Patent Publication Number: US-2021168058-A1

Title: Flexible Ethernet Operations, Administration, and Maintenance systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present patent/application is a continuation of U.S. patent application Ser. No. 16/522,392, filed Jul. 25, 2019, and entitled “FLEXIBLE ETHERNET OPERATIONS, ADMINISTRATION, AND MAINTENANCE SYSTEMS AND METHODS,” which is a continuation of U.S. patent application Ser. No. 15/801,654, filed Nov. 2, 2017 (which is now U.S. Pat. No. 10,397,088, issued Aug. 27, 2019), and entitled “FLEXIBLE ETHERNET OPERATIONS, ADMINISTRATION, AND MAINTENANCE SYSTEMS AND METHODS,” which is a continuation of U.S. patent application Ser. No. 14/824,667, filed Aug. 12, 2015 (which is now U.S. Pat. No. 9,838,290, issued Dec. 5, 2017), and entitled “FLEXIBLE ETHERNET OPERATIONS, ADMINISTRATION, AND MAINTENANCE SYSTEMS AND METHODS,” which claims priority to U.S. Provisional Patent Application No. 62/186,502, filed Jun. 30, 2015, and entitled “FLEXIBLE ETHERNET OPERATIONS, ADMINISTRATION, AND MAINTENANCE SYSTEMS AND METHODS,” the content of each is incorporated herein by reference. 
    
