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Internet Engineering Task Force                             Q. Wang, Ed.
Internet-Draft                                               X. Niu, Ed.
Intended status: Informational                           ZTE Corporation
Expires: January 9, 2020                                           Y. Xu
                                                            July 8, 2019

                       Analysis for FlexE control


   This document gives some analysis about the control of FlexE.

Status of This Memo

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Analysis  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  General Introduction of FlexE . . . . . . . . . . . . . .   3
       3.1.1.  FlexE Group . . . . . . . . . . . . . . . . . . . . .   3
       3.1.2.  FlexE Client  . . . . . . . . . . . . . . . . . . . .   4
       3.1.3.  Adaptation function between FlexE Client and FlexE
               Group . . . . . . . . . . . . . . . . . . . . . . . .   4
       3.1.4.  MAC Frame . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.5.  Adaptation between MAC frames and FlexE Client  . . .   5
     3.2.  General requirements  . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Configuration Mode for FlexE client . . . . . . . . .   6
       3.2.2.  Configuration of FlexE group  . . . . . . . . . . . .   6
       3.2.3.  Allocate Resources for FlexE Client . . . . . . . . .   7
     3.3.  Control Requirements Derived  . . . . . . . . . . . . . .   7
   4.  Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   OIF published the first version of FlexE Implementation Agreement in
   March 2016, aiming to provide a generic mechanism for supporting a
   variety of Ethernet MAC rates that may or may not correspond to any
   existing Ethernet PHY rate.  SG15 in ITU-T has endorsed the OIF FlexE
   data plane and parts of [ITU-T G.872], [ITU-T G.709], [ITU-T G.798]
   and [ITU-T G.8023].  The Recommendations depend on or are based on
   the FlexE data plane.

   This draft is intended to trigger discussion of the FlexE control
   requirements, which can be found in section 2.  What kind of model
   should we employed when configuring FlexE capable equipments, how to
   configure the FlexE group and FlexE client, and what kind of
   parameters do we need to take into consideration when configuring
   FlexE group and FlexE client.  The analysis is based on the
   description in section 7 and 8 of [ITU-T G.8023] and FlexE IA 2.0.

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2.  Terminology

2.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Analysis

3.1.  General Introduction of FlexE

   The FlexE shim is built into the Ethernet PCS (physical coding
   sublayer).  If a FlexE group is set up, a corresponding n*100G (or
   n*200G, n*400G) PCS module with multiple FlexE client ports could be
   created as well.

   The difference between the FlexE and the traditional 100G Ethernet is
   that the traditional Ethernet PCS has a 1:1 relationship with the
   client MAC flow, while with FlexE one bonded huge PCS module can be
   used to transport more than one client MAC flow i.e., the
   relationship is 1:n, with each MAC flow mapped into one FlexE client.

3.1.1.  FlexE Group

   A FlexE Group is consisted of from 1 to n 100G FlexE instances, which
   are carried over from 1 to m 100G, 200G or 400G Ethernet PHYs.  All
   PHYs in the group must operate at the same rate.

   FlexE group is consisted of a number of FlexE instances, and each
   instance is consisted of 66B blocks stream.  Section monitoring
   overhead is added/extracted as one 66B block at the FlexE group
   source and destination (i.e., trail termination) to determine the
   status of the FlexE group (i.e., FlexE trail in ITU-T terminology).
   Currently, only RPF (Remote PHY Fault) indication is used to report
   the state of FlexE group.

   The FlexE group exists between two FlexE shim, there is no slot
   switching defined in FlexE.  Only one fault indication is defined,
   there is no other OAM function developed yet.  Based on these
   analysis, we should be able to understand that FlexE is just an
   interface technology, and once a FlexE group is configured, it only
   functions as one Ethernet link, similar to Ethernet PHY.

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3.1.2.  FlexE Client

   A FlexE Client is an Ethernet flow based on a MAC data rate that may
   or may not correspond to any Ethernet PHY rate.  The FlexE Client MAC
   rates supported by a FlexE Groups could be 10Gb/s, 40Gb/s, or m*25Gb/
   s.  The FlexE Client MAC rates supported by FlexE Groups may support
   all, or only a subset of these FlexE Client rates.  Each FlexE Client
   is presented to the FlexE Shim as a 64B/66B encoded bit stream
   according to clause 82 of [IEEE 802.3].  FlexE clients have the
   semantics of an Ethernet PHY.  There is no new layer network.  Both
   FlexE group and FlexE client are processed at Ethernet PHY layer.
   From the network management perspective, the FlexE client can be
   created and the calendar slots information of one FlexE group can be
   allocated to one FlexE client.  The FlexE client could be generated
   internally within a system, or created from a traditional Ethernet
   PHY.  What kind of FlexE clients will be created depends on the
   operator's needs.

   According to the description in clause 8.1 of [ITU-T G.8023], there
   is no overhead defined for monitoring a FlexE client, so the trail
   for FlexE client in the equipment does not exist.  The FlexE client
   trail termination function is a null function.  Therefore, modelling
   FlexE client as a network layer is not correct.

3.1.3.  Adaptation function between FlexE Client and FlexE Group

   In order to distribute the FlexE client over PHYs of one FlexE group,
   a number of management information command should be sent to the
   adaptation function which performs the mapping of FlexE client over
   FlexE group.

   According to the description in clause 7.2 of [ITU-T G.8023], the
   external management information command sent to the source adaptation
   function is listed below:

      TxCC, TxCCA, TxCCB, TxCR, TxCA


   The TxCC, TxCCA and TxCCB are used to configure the calendar for use,
   which could be type A or type B calendar configuration, slots
   allocated for a specific FlexE client and FlexE client number.

   TxCR and TxCA are used to coordinate the switch of calendar
   configuration between the FlexE source and destination node.

   The TxGID is used to configure the FlexE group identifier.  The
   TxPHYMAP is used to configure the set of PHYs in the FlexE group.  If

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   200G and 400G are used, the 100G FlexE instance should be used in the
   case of PHYMAP, as current version of [ITU-T G.8023] only cover the
   scope of 100G PHY.

   The built-in function multiplexer performs the action of assigning
   the individual FlexE Client to specific calendar slots of the FlexE
   group according to the input management information.

   At the destination side, the Demultiplexer function could use
   activate the FlexE Client and assigns the calendar slots of the FlexE
   group payload area to the individual FlexE client accordng to
   external configuration or the client calendar information carried in
   the overhead.  Expected group ID, PHYMAP and calendar allocation
   information are needed sometimes to help verify the correctness of
   FlexE configuration.

3.1.4.  MAC Frame

   Defined in IEEE.

3.1.5.  Adaptation between MAC frames and FlexE Client

   The external management information commands used as input to the
   adaptation function are defined by [IEEE 802.3], according to the
   description in [ITU-T G.8023].  The [IEEE 802.3] process mainly
   includes the 64B/66B encoding, as well as MAC frame check sequence
   generation and frame counting.  The FlexE client stream is generated
   at the determined FlexE Client MAC rate and 64B/66B encoded.

3.2.  General requirements

   It can be inferred from section 2.1.2 and section 2.1.5 that process
   involved when producing the FlexE Client from MAC frames is 64b/66b
   encoding, and this encoding has already been defined by [IEEE 802.3],
   no extra overhead is added during this process.  Therefore,
   configuration for mapping MAC frames into FlexE client from external
   management system is not needed.

   Based on the above analysis, two high-level requirements for control/
   management of FlexE are considered in this draft.

      Configuration mode

      Configuration of FlexE group

      Creation of FlexE client and allocation of one or more FlexE group
      calendar slot resources to a FlexE client.

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3.2.1.  Configuration Mode for FlexE client

   There are two different configuration modes for bring one FlexE
   client into service.  The first one is static model, which is to use
   external management system to configure the FlexE client and
   resources allocated for the FlexE client at source and destination
   FlexE shims.  In this case, the CR/CA mechanism does not work.
   Verification of configuration consistensy at FlexE source and
   destination site by comparing the inband FlexE overhead with the
   configuration at FlexE destination are needed; The other one is
   MASTER/SLAVE mode, which is to use the FlexE overhead to coordinate
   the resource configuration between FlexE source and destination, the
   external resource configuration information is only sent the source

3.2.2.  Configuration of FlexE group

   It can be concluded from the above analysis that external
   configuration tools should be involved to bring one FlexE group into
   service.  The initial configuration commands could be from external
   management system, SDN controller etc.

   A FlexE group must be configured first before any client signals are
   carried over it.  When a new FlexE Group is brought into service, the
   initial configuration must be provisioned for both ends, and the
   initial configuration must be the same for both direction.  The group
   is configured to be consist of from 1 to n 100G FlexE Instances
   carried over from 1 to m PHYs of the same rate (100GBASE-R, 200GBASE-
   R, or 400GBASE-R).  A PHY number may correspond to the physical port
   ordering on equipment, but the FlexE Shim at each end of the group
   must identify each PHY in the group using the same PHY number, and
   each 100G FlexE Instance with the same 100G FlexE Instance number.
   In certain cases, it may be desirable not to populate all 100G FlexE
   instances on a 200G or 400G PHY, and these so-called unequipped FlexE
   instance should also be configured.  Unequipped instances must always
   be the highest numbered instance(s) on a PHY of the FlexE Group, and
   there must always be at least one equipped 100G FlexE Instance on
   every PHY.

   If aware case is needed to be considered, unavailable slot
   information should be configured at FlexE aware node to discard
   unavailable slot first, so as to put the rest of available slots onto
   the lower rate physical port.

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3.2.3.  Allocate Resources for FlexE Client

   The FlexE client MAC flows are encapsulated in one or more FlexE
   calendar slots.

   According to the analysis in section 3.2.1, there are two different
   configuration modes.  For the first one, static mode, after the FlexE
   group is configured, the FlexE client resource allocation information
   are sent both to FlexE souce and destination to help create the FlexE
   client.  A number of expected configuration parameters are sent to
   FlexE destination to help verify the correctness of configuration at
   both sides.  Information sent can be found in [draft-xiaobn-ccamp-
   flexe-yang-mod].  For the Master/slave mode, the FlexE client
   resource allocation information are only sent to the FlexE source
   site.  The FlexE source site first create the FlexE clients, and then
   the built-in multiplexer at the FlexE source site allocates the
   calendar slots to a specific FlexE client according to the input from
   external management system, and insert these configuration
   information into the FlexE overhead.  When these overheads arrives at
   the destination site, the demultiplexer function at the destination
   site extracts FlexE overhead first and get the information of
   calendar slot allocation information.  Based on these information,
   the FlexE destination site finish the configuration of FlexE clients.
   In order to verify the correctness of the resource configuration, the
   expected FlexE group ID, PHY number and instance number information,
   FlexE client number and slot allocation information for a specific
   FlexE client should also be configured to FlexE destination site.

   The FlexE client port is an internal port which only perform the
   function of encapsulating upper layer packets into MAC frames,
   64b/66b encoding.  The bandwidth capability of these internal ports
   should be known by external management/control tools in order to be
   used by the upper layer (e.g., MPLS-TP) flow correctly.

3.3.  Control Requirements Derived

   a.  Using external control/management system to configure FlexE
       group, which may include the configuration of group number, PHY
       number and instance number, as well as correlation between
       logical PHY number and physical port number.  A number of
       expected configuration parameters are also needed to help verify
       the consisten between FlexE source and destination.

   b.  Using eternal control/management system to create the FlexE
       client, which include the FlexE client number, FlexE client type
       and slots allocation information.  Different configuration mode
       for FlexE client are needed.

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   c.  External control command could be provide to trigger the switch
       of calendar slots.

   d.  Interworking between 5G slot granularity capable node and 25G
       slot granularity node.

   e.  Configuration of unequipped instance, unavailable slots, which
       include the number of unequipped instance and number of
       unavailable slots on each instances

   Different kinds of alarms should be taken into consideration when
   modelling FlexE technology, which may include PHY failed, skew exceed
   threshold, inconsistent configuration between two ends.

4.  Summary

   According to the analysis in section 2, the main control/management
   requirement for FlexE technology is to configure the FlexE group and
   FlexE client.  Once a FlexE group is configured and the FlexE client
   ports is created, slots allocation is configured, use of the FlexE
   technology is the same as that in traditional Ethernet.

5.  Acknowledgements

6.  IANA Considerations

   This memo includes no request to IANA.

7.  Security Considerations


8.  References

8.1.  Normative References

              ITU-T, "ITU-T G.709: Optical Transport Network Interfaces;
              07/2016",  http://www.itu.int/rec/T-REC-
              G..709-201606-P/en, July 2016.

              ITU-T, "ITU-T G.798: Characteristics of optical transport
              network hierarchy equipment functional blocks", August

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              ITU-T, "ITU-T G.8023: Characteristics of equipment
              functional blocks supporting Ethernet physical layer and
              Flex Ethernet interfaces",  , 2016.

              ITU-T, "ITU-T G.872: The Architecture of Optical Transport
              Networks; 2017",  http://www.itu.int/rec/T-REC-G.872/en,
              January 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

8.2.  Informative References

              Hussain, I., Valiveti, R., Pithewan, K., Wang, Q.,
              Andersson, L., Zhang, F., Chen, M., Dong, J., Du, Z.,
              zhenghaomian@huawei.com, z., Zhang, X., Huang, J., and Q.
              Zhong, "GMPLS Routing and Signaling Framework for Flexible
              Ethernet (FlexE)", draft-izh-ccamp-flexe-fwk-00 (work in
              progress), October 2016.

              NIU, X., Wang, Q., Xu, Y., and S. Munagapati, "A YANG Data
              Model for Flex Ethernet(FlexE)", draft-xiaobn-ccamp-flexe-
              yang-mod-01 (work in progress), May 2019.

Authors' Addresses

   Qilei Wang (editor)
   ZTE Corporation

   Email: wang.qilei@zte.com.cn

   Xiaobing Niu (editor)
   ZTE Corporation

   Email: niu.xiaobing@zte.com.cn

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   Yunbin Xu

   Email: xuyunbin@caict.ac.cn

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