egress circuit at the receiving end recovers the modulated signal and extracts the data stream. Each independent data stream is mapped to a local clock domain via IDLE character insertion or removal. Therefore, the input and output signals are transparent and identical in content.

Full Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/436,401, filed Dec. 24, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a computer system that permits multiplexing and transparent transportation of multiple Gigabit Ethernet, Fibre Channel and other packet based data streams without protocol conversion over a high-speed data channel with Forward Error Correction.  
         BACKGROUND OF THE INVENTION  
         [0003]    Gigabit Ethernet (GBE) and Fibre Channel (FC) dominate the enterprise data communications market today. Gigabit Ethernet is a dominant player in high-speed Local Area Network (LAN) backbones and server connectivity. Fibre Channel is the dominant protocol today for connecting Storage Area Networks (SAN). There are other protocols such as FICON that have the same physical layer interface as Fibre Channel and can be transported using the methods described here. Gigabit Ethernet and Fibre Channel protocols enable transmission of high-speed signals across geographically disperse computers and storage systems.  
           [0004]    Traditionally, file servers with large external disks or disk farms using the SCSI standard have been used to support applications requiring large amounts of data storage. As applications increased, the storage system capacities and bandwidth (data transfer speed) requirements increased. The SCSI standard limitations made scaling difficult. The servers could only access data on devices directly attached to them. Failure of the server or SCSI hardware could cause an access failure. Also, SCSI supports only a finite number of devices and is therefore not scalable. The parallel structure of SCSI results in distance limitations that require equipment to be co-located.  
           [0005]    Storage Area Networks (SAN) were implemented to overcome the limitations of the SCSI architecture. The SAN is a network between the servers and the storage devices. A SAN allows multiple servers to access any storage device. This increases fault tolerance and overcomes the distance limitation since the server and storage do not need to be co-located. The dominant networking technology for implementing SAN is Fibre Channel.  
           [0006]    Fibre Channel technology [ANSI X3T11] was designed to enable high-speed data transfer between computer systems and storage devices. It supports common transport protocols including Internet Protocol and SCSI. It supports high-speed data transfer at standard rates of 1 Gbps, 2 Gbps, 4 Gbps, and 10 Gbps. It also supports communications across extended distances enabling corporations to have off-site storage thus enabling applications like disaster recovery and business continuity.  
           [0007]    The Ethernet standard defined by IEEE 802.3 has been the dominant networking protocol since its inception in the early 1970&#39;s. Ethernet has the highest number of installed ports and provides the greatest cost performance of all the networking protocols. Fast Ethernet boosted the transmission speed of Ethernet from 10 Mbps to 100 Mbps. Gigabit Ethernet builds on top of Fast Ethernet and increases the speed to 1 Gbps.  
           [0008]    The Gigabit Ethernet protocol, which was standardized in June 1998, combines the networking features of Ethernet and the physical interface of Fibre Channel. IEEE 802.3 Ethernet and ANSI X3T11 Fibre Channel were merged to accelerate the Ethernet physical interface from 100 Mbps to 1 Gbps. It allows higher speed communications while leveraging the knowledge base of Ethernet for manageability and maintainability. Leveraging the two technologies allows the standard to take advantage of the existing high speed Fibre Channel physical interface while maintaining compatibility with IEEE 802.3 Ethernet.  
           [0009]    Gigabit Ethernet itself can also be used to connect SAN. Recent advancements in SCSI have resulted in the iSCSI standard. This standard connects SAN via Gigabit Ethernet protocol.  
           [0010]    Gigabit Ethernet adopted the 8B/10B -encoding scheme from Fibre Channel FC-1 layer. The 1 Gbps Ethernet Data or the 800 Mbps Fibre Channel data are 8b/10b encoded to generate output data rates of 1.25 Gbps and 1.0625 Gbps respectively. FC-1 defines the transmission protocol, serial encoding/decoding, special characters, and error control. Encoding the data has several advantages. It maintains DC balance, enhances bit-level clock recovery, enables error correction, and allows separation of data and control characters.  
           [0011]    Gigabit Ethernet and Fibre Channel use disparity in the FC-1 layer to maintain DC balance. Depending on the DC balance, positive or negative disparity is chosen when converting from 8b to 10b. The disparity is adjusted to maintain the DC balance at zero (equal number of ones and zeroes in the signal). Positive or negative disparity is chosen to make the DC balance more positive or more negative depending on the error. Alternate sets of control characters are transmitted depending on disparity chosen. Gigabit Ethernet may use either positive or negative running disparity at the beginning of transmission. The Fibre Channel specification fixes the beginning running disparity as negative.  
           [0012]    From a transport perspective, the data may be sent in the 8b format or 10b format. However, since Ethernet can choose either positive or negative beginning disparity, if the data is sent in the 8b mode, it is no longer transparent. If user defined control characters are inserted that do not have an alternate for disparity, then transparency may be lost. Therefore it is optimal to send Ethernet data in the 10 b mode. Since the Fibre Channel specification defines the beginning running disparity as negative always, Fibre Channel may be sent in either 8b or 10b mode. Sending in the 8b mode reduces the amount of data sent and has advantages in terms of reducing credit-buffering requirements in flow control implementations.  
