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RFC 6808 - Test Plan and Results Supporting Advancement of RFC 2


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Internet Engineering Task Force (IETF)                     L. Ciavattone
Request for Comments: 6808                                     AT&T Labs
Category: Informational                                          R. Geib
ISSN: 2070-1721                                         Deutsche Telekom
                                                               A. Morton
                                                               AT&T Labs
                                                               M. Wieser
                                          Technical University Darmstadt
                                                           December 2012

            Test Plan and Results Supporting Advancement of
                    RFC 2679 on the Standards Track

Abstract

   This memo provides the supporting test plan and results to advance
   RFC 2679 on one-way delay metrics along the Standards Track,
   following the process in RFC 6576.  Observing that the metric
   definitions themselves should be the primary focus rather than the
   implementations of metrics, this memo describes the test procedures
   to evaluate specific metric requirement clauses to determine if the
   requirement has been interpreted and implemented as intended.  Two
   completely independent implementations have been tested against the
   key specifications of RFC 2679.  This memo also provides direct input
   for development of a revision of RFC 2679.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6808.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
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   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

Table of Contents

   1. Introduction ....................................................3
      1.1. Requirements Language ......................................5
   2. A Definition-Centric Metric Advancement Process .................5
   3. Test Configuration ..............................................5
   4. Error Calibration, RFC 2679 .....................................9
      4.1. NetProbe Error and Type-P .................................10
      4.2. Perfas+ Error and Type-P ..................................12
   5. Predetermined Limits on Equivalence ............................12
   6. Tests to Evaluate RFC 2679 Specifications ......................13
      6.1. One-Way Delay, ADK Sample Comparison: Same- and Cross-
           Implementation ............................................13
           6.1.1. NetProbe Same-Implementation Results ...............15
           6.1.2. Perfas+ Same-Implementation Results ................16
           6.1.3. One-Way Delay, Cross-Implementation ADK
                  Comparison .........................................16
           6.1.4. Conclusions on the ADK Results for One-Way Delay ...17
           6.1.5. Additional Investigations ..........................17
      6.2. One-Way Delay, Loss Threshold, RFC 2679 ...................20
           6.2.1. NetProbe Results for Loss Threshold ................21
           6.2.2. Perfas+ Results for Loss Threshold .................21
           6.2.3. Conclusions for Loss Threshold .....................21
      6.3. One-Way Delay, First Bit to Last Bit, RFC 2679 ............21
           6.3.1. NetProbe and Perfas+ Results for Serialization .....22
           6.3.2. Conclusions for Serialization ......................23
      6.4. One-Way Delay, Difference Sample Metric ...................24
           6.4.1. NetProbe Results for Differential Delay ............24
           6.4.2. Perfas+ Results for Differential Delay .............25
           6.4.3. Conclusions for Differential Delay .................25
      6.5. Implementation of Statistics for One-Way Delay ............25
   7. Conclusions and RFC 2679 Errata ................................26
   8. Security Considerations ........................................26
   9. Acknowledgements ...............................................27
   10. References ....................................................27
      10.1. Normative References .....................................27
      10.2. Informative References ...................................28

1.  Introduction

   The IETF IP Performance Metrics (IPPM) working group has considered
   how to advance their metrics along the Standards Track since 2001,
   with the initial publication of Bradner/Paxson/Mankin's memo
   [METRICS-TEST].  The original proposal was to compare the performance
   of metric implementations.  This was similar to the usual procedures
   for advancing protocols, which did not directly apply.  It was found
   to be difficult to achieve consensus on exactly how to compare
   implementations, since there were many legitimate sources of

   variation that would emerge in the results despite the best attempts
   to keep the network paths equal, and because considerable variation
   was allowed in the parameters (and therefore implementation) of each
   metric.  Flexibility in metric definitions, essential for
   customization and broad appeal, made the comparison task quite
   difficult.

   A renewed work effort investigated ways in which the measurement
   variability could be reduced and thereby simplify the problem of
   comparison for equivalence.

   The consensus process documented in [RFC6576] is that metric
   definitions rather than the implementations of metrics should be the
   primary focus of evaluation.  Equivalent test results are deemed to
   be evidence that the metric specifications are clear and unambiguous.
   This is now the metric specification equivalent of protocol
   interoperability.  The [RFC6576] advancement process either produces
   confidence that the metric definitions and supporting material are
   clearly worded and unambiguous, or it identifies ways in which the
   metric definitions should be revised to achieve clarity.

   The metric RFC advancement process requires documentation of the
   testing and results.  [RFC6576] retains the testing requirement of
   the original Standards Track advancement process described in
   [RFC2026] and [RFC5657], because widespread deployment is
   insufficient to determine whether RFCs that define performance
   metrics result in consistent implementations.

   The process also permits identification of options that were not
   implemented, so that they can be removed from the advancing
   specification (this is a similar aspect to protocol advancement along
   the Standards Track).  All errata must also be considered.

   This memo's purpose is to implement the advancement process of
   [RFC6576] for [RFC2679].  It supplies the documentation that
   accompanies the protocol action request submitted to the Area
   Director, including description of the test setup, results for each
   implementation, evaluation of each metric specification, and
   conclusions.

   In particular, this memo documents the consensus on the extent of
   tolerable errors when assessing equivalence in the results.  The IPPM
   working group agreed that the test plan and procedures should include
   the threshold for determining equivalence, and that this aspect
   should be decided in advance of cross-implementation comparisons.
   This memo includes procedures for same-implementation comparisons
   that may influence the equivalence threshold.

   Although the conclusion reached through testing is that [RFC2679]
   should be advanced on the Standards Track with modifications, the
   revised text of RFC 2679 is not yet ready for review.  Therefore,
   this memo documents the information to support [RFC2679] advancement,
   and the approval of a revision of RFC 2769 is left for future action.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  A Definition-Centric Metric Advancement Process

   As a first principle, the process described in Section 3.5 of
   [RFC6576] takes the fact that the metric definitions (embodied in the
   text of the RFCs) are the objects that require evaluation and
   possible revision in order to advance to the next step on the
   Standards Track.  This memo follows that process.

3.  Test Configuration

   One metric implementation used was NetProbe version 5.8.5 (an earlier
   version is used in AT&T's IP network performance measurement system
   and deployed worldwide [WIPM]).  NetProbe uses UDP packets of
   variable size, and it can produce test streams with Periodic
   [RFC3432] or Poisson [RFC2330] sample distributions.

   The other metric implementation used was Perfas+ version 3.1,
   developed by Deutsche Telekom [Perfas].  Perfas+ uses UDP unicast
   packets of variable size (but also supports TCP and multicast).  Test
   streams with Periodic, Poisson, or uniform sample distributions may
   be used.

   Figure 1 shows a view of the test path as each implementation's test
   flows pass through the Internet and the Layer 2 Tunneling Protocol,
   version 3 (L2TPv3) tunnel IDs (1 and 2), based on Figures 2 and 3 of
   [RFC6576].

           +----+  +----+                                +----+  +----+
           |Imp1|  |Imp1|           ,---.                |Imp2|  |Imp2|
           +----+  +----+          /     \    +-------+  +----+  +----+
             | V100 | V200        /       \   | Tunnel|   | V300  | V400
             |      |            (         )  | Head  |   |       |
            +--------+  +------+ |         |__| Router|  +----------+
            |Ethernet|  |Tunnel| |Internet |  +---B---+  |Ethernet  |
            |Switