Internet DRAFT - draft-xiong-detnet-enhanced-detnet-gap-analysis
draft-xiong-detnet-enhanced-detnet-gap-analysis
DETNET Q. Xiong
Internet-Draft A. Liu
Intended status: Informational ZTE Corporation
Expires: 28 August 2024 25 February 2024
Gap Analysis for Enhanced DetNet
draft-xiong-detnet-enhanced-detnet-gap-analysis-03
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 discusses the characteristics of scaling deterministic
networks and analyzes the gaps of the existing technologies
especially applying the DetNet data plane as per RFC8938.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 28 August 2024.
Copyright Notice
Copyright (c) 2024 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. Characteristics of Scaling Deterministic Networks . . . . . . 3
3.1. Large-scale Dynamic Flows . . . . . . . . . . . . . . . . 3
3.1.1. Flows with Different T-Spec . . . . . . . . . . . . . 3
3.1.2. Flows with Different Levels of Applications . . . . . 4
3.1.3. Flows with Different SLAs . . . . . . . . . . . . . . 4
3.2. Large-scale Network Topology . . . . . . . . . . . . . . 4
3.2.1. Large Number of Hops and Complex Topology within a
DetNet Domain . . . . . . . . . . . . . . . . . . . . 4
3.2.2. Long Distance links within a DetNet Domain . . . . . 5
3.2.3. Topology across Multiple Domains . . . . . . . . . . 5
3.2.4. Topology across Heterogeneous Networks . . . . . . . 5
4. Gap Analysis for Enhanced DetNet . . . . . . . . . . . . . . 5
4.1. Gap Analysis of Providing Flows Identification . . . . . 5
4.2. Gap Analysis of Providing Deterministic Latency . . . . . 6
4.2.1. Gap Analysis of Explicit Routes . . . . . . . . . . . 6
4.2.2. Gap Analysis of Resources Allocation . . . . . . . . 7
4.2.3. Gap Analysis of Queuing Mechanisms . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 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,
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service protection and resource allocation defined by DetNet.
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. [I-D.ietf-detnet-scaling-requirements] has
described the enhanced DetNet data plane requirements for scaling
deterministic networks. As per [I-D.zhao-detnet-enhanced-use-cases],
various deterministic applications are co-existed with different SLAs
guarantees in scaling networks. It is required to analyse the
characteristics of the scaling networks and applicability for
existing DetNet technologies.
This document discusses the characteristics of scaling deterministic
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. Characteristics of Scaling Deterministic Networks
3.1. Large-scale Dynamic Flows
3.1.1. Flows with Different T-Spec
As described in [RFC8557], deterministic forwarding can only apply to
flows with such well-defined Traffic Specification (T-Spec)
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
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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.
3.1.2. Flows with Different Levels of Applications
In scaling networks, [I-D.ietf-detnet-scaling-requirements] has
described the enhanced requirements for DetNet enhanced data plane
including the deterministic latency guarantees and it also mentioned
the enhanced DetNet should support different levels of application
requirements which is an important requirement for the DetNet
deployment. Moreover, mutiple services and traffic flows with
different bounded latency requirements may be also co-existed in the
same application.
3.1.3. Flows with Different SLAs
In scaling networks, multiple flows may demand different set of SLAs
and it may define more than one DetNet QoS levels according to
different application scenarios as per
[I-D.xiong-detnet-differentiated-detnet-qos]. These flows should be
transmitted and forwarded with different DetNet QoS forwarding
behaviors.
3.2. Large-scale Network Topology
3.2.1. Large Number of Hops and Complex Topology within a DetNet Domain
In scaling networks, the topology may consists of a large number
nodes and links which may lead to burst accumulation when a flow may
traverse a path with a large number of hops. And it may also impact
the controlling of end-to-end delay and jitter with the increasing of
transmission hops. And the topology may be complex including star,
ring, mesh, and their combinations can possibly be hierarchical. It
may lead to the difficulty with path computation.
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3.2.2. Long Distance links within a DetNet Domain
In scaling networks, 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.
3.2.3. Topology across Multiple Domains
In scaling networks, the flows may be transmitted through the
topology across multiple domains within a single administrative
control or a closed group of administrative control as per [RFC8655].
The interworking of mechanisms within different domains, end-to-end
path computation and resources scheduling with bounded latency
constraint should be considered.
3.2.4. Topology across Heterogeneous Networks
In scaling networks, the network topology may across heterogeneous
networks and the 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.
4. Gap Analysis for Enhanced DetNet
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.
[I-D.xiong-detnet-large-scale-enhancements] has proposed the overall
framework of DetNet enhancements for scaling deterministic networks
based on the gaps.
4.1. Gap Analysis of Providing 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
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large number of deterministic flows and network nodes in large-scale
networks. It may consider the aggregation based on the flow
classification to futher improve the scalability. And the flow
identification is required to be dynamic and simplified to ensure the
aggregated flows have compatible DetNet flow-specific
characteristics.
4.2. 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.
4.2.1. 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.
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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.
4.2.2. 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. The reservation of the bandwidth can not
guarantee the deterministic latency. In large-scale networks, the
bandwidth, buffer and scheduling resources are combined with queuing
mechanisms to guarantee the deterministic latency. The deterministic
resources may be include the resources that can guarantee the
deterministic latency such as the nodes, links, interfaces, buffers,
bandwidth, queuing and scheduling mechanisms and so on. The
planning, reservation and allocation of deterministic resources
should be taken into consideration in DetNet data plane.
4.2.3. 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 (e.g. Tagged Cyclic Queuing
and Forwarding (TCQF)[I-D.eckert-detnet-tcqf], and Cycle Specified
Queuing and Forwarding (CSQF)
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[I-D.chen-detnet-sr-based-bounded-latency]), deadline-scheduling
queuing mechanism (e.g. Earlist Deadline Forwarding (EDF)
[I-D.peng-detnet-deadline-based-forwarding]), timeslot-scheduling
queuing mechanism (e.g. Timeslot Queuing and Forwarding (TQF)
[I-D.peng-detnet-packet-timeslot-mechanism]), and asynchronous
queuing mechanism (e.g. Work Conserving Stateless Core Fair Queuing
(C-SCORE) [I-D.joung-detnet-stateless-fair-queuing]). The queuing-
based requirements in DetNet enhanced data plane has been described
in [I-D.ietf-detnet-scaling-requirements]. The function of multiple
queuing mechanisms and related DetNet-Specific metadata should be
defined in DetNet data plane as per
[I-D.xiong-detnet-data-fields-edp].
5. Security Considerations
TBA
6. Acknowledgements
TBA
7. IANA Considerations
TBA
8. Normative References
[I-D.chen-detnet-sr-based-bounded-latency]
Chen, M., Geng, X., Li, Z., Joung, J., and J. Ryoo,
"Segment Routing (SR) Based Bounded Latency", Work in
Progress, Internet-Draft, draft-chen-detnet-sr-based-
bounded-latency-03, 7 July 2023,
<https://datatracker.ietf.org/doc/html/draft-chen-detnet-
sr-based-bounded-latency-03>.
[I-D.eckert-detnet-tcqf]
Eckert, T. T., Li, Y., Bryant, S., Malis, A. G., Ryoo, J.,
Liu, P., Li, G., Ren, S., and F. Yang, "Deterministic
Networking (DetNet) Data Plane - Tagged Cyclic Queuing and
Forwarding (TCQF) for bounded latency with low jitter in
large scale DetNets", Work in Progress, Internet-Draft,
draft-eckert-detnet-tcqf-05, 5 January 2024,
<https://datatracker.ietf.org/doc/html/draft-eckert-
detnet-tcqf-05>.
[I-D.ietf-detnet-scaling-requirements]
Liu, P., Li, Y., Eckert, T. T., Xiong, Q., Ryoo, J.,
zhushiyin, and X. Geng, "Requirements for Scaling
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Deterministic Networks", Work in Progress, Internet-Draft,
draft-ietf-detnet-scaling-requirements-05, 20 November
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
detnet-scaling-requirements-05>.
[I-D.joung-detnet-stateless-fair-queuing]
Joung, J., Ryoo, J., Cheung, T., Li, Y., and P. Liu,
"Latency Guarantee with Stateless Fair Queuing", Work in
Progress, Internet-Draft, draft-joung-detnet-stateless-
fair-queuing-01, 19 October 2023,
<https://datatracker.ietf.org/doc/html/draft-joung-detnet-
stateless-fair-queuing-01>.
[I-D.peng-detnet-deadline-based-forwarding]
Peng, S., Du, Z., Basu, K., cheng, Yang, D., and C. Liu,
"Deadline Based Deterministic Forwarding", Work in
Progress, Internet-Draft, draft-peng-detnet-deadline-
based-forwarding-08, 14 December 2023,
<https://datatracker.ietf.org/doc/html/draft-peng-detnet-
deadline-based-forwarding-08>.
[I-D.peng-detnet-packet-timeslot-mechanism]
Peng, S., Liu, P., Basu, K., Liu, A., Yang, D., and G.
Peng, "Timeslot Queueing and Forwarding Mechanism", Work
in Progress, Internet-Draft, draft-peng-detnet-packet-
timeslot-mechanism-05, 14 December 2023,
<https://datatracker.ietf.org/doc/html/draft-peng-detnet-
packet-timeslot-mechanism-05>.
[I-D.xiong-detnet-data-fields-edp]
Xiong, Q., Liu, A., Gandhi, R., and D. Yang, "Data Fields
for DetNet Enhanced Data Plane", Work in Progress,
Internet-Draft, draft-xiong-detnet-data-fields-edp-01, 10
July 2023, <https://datatracker.ietf.org/doc/html/draft-
xiong-detnet-data-fields-edp-01>.
[I-D.xiong-detnet-differentiated-detnet-qos]
Xiong, Q., Zhao, J., Du, Z., Zeng, Q., and C. Liu,
"Differentiated DetNet QoS for Deterministic Services",
Work in Progress, Internet-Draft, draft-xiong-detnet-
differentiated-detnet-qos-00, 23 October 2023,
<https://datatracker.ietf.org/doc/html/draft-xiong-detnet-
differentiated-detnet-qos-00>.
[I-D.xiong-detnet-large-scale-enhancements]
Xiong, Q., Du, Z., Zhao, J., and D. Yang, "Enhanced DetNet
Data Plane (EDP) Framework for Scaling Deterministic
Networks", Work in Progress, Internet-Draft, draft-xiong-
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detnet-large-scale-enhancements-03, 10 July 2023,
<https://datatracker.ietf.org/doc/html/draft-xiong-detnet-
large-scale-enhancements-03>.
[I-D.zhao-detnet-enhanced-use-cases]
Zhao, J., Xiong, Q., and Z. Du, "Enhanced Use cases for
Scaling Deterministic Networks", Work in Progress,
Internet-Draft, draft-zhao-detnet-enhanced-use-cases-00,
23 October 2023, <https://datatracker.ietf.org/doc/html/
draft-zhao-detnet-enhanced-use-cases-00>.
[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>.
[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>.
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[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>.
Authors' Addresses
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan
Hubei, 430223
China
Email: xiong.quan@zte.com.cn
Aihua Liu
ZTE Corporation
China
Email: liu.aihua@zte.com.cn
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