    
     FIELD OF THE DISCLOSURE 
     The present disclosure generally relates to networking systems and methods. More particularly, the present disclosure relates to Flexible Ethernet (also referred to variously as Flex Ethernet or FlexE) Operations, Administration, and Maintenance (OAM) systems and methods. 
     BACKGROUND OF THE DISCLOSURE 
     Layer 1 protocols and technologies have evolved including Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH) in the 1990s to Optical Transport Network (OTN) in the 2000s. SONET/SDH were synchronous protocols optimized for circuit switching and transmission. OTN evolved from SONET/SDH to provide transparency and support for Wavelength Division Multiplexing (WDM) as well as for optimized transmission of packet traffic. SONET, SDH, and OTN each have a rich suite of Operations, Administration, and Maintenance (OAM) functions and support for a wide range of services and applications. Conventionally, as OTN scales beyond 100 G (B100G), there are emerging frameworks for Layer 1 functionality, namely Flexible OTN (FlexO or B100G) initiatives in the International Telecommunication Union (ITU) and Flex Ethernet in the Optical Internetworking Forum (OIF). 
     Traditionally, Ethernet rates were defined in steps of 10×, i.e., 10 Mb/s, 100 Mb/s, 1 Gb/s (GbE), etc. There is a wrinkle in this 10× progression where 40 Gb/s Ethernet (40 GbE) was defined. Today, there are various Ethernet rates defined, including rates in-between established rates. IEEE 802.3 standards group is discussing 2.5 Gb/s, 5 Gb/s, 25 Gb/s and other various odd rates. Specifically, different rates are established for different applications, such as wireless applications, data center group applications, data center interconnections, etc. There is an expectation that different Ethernet rates will continue as new high-volume applications require optimized solutions. Specifically, router/switch equipment and optical transmission equipment are evolving at different rates. There is a desire to support simple transport of n x Ethernet streams across a faster interface. IEEE historically defines Ethernet rates (Media Access Control (MAC) layer) with projects that also define the Physical (PHY)/Physical Medium Dependent (PMD) rates; the MAC rates and PMD rates are tied and defined together. To address evolution in Ethernet and dissociate the MAC/client rate from the PHY/PMD, Flexible Ethernet has been proposed. Note, as described herein, the terms Flexible Ethernet, Flex Ethernet, and FlexE can be used interchangeably. 
     In transport applications, FlexE can be used to match the flexibility of optical transmission equipment. Specifically, optical transmission equipment (e.g., Dense Wave Division Multiplexing (DWDM)) is evolving to support variable modulation formats, Forward Error Correction (FEC) schemes, baud rates, etc. DWDM equipment can support a variable line rate with the same hardware, relying on configuration and provisioning. FlexE is based on Ethernet constructs, e.g., 64b/66b encoding, recognizing the primary client being transported is Ethernet. Note, the current scope of FlexE is limited to interfacing applications (e.g., bonding, subrating, and channelization). However, it may be advantageous to leverage Flexible Ethernet to augment or even replace OTN and/or FlexO in some transport and switching applications. 
     OAM functionality is critical for operating networks, fault isolation, service and path awareness, and the like. Again, OTN provides a rich set of OAM capabilities for layer 1 circuit switching and transport applications. Ethernet also provides a rich set of OAM capabilities for layer 2 packet networking and transport applications, such as through the efforts of the Metro Ethernet Forum (MEF). However, FlexE clients (in current IA) do not have defined OAM functionality and cannot be transported and switched as a service or private line service in a provider&#39;s network. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     In an embodiment, a node includes circuitry configured to interface a stream of encoded blocks with the blocks including i) data blocks from one or more clients and ii) overhead blocks, wherein a calendar is utilized for block distribution in the stream of encoded blocks; and circuitry configured to process one or more Operations, Administration, and Maintenance (OAM) fields in the overhead blocks, wherein the OAM fields are associated with the one or more clients in the data blocks. 
     In an embodiment, a node configured to support a Flexible Ethernet (FlexE) client service in a network includes circuitry configured to interface a FlexE client; and circuitry configured to monitor and update one or more Operations, Administration, and Maintenance (OAM) fields associated with the FlexE client, wherein the one or more OAM fields include a monitoring field that covers 64b/66b codes for a path of the FlexE client. The monitoring field can provide an error check for the FlexE client instead of a Cyclic Redundancy Check (CRC) at a packet level. The monitoring field can utilize a bitstream Bit Interleaved Parity (BIP) code. The one or more OAM fields can include a plurality of a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. The one or more OAM fields can have a different “O” code from standard Local Fault and Remote Fault information for an associated FlexE group/PHY. The one or more OAM fields can use a multiframe scheme with the one or more OAM fields switched along with calendar slots over the path. The one or more OAM fields can be located in the path in a Reconciliation Sublayer. The one or more OAM fields can be located in a frame header in a FlexE shim. The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     In another embodiment, a method, implemented in a node, for supporting a Flexible Ethernet (FlexE) client service in a network includes interfacing a FlexE client; and updating and monitoring one or more Operations, Administration, and Maintenance (OAM) fields associated with the FlexE client, wherein the one or more OAM fields include a monitoring field that covers 64b/66b codes for a path of the FlexE client. The monitoring field can provide an error check for the FlexE client instead of a Cyclic Redundancy Check (CRC) at a packet level. The monitoring field can utilize a bitstream Bit Interleaved Parity (BIP) code. The one or more OAM fields can include a plurality of a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. The one or more OAM fields can have a different “O” code from standard Local Fault and Remote Fault information for an associated FlexE group/PHY. The one or more OAM fields can use a multiframe scheme with the one or more OAM fields switched along with calendar slots over the path. The one or more OAM fields can be located in the path in a Reconciliation Sublayer. The one or more OAM fields can be located in a frame header in a FlexE shim. The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     In a further embodiment, a network supporting a Flexible Ethernet (FlexE) client includes a plurality of nodes interconnected to one another, wherein the FlexE client is configured between two nodes and traverses one or more of the nodes; wherein each of the two nodes include circuitry configured to interface a FlexE client; and circuitry configured to monitor and update one or more Operations, Administration, and Maintenance (OAM) fields associated with the FlexE client, wherein the one or more OAM fields include a monitoring field that covers 64b/66b codes for a path of the FlexE client. The monitoring field can provide an error check for the FlexE client instead of a Cyclic Redundancy Check (CRC) at a packet level. 
     In an embodiment, a node configured to support a Flexible Ethernet (FlexE) client service in a network includes circuitry configured to receive a FlexE client; and circuitry configured to at least one of monitor and update one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client. The one or more OAM fields can include a client service error monitoring field which does not rely on packet Cyclic Redundancy Check (CRC). The one or more OAM fields can include a client service error monitoring field including a bitstream Bit Interleaved Parity (BIP) code. The one or more OAM fields can include any of a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. The one or more OAM fields can be disassociated from standard Local Fault and Remote Fault information for an associated FlexE group/PHY. The one or more OAM fields can be located using a multiframe scheme in the FlexE overhead. The one or more OAM fields can be implemented in a Reconciliation Sublayer. The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     In another embodiment, a method, implemented in a node, for supporting a Flexible Ethernet (FlexE) client service in a network includes receiving a FlexE client; and at least one of updating and monitoring one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client. The one or more OAM fields can include a client service error monitoring field which does not rely on packet Cyclic Redundancy Check (CRC). The one or more OAM fields can include a client service error monitoring field including a bitstream Bit Interleaved Parity (BIP) code. The one or more OAM fields can include any of a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. The one or more OAM fields can be disassociated from standard Local Fault and Remote Fault information for an associated FlexE group/PHY. The one or more OAM fields can be located using a multiframe scheme in the FlexE overhead. The one or more OAM fields can be implemented in a Reconciliation Sublayer. The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     In a further embodiment, a network supporting a Flexible Ethernet (FlexE) client includes a plurality of nodes interconnected to one another, wherein the FlexE client is configured between two nodes and traverses one or more of the nodes; wherein each of the two nodes include circuitry configured to receive the FlexE client, and circuitry configured to at least one of monitor and update one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client. The one of the two nodes can be a service terminating subscriber equipment and another of the two nodes is a network element in a transport network, wherein the FlexE client includes a User-Network Interface (UNI). Each of the two nodes can be a network element in a transport network, and each of the two nodes is configured to operate as an OAM monitoring point for the FlexE client in the transport network. The one or more OAM fields can include any of a client service monitoring field, a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components/method steps, as appropriate, and in which: 
         FIG. 1  is a diagram of a general structure of FlexE; 
         FIG. 2A  is a block diagram of FlexE mux functions; 
         FIG. 2B  is a block diagram of FlexE demux functions; 
         FIG. 3  is a diagram of a transport network aware or unaware of a router to transport FlexE connection; 
         FIG. 4  is a network diagram of a transport network aware of FlexE; 
         FIG. 5  is a network diagram of a transport network of an example of partial-rate transport of Ethernet PHYs of a FlexE group; 
         FIG. 6  is a diagram of FlexE calendar distribution; 
         FIG. 7  is a diagram of FlexE overhead on each PHY of the FlexE group; 
         FIG. 8  is an example diagram of FlexE calendar slots where 25% of the calendar slots are unavailable; 
         FIG. 9  is a diagram of encoding of ordered set block for FlexE overhead; 
         FIG. 10  is a diagram of FlexE overhead; 
         FIG. 11  is a diagram of data flow and interleaving for a FlexE client mux in calendar slots; 
         FIG. 12  is a diagram of a standard Ethernet local fault ordered set; 
         FIG. 13  is a diagram of an Ethernet remote fault ordered set; 
         FIG. 14  is a diagram of data flow and de-interleaving for a FlexE client demux in calendar slots; 
         FIG. 15  is a diagram of a comparison between the layer stack and atomic functions of FlexO and FlexE; 
         FIG. 16  is a network diagram of a comparison of FlexO service OAM with the FlexE service OAM systems and methods described herein; 
         FIG. 17  is a network diagram with various FlexE OAM monitoring points; 
         FIG. 18  is a diagram of a FlexE OAM implementation with FlexE overhead; 
         FIG. 19  is a block diagram of the FlexE overhead from  FIG. 9  with a new “O” code for implementing FlexE OAM at the RS layer; 
         FIG. 20  is the logical diagram of  FIG. 2  illustrating a location of first and second options for locating FlexE OAM in the IEEE 802.3 stack; and 
         FIG. 21  is a flowchart of a process, implemented in a node, for monitoring a Flexible Ethernet (FlexE) client service in a network. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     In various embodiments, FlexE OAM systems and methods are described to extend and use FlexE clients as a maintenance entity and service with defined OAM functionality. The FlexE OAM systems and methods described various different approaches to an OAM layer in FlexE client overhead. The FlexE OAM systems and methods also address transport performance monitoring complexities introduced by FlexE including error checking allowing monitoring and fault isolation of FlexE clients, without having to perform packet-level error checking (i.e., MAC Frame Check Sequence (FCS)). There are markets (such as intra data-center) that could benefit from layer 1 techniques to bond, possibly switch large (elephant) flows and bypass layer 2 switches. These markets have not adopted OTN for such applications. FlexE could be used in such markets to bypass layer 2 switches, providing cost, power, latency, etc. benefits. Adding FlexE client OAM would enable such application using FlexE client as a service in a provider&#39;s network, and it would help with fault isolation and error checking of variable number/size of flows. 
     Advantageously, the FlexE OAM systems and method augment/create the concept/application of a FlexE client service with simplified performance monitoring for transport equipment. The FlexE OAM systems and methods add OAM fields to the FlexE client, including new Local Fault (LF)/Remote Fault (RF) client service fields independent of the FlexE group, which is tied to PHY LF/RF. The FlexE Client OAM provides fields in the FlexE frame overhead and/or in the path Reconciliation Sublayer (RS); two approaches are considered. 
     Flexible Ethernet 
     FlexE provides a generic mechanism for supporting a variety of Ethernet Media Access Control (MAC) rates that may or may not correspond to any existing Ethernet PHY rate. This includes MAC rates that are both greater than (through bonding) and less than (through sub-rate and channelization) the Ethernet PHY (Physical Layer) rates used to carry FlexE. This can be viewed as a generalization of the Multi-Link Gearbox implementation agreements, removing the restrictions on the number of bonded PHYs (MLG2.0, for example, supports one or two 100GBASE-R PHYs) and the constraint that the client signals correspond to Ethernet rates (MLG2.0 supports only 10 G and 40 G clients). The Multi-Link Gearbox implementation agreements are described in IA #OIF-MLG-01.0 “Multi-link Gearbox Implementation Agreement” (May 2012) and IA #OIF-MLG-02.0 “Multi-link Gearbox Implementation Agreement” (April 2013), the contents of each are incorporated herein by reference. 
     Referring to  FIG. 1 , in an embodiment, a diagram illustrates a general structure of FlexE  10 . Again, conventionally, the general capabilities supported by the FlexE include (i) bonding of Ethernet PHYs, e.g., supporting a 200 G MAC over two bonded 100GBASE-R PHYs, (ii) sub-rates of Ethernet PHYs, e.g., supporting a 50 G MAC over a 100GBASE-R PHY, and (iii) channelization within a PHY or a group of bonded PHYs, e.g., support a 150 G and two 25 G MACs over two bonded 100GBASE-R PHYs. Note, combinations are also contemplated, for example, a sub-rate of a group of bonded PHYs, for example, a 250 G MAC over three bonded 100GBASE-R PHYs. 
     The general structure of FlexE  10  includes a FlexE group  12 , one or more FlexE clients  14 , and a FlexE shim  16 . The FlexE group  12  refers to a group including 1 to n bonded Ethernet PHYs. The FlexE group  12  can include one or more bonded 100GBASE-R PHYs as well as including other rates, including new, higher rates once those standards are complete. The one or more FlexE clients  14  are each an Ethernet flow based on a MAC data rate that may or may not correspond to any Ethernet PHY rate. The FlexE client  14  MAC rates supported are 10, 40, and m×25 Gb/s. The FlexE shim  16  is the layer that maps or demaps the FlexE clients  14  carried over the FlexE group  12 . Similar to the terminology of MLG, a FlexE mux refers to the transmit direction which maps the FlexE clients  14  over the FlexE group  12 . The FlexE demux refers to the receive direction which demaps the FlexE clients  14  from the FlexE group  12 . 
     Referring to  FIGS. 2A and 2B , in an embodiment, block diagrams illustrate FlexE mux functions ( FIG. 2A ) and FlexE demux functions ( FIG. 2B ). The FlexE shim  16  can be envisioned as being in the middle of the Physical Coding Sublayer (PCS) in the 100GBASE-R stack as illustrated in FIG. 80-1 of IEEE Std 802.3-2015, the entirety of which is incorporated herein by reference. The Media Independent Interface (MII), Reconciliation Sublayer (RS), and MAC above the FlexE shim  16  are separate for each FlexE client  14  and operate at the FlexE client rate. The layers below the PCS (100GBASE-R Physical Medium Attachment (PMA), optional FEC, PMD) are used intact as specified for Ethernet. IEEE 802.3 is a working group, and a collection of IEEE standards produced by the working group defining the physical layer and data link layer&#39;s MAC of wired Ethernet. 
       FIG. 2A  illustrates the functions of the FlexE mux (the FlexE shim  16  functions in the transmit direction). Where the 64b/66b encode and idle insert/delete functions and whether these functions are part of the FlexE is application specific. What is presented for insertion into the slots of the FlexE master calendar is a stream of 64b/66b encoded blocks encoded per IEEE Std 802.3-2015 Table 82-4 which has been rate-matched to other clients of the same FlexE shim  16 . This stream of 66b blocks might be created directly at the required rate using back-pressure from a Network Processing Unit (NPU). It might come from a single-lane Ethernet PHY such as 10 G or 25 G, where the process of rate-matching involves both idle insertion/deletion, plus converting the rate-aligned stream from the 4-byte alignment of IEEE Std 802.3-2015 clause 49 to the 8-byte alignment of IEEE Std 802.3-2015 clause 82. Note that the IEEE 802.3 diagrammatic convention of showing idle insertion/deletion as though this were an operation that operates on a stream of 64b/66b blocks, even though strictly speaking this may require 64b/66b decoding and recoding, particularly in the case of converting between 4-byte alignment and 8-byte alignment. The stream of blocks may come from a multi-lane Ethernet PHY, where the lanes need to be deskewed and re-interleaved with alignment markers removed prior to performing idle insertion/deletion to rate match with other clients of the same FlexE shim  16 . Or the stream may have come from another FlexE shim  16 , for example, connected across an OTN network, where all that is required is to perform idle insertion/deletion to rate match with other clients of the same FlexE shim  16 . 
     The 66b blocks from each FlexE client  14  are distributed sequentially into the master calendar in the order described herein. The 66b blocks from the master calendar are distributed to each PHY of the FlexE group  12  according to the ordering described herein. The FlexE overhead is inserted into the sub-calendar of each PHY. The stream of 66b blocks of each PHY is distributed to the PCS lanes of that PHY with the insertion of alignment markers, and this is presented at the PMA service interface in the 100GBASE-R stack. Lower layers and interfaces of the 100GBASE-R Ethernet PHY (e.g., CAUI, FEC, PMA, PMD) are used as specified in IEEE Std 802.3-2015. Error Control blocks are generated for insertion into calendar slots that are unused or unavailable. LF blocks are generated for insertion into the calendar slots of any failed FlexE client. 
       FIG. 2B  illustrates the functions of the FlexE demux (the FlexE shim  16  in the receive direction). The layers of each 100GBASE R PHYs below the PCS are used as specified in IEEE Std 802.3-2012, the entirety of which is incorporated herein by reference. The PCS lanes are recovered, deskewed, reinterleaved, and the alignment markers are removed. The aggregate stream is descrambled. The calendar slots of the each PHY are logically interleaved in the order specified herein. The FlexE overhead is recovered from each PHY. In the case that any PHY of the FlexE group  12  has failed (PCS_Status=FALSE) or overhead lock or calendar lock has not been achieved on the overhead of any of the PHYs, LF is generated to be demapped from the master calendar for each FlexE PHY. The 66b blocks are extracted from the master calendar positions assigned to each FlexE client in the order described herein. 
     Where the Idle Insertion/Deletion, 66B Decoding functions are performed and whether they are inside or outside the FlexE is application specific. The 66b blocks could be delivered directly to an NPU. If delivered to a single-lane PHY, idle insertion/deletion may be used to increase the rate to the PHY rate, realigning to 4-byte boundaries in the process (for 10 G or 25 G) and recoding 64b/66b according to clause 49. For a multi-lane PHY, idle insertion/deletion is used to increase the rate to the PHY rate less the space needed for alignment markers, the blocks are distributed to PCS lanes with AM insertion. For a FlexE client mapped over OTN, idle insertion/deletion may be used to adjust the rate as required for the OTN mapping. 
     FlexE Applications 
     FlexE can support a variety of applications. A non-exhaustive list includes:
         Router to Transport Connection.   Intra-Data Center “Fat Pipe” application: bonded PHYs for flows exceeding the PHY rate, or carrying traffic that doesn&#39;t distribute efficiently with LAG.   Generalized MLG for port expansion applications, e.g., an n×100 G PHY as an umbilicus to a satellite shelf of lower rate ports.       

