Deterministic Networking (DetNet): PREOF for DetNet IP
draft-varga-detnet-ip-preof-00

Document Type Active Internet-Draft (individual)
Authors Balazs Varga  , J├ínos Farkas  , Andy Malis 
Last updated 2021-06-09
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DetNet                                                          B. Varga
Internet-Draft                                                 J. Farkas
Intended status: Informational                                  Ericsson
Expires: December 11, 2021                                      A. Malis
                                                        Malis Consulting
                                                            June 9, 2021

         Deterministic Networking (DetNet): PREOF for DetNet IP
                     draft-varga-detnet-ip-preof-00

Abstract

   This document describes how DetNet IP data plane can support the
   Packet Replication, Elimination, and Ordering Functions (PREOF) based
   on [RFC9025].

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 December 11, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Terms Used in This Document . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   3.  Requirements for adding PREOF to DetNet IP  . . . . . . . . .   4
   4.  Adding PREOF to DetNet IP . . . . . . . . . . . . . . . . . .   4
     4.1.  Solution Basics . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Encapsulation . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Packet Processing . . . . . . . . . . . . . . . . . . . .   6
     4.4.  Flow Aggregation  . . . . . . . . . . . . . . . . . . . .   6
     4.5.  PREOF Procedures  . . . . . . . . . . . . . . . . . . . .   7
     4.6.  PREOF capable DetNet IP domain  . . . . . . . . . . . . .   8
   5.  Control and Management Plane Parameters . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   The DetNet Working Group has defined packet replication (PRF), packet
   elimination (PEF) and packet ordering (POF) functions to provide
   service protection by the DetNet service sub-layer [RFC8655].  The
   PREOF service protection method relies on copies of the same packet
   sent over multiple maximally disjoint paths and uses sequencing
   information to eliminate duplicates.  A possible implementation of
   the PRF and PEF functions is described in [IEEE8021CB] and the
   related YANG data model is defined in [IEEEP8021CBcv].  A possible
   implementation of POF function is described in
   [I-D.varga-detnet-pof].  Figure 1 shows a DetNet flow on which PREOF
   functions are applied during forwarding from the source to the
   destination.

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                                          +------------+
                +---------------E1---+    |            |
    +---+       |               |    +---R3---+        |          +---+
    |src|------R1           +---+             |        E3----O----+dst|
    +---+       |           |                 E2-------+          +---+
                +----------R2                 |
                            +-----------------+

    R: replication function (PRF)
    E: elimination function (PEF)
    O: ordering function (POF)

               Figure 1: PREOF scenario in a DetNet network

   In general, the use of PREOF functions require sequencing information
   to be included in the packets of a DetNet compound flow.  This may be
   done by adding a sequence number or time stamp as part of DetNet
   encapsulation.  Sequencing information is typically added once, at or
   close to the source.

   The DetNet MPLS data plane [RFC8939] specifies how sequencing
   information is encoded in the MPLS header.  However, the DetNet IP
   data plane described in [RFC8939] does not specify how sequencing
   information can be encoded in the IP header.  This document describes
   a DetNet IP encapsulation that includes sequencing information based
   on the DetNet MPLS over UDP/IP data plane [RFC9025], i.e., leveraging
   the MPLS-over-UDP technology.

2.  Terminology

2.1.  Terms Used in This Document

   This document uses the terminology established in the DetNet
   architecture [RFC8655], and the reader is assumed to be familiar with
   that document and its terminology.

2.2.  Abbreviations

   The following abbreviations are used in this document:

   DetNet        Deterministic Networking.

   PEF           Packet Elimination Function.

   POF           Packet Ordering Function.

   PREOF         Packet Replication, Elimination and Ordering Functions.

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   PRF           Packet Replication Function.

2.3.  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.  Requirements for adding PREOF to DetNet IP

   The requirements for adding PREOF to DetNet IP are:

   o  to reuse existing DetNet data plane solutions (e.g., [RFC8964],
      [RFC9025]).

   o  to allow with minimal implementation effort the DetNet service
      sub-layer for IP packet switched networks.

   The described solution practically gains from MPLS header fields
   without adding MPLS protocol stack complexity to the nodal
   requirements.

4.  Adding PREOF to DetNet IP

4.1.  Solution Basics

   The DetNet IP encapsulation supporting DetNet Service sub-layer is
   based on the "UDP tunneling" concept.  At the edge of a PREOF capable
   DetNet IP domain the DetNet flow is encapsulated in an UDP packet
   containing the sequence number used by PREOF functions within the
   domain.  This solution maintains the 6-tuple-based DetNet flow
   identification in DetNet transit nodes, which operate at the DetNet
   forwarding sub-layer between the DetNet service sub-layer nodes;
   therefore, it is compatible with [RFC8939].  Figure 2 shows how the
   PREOF capable DetNet IP data plane fits into the DetNet sub-layers.

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                    DetNet          IP
                       .
                       .
                 +------------+
                 |  Service   | d-CW, Service-ID (S-label)
                 +------------+
                 | Forwarding | UDP/IP Header
                 +------------+

               Figure 2: PREOF capable DetNet IP data plane

4.2.  Encapsulation

   The PREOF capable DetNet IP encapsulation builds on encapsulating
   DetNet PW directly over UDP.  That is, it combines DetNet MPLS
   [RFC8964] with DetNet MPLS-in-UDP [RFC9025], without using any
   F-Labels as shown in Figure 3.  DetNet flows are identified at the
   receiving DetNet service sub-layer processing node via the S-Label
   and/or the UDP/IP header information.  Sequencing information for
   PREOF is provided by the DetNet Control Word (d-CW) as per [RFC8964].
   The S-label is used to identify both the DetNet flow and the DetNet
   App-flow type.  The UDP tunnel is used to direct the packet across
   the DetNet domain to the next DetNet service sub-layer processing
   node.

      +---------------------------------+
      |                                 |
      |         DetNet App-Flow         |
      |       (original IP) Packet      |
      |                                 |
      +---------------------------------+ <--\
      |       DetNet Control Word       |    |
      +---------------------------------+    +--> PREOF capable
      |       Service-ID (S-Label)      |    |    DetNet IP data
      +---------------------------------+    |    plane encapsulation
      |            UDP Header           |    |
      +---------------------------------+    |
      |            IP Header            |    |
      +---------------------------------+ <--/
      |            Data-Link            |
      +---------------------------------+
      |             Physical            |
      +---------------------------------+

              Figure 3: PREOF capable DetNet IP encapsulation

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4.3.  Packet Processing

   IP ingress and egress nodes of the PREOF capable DetNet IP domain
   MUST add and remove a DetNet service-specific d-CW and Service-ID
   (i.e., S-Label).  Relay nodes MAY change Service-ID values when
   processing a DetNet flow, i.e., incoming and outgoing Service-IDs of
   a DetNet flow can be different.  Service-ID values MUST be
   provisioned per DetNet service via configuration, i.e., via the
   Controller Plane described in [RFC8938].  In some PREOF topologies,
   the node performing replication sends the packets to multiple nodes
   performing PEF or POF and the replication node may need to use
   different Service-ID values for the different member flows for the
   same DetNet service.

   Note, that Service-IDs provide identification at the downstream
   DetNet service sub-layer receiver, not the sender.

4.4.  Flow Aggregation

   Two methods can be used for flow aggregation:

   o  aggregation using same UDP tunnel,

   o  aggregating DetNet flows as a new DetNet flow.

   In the first case, the different DetNet PWs use the same UDP tunnel,
   so they are treated as a single (aggregated) flow on all transit
   nodes.

   For the second option, an additional Service-ID and d-CW tuple is
   added to the encapsulation.  The Aggregate-ID is a special case of a
   Service-ID, whose properties are known only at the aggregation and
   de-aggregation end points.  It is a property of the Aggregate-ID that
   it is followed by a d-CW followed by an Service-ID/d-CW tuple.
   Figure 4 shows the encapsulation in case of aggregation.

