Abstract:
An apparatus comprises a 64b66b encoder configured to process operations, administration, and maintenance (OAM) information, determine a bit pattern based on the OAM information, form forward error correction (FEC) parity sync-headers based on the bit pattern, and form an FEC codeword with the FEC parity sync-headers, and a transmitter coupled to the 64b66b encoder and configured to transmit the FEC codeword. A method comprises processing OAM information, determining a bit pattern based on the OAM information, forming FEC parity sync-headers based on the bit pattern, forming an FEC codeword with the FEC parity sync-headers, and transmitting the FEC codeword. An apparatus comprises a receiver configured to receive an FEC codeword, and a 64b66b decoder coupled to the receiver and configured to extract FEC parity sync-headers from the FEC codeword, determine a bit pattern of the FEC parity sync-headers, and determine OAM information based on the bit pattern.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. provisional patent application No. 62/077,467 filed Nov. 10, 2014 by Frank Effenberger, et al., and titled “Adding Operations, Administration, and Maintenance (OAM) Information in 66-Bit Code,” which is incorporated by reference. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND 
     A passive optical network (PON) is one system for providing network access over the last mile, which is the final portion of a telecommunications network that delivers communication to customers. A PON is a point-to-multipoint (P2MP) network comprised of an optical line terminal (OLT) at a central office (CO), an optical distribution network (ODN), and optical network units (ONUs) at the user premises. PONs may also comprise remote nodes (RNs) located between the OLTs and the ONUs, for instance at the end of a road where multiple customers reside. In recent years, time-division multiplexing (TDM) PONs such as gigabit-capable PONs (GPONs) and Ethernet PONs (EPONs) have been deployed worldwide for multimedia applications. 
     SUMMARY 
     In one embodiment, the disclosure includes an apparatus comprising a 64b66b encoder configured to process operations, administration, and maintenance (OAM) information, determine a bit pattern based on the OAM information, form forward error correction (FEC) parity sync-headers based on the bit pattern; and form an FEC codeword with the FEC parity sync-headers; and a transmitter coupled to the 64b66b encoder and configured to transmit the FEC codeword. In some embodiments, the FEC parity sync-headers comprise a first sync-header, a second sync-header, a third sync-header, and a fourth sync-header. In some embodiments, the 64b66b encoder is further configured to the FEC parity sync-headers comprise a first sync-header, a second sync-header, a third sync-header, and a fourth sync-header, and/or when the OAM information is a binary 1 bit, form the first sync-header with binary 11 bits, form the second sync-header with binary 00 bits; form the third sync-header with binary 00 bits, and form the fourth sync-header with binary 11 bits, and/or when the OAM information is a binary 0 bit, the 64b66b encoder is further configured to form a first pattern with the FEC parity sync-headers, and/or when the OAM information is a binary 1 bit, the 64b66b encoder is further configured to form a second pattern with the FEC parity sync-headers, wherein the second pattern is a complement of the first pattern. In some embodiments, the OAM information comprises one bit so that an OAM rate is about 5 megabits per second (Mb/s). In some embodiments, the 64b66b encoder is further configured to form 27 data blocks, form 4 parity blocks comprising the FEC parity sync-headers, and further form the FEC codeword with the 27 data blocks and the 4 parity blocks so that the OAM information is carried in the FEC codeword of 31 blocks of data. 
     In another embodiment, the disclosure includes a method comprising processing OAM information, determining a bit pattern based on the OAM information, forming FEC parity sync-headers based on the bit pattern, forming an FEC codeword with the FEC parity sync-headers, and transmitting the FEC codeword. In some embodiments, the FEC parity sync-headers comprise a first sync-header, a second sync-header, a third sync-header, and a fourth sync-header. In some embodiments, when the OAM information is a binary 0 bit, the method further comprises forming the first sync-header with binary 00 bits, forming the second sync-header with binary 11 bits, forming the third sync-header with binary 11 bits, and forming the fourth sync-header with binary 00 bit, and/or when the OAM information is a binary 1 bit, the method further comprises forming the first sync-header with binary 11 bits, forming the second sync-header with binary 00 bits, forming the third sync-header with binary 00 bits, and forming the fourth sync-header with binary 11 bits. In some embodiments, when the OAM information is a binary 0 bit, the method further comprises forming a first pattern with the FEC parity sync-headers, and/or when the OAM information is a binary 1 bit, the method further comprises forming a second pattern with the FEC parity sync-headers, wherein the second pattern is a complement of the first pattern. In some embodiments, the OAM information comprises one bit so that an OAM rate is about 5 Mb/s. In some embodiments, the method further comprises forming 27 data blocks, forming 4 parity blocks comprising the FEC parity sync-headers, and further forming the FEC codeword with the 27 data blocks and the 4 parity blocks so that the OAM information is carried in the FEC codeword of 31 blocks of data. 
     In yet another embodiment, the disclosure includes an apparatus comprising a receiver configured to receive an FEC codeword, and a 64b66b decoder coupled to the receiver and configured to: extract FEC parity sync-headers from the FEC codeword, determine a bit pattern of the FEC parity sync-headers; and determine OAM information based on the bit pattern. In some embodiments, the FEC parity sync-headers comprise a first sync-header, a second sync-header, a third sync-header, and a fourth sync-header. In some embodiments, the 64b66b decoder is further configured to determine that the OAM information is a binary 0 bit when the OAM information is a binary 0 bit when the first sync-header comprises binary 00 bits, the second sync-header comprises binary 11 bits, the third sync-header comprises binary 11 bits, and the fourth sync-header comprises binary 00 bits; and/or determine that the OAM information is a binary 1 bit when the first sync-header comprises binary 11 bits, the second sync-header comprises binary 00 bits, the third sync-header comprises binary 00 bits, and the fourth sync-header comprises binary 11 bits. 
     These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. 
         FIG. 1  is a schematic diagram of an embodiment of a PON. 
         FIG. 2  is an illustration of an embodiment of a mechanism for adding FEC. 
         FIG. 3  is an illustration of an embodiment of a mechanism for adding FEC with OAM information according to an embodiment of the disclosure. 
         FIG. 4  is a schematic diagram of a network device according to an embodiment of the disclosure. 
         FIG. 5  is a flowchart of a method for receiving an FEC codeword according to an embodiment of the disclosure. 
         FIG. 6  is a flowchart of a method for transmitting an FEC codeword according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     It should be understood at the outset that, although illustrative implementations of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
       FIG. 1  is a schematic diagram of a PON  100 . The PON  100  may be suitable for implementing the disclosed embodiments. The PON  100  may comprise an OLT  120  located in a CO  110 , ONUs 1-n    180   1-n  located at the customers&#39; premises, and an ODN  170  that couples the OLT  120  to the ONUs 1-n    180   1-n . N may be any positive integer. The PON  100  may provide wavelength-division multiplexing (WDM) capability by associating a downstream wavelength and an upstream wavelength with each OLT port 1-n    130   1-n  so that a plurality of wavelengths is present, then combining those wavelengths into a single optical fiber cable  150  via a wavelength multiplexer/demultiplexer (WM)  140  and distributing the wavelengths to the ONUs 1-n    180   1-n  through an RN  160 . The PON  100  may provide TDM as well. 
     The PON  100  may be a communications network that does not require any active components to distribute data between the OLT  120  and the ONUs 1-n    180   1-n . Instead, the PON  100  may use passive optical components in the ODN  170  to distribute data between the OLT  120  and the ONUs 1-n    180   1-n . The PON  100  may adhere to any standard related to multiple-wavelength PONs. 
     The CO  110  may be a physical building and may comprise servers and other backbone equipment designed to service a geographical area with data transfer capability. The CO  110  may comprise the OLT  120 , as well as additional OLTs. If multiple OLTs are present, then any suitable access scheme may be used among them. 