     Referring to  FIG. 3 , in an embodiment, a network diagram illustrates a transport network  20  unaware of a router to transport FlexE connection. In  FIG. 3 , the FlexE shim  16 , e.g., in a router or switch, maps the FlexE client(s)  14  over a group of bonded Ethernet PHYs  22 . Each of the Ethernet PHYs  22  is carried independently over the transport network  20  using a PCS codeword transparent mapping (e.g., the mapping of 100GBASE-R into Optical channel Path Unit 4 (OPU4) as described in ITU-T Recommendation G.709 clause 17.7.5), the entirety of which is incorporated herein by reference. The Ethernet PHYs  22  are intended to be carried over the same fiber route. All of the PHYs  22  of the FlexE group  12  need to be interconnected between the same two FlexE shims  16 . In this case, the FlexE shim  16  will need to tolerate and accommodate considerably more skew than if the FlexE shims  16  were only separated by an Ethernet link distance of 40 km or less, as the transport network  20  could carry the signal over thousands of kilometers. For the case illustrated in  FIG. 3 , it is the PHYs  22  of the FlexE group  12  which are carried over the transport network  20 . Note, in  FIG. 3 , the transport network  20  is unaware of FlexE  10 . 
     Referring to  FIG. 4 , in an embodiment, a network diagram illustrates a transport network  30  aware of FlexE. In  FIG. 4 , the distance between any pair of FlexE shims  16  is limited to the Ethernet link distance (about 40 km maximum), so the amount of skew that needs to be tolerated and compensated is considerably less. The other important distinction here is that it is the FlexE clients  14  rather than the PHYs  22  of the FlexE group  12  which are carried over the transport network  30 . The FlexE client  14  could be constructed to be the complete size of the payload that can be carried over a single wavelength (e.g., construct 200 G to fill a Dual Polarization (DP) 16-Quadrature Amplitude Modulation (16QAM) wavelength with the bonding of two 100GBASE-R PHYs), or could be a smaller client which is multiplexed and switched at a sub-wavelength level, using the mapping described in ITU-T Recommendation G.709 clause 17.9 to carry the FlexE client signal over an Optical channel Data Unit flex (ODUflex) Constant Bit Rate (CBR). 
     Referring to  FIG. 5 , in an embodiment, a network diagram illustrates a transport network  40  of an example of partial-rate transport of Ethernet PHYs  22  of a FlexE group  12 . Here, the Ethernet PHY rate may be greater than the wavelength rate, and there is a reason (for example, wavelengths terminated on different line cards) that it is not desirable to terminate the FlexE shim  16  in transport equipment  42 . The example illustrated here is a 150 G FlexE client carried over two 75 G wavelengths, but one can imagine a possible future 200 GbE rate where one would want to carry a 300 G FlexE client over two bonded 200 GbE and be able to carry the two partially-filled Ethernet PHYs over 150 G wavelengths. 
     FlexE Group 
     The FlexE group  12  includes from 1 to n 100GBASE-R Ethernet PHYs  22 . Each PHY can be identified by a number in the range [1-254]. The values of 0 and 255 are reserved. A PHY number may correspond to the physical port ordering on equipment, but the FlexE shim  16  at each end of the group must identify each PHY in the group  12  using the same PHY number. PHY numbers do not need to be contiguous: even if a FlexE group  12  is composed of initially contiguous PHY numbers, this may not be preserved as PHYs are added to or removed from the group  12 . 
     Each of these PHYs  22  uses the bulk of the PCS functions described in IEEE Std 802.3-2015 clause 82 including PCS lane distribution, lane marker insertion, alignment, and deskew. All the PHYs  22  of the FlexE group  12  must use the same physical layer clock. Each PHY  22  of the FlexE group  12  is able to deliver a logically serial stream of 64b/66b encoded blocks from the FlexE mux to the FlexE demux at a data rate of: 
       103.125 Gb/s×16383/16384±100 ppm
 
     FlexE supports a value of n (number of PHYs  22  in the FlexE group  12 ) up to 256, although practical implementations are likely limited to the range of 4-8 PHYs  22 . The fraction applied to the base rate reflects the fact that 1/16K of the space of the interface is occupied by PCS lane alignment markers which are not space available to carry the FlexE payload. The FlexE payload carried over each PHY  22  of the FlexE group  12  has the format of a logically serial stream of (mostly) legal 64b/66b blocks with the format described in IEEE Std 802.3-2015 FIG. 82-4, although the blocks do not appear in a sequence that makes sense to interpret as an Ethernet interface. The actual PHYs  22  of the FlexE group  12  may transcode these blocks to 256b/257b format according to IEEE Std 802.3-2015 clause 91.5.2.5 according to the PHY type, but they are trans-decoded back to 64b/66b blocks prior to delivery to the FlexE demux. 
     FlexE Client 
     Each FlexE client  14  is a logically serial stream of 64b/66b blocks representing an Ethernet MAC layer. The MAC layer of a FlexE client  14  may operate at a rate of 10, 40, or n×25 Gb/s. The 64b/66b encoding is according to IEEE Std 802.3-2015 FIG. 82-4. For certain cases where the FlexE client  14  originates from an Ethernet PHY, this may require conversion from the 4-byte alignment of start-of-packet for a PHY which uses the clause-49 PCS to the 8-byte alignment of FIG. 82-4 as part of the idle insertion/deletion process. 
     In the case where the FlexE client  14  comes from an Ethernet PHY which uses PCS lane alignment markers (e.g., 40GBASE-R), the lanes must be deskewed, re-interleaved and serialized, removing the alignment markers to produce the 64b/66b stream which is treated as a FlexE client  14 . All FlexE clients  14  transmitted over the same FlexE group  12  must be aligned to a common clock. This is accomplished using idle insertion/deletion as described in IEEE Std 802.3-2015 clause 82.2.3.6. In addition, the bit-rate of each FlexE client  14  is reduced slightly from nominal as part of this process to allow room for insertion of FlexE overhead and the PCS lane alignment markers of the FlexE group  12 . So the 64b/66b encoded format of a FlexE client  14  operates at a data rate of: 
       FlexE Client MAC rate×66/64×16383/16384×20460/20461±100 ppm
 
