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.

   Internet-Drafts are working documents of the Internet Engineering
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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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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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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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