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      +---------------------------------+
      |                                 |
      |         DetNet App-Flow         |
      |         Payload  Packet         |
      |                                 |
      +---------------------------------+ <--\
      |       DetNet Control Word       |    |
      +---------------------------------+    +--> PREOF capable
      |       Service-ID (S-Label)      |    |    DetNet IP data
      +---------------------------------+    |    plane encapsulation
      |       DetNet Control Word       |    |
      +---------------------------------+    |
      |      Aggregate-ID (A-Label)     |    |
      +---------------------------------+    |
      |           UDP Header            |    |
      +---------------------------------+    |
      |            IP Header            |    |
      +---------------------------------+ <--/
      |            Data-Link            |
      +---------------------------------+
      |             Physical            |
      +---------------------------------+

          Figure 4: Aggregating DetNet flows as a new DetNet flow

4.5.  PREOF Procedures

   A node operating on a received DetNet flow at the DetNet service sub-
   layer uses the local context associated with a received Service-ID to
   determine which local DetNet operation(s) are applied to received
   packet.  A Service-ID may be allocated to be unique and enabling
   DetNet flow identification regardless of which input interface or UDP
   tunnel the packet is received.  It is important to note that Service-
   ID values are driven by the receiver, not the sender.

   The DetNet forwarding sub-layer is supported by the UDP tunnel and is
   responsible for providing resource allocation and explicit routes.

   To support outgoing PREOF capable DetNet IP encapsulation, an
   implementation MUST support the provisioning of UDP and IP header
   information.  Note, when PRF is performed at the DetNet service sub-
   layer, there are multiple member flows, and each member flow requires
   the of their own Service-ID, UDP and IP header information.  The
   headers for each outgoing packet MUST be formatted according to the
   configuration information, and the UDP Source Port value MUST be set
   to uniquely identify the DetNet flow.  The packet MUST then be
   handled as a PREOF capable DetNet IP packet.

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   To support the receive processing, an implementation MUST also
   support the provisioning of received Service-ID, UDP and IP header
   information.  The provisioned information MUST be used to identify
   incoming app-flows based on the combination of Service-ID and/or
   incoming encapsulation header information.

   The challenge for POF initialization is that, for example, after a
   reset, it is not known whether the first received packet is in-order
   or out-of-order.  The original initialization (see
   [I-D.varga-detnet-pof]) considers the first packet as in-order, so
   out-of-order packet(s) during "POFMaxTime"/"POFMaxTime_path_i" time -
   after the first packet was received - may not be corrected.  The
   motivation behind such an initialization is POF implementation
   simplicity.

4.6.  PREOF capable DetNet IP domain

   Figure 5 shows using PREOF in a PREOF capable DetNet IP network.

             <---------- PREOF capable DetNet IP --------------->
                                       ______
                             ____     /      \__
                  ____      /     \__/          \____________
   +----+      __/    \____/                                 \    +----+
   |src |_____/                                               \___| dst|
   +----+     \_______            DetNet network    __________/   +----+
                      \_______                    _/
                              \         __     __/
                               \_______/  \___/

                                          +------------+
                +---------------E1---+    |            |
   +----+       |               |    +---R3---+        |          +----+
   |src |------R1           +---+             |        E3----O----+ dst|
   +----+       |           |                 E2-------+          +----+
                +----------R2                 |
                            +-----------------+

                 Figure 5: PREOF capable DetNet IP domain

5.  Control and Management Plane Parameters

   The information needed to identify individual and aggregated DetNet
   flows is summarized as follows:

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   o  Service-ID information to be mapped to UDP/IP flows.  Note that,
      for example, a single Service-ID can map to multiple sets of UDP/
      IP information when PREOF is used.

   o  IPv4 or IPv6 source address field.

   o  IPv4 or IPv6 source address prefix length, where a zero (0) value
      effectively means that the address field is ignored.

   o  IPv4 or IPv6 destination address field.

   o  IPv4 or IPv6 destination address prefix length, where a zero (0)
      effectively means that the address field is ignored.

   o  IPv4 protocol field set to "UDP".

   o  IPv6 next header field set to "UDP".

   o  For the IPv4 Type of Service and IPv6 Traffic Class Fields:

      *  Whether or not the DSCP field is used in flow identification as
         the use of the DSCP field for flow identification is optional.

