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Versions: (draft-morton-ippm-capacity-metric-method) 00 01 02 03 04 05 06 07 08 09 10 Draft is active
In: IESG_Evaluation
Network Working Group                                          A. Morton
Internet-Draft                                                 AT&T Labs
Intended status: Standards Track                                 R. Geib
Expires: October 28, 2021                               Deutsche Telekom
                                                           L. Ciavattone
                                                               AT&T Labs
                                                          April 26, 2021


              Metrics and Methods for One-way IP Capacity
               draft-ietf-ippm-capacity-metric-method-10

Abstract

   This memo revisits the problem of Network Capacity metrics first
   examined in RFC 5136.  The memo specifies a more practical Maximum
   IP-Layer Capacity metric definition catering for measurement
   purposes, and outlines the corresponding methods of measurement.

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 October 28, 2021.

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



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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Scope, Goals, and Applicability . . . . . . . . . . . . . . .   4
   3.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  General Parameters and Definitions  . . . . . . . . . . . . .   6
   5.  IP-Layer Capacity Singleton Metric Definitions  . . . . . . .   7
     5.1.  Formal Name . . . . . . . . . . . . . . . . . . . . . . .   7
     5.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.3.  Metric Definitions  . . . . . . . . . . . . . . . . . . .   8
     5.4.  Related Round-Trip Delay and One-way Loss Definitions . .   9
     5.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .  10
     5.6.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  10
   6.  Maximum IP-Layer Capacity Metric Definitions (Statistic)  . .  10
     6.1.  Formal Name . . . . . . . . . . . . . . . . . . . . . . .  10
     6.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  10
     6.3.  Metric Definitions  . . . . . . . . . . . . . . . . . . .  10
     6.4.  Related Round-Trip Delay and One-way Loss Definitions . .  12
     6.5.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .  12
     6.6.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  13
   7.  IP-Layer Sender Bit Rate Singleton Metric Definitions . . . .  13
     7.1.  Formal Name . . . . . . . . . . . . . . . . . . . . . . .  13
     7.2.  Parameters  . . . . . . . . . . . . . . . . . . . . . . .  14
     7.3.  Metric Definition . . . . . . . . . . . . . . . . . . . .  14
     7.4.  Discussion  . . . . . . . . . . . . . . . . . . . . . . .  15
     7.5.  Reporting the Metric  . . . . . . . . . . . . . . . . . .  15
   8.  Method of Measurement . . . . . . . . . . . . . . . . . . . .  15
     8.1.  Load Rate Adjustment Algorithm  . . . . . . . . . . . . .  15
     8.2.  Measurement Qualification or Verification . . . . . . . .  20
     8.3.  Measurement Considerations  . . . . . . . . . . . . . . .  22
     8.4.  Running Code  . . . . . . . . . . . . . . . . . . . . . .  23
   9.  Reporting Formats . . . . . . . . . . . . . . . . . . . . . .  24
     9.1.  Configuration and Reporting Data Formats  . . . . . . . .  26
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  26
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  27
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  27
   13. Appendix A - Load Rate Adjustment Pseudo Code . . . . . . . .  27
   14. Appendix B - RFC 8085 UDP Guidelines Check  . . . . . . . . .  28
     14.1.  Assessment of Mandatory Requirements . . . . . . . . . .  28
     14.2.  Assessment of Recommendations  . . . . . . . . . . . . .  30
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     15.2.  Informative References . . . . . . . . . . . . . . . . .  34
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  36



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1.  Introduction

   The IETF's efforts to define Network and Bulk Transport Capacity have
   been chartered and progressed for over twenty years.  Over that time,
   the performance community has seen development of Informative
   definitions in [RFC3148] for Framework for Bulk Transport Capacity
   (BTC), RFC 5136 for Network Capacity and Maximum IP-Layer Capacity,
   and the Experimental metric definitions and methods in [RFC8337],
   Model-Based Metrics for BTC.

   This memo revisits the problem of Network Capacity metrics examined
   first in [RFC3148] and later in [RFC5136].  Maximum IP-Layer Capacity
   and [RFC3148] Bulk Transfer Capacity (goodput) are different metrics.
   Maximum IP-Layer Capacity is like the theoretical goal for goodput.
   There are many metrics in [RFC5136], such as Available Capacity.
   Measurements depend on the network path under test and the use case.
   Here, the main use case is to assess the maximum capacity of the
   access network, with specific performance criteria used in the
   measurement.

   This memo recognizes the importance of a definition of a Maximum IP-
   Layer Capacity Metric at a time when access speeds have increased
   dramatically; a definition that is both practical and effective for
   the performance community's needs, including Internet users.  The
   metric definition is intended to use Active Methods of Measurement
   [RFC7799], and a method of measurement is included.

   The most direct active measurement of IP-Layer Capacity would use IP
   packets, but in practice a transport header is needed to traverse
   address and port translators.  UDP offers the most direct assessment
   possibility, and in the [copycat] measurement study to investigate
   whether UDP is viable as a general Internet transport protocol, the
   authors found that a high percentage of paths tested support UDP
   transport.  A number of liaisons have been exchanged on this topic
   [LS-SG12-A] [LS-SG12-B], discussing the laboratory and field tests
   that support the UDP-based approach to IP-Layer Capacity measurement.

   This memo also recognizes the many updates to the IP Performance
   Metrics Framework [RFC2330] published over twenty years, and makes
   use of [RFC7312] for Advanced Stream and Sampling Framework, and
   [RFC8468] with IPv4, IPv6, and IPv4-IPv6 Coexistence Updates.

   Appendix A describes the load rate adjustment algorithm in pseudo-
   code.  Appendix B discusses the algorithm's compliance with
   [RFC8085].






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1.1.  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.

2.  Scope, Goals, and Applicability

   The scope of this memo is to define a metric and corresponding method
   to unambiguously perform Active measurements of Maximum IP-Layer
   Capacity, along with related metrics and methods.

   Another goal is to harmonize the specified metric and method across
   the industry, and this memo is the vehicle that captures IETF
   consensus, possibly resulting in changes to the specifications of
   other Standards Development Organizations (SDO) (through each SDO's
   normal contribution process, or through liaison exchange).

   A local goal is to aid efficient test procedures where possible, and
   to recommend reporting with additional interpretation of the results.
   Fostering the development of protocol support for this metric and
   method of measurement is also a goal of this memo (all active testing
   protocols currently defined by the IPPM WG are UDP-based, meeting a
   key requirement of these methods).  The supporting protocol
   development to measure this metric according to the specified method
   is a key future contribution to Internet measurement.

   The load rate adjustment algorithm's scope is limited to helping
   determine the Maximum IP-Layer Capacity in the context of an
   infrequent, diagnostic, short term measurement.  It is RECOMMENDED to
   discontinue non-measurement traffic that shares a subscriber's
   dedicated resources while testing: measurements may not be accurate
   and throughput of competing elastic traffic may be greatly reduced.

   The primary application of the metric and method of measurement
   described here is the same as in Section 2 of [RFC7497] where:

   o  The access portion of the network is the focus of this problem
      statement.  The user typically subscribes to a service with
      bidirectional access partly described by rates in bits per second.

   In addition, the use of the load rate adjustment algorithm described
   in section 8.1 has the following additional applicability
   limitations:





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   - MUST only be used in the application of diagnostic and operations
   measurements as described in this memo

   - MUST only be used in circumstances consistent with Section 10,
   Security Considerations

   - If a network operator is certain of the access capacity to be
   validated, then testing MAY start with a fixed rate test at the
   access capacity and avoid activating the load adjustment algorithm.
   However, the stimulus for a diagnostic test (such as a subscriber
   request) strongly implies that there is no certainty and the load
   adjustment algorithm will be needed.

   Further, the metric and method of measurement are intended for use
   where specific exact path information is unknown within a range of
   possible values:

   - the subscriber's exact Maximum IP-Layer Capacity is unknown (which
   is sometimes the case; service rates can be increased due to upgrades
   without a subscriber's request, or to provide a surplus to compensate
   for possible underestimates of TCP-based testing.

   - the size of the access bottleneck buffer is unknown.

   Finally, the measurement system's load rate adjustment algorithm
   SHALL NOT be provided with the exact capacity value to be validated a
   priori.  This restriction fosters a fair result, and removes an
   opportunity for bad actors to operate with knowledge of the "right
   answer".

3.  Motivation

   As with any problem that has been worked for many years in various
   SDOs without any special attempts at coordination, various solutions
   for metrics and methods have emerged.