     This is a rate reduction slightly under 0.011%, which is well within what can be accomplished with idle insertion/deletion without packet loss. Note that this does not actually correspond to any clock that needs to be generated in an implementation, as the idle insertion-deletion process will simply operate by filling the allocated block positions in the FlexE group  12  from a FlexE client  14  First-In First-Out (FIFO) with its own deficit idle counter and inserting or deleting idles in the process of filling the block positions in the FlexE group  12  according to a FlexE calendar. 
     FlexE Calendar 
     The FlexE operates using a calendar which assigns 66b block positions on each PHY  22  of the FlexE group  12  to each of the FlexE clients  14 . The calendar has a granularity of 5 G and has a length of 20 slots per 100 G of FlexE group  12  capacity. Two calendars are supported: an “A” and a “B” calendar. At any given time, one of the calendars is used for mapping the FlexE clients  14  into the FlexE group  12  and demapping the FlexE clients  14  from the FlexE group  12 . The two calendars are provided to facilitate reconfiguration. 
     For a FlexE group  12  including n bonded 100GBASE-R PHYs, the logical length of the master calendar is 20n. The blocks as allocated per the master calendar are distributed to n sub-calendars of length 20 on each of the PHYs of the FlexE group as shown in  FIG. 6 .  FIG. 6  is a diagram illustrating FlexE calendar distribution. The order of distribution of twenty blocks at a time is selected over simple “round robin” distribution of 66b blocks to facilitate addition of PHYs  22  to a FlexE group  12  without the need to change the calendar slots allocated to existing FlexE clients  14 . Calendar slots are identified by their PHY number and the slot [0-19] (within that PHY). The calendar slots assigned to FlexE clients  14  do not change when PHYs are added or removed from the group  12 . PHYs with calendar slots assigned to FlexE clients  14  cannot be removed from the group (or all FlexE clients  14  need to be moved to other PHYs or removed BEFORE a PHY is removed from the group). The “logical” sequence number of a calendar slot is 20×the PHY number plus the calendar slot number within the PHY. The sequence is ascending order. Note that the sequence numbering is not necessarily consecutive when the assigned PHY numbers are not contiguous. This logical order only matters when calendar slots on different PHYs are assigned to the same FlexE client  14 . 
     FlexE Overhead and Alignment 
     The alignment of the data from the PHYs  22  of the FlexE group  12  is accomplished by the insertion of FlexE overhead into a stream of 66b blocks carried over the FlexE group  12 . The FlexE overhead is encoded as a 66b block which can be recognized independently of the FlexE client data. An illustration of the FlexE overhead on each PHY of the FlexE group is shown in  FIG. 7 . 
     On a  100 GBASE-R PHY, a FlexE overhead block will occur approximately once per 13.1 μs. The actual format of the FlexE overhead blocks is such that they occur in a repeating sequence of four blocks, so the sequence has a period of approximately 52.4 μs. This sequence is used to align all of the PHYs  22  of the FlexE group  12  at the FlexE demux to reconstruct the sequence in the order of the master calendar so that the FlexE clients  14  can be recovered. 
     The scenario illustrated in  FIG. 5  is supported by marking a certain number of the calendar slots as unavailable. This is different from “unused”, in that it is known, due to transport network constraints, that not all of the calendar slots generated from the FlexE mux will reach the FlexE demux and, therefore, no FlexE client  14  should be assigned to those slots. The intention is that when a PHY  22  of the FlexE group  12  is carried across the transport network, the mapping is able to compress the signal to less than the PHY rate by dropping the unavailable calendar slots. A case where 25% of the calendar slots are unavailable is illustrated in  FIG. 8 . 
     The anchor position FlexE overhead is encoded as an ordered set (control block type Ox4B). A different “O” code (Operational Code) is selected (i.e. 0x5) which is different from that for the sequence ordered set used by Ethernet or the signal ordered set used by Fibre channel. The information to be transmitted in the FlexE overhead is encoded into the bytes D 1 , D 2 , and D 3  of the overhead set block is shown in  FIG. 9 . 
     The information which needs to be included in the overhead includes:
         The number of PHYs  22  in the FlexE group  12 ;   The identity (sequence) of this PHY  22  within the FlexE group  12 ;   A way to transmit the programming of the calendars from the FlexE mux to the FlexE demux;   A way to indicate which calendar (“A” or “B”) is in use at this time; and   A management channel. This may not be necessary in all applications (for example, if a network management system has direct access to the FlexE shim  16  at both ends of the connection), but may be useful for applications such as using FlexE for an n x×100 G umbilicus to a remote shelf of lower-rate ports.       