     The OLT  120  may comprise the OLT ports 1-n    130   1-n  and the WM  140 . The OLT  120  may be any device suitable for communicating with the ONUs 1-n    180   1-n  and another network. Specifically, the OLT  120  may act as an intermediary between the other network and the ONUs 1-n    180   1-n . For instance, the OLT  120  may forward data received from the network to the ONUs 1-n    180   1-n  and may forward data received from the ONUs 1-n    180   1-n  to the other network. When the other network uses a network protocol that differs from the PON protocol used in the PON  100 , the OLT  120  may comprise a converter that converts the network protocol to the PON protocol. The OLT  120  converter may also convert the PON protocol into the network protocol. Though the OLT  120  is shown as being located at the CO  110 , the OLT  130  may be located at other locations as well. 
     The OLT ports 1-n    130   1-n  may be any ports suitable for transmitting waves to and receiving waves from the WM  140 . For instance, the OLT ports 1-n    130   1-n  may comprise laser transmitters to transmit waves and photodiodes to receive waves, or the OLT ports 1-n    130   1-n  may be connected to such transmitters and photodiodes. The OLT ports 1-n    130   1-n  may transmit and receive waves in any suitable wavelength bands. 
     The WM  140  may be any suitable wavelength multiplexer/demultiplexer such as an arrayed waveguide grating (AWG). The WM  140  may multiplex the waves received from the OLT ports 1-n    130   1-n  then forward the combined waves to the RN  160  via the optical fiber cable  150 . The WM  140  may also demultiplex the waves received from the RN  160  via the optical fiber cable  150 . 
     The RN  160  may be any component positioned within the ODN  170  that provides partial reflectivity, polarization rotation, and WDM capability. For example, the RN  160  may comprise a WM similar to the WM  140 . The RN  160  may exist closer to the ONUs 1-n    180   1-n  than to the CO  110 , for instance at the end of a road where multiple customers reside, but the RN  160  may also exist at any suitable point in the ODN  170  between the ONUs 1-n    180   1-n  and the CO  110 . 
     The ODN  170  may be any suitable data distribution network, which may comprise optical fiber cables such as the optical fiber cable  150 , couplers, splitters, distributors, or other equipment. The optical fiber cables, couplers, splitters, distributors, or other equipment may be passive optical components and therefore not require any power to distribute data signals between the OLT  120  and the ONUs 1-n    180   1-n . Alternatively, the ODN  170  may comprise one or more active components such as optical amplifiers or a splitter. The ODN  170  may typically extend from the OLT  120  to the ONUs 1-n    180   1-n  in a branching configuration as shown, but the ODN  170  may be configured in any suitable P2MP configuration. 
     The ONUs 1-n    180   1-n  may comprise laser transmitters to transmit waves and photodiodes to receive waves. The ONUs 1-n    180   1-n  may be any devices suitable for communicating with the OLT  120  and customers. Specifically, the ONUs 1-n    180   1-n  may act as intermediaries between the OLT  120  and the customers. For instance, the ONUs 1-n    180   1-n  may forward data received from the OLT  120  to the customers and forward data received from the customers to the OLT  120 . The ONUs 1-n    180   1-n  may be similar to optical network terminals (ONTs), so the terms may be used interchangeably. The ONUs 1-n    180   1-n  may typically be located at distributed locations such as the customer premises, but may be located at other suitable locations as well. 
     An EPON is an emerging access network that provides low-cost methods of deploying optical access lines between a CO and customers&#39; premises. EPONs seek to bring forth a full-service access network that delivers data, video, and voice over a single optical access system. Optional FEC methods are used to improve communication reliability in error-prone environments like EPONs. In an FEC process, an EPON frame may be encapsulated into an FEC frame carrying parity and other FEC bits. Use of FEC results in an increased link budget, which enables higher bit rates, longer optical terminal to optical network unit distances, and higher split ratios for a single PON. 
     Institute of Electrical and Electronics Engineers (IEEE) 802.3-2012, Section Four, which is incorporated by reference, discusses 64B/66B in clause 49. 64B/66B is a line code that transforms 64-bit data to 66-bit line code to provide enough state changes to allow reasonable clock recovery and facilitate alignment of a data stream at a receiver. 64B/66B provides for the transmission of Ethernet frames using 66-bit blocks. Each block contains a 64-bit payload and a 2-bit sync header. For some applications, the transmission of 10 gigabit/second (Gb/s) Ethernet-formatted data requires additional features that are not provided in the basic format. Two such features are the inclusion of FEC and low-level OAM information. 