   There are five factors that have changed (or begun to change) in the
   2013-2019 time frame, and the presence of any one of them on the path
   requires features in the measurement design to account for the
   changes:

   1.  Internet access is no longer the bottleneck for many users.

   2.  Both transfer rate and latency are important to user's
       satisfaction.

   3.  UDP's growing role in Transport, in areas where TCP once
       dominated.



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   4.  Content and applications are moving physically closer to users.

   5.  There is less emphasis on ISP gateway measurements, possibly due
       to less traffic crossing ISP gateways in future.

4.  General Parameters and Definitions

   This section lists the REQUIRED input factors to specify a Sender or
   Receiver metric.

   o  Src, the address of a host (such as the globally routable IP
      address).

   o  Dst, the address of a host (such as the globally routable IP
      address).

   o  MaxHops, the limit on the number of Hops a specific packet may
      visit as it traverses from the host at Src to the host at Dst
      (implemented in the TTL or Hop Limit).

   o  T0, the time at the start of measurement interval, when packets
      are first transmitted from the Source.

   o  I, the nominal duration of a measurement interval at the
      destination (default 10 sec)

   o  dt, the nominal duration of m equal sub-intervals in I at the
      destination (default 1 sec)

   o  dtn, the beginning boundary of a specific sub-interval, n, one of
      m sub-intervals in I

   o  FT, the feedback time interval between status feedback messages
      communicating measurement results, sent from the receiver to
      control the sender.  The results are evaluated throughout the test
      to determine how to adjust the current offered load rate at the
      sender (default 50ms)

   o  Tmax, a maximum waiting time for test packets to arrive at the
      destination, set sufficiently long to disambiguate packets with
      long delays from packets that are discarded (lost), such that the
      distribution of one-way delay is not truncated.

   o  F, the number of different flows synthesized by the method
      (default 1 flow)

   o  flow, the stream of packets with the same n-tuple of designated
      header fields that (when held constant) result in identical



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      treatment in a multi-path decision (such as the decision taken in
      load balancing).  Note: The IPv6 flow label MAY be included in the
      flow definition when routers have complied with [RFC6438]
      guidelines.

   o  Type-P, the complete description of the test packets for which
      this assessment applies (including the flow-defining fields).
      Note that the UDP transport layer is one requirement for test
      packets specified below.  Type-P is a parallel concept to
      "population of interest" defined in clause 6.1.1 of[Y.1540].

   o  PM, a list of fundamental metrics, such as loss, delay, and
      reordering, and corresponding target performance threshold.  At
      least one fundamental metric and target performance threshold MUST
      be supplied (such as One-way IP Packet Loss [RFC7680] equal to
      zero).

   A non-Parameter which is required for several metrics is defined
   below:

   o  T, the host time of the *first* test packet's *arrival* as
      measured at the destination Measurement Point, or MP(Dst).  There
      may be other packets sent between Source and Destination hosts
      that are excluded, so this is the time of arrival of the first
      packet used for measurement of the metric.

   Note that time stamp format and resolution, sequence numbers, etc.
   will be established by the chosen test protocol standard or
   implementation.

5.  IP-Layer Capacity Singleton Metric Definitions

   This section sets requirements for the singleton metric that supports
   the Maximum IP-Layer Capacity Metric definition in Section 6.

5.1.  Formal Name

   Type-P-One-way-IP-Capacity, or informally called IP-Layer Capacity.

   Note that Type-P depends on the chosen method.

5.2.  Parameters

   This section lists the REQUIRED input factors to specify the metric,
   beyond those listed in Section 4.

   No additional Parameters are needed.




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5.3.  Metric Definitions

   This section defines the REQUIRED aspects of the measurable IP-Layer
   Capacity metric (unless otherwise indicated) for measurements between
   specified Source and Destination hosts:

   Define the IP-Layer Capacity, C(T,dt,PM), to be the number of IP-
   Layer bits (including header and data fields) in packets that can be
   transmitted from the Src host and correctly received by the Dst host
   during one contiguous sub-interval, dt in length.  The IP-Layer
   Capacity depends on the Src and Dst hosts, the host addresses, and
   the path between the hosts.

   The number of these IP-Layer bits is designated n0[dtn,dtn+1] for a
   specific dt.

   When the packet size is known and of fixed size, the packet count
   during a single sub-interval dt multiplied by the total bits in IP
   header and data fields is equal to n0[dtn,dtn+1].

   Anticipating a Sample of Singletons, the number of sub-intervals with
   duration dt MUST be set to a natural number m, so that T+I = T + m*dt
   with dtn+1 - dtn = dt for 1 <= n <= m.

   Parameter PM represents other performance metrics [see section 5.4
   below]; their measurement results SHALL be collected during
   measurement of IP-Layer Capacity and associated with the
   corresponding dtn for further evaluation and reporting.  Users SHALL
   specify the parameter Tmax as required by each metric's reference
   definition.

   Mathematically, this definition is represented as (for each n):

                                      ( n0[dtn,dtn+1] )
                      C(T,dt,PM) = -------------------------
                                             dt


                      Equation for IP-Layer Capacity

   and:

   o  n0 is the total number of IP-Layer header and payload bits that
      can be transmitted in standard-formed packets [RFC8468] from the
      Src host and correctly received by the Dst host during one
      contiguous sub-interval, dt in length, during the interval [T,
      T+I],




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   o  C(T,dt,PM) the IP-Layer Capacity, corresponds to the value of n0
      measured in any sub-interval beginning at dtn, divided by the
      length of sub-interval, dt.

   o  PM represents other performance metrics [see section 5.4 below];
      their measurement results SHALL be collected during measurement of
      IP-Layer Capacity and associated with the corresponding dtn for
      further evaluation and reporting.

   o  all sub-intervals MUST be of equal duration.  Choosing dt as non-
      overlapping consecutive time intervals allows for a simple
      implementation.

   o  The bit rate of the physical interface of the measurement devices
      MUST be higher than the smallest of the links on the path whose
      C(T,I,PM) is to be measured (the bottleneck link).

   Measurements according to these definitions SHALL use the UDP
   transport layer.  Standard-formed packets are specified in Section 5
   of [RFC8468].  The measurement SHOULD use a randomized Source port or
   equivalent technique, and SHOULD send responses from the Source
   address matching the test packet destination address.

   Some compression affects on measurement are discussed in Section 6 of
   [RFC8468].

5.4.  Related Round-Trip Delay and One-way Loss Definitions

   RTD[dtn,dtn+1] is defined as a Sample of the [RFC2681] Round-trip
   Delay between the Src host and the Dst host over the interval [T,T+I]
   (that contains equal non-overlapping intervals of dt).  The
   "reasonable period of time" in [RFC2681] is the parameter Tmax in
   this memo.  The statistics used to summarize RTD[dtn,dtn+1] MAY
   include the minimum, maximum, median, and mean, and the range =
   (maximum - minimum) is referred to below in Section 8.1 for load
   adjustment purposes.

   OWL[dtn,dtn+1] is defined as a Sample of the [RFC7680] One-way Loss
   between the Src host and the Dst host over the interval [T,T+I] (that
   contains equal non-overlapping intervals of dt).  The statistics used
   to summarize OWL[dtn,dtn+1] MAY include the lost packet count and the
   lost packet ratio.

   Other metrics MAY be measured: one-way reordering, duplication, and
   delay variation.






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5.5.  Discussion

   See the corresponding section for Maximum IP-Layer Capacity.

5.6.  Reporting the Metric

   The IP-Layer Capacity SHOULD be reported with at least single Megabit
   resolution, in units of Megabits per second (Mbps), (which is
   1,000,000 bits per second to avoid any confusion).

   The related One-way Loss metric and Round Trip Delay measurements for
   the same Singleton SHALL be reported, also with meaningful resolution
   for the values measured.

   Individual Capacity measurements MAY be reported in a manner
   consistent with the Maximum IP-Layer Capacity, see Section 9.

6.  Maximum IP-Layer Capacity Metric Definitions (Statistic)

   This section sets requirements for the following components to
   support the Maximum IP-Layer Capacity Metric.

6.1.  Formal Name

   Type-P-One-way-Max-IP-Capacity, or informally called Maximum IP-Layer
   Capacity.

   Note that Type-P depends on the chosen method.

6.2.  Parameters

   This section lists the REQUIRED input factors to specify the metric,
   beyond those listed in Section 4.

   No additional Parameters or definitions are needed.