           [0013]    An aggregation function is required to multiplex multiple Gigabit Ethernet data streams and Fibre Channel data streams over one high-speed optical link. The speed of data transmission over optical networks has increased drastically in recent years. Consequently, as new high-speed equipment is connected into optical networks, it is often desirable to multiplex lower speed equipment into the higher speed network for transport in order to take advantage of the transport capacity at the higher speed.  
           [0014]    Multiplexing slower data streams gives rise to certain problems. For instance, the input and output clocks may be +/−100 ppm apart and still satisfy the Ethernet standard. In order to multiplex data streams from a slower GBE clock to a faster GBE clock, characters have to be added that do not affect the overall data transmission. Going from a faster to a slower clock requires characters to be removed from the data stream without affecting the data transmission. Transport service customers using the network often find changes to the frames unacceptable, preferring a “seamless” or “transparent” transport of packets. In the art, “seamless” transport is known as “transparency”. So, a method of matching the clocks is required that maintains transparency.  
           [0015]    High-speed optical networks must reproduce each packet exactly in order to maintain transparency. Any operations that alter the packets can result in loss of data. Thus, transparency for Ethernet and Fibre Channel signals is the ability to transport packets across the network without errors and with the same disparity.  
           [0016]    Input data must be mapped to a common clock domain for aggregation. The input data from the client arrives at the transport system client interface having different clock domains. The clock rates may be +/−100 ppm apart per the Ethernet specification. This data must be mapped to a single clock domain at the FEC interface prior to transport. The Ingress circuitry is designed to map these client data streams to the same clock domain without affecting transparency. Therefore, a stuffing method is required that does not affect disparity.  
           [0017]    Idle characters may be inserted or removed from the data stream in order to maintain the same disparity and transparency. The Gigabit Ethernet data stream consists of packets of data separated by Idle characters. There are two types of Idle characters: Idle 1 characters toggle the disparity whereas Idle 2 characters maintain the same disparity. The method of insertion and removal of Idle 2 characters is used to maintain the same disparity. In Fibre Channel, a single ordered set is used for the Idle character in ANSI X3T11.  
           [0018]    An output data rate in the FEC clock domain is maintained such that it is much higher then the aggregate data rate of the input data streams. This allows stuffing opportunities for Idle characters and proprietary data across the link. This enables mapping of data streams with +/−100 ppm variation to the same clock domain.  
           [0019]    Transported data recovered at the far end of the network must be mapped to the client clock domain. A fixed oscillator is selected for the clock output to the client to maintain low jitter and output clock characteristics that are within the physical layer specifications. This fixed data rate may be +/−100 ppm from the center frequency (1.25 Gbps for Ethernet, 1.0625 Gbps for FC, and 2.125 Gbps for 2FC). Therefore, there may be a mismatch between the data arriving from the Ingress path across the network to the Egress clock domain. As before, Idle 2 characters may be added or removed to match the input data rate to the fixed oscillator that generates the output signal to the client.  
           [0020]    In the past, transparency has been difficult to achieve because the data stream timing variations required large amounts of buffering. There are physical limits to the size of the buffers when used in data path devices such as field programmable gate arrays (FPGAs). When data is passing through FPGAs at high data rates (greater than 155 megabits per second), often data tends to overflow the buffers. This method of addition and removal of Idle 2 characters from the data stream in order to align the input and output clocks maintains 10b transparency without overflowing the buffers.  
           [0021]    In the prior art, aggregation of packet-based data streams is achieved by encapsulating in SONET, GFP, or other framing protocol. The Ethernet data is often decoded to 8b and then encapsulated prior to transport, which may affect transparency. This method of sending Ethernet and Fibre Channel in its native format reduces costs since this can be done cost effectively in an FPGA and alleviates the need for more expensive ASIC. Several prior art inventions have attempted to maintain transparency with varying success.  
           [0022]    U.S. Pat. No. 6,151,334 to Kim, et al., entitled SYSTEM AND METHOD FOR SENDING MULTIPLE DATA SIGNALS OVER A SERIAL LINK, discloses a method and system for sending multiple data signals over a serial link that uses an embedding unit to encode data streams and then merge the encoded data into a serial stream that is output across a serial line to a removing unit. The removing unit receives the serial steam of data, decodes the serial stream and separates the decoded serial stream into separate streams and reconstructing the input streams. The encoding and transmission are transparent, but are not packet-based streams like Ethernet. The invention of Kim only moves data in time with respect to a radio synchronization signal, but does not address problems with packet based data transparency.  
           [0023]    U.S. Pat. Publication No. 2002/0080809 to Nicholson, et al., entitled SYSTEM AND METHOD FOR MULTIPLEXING SYNCHRONOUS DIGITAL DATA STREAMS, discloses a method and system for multiplexing synchronous parallel digital data streams with different clock frequencies into a single data stream while preserving each data stream&#39;s timing integrity. Digital data inputs and separate corresponding clock inputs are coupled to corresponding first-in-first-out (FIFOs) buffering. Additionally, clock inputs are coupled to a clock multiplexer (MUX). Nicholson does not address problems arising from packet based data streams that are not synchronous.  
           [0024]    U.S. Pat. Publication No. 2002/0075903 to Hind, entitled MULTIPLEXING SONET/SDH DATA STREAMS USING INDEPENDENT ENCODING SCHEMES, discloses a system and method for transparently multiplexing/demultiplexing synchronous data streams without pointer processing or protocol conversion. The system uses encoding schemes to enable recovery of the respective data streams from the aggregate data stream. However, in Hind the synchronous data streams must all have the same bit rate. Hind does not address or solve the problems arising from multiple packet based data streams that have different clock domains.  
           [0025]    U.S. Pat. No. 6,396,853 to Humphrey et al., entitled PROVIDING DATA SERVICES TO TELECOMMUNICATIONS USER TERMINALS, discloses a method of multiplexing one or more plesiochronous packet data channels together with lower priority asynchronous traffic into a single composite data stream. The plesiochronous data packets each comprise a number of bytes together with a header element containing channel identification information and a packet length indicator. In Humphrey, et al., the frames are not transparent and, moreover, Humphrey does not address or solve the problems of transparent transportation of packet based data streams that have different clock domains.  
           [0026]    Therefore, a need exists for a system to aggregate packet based data streams on to one high-speed optical path in order to achieve transparency and preserve user data wherein the data is produced identically across the network. It is, therefore, desirable to provide a method and apparatus that permits a plurality of low-speed data streams to be multiplexed onto a high-speed data channel.  
         SUMMARY OF INVENTION  
         [0027]    The invention provides an apparatus and method for transparently multiplexing up to 8 Gigabit Ethernet (GBE) data streams; 8 Gigabit Fibre Channel (GFC) data streams; or 4 two Gigabit Fibre Channel (2GFC) data streams over a 10 Gbps optical transport link. Columns 1, 2 and 3 of Table 1 define the input data format. In the preferred embodiment, four Gigabit Ethernet channels; or four Gigabit Fibre Channels; or four 2 Gigabit Fibre Channels implementations are as shown in the first 3 rows of Table 1. Transparent aggregation of 8b/10b encoded data streams and synchronization of input and output clocks via Idle character addition or removal is described.  
                                                                                         Data                   Line       Data   Rate           Total   FEC Rate   Rate       Type   (Gbps)   Encoding   Channels   (Gbps)   (Gbps)   (Gbps)                                GBE   1.25   10b   4   6   10   12.5       GFC   1.0625    8b   4   3.2    9.95   12.5       2GFC   2.125    8b   4   6.4    9.95   12.5       GBE   1.25   10b   8   10   10+   12.5+       FC   1.0625    8b   8   6.4   10   12.5                  
 
           [0028]    In the present invention, multiple packet-based data streams (column 4) are aggregated onto an independent clock source (column 6: 16 bits×622.08 MHz=9.953 Gbps) through the “stuffing” of Idle and Status bits. The independent clock is selected such that the output data rate (column 6) is greater than the composite input data rate (column 5) of all the individual data streams. The independent clock prevents buffer overflow and provides an opportunity to embed Status information into the data.  
           [0029]    The resulting signal is encapsulated with forward error correction (FEC) at the transport interface, serialized, and modulated across the transport system. The FEC provides for correction of errors caused due to data impairments in the transport system.  
           [0030]    The FEC also provides a reciprocal 16-bit SFI-4 interface that allows mapping of individual data streams to individual bits of the FEC interface. For example, the Gigabit Ethernet data stream arrives as 10-bit wide data at 125 MHz or 1.25 Gbps. The FEC has a 16-bit interface at a clock rate of 625 MHz to accommodate a date rate of 10 Gbps. Therefore, each Gigabit Ethernet data stream may be mapped to 2 bits of the FEC [# bits=(FEC data rate/GBE data rate)×# bits]. Therefore, up to 8 data streams may be mapped to the FEC. The encoded data arrives at the same two bit positions at the far end of the network since the interface is reciprocal. This method enables transmission of data in its native format without encoding channel ID or other wrapper.  
           [0031]    An egress circuit at the receiving end recovers the modulated signal and inputs it into a FEC circuit that corrects errors in the transmission. The egress circuit extracts the Status information resulting in a return of the original data frames. The output timing is derived from a fixed oscillator. The Egress circuit maps the input timing to the output timing via the addition/subtraction of Idle characters. In this manner, the packet data is reproduced identical to the incident signal at the ingress path, ensuring the data is identical in content and disparity.  
           [0032]    One advantage of the invention is transparent data communication of packet-based data over the transport system.  
           [0033]    Another advantage is having two or more sets of signals aggregated into one optical fiber data stream. Without aggregation, the two or more set of signals would each have to be independently transported over the network at a higher cost.  
           [0034]    Another advantage is that the input signals do not require a common timing source. In other words, many different users can all use the same system without the need for clock synchronization.  
           [0035]    Still another advantage of the current invention is that packet-based data in many variations can be transported transparently. Different users can transport different packet based data. Compatibility adds to the flexibility of the system and reduces overall cost to the user.  
           [0036]    Yet another advantage is integrated error correction for each data stream. Instead of required error correction for each signal, only error correction for a combined signal is required. Overall system cost is reduced and efficiency is increased.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]    A better understanding of the invention can be obtained from the following detailed description of one exemplary embodiment when considered in conjunction with the following drawings in which:  
         [0038]    [0038]FIG. 1 is a block diagram depicting a transport system for the aggregation of packet-based plesiochronous signals according to the preferred embodiment of the present invention.  
         [0039]    [0039]FIG. 2 is a block diagram depicting an ingress circuit according to the preferred embodiment of the present invention.  
         [0040]    [0040]FIG. 3 is a block diagram depicting an ingress field programmable gate array according to the preferred embodiment of the present invention.  
         [0041]    [0041]FIG. 4 is a block diagram depicting the 10-bit aligner circuit according to the preferred embodiment of the present invention.  
         [0042]    [0042]FIG. 5 is a block diagram depicting an egress circuit according to the preferred embodiment of the present invention.  
         [0043]    [0043]FIG. 6 is a block diagram depicting an egress field programmable gate array according to the preferred embodiment of the present invention.  
         [0044]    [0044]FIG. 7 is a block diagram depicting a forward error correction system according to the ingress block of the preferred embodiment of the present invention.  
         [0045]    [0045]FIG. 8 is a block diagram depicting a 10-bit aligner circuit according to the preferred embodiment of the present invention.  
         [0046]    [0046]FIG. 9 is a block diagram depicting a forward error correction system according to the egress block of the preferred embodiment of the invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0047]    [0047]FIG. 1 shows a block diagram of the transport system for aggregation and transportation of packet-based data formats  100 . System  100  is a fall duplex transport system, the circuits used for aggregation and recovery at both ends of the network are mirror images.  
         [0048]    In the preferred embodiment, four independent 10b encoded Gigabit Ethernet data streams  105 ,  110 ,  115 , and  120  are aggregated by ingress block  145  and transported across transport system  125  in a composite stream  130 . Greater (up to 8) or fewer data streams may be accommodated in alternate embodiments by scaling the disclosed components. Other packet based formats such as Gigabit Fibre Channel or FICON that are at data rates of 1.0625 Gbps can be accommodated. Alternately, up to four 2 Gigabit Fibre Channel data streams that are at data rates of 2.125 Gbps can also be accommodated. At ingress block  145 , there is a timing uncertainty of approximately +/−100 parts per million (ppm) from the received nominal GBE of 1.25 Gbps from each data stream. The timing uncertainty is tracked and corrected in the ingress block  145 . Preferably, composite stream  130  has a faster line clock rate greater than 400 ppm faster than the combined input data rate of the data streams. The fast line clock rate prevents buffer overflow and ensures there are stuffing opportunities between packets to embed Idle characters and Status information. In order to increase the clock rate, data bytes are added or “stuffed” between packets in the ingress block  145 . The result is that composite stream  130  contains a serial stream that is comprised of 16 data bits serialized in SERDES  254 . In the preferred embodiment, each GBE channel is mapped to 4 of the 16 bits of the composite data stream  130 . However, it is possible to map each data stream to 2 of the 16 bits thus aggregating 8 channels. Alternately, it is possible to map four 2 GFC channels with each 2 GFC mapped to 4 bits.  
         [0049]    Composite stream  130  is transported across transport system  125  to egress block  140 . Egress block  140  removes the stuffed data from composite stream  130  and maps the data to a fixed clock rate of 1.25 Gbps for each GBE data stream. A fixed oscillator  680  (described in detail in reference to FIG. 6) in egress block  140  is implemented to clock the received GBE channels for each data stream. The recovered data for data streams  146 ,  150 ,  155 , and  160  is identical to the Ingress path received data  105 ,  110 ,  115 , and  120 . Thereby multiple packet-based data streams are transparently transported over transport system  125 .  
         [0050]    Processor  170  connected to ingress block  145  can add user data to a stuffing word through line  171 . Downstream processor  172  through line  173  connected to egress block  140  reads the user data.  
         [0051]    Referring to FIG. 2, a block diagram of the preferred embodiment of ingress block  145  is shown in greater detail. Ingress block  145  is shown in FIG. 2 as ingress block  201 . The ingress path consists of four optical transceivers  200 , each capable of receiving a single Gigabit Ethernet data stream  202 ,  204 ,  206 , and  208 . In the preferred embodiment, each optical transceiver  200  is a small form-factor pluggable (SFP) optical transceiver. The four GBE data streams are converted into electrical output signals  210 ,  20   212 ,  214 , and  216  by optical transceivers  200 . Electrical output signals  210 ,  212 ,  214 , and  216  are transmitted to Serializer/Deserializer (SerDes)  218 . SerDes  218  receives electrical output signals  210 ,  212 ,  214 , and  216  from the optical transceivers  200  and generates recovered GBE clock  220 ,  222 ,  224  and  226 ; and 10b encoded GBE data  228   230   232  and  234 . Alternately, in the case of Fibre Channel, the SERDES may contain an encoder/decoder block to provide the data in 8b format.  