     There are two standardized methods to add FEC to 64B/66B data. The first method adds a small amount of error tolerance and is described in clause 74 of IEEE 802.3-2012, Section Five, which is incorporated by reference. The second method adds a large amount of error tolerance and is described in clause 76 of IEEE 802.3-2012, Section Five, as well as U.S. Pat. Nos. 8,171,370; 8,281,228; 8,270,832; 8,245,095; 8,208,809; 8,880,975; and 8,122,325, which are incorporated by reference. The second method is the most relevant FEC method for optical transmission systems. 
       FIG. 2  is an illustration of a mechanism  200  for providing FEC with 64b/66b data which may be used in conjunction with the inclusion of OAM information as described further below. The mechanism  200  shows how the second method described above adds FEC through the generation of parity blocks and the insertion of the parity blocks into a codeword  202  including both the payload data and the parity blocks. Specifically, for every 27 payload blocks  203 , 4 parity blocks are added, as described further below. Each of the 27 payload blocks comprises a 64-bit payload and a two-bit payload block sync header loaded into each payload block. Thus, the first payload block  204  of the 27 payload blocks  203  comprises a 64-bit payload  212  and a two-bit payload block sync header  210 , having the value “01” by way of example. Similarly, the second payload block  206  includes a 64-bit payload  216  and a two-bit payload block sync header  214  containing the value “10” by way of example, and the twenty-seventh payload block  208  comprises a 64-bit payload  220  and a payload block sync header  218  containing the value “01”. The values of the payload block sync headers are examples, and may change depending on the type of the payload in the corresponding payload block. 
     The FEC is based on a Reed-Solomon code comprising 32 parity bytes, and 223 data bytes. This Reed-Solomon code is referred to as an RS( 255 ,  223 ) code. Thus, to provide the 223 data bytes to a Reed-Solomon encoder, the 27 payload blocks  203  are mapped onto a codeword payload  221  comprising 27 65-bit blocks. Each of the 65-bit blocks may comprise a 1-bit header derived from a corresponding payload block sync header and the 64-bit payload. For example, the first 65-bit block  222  comprises a 64-bit payload  212  and a header  230  containing the value “1” corresponding to the least significant bit (LSB) of the payload block sync header  210 , the second 65-bit block  224  may comprise a 64-bit payload  216  and a header  234  containing the value “0” corresponding to the LSB of payload block sync header  214 , and the 27 th  65-bit block  226  comprises a 64-bit payload  220  and a 1-bit header  238  containing the value “1” corresponding to the payload block sync header  218 . The values contained in the 1-bit headers are examples and may change with changes in values of the payload block sync headers, such as payload block sync headers  210 ,  214 ,  218 . The twenty-seven 65-bit blocks encompass a total of 1755 bits, leaving 29 padding bits  240  to pad out a total of 223 bytes. The padding bits  240  in codeword payload  221  may be padded stuffed with zeros for example. Alternatively, the padding bits  240  may be used to encode OAM data as described further below in conjunction with  FIG. 3 . 
     The twenty-seven 65-bit blocks  203  and the 29 padding bits  240  are input to a RS( 255 ,  223 ) encoder  223  as indicated by the path  242 . The RS( 255 ,  223 ) encoder  223  outputs four 64-bit parity blocks  246 ,  248 ,  250 , and  252 . Thus, the four parity blocks  246 ,  248 ,  250 ,  252  are calculated based on the twenty-seven 65-bit blocks  203  and the 29 padding bits  240 . The group of 31 blocks  225  then is mapped to a FEC codeword  202  which includes the group of 31 blocks  225  and four parity sync headers  254 ,  256 ,  258 , and  260 . To decode the codeword, a receiver needs to find the start and end of the codeword. This is accomplished by marking the parity blocks  246 ,  248 ,  250 , and  252  with a special pattern for the parity sync headers  254 ,  256 ,  258 ,  260 . Those parity sync headers  254 ,  256 ,  258 ,  260  comprise two bits, and are different from the payload block sync headers  210 ,  214 ,  218  because the parity sync headers  254 ,  256 ,  258 ,  260  have a specific pattern, namely 00, 11, 11, 00. This distinction makes it simple for the receiver to determine the codeword alignment and decode the data. 
