



MPLS Working Group                                        S. Bryant (Ed)
Internet-Draft                               Futurewei Technologies Inc.
Intended status: Standards Track                              G. Swallow
Expires: September 6, 2021                     Southend Technical Center
                                                                 M. Chen
                                                                  Huawei
                                                             G. Fioccola
                                                     Huawei Technologies
                                                               G. Mirsky
                                                               ZTE Corp.
                                                          March 05, 2021


                     RFC6374 Synonymous Flow Labels
                     draft-ietf-mpls-rfc6374-sfl-10

Abstract

   RFC 6374 describes methods of making loss and delay measurements on
   Label Switched Paths (LSPs) primarily as used in MPLS Transport
   Profile (MPLS-TP) networks.  This document describes a method of
   extending RFC 6374 performance measurements from flows carried over
   MPLS-TP to flows carried over generic MPLS LSPs.  In particular, it
   extends the technique to allow loss and delay measurements to be made
   on multi-point to point LSPs and introduces some additional
   techniques to allow more sophisticated measurements to be made in
   both MPLS-TP and generic MPLS networks.

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 September 6, 2021.







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Copyright Notice

   Copyright (c) 2021 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
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  RFC6374 Packet Loss Measurement with SFL  . . . . . . . . . .   4
   4.  RFC6374 Single Packet Delay Measurement . . . . . . . . . . .   4
   5.  Data Service Packet Delay Measurement . . . . . . . . . . . .   5
   6.  Some Simplifying Rules  . . . . . . . . . . . . . . . . . . .   6
   7.  Multiple Packet Delay Characteristics . . . . . . . . . . . .   7
     7.1.  Method 1: Time Buckets  . . . . . . . . . . . . . . . . .   7
     7.2.  Method 2 Classic Standard Deviation . . . . . . . . . . .   9
       7.2.1.  Multi-Packet Delay Measurement Message Format . . . .  10
     7.3.  Per Packet Delay Measurement  . . . . . . . . . . . . . .  11
     7.4.  Average Delay . . . . . . . . . . . . . . . . . . . . . .  11
   8.  Sampled Measurement . . . . . . . . . . . . . . . . . . . . .  13
   9.  Carrying RFC6374 Packets over an LSP using an SFL . . . . . .  13
     9.1.  RFC6374 SFL TLV . . . . . . . . . . . . . . . . . . . . .  15
   10. RFC6374 Combined Loss-Delay Measurement . . . . . . . . . . .  16
   11. Privacy Considerations  . . . . . . . . . . . . . . . . . . .  17
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  17
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  17
     13.1.  Allocation of MPLS Generalized Associated Channel
            (G-ACh) Types  . . . . . . . . . . . . . . . . . . . . .  17
     13.2.  Allocation of MPLS Loss/Delay TLV Object . . . . . . . .  18
   14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   15. Contributing Authors  . . . . . . . . . . . . . . . . . . . .  18
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     16.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20






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1.  Introduction

   [RFC6374] was originally designed for use as an Operations,
   Administration, and Maintenance (OAM) protocol for use with MPLS
   Transport Profile (MPLS-TP) [RFC5921] LSPs.  MPLS-TP only supports
   point-to-point and point-to-multi-point LSPs.  This document
   describes how to use RFC6374 in the generic MPLS case, and also
   introduces a number of more sophisticated measurements of
   applicability to both cases.

   [RFC8372] describes the requirement for introducing flow identities
   when using RFC6374 [RFC6374] packet Loss Measurements (LM).  In
   summary RFC6374 uses the loss-measurement (LM) packet as the packet
   accounting demarcation point.  Unfortunately this gives rise to a
   number of problems that may lead to significant packet accounting
   errors in certain situations.  For example:

   1.  Where a flow is subjected to Equal Cost Multi-Path (ECMP)
       treatment packets can arrive out of order with respect to the LM
       packet.

   2.  Where a flow is subjected to ECMP treatment, packets can arrive
       at different hardware interfaces, thus requiring reception of an
       LM packet on one interface to trigger a packet accounting action
       on a different interface which may not be co-located with it.
       This is a difficult technical problem to address with the
       required degree of accuracy.

   3.  Even where there is no ECMP (for example on RSVP-TE, MPLS-TP LSPs
       and pseudowires(PWs)) local processing may be distributed over a
       number of processor cores, leading to synchronization problems.

   4.  Link aggregation techniques [RFC7190] may also lead to
       synchronization issues.

   5.  Some forwarder implementations have a long pipeline between
       processing a packet and incrementing the associated counter,
       again leading to synchronization difficulties.

   An approach to mitigating these synchronization issue is described in
   [RFC8321] in which packets are batched by the sender and each batch
   is marked in some way such that adjacent batches can be easily
   recognized by the receiver.

   An additional problem arises where the LSP is a multi-point to point
   LSP, since MPLS does not include a source address in the packet.
   Network management operations require the measurement of packet loss
   between a source and destination.  It is thus necessary to introduce



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   some source specific information into the packet to identify packet
   batches from a specific source.

   [RFC8957] describes a method of encoding per flow instructions in an
   MPLS label stack using a technique called Synonymous Flow Labels
   (SFL) in which labels which mimic the behavior of other labels
   provide the packet batch identifiers and enable the per batch packet
   accounting.  This memo specifies how SFLs are used to perform RFC6374
   packet loss and RFC6374 delay measurements.

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.  RFC6374 Packet Loss Measurement with SFL

   The data service packets of the flow being instrumented are grouped
   into batches, and all the packets within a batch are marked with the
   SFL [RFC8372] corresponding to that batch.  The sender counts the
   number of packets in the batch.  When the batch has completed and the
   sender is confident that all of the packets in that batch will have
   been received, the sender issues an RFC6374 Query message to
   determine the number actually received and hence the number of
   packets lost.  The RFC6374 Query message is sent using the same SFL
   as the corresponding batch of data service packets.  The format of
   the Query and Response packets is described in Section 9.

4.  RFC6374 Single Packet Delay Measurement

   RFC6374 describes how to measure the packet delay by measuring the
   transit time of an RFC6374 packet over an LSP.  Such a packet may not
   need to be carried over an SFL since the delay over a particular LSP
   should be a function of the Traffic Class (TC) bits.

   However, where SFLs are being used to monitor packet loss or where
   label inferred scheduling is used [RFC3270] then the SFL would be
   REQUIRED to ensure that the RFC6374 packet which was being used as a
   proxy for a data service packet experienced a representative delay.
   The format of an RFC6374 packet carried over the LSP using an SFL is
   shown in Section 9.







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5.  Data Service Packet Delay Measurement

   Where it is desired to more thoroughly instrument a packet flow and
   to determine the delay of a number of packets it is undesirable to
   send a large number of RFC6374 packets acting as a proxy data service
   packets (see Section 4).  A method of directly measuring the delay
   characteristics of a batch of packets is therefore needed.

   Given the long intervals over which it is necessary to measure packet
   loss, it is not necessarily the case that the batch times for the two
   measurement types would be identical.  Thus, we use a technique that
   permits the two measurements are made concurrently and yet relatively
   independent from each other.  The notion that they are relatively
   independent arises from the potential for the two batches to overlap
   in time, in which case either the delay batch time will need to be
   cut short or the loss time will need to be extended to allow correct
   reconciliation of the various counters.

   The problem is illustrated in Figure 1 below:

      (1) AAAAAAAAAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB

      SFL Marking of a packet batch for loss measurement

      (2) AADDDDAAAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB

      SFL Marking of a subset of the packets for delay

      (3) AAAAAAAADDDDBBBBBBBBAAAAAAAAAABBBBBBBBBB

      SFL Marking of a subset of the packets across a
      packet loss measurement boundary

      (4) AACDCDCDAABBBBBBBBBBAAAAAAAAAABBBBBBBBBB

      The case of multiple delay measurements within
      a packet loss measurement

      A & B are packets where loss is being measured
      C & D are pacekts where loss and delay is being measured

                  Figure 1: RFC6734 Query Packet with SFL

   In case 1 of Figure 1 we show the case where loss measurement alone
   is being carried out on the flow under analysis.  For illustrative
   purposes consider that 10 packets are used in each flow in the time
   interval being analyzed.