         [0052]    System clock  258  is a GBE reference clock that is used to generate the 125 MHz SERDES reference signal; the 625 MHz line rate signal; and also as a clock for the recovered Egress signals to the client interface. In the preferred embodiment, a 125 MHz signal is generated as the SERDES and FPGA clocks. The SERDES uses the clock as a reference to recover input signal. The Ingress FPGA uses it to generate the 625 MHz line rate to the FEC. The Egress FPGA uses it to clock recovered data back to the client. This does not preclude use of a 106.25 MHz or other clock to generate 1G and 2G Fibre Channel signals.  
         [0053]    Recovered GBE clock signals  220 ,  222 ,  224 , and  226  with nominal frequency of 125 MHz for GBE; and 10b encoded data signals  228 ,  230 ,  232 , and  234 , are transmitted from SerDes  218  to Ingress field programmable gate array (FPGA)  244  where data signals  228 ,  230 ,  232 , and  234  are processed into composite signal  246  as discussed below. Line clock rate signal  262  is also transmitted to FPGA  244 . Composite signal  246  is comprised of n×625 MHz parallel signals governed by the line clock rate signal  262 . In the preferred embodiment n is 16 and each GBE, 1GFC, or 2G FC is mapped to 4 of the 16 FEC channels. However, n can be as low as 2 where each GBE is mapped to 2 of the 16 FEC channels thus accomplishing 8 GBE channel aggregation. In the preferred embodiment, a 625 MHz clock is used for aggregating the individual data streams. However, alternate clock rates of 100 MHz to 810 MHz may be used depending on the application. The only restriction is that the output data rate must be greater than the aggregate input data rate as described earlier.  
         [0054]    Composite signal  246  is received by ingress FEC  248  and processed into transport composite signal  256 . Composite signal  256  contains 16 parallel FEC output signals at the faster line clock rate. As is known in the art, the FEC output signals contain both the data and the input clock encapsulated in the FEC code. When the receiving FEC performs error correction on the signal, both the data and clock are recovered by a method know in the art as “through timing”.  
         [0055]    Transport composite signal  256  is transmitted to SerDes  254 . SerDes  254  serializes transport composite signal  256  into composite stream  250  comprised of a single bit wide channel at the fast clock rate of nominal speed of 12.5 Gbps. SerDes  254  transmits composite stream  250  to transport system  252  for transmission.  
         [0056]    [0056]FIG. 3 is a block diagram showing a portion of the preferred embodiment of ingress FPGA  244  in greater detail. Ingress FPGA  244  is shown in FIG. 3 as ingress FPGA  300 . Ingress FPGA  300  receives recovered GBE or FC clock signals  220 ,  222 ,  224 , and  226 , data signals  228 ,  230 ,  232 , and  234 , transmitted from SerDes  218  (FIG. 2). Ingress FPGA  300  receives signal present status signals  236 ,  238 ,  240 , and  242  transmit from SFP  200  (FIG. 2). Signal present status signal  236  is sent to remove idle controller  336 . GBE or FC clock signal  220  and data signal  228  are sent to remove idle controller  336 . In the preferred embodiment, data signal  228  is at a rate of 125 MHz 10 bits wide (10b) for GBE or 106.25 MHz 10 bits wide (8 bits data (8b)+1 control bit+1 status bit) for FC. Each GBE or FC clock signal  220 ,  222 ,  224 , and  226  is plesiochronous to the other GBE or FC clock signals  220 ,  222 ,  224 , and  226 .  
         [0057]    Remove idle controller  336  recognizes idles (GBE idle2 or FC idle order set). It will remove an idle when the FIFO depth status signal  360  indicates the FIFO depth reaches a maximum threshold. The FIFO buffer depth has a programmable threshold range with a requirement that the maximum threshold be set greater that the minimum threshold. The maximum threshold has a range from 10 to 90%. The preferred maximum threshold is 75% of the total FIFO depth or (1024×0.75=768). An idle is removed by turning off the write enable signal 333 to the FIFO circuit  354 . The GBE idle 2 is represented by K28.5 followed by D16.2 and the FC idle order set is represented by K28.5 followed by D21.4 followed by D21.5 followed by D21.5 as defined in ANSI X3.230 FC-1. The remove idle controller  336  transmits the 125 MHz clock for GBE or 106.25 MHz clock for FC signal  332  and  330  data stream to first-in/first-out buffer (FIFO)  354 .  
         [0058]    Clock Divider  320  converts the FEC clock a 625 MHz clock signal  262  into a 156.25 MHz clock signal  263  to the FIFO.  