     The padding bits  240  are not transmitted over the link. Thus, if one or more of these bits were used to transmit OAM data, the receiver would have an incomplete codeword, which would contain the 27 payload blocks  203  and the 4 parity blocks  246 ,  248 ,  250 ,  252 , but not the OAM data. This OAM data can be considered an “erasure” of the channel—that is, data that is known to be lost. The receiver can use the FEC algorithm to deduce the OAM data that is missing. However, doing so takes away from some of the error correcting capacity of the system. Thus, there remains a need for carrying OAM information in 66-bit systems that does not diminish the error correcting capacity of the system. 
     Disclosed herein are embodiments for carrying OAM information in 66-bit systems. Specifically, a single OAM bit is sent in every FEC codeword. The OAM bit may be used to determine the FEC block sync-header patterns. The disclosed embodiments are described in the context of the FEC mechanism described in clause 76, but the disclosed embodiments apply to any coded systems with sync-header patterns. 
     When sending OAM information, it may be desirable to keep the code format as close as practicable to the standardized format. Thus, in at least some embodiments, the amount of OAM information transmitted in a single codeword may be minimized. The smallest amount of OAM information would be 1 bit per FEC codeword. The sync headers may be adapted for sending the OAM information, thus preserving the actively used payload bits and parity bits. In particular, as described above, in the FEC codeword, the sync headers have a fixed bit pattern. To incorporate OAM information, the encoding rule for the parity sync headers may be changed to include two predetermined bit patterns. The 1 bit of OAM information can be used to determine which of the two bit patterns should be transmitted. One of the bit patterns is the existing pattern, 00, 11, 11, 00, and the other bit pattern is the complement, 11, 00, 00, 11. The bit patterns may thus each have 8 bits. 
     Using two bit patterns roughly doubles the chances of seeing a false sync-header pattern. However, the functioning of the receiver synchronization state machine already results in a very low probability of false alignment. The mean time to false lock is measured in millions of years. This small impact is therefore tolerable. 
       FIG. 3  is an illustration of a mechanism  300  for adapting an FEC codeword like the codeword  202  to include OAM information according to an embodiment of the disclosure. The mechanism may be implemented, for example, by a network device as shown in  FIG. 5  described below. As in  FIG. 2 , each of the 27 payload blocks  203  comprises a 64-bit payload block  204 ,  216 ,  208  and a two-bit payload block sync header  210 ,  214 ,  218  loaded into each block. As described above, the FEC is based on a Reed-Solomon code comprising 32 parity bytes and 223 data bytes. This Reed-Solomon code is referred to as an RS( 255 ,  223 ) code. To provide the 223 data bytes to a Reed-Solomon encoder  311 , the 27 payload blocks  203  are mapped onto a codeword payload  302  comprising 27 65-bit blocks. Similarly to  FIG. 2 , each of the 65-bit blocks comprises a 1-bit header derived from a corresponding payload block sync header and the 64-bit payload. For example, the first 65-bit block  222  comprises a 64-bit payload  212  and a header  230  containing the value “1” corresponding to the LSB of the payload block sync header  210 , the second 65-bit block  224  comprises a 64-bit payload  216  and a header  234  containing the value “0” corresponding to the LSB of the payload block sync header  214 , and the twenty-seventh 65-bit block  226  comprises a 64-bit payload  220  and a 1-bit header  238  containing the value “1” corresponding to the LSB of the payload block sync header  218 . The values contained in the 1-bit headers are examples and may change with changes in values of the payload block sync headers. Again the twenty-seven 65-bit blocks encompass a total of 1755 bits, leaving the 29 padding bits  240  to pad out a total of 223 bytes. In the mechanism  300 , the 29 padding bits  240  comprise a 28-bit padding  304  and a 1-bit OAM datum  306 . The OAM datum  306  may contain either a “0” or “1”. 