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   Now consider case 2 of Figure 1 where a small batch of packets need
   to be analyzed for delay.  These are marked with a different SFL type
   indicating that they are to be monitored for both loss and delay.
   The SFL=A indicates loss batch A, SFL=D indicates a batch of packets
   that are to be instrumented for delay, but SFL D is synonymous with
   SFL A, which in turn is synonymous with the underlying Forwarding
   Equivalence Class (FEC).  Thus, a packet marked D will be accumulated
   into the A loss batch, into the delay statistics and will be
   forwarded as normal.  Whether the packet is actually counted twice
   (for loss and delay) or whether the two counters are reconciled
   during reporting is a local matter.

   Now consider case 3 of Figure 1 where a small batch of packets are
   marked for delay across a loss batch boundary.  These packets need to
   be considered as part of batch A or a part of batch B, and any
   RFC6374 Query needs to take place after all the packets A or D
   (whichever option is chosen) have arrived at the receiving LSR.

   Now consider case 4 of Figure 1.  Here we have a case where it is
   required to take a number of delay measurements within a batch of
   packets that we are measuring for loss.  To do this we need two SFLs
   for delay (C and D) and alternate between them (on a delay batch by
   delay batch basis) for the purposes of measuring the delay
   characteristics of the different batches of packets.

6.  Some Simplifying Rules

   It is possible to construct a large set of overlapping measurement
   types, in terms of loss, delay, loss and delay and batch overlap.  If
   we allow all combinations of cases, this leads to configuration,
   testing and implementation complexity and hence increased costs.  The
   following simplifying rules represent the default case:

   1.  Any system that needs to measure delay MUST be able to measure
       loss.

   2.  Any system that is to measure delay MUST be configured to measure
       loss.  Whether the loss statistics are collected or not is a
       local matter.

   3.  A delay measurement MAY start at any point during a loss
       measurement batch, subject to rule 4.

   4.  A delay measurement interval MUST be short enough that it will
       complete before the enclosing loss batch completes.

   5.  The duration of a second delay (D in Figure 1 batch must be such
       that all packets from the packets belonging to a first delay



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       batch (C in Figure 1)will have been received before the second
       delay batch completes.  This condition is satisfied when the time
       to send a batch is long compared to the network propagation time,
       and is a parameter that can be established by the network
       operator.

   Given that the sender controls both the start and duration of a loss
   and a delay packet batch, these rules are readily implemented in the
   control plane.

7.  Multiple Packet Delay Characteristics

   A number of methods are described which add to the set of
   measurements originally specified in [RFC6374].  Each of these
   methods has different characteristics and different processing
   demands on the packet forwarder.  The choice of method will depend on
   the type of diagnostic that the operator seeks.

   Three Methods are discussed:

   1.  Time Buckets

   2.  Classic Standard Deviation

   3.  Average Delay

7.1.  Method 1: Time Buckets

   In this method the receiving LSR measures the inter-packet gap,
   classifies the delay into a number of delay buckets and records the
   number of packets in each bucket.  As an example, if the operator
   were concerned about packets with a delay of up to 1us, 2us, 4us,
   8us, and over 8us then there would be five buckets and packets that
   arrived up to 1us would cause the 1us bucket counter to increase,
   between 1us and 2us the 2us bucket counter would increase etc.  In
   practice it might be better in terms of processing and potential
   parallelism if, when a packet had a delay relative to its predecessor
   of 2us, then both the up to 1us and the 2us counter were incremented,
   and any more detailed information was calculated in the analytics
   system.

   This method allows the operator to see more structure in the jitter
   characteristics than simply measuring the average jitter, and avoids
   the complication of needing to perform a per packet multiply, but
   will probably need the time intervals between buckets to be
   programmable by the operator.





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   The packet format of a Time Bucket Jitter Measurement Message is
   shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version| Flags |  Control Code |        Message Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  QTF  |  RTF  | RPTF  |              Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Session Identifier          |    DS     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Number of     |      Reserved 1                               |
   | Buckets       |                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Interval in 10ns units                      |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Number pkts in Bucket                       |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                           TLV Block                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 2: Time Bucket Jitter Measurement Message Format

   The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
   Session Identifier, Reserved and DS Fields are as defined in section
   3.2 of RFC6374.  The remaining fields, which are unsigned integers,
   are as follows:

   o Number of Buckets in the measurement

   o Reserved 1 must be sent as zero and ignored on receipt

   o Interval in 10ns units is the inter-packet interval for
     this bucket

   o Number Pkts in Bucket is the number of packets found in
     this bucket.

   There will be a number of Interval/Number pairs depending on the
   number of buckets being specified by the Querier.  If an RFC6374
   message is being used to configure the buckets, (i.e. the responder



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   is creating or modifying the buckets according to the intervals in
   the Query message), then the Responder MUST respond with 0 packets in
   each bucket until it has been configured for a full measurement
   period.  This indicates that it was configured at the time of the
   last response message, and thus the response is valid for the whole
   interval.  As per the [RFC6374] convention the Number of pkts in
   Bucket fields are included in the Query message and set to zero.

   Out of band configuration is permitted by this mode of operation.

   Note this is a departure from the normal fixed format used in
   RFC6374.

   The time bucket jitter measurement message is carried over an LSP in
   the way described in [RFC6374] and over an LSP with an SFL as
   described in Section 9.

7.2.  Method 2 Classic Standard Deviation

   In this method, provision is made for reporting the following delay
   characteristics:

   1.  Number of packets in the batch (n).

   2.  Sum of delays in a batch (S)

   3.  Maximum Delay.

   4.  Minimum Delay.

   5.  Sum of squares of Inter-packet delay (SS).

   Characteristics 1 and 2 give the mean delay.  Measuring the delay of
   each pair in the batch is discussed in Section 7.3.

   Characteristics 3 and 4 give the outliers.

   Characteristics 1, 2 and 5 can be used to calculate the variance of
   the inter-packet gap and hence the standard deviation giving a view
   of the distribution of packet delays and hence the jitter.  The
   equation for the variance (var) is given by:

   var = (SS - S*S/n)/(n-1)

   There is some concern over the use of this algorithm for measuring
   variance, because SS and S*S/n can be similar numbers, particularly
   where variance is low.  However the method commends it self by not
   requiring a division in the hardware.



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7.2.1.  Multi-Packet Delay Measurement Message Format

   The packet format of a Multi-Packet Delay Measurement Message is
   shown below:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version| Flags |  Control Code |        Message Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  QTF  |  RTF  | RPTF  |              Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Session Identifier          |    DS     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number of Packets                        |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Sum of Delays for Batch                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Minimum Delay                           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Maximum Delay                           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                Sum of squares of Inter-packet delay           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~                           TLV Block                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

          Figure 3: Multi-packet Delay Measurement Message Format

   The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
   Session Identifier, Reserved and DS Fields are as defined in section
   3.2 of RFC6374.  The remaining fields are as follows:













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   o Number of Packets is the number of packets in this batch

   o Sum of Delays for Batch is the duration of the batch in the
     time measurement format specified in the RTF field.

   o Minimum Delay is the minimum inter-packet gap observed during
     the batch in the time format specified in the RTF field.

   o Maximum Delay is the maximum inter-packet gap observed during
     the batch in the time format specified in the RTF field.

   The multi-packet delay measurement message is carried over an LSP in
   the way described in [RFC6374] and over an LSP with an SFL as
   described in Section 9.

7.3.  Per Packet Delay Measurement

   If detailed packet delay measurement is required then it might be
   possible to record the inter-packet gap for each packet pair.  In
   other than exception cases of slow flows or small batch sizes, this
   would create a large (per packet) demand on storage in the
   instrumentation system, a large bandwidth to such a storage system
   and large bandwidth to the analytics system.  Such a measurement
   technique is outside the scope of this document.

7.4.  Average Delay

   Introduced in [RFC8321] is the concept of a one way delay measurement
   in which the average time of arrival of a set of packets is measured.
   In this approach the packet is time-stamped at arrival and the
   Responder returns the sum of the time-stamps and the number of times-
   tamps.  From this the analytics engine can determine the mean delay.
   An alternative model is that the Responder returns the time stamp of
   the first and last packet and the number of packets.  This later
   method has the advantage of allowing the average delay to be
   determined at a number of points along the packet path and allowing
   the components of the delay to be characterized.  Unless specifically
   configured otherwise, the responder may return either or both types
   of response and the analytics engine should process the response
   appropriately.

   The packet format of an Average Delay Measurement Message is shown
   below:








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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Version| Flags |  Control Code |        Message Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  QTF  |  RTF  | RPTF  |              Reserved                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Session Identifier          |    DS     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Number of Packets                        |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Time of First Packet                     |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Time of Last Packet                      |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                   Sum of Timestamps of Batch                  |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ~                                                               ~
   ~                           TLV Block                           ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 4: Average Delay Measurement Message Format

   The Version, Flags, Control Code, Message Length, QTF, RTF, RPTF,
   Session Identifier, and DS Fields are as defined in section 3.2 of
   RFC6374.  The remaining fields are as follows:

   o Number of Packets is the number of packets in this batch.

   o Time of First Packet is the time of arrival of the first
     packet in the batch.

   o Time of Last Packet is the time of arrival of the last
     packet in the batch.

   o Sum of Timestamps of Batch.

   The average delay measurement message is carried over an LSP in the
   way described in [RFC6374] and over an LSP with an SFL as described
   in Section 9.  As is the convention with RFC6374, the Query message
   contains placeholders for the Response message.  The placeholders are
   sent as zero.




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8.  Sampled Measurement

   In the discussion so far it has been assumed that we would measure
   the delay characteristics of every packet in a delay measurement
   interval defined by an SFL of constant color.  In [RFC8321] the
   concept of a sampled measurement is considered.  That is the
   Responder only measures a packet at the start of a group of packets
   being marked for delay measurement by a particular color, rather than
   every packet in the marked batch.  A measurement interval is not
   defined by the duration of a marked batch of packets but the interval
   between a pair of RFC6374 packets taking a readout of the delay
   characteristic.  This approach has the advantage that the measurement
   is not impacted by ECMP effects.

   This sampled approach may be used if supported by the Responder and
   configured by the opertor.

9.  Carrying RFC6374 Packets over an LSP using an SFL

   We illustrate the packet format of an RFC6374 Query message using
   SFLs for the case of an MPLS direct loss measurement in Figure 5.






























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   +-------------------------------+
   |                               |
   |             LSP               |
   |            Label              |
   +-------------------------------+
   |                               |
   |        Synonymous Flow        |
   |            Label              |
   +-------------------------------+
   |                               |
   |            GAL                |
   |                               |
   +-------------------------------+
   |                               |
   |      ACH Type = 0xA           |
   |                               |
   +-------------------------------+
   |                               |
   |  RFC6374 Measurement Message  |
   |                               |
   |  +-------------------------+  |
   |  |                         |  |
   |  |      Fixed-format       |  |
   |  |      portion of msg     |  |
   |  |                         |  |
   |  +-------------------------+  |
   |  |                         |  |
   |  |      Optional SFL TLV   |  |
   |  |                         |  |
   |  +-------------------------+  |
   |  |                         |  |
   |  |      Optional Return    |  |
   |  |      Information        |  |
   |  |                         |  |
   |  +-------------------------+  |
   |                               |
   +-------------------------------+

                  Figure 5: RFC6734 Query Packet with SFL

   The MPLS label stack is exactly the same as that used for the user
   data service packets being instrumented except for the inclusion of
   the Generic Associated Channel Label (GAL) [RFC5586] to allow the
   receiver to distinguish between normal data packets and OAM packets.
   Since the packet loss measurements are being made on the data service
   packets, an RFC6374 direct loss measurement is being made, and which
   is indicated by the type field in the ACH (Type = 0x000A).




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   The RFC6374 measurement message consists of the three components, the
   RFC6374 fixed-format portion of the message as specified in [RFC6374]
   carried over the ACH channel type specified the type of measurement
   being made (currently: loss, delay or loss and delay) as specified in
   RFC6374.

   Two optional TLVs MAY also be carried if needed.  The first is the
   SFL TLV specified in Section 9.1.  This is used to provide the
   implementation with a reminder of the SFL that was used to carry the
   RFC6374 message.  This is needed because a number of MPLS
   implementations do not provide the MPLS label stack to the MPLS OAM
   handler.  This TLV is required if RFC6374 messages are sent over UDP
   [RFC7876].  This TLV MUST be included unless, by some method outside
   the scope of this document, it is known that this information is not
   needed by the RFC6374 Responder.

   The second set of information that may be needed is the return
   information that allows the responder send the RFC6374 response to
   the Querier.  This is not needed if the response is requested in-band
   and the MPLS construct being measured is a point to point LSP, but
   otherwise MUST be carried.  The return address TLV is defined in
   [RFC6374] and the optional UDP Return Object is defined in [RFC7876].

   Where a measurement other than an MPLS direct loss measurement is to
   be made, the appropriate RFC6374 measurement message is used (for
   example, one of the new types defined in this document) and this is
   indicated to the receiver by the use of the corresponding ACH type.

9.1.  RFC6374 SFL TLV

   The RFC6374 SFL TLV is shown in Figure 6.  This contains the SFL that
   was carried in the label stack, the FEC that was used to allocate the
   SFL and the index into the batch of SLs that were allocated for the
   FEC that corresponds to this SFL.

    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     |MBZ| SFL Batch |    SFL Index  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 SFL                   |        Reserved       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                 FEC                                           |
   .                                                               .
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             Figure 6: SFL TLV




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   Where:

   Type      Type is set to Synonymous Flow Label (SFL-TLV).

   Length    The length of the TLV as specified in RFC6374.

   MBZ       MUST be sent as zero and ignored on receive.

   SFL Batch The SFL batch that this SFL was allocated as part
             of see [I-D.bryant-mpls-sfl-control]

   SPL Index The index into the list of SFLs that were assigned
             against the FEC that corresponds to the SFL.

             Multiple SFLs can be assigned to a FEC each
             with different actions. This index is an optional
             convenience for use in mapping between the TLV
             and the associated data structures in the LSRs.
             The use of this feature is agreed between the
             two parties during configuration. It is not required,
             but is a convenience for the receiver if both parties
             support the facility,

   SFL       The SFL used to deliver this packet.  This is an MPLS
             label which is a component of a label stack entry as
             defined in Section 2.1 of [RFC3032].

   Reserved  MUST be sent as zero and ignored on receive.

   FEC       The Forwarding Equivalence Class that was used to
             request this SFL.  This is encoded as per
             Section 3.4.1 of [RFC5036]

   This information is needed to allow for operation with hardware that
   discards the MPLS label stack before passing the remainder of the
   stack to the OAM handler.  By providing both the SFL and the FEC plus
   index into the array of allocated SFLs a number of implementation
   types are supported.

10.  RFC6374 Combined Loss-Delay Measurement

   This mode of operation is not currently supported by this
   specification.








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11.  Privacy Considerations

   The inclusion of originating and/or flow information in a packet
   provides more identity information and hence potentially degrades the
   privacy of the communication.  Whilst the inclusion of the additional
   granularity does allow greater insight into the flow characteristics
   it does not specifically identify which node originated the packet
   other than by inspection of the network at the point of ingress, or
   inspection of the control protocol packets.  This privacy threat may
   be mitigated by encrypting the control protocol packets, regularly
   changing the synonymous labels and by concurrently using a number of
   such labels.

12.  Security Considerations

   The security considerations documented in [RFC6374] and [RFC8372]
   (which in turn calls up [RFC7258] and [RFC5920]) are applicable to
   this protocol.

   The issue noted in Section 11 is a security consideration.  There are
   no other new security issues associated with the MPLS dataplane.  Any
   control protocol used to request SFLs will need to ensure the
   legitimacy of the request.

   An attacker that manages to corrupt the RFC6374 SFL TLV Section 9.1
   could disrupt the measurements in a way that the RFC6374 responder is
   unable to detect.  However, the network opertator is likely to notice
   the anomalous network performance measurements, and in any case
   normal MPLS network security proceedures make this type of attack
   extremely unlikley.

13.  IANA Considerations

13.1.  Allocation of MPLS Generalized Associated Channel (G-ACh) Types

   As per the IANA considerations in [RFC5586] updated by [RFC7026] and
   [RFC7214], IANA is requested to allocate the following codeponts in
   the "MPLS Generalized Associated Channel (G-ACh) Type" registry, in
   the "Generic Associated Channel (G-ACh) Parameters" name space:












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   Value  Description                            Reference
   -----  ---------------------------------      -----------
   TBD    RFC6374 Time Bucket Jitter Measurement This


   TBD    RFC6374 Multi-Packet Delay             This
          Measurement

   TBD    RFC6374 Average Delay Measurement      This

13.2.  Allocation of MPLS Loss/Delay TLV Object

   IANA is requested to allocate a new TLV from the 0-127 range of the
   MPLS Loss/Delay Measurement TLV Object Registry in the "Generic
   Associated Channel (G-ACh) Parameters" namespace:

     Type Description                       Reference
     ---- --------------------------------- ---------
     TBD  Synonymous Flow Label             This

   A value of 4 is recommended.

   RFC Editor please delete this para
   [RFC3032][I-D.bryant-mpls-sfl-control][RFC5036]

14.  Acknowledgments

   The authors thank Benjamin Kaduk and Elwyn Davies for their thorough
   and thoughtful review of this document.

15.  Contributing Authors

    Zhenbin Li
    Huawei
    Email: lizhenbin@huawei.com

    Siva Sivabalan
    Ciena Corporation
    Email: ssivabal@ciena.com

16.  References

16.1.  Normative References

   [I-D.bryant-mpls-sfl-control]
              Bryant, S., Swallow, G., and S. Sivabalan, "A Simple
              Control Protocol for MPLS SFLs", draft-bryant-mpls-sfl-
              control-09 (work in progress), December 2020.



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   [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>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC5036]  Andersson, L., Ed., Minei, I., Ed., and B. Thomas, Ed.,
              "LDP Specification", RFC 5036, DOI 10.17487/RFC5036,
              October 2007, <https://www.rfc-editor.org/info/rfc5036>.

   [RFC5586]  Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
              "MPLS Generic Associated Channel", RFC 5586,
              DOI 10.17487/RFC5586, June 2009,
              <https://www.rfc-editor.org/info/rfc5586>.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374,
              DOI 10.17487/RFC6374, September 2011,
              <https://www.rfc-editor.org/info/rfc6374>.

   [RFC7026]  Farrel, A. and S. Bryant, "Retiring TLVs from the
              Associated Channel Header of the MPLS Generic Associated
              Channel", RFC 7026, DOI 10.17487/RFC7026, September 2013,
              <https://www.rfc-editor.org/info/rfc7026>.

   [RFC7214]  Andersson, L. and C. Pignataro, "Moving Generic Associated
              Channel (G-ACh) IANA Registries to a New Registry",
              RFC 7214, DOI 10.17487/RFC7214, May 2014,
              <https://www.rfc-editor.org/info/rfc7214>.

   [RFC7876]  Bryant, S., Sivabalan, S., and S. Soni, "UDP Return Path
              for Packet Loss and Delay Measurement for MPLS Networks",
              RFC 7876, DOI 10.17487/RFC7876, July 2016,
              <https://www.rfc-editor.org/info/rfc7876>.

   [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>.

   [RFC8957]  Bryant, S., Chen, M., Swallow, G., Sivabalan, S., and G.
              Mirsky, "Synonymous Flow Label Framework", RFC 8957,
              DOI 10.17487/RFC8957, January 2021,
              <https://www.rfc-editor.org/info/rfc8957>.




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16.2.  Informative References

   [RFC3270]  Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
              P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
              Protocol Label Switching (MPLS) Support of Differentiated
              Services", RFC 3270, DOI 10.17487/RFC3270, May 2002,
              <https://www.rfc-editor.org/info/rfc3270>.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010,
              <https://www.rfc-editor.org/info/rfc5920>.

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, DOI 10.17487/RFC5921, July 2010,
              <https://www.rfc-editor.org/info/rfc5921>.

   [RFC7190]  Villamizar, C., "Use of Multipath with MPLS and MPLS
              Transport Profile (MPLS-TP)", RFC 7190,
              DOI 10.17487/RFC7190, March 2014,
              <https://www.rfc-editor.org/info/rfc7190>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <https://www.rfc-editor.org/info/rfc7258>.

   [RFC8321]  Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli,
              L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
              "Alternate-Marking Method for Passive and Hybrid
              Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321,
              January 2018, <https://www.rfc-editor.org/info/rfc8321>.

   [RFC8372]  Bryant, S., Pignataro, C., Chen, M., Li, Z., and G.
              Mirsky, "MPLS Flow Identification Considerations",
              RFC 8372, DOI 10.17487/RFC8372, May 2018,
              <https://www.rfc-editor.org/info/rfc8372>.

Authors' Addresses

   Stewart Bryant
   Futurewei Technologies Inc.

   Email: sb@stewartbryant.com








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   George Swallow
   Southend Technical Center

   Email: swallow.ietf@gmail.com


   Mach Chen
   Huawei

   Email: mach.chen@huawei.com


   Giuseppe Fioccola
   Huawei Technologies

   Email: giuseppe.fioccola@huawei.com


   Gregory Mirsky
   ZTE Corp.

   Email: gregimirsky@gmail.com





























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