         [0059]    Preferably, FIFO  354  is a 1024 deep by 10 bits wide dual port, dual clock domain FIFO. FIFO  354  outputs aligned fast data signal  334  to multiplexer (MUX)  370 . Aligned fast data signal  334  is synchronized to faster line clock rate signal  263  via clock divider circuit  320 -output signal  263 . The FIFO  354  is written to at a maximum rate of 10 bits at 125 MHz or 1.25 M Bits/Second in the case of GBE and 10 bits at 106.25 MHz or 1.0625 M Bits/Second in the case of FC. The FIFO 354 is read at a maximum rate of 10 bits at 80% of 156 MHz or 1.25 M Bits/Second. At least every 5th clock the FIFO read is skipped to allow the barrel MUX  910  to convert the 10 bit data  378  into 8 bit data  386 . Occasionally more FIFO reads will be skipped if idles need to be inserted to adjust ingress timing.  
         [0060]    It should be noted that the remove idle function is not necessary when FC is transported. This is due to the fact that the data rate coming into the FIFO will always be slower than the rate the FIFO is being read. The max rate of FIFO write is 10 bits at 106.25 MHz the max FIFO read is 10 bits at 80% of 156.25 MHz. (FIFO read is skipped every 5 clocks). As is required, 1.0625 M Bits /Sec is less than 1.25 M Bits/Sec.  
         [0061]    Add idle controller  356  coordinates the processes necessary to add GBE or FC idles between frames and adjust timing of the ingress circuit. Add idle controller  356  calculates the number of idles needed to adjust timing and transmits this number of idles to MUX  370 . It also calculates the necessary advancement of barrel MUX  910  to properly align the output signal via the control signal  384 . The ADD IDLE controller  356  will add idles when the FIFO depth status signal  360  indicates the FIFO depth falls below a minimum threshold. The FIFO buffer depth has a programmable threshold range with a requirement that the minimum threshold be set less than the maximum threshold. The minimum threshold has a range from 10 to 90%. The preferred minimum threshold is 25% of the total FIFO depth or (1024×0.25=256). The add idle controller  356  adds idles by selecting idle data signal  378  from the idle data logic  361  via the MUX select signal  374 . The MUX select signal  374  also, controls the read of the FIFO circuit  354 .  
         [0062]    Idle data logic  372  transmits the idle data signal  361  to the MUX  372 . MUX  370  will pass through the data signal  334  or data signal  361  to the barrel MUX  910  via data signal  378  depending on the MUX select signal  374  transmitted by the add idle controller  356 .  
         [0063]    Pipeline barrel roller MUX  910  is shown in FIG. 8. Pipeline barrel roller MUX  910  is used to convert the 10 bit data  378  into 8 bit data  386 . Combined word signal  378  enters pipeline barrel roller MUX  910  and is 10 bits wide at 156.25 MHz. Signal  378  enters register  905 , which is a register 10 bits wide. Signal  378  is also shunted to the input of pipeline barrel roller MUX  910 . Register  905  delays signal  378  by a single clock tick resulting in delayed signal  379 . Pipeline barrel roller  910  allows the data from register  905  to be shifted in time by 0 to 10 bits in 2 bit increments according to an offset signal  384  from add idle controller  356 . Once shifted, the data is released through MUX  382 . For example, if offset signal  384  is 0, the data is shifted 2 bits MUX  382  passes bits  9  through  2  of signal  378  to signal  386 . If offset signal  384  is set to 1, the data is shifted 4 bits. MUX  382  then releases bits  1  through  0  from register  905  and bits  9  through  4  of signal  378  to signal  386 . If offset  2  is selected on line  384 , data bits  3  through  0  from register  905  and bits  9  through  6  of signal  378  will be passed to signal  386 . If offset  3  is selected on line  384 , data bits  5  through  0  from register  905  and bits  9  through  8  of signal  378  will be passed to signal  386 . If offset  4  is selected on line  384 , data bits  7  through  0  from register  905  will be passed without being shifted to signal  386 .  
         [0064]    Returning to FIG. 3, signal  386  is an 8 bit×156.25 MHz signal and is transmitted from pipeline barrel roller MUX  910  to Serializer  388 . Second group of signals  222 ,  230  and  238 , third group of signals  224 ,  232  and  240 , fourth group of signals  226 ,  234  and  242 , proceed along an analogous path through a parallel and duplicative set of devices to achieve signals analogous to signal  386  produced from first group of signals. Second group of signals produce signal  390 . Third group of signals produce signal  392 . Fourth group of signals produce signal  394 . Signal  386  and signals  390 ,  392  and  394  are transmitted to Serializer  388 . Serializer  388  serializes the 8×156.25 MHz signals  386 ,  390 ,  392 , and  394  into four 2×625 MHz signals, creating a 8×625 MHz composite signal  396 . By adding idles when and if needed the add idle controller  356  ensures that all of the data streams are outputted at a common clock rate. Composite signal  396  emerges as composite signal  246  in FIG. 2 and is transmitted to FEC  248  as an 8 bit×625 MHz signal. In the case of 8 GBE or 8 1Gig FC the composite signal  246  will be a 16 bit×625 MHz signal.  