     The amount of information to be conveyed from the FlexE mux to the FlexE demux exceeds the 24 bits available. This is addressed by spreading the relevant overhead across a sequence of four FlexE overhead blocks, each separated by 20×1023 FlexE data blocks. The encoding of the information in the sequence of four FlexE overhead blocks is illustrated in  FIG. 10 . The meaning, interpretation and processing of this overhead is explained in clause 7 of Contribution Number: oif2015.127.01, the entirety of which is incorporated herein by reference. The first of each sequence of four FlexE overhead blocks is encoded as an ordered set as shown in  FIG. 9 . The next three FlexE overhead blocks are encoded as data 66b blocks at known locations based on the position of the ordered set block. The block with the higher order 2 bits of D1=00 serves as a marker to be used for alignment and re-interleaving of the sub-calendars from each of the PHYs  22  of the FlexE group  12  at the FlexE demux. The full sequence repeats once per approximately 52.4 μs. Subject to the amount of buffer provided in a given implementation, skew detection and compensation across the PHYs  22  of the FlexE group  12  can be compensated up to a bit less than half of this amount. 
     FlexE Group Functions 
     The FlexE group  12  includes from 1 to n 100GBASE-R PHYs  22 . Each 100GBASE-R PHY  22  reuses nearly all of the functions as described for 100GBASE-R in IEEE Std 802.3-2015. This includes a subset of the functions of the PCS as described in clause 82, and all of the functions from sub-layers below the PCS as described in clauses 83, 86, 88, and 91-95 as appropriate according to the PHY type. 
     The FlexE shim  16  provides to each FlexE group PHY  22  a set of 64b/66b encoded blocks that are encoded according to FIG. 82-4 in IEEE Std 802.3-2015. Within the PCS, clause 82, each FlexE group PHY reuses (with reference to FIG. 82-2 in IEEE Std 802.3-2015) in the transmit direction, the scrambler, block distribution, and alignment insertion processes. In the receive direction, each FlexE group PHY reuses the lane block sync, alignment lock, and lane deskew (including Bit Error Rate (BER) monitor), lane reorder, alignment removal, and descrambling. 
     FlexE Clients 
     The format and standard bit rate of FlexE client  14  are described in clause 6.2 in IEEE Std 802.3-2015. However, FlexE also introduced the concept of flexible non-standard rates such as n×25 G (i.e. 175 G, 225 G, 300 G . . . ). FlexE clients  14  generally originate from one of the following sources. A FlexE client  14  may be generated internally within a system, for example from a Network Processing Unit (NPU) within a router or the like. The packet flow is generated at the determined FlexE client  14  MAC rate and 64b/66b encoded according to IEEE Std 802.3-2015 FIG. 82-4. 
     FlexE clients  14  at the rates of 10 G, 40 G, 100 G, and in the future 25 G and 400 G can be created from an Ethernet PHY  22  at the corresponding rate with some processing to convert to the FlexE client  14  format and rate. 
     A 10GBASE-R signal will be converted to a 10 G FlexE client signal format before presenting to a FlexE mux by using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 82.2.3.6 (which will actually be doing idle deletion) to adapt the signal to the 10 G FlexE client rate and align start of packet to an 8-byte boundary, encoding according to the 66b block format of FIG. 82-4 in IEEE Std 802.3-2015 from the received format which uses the blocks according to FIG. 49-7 in IEEE Std 802.3-2015. A 10 G FlexE client signal coming from a FlexE demux can be converted to a 10GBASE-R signal format by using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 49.2.4.7 (which will actually be doing idle insertion to compensate for the space that had been occupied by FlexE group lane alignment markers and FlexE overhead), which also aligns to 4-byte boundaries, and encodes the blocks according to FIG. 49-7 in IEEE Std 802.3-2015. 
     The 25GBASE-R specification is under development in the IEEE P802.3by project, which is incorporated herein by reference. While the specification has not been finalized, judging from currently adopted baselines, converting a 25GBASE-R signal to a 25 G FlexE client signal format is expected to involve correcting FEC errors (if FEC present), removing the FEC, removing the CWM (if present), trans-decoding to 64b/66b, and using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 82.2.3.6 (which will actually be doing idle deletion to make room for the FlexE overhead) to adapt the signal to the 25 G FlexE client rate and align start of packet to an 8-byte boundary, encoding according to the 66b block format of FIG. 82-4 in IEEE Std 802.3-2015 from the received format which uses the blocks according to FIG. 49-7 of the same standard. The conversion of a 25 G FlexE client signal coming from a FlexE demux to a 25GBASE-R signal is expected to involve using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 49.2.4.7 (which will actually be doing idle insertion to compensate for the space that had been occupied by FlexE overhead—the FlexE group lane alignment markers take the same proportion of the space as the CWM), 256b/257b transcoding, insertion of the CWM, and calculation and insertion of FEC, if appropriate. 
     A 40GBASE-R signal can be converted to a FlexE client  14  by serializing and deskewing the PCS lanes, removing the PCS lane alignment markers, and using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 82.2.3.6 (which will actually be doing idle deletion to make room for the FlexE overhead) to adapt the signal to the 40 G FlexE client rate. A 40 G FlexE client  14  coming from a FlexE demux is converted to a 40GBASE-R interface by using the idle insertion/deletion process as described in IEEE Std 802.3-2015 clause 82.2.3.6 (which in this direction is generally doing idle insertion to restore the nominal bit-rate after removal of FlexE overhead), distributing the blocks round-robin to the four PCS lanes, and inserting PCS lane alignment markers. 
     A 100GBASE-R signal without FEC can be converted to and from a FlexE client  14  in the same manner as 40GBASE-R described above (except that the number of PCS lanes is 20 rather than 4). A 100GBASE-R signal with FEC, in converting to a FlexE client  14 , also will correct any errors per the FEC code, remove the FEC, and trans-decode from 256b/257b prior to the idle insertion/deletion process. To convert a 100 G FlexE client  14  coming from a FlexE demux to a 100GBASE-R signal with FEC involves the same processes as for 40GBASE-R, but in addition, transcoding the signal to 256b/257b, inserting the FEC lane alignment markers, and adding the FEC. 
     400GBASE-R is under development in the P802.3bs task force. This standard is not complete, but the process of converting to and from a 400 G FlexE client  14  is expected to be similar to that for converting a 100GBASE-R client with FEC to and from a 100 G FlexE client  14 . 
     A FlexE client might come from another FlexE shim. In the case of transport network equipment which implements the FlexE shim  16 , FlexE clients  14  can be delivered from the FlexE shim  16  at the transport network ingress to another FlexE shim at the transport network egress. The FlexE flow as a sequence of 64b/66b encoded blocks is expected to be carried over the transport network without packet loss. As no timing information is carried by this stream, idle insertion or padding is possible in the mapping over the transport network. The FlexE shim  16  at the network egress will only need to perform idle insertion/deletion according to IEEE Std 802.3-2015 clause 82.2.3.6, not due to any expected change in the nominal bit-rate, but simply to align the clock with that of the other FlexE clients  14  for the same shim. 
     Interconnect Flexibility 
     Note that since the format of the FlexE client  14  is simply a logically serial stream of 66b blocks at a given rate, FlexE clients  14  do not need to be produced or received in the same manner at both ends of the connection. For example, a 10 G, 25 G, or 40 G FlexE client  14  might be generated as a system internal signal in the main chassis of a system, connected using an n×100 G FlexE umbilicus to a satellite shelf, and connected to physical 10GBASE-R, 25GBASE-R, and 40GBASE-R ports on the satellite shelf. In the case where the FlexE mux is receiving a FlexE client  14  from a physical Ethernet port and the FlexE demux is delivering that FlexE client  14  to a physical Ethernet port, the two ports have to be the same rate, but they do not have to be the same PHY type. 
     FlexE Overhead 
     The format of the FlexE overhead is indicated in  FIG. 10 . The FlexE overhead is encoded as a 66b block and is inserted on each PHY  22  of the FlexE group  12 . One overhead block is inserted after every 1023 iterations of the length 20 calendar of FlexE data blocks, so the sequence is one block of overhead followed by 1023×20 blocks of data followed by one block of overhead. 
     A FlexE overhead lock is achieved at the receiver (FlexE demux) by recognizing the FlexE “O” code used to send the first of every four FlexE overhead blocks, so the sync header is 10, the control block type is 0x4B (ordered set), and the “O” code is 0x5. Once FlexE overhead lock is achieved, the next expected FlexE overhead will be 1023×20 +1 block positions later. While in FlexE overhead lock, bytes D 1 -D 3  of the ordered set block, plus the data blocks occurring at 66B block positions 20461, 40922, and 122766 blocks beyond the ordered set block will be interpreted as FlexE overhead multiframe. FlexE overhead is not interpreted if not in FlexE overhead lock. FlexE overhead lock will be lost if the sync header, control block type, or O code do not match at the expected position, such as for 5 occurrences. 
     Calendar 
     There are two calendars for each PHY  22  of the FlexE group  12 : the “A” calendar (encoded as 0) and the “B” calendar (encoded as 1). The two calendars are used to facilitate hitless reconfiguration. Normally, changes are only made to the calendar which is not currently in use. Exceptions would include initial link configuration or replacement of a failed circuit pack where it is necessary to download the calendar information into the replacement pack. 
     The calendar in use is signaled from the FlexE mux to the FlexE demux in bit position 2 of the first three of the four codewords in the FlexE multiframe sequence. While most of the FlexE overhead can be reliably protected by the Cyclic Redundancy Check (CRC), the calendar in use must be interpreted even if the CRC is bad, since the FlexE demux must switch its calendar in use at precisely the same multiframe boundary as the FlexE mux. So that this can be done reliably, three copies of the calendar in use are transmitted and interpreted by the receiver by majority vote. Since the three copies are separated into different FlexE overhead blocks across the multiframe (1,351,704 bits apart from each other), the different copies will never be affected by the same burst error. Since each PHY should have a BER of 10 −12  or better, the probability of two instances of the calendar in use being wrong is no more than 10 −24 , which can safely be ignored. 
     When the calendar in use changes from a 0 to a 1, or from a 1 to a 0, the calendar used by both the FlexE mux and the FlexE demux will be changed beginning with the first FlexE data block of the next FlexE overhead ordered set block. 
     The set of PHYs  22  in the FlexE group  12  (not necessarily consecutive) are indicated in the “PHY Map Active” portion of the PHY Map field of the FlexE overhead, distributed over the same group of forty sets of four blocks of FlexE overhead as are used to transmit the contents of the two calendars as described herein. The identity of this PHY  22  in the FlexE group (from 1 to n) is encoded in the D 3  byte of the FlexE overhead ordered set block. Note that this is persistent information which does not change frequently. The receiver accepts a value for “This PHY” when seen identically for the second time in frames with a good CRC, and updates to the PHY map bit map are accepted from frames with good CRC. The “PHY Map Request” bits of the PHY map are used for a protocol for the addition and removal of PHYs from the FlexE server group as described herein. 
     The contents of both the A and B calendar are transmitted continuously from the FlexE mux to the FlexE demux, with one calendar slot being programmed in each multiframe of the FlexE overhead. The PC bit indicates which calendar (0=the “A” calendar and 1=the “B” calendar). All slots of the A calendar are programmed (20 muliframes, one for each slot), followed by all slots of the B calendar (20 multiframes). The PC bit will be equal to 0 for the twenty multiframes for programming of the “A” calendar, and equal to 1 for the twenty multiframes for programming of the “B” calendar. The receiver (FlexE demux) achieves calendar lock when the PC bit changes from 0 to 1 or from 1 to 0 in consecutive multiframes with a good CRC. The receiver loses calendar lock if the expected value of the PC bit is wrong in a multiframe with a good CRC. 
     The calendar is programmed in the same order as the calendar is in the frame from slots 0 to 19, starting with the first multiframe where PC=0 (or is expected to be zero while in calendar lock) for the A calendar and the first multiframe where PC=1 (or is expected to be 1 while in calendar lock) for the B calendar. 
     The Client field indicates which of the FlexE clients is mapped into a given calendar slot. The size of a given FlexE client can be calculated based on the number of calendar slots that client is assigned to. The Client is a 16-bit field transmitted in the 2 nd  and 3 rd  octets in the second “row” of the multiframe (the first data block after the ordered set). The value 0x000 indicates a calendar slot which is unused (but available). The value OxFFFF (all ones) indicates a calendar slot which is unavailable, for the case indicated in  FIG. 5  where the full FlexE group PHY rate cannot be carried over the transport network. 
     Calendar slot assignment changes are ignored while not in Calendar lock. Any change to which client is mapped into a calendar slot is ignored in a frame with a bad CRC. The full contents of both calendars are transmitted from the FlexE mux to the FlexE demux approximately once every 2 ms. The fact that the calendars are transmitted continuously avoids an inconsistency between the calendars at the FlexE mux and the FlexE demux due to a lost message. 
     The normal process of reconfiguration (e.g., adding new FlexE clients  14  to the FlexE group  12  or resizing a FlexE client  14 ) will involve programming the new configuration into the calendar which is not in use, then switching to the updated calendar, and finally updating the original calendar. The FlexE mux should wait for at least 3 cycles of transmission of the full calendar after the last update before switching the updated calendar to be the new calendar in use as described in clause 7.3.2 in IEEE Std 802.3-2015. This provides a vanishingly small probability that a calendar update has not been successfully received without requiring an Acknowledgement (ACK). 
     Management Channel 
     Certain applications may require the use of a management channel between the FlexE mux and the FlexE demux. The management channel may not be required for an application where a single management system or controller has access to the FlexE shims  16  on both ends of the FlexE group  12 , but certain applications such as using FlexE for an n×100 G umbilicus to a remote shelf may use the management channel for communication with the controller in the remote shelf for configuration, alarming, software update, etc. When the management channel is not used, it is transmitted as zeros before scrambling 
     The format of the management channel is not specified and is application specific. The management channel occupies 18 bytes of each FlexE. The total capacity of the management channel is approximately 2.749 Mb/s. 
     Each PHY  22  of the FlexE group can carry its own management channel. The management channels are not aggregated across the FlexE group to keep open the possibility to pass back remote failure indications, for example, losing one of the PHYs  22  of the FlexE group  12 . Most likely protocols that would be carried over this type of channel would be message oriented and would have some sort of frame check sequence on each packet, and therefore not require marking bytes of the management channel as bad if the CRC on the FlexE overhead is bad. 
     FlexE Group Number 
     For some applications, it may be desirable to be able to distinguish one FlexE group  12  from another: for example, an 8-port device which is capable of being provisioned as a single 8-port group or two 4-port groups may create a situation where the PHY numbers could overlap between different groups. For such a situation, a 7-bit FlexE group number is provided which allows for checking that the correct PHY  22  is being received from the correct group number. When this field is used, it must be provisioned to the same value in both directions. When a non-zero value is provisioned, the received group number will be checked against the provisioned group number, and any mismatch will be alarmed to indicate the misconnection. 
     Reserved Bits 
     18 bits per FlexE overhead multiframe are reserved for possible future extensions to this implementation. The reserved bits can be transmitted as zero before scrambling. An implementation could choose to treat receipt of non-zero in the reserved bits in a multi-frame with a good CRC as a minor alarm, as it could indicate interconnection with a future version of this implementation that is not known to be interoperable. An implementation could also choose to ignore these bits on receipt and leave the responsibility to an implementation of a newer version of the implementation to recognize receipt of zeros as an indication of interconnection with an older version, and presumably the newer version knows whether it is interoperable with the older version. 
     CRC-16 
     Primarily to avoid corrupting the content of the calendars in the presence of bit errors, the FlexE overhead is protected by a CRC. The CRC is calculated over the following bits across the four rows of the FlexE overhead multiframe (in the order transmitted and received, not the order described):
         The D 1 , D 2 , and D 3  bytes of the ordered set overhead block   All eight octets after the sync header of the 2 nd  and 3 rd  overhead data blocks   The first six octets after the sync header of the 4 th  overhead data block.       