6.3.  Metric Definitions

   This section defines the REQUIRED aspects of the Maximum IP-Layer
   Capacity metric (unless otherwise indicated) for measurements between
   specified Source and Destination hosts:

   Define the Maximum IP-Layer Capacity, Maximum_C(T,I,PM), to be the
   maximum number of IP-Layer bits n0[dtn,dtn+1] divided by dt that can
   be transmitted in packets from the Src host and correctly received by
   the Dst host, over all dt length intervals in [T, T+I], and meeting
   the PM criteria.  Equivalently the Maximum of a Sample of size m of




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   C(T,I,PM) collected during the interval [T, T+I] and meeting the PM
   criteria.

   The number of sub-intervals with duration dt MUST be set to a natural
   number m, so that T+I = T + m*dt with dtn+1 - dtn = dt for 1 <= n <=
   m.

   Parameter PM represents the other performance metrics (see
   Section 6.4 below) and their measurement results for the Maximum IP-
   Layer Capacity.  At least one target performance threshold (PM
   criterion) MUST be defined.  If more than one metric and target
   performance threshold are defined, then the sub-interval with maximum
   number of bits transmitted MUST meet all the target performance
   thresholds.  Users SHALL specify the parameter Tmax as required by
   each metric's reference definition.

   Mathematically, this definition can be represented as:

                                      max  ( n0[dtn,dtn+1] )
                                     [T,T+I]
                Maximum_C(T,I,PM) = -------------------------
                                               dt
               where:
                  T                                      T+I
                  _________________________________________
                  |   |   |   |   |   |   |   |   |   |   |
              dtn=1   2   3   4   5   6   7   8   9  10  n+1
                                                     n=m


                       Equation for Maximum Capacity

   and:

   o  n0 is the total number of IP-Layer header and payload bits that
      can be transmitted in standard-formed packets from the Src host
      and correctly received by the Dst host during one contiguous sub-
      interval, dt in length, during the interval [T, T+I],

   o  Maximum_C(T,I,PM) the Maximum IP-Layer Capacity, corresponds to
      the maximum value of n0 measured in any sub-interval beginning at
      dtn, divided by the constant length of all sub-intervals, dt.

   o  PM represents the other performance metrics (see Section 5.4) and
      their measurement results for the Maximum IP-Layer Capacity.  At
      least one target performance threshold (PM criterion) MUST be
      defined.




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   o  all sub-intervals MUST be of equal duration.  Choosing dt as non-
      overlapping consecutive time intervals allows for a simple
      implementation.

   o  The bit rate of the physical interface of the measurement systems
      MUST be higher than than the smallest of the links on the path
      whose Maximum_C(T,I,PM) is to be measured (the bottleneck link).

   In this definition, the m sub-intervals can be viewed as trials when
   the Src host varies the transmitted packet rate, searching for the
   maximum n0 that meets the PM criteria measured at the Dst host in a
   test of duration, I.  When the transmitted packet rate is held
   constant at the Src host, the m sub-intervals may also be viewed as
   trials to evaluate the stability of n0 and metric(s) in the PM list
   over all dt-length intervals in I.

   Measurements according to these definitions SHALL use the UDP
   transport layer.

6.4.  Related Round-Trip Delay and One-way Loss Definitions

   RTD[dtn,dtn+1] and OWL[dtn,dtn+1] are defined in Section 5.4.  Here,
   the test intervals are increased to match the capacity Samples,
   RTD[T,I] and OWL[T,I].

   The interval dtn,dtn+1 where Maximum_C[T,I,PM] occurs is the
   reporting sub-interval within RTD[T,I] and OWL[T,I].

   Other metrics MAY be measured: one-way reordering, duplication, and
   delay variation.

6.5.  Discussion

   If traffic conditioning (e.g., shaping, policing) applies along a
   path for which Maximum_C(T,I,PM) is to be determined, different
   values for dt SHOULD be picked and measurements be executed during
   multiple intervals [T, T+I].  Each duration dt SHOULD be chosen so
   that it is an integer multiple of increasing values k times
   serialization delay of a path MTU at the physical interface speed
   where traffic conditioning is expected.  This should avoid taking
   configured burst tolerance singletons as a valid Maximum_C(T,I,PM)
   result.

   A Maximum_C(T,I,PM) without any indication of bottleneck congestion,
   be that an increasing latency, packet loss or ECN marks during a
   measurement interval I, is likely to underestimate Maximum_C(T,I,PM).





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6.6.  Reporting the Metric

   The IP-Layer Capacity SHOULD be reported with at least single Megabit
   resolution, in units of Megabits per second (Mbps) (which is
   1,000,000 bits per second to avoid any confusion).

   The related One-way Loss metric and Round Trip Delay measurements for
   the same Singleton SHALL be reported, also with meaningful resolution
   for the values measured.

   When there are demonstrated and repeatable Capacity modes in the
   Sample, then the Maximum IP-Layer Capacity SHALL be reported for each
   mode, along with the relative time from the beginning of the stream
   that the mode was observed to be present.  Bimodal Maximum IP-Layer
   Capacities have been observed with some services, sometimes called a
   "turbo mode" intending to deliver short transfers more quickly, or
   reduce the initial buffering time for some video streams.  Note that
   modes lasting less than dt duration will not be detected.

   Some transmission technologies have multiple methods of operation
   that may be activated when channel conditions degrade or improve, and
   these transmission methods may determine the Maximum IP-Layer
   Capacity.  Examples include line-of-sight microwave modulator
   constellations, or cellular modem technologies where the changes may
   be initiated by a user moving from one coverage area to another.
   Operation in the different transmission methods may be observed over
   time, but the modes of Maximum IP-Layer Capacity will not be
   activated deterministically as with the "turbo mode" described in the
   paragraph above.

7.  IP-Layer Sender Bit Rate Singleton Metric Definitions

   This section sets requirements for the following components to
   support the IP-Layer Sender Bitrate Metric.  This metric helps to
   check that the sender actually generated the desired rates during a
   test, and measurement takes place at the Src host to network path
   interface (or as close as practical within the Src host).  It is not
   a metric for path performance.

7.1.  Formal Name

   Type-P-IP-Sender-Bit-Rate, or informally called IP-Layer Sender
   Bitrate.

   Note that Type-P depends on the chosen method.






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7.2.  Parameters

   This section lists the REQUIRED input factors to specify the metric,
   beyond those listed in Section 4.

   o  S, the duration of the measurement interval at the Source

   o  st, the nominal duration of N sub-intervals in S (default st =
      0.05 seconds)

   o  stn, the beginning boundary of a specific sub-interval, n, one of
      N sub-intervals in S

   S SHALL be longer than I, primarily to account for on-demand
   activation of the path, or any preamble to testing required, and the
   delay of the path.

   st SHOULD be much smaller than the sub-interval dt and on the same
   order as FT, otherwise the rate measurement will include many rate
   adjustments and include more time smoothing, thus missing the Maximum
   IP-Layer Capacity.  The st parameter does not have relevance when the
   Source is transmitting at a fixed rate throughout S.

7.3.  Metric Definition

   This section defines the REQUIRED aspects of the IP-Layer Sender
   Bitrate metric (unless otherwise indicated) for measurements at the
   specified Source on packets addressed for the intended Destination
   host and matching the required Type-P:

   Define the IP-Layer Sender Bit Rate, B(S,st), to be the number of IP-
   Layer bits (including header and data fields) that are transmitted
   from the Source with address pair Src and Dst during one contiguous
   sub-interval, st, during the test interval S (where S SHALL be longer
   than I), and where the fixed-size packet count during that single
   sub-interval st also provides the number of IP-Layer bits in any
   interval, [stn,stn+1].

   Measurements according to these definitions SHALL use the UDP
   transport layer.  Any feedback from Dst host to Src host received by
   Src host during an interval [stn,stn+1] SHOULD NOT result in an
   adaptation of the Src host traffic conditioning during this interval
   (rate adjustment occurs on st interval boundaries).








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7.4.  Discussion

   Both the Sender and Receiver or (Source and Destination) bit rates
   SHOULD be assessed as part of an IP-Layer Capacity measurement.
   Otherwise, an unexpected sending rate limitation could produce an
   erroneous Maximum IP-Layer Capacity measurement.

7.5.  Reporting the Metric

   The IP-Layer Sender Bit Rate SHALL be reported with meaningful
   resolution, in units of Megabits per second (which is 1,000,000 bits
   per second to avoid any confusion).

   Individual IP-Layer Sender Bit Rate measurements are discussed
   further in Section 9.

8.  Method of Measurement

   The architecture of the method REQUIRES two cooperating hosts
   operating in the roles of Src (test packet sender) and Dst
   (receiver), with a measured path and return path between them.

   The duration of a test, parameter I, MUST be constrained in a
   production network, since this is an active test method and it will
   likely cause congestion on the Src to Dst host path during a test.

8.1.  Load Rate Adjustment Algorithm

   The algorithm described in this section MUST NOT be used as a general
   Congestion Control Algorithm (CCA).  As stated in the Scope
   Section 2, the load rate adjustment algorithm's goal is to help
   determine the Maximum IP-Layer Capacity in the context of an
   infrequent, diagnostic, short term measurement.  There is a tradeoff
   between test duration (also the test data volume) and algorithm
   agressiveness (speed of ramp-up and down to the Maximum IP-Layer
   Capacity).  The parameter values chosen below strike a well-tested
   balance among these factors.

   A table SHALL be pre-built defining all the offered load rates that
   will be supported (R1 through Rn, in ascending order, corresponding
   to indexed rows in the table).  It is RECOMMENDED that rates begin
   with 0.5 Mbps at index zero, use 1 Mbps at index one, and then
   continue in 1 Mbps increments to 1 Gbps.  Above 1 Gbps, and up to 10
   Gbps, it is RECOMMENDED that 100 Mbps increments be used.  Above 10
   Gbps, increments of 1 Gbps are RECOMMENDED.  A higher initial IP-
   Layer Sender Bitrate might be configured when the test operator is
   certain that the Maximum IP-Layer Capacity is well-above the initial




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   IP-Layer Sender Bitrate and factors such as test duration and total
   test traffic play an important role.

   Each rate is defined as datagrams of size ss, sent as a burst of
   count cc, each time interval tt (default for tt is 1ms, a likely
   system tick-interval).  While it is advantageous to use datagrams of
   as large a size as possible, it may be prudent to use a slightly
   smaller maximum that allows for secondary protocol headers and/or
   tunneling without resulting in IP-Layer fragmentation.  Selection of
   a new rate is indicated by a calculation on the current row, Rx.  For
   example:

   "Rx+1": the sender uses the next higher rate in the table.

   "Rx-10": the sender uses the rate 10 rows lower in the table.

   At the beginning of a test, the sender begins sending at rate R1 and
   the receiver starts a feedback timer of duration FT (while awaiting
   inbound datagrams).  As datagrams are received they are checked for
   sequence number anomalies (loss, out-of-order, duplication, etc.) and
   the delay range is measured (one-way or round-trip).  This
   information is accumulated until the feedback timer FT expires and a
   status feedback message is sent from the receiver back to the sender,
   to communicate this information.  The accumulated statistics are then
   reset by the receiver for the next feedback interval.  As feedback
   messages are received back at the sender, they are evaluated to
   determine how to adjust the current offered load rate (Rx).

   If the feedback indicates that no sequence number anomalies were
   detected AND the delay range was below the lower threshold, the
   offered load rate is increased.  If congestion has not been confirmed
   up to this point, the offered load rate is increased by more than one
   rate (e.g., Rx+10).  This allows the offered load to quickly reach a
   near-maximum rate.  Conversely, if congestion has been previously
   confirmed, the offered load rate is only increased by one (Rx+1).
   However, if a rate threshold between high and very high sending rates
   (such as 1 Gbps) is exceeded, the offered load rate is only increased
   by one (Rx+1) above the rate threshold in any congestion state.

   If the feedback indicates that sequence number anomalies were
   detected OR the delay range was above the upper threshold, the
   offered load rate is decreased.  The RECOMMENDED values are 0 for
   sequence number gaps and 30 ms for lower and 90 ms for upper delay
   thresholds, respectively.  Also, if congestion is now confirmed for
   the first time by the current feedback message being processed, then
   the offered load rate is decreased by more than one rate (e.g., Rx-
   30).  This one-time reduction is intended to compensate for the fast




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   initial ramp-up.  In all other cases, the offered load rate is only
   decreased by one (Rx-1).

   If the feedback indicates that there were no sequence number
   anomalies AND the delay range was above the lower threshold, but
   below the upper threshold, the offered load rate is not changed.
   This allows time for recent changes in the offered load rate to
   stabilize, and the feedback to represent current conditions more
   accurately.

   Lastly, the method for inferring congestion is that there were
   sequence number anomalies AND/OR the delay range was above the upper
   threshold for two consecutive feedback intervals.  The algorithm
   described above is also illustrated in ITU-T Rec. Y.1540, 2020
   version[Y.1540], in Annex B, and implemented in the Appendix on Load
   Rate Adjustment Pseudo Code in this memo.

   The load rate adjustment algorithm MUST include timers that stop the
   test when received packet streams cease unexpectedly.  The timeout
   thresholds are provided in the table below, along with values for all
   other parameters and variables described in this section.  Operation
   of non-obvious parameters appear below:

   load packet timeout  Operation: The load packet timeout SHALL be
      reset to the configured value each time a load packet received.
      If the timeout expires, the receiver SHALL be closed and no
      further feedback sent.

   feedback message timeout  Operation: The feedback message timeout
      SHALL be reset to the configured value each time a feedback
      message is received.  If the timeout expires, the sender SHALL be
      closed and no further load packets sent.

   +-------------+-------------+---------------+-----------------------+
   | Parameter   | Default     | Tested Range  | Expected Safe Range   |
   |             |             | or values     | (not entirely tested, |
   |             |             |               | other values NOT      |
   |             |             |               | RECOMMENDED)          |
   +-------------+-------------+---------------+-----------------------+
   | FT,         | 50ms        | 20ms, 50ms,   | 20ms <= FT <= 250ms   |
   | feedback    |             | 100ms         | Larger values may     |
   | time        |             |               | slow the rate         |
   | interval    |             |               | increase and fail to  |
   |             |             |               | find the max          |
   +-------------+-------------+---------------+-----------------------+
   | Feedback    | L*FT, L=20  | L=100 with    | 0.5sec <= L*FT <=     |
   | message     | (1sec with  | FT=50ms       | 30sec Upper limit for |
   | timeout     | FT=50ms)    | (5sec)        | very unreliable test  |



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   | (stop test) |             |               | paths only            |
   +-------------+-------------+---------------+-----------------------+
   | load packet | 1sec        | 5sec          | 0.250sec - 30sec      |
   | timeout     |             |               | Upper limit for very  |
   | (stop test) |             |               | unreliable test paths |
   |             |             |               | only                  |
   +-------------+-------------+---------------+-----------------------+
   | table index | 0.5Mbps     | 0.5Mbps       | when testing <=10Gbps |
   | 0           |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | table index | 1Mbps       | 1Mbps         | when testing <=10Gbps |
   | 1           |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | table index | 1Mbps       | 1Mbps<=rate<= | same as tested        |
   | (step) size |             | 1Gbps         |                       |
   +-------------+-------------+---------------+-----------------------+
   | table index | 100Mbps     | 1Gbps<=rate<= | same as tested        |
   | (step)      |             | 10Gbps        |                       |
   | size,       |             |               |                       |
   | rate>1Gbps  |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | table index | 1Gbps       | untested      | >10Gbps               |
   | (step)      |             |               |                       |
   | size,       |             |               |                       |
   | rate>10Gbps |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | ss, UDP     | none        | <=1222        | Recommend max at      |
   | payload     |             |               | largest value that    |
   | size, bytes |             |               | avoids fragmentation; |
   |             |             |               | use of too-small      |
   |             |             |               | payload size might    |
   |             |             |               | result in unexpected  |
   |             |             |               | sender limitations.   |
   +-------------+-------------+---------------+-----------------------+
   | cc, burst   | none        | 1<=cc<= 100   | same as tested. Vary  |
   | count       |             |               | cc as needed to       |
   |             |             |               | create the desired    |
   |             |             |               | maximum sending rate. |
   |             |             |               | Sender buffer size    |
   |             |             |               | may limit cc in       |
   |             |             |               | implementation.       |
   +-------------+-------------+---------------+-----------------------+
   | tt, burst   | 100microsec | 100microsec,  | available range of    |
   | interval    |             | 1msec         | "tick" values (HZ     |
   |             |             |               | param)                |
   +-------------+-------------+---------------+-----------------------+
   | low delay   | 30ms        | 5ms, 30ms     | same as tested        |
   | range       |             |               |                       |



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   | threshold   |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | high delay  | 90ms        | 10ms, 90ms    | same as tested        |
   | range       |             |               |                       |
   | threshold   |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | sequence    | 0           | 0, 100        | same as tested        |
   | error       |             |               |                       |
   | threshold   |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | consecutive | 2           | 2             | Use values >1 to      |
   | errored     |             |               | avoid misinterpreting |
   | status      |             |               | transient loss        |
   | report      |             |               |                       |
   | threshold   |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | Fast mode   | 10          | 10            | 2 <= steps <= 30      |
   | increase,   |             |               |                       |
   | in table    |             |               |                       |
   | index steps |             |               |                       |
   +-------------+-------------+---------------+-----------------------+
   | Fast mode   | 3 * Fast    | 3 * Fast mode | same as tested        |
   | decrease,   | mode        | increase      |                       |
   | in table    | increase    |               |                       |
   | index steps |             |               |                       |
   +-------------+-------------+---------------+-----------------------+

               Parameters for Load Rate Adjustment Algorithm

   As a consequence of default parameterization, the Number of table
   steps in total for rates <10Gbps is 2000 (excluding index 0).