         [0065]    FEC  248  of FIG. 2 is shown in FIG. 7 as FEC  800  and its functions will be described with respect to FIG. 7. FEC  800  assigns each outputted data stream in composite signal  246  to one of four FEC lanes  802 ,  804 ,  806 , and  808  for transport. FEC  800  has a 16-bit SFI-4 interface running at 625 MHz clock rate to match the output of ingress FPGA  244 . Ports  842 - 872  in FEC  800  act as 16 independent serial data ports. Assigning  4  FEC lanes  802 ,  804 ,  806 , and  808  to GBE or FC stream  246  may map any format data mapped to any combination of transport channels to achieve serial communications without embedding control codes for channel identification. FEC  800  encapsulates the data in composite signal  246  mapping it to signals  874 - 904  providing a 25% overhead error correction code, which provides greater than 9 dB of coding gain. FEC  800  receives signal  262  and passes it through line side oscillator  908  to be reproduced and transmitted as signal  263  (shown in FIG. 2) to SerDes  254  (also shown in FIG. 2). It must be understood that a plurality of clock rates may be specified for use in the operation of the present invention, but clocks rates exacting a ratio of 25% should be maintained in the preferred embodiment. For example, the clock rate for composite signal  246  can be up to 810 MHz and the clock rate for signal  262  can be up to 650 MHz. A plurality of FEC algorithms with overhead ratios up to 25% may be used depending on system requirements.  
         [0066]    [0066]FIG. 5 is a block diagram of the preferred embodiment of egress block  140  shown in greater detail. Egress block  140  of FIG. 1 is shown in FIG. 5 as  500 . Incoming signal  548  is 1 bit wide 12.5 Gigabit per second optical signal at the aggregated transport rate. SerDes  542  deserializes composite signal  548  into 16-bit FEC encoded data signal  550 , at a clock rate of 781.25 MHz, and transmits deserialized signal  550  to FEC  502 . SerDes  542  also recovers clock signal  545 , which is at a rate of 781.25 MHz and transmits it to FEC  502 . FEC  502  performs error correction on deserialized signal  550  and recovers composite data signal  544  and composite 625 MHz clock signal  546 . Composite clock signal  546  is at the 625 MHz clock rate of the ingress block and is 16 data bits wide. Composite data signal  544  and composite clock signal  546  are transmitted to egress FPGA  504  for data stream and timing extraction.  
         [0067]    The structure and function of FEC  502  is shown and described in reference to FIG. 9. FEC  502  assigns each output of data stream in composite signal  550  to one of four FEC lanes,  1002 ,  1004 ,  1006  and  1008 , for decoding. FEC  502  has a 16-bit SFI 4 interface running at  625 . MHz clock rate to match the output of SerDes  542 . Ports  1002  through  1008  in FEC  502  act as sixteen independent serial data ports. Thus, FEC  502  strips the error correction from the encapsulated data in composite signal  550 , mapping it to signals  1074 - 1104 , extracting the 25% overhead error correction code to obtain the 9 decibels of coding gain. FEC  502  receives 781.25 MHz clock signal  545 , passes it through oscillator  1108  to reproduce 625 MHz clock signal  546 .  
         [0068]    Referring again to FIG. 5, Egress FPGA  504  re-clocks the signal and transmits four synchronous GBE or FC channels  506 ,  508 ,  510 , and  512  to SerDes  522  as 10 bit wide (10b) 125 MHz data clocked signals for GBE or 10 bit wide (8 b+1 control bit+status bit) 106.25 MHz wide for Fibre Channel (FC). Alternatively, if 8 synchronous GBE or FC channels were transmitted, channels  507 ,  509 ,  511 , and  513  may be used in addition to channels  506 ,  508 ,  510 , and  512 .  
         [0069]    SerDes  522  serializes synchronous GBE or FC channels  506 ,  508 ,  510 , and  512  which are each 125 MHz for GBE or 106.25 MHz for FC signals, and transmits four synchronous GBE or FC data streams  524 ,  526 ,  528 , and  530  which are 1 bit wide 1.25 GHz for GBE or 1.0625 GHz for FC signals containing the same data as the four input synchronous GBE or FC data streams  105 ,  110 ,  115 , and  120  (FIG. 1) to SFP  532 . SFP  532  converts the electrical synchronous GBE or FC data streams  524 ,  526 ,  528 , and  530  to optical outputted synchronous GBE or FC data streams  534 ,  536 ,  538 , and  540 .  
         [0070]    [0070]FIG. 6 is a block diagram showing the preferred embodiment of egress FPGA  504  in greater detail. FPGA  504  is shown in FIG. 6 as  600 . Deserializer  602  deserializes composite signal  544  from a 2×625 MHz signal into an 8×156.25 MHz deserialized signal  606 . Deserialized signal  606  is transmitted from Deserializer  602  to 10 bit aligner circuit  608 . Composite clock signal  546  runs at 625 MHz and is connected to clock manager  603  where it is converted into a 156.25 MHz clock signal  604 . Clock signal  604  is connected to Deserializer  602  and 10 bit aligner circuit  608  and remove idle controller and the input side of FIFO  612 .  
         [0071]    [0071]FIG. 4 is a block diagram showing the preferred embodiment of the 10 bit aligner circuit  608  and is shown in greater detail. The 10-bit aligner circuit  608  is used to convert the 8 bit data  606  into 10 bit data  620 . The signal  606  enters the 10-bit aligner circuit  608  and is 8 bits wide at 156.25 MHz. Signal  606  enters register  405 , which is a register 8 bits wide. Signal  606  is also shunted to the input of the special character compare  415 . Register  405  delays signal  606  by a single clock tick resulting in delayed signal  410 . The 10-bit aligner circuit  608  allows the combined 16 bits data stream of  606  and  410  to be multiplexed by MUX  425  into a single 10-bit data stream  620 . For example if the special character (K28.5) is detected on data bits  7  to  0  of signal  410  and data bits  7  to  6  of signal  606  the offset signal  420  will be reset to 0. If the special character (K28.5) is detected on data bits  5  to  0  of signal  410  and data bits  7  to  4  of signal  606  the offset signal  420  will be reset to 1. If the special character (K28.5) is detected on data bits  3  to  0  of signal  410  and data bits  7  to  2  of signal  606  the offset signal  420  will be reset to 2. If the special character (K28.5) is detected on data bits  1  to  0  of signal  410  and data bits  7  to  0  of signal  606  the offset signal  420  will be reset to 3. The offset is incremented after every clock once the special character (K28.5) is detected by the special character compare  415 . A shifted 10-bit data word is passed through to signal  620  when the offset signal  420  equals 0, 1, 2, or 3. When the offset signal  420  equals 4 a constant filler value is sent to signal  620  and the FIFO write enable signal is turned off to FIFO  612 . The 10-bit data aligner transmits an alignment status signal to remove idle controller  610  when the special character (K28.5) is detected.  
         [0072]    Referring again to FIG. 6, the remove idle circuit  610  recognizes and removes idles from each stream in the same process as described with respect to remove idle circuit  336 . The remove idle circuit  610  uses the alignment status signal  621  and the FIFO depth status signal  651  from the FIFO circuit  612  to control the FIFO write signal  650 .  
         [0073]    The add idle circuit  624  recognizes and adds idles to the data stream  640  in the same process as described with respect to add idle circuit  356  (shown in FIG. 3). The add idle circuit  624  uses the FIFO depth status signal  651  from the FIFO circuit  612  to control the FIFO read signal  625 . The FIFO read signal  625  also serves as select control to MUX  634 .  
         [0074]    The MUX circuit  634  will pass through the FIFO 10 bit output data stream  638  or the output signal  636  of the idle logic  613  to the 10-bit data stream  640  based on the value of the select control signal  625 . The idle logic  613  will transmit the appropriate GBE idle2 or FC idle ordered set.  
         [0075]    Preferably, FIFO  612  is a 1024 deep by 10 bits wide dual port, dual clock domain FIFO. FIFO  612  outputs aligned slow data signal  612  to multiplexer (MUX)  634 . Aligned slow data signal  638  is synchronized to slower line clock rate signal  680 . The FIFO  612  is written to at a maximum rate of 10 bits at 80% of 156 MHz or 1.25 M Bits/Second. At least every 5th clock the FIFO write is skipped to allow the 10-bit aligner  608  to convert the 8 bit data  606  into 10 bit data  620 . The FIFO  612  is read at a maximum rate of 10 bits at 125 MHz or 1.25 M Bits/Second in the case of GBE and 10 bits at 106.25 MHz or 1.0625 M Bits/Second in the case of FC. Occasionally more FIFO reads will be skipped if idles need to be inserted to adjust egress timing. The egress FPGA  600  transmits the 125 MHz GBE clock or 106.25 MHz clock signal  670  to SerDes  522  of FIG. 5.  
         [0076]    Egress FIFO  612  transmits output signal  638  to MUX  634 . Output signal  638  is a 10×125 MHz GBE signal or 10 bit 106.25 MHz FC signal. MUX  634  is used to transmit data from the FIFO  612  or added idles from idle logic  613 . Output signal  640  is a 10 bit (10b)×125 MHz GBE or 10 bit (8b+1 control bit+1 status bit)×106.25 MHz FC. Channel  640  is sent to SerDes  522  (FIG. 5) and is analogous to signal  506 .  
         [0077]    The structure and function of components described with respect to signal  544  are duplicated for signals  545 ,  547 , and  548  resulting in signals  1200 ,  1202 ,  1204 ,  1206 ,  1208 , and  1210  which are sent to SerDes  522 . Signals  1200 ,  1202 ,  1204 ,  1206 ,  1208 , and  1210  are analogous to signals  508 - 513 .  
         [0078]    Although the invention has been described with reference to one or more preferred embodiments, this description is not to be construed in a limiting sense. For example the method and apparatus can be used to aggregate and transparently transport a variety of formats and is not limited to Gigabit Ethernet, Fibre Channel, and FICON formats. There is modification of the disclosed embodiments, as well as alternative embodiments of this invention, which will be apparent to persons of ordinary skill in the art, and the invention shall be viewed as limited only by reference to the following claims.

Technology Classification (CPC): 7