     The CRC is calculated using the polynomial x 16 +x 12 +x 5 +1. This value is inserted by the FlexE mux into the transmitted overhead. It is calculated by the FlexE demux over the same set of bits and compared to the received value. Various overhead described in the previous clauses is either accepted or ignored based on whether the CRC matches the expected value. 
     FlexE Mux Data Flow 
     The FlexE Mux creates a logically serial stream of 66b blocks by interleaving FlexE client signals, according to a master calendar of length 20 n slots for a FlexE group including n 100GBASE-R PHYs. Each slot corresponds to 5 G of bandwidth. A FlexE client is assigned a number of slots according to its bandwidth divided by 5 G. The master calendar is distributed as described earlier in  FIG. 6 . 
       FIG. 11  presents an example of insertion of different bandwidth FlexE clients  14  into a logical master calendar. The slots assigned to a particular FlexE client  14  do not all need to be on the same PHY  22  of the FlexE group  12 , and new clients  14  can be added as long as there are sufficient slots available. Any slot in the master calendar which is either “unassigned” or “unavailable” will be filled with Ethernet Error control blocks with the format given in  FIG. 12 . This ensures that any error in calendar slot assignment cannot appear to the FlexE demux as valid FlexE client data. Any incoming FlexE client  14  which has failed (e.g., one created from a physical Ethernet signal where the signal has failed, or failure to achieve block lock) will cause the slots assigned to that FlexE client  14  to be filled with Ethernet Local Fault ordered sets with the format as given in  FIG. 13 . 
     These rules allow for the creation of the complete data sequence on each PHY  22  of the FlexE group  12 . The FlexE overhead is inserted onto each FlexE group PHY after every 1023 repetitions of the calendar sequence in the same relative position to the calendar sequence on every PHY  22 . This provides a marker which allows the data from the different PHYs  22  of the FlexE group  12  to be re-interleaved in the original sequence so that the FlexE clients  14  can be extracted. The 66b block stream is then converted into the format for the individual FlexE group PHY, which includes block distribution and alignment marker insertion, along with (if applicable) 256b/257b transcoding and FEC calculation and insertion. 
     FlexE Demux Data Flow 
     The FlexE Demux operates on a sequence of 66b blocks received from each PHY  22  of the FlexE group  12 . Recovering this sequence of blocks includes (if applicable), FEC error correction and FEC remove and trans-decoding to 64b/66b, PCS or FEC lane alignment, reinterleaving, and alignment marker removal. Once this has occurred, the PHYs  22  of the FlexE group  12  are re-interleaved so that FlexE clients  14  can be recovered as illustrated in  FIG. 14 . Note that the FlexE overhead multiframe repeats on a cycle of approximately 52.4 μs, which allows measuring skew differences between PHYs  22  of the FlexE group  12  of approximately ±25 μs. 
     Skew Tolerance Requirements 
     The amount of skew to be expected between the PHYs  22  of the FlexE group  12  are application specific. Skew requirements are specified for two classes of applications—low skew and high skew applications. Low Skew Applications include intra-data-center applications, plus those transport network applications where the FlexE shim  16  is implemented in the transport equipment, and the FlexE clients  14  rather than the PHYs  22  of the FlexE group  12  are carried across the transport network. The skew tolerance requirement for low skew applications is about 300 ns. Note that the intra-PCS-lane skew tolerance requirement for 100GBASE-R is about 49 ns. A larger skew budget is established for FlexE applications of similar reach to account for the fact that the PCS lane deskew is not synchronized across the PHYs  22  of the FlexE group  12 , and there may be other variation, such as cable length, or even heterogeneous 100GBASE-R PHY types which are not present in a single 100GBASE-R interface. 
     High Skew Applications include transport network applications where the PHYs  22  of the FlexE group  12  rather than the FlexE clients  14  are carried over the transport network (FlexE unaware transport). The skew tolerance requirement for high skew applications is about 10 μs. This is established to account for about 6 μs of dispersion-related skew if the PHYs are mapped over lambdas at opposite ends of the “C” band over large distances (e.g., trans-pacific), with extra margin for things like split-band amplifiers and patch cords or the processing time to crunch and uncrunch the signal in the case where not all of the calendar slots can be carried over the transport network connection. 
     If the intra-PHY skew exceeds the skew tolerance, the FlexE clients  14  will not be demapped from the incoming PHYs  22 , but will be sent continuous Ethernet Local Fault Ordered sets as illustrated in  FIG. 13  at the FlexE client rate. If one or more of the PHYs  22  of the FlexE group  12  has failed (e.g., loss of signal, failure to achieve block lock or alignment lock, high BER, or any other condition that results in PCS_Status=FALSE), the FlexE clients  14  will be sent continuous Ethernet Local Fault Ordered sets as illustrated in  FIG. 13  at the FlexE client rate. In addition, when one or more of the PHYs  22  of the FlexE group  12  have failed continuous remote fault ordered sets will be sent back over the FlexE group  12  in the calendar slots assigned to any FlexE clients  14 , and the RF bit will be set in the FlexE overhead of every PHY in the FlexE group toward the far-end shim. 
     Addition and Removal of PHYs from a FlexE Group 
     In general, only one PHY  22  should be added to or removed from a FlexE group  12  at a time. An added PHY  22  begins with all of its calendar slots (except those provisioned as unavailable) as unused. Prior to removing a PHY  22 , all clients must be removed from all of its calendar slots in both the “A” and the “B” calendar, i.e., all calendar slots which are not provisioned as “unavailable” will be “unused”. Addition and removal of PHYs does not change the (PHY,slot) identifier for any calendar slot on any other PHY, and does not change the order of calendar slots assigned to any currently provisioned FlexE client  14 . 
     Addition and removal of PHYs are controlled by the “PHY map active” and “PHY map request” fields of the FlexE overhead. Changes to either of these fields are only accepted from overhead multiframes with a good CRC. These fields are sent identically on every current PHY of the FlexE group. The receiver may choose to receive these fields from multiple PHYs (so if a CRC is bad on one PHY, it receives it from another), or may choose to receive the overhead from only one PHY and rely on the fact that the overhead is repeated in a continuous cycle to receive eventually updates through repetition. 
     Whether the PHY addition procedure to add a new PHY to the group is initiated from one or both ends is application dependent. The new PHY might be added at both ends by the management or control system, or one end might be the master and the other the slave, with the slave echoing back the PHY addition request initiated by the master. The initiation procedure begins by changing the bit position in the “PHY map request field” from a zero to a one, bringing up the new PHY, and transmitting the FlexE overhead on the PHY to be added. 
     The PHY is considered added once the following conditions are met: 
     The far end has also changed the bit position for the PHY to be added from 0 to 1 in the “PHY map request” field. 
     PCS_status=TRUE for the PHY to be added (no Loss of Signal (LOS), block lock and AM lock have been achieved on every PCS lane, no hi_ber). 
     FlexE overhead lock and calendar lock are achieved on the added PHY, the expected value is being received in the “This PHY” field, and the FlexE overhead being received is within the skew tolerance with the rest of the FlexE group. 
     Once these conditions are met, the bit position corresponding to the added PHY is changed from a 0 to a 1 in the “PHY map active” field. FlexE clients  14  may not be assigned to the newly added PHY until both the near end and the far end are indicating a one in the “PHY map active” field for the new PHY. 
     For PHY removal, all FlexE clients  14  must be removed from the A and the B calendars on a PHY before it can be removed. Any calendar slot not provisioned as “unavailable” must be “unused” in both calendars on the PHY. Whether the initiation procedure occurs from one or both ends is implementation dependent—both ends could be configured, or the controller at the far end could echo back the near end request in a master/slave configuration. The procedure begins by changing the PHY Map Request bit corresponding to the PHY to be deleted from a 1 to a 0. After the near end has changed the PHY Map Request bit to a 0, when the far end also has changed its PHY Map Request bit to a zero, the near end changes its PHY Map Active bit to a 0. The PHY is considered deleted once a 0 is being received in the PHY Map Active bit from the far end. The FlexE overhead continues to be sent on the PHY being deleted until the far end is indicating 0 in its PHY Map Active bit corresponding to the PHY. 
     FlexE Management 
     For FlexE group management, the control variables are the number of PHYs  22  in the FlexE group. The status variables are PHY_align—True if all PHYs in the FlexE group are being received and are within the skew tolerance of the implementation. False if one or more of the incoming PHYs has failed or if the inter-PHY skew exceeds the skew tolerance of the implementation. 
     For FlexE group management, per PHY, note that all 100GBASE-R control and status variables in or blow the PCS are applicable to each PHY of the FlexE group  12 . 
     Control Variables:
         PHY number (within the FlexE Group)   Number of available Calendar Slots (20 except when entire PHY can&#39;t be carried across the transport network)   Mux_Calendar_A[0..19] and Mux_Calendar_B[0..19] The FlexE client that is mapped into each of the respective calendar slots in the transmit direction. The initial default for all calendar slots is UNUSED, except in the case where the number of available calendar slots is less than 20, in which case the first AVAILABLE number of slots default to UNUSED and the rest default to UNAVAILABLE.   Tx_Calander_in_use—Indicates whether the A or the B calendar is currently active. Status Variables   Demux_Calendar_A[0..19] and Demux_Calendar_B[0..19] The FlexE client that the far end has mapped into each of the calendar slots in the received direction. The initial default for all calendar slots (prior to information received from the far end) is UNUSED, except in the case where the number of available calendar slots is less than 20, in which case the first AVAILABLE number of slots default to UNUSED and the rest default to UNAVAILABLE.   Rx_Calendar_in_use—Indicates the calendar being used at the current time by the far end.       