     The twenty-seven 65-bit blocks  325  and the 28-bit padding  304 , and the OAM datum  306  are input to an RS( 255 ,  223 ) encoder  311  as indicated by the path  307 . The RS( 255 ,  223 ) encoder  311  generates, four 64-bit parity blocks  312 ,  314 ,  316  and  318 . Thus, the four parity blocks  312 ,  314 ,  316 ,  318  are calculated based on the twenty-seven 65-bit blocks  222 ,  224 ,  226 , the 28 padding bits  304 , and the 1-bit OAM datum  306 . Consequently, the values of the parity bits reflect not only the twenty-seven payload blocks  203 , but also the OAM datum  306 . The group of 31 blocks and four parity sync headers that delimit the parity blocks  312 ,  314 ,  316  and  318  constitute an FEC codeword  331 . 
     In the FEC codeword  331 , the four parity blocks  312 ,  314 ,  316  and  318  each comprise two bits and together form a pattern. Rather than a fixed pattern comprising alternating pairs of complementary values, the pattern comprises one of two alternating complementary values based on the value of the 1-bit OAM datum  306 . Thus, the symbol “XX” in parity sync headers  324 ,  330  of a sync header-pattern denotes a pair of bits having either the value “00” or “11.” The symbol the “ XX ” in sync headers  326 ,  328  denotes the complement of the pair of bits in the parity sync headers  324 ,  330 . As would be appreciated by those of ordinary skill in the art, the complement of a bit “0” is “1” and vice versa. By detecting the sync-header pattern, the receiver can determine which OAM bit was contained in the 1-bit OAM datum  306 . For example, a “0” in the 1-bit OAM datum  306  corresponds to the pattern 00 11 11 00 contained in the parity sync headers  324 ,  326 ,  328  and  330 , respectively. Conversely, a “1” in the OAM datum  306  corresponds to the complementary pattern 11 00 00 11 contained in parity sync headers  324 ,  326 ,  328  and  330 , respectively. Alternatively, a “0” in the OAM datum  306  corresponds to the pattern 11 00 00 11 contained in the parity sync headers  324 ,  326 ,  328  and  330 , respectively, and a “1” in the OAM datum  306  corresponds to the pattern 00 11 11 00 contained in the parity sync headers  324 ,  326 ,  328  and  330 , respectively. 
     On receiving the codeword  331 , the receiver calculates its own parity blocks to verify the error-free receipt of the payload and corrects the payload data if there are errors. As previously described, the 29 bits comprising the 28 padding bits  304  and the 1-bit OAM datum  306  are not transmitted down the link. However, by detecting the sync-header pattern, the receiver can infer the value of the OAM data as either “0” or “1” and regenerate the value and use it along with the received payload to calculate its four 64-bit parity blocks. If the parity blocks compare, the receiver knows there is no error in the payload data. If the parity blocks do not compare, then the receiver may use the difference between the received and calculated parity blocks to correct the received payload data. 
     Thus, OAM information is reflected in the mechanism  300  in three ways. First, there is an addition of a 1-bit OAM datum  306 . Second, the 1-bit OAM datum  306  replaces one of the padding bits  240  in  FIG. 2 . The symbol “X” denotes a bit which may take a binary value “0” or “1.” The values “0” and “1” represent complementary logical values taken by a parameter in an embodiment of the codeword  331  and do not necessarily correspond to values of the physical embodiment of the parameter. Third, the 1-bit OAM datum  306  determines the parity sync-header pattern. The symbol “XX” in sync header-pattern denotes a pair of bits having either the value “00” or “11”. The symbol “ XX ” denotes a pair of bits having the complementary value. 
     The FEC algorithm used in 64b66b code format is RS ( 255 ,  223 ), and this algorithm actually has a small number of unused payload bits. These unused bits are filled with zero before the parity is calculated. In order to keep as close to the standardized 64b66b code with FEC format as possible, the amount of Point-to-Point (PtP) WDM OAM information to be sent with 64b66b coded services must be reduced.  FIG. 3  shows a way of sending 1-bit OAM information per FEC codeword. 
