Internet DRAFT - draft-xiong-detnet-enhanced-detnet-gap-analysis
draft-xiong-detnet-enhanced-detnet-gap-analysis
DETNET Q. Xiong
Internet-Draft ZTE Corporation
Intended status: Informational 7 December 2022
Expires: 10 June 2023
Gap Analysis for Enhanced DetNet Data Plane
draft-xiong-detnet-enhanced-detnet-gap-analysis-00
Abstract
From charter and milestones, the enhanced Deterministic Networking
(DetNet) is required to provide the enhancement of flow
identification and packet treatment for data plane to achieve the
DetNet QoS in large-scale networks.
This document analyzes the gaps of the existing technologies
especially applying the DetNet data plane as per RFC8938.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 10 June 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Service Requirements of Large-Scale Deterministic Networks . 3
3.1. Support the Differentiated DetNet QoS of Multiple
Services . . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. Support the Utilization of Network Resources . . . . . . 5
4. Characteristics of Large-Scale Deterministic Networks . . . . 6
4.1. Large-scale Dynamic Flows . . . . . . . . . . . . . . . . 6
4.2. Large-scale Network Topology . . . . . . . . . . . . . . 6
5. Gap Analysis of Large-Scale Deterministic Networks . . . . . 7
5.1. Gap Analysis of Providing Aggregated Flows
Identification . . . . . . . . . . . . . . . . . . . . . 7
5.2. Gap Analysis of Providing Deterministic Latency . . . . . 7
5.2.1. Gap Analysis of Explicit Routes . . . . . . . . . . . 8
5.2.2. Gap Analysis of Resources Allocation . . . . . . . . 8
5.2.3. Gap Analysis of Queuing Mechanisms . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
As per [RFC8655], it defined the overall architecture for
Deterministic Networking (DetNet) , which provides a capability for
real-time applications with extremely low data loss rates and bounded
latency within a network domain. It has three goals: minimum and
maximum end-to-end latency from source to destination, bounded jitter
(packet delay variation), packet loss ratio and upper bound on out-
of-order packet delivery. To achieve the above objectives, multiple
techniques need to be used in combination, including explicit routes,
service protection and resource allocation defined by DetNet.
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As defined in [RFC8938], the DetNet data plane describes how
application flows, or App-flows are carried over DetNet networks and
it is provided by the DetNet service and forwarding sub-layers with
DetNet-related data plane functions and mechanisms. The enhanced
DetNet is required to provide the enhancement of flow identification
and packet treatment for data plane to achieve the DetNet QoS in
large-scale networks. It is required to analyse the applicability in
DetNet for large-scale networks.
This document describes the requirements for multiple deterministic
services, discusses the characteristics of large-scale networks and
analyzes the gaps of the existing technologies especially applying
the DetNet data plane as per RFC8938.
2. Conventions used in this document
2.1. Terminology
The terminology is defined as [RFC8655] and [RFC8938].
2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Service Requirements of Large-Scale Deterministic Networks
3.1. Support the Differentiated DetNet QoS of Multiple Services
5G network is oriented to the internet of everything. It need to
supports the Ultra-reliable Low Latency Communications (uRLLC)
services. The uRLLC services demand SLA guarantees such as low
latency and high reliability and other deterministic and precise
properties especially in Wide Area Network (WAN) applications.The
uRLLC services should be provided in large-scale networks which cover
the industries such as intelligent electrical network, intelligent
factory, internet of vehicles, industry automation and other
industrial internet scenarios. The industrial internet is the key
infrastructure that coordinate various units of work over various
system components, e.g. people, machines and things in the industrial
environment including big data, cloud computing, Internet of Things
(IOT), Augment Reality (AR), industrial robots, Artificial
Intelligence (AI) and other basic technologies. For the intelligent
electrical network, there are deterministic requirements for
communication delay, jitter and packet loss rate. For example, in
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the electrical current difference model, a delay of 3~10ms and a
jitter variation is no more than 100us are required. For the
automation control, it is one of the basic application and the the
core is closed-loop control system. The control process cycle is as
low as millisecond level, so the system communication delay needs to
reach millisecond level or even lower to ensure the realization of
precise control. There are three levels of real-time requirements
for industrial interconnection: factory level is about 1s, and
process level is 10~100ms, and the highest real-time requirement is
motion control, which requires less than 1ms. So the deterministic
latency requirements are different with varying services and network
scenarios.
As defined in [RFC8655], the DetNet QoS can be expressed in terms of
: Minimum and maximum end-to-end latency, bounded jitter (packet
delay variation), packet loss ratio and an upper bound on out-of-
order packet delivery. As described in [RFC8578], DetNet
applications differ in their network topologies and specific desired
behavior and different services requires differentiated DetNet QoS.
In the large-scale networks, multiple services with differentiated
DetNet QoS is co-existed in the same DetNet network. The
classification of the deterministic flows within different levels is
should be taken into considerations. It is required to provide
Latency, bounded jitter and packet loss dynamically and flexibly in
all scenarios for each characterized flow.
As the Figure 1 shows, the services can be divided into 5 levels and
level 2~5 is the DetNet flows and level-1 is non-DetNet flow. DetNet
applications and DetNet QoS is differentiated within each level.
+-------------+-----------+----------+----------+----------+-----------+
| Item | Level-1 | Level-2 | Level-3 | Level-4 | Level-5 |
+-------------+-----------+----------+----------+----------+-----------+
| Applications| Broadcast | Voice | Audio and| AR/VR | Industrial|
| Examples | | | Video | | |
+-------------+-----------+----------+----------+----------+-----------+
| DetNet QoS | Bandwidth | Jitter | Delay | Low | Ultra-low |
| | Guarantee | Guarantee| Guarantee| delay | delay and|
| | | | |and jitter| jitter |
+-------------+-----------+----------+----------+----------+-----------+
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Figure 1: The classification of multiple services
From the perspective of deterministic service requirements,
deterministic Quality of Service (QoS) in the network can be divided
into five types or levels:
Level-1: bandwidth guarantee. The indicator requirements include
basic bandwidth guarantee and certain packet loss tolerance. There
is no requirement for the upper bound of the latency, and no
requirement for the jitter. Typical services include download and
FTP services.
Level-2: jitter guarantee. The indicator requirements include:
jitter 50ms, delay 300ms. Typical services include synchronous voice
services, such as voice call.
Level-3: delay guarantee. The indicator requirements include: delay
50ms, jitter 50ms. Typical services include real-time communication
services, such as video, production monitoring, and communication
services.
Level-4: low delay and jitter guarantee. The indicator requirements
include: delay 20ms, jitter 5ms. Typical services include video
interaction services, such as AR/VR, holographic communication, cloud
video and cloud games.
Level-5: ultra-low delay and jitter guarantee. The indicator
requirements include: delay 10ms, jitter 100us. Typical services
include production control services, such as power protection and
remote control.
Moreover, different DetNet services is required to tolerate different
percentage of packet loss ratio such as 99.9%, 99.99%, 99.999%, and
so on.
3.2. Support the Utilization of Network Resources
Traditional Ethernet, IP and MPLS networks which is based on
statistical multiplexing provides best-effort packet service and
offers no delivery and SLA guarantee. As described in [RFC8655], the
primary technique by which DetNet achieves its QoS is to allocate
sufficient resources. But it can not be achieved by not sufficient
resource which can be allocated due to practical and cost reason. So
it is required to achieve the high-efficiency of resources
utilization when provide the DetNet service.
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4. Characteristics of Large-Scale Deterministic Networks
4.1. Large-scale Dynamic Flows
As described in [RFC8557], deterministic forwarding can only apply to
flows with such well-defined characteristics as periodicity and
burstiness. As defined in DetNet architecture [RFC8655], the traffic
characteristics of an App-flow can be CBR (constant bit rate) or VBR
(variable bit rate) of L1, L2 and L3 layers (VBR takes the maximum
value when reserving resources). But the current scenarios and
technical solutions only consider CBR flow, without considering the
coexistence of VBR and CBR, the burst and aperiodicity of flows. The
operations such as shaping or scheduling have not been specified.
Even TSN mechanisms are based on a constant and forecastable traffic
characteristics.
It will be more complicated in a large-scale network where much more
flows coexist and the traffic characteristics is more dynamic. A
huge number of flows with different DetNet QoS requirements is
dynamically concurrent and the state of each flow cannot be
maintained. It is required to offer reliable delivery and SLA
guarantee for dynamic flows. For example, periodic flow and
aperiodic flow (including micro burst flow, etc.), CBR and VBR flow,
flow with different periods or phases, etc. When the network needs
to forward these deterministic flows at the same time, it must solve
the problems of time micro bursts, queue processing and aggregation
of multiple flows.
4.2. Large-scale Network Topology
In large-scale applications, the network topology may consists of a
large number of nodes and links which leads to difficulty with
controlling the end-to-end delay and jitter. High speed, long-
distance transmission and asymmetric links may also co-exists and
affects the bounded latency such as increasing transmission latency,
jitter and packet loss in large-scale networks.
The network topology in a large-scale network may across multiple
domains within a single administrative control or a closed group of
administrative control as per [RFC8655]. Moreover, DetNet domains or
nodes may be interconnected with different sub-network technologies
such as FlexE tunnels, TSN sub-network, IP/MPLS/SRv6 tunnels and so
on. It is required to support the inter-domain deterministic metric
and routes to achieve the end-to-end bounded latency.
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5. Gap Analysis of Large-Scale Deterministic Networks
As defined in [RFC8938], the DetNet data plane describes how
application flows, or App-flows are carried over DetNet networks and
it is provided by the DetNet service and forwarding sub-layers with
DetNet-related data plane functions and mechanisms. This section
analyzes the DetNet technical gaps when applying the DetNet data
plane as per RFC8938 in large-scale networks.
5.1. Gap Analysis of Providing Aggregated Flows Identification
In [RFC8938], the DetNet data plane can provide the DetNet-Specific
Metadata such as Flow-ID for both the service and forwarding sub-
layers. The flow-based state information is required to be
maintained for per-flow processing rules. For example, the resource
reservation configuration is required for each flow. DetNet as per
[RFC8938] provides the capability to aggregate the individual flows
to downscale the operations of flow states. However, it still
requires large amount of control signaling to establish and maintain
DetNet flows. It may be challenging for network operations with a
large number of deterministic flows and network nodes in large-scale
networks.
5.2. Gap Analysis of Providing Deterministic Latency
As described in [RFC8655], the primary goals are to achieve the
DetNet QoS to provide minimum and maximum end-to-end latency and
bounded jitter, low packet loss ratio and an upper bound on out-of-
order packet delivery. But the data plane [RFC8938] particularly
focuses on the DetNet service sub-layer which provides a set of
Packet Replication, Elimination, and Ordering Functions (PREOF)
functions to provide end-to-end service assurance. It mainly
provides the capabilities for DetNet to guarantee the reliability.
The DetNet forwarding sub-layer provides corresponding forwarding
assurance with IETF existing functions using resource allocations and
explicit routes. But these functions can not provide the
deterministic latency (bounded latency, low packet loss and in-order
delivery) assurance in large-scale networks. The following sections
mainly discuss the gap analysis for the forwarding sub-layer
functions to provide deterministic latency assurance.
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5.2.1. Gap Analysis of Explicit Routes
Traditional routes only have reachability. As per [RFC8938],
explicit optimized paths with allocation of resources should be
provided to achieve the DetNet QoS. But the deterministic
requirements such as end-to-end delay and jitter are only used as
path computation constraints. Multiple network metrics which are
measured and distributed by the routing system should be taken into
consideration.
In large-scale networks, it may be challenging to compute the best
path to meet all of the requirements. In multi-domain scenarios, the
inter-domain deterministic routes need to be established and
provisioned. Especially when interconnecting with sub-networks, the
selection of intra-domain paths acrossing cooperating domains should
consider the bounded latency in each domain and the stitching of the
paths.
Moreover, the paths vary with the real-time change of the network
topology. On the basic of the resources, the steering path and
routes for deterministic flows should be programmed before the flows
coming and able to provide SLA capability. And the routes should be
considered to be established in distributed and centralized control
Plane.
As described in [RFC8557], the packet replication and elimination
service protection should be provided to achieve the low packet loss
ratio. It will copy the flows and spread the data over multiple
disjoint forwarding paths. The bounded latency and jitter of each
path should be meet service deterministic requirement. And the
difference of latency within these paths should be limited. So the
replication and elimination deterministic routes with configured
latency and jitter policy should be taken into consideration. It is
required to generate two disjoint paths with very close delay to form
1+1 protection and perform concurrent transmission and dual
reception, and make replication and elimination on the egress PE.
5.2.2. Gap Analysis of Resources Allocation
As per [RFC8938], the forwarding sub-layer uses buffer resources for
packet queuing, as well as reservation and allocation of bandwidth
capacity resources. In large-scale networks, the bandwidth, buffer
and scheduling resources are combined with queuing mechanisms to
guarantee the deterministic latency. The reservation and allocation
of queuing related resources or deterministic latency resources
should be taken into consideration in DetNet data plane.
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5.2.3. Gap Analysis of Queuing Mechanisms
As per [RFC8938], the forwarding sub-layer provides the QoS-related
functions needed by the DetNet flow including the use of queuing
techniques. But the queuing techniques which are defined in existing
IETF technologies can not guarantee the bounded latency such as
Active Queue Management(AQM). And the queuing mechanisms which are
defined in IEEE802.1 TSN can not be directly applied in large-scale
networks such Time Aware Shaping [IIEEE802.1Qbv] and Cyclic Queuing
and Forwarding [IEEE802.1Qch] with time synchronization.
Enhancement of queuing mechanisms have been discussed in DetNet such
as cyclic-scheduling queuing mechanism
[I-D.dang-queuing-with-multiple-cyclic-buffers], deadline-scheduling
queuing mechanism [I-D.stein-srtsn] and
[I-D.peng-detnet-deadline-based-forwarding], and asynchronous queuing
mechanism [I-D.joung-detnet-asynch-detnet-framework]. The function
of multiple queuing mechanisms and related DetNet-Specific Metadata
has not been defined in DetNet data plane.
6. Security Considerations
TBA
7. Acknowledgements
TBA
8. IANA Considerations
TBA
9. Normative References
[I-D.dang-queuing-with-multiple-cyclic-buffers]
Liu, B. and J. Dang, "A Queuing Mechanism with Multiple
Cyclic Buffers", Work in Progress, Internet-Draft, draft-
dang-queuing-with-multiple-cyclic-buffers-00, 22 February
2021, <https://www.ietf.org/archive/id/draft-dang-queuing-
with-multiple-cyclic-buffers-00.txt>.
[I-D.joung-detnet-asynch-detnet-framework]
Joung, J., Ryoo, J., Cheung, T., Li, Y., and P. Liu,
"Asynchronous Deterministic Networking Framework for
Large-Scale Networks", Work in Progress, Internet-Draft,
draft-joung-detnet-asynch-detnet-framework-01, 24 October
2022, <https://www.ietf.org/archive/id/draft-joung-detnet-
asynch-detnet-framework-01.txt>.
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[I-D.peng-detnet-deadline-based-forwarding]
Peng, S., Tan, B., and P. Liu, "Deadline Based
Deterministic Forwarding", Work in Progress, Internet-
Draft, draft-peng-detnet-deadline-based-forwarding-03, 22
October 2022, <https://www.ietf.org/archive/id/draft-peng-
detnet-deadline-based-forwarding-03.txt>.
[I-D.stein-srtsn]
Stein, Y. J., "Segment Routed Time Sensitive Networking",
Work in Progress, Internet-Draft, draft-stein-srtsn-01, 29
August 2021, <https://www.ietf.org/archive/id/draft-stein-
srtsn-01.txt>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
<https://www.rfc-editor.org/info/rfc8557>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
[RFC8938] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
Bryant, "Deterministic Networking (DetNet) Data Plane
Framework", RFC 8938, DOI 10.17487/RFC8938, November 2020,
<https://www.rfc-editor.org/info/rfc8938>.
[RFC8956] Loibl, C., Ed., Raszuk, R., Ed., and S. Hares, Ed.,
"Dissemination of Flow Specification Rules for IPv6",
RFC 8956, DOI 10.17487/RFC8956, December 2020,
<https://www.rfc-editor.org/info/rfc8956>.
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[RFC8964] Varga, B., Ed., Farkas, J., Berger, L., Malis, A., Bryant,
S., and J. Korhonen, "Deterministic Networking (DetNet)
Data Plane: MPLS", RFC 8964, DOI 10.17487/RFC8964, January
2021, <https://www.rfc-editor.org/info/rfc8964>.
[RFC9023] Varga, B., Ed., Farkas, J., Malis, A., and S. Bryant,
"Deterministic Networking (DetNet) Data Plane: IP over
IEEE 802.1 Time-Sensitive Networking (TSN)", RFC 9023,
DOI 10.17487/RFC9023, June 2021,
<https://www.rfc-editor.org/info/rfc9023>.
[RFC9024] Varga, B., Ed., Farkas, J., Malis, A., Bryant, S., and D.
Fedyk, "Deterministic Networking (DetNet) Data Plane: IEEE
802.1 Time-Sensitive Networking over MPLS", RFC 9024,
DOI 10.17487/RFC9024, June 2021,
<https://www.rfc-editor.org/info/rfc9024>.
Author's Address
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan
Hubei, 430223
China
Email: xiong.quan@zte.com.cn
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