IGP Flexible Algorithm with Deterministic Routing
draft-peng-lsr-flex-algo-deterministic-routing-00

Network Working Group                                       Shaofu. Peng
Internet-Draft                                                  Bin. Tan
Intended status: Standards Track                             Quan. Xiong
Expires: July 17, 2022                                   ZTE Corporation
                                                        January 13, 2022

           IGP Flexible Algorithm with Deterministic Routing
           draft-peng-lsr-flex-algo-deterministic-routing-00

Abstract

   IGP Flex Algorithm proposes a solution that allows IGPs themselves to
   compute constraint based paths over the network, and it also
   specifies a way of using Segment Routing (SR) Prefix-SIDs and SRv6
   locators, or pure IP prefix to steer packets along the constraint-
   based paths.  This document describes how to compute deterministic
   paths within Flex-algo plane.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 17, 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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 and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of

Peng, et al.              Expires July 17, 2022                 [Page 1]
Internet-Draft           flex-algo deterministic            January 2022

   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Determinisitc Links . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Deterministic Link Bound with CQF . . . . . . . . . . . .   4
       3.1.1.  ISIS Advertisement of Deterministic Link Bound with
               CQF . . . . . . . . . . . . . . . . . . . . . . . . .   5
       3.1.2.  OSPF Advertisement of Deterministic Link Bound with
               CQF . . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.2.  Deterministic Link Bound with Deadline  . . . . . . . . .   7
   4.  Deterministic Routes Computation  . . . . . . . . . . . . . .   7
     4.1.  Bind CQF parameters with Flex-Algo  . . . . . . . . . . .   7
       4.1.1.  ISIS Advertisement of Flex-algo Binding CQF . . . . .   8
       4.1.2.  FAD Flags Extensions  . . . . . . . . . . . . . . . .   8
       4.1.3.  OSPF Advertisement of Flex-algo Binding CQF . . . . .   9
       4.1.4.  CQF based Deterministic Routes Computation  . . . . .   9
     4.2.  Bind Deadline parameters with Flex-Algo . . . . . . . . .  10
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   IGP Flex Algorithm [I-D.ietf-lsr-flex-algo] proposes a solution that
   allows IGPs themselves to compute constraint based paths over the
   network, and it also specifies a way of using Segment Routing
   [RFC8402] Prefix-SIDs and SRv6 locators, or pure IP prefix
   [I-D.ietf-lsr-ip-flexalgo] to steer packets along the constraint-
   based paths.  It specifies a set of extensions to ISIS, OSPFv2 and
   OSPFv3 that enable a router to send TLVs that identify (a)
   calculation-type, (b) specify a metric-type, and (c )describe a set
   of constraints on the topology, that are to be used to compute the
   best paths along the constrained topology.  A given combination of
   calculation-type, metric-type, and constraints is known as an FAD
   (Flexible Algorithm Definition).

   [RFC8655] describes the architecture of deterministic network and
   defines the QoS goals of deterministic forwarding: Minimum and
   maximum end-to-end latency from source to destination, timely
   delivery, and bounded jitter (packet delay variation); packet loss

Peng, et al.              Expires July 17, 2022                 [Page 2]
Internet-Draft           flex-algo deterministic            January 2022

   ratio under various assumptions as to the operational states of the
   nodes and links; an upper bound on out-of-order packet delivery.  In
   order to achieve these goals, deterministic networks use resource
   reservation, explicit routing, service protection and other means.  A
   deterministic path is typically (but not necessarily) explicit routes
   so that it does not normally suffer temporary interruptions caused by
   the convergence of routing or bridging protocols.

   IGP Flex-algo has the characteristic mentioned in [RFC8655]: under a
   single administrative control or within a closed group of
   administrative control.  IGP Flex-algo supports Min Unidirectional
   Link Delay (defined in [RFC8570]) metric type to compute shortest
   paths with minimum delay, however, the cumulative delay is
   essentially the accumulation of transmission delay of all links,
   excluding node delay.  In order to make up for this gap, it is
   necessary to enhance IGP flex-algo to compute the path with
   deterministic delay, i.e., including deterministic node delay and
   link transmission delay.

   This document describes how to compute distributed shortest paths
   with deterministic delay metric within Flex-algo plane, as the basis
   of the whole distributed deterministic scheme.  It should be noted
   that relying on this enhancement alone does not guarantee complete
   determinacy, it needs to be used in conjunction with other tools,
   such as creating additional backup explicit path with consistent
   delay metric for PREOF (Packet Replication, Elimination, and Ordering
   Functions), turning off local repair, smoothing the delay jitter
   during route convergence, providing deterministic forwarding
   mechanism, etc.

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.  Determinisitc Links

   When a packet is forwarded to a link, the delay produced includes two
   parts: the first part is the dwell delay of the packet in the node,
   and the second part is the transmission delay of the packet on the
   link.  In packet switching networks, priority based queuing scheme is
   generally used.  It may give better average latency, but may have
   worst case latency.  We call those links bound with a queue mechanism
   that can not guarantee node delay are non-determinisitc links.

Peng, et al.              Expires July 17, 2022                 [Page 3]
Internet-Draft           flex-algo deterministic            January 2022

   On the contrary, those links bound with a queue mechanism that can
   provide deterministic node delay are called deterministic links.
   Typical queue mechanisms are:

   o  IEEE 802.1 WG has specified IEEE802.1Qch [CQF] which uses cyclic
      queuing and forwarding (CQF) mechanism and relies on time
      synchronization.  According to CQF, the maximum delay experienced
      by a given packet is (H+1)*D, the minimum delay experienced by a
      given packet is (H-1)*D, and the delay jitter is 2*D, where H is
      the number of hops and D is cycle duration.  Other variants based
      on CQF can avoid relying on time synchronization, but only the
      same cycle duration for all nodes.  Basically, the packet received
      in the current sending window (i.e., cycle) will ensure that it
      can be sent in the next sending window, then the deterministic
      node delay, on average, is one cycle duration, or seveval cycle
      durations if the forwarding delay (from incoming port to outgoing
      port) inside the node can't be ignored.

   o  [I-D.peng-detnet-deadline-based-forwarding] introduced a deadline
      based forwarding mechanism that allow packet to control its
      expected dwell time in the node according to the planned deadline.
      There are two policies for deadline queue to schedule packets.
      For early sending policy, the end-to-end delay is H*(P~D), jitter
      is H*Q, where, H is the number of hops, P is the forwarding delay
      inside the node, D is the planned deadline; For punctual sending
      policy, the end-to-end delay is H*D, jitter is a single
      authorization time.  That is, the packet received at any time will
      ensure that it can be sent in offset time P~D or D respectively
      for these two policies.

3.1.  Deterministic Link Bound with CQF

   A node may configure the CQF based packet scheduling parameter
   information for its local link, including CQF scheduling enable/
   disable, one or more cycle durations.  Accordingly, for each cycle
   duration, the node delay/jitter attributes of the link will be
   obtained.  The meanings of these parameters or attributes of the link
   are as follows:

   o  CQF scheduling enable/disable: the CQF scheduling algorithm can be
      enabled for a link, then the packets sent to that link will be
      scheduled by the CQF scheduling algorithm.

   o  Cycle duration: the duration of the cycle of CQF, which is also
      called cycle_size.  One or more cycle_size with different lengths
      can be configured for a link, such as 10us, 20us, 30us, and so on.

   o  Node delay/jitter:

Peng, et al.              Expires July 17, 2022                 [Page 4]
Internet-Draft           flex-algo deterministic            January 2022

      *  According to classical TSN CQF, for a given cycle_size, it can
         be deduced that the minimum delay in the node of the packet is
         0, the maximum delay in the node is 2*cycle_size, the average
         delay in the node is cycle_size, and the delay jitter in the
         node is 2*cycle_size.  The detailed reasons for these data are
         as follows: if a node receives a packet at the tail end of
         cycle i and sends that packet at the head end of cycle i+1, the
         resulting node delay, i.e., the minimum node delay, is 0; if a
         node receives a packet at the head end of cycle i and sends
         that packet at the tail end of cycle i+1, the resulting node
         delay, i.e., the maximum node delay, is 2*cycle_ size; the
         average node delay is one cycle_size, and the node delay jitter
         is 2*cycle_size.  Each cycle_size corresponds to a different
         set of delay/jitter attributes.

      *  However, for some variants based on TSN CQF, if the forwarding
         delay inside the node can't be ignored, e.g, wasting 2 cycle
         duration, then the minimum node delay, the maximum node delay,
         and the average node delay need to add 2 cycle_size
         respectively, but the node delay jitter is still 2*cycle_size.

3.1.1.  ISIS Advertisement of Deterministic Link Bound with CQF

3.1.1.1.  Advertisement of Forwarding Delay in Node

   The forwarding delay is related to the chip implementation and is
   generally constant.

   A new IS-IS sub-TLV is defined: the Forwarding Delay sub-TLV, which
   is advertised within TLV-22, 222, 23, 223, 141, 25.  At most only one
   Forwarding Delay sub-TLV can be included.

   The following format is defined for the Forwarding Delay sub-TLV:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |       Forwarding Delay        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 1

   where:

      Type: TBD

      Length: 2

Peng, et al.              Expires July 17, 2022                 [Page 5]
Internet-Draft           flex-algo deterministic            January 2022

      Forwarding Delay: The latency of packet from the incoming port (or
      generated from control plane) to the outgoing port, in units of
      microseconds.  If the forwarding delay can be ignored, it is set
      to 0.  If this sub-TLV is not advertised, the forwarding delay can
      be regarded as 0.

      NOTE: for all links of a specific node, it may be possible that
      they have the same forwarding delay, therefore the forwarding
      delay can also be advertised by a unified node attribute.  This
      would be considered in future versions.

3.1.1.2.  Advertisement of CQF Parameters

   A new IS-IS sub-TLV is defined: the Cycle Durations sub-TLV, which is
   advertised within TLV-22, 222, 23, 223, 141, 25.  At most only one
   Cycle Durations sub-TLV can be included.

   The following format is defined for the Cycle Durations sub-TLV:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |          Cycle_size 1         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Cycle_size 2          |             ... ...           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Cycle_size N          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 2

   where:

      Type: TBD

      Length: 2*N, depending on the count of the cycle_size.

      Cycle_size: The length of cycle duration, in units of
      microseconds.  A link can support multiple cycle durations, for
      example, 10us, 20us, 30us, etc, each for a specific service
      requirement.

   Only those links that enable CQF scheduling algorithm need to
   advertise the Cycle Durations sub-TLV, otherwise there is no need to
   advertise.

   Note that the advertised cycle_size must be consistent with the CQF
   queue scheduling mechanism actually instantiated by the link in the

Peng, et al.              Expires July 17, 2022                 [Page 6]
Internet-Draft           flex-algo deterministic            January 2022

   forwarding plane.  If the forwarding plane does not instantiate a CQF
   queue scheduling supporting a certain cycle_size, which is however
   advertised in the Cycle Durations sub-TLV, the subsequent route
   computation may get wrong results.

   For a given cycle_size, it can deduce the corresponding node delay
   and jitter attributes, so these attributes can no longer be
   explicitly included in the Cycle Durations sub-TLV.  As mentioned
   earlier, if the forwarding delay (assuming P) is not 0, the minimum
   node delay, the maximum node delay, and the average node delay need
   to take P into account respectively.  P is replaced by ((P/
   cycle_size)+1)*cycle_size for deducing.  That is:

   o  If P is 0, for a given cycle_size, the minimum node delay is 0,
      the maximum node delay is 2*cycle_size, the average node delay is
      cycle_size, and the node delay jitter is 2*cycle_size.

   o  If P is not 0, for a given cycle_size, the minimum node delay is
      ((P/cycle_size)+1)*cycle_size, the maximum node delay is ((P/
      cycle_size)+3)*cycle_size, the average node delay is ((P/
      cycle_size)+2)*cycle_size, and the node delay jitter is
      2*cycle_size.

3.1.2.  OSPF Advertisement of Deterministic Link Bound with CQF

   To be defined in next version.

3.2.  Deterministic Link Bound with Deadline

   To be described in next version.

4.  Deterministic Routes Computation

4.1.  Bind CQF parameters with Flex-Algo

   The binding relationship <algorithm, cycle_size> can be configured on
   one or more nodes participating in the same IGP Flex-algo plane, and
   then advertised in the IGP domain.  If there are multiple binding
   relationship advertised for the same algorithm, it should choose to
   use the binding cycle_size contained in the FAD with the highest
   priority.

   If a Flex-algo plane eventually uses a binding cycle_size, all links
   participated to the Flex-algo plane must be configured with CQF
   scheduling enabled and corresponding cycle_size, otherwise, links
   that do not meet the conditions must be excluded from the Flex-algo
   plane.

Peng, et al.              Expires July 17, 2022                 [Page 7]
Internet-Draft           flex-algo deterministic            January 2022

4.1.1.  ISIS Advertisement of Flex-algo Binding CQF

   The Flexible Algorithm definition can specify the binding cycle_size
   that are used to determine the deterministic delay metric for the
   computed path within the Flex-algo plane.

   A new IS-IS sub-TLV is defined: the FAD Binding Cycle-size Sub-TLV,
   which is advertised within IS-IS Flexible Algorithm Definition Sub-
   TLV.  At most only one FAD Binding Cycle-size Sub-TLV can be
   included.

   The following format is defined for the FAD Binding Cycle-size Sub-
   TLV:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Type        |     Length    |       Binding Cycle_size      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                 Figure 3

   where:

      Type: TBD

      Length: 2

      Binding Cycle_size: Cycle_size of CQF scheduling bound by Flex-
      algo, in units of microseconds.

   The binding cycle_size contained in the FAD with the highest priority
   will take effect.  If the FAD with the highest priority does not
   contain the FAD Binding Cycle-size Sub-TLV, assuming the Metric-Type
   is Min Unidirectional Link Delay, the traditional path considering
   only link transmission delay will be calculated, otherwise, the path
   will consider both node delay and link delay.

4.1.2.  FAD Flags Extensions

   A new flag (C-flag) is introduced to ISIS Flexible Algorithm
   Definition Flags Sub-TLV, to indicate to compute CQF based SPF path
   when Metric-Type is Min Unidirectional Link Delay.  In other words,
   it will compute shortest path with minimum deterministic end-to-end
   delay, which contains accumulated node delay provided by CQF and
   accumulated link transmission delay.

Peng, et al.              Expires July 17, 2022                 [Page 8]
Internet-Draft           flex-algo deterministic            January 2022

                    0 1 2 3 4 5 6 7...
                   +-+-+-+-+-+-+-+-+...
                   |M|C| |          ...
                   +-+-+-+-+-+-+-+-+...

                                 Figure 4

   where:

   C-flag: introduced by this document.  When set, CQF based SPF path is
   computed.

4.1.3.  OSPF Advertisement of Flex-algo Binding CQF

   To be defined in next version.

4.1.4.  CQF based Deterministic Routes Computation

   This document reuse the existing Metric-Type, Min Unidirectional Link
   Delay, combined with the C-flag, to compute CQF based shortest path
   with minimum deterministic end-to-end delay, which contains
   accumulated node delay provided by CQF and accumulated link
   transmission delay.

   NOTE: Whether new metric type need to be introduced needs to be
   discussed in the WG.

   For a Flex-algo plane that bound to a specific cycle_size, the delay
   metric of a candidate path within the Flex-algo plane equals:

      H * node delay, where H is the number of hops, and node delay can
      be deduced by the cycle_size and forwarding delay as above; plus

      Accumulated link transmission delay;

   From the source node to the destination node, the candidate path with
   minimum deterministic delay metric is the best one.  This calculation
   result may be different from the traditional calculation result
   considering only link transmission delay, depending on the proportion
   of node delay.

   The deterministic delay jitter of a candidate path within the Flex-
   algo plane equals:

      node delay jitter, which is 2*cycle_size; plus

      Accumulated link delay jitter, which is almost 0;

Peng, et al.              Expires July 17, 2022                 [Page 9]
Internet-Draft           flex-algo deterministic            January 2022

4.2.  Bind Deadline parameters with Flex-Algo

   To be described in next version.

5.  IANA Considerations

   TBD

6.  Security Considerations

   TBD.

7.  Acknowledgements

   TBD

8.  References

8.1.  Normative References

   [I-D.ietf-lsr-flex-algo]
              Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and
              A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex-
              algo-18 (work in progress), October 2021.

   [I-D.ietf-lsr-ip-flexalgo]
              Britto, W., Hegde, S., Kaneriya, P., Shetty, R., Bonica,
              R., and P. Psenak, "IGP Flexible Algorithms (Flex-
              Algorithm) In IP Networks", draft-ietf-lsr-ip-flexalgo-04
              (work in progress), December 2021.

   [I-D.peng-detnet-deadline-based-forwarding]
              Peng, S. and B. Tan, "Deadline Based Deterministic
              Forwarding", draft-peng-detnet-deadline-based-
              forwarding-00 (work in progress), January 2022.

   [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>.

Peng, et al.              Expires July 17, 2022                [Page 10]
Internet-Draft           flex-algo deterministic            January 2022

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

   [RFC8570]  Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
              D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
              Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
              2019, <https://www.rfc-editor.org/info/rfc8570>.

   [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>.

8.2.  Informative References

   [CQF]      "IEEE802.1Qch", 2017,
              <https://ieeexplore.ieee.org/document/7961303>.

Authors' Addresses

   Shaofu Peng
   ZTE Corporation
   China

   Email: peng.shaofu@zte.com.cn

   Bin Tan
   ZTE Corporation
   China

   Email: tan.bin@zte.com.cn

   Quan Xiong
   ZTE Corporation
   China

   Email: xiong.quan@zte.com.cn

Peng, et al.              Expires July 17, 2022                [Page 11]