   A related sender backoff response to network conditions occurs when
   one or more status feedback messages fail to arrive at the sender.

   If no status feedback messages arrive at the sender for the interval
   greater than the Lost Status Backoff timeout:

              UDRT + (2+w)*FT = Lost Status Backoff timeout

      where:
      UDRT = upper delay range threshold (default 90ms)
      FT   = feedback time interval (default 50ms)
      w    = number of repeated timeouts (w=0 initially, w++ on each
             timeout, and reset to 0 when a message is received)

   beginning when the last message (of any type) was successfully
   received at the sender:



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   Then the offered load SHALL be decreased, following the same process
   as when the feedback indicates presence of one or more sequence
   number anomalies OR the delay range was above the upper threshold (as
   described above), with the same load rate adjustment algorithm
   variables in their current state.  This means that rate reduction and
   congestion confirmation can result from a three-way OR that includes
   lost status feedback messages, sequence errors, or delay variation.

   The RECOMMENDED initial value for w is 0, taking Round Trip Time
   (RTT) less than FT into account.  A test with RTT longer than FT is a
   valid reason to increase the initial value of w appropriately.
   Variable w SHALL be incremented by 1 whenever the Lost Status Backoff
   timeout is exceeded.  So with FT = 50ms and UDRT = 90ms, a status
   feedback message loss would be declared at 190ms following a
   successful message, again at 50ms after that (240ms total), and so
   on.

   Also, if congestion is now confirmed for the first time by a Lost
   Status Backoff timeout, then the offered load rate is decreased by
   more than one rate (e.g., Rx-30).  This one-time reduction is
   intended to compensate for the fast initial ramp-up.  In all other
   cases, the offered load rate is only decreased by one (Rx-1).

   Appendix B discusses compliance with the applicable mandatory
   requirements of [RFC8085], consistent with the goals of the IP-Layer
   Capacity Metric and Method, including the load rate adjustment
   algorithm described in this section.

8.2.  Measurement Qualification or Verification

   It is of course necessary to calibrate the equipment performing the
   IP-Layer Capacity measurement, to ensure that the expected capacity
   can be measured accurately, and that equipment choices (processing
   speed, interface bandwidth, etc.) are suitably matched to the
   measurement range.

   When assessing a Maximum rate as the metric specifies, artificially
   high (optimistic) values might be measured until some buffer on the
   path is filled.  Other causes include bursts of back-to-back packets
   with idle intervals delivered by a path, while the measurement
   interval (dt) is small and aligned with the bursts.  The artificial
   values might result in an un-sustainable Maximum Capacity observed
   when the method of measurement is searching for the Maximum, and that
   would not do.  This situation is different from the bi-modal service
   rates (discussed under Reporting), which are characterized by a
   multi-second duration (much longer than the measured RTT) and
   repeatable behavior.




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   There are many ways that the Method of Measurement could handle this
   false-max issue.  The default value for measurement of singletons (dt
   = 1 second) has proven to a be of practical value during tests of
   this method, allows the bimodal service rates to be characterized,
   and it has an obvious alignment with the reporting units (Mbps).

   Another approach comes from Section 24 of RFC 2544[RFC2544] and its
   discussion of Trial duration, where relatively short trials conducted
   as part of the search are followed by longer trials to make the final
   determination.  In the production network, measurements of Singletons
   and Samples (the terms for trials and tests of Lab Benchmarking) must
   be limited in duration because they may be service-affecting.  But
   there is sufficient value in repeating a Sample with a fixed sending
   rate determined by the previous search for the Maximum IP-Layer
   Capacity, to qualify the result in terms of the other performance
   metrics measured at the same time.

   A qualification measurement for the search result is a subsequent
   measurement, sending at a fixed 99.x % of the Maximum IP-Layer
   Capacity for I, or an indefinite period.  The same Maximum Capacity
   Metric is applied, and the Qualification for the result is a Sample
   without packet loss or a growing minimum delay trend in subsequent
   singletons (or each dt of the measurement interval, I).  Samples
   exhibiting losses or increasing queue occupation require a repeated
   search and/or test at reduced fixed sender rate for qualification.

   Here, as with any Active Capacity test, the test duration must be
   kept short. 10 second tests for each direction of transmission are
   common today.  The default measurement interval specified here is I =
   10 seconds.  The combination of a fast and congestion-aware search
   method and user-network coordination make a unique contribution to
   production testing.  The Maximum IP Capacity metric and method for
   assessing performance is very different from classic [RFC2544]
   Throughput metric and methods : it uses near-real-time load
   adjustments that are sensitive to loss and delay, similar to other
   congestion control algorithms used on the Internet every day, along
   with limited duration.  On the other hand, [RFC2544] Throughput
   measurements can produce sustained overload conditions for extended
   periods of time.  Individual trials in a test governed by a binary
   search can last 60 seconds for each step, and the final confirmation
   trial may be even longer.  This is very different from "normal"
   traffic levels, but overload conditions are not a concern in the
   isolated test environment.  The concerns raised in [RFC6815] were
   that [RFC2544] methods would be let loose on production networks, and
   instead the authors challenged the standards community to develop
   metrics and methods like those described in this memo.





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8.3.  Measurement Considerations

   In general, the wide-spread measurements that this memo encourages
   will encounter wide-spread behaviors.  The bimodal IP Capacity
   behaviors already discussed in Section 6.6 are good examples.

   In general, it is RECOMMENDED to locate test endpoints as close to
   the intended measured link(s) as practical (this is not always
   possible for reasons of scale; there is a limit on number of test
   endpoints coming from many perspectives, management and measurement
   traffic for example).  The testing operator MUST set a value for the
   MaxHops parameter, based on the expected path length.  This parameter
   can keep measurement traffic from straying too far beyond the
   intended path.

   The path measured may be state-full based on many factors, and the
   Parameter "Time of day" when a test starts may not be enough
   information.  Repeatable testing may require the time from the
   beginning of a measured flow, and how the flow is constructed
   including how much traffic has already been sent on that flow when a
   state-change is observed, because the state-change may be based on
   time or bytes sent or both.  Both load packets and status feedback
   messages MUST contain sequence numbers, which helps with measurements
   based on those packets.

   Many different traffic shapers and on-demand access technologies may
   be encountered, as anticipated in [RFC7312], and play a key role in
   measurement results.  Methods MUST be prepared to provide a short
   preamble transmission to activate on-demand access, and to discard
   the preamble from subsequent test results.

   Conditions which might be encountered during measurement, where
   packet losses may occur independently from the measurement sending
   rate:

   1.  Congestion of an interconnection or backbone interface may appear
       as packet losses distributed over time in the test stream, due to
       much higher rate interfaces in the backbone.

   2.  Packet loss due to use of Random Early Detection (RED) or other
       active queue management may or may not affect the measurement
       flow if competing background traffic (other flows) are
       simultaneously present.

   3.  There may be only small delay variation independent of sending
       rate under these conditions, too.





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   4.  Persistent competing traffic on measurement paths that include
       shared transmission media may cause random packet losses in the
       test stream.

   It is possible to mitigate these conditions using the flexibility of
   the load-rate adjusting algorithm described in Section 8.1 above
   (tuning specific parameters).

   If the measurement flow burst duration happens to be on the order of
   or smaller than the burst size of a shaper or a policer in the path,
   then the line rate might be measured rather than the bandwidth limit
   imposed by the shaper or policer.  If this condition is suspected,
   alternate configurations SHOULD be used.

   In general, results depend on the sending stream characteristics; the
   measurement community has known this for a long time, and needs to
   keep it front of mind.  Although the default is a single flow (F=1)
   for testing, use of multiple flows may be advantageous for the
   following reasons:

   1.  the test hosts may be able to create higher load than with a
       single flow, or parallel test hosts may be used to generate 1
       flow each.

   2.  there may be link aggregation present (flow-based load balancing)
       and multiple flows are needed to occupy each member of the
       aggregate.

   3.  access policies may limit the IP-Layer Capacity depending on the
       Type-P of packets, possibly reserving capacity for various stream
       types.

   Each flow would be controlled using its own implementation of the
   load rate adjustment (search) algorithm.

   As testing continues, implementers should expect some evolution in
   the methods.  The ITU-T has published a Supplement (60) to the
   Y-series of Recommendations, "Interpreting ITU-T Y.1540 Maximum IP-
   Layer Capacity measurements", [Y.Sup60], which is the result of
   continued testing with the metric, and those results have improved
   the method described here.

8.4.  Running Code

   This section is for the benefit of the Document Shepherd's form, and
   will be deleted prior to final review.





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   Much of the development of the method and comparisons with existing
   methods conducted at IETF Hackathons and elsewhere have been based on
   the example udpst Linux measurement tool (which is a working
   reference for further development) [udpst].  The current project:

   o  is a utility that can function as a client or server daemon

   o  requires a successful client-initiated setup handshake between
      cooperating hosts and allows firewalls to control inbound
      unsolicited UDP which either go to a control port [expected and w/
      authentication] or to ephemeral ports that are only created as
      needed.  Firewalls protecting each host can both continue to do
      their job normally.  This aspect is similar to many other test
      utilities available.

   o  is written in C, and built with gcc (release 9.3) and its standard
      run-time libraries

   o  allows configuration of most of the parameters described in
      Sections 4 and 7.

   o  supports IPv4 and IPv6 address families.

   o  supports IP-Layer packet marking.

9.  Reporting Formats

   The singleton IP-Layer Capacity results SHOULD be accompanied by the
   context under which they were measured.

   o  timestamp (especially the time when the maximum was observed in
      dtn)

   o  Source and Destination (by IP or other meaningful ID)

   o  other inner parameters of the test case (Section 4)

   o  outer parameters, such as "test conducted in motion" or other
      factors belonging to the context of the measurement

   o  result validity (indicating cases where the process was somehow
      interrupted or the attempt failed)

   o  a field where unusual circumstances could be documented, and
      another one for "ignore/mask out" purposes in further processing

   The Maximum IP-Layer Capacity results SHOULD be reported in the
   format of a table with a row for each of the test Phases and Number



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   of Flows.  There SHOULD be columns for the phases with number of
   flows, and for the resultant Maximum IP-Layer Capacity results for
   the aggregate and each flow tested.

   As mentioned in Section 6.6, bi-modal (or multi-modal) maxima SHALL
   be reported for each mode separately.

   +-------------+-------------------------+----------+----------------+
   | Phase, #    | Maximum IP-Layer        | Loss     | RTT min, max,  |
   | Flows       | Capacity, Mbps          | Ratio    | msec           |
   +-------------+-------------------------+----------+----------------+
   | Search,1    | 967.31                  | 0.0002   | 30, 58         |
   +-------------+-------------------------+----------+----------------+
   | Verify,1    | 966.00                  | 0.0000   | 30, 38         |
   +-------------+-------------------------+----------+----------------+

                     Maximum IP-layer Capacity Results

   Static and configuration parameters:

   The sub-interval time, dt, MUST accompany a report of Maximum IP-
   Layer Capacity results, and the remaining Parameters from Section 4,
   General Parameters.

   The PM list metrics corresponding to the sub-interval where the
   Maximum Capacity occurred MUST accompany a report of Maximum IP-Layer
   Capacity results, for each test phase.

   The IP-Layer Sender Bit rate results SHOULD be reported in the format
   of a table with a row for each of the test phases, sub-intervals (st)
   and number of flows.  There SHOULD be columns for the phases with
   number of flows, and for the resultant IP-Layer Sender Bit rate
   results for the aggregate and each flow tested.

     +--------------------------+-------------+----------------------+
     | Phase, Flow or Aggregate | st, sec     | Sender Bitrate, Mbps |
     +--------------------------+-------------+----------------------+
     | Search,1                 | 0.00 - 0.05 | 345                  |
     +--------------------------+-------------+----------------------+
     | Search,2                 | 0.00 - 0.05 | 289                  |
     +--------------------------+-------------+----------------------+
     | Search,Agg               | 0.00 - 0.05 | 634                  |
     +--------------------------+-------------+----------------------+

                     IP-layer Sender Bit Rate Results

   Static and configuration parameters:




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   The subinterval time, st, MUST accompany a report of Sender IP-Layer
   Bit Rate results.

   Also, the values of the remaining Parameters from Section 4, General
   Parameters, MUST be reported.

9.1.  Configuration and Reporting Data Formats

   As a part of the multi-Standards Development Organization (SDO)
   harmonization of this metric and method of measurement, one of the
   areas where the Broadband Forum (BBF) contributed its expertise was
   in the definition of an information model and data model for
   configuration and reporting.  These models are consistent with the
   metric parameters and default values specified as lists is this memo.
   [TR-471] provides the Information model that was used to prepare a
   full data model in related BBF work.  The BBF has also carefully
   considered topics within its purview, such as placement of
   measurement systems within the access architecture.  For example,
   timestamp resolution requirements that influence the choice of the
   test protocol are provided in Table 2 of [TR-471].

10.  Security Considerations

   Active metrics and measurements have a long history of security
   considerations.  The security considerations that apply to any active
   measurement of live paths are relevant here.  See [RFC4656] and
   [RFC5357].

   When considering privacy of those involved in measurement or those
   whose traffic is measured, the sensitive information available to
   potential observers is greatly reduced when using active techniques
   which are within this scope of work.  Passive observations of user
   traffic for measurement purposes raise many privacy issues.  We refer
   the reader to the privacy considerations described in the Large Scale
   Measurement of Broadband Performance (LMAP) Framework [RFC7594],
   which covers active and passive techniques.

   There are some new considerations for Capacity measurement as
   described in this memo.

   1.  Cooperating Source and Destination hosts and agreements to test
       the path between the hosts are REQUIRED.  Hosts perform in either
       the Src or Dst roles.

   2.  It is REQUIRED to have a user client-initiated setup handshake
       between cooperating hosts that allows firewalls to control
       inbound unsolicited UDP traffic which either goes to a control
       port [expected and w/authentication] or to ephemeral ports that



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       are only created as needed.  Firewalls protecting each host can
       both continue to do their job normally.

   3.  Client-server authentication and integrity protection for
       feedback messages conveying measurements is RECOMMENDED.

   4.  Hosts MUST limit the number of simultaneous tests to avoid
       resource exhaustion and inaccurate results.

   5.  Senders MUST be rate-limited.  This can be accomplished using a
       pre-built table defining all the offered load rates that will be
       supported (Section 8.1).  The recommended load-control search
       algorithm results in "ramp-up" from the lowest rate in the table.

   6.  Service subscribers with limited data volumes who conduct
       extensive capacity testing might experience the effects of
       Service Provider controls on their service.  Testing with the
       Service Provider's measurement hosts SHOULD be limited in
       frequency and/or overall volume of test traffic (for example, the
       range of I duration values SHOULD be limited).

   The exact specification of these features is left for the future
   protocol development.

11.  IANA Considerations

   This memo makes no requests of IANA.

12.  Acknowledgments

   Thanks to Joachim Fabini, Matt Mathis, J.Ignacio Alvarez-Hamelin,
   Wolfgang Balzer, Frank Brockners, Greg Mirsky, Martin Duke, Murray
   Kucherawy, and Benjamin Kaduk for their extensive comments on the
   memo and related topics.

13.  Appendix A - Load Rate Adjustment Pseudo Code

   The following is a pseudo-code implementation of the algorithm
   described in Section 8.1.