     Transport Network Mappings for Flex Ethernet Signals 
     Three different methods of mapping of FlexE signals over transport networks are possible. The case of FlexE unaware transport involves the transport network mapping each of the Ethernet PHYs is independently over the transport network using a PCS codeword transparent mapping. Since the FlexE mux and FlexE demux are separated by transport network distances, this requires a “high skew” implementation of the FlexE shim  16 . 
     Note that certain existing OTN mappers/demappers are not fully PCS codeword transparent with respect to LF and RF ordered sets, and may mistake an LF or RF sent for an individual FlexE client as an LF or RF for the entire link and bring the link down. This is not an issue in the case of FlexE unaware transport of simple bonding to carry a larger rate flow, as a failure of the single high-rate FlexE client is equivalent to a failure of the group. But it may be an issue if FlexE unaware transport is used to carry a group of multiple lower-rate FlexE client services using less than fully PCS codeword transparent mappings. 
     The next case is where the FlexE shim  16  is implemented in the transport network equipment, and rather than carrying the PHYs  22  of the FlexE group  12  over the transport network, the FlexE clients  14  are carried over the transport network. Since the 64b/66b encoded FlexE client rate is: 
       FlexE Client MAC rate×66/64×16383/16384×20460/20461±100 ppm
 
     Note that while this is the stream of blocks presented to the transport network from the FlexE shim  16  to be carried, since this stream does not have any timing information, the transport network is not required to signal at this rate: idle insertion/deletion or padding may be used in the mapping specified by ITU-T if it provides a more convenient rate for the transport. 
     When a FlexE client  14  is mapped in this manner, it may be connected at the OTN egress to another FlexE shim  16  where it will be clock aligned with other FlexE clients  14  carried over the same FlexE group  12 . It may also be connected to an Ethernet PHY  22  with the same nominal MAC rate as the FlexE client  14  using the appropriate conversion as described herein. 
     Note that in the case where it is necessary to connect a FlexE client  14  to an Ethernet PHY  22  across an OTN where the Ethernet PHY  22  uses a legacy mapper/demapper, it may be necessary to perform the conversion of the FlexE client  14  to the Ethernet PHY format according to clause 7.2.2 immediately after the FlexE shim  16  and to map the FlexE client  14  over OTN as if it were an Ethernet PHY  22  of the corresponding rate. This second case can use a “low skew” implementation of the FlexE shim  16  as described herein. 
     The third case is where the FlexE shim  16  is not terminated in the transport network equipment, but the transport network equipment “crunches” the PHY  22  of the FlexE group  12  by discarding unavailable calendar slots at the transport network ingress and re-inserting them at the transport network egress. The mapping of this requires serializing and deskewing the PCS lanes of the PHY, then discarding all “UNAVAILABLE” calendar slots from the structure to reduce the bit-rate. For example, if only 15 of 20 calendar slots are available, there are effectively 1023 repetitions of a length 15 calendar after discarding the unavailable slots. At the transport network egress, the unavailable slots are restored to the FlexE PHY stream of 66b blocks (inserting error control blocks as illustrated in  FIG. 12 ). The net bit-rate of this reduced-rate flow when there are “n” available calendar slots is: 
     
       
         
           
             