      *  If the DSCP field is used to identify a flow, then the flow
         identification information (for that flow) includes a list of
         DSCPs used by the given DetNet flow.

   o  UDP Source Port.  Support for both exact and wildcard matching is
      required.  Port ranges can optionally be used.

   o  UDP Destination Port.  Support for both exact and wildcard
      matching is required.  Port ranges can optionally be used.

   o  For end systems, an optional maximum IP packet size that should be
      used for that outgoing DetNet IP flow.

   This information MUST be provisioned per DetNet flow via
   configuration, e.g., via the controller plane.

   An implementation MUST support ordering of the set of information
   used to identify an individual DetNet flow.  This can, for example,
   be used to provide a DetNet service for a specific UDP flow, with
   unique Source and Destination Port field values, while providing a
   different service for the aggregate of all other flows with that same
   UDP Destination Port value.

   The minimum set of information for the configuration of the DetNet
   service sub-layer is summarized as follows:

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   o  App-flow identification information.

   o  Sequence number length.

   o  PREOF + related Service-ID(s).

   o  Associated forwarding sub-layer information.

   o  Service aggregation information.

   The minimum set of information for the configuration of the DetNet
   forwarding sub-layer is summarized as follows:

   o  UDP tunnel specific information.

   o  Traffic parameters.

6.  Security Considerations

   There are no new DetNet related security considerations introduced by
   this solution.

7.  IANA Considerations

   This document makes no IANA requests.

8.  References

8.1.  Normative References

   [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>.

   [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>.

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   [RFC8939]  Varga, B., Ed., Farkas, J., Berger, L., Fedyk, D., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              IP", RFC 8939, DOI 10.17487/RFC8939, November 2020,
              <https://www.rfc-editor.org/info/rfc8939>.

   [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>.

   [RFC9025]  Varga, B., Ed., Farkas, J., Berger, L., Malis, A., and S.
              Bryant, "Deterministic Networking (DetNet) Data Plane:
              MPLS over UDP/IP", RFC 9025, DOI 10.17487/RFC9025, April
              2021, <https://www.rfc-editor.org/info/rfc9025>.

8.2.  Informative References

   [I-D.varga-detnet-pof]
              Varga, B., Farkas, J., Kehrer, S., and T. Heer,
              "Deterministic Networking (DetNet): Packet Ordering
              Function", draft-varga-detnet-pof-00 (work in progress),
              April 2021.

   [IEEE8021CB]
              IEEE, "IEEE Standard for Local and metropolitan area
              networks -- Frame Replication and Elimination for
              Reliability", DOI 10.1109/IEEESTD.2017.8091139, October
              2017,
              <https://standards.ieee.org/standard/802_1CB-2017.html>.

   [IEEEP8021CBcv]
              Kehrer, S., "FRER YANG Data Model and Management
              Information Base Module", IEEE P802.1CBcv
              /D1.2 P802.1CBcv, March 2021,
              <https://www.ieee802.org/1/files/private/cv-drafts/d1/802-
              1CBcv-d1-2.pdf>.

Authors' Addresses

   Balazs Varga
   Ericsson
   Magyar Tudosok krt. 11.
   Budapest  1117
   Hungary

   Email: balazs.a.varga@ericsson.com

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   Janos Farkas
   Ericsson
   Magyar Tudosok krt. 11.
   Budapest  1117
   Hungary

   Email: janos.farkas@ericsson.com

   Andrew G. Malis
   Malis Consulting

   Email: agmalis@gmail.com

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