     The best place to send this information is in the sync-headers, as the payload and parity bits are actively used. The 1 bit of OAM information determines which of the two bit patterns should be transmitted in the parity sync-headers. For example, as shown in  FIG. 3 , when the PtP WDM OAM bit is 0, the FEC parity sync-header pattern is the existing pattern (00, 11, 11, 00). When the PtP WDM OAM bit is 1, the FEC parity sync-header pattern is the complement, in other word, (11, 00, 00, 11). 
     In this way, one bit of OAM information is carried in each codeword of 31 blocks of data. Because this format is used for 10 Gb/s data links, the data rate is approximately 5 megabits per second (Mb/s), which is fast enough for the OAM application. The OAM information can also be carried via the FEC payload block sync-header patterns. 
       FIG. 4  is schematic diagram of a network device  400  according to an embodiment of the disclosure. The network device  400  is suitable for implementing the disclosed embodiments. The network device  400  comprises ingress ports  410  and receiver units (Rx)  420  for receiving data; a processor, logic unit, or central processing unit (CPU)  430  to process the data; transmitter units (Tx)  440  and egress ports  450  for transmitting the data; and a memory  460  for storing the data. The network device  400  may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports  410 , the receiver units  420 , the transmitter units  440 , and the egress ports  450  for egress or ingress of optical or electrical signals. 
     The processor  430  is implemented by hardware and software. The processor  430  may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor  430  is coupled to and in communication with the ingress ports  410 , receiver units  420 , transmitter units  440 , egress ports  450 , and memory  460 . The processor  430  comprises a 64b66b encoder/decoder  470 . The 64b66b encoder/decoder  470  assists in implementing the disclosed embodiments. The inclusion of the 64b66b encoder/decoder  470  therefore provides a substantial improvement to the functionality of the network device  400  and effects a transformation of the network device  400  to a different state. Alternatively, the 64b66b encoder/decoder  470  is implemented as instructions stored in the memory  460  and executed by the processor  430 . 
     The memory  460  comprises one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory  460  may be volatile and non-volatile and may be read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), and static random-access memory (SRAM). 
       FIG. 5  is a flowchart of a method  500  for receiving an FEC codeword according to an embodiment of the disclosure. At step  502 , an FEC codeword is received. For instance, the receiver  420  of the network device  400  receives the FEC codeword  331 . At step  504 , FEC parity sync-headers are extracted from the FEC codeword. For instance, the 64b66b encoder/decoder  470  extracts the parity sync headers  324 ,  326 ,  328 ,  330  from the FEC codeword  331 . At step  506 , a bit pattern is determined from the FEC parity sync-headers. For instance, the 64b66b encoder/decoder  470  determines whether the parity sync headers  324 ,  326 ,  328 ,  330  have a (00, 11, 11, 00) pattern or a (11, 00, 00, 11) pattern. Finally, at step  508 , OAM information is determined based on the bit pattern. For instance, the 64b66b encoder/decoder  470  determines that the OAM information is a binary 0 if the bit pattern is (00, 11, 11, 00) or a binary 1 if the bit pattern is (11, 00, 00, 11). 
       FIG. 6  is a flowchart of a method  600  for transmitting an FEC codeword according to an embodiment of the disclosure. At step  602 , OAM information is processed. For instance, the 64b66b encoder/decoder  470  in the network device  400  processes the 1-bit OAM datum  306 . At step  604 , a bit pattern is determined based on the OAM information. For instance, the 64b66b encoder/decoder  470  determines that a bit pattern is (00, 11, 11, 00) if the 1-bit OAM datum  306  is a binary 0 or (11, 00, 00, 11) if the 1-bit OAM datum  306  is a binary 1. At step  606 , FEC parity sync-headers are formed based on the bit pattern. For instance, the 64b66b encoder/decoder  470  forms the parity sync headers  324 ,  326 ,  328 ,  330  based on the bit pattern. At step  608 , an FEC codeword is formed with the FEC parity sync-headers. For instance, the 64b66b encoder/decoder  470  forms the FEC codeword  331  with the parity sync headers  324 ,  326 ,  328 ,  330 . Finally, at step  610 , the FEC codeword is transmitted. For instance, the transmitter  440  of the network device  400  transmits the FEC codeword  331 . 
     While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented. 
     In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.