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     FlexO and FlexE 
     Referring to  FIG. 15 , in an embodiment, a diagram illustrates a comparison between the layer stack and atomic functions of FlexO and FlexE. Of note, FlexO and FlexE are converging and look alike in the layer stack and atomic functions. In various embodiments, the systems and methods described herein contemplate FlexE as becoming the next B 100 G multiplexed structure. For example, map Low Order (LO) Optical channel Data Unit-j (ODUj), High Order (HO) Optical channel Data Unit-k (ODUk) and ETY right into a FlexE shim  16 . The FlexE group  12  can be a section layer, and the FlexE client  14  (the 64b/66b stream, which could be OTN) can become a switchable Operations, Administration, and Maintenance (OAM) service. 
     FlexE Service OAM 
     Referring to  FIG. 16 , in an embodiment, a network diagram illustrates a comparison of FlexO service OAM with the FlexE Client service OAM systems and methods described herein. Specifically, the same equipment is shown in  FIG. 16  for FlexO and FlexE, including a transport network  100  with network elements  102 ,  104  coupled to switches/routers  106 ,  108 . In an embodiment, the FlexE Client OAM systems and methods enable a FlexE client to be transported as a service (or private line service) in a provider network. The switches/routers  106 ,  108  can be referred to as subscriber equipment where a service originates or terminates, i.e., a maintenance entity. In FlexO, the service can be an ODUflex, and, in FlexE, the service can be a FlexE client. The network elements  102 ,  104  are communicatively coupled to one another. In FlexO, the interconnection between the network elements  102 ,  104  and the switches/routers  106 ,  108 , respectively, can be m×OTUCn, and, in FlexE, the interconnection can be m×FlexE groups. 
     The transport network  100  can include a plurality of network elements in addition to the network elements  102 ,  104 . The various network elements in the transport network  100  are configured to perform transport/switching. In FlexO, the transport/switching can be at ODUk/flex or some other variant of OTN. In FlexE, the transport/switching can be ODUk/flex and/or FlexE-based switching. An example of FlexE-based switching is described in U.S. Patent Application No. 62/186,489, filed on Jun. 30, 2015, and entitled “FLEXIBLE ETHERNET SWITCHING SYSTEMS AND METHODS,” the contents of which are incorporated herein by reference. In FlexO, the network elements  102 ,  104  provide User-Network Interface (UNI)/Inter-Domain Interface (IrDI)/External Network-Network (E-NNI) interfaces. Conversely, the FlexE Client OAM systems and methods enable FlexE UNI/IrDI interfaces at the network elements  102 ,  104 . 
     In an embodiment, the network  100  can support a FlexE client, and the network  100  can include a plurality of nodes interconnected to one another, wherein the FlexE client is configured between two nodes; wherein each of the two nodes include circuitry configured to receive the FlexE client, and circuitry configured to update or monitor one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client. One of the two nodes can be a service terminating subscriber equipment and another of the two nodes can be a network element in a transport network, wherein the FlexE client can include a User-Network Interface (UNI). Each of the two nodes can be a network element in a transport network, and each of the two nodes can be configured to operate as an OAM monitoring point for the FlexE client in the transport network. The one or more OAM fields can include any of a client service monitoring field, a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. 
     FlexE Client Performance Monitoring 
     Referring to  FIG. 17 , in an embodiment, a network diagram illustrates a network with various FlexE Client OAM monitoring points. In  FIG. 17 , the transport network  100  is illustrated with additional network elements  110 ,  112 , and each of the network elements  102 ,  104 ,  110 ,  112  can be configured as a monitoring point for FlexE service OAM. In Ethernet, current transport equipment typically relies on MAC CRC (layer 2) for fault isolation and performance monitoring. In FlexE, this becomes complicated as FlexE introduces a variable amount of clients on a single/multiple ports (groups) and a variable rate for the clients (Flexible MAC). The FlexE Client OAM systems and methods can include a simpler FlexE client service monitoring field (e.g., Bit Interleaved Parity  8  (BIP 8 ) or the like) that covers only the 64b/66b codes for a single client path, i.e., a single error check per client, instead of CRC at the packet level. This can be viewed analogously to the PM BIP 8  that covers an ODUflex service path. Such an approach with a FlexE client service monitoring field simplifies monitoring and fault isolation. Nodes in a transport network could be 3R regens (i.e. Regenerator Section (RS)-OTN) or switches (i.e., Multiplex Section (MS)-OTN or FlexE switches). 
     In an embodiment, a node configured to monitor a Flexible Ethernet (FlexE) client service in a network includes circuitry configured to receive a FlexE client; and circuitry configured to monitor or update one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client. The one or more OAM fields can include a client service monitoring field which does not rely on packet Cyclic Redundancy Check (CRC). The one or more OAM fields can include a client service monitoring field including a bitstream Bit Interleaved Parity (BIP) code. The one or more OAM fields can include any of a connectivity/trace, link fault, remote fault, maintenance states, test signals, link neighbor discovery, and backwards fault and error indication. The one or more OAM fields can be disassociated from Local Fault and Remote Fault information for an associated FlexE PHY/group. The one or more OAM fields can be located in the FlexE overhead in a multiframe scheme. The one or more OAM fields can be implemented in a Reconciliation Sublayer with an associated Operational code, different from the one used for FlexE OH (or current IEEE/FC codes). The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     FlexE OAM Fields 
     The following table includes proposed FlexE OAM fields: 
     
       
         
           
               
             
               
                   
               
             
            
               
                 Bit Error Check (e.g., BIP8) 
               
               
                 Connectivity/Trace (e.g., Trail Trace Identifier (TTI)) 
               
               
                 Link Neighbor Discovery (i.e. LLDP) 
               
               
                 Link Fault 
               
               
                 Remote Fault 
               
               
                 Maintenance States (e.g., locked, loop-back, test) 
               
               
                 Test signals (e.g., Pseudorandom binary sequence (PRBS)) for turn-up 
               
               
                 Backwards fault and error indication 
               
               
                   
               
            
           
         
       
     
     Referring back to  FIG. 2 , the FlexE group Remote Fault (RF)/Local Fault (LF) is handled at the Reconciliation Sub layer (RS), above the FlexE shim. The FlexE OAM cannot reuse the group RF/LF for clients as this would flag group/PHY faults in the transport equipment. Instead, the FlexE OAM could define a new “O code” (e.g., 0x9) for client RF/LF to disassociate from the group/PHY. Again, drawing analogies to the OTN implementations, this is analogous to LO ODUk-AIS Path Monitoring (PM) relative to LO/HO Section Monitoring (SM). 
     Referring to  FIG. 18 , in an embodiment, a diagram illustrates an FlexE Client OAM implementation with FlexE overhead. Specifically,  FIG. 18  illustrates a first option for OAM where the fields are included in the FlexE Time Division Multiplexing (TDM) frame overhead. The FlexE TDM frame overhead has a portion for all calendar slots and paths. For example, the FlexE Client OAM could occupy some or all of the reserved portions of the FlexE TDM frame overhead. However, it might be tight fitting OAM overhead for up to 10 clients (per group) in these portions. As such, an option could be to multiframe the OAM overhead, analogous to what OTN does with the HO OPUk path OH. The FlexE OAM could be switched along with the calendar slots to provide a path. Another option could include reducing the management channel to provide more room for the FlexE Client OAM or reusing the management channel capacity with a messaged based OAM approach on a general communications channel. 
     Referring to  FIG. 19 , in an embodiment, a block diagram illustrates the FlexE overhead from  FIG. 9  with a new “O” code for implementing FlexE OAM at the RS layer. This embodiment includes injecting a new “O” code (e.g., 0x9), 1/16k occurrence and steal bandwidth of the client (e.g., 59 parts per million (ppm))—worst case standard Ethernet at 100 G has 400 ppm of idles in there. This can be used for a new client LF/RF and to differentiate from group LF/RF (0x0), and this can include specific OAM per client stream, which is then mapped to calendar slots along with the client stream. These OAM fields are tied to FlexE clients and not calendar slots. This second option is analogous to LO ODUk PM overhead. 
     Referring to  FIG. 20 , in an embodiment, the logical diagram of  FIG. 2  illustrates a location of the first and second options in the IEEE 802.3 stack. The first option is located in the FlexE shim in the frame header, stealing OH bandwidth of the FlexE OH (O code 0x5). The second option is implemented in the RS layer creating the concept of a path, like an ODUflex, stealing bandwidth from the client with new O code (i.e. 0x9). This can be snooped without requiring knowledge of packets and boundaries of FlexE client for performance monitoring and can be switched along with client 64b/66b bitstream as a path layer. 
     FlexE Monitoring Process 
     Referring to  FIG. 21 , in an embodiment, a flowchart illustrates a process  200 , implemented in a node, for monitoring a Flexible Ethernet (FlexE) client service in a network. For example, the node can include the network elements  102 ,  104  or the switches/routers  106 ,  108 . The process  200  includes receiving a FlexE client (step  202 ); and at least one of monitoring and updating one or more Operations, Administration, and Maintenance (OAM) fields in FlexE overhead, wherein the OAM fields cover a single client path for the FlexE client (step  204 ). The one or more OAM fields can include a client service monitoring field which does not rely on Cyclic Redundancy Check (CRC). The one or more OAM fields can include a client service monitoring field including a Bit Interleaved Parity (BIP) code. The one or more OAM fields can include any of a connectivity/trace, link fault, remote fault, maintenance states, test signals, and backwards fault and error indication. The one or more OAM fields can be disassociated from Local Fault and Remote Fault information for an associated FlexE group/PHY. The one or more OAM fields can be located in the FlexE overhead, possibly using a multiframe scheme. The one or more OAM fields can be implemented in a Reconciliation Sublayer with a new associated Operational code. The node can be one of a Regenerator Section (RS) Optical Transport Network (OTN) switch, a Multiplex Section (MS) OTN switch, and a FlexE switch. 
     It will be appreciated that some embodiments described herein may include one or more generic or specialized processors (“one or more processors”) such as microprocessors, digital signal processors, customized processors, and field programmable gate arrays (FPGAs) and unique stored program instructions (including both software and firmware) that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the methods and/or systems described herein. Alternatively, some or all functions may be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the aforementioned approaches may be used. Moreover, some embodiments may be implemented as a non-transitory computer-readable storage medium having computer readable code stored thereon for programming a computer, group, appliance, device, etc. each of which may include a processor to perform methods as described and claimed herein. Examples of such computer-readable storage mediums include, but are not limited to, a hard disk, an optical storage device, a magnetic storage device, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory), an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), Flash memory, and the like. When stored in the non-transitory computer readable medium, software can include instructions executable by a processor that, in response to such execution, cause a processor or any other circuitry to perform a set of operations, steps, methods, processes, algorithms, etc. 
     Although the present disclosure has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present disclosure, are contemplated thereby, and are intended to be covered by the following claims.