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Rx = 0  # The current sending rate (equivalent to a row of the table)
seqErr = 0  # Measured count of any of Loss or Reordering impairments
delay = 0 # Measured Range of Round Trip Delay, RTD, ms
lowThresh = 30 # Low threshold on the Range of RTD, ms
upperThresh = 90 # Upper threshold on the Range of RTD, ms
hSpeedTresh = 1 Gbps # Threshold for transition between sending rate step
 sizes (such as 1 Mbps and 100 Mbps)
slowAdjCount = 0 # Measured Number of consecutive status reports
 indicating loss and/or delay variation above upperThresh
slowAdjThresh = 2 # Threshold on slowAdjCount used to infer congestion.
 Use values >1 to avoid misinterpreting transient loss
highSpeedDelta = 10 # The number of rows to move in a single adjustment
 when initially increasing offered load (to ramp-up quickly)
maxLoadRates = 2000 # Maximum table index (rows)


if ( seqErr == 0 && delay < lowThresh ) {
        if ( Rx < hSpeedTresh && slowAdjCount < slowAdjThresh ) {
                        Rx += highSpeedDelta;
                        slowAdjCount = 0;
        } else {
                        if ( Rx < maxLoadRates - 1 )
                                        Rx++;
        }
} else if ( seqErr > 0 || delay > upperThresh ) {
        slowAdjCount++;
        if ( Rx < hSpeedTresh && slowAdjCount == slowAdjThresh ) {
                        if ( Rx > highSpeedDelta * 3 )
                                        Rx -= highSpeedDelta * 3;
                        else
                                        Rx = 0;
        } else {
                        if ( Rx > 0 )
                                        Rx--;
        }
}

14.  Appendix B - RFC 8085 UDP Guidelines Check

   The BCP on UDP usage guidelines [RFC8085] focuses primarily on
   congestion control in section 3.1.  The Guidelines appear in
   mandatory (MUST) and recommendation (SHOULD) categories.

14.1.  Assessment of Mandatory Requirements

   The mandatory requirements in Section 3 of [RFC8085] include:





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      Internet paths can have widely varying characteristics, ...
      Consequently, applications that may be used on the Internet MUST
      NOT make assumptions about specific path characteristics.  They
      MUST instead use mechanisms that let them operate safely under
      very different path conditions.  Typically, this requires
      conservatively probing the current conditions of the Internet path
      they communicate over to establish a transmission behavior that it
      can sustain and that is reasonably fair to other traffic sharing
      the path.

   The purpose of the load rate adjustment algorithm in Section 8.1 is
   to probe the network and enable Maximum IP-Layer Capacity
   measurements with as few assumptions about the measured path as
   possible, and within the range application described in Section 2.
   The degree of probing conservatism is in tension with the need to
   minimize both the traffic dedicated to testing (especially with
   Gigabit rate measurements) and the duration of the test (which is one
   contributing factor to the overall algorithm fairness).

   The text of Section 3 of [RFC8085] goes on to recommend alternatives
   to UDP to meet the mandatory requirements, but none are suitable for
   the scope and purpose of the metrics and methods in this memo.  In
   fact, ad hoc TCP-based methods fail to achieve the measurement
   accuracy repeatedly proven in comparison measurements with the
   running code [LS-SG12-A] [LS-SG12-B] [Y.Sup60].  Also, the UDP aspect
   of these methods is present primarily to support modern Internet
   transmission where a transport protocol is required [copycat]; the
   metric is based on the IP-Layer and UDP allows simple correlation to
   the IP-Layer.

   Section 3.1.1 of [RFC8085] discusses protocol timer guidelines:

      Latency samples MUST NOT be derived from ambiguous transactions.
      The canonical example is in a protocol that retransmits data, but
      subsequently cannot determine which copy is being acknowledged.

   Both load packets and status feedback messages MUST contain sequence
   numbers, which helps with measurements based on those packets, and
   there are no retransmissions needed.

      When a latency estimate is used to arm a timer that provides loss
      detection -- with or without retransmission -- expiry of the timer
      MUST be interpreted as an indication of congestion in the network,
      causing the sending rate to be adapted to a safe conservative
      rate...

   The method described in this memo uses timers for sending rate
   backoff when status feedback messages are lost (Lost Status Backoff



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   timeout), and for stopping a test when connectivity is lost for an
   longer interval (Feedback message or load packet timeouts).

   There is no specific benefit foreseen by using Explicit Congestion
   Notification (ECN) in this memo.

   Section 3.2 of [RFC8085] discusses message size guidelines:

      To determine an appropriate UDP payload size, applications MUST
      subtract the size of the IP header (which includes any IPv4
      optional headers or IPv6 extension headers) as well as the length
      of the UDP header (8 bytes) from the PMTU size.

   The method uses a sending rate table with a maximum UDP payload size
   that anticipates significant header overhead and avoids
   fragmentation.

   Section 3.3 of [RFC8085] provides reliability guidelines:

      Applications that do require reliable message delivery MUST
      implement an appropriate mechanism themselves.

   The IP-Layer Capacity Metric and Method do not require reliable
   delivery.

      Applications that require ordered delivery MUST reestablish
      datagram ordering themselves.

   The IP-Layer Capacity Metric and Method does not need to reestablish
   packet order; it is preferred to measure packet reordering if it
   occurs [RFC4737].

14.2.  Assessment of Recommendations

   The load rate adjustment algorithm's goal is to determine the Maximum
   IP-Layer Capacity in the context of an infrequent, diagnostic, short
   term measurement.  This goal is a global exception to many [RFC8085]
   SHOULD-level requirements, of which many are intended for long-lived
   flows that must coexist with other traffic in more-or-less fair way.
   However, the algorithm (as specified in Section 8.1 and Appendix A
   above) reacts to indications of congestion in clearly defined ways.

   A specific recommendation is provided as an example.  Section 3.1.5
   of [RFC8085] on implications of RTT and Loss Measurements on
   Congestion Control says:

      A congestion control designed for UDP SHOULD respond as quickly as
      possible when it experiences congestion, and it SHOULD take into



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      account both the loss rate and the response time when choosing a
      new rate.

   The load rate adjustment algorithm responds to loss and RTT
   measurements with a clear and concise rate reduction when warrented,
   and the response makes use of direct measurements (more exact than
   can be inferred from TCP ACKs).

   Section 3.1.5 of [RFC8085] goes on to specify:

      The implemented congestion control scheme SHOULD result in
      bandwidth (capacity) use that is comparable to that of TCP within
      an order of magnitude, so that it does not starve other flows
      sharing a common bottleneck.

   This is a requirement for coexistent streams, and not for diagnostic
   and infrequent measurements using short durations.  The rate
   oscillations during short tests allow other packets to pass, and
   don't starve other flows.

   Ironically, ad hoc TCP-based measurements of "Internet Speed" are
   also designed to work around this SHOULD-level requirement, by
   launching many flows (9, for example) to increase the outstanding
   data dedicated to testing.

   The load rate adjustment algorithm cannot become a TCP-like
   congestion control, or it will have the same weaknesses of TCP when
   trying to make a Maximum IP-Layer Capacity measurement, and will not
   achieve the goal.  The results of the referenced testing [LS-SG12-A]
   [LS-SG12-B] [Y.Sup60] supported this statement hundreds of times,
   with comparisons to multi-connection TCP-based measurements.

   A brief review of some of the other SHOULD-level requirements follows
   (Yes or Not applicable = NA) :

+--+---------------------------------------------------------+---------+
|Y?| RFC 8085 Recommendation                                 | Section |
+--+---------------------------------------------------------+---------+
Yes| MUST tolerate a wide range of Internet path conditions  | 3       |
NA | SHOULD use a full-featured transport (e.g., TCP)        |         |
   |                                                         |         |
Yes| SHOULD control rate of transmission                     | 3.1     |
NA | SHOULD perform congestion control over all traffic      |         |
   |                                                         |         |
   | for bulk transfers,                                     | 3.1.2   |
NA | SHOULD consider implementing TFRC                       |         |
NA | else, SHOULD in other ways use bandwidth similar to TCP |         |
   |                                                         |         |



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   | for non-bulk transfers,                                 | 3.1.3   |
NA | SHOULD measure RTT and transmit max. 1 datagram/RTT     | 3.1.1   |
NA | else, SHOULD send at most 1 datagram every 3 seconds    |         |
NA | SHOULD back-off retransmission timers following loss    |         |
   |                                                         |         |
Yes| SHOULD provide mechanisms to regulate the bursts of     | 3.1.6   |
   | transmission                                            |         |
   |                                                         |         |
NA | MAY implement ECN; a specific set of application        | 3.1.7   |
   | mechanisms are REQUIRED if ECN is used.                 |         |
   |                                                         |         |
Yes| for DiffServ, SHOULD NOT rely on implementation of PHBs | 3.1.8   |
   |                                                         |         |
Yes| for QoS-enabled paths, MAY choose not to use CC         | 3.1.9   |
   |                                                         |         |
Yes| SHOULD NOT rely solely on QoS for their capacity        | 3.1.10  |
   | non-CC controlled flows SHOULD implement a transport    |         |
   | circuit breaker                                         |         |
   | MAY implement a circuit breaker for other applications  |         |
   |                                                         |         |
   | for tunnels carrying IP traffic,                        | 3.1.11  |
NA | SHOULD NOT perform congestion control                   |         |
NA | MUST correctly process the IP ECN field                 |         |
   |                                                         |         |
   | for non-IP tunnels or rate not determined by traffic,   |         |
NA | SHOULD perform CC or use circuit breaker                | 3.1.11  |
NA | SHOULD restrict types of traffic transported by the     |         |
   | tunnel                                                  |         |
   |                                                         |         |
Yes| SHOULD NOT send datagrams that exceed the PMTU, i.e.,   | 3.2     |
Yes| SHOULD discover PMTU or send datagrams < minimum PMTU;  |         |
NA | Specific application mechanisms are REQUIRED if PLPMTUD |         |
   | is used.                                                |         |
   |                                                         |         |
Yes| SHOULD handle datagram loss, duplication, reordering    | 3.3     |
NA | SHOULD be robust to delivery delays up to 2 minutes     |         |
   |                                                         |         |
Yes| SHOULD enable IPv4 UDP checksum                         | 3.4     |
Yes| SHOULD enable IPv6 UDP checksum; Specific application   | 3.4.1   |
   | mechanisms are REQUIRED if a zero IPv6 UDP checksum is  |         |
   | used.                                                   |         |
   |                                                         |         |
NA | SHOULD provide protection from off-path attacks         | 5.1     |
   | else, MAY use UDP-Lite with suitable checksum coverage  | 3.4.2   |
   |                                                         |         |
NA | SHOULD NOT always send middlebox keep-alive messages    | 3.5     |
NA | MAY use keep-alives when needed (min. interval 15 sec)  |         |
   |                                                         |         |



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Yes| Applications specified for use in limited use (or       | 3.6     |
   | controlled environments) SHOULD identify equivalent     |         |
   | mechanisms and describe their use case.                 |         |
   |                                                         |         |
NA | Bulk-multicast apps SHOULD implement congestion control | 4.1.1   |
   |                                                         |         |
NA | Low volume multicast apps SHOULD implement congestion   | 4.1.2   |
   | control                                                 |         |
   |                                                         |         |
NA | Multicast apps SHOULD use a safe PMTU                   | 4.2     |
   |                                                         |         |
Yes| SHOULD avoid using multiple ports                       | 5.1.2   |
Yes| MUST check received IP source address                   |         |
   |                                                         |         |
NA | SHOULD validate payload in ICMP messages                | 5.2     |
   |                                                         |         |
Yes| SHOULD use a randomized source port or equivalent       | 6       |
   | technique, and, for client/server applications, SHOULD  |         |
   | send responses from source address matching request     |         |
   | 5.1                                                     |         |
NA | SHOULD use standard IETF security protocols when needed | 6       |
   +---------------------------------------------------------+---------+

15.  References

15.1.  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>.

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              DOI 10.17487/RFC2330, May 1998,
              <https://www.rfc-editor.org/info/rfc2330>.

   [RFC2681]  Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
              Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
              September 1999, <https://www.rfc-editor.org/info/rfc2681>.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
              <https://www.rfc-editor.org/info/rfc4656>.






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   [RFC4737]  Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
              S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
              DOI 10.17487/RFC4737, November 2006,
              <https://www.rfc-editor.org/info/rfc4737>.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, DOI 10.17487/RFC5357, October 2008,
              <https://www.rfc-editor.org/info/rfc5357>.

   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
              <https://www.rfc-editor.org/info/rfc6438>.

   [RFC7497]  Morton, A., "Rate Measurement Test Protocol Problem
              Statement and Requirements", RFC 7497,
              DOI 10.17487/RFC7497, April 2015,
              <https://www.rfc-editor.org/info/rfc7497>.

   [RFC7680]  Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
              Ed., "A One-Way Loss Metric for IP Performance Metrics
              (IPPM)", STD 82, RFC 7680, DOI 10.17487/RFC7680, January
              2016, <https://www.rfc-editor.org/info/rfc7680>.

   [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>.

   [RFC8468]  Morton, A., Fabini, J., Elkins, N., Ackermann, M., and V.
              Hegde, "IPv4, IPv6, and IPv4-IPv6 Coexistence: Updates for
              the IP Performance Metrics (IPPM) Framework", RFC 8468,
              DOI 10.17487/RFC8468, November 2018,
              <https://www.rfc-editor.org/info/rfc8468>.

15.2.  Informative References

   [copycat]  Edleine, K., Kuhlewind, K., Trammell, B., and B. Donnet,
              "copycat: Testing Differential Treatment of New Transport
              Protocols in the Wild (ANRW '17)", July 2017,
              <https://irtf.org/anrw/2017/anrw17-final5.pdf>.

   [LS-SG12-A]
              12, I. S., "LS - Harmonization of IP Capacity and Latency
              Parameters: Revision of Draft Rec. Y.1540 on IP packet
              transfer performance parameters and New Annex A with Lab
              Evaluation Plan", May 2019,
              <https://datatracker.ietf.org/liaison/1632/>.



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   [LS-SG12-B]
              12, I. S., "LS on harmonization of IP Capacity and Latency
              Parameters: Consent of Draft Rec. Y.1540 on IP packet
              transfer performance parameters and New Annex A with Lab &
              Field Evaluation Plans", March 2019,
              <https://datatracker.ietf.org/liaison/1645/>.

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,
              <https://www.rfc-editor.org/info/rfc2544>.

   [RFC3148]  Mathis, M. and M. Allman, "A Framework for Defining
              Empirical Bulk Transfer Capacity Metrics", RFC 3148,
              DOI 10.17487/RFC3148, July 2001,
              <https://www.rfc-editor.org/info/rfc3148>.

   [RFC5136]  Chimento, P. and J. Ishac, "Defining Network Capacity",
              RFC 5136, DOI 10.17487/RFC5136, February 2008,
              <https://www.rfc-editor.org/info/rfc5136>.

   [RFC6815]  Bradner, S., Dubray, K., McQuaid, J., and A. Morton,
              "Applicability Statement for RFC 2544: Use on Production
              Networks Considered Harmful", RFC 6815,
              DOI 10.17487/RFC6815, November 2012,
              <https://www.rfc-editor.org/info/rfc6815>.

   [RFC7312]  Fabini, J. and A. Morton, "Advanced Stream and Sampling
              Framework for IP Performance Metrics (IPPM)", RFC 7312,
              DOI 10.17487/RFC7312, August 2014,
              <https://www.rfc-editor.org/info/rfc7312>.

   [RFC7594]  Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
              Aitken, P., and A. Akhter, "A Framework for Large-Scale
              Measurement of Broadband Performance (LMAP)", RFC 7594,
              DOI 10.17487/RFC7594, September 2015,
              <https://www.rfc-editor.org/info/rfc7594>.

   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC8085]  Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
              March 2017, <https://www.rfc-editor.org/info/rfc8085>.






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   [RFC8337]  Mathis, M. and A. Morton, "Model-Based Metrics for Bulk
              Transport Capacity", RFC 8337, DOI 10.17487/RFC8337, March
              2018, <https://www.rfc-editor.org/info/rfc8337>.

   [TR-471]   Morton, A., "Broadband Forum TR-471: IP Layer Capacity
              Metrics and Measurement", July 2020,
              <https://www.broadband-forum.org/technical/download/TR-
              471.pdf>.

   [udpst]    udpst Project Collaborators, "UDP Speed Test Open
              Broadband project", December 2020,
              <https://github.com/BroadbandForum/obudpst>.

   [Y.1540]   Y.1540, I. R., "Internet protocol data communication
              service - IP packet transfer and availability performance
              parameters", December 2019,
              <https://www.itu.int/rec/T-REC-Y.1540-201912-I/en>.

   [Y.Sup60]  Morton, A., "Recommendation Y.Sup60, (09/20) Interpreting
              ITU-T Y.1540 maximum IP-layer capacity measurements, and
              Errata", September 2020,
              <https://www.itu.int/rec/T-REC-Y.Sup60/en>.

Authors' Addresses

   Al Morton
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748
   USA

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acm@research.att.com


   Ruediger Geib
   Deutsche Telekom
   Heinrich Hertz Str. 3-7
   Darmstadt  64295
   Germany

   Phone: +49 6151 5812747
   Email: Ruediger.Geib@telekom.de







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   Len Ciavattone
   AT&T Labs
   200 Laurel Avenue South
   Middletown,, NJ  07748
   USA

   Email: lencia@att.com












































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