Analysis for FlexE control
draft-wang-ccamp-flexe-control-analysis-01
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| Last updated | 2019-05-22 | ||
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draft-wang-ccamp-flexe-control-analysis-01
Internet Engineering Task Force Q. Wang, Ed.
Internet-Draft X. Niu, Ed.
Intended status: Informational ZTE Corporation
Expires: November 23, 2019 Y. Xu
CAICT
May 22, 2019
Analysis for FlexE control
draft-wang-ccamp-flexe-control-analysis-01
Abstract
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 . . . . . . . . . . . . . . . . . 5
3.2.2. Configuration of FlexE group . . . . . . . . . . . . 6
3.2.3. Allocate Resources for Client MAC flows . . . . . . . 6
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
architecture according to the analysis 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], which is about
"Characteristics of equipment functional blocks supporting Flex
Ethernet interfaces".
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2. Terminology
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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.
One FlexE group exists between two FlexE shim, there is no slot
switching defined in FlexE. In addition, 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 is able to
see the calendar slots information. 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
TxGID, TxPHYMAP
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
200G and 400G are used, the 100G FlexE instance should be used in the
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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.
3.1.4. MAC Frame
Defined in IEEE.
3.1.5. Adaptation between MAC frames and FlexE Client
It can be seen from the Figure 8-6 of [ITU-T G.8023] that the
external management information commands used as input to the
adaptation function are defined by [IEEE 802.3]. 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].
as 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 of FlexE group
Allocation of one or more FlexE group calendar slot resources to a
client MAC flow.
3.2.1. Configuration Mode
There are two different configuration modes for bring one FlexE link
into service. The first one is static model, which is to use
external management system to configure the source and destination
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FlexE shims. There is no need for the FlexE source and destination
to coordinate through the FlexE overhead as all the configuration
work mentioned above is finished by the external management system.
In this case, the CR/CA mechanism does not work; 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
node.
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. 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.
3.2.3. Allocate Resources for Client MAC flows
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, the FlexE group
bonding information and resource allocation information are sent both
to FlexE souce and destination to help enable the FlexE link.
Information sent is described in section 3.3.1, 3.3.2 and 3.3.3,
which can also be found in [draft-xiaobn-ccamp-flexe-yang-mod]. A
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FlexE group and a number of FlexE clients are created according to
the configuration information. For the Master/slave mode, the FlexE
group bonding information and resource allocation information are
only sent to the FlexE source site. The FlexE source site first
create the corresponding FlexE group and 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 group and 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.
b. Using eternal control/management system to configure the FlexE
client, which include the FlexE client number, FlexE client type
and slots allocation information.
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
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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
None.
8. References
8.1. Normative References
[ITU-T_G709]
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_G798]
ITU-T, "ITU-T G.798: Characteristics of optical transport
network hierarchy equipment functional blocks", August
2018.
[ITU-T_G8023]
ITU-T, "ITU-T G.8023: Characteristics of equipment
functional blocks supporting Ethernet physical layer and
Flex Ethernet interfaces", , 2016.
[ITU-T_G872]
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.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References
[I-D.izh-ccamp-flexe-fwk]
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.
[I-D.xiaobn-ccamp-flexe-yang-mod]
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
Nanjing
CN
Email: wang.qilei@zte.com.cn
Xiaobing Niu (editor)
ZTE Corporation
Beijing
CN
Email: niu.xiaobing@zte.com.cn
Yunbin Xu
CAICT
Beijing
CN
Email: xuyunbin@caict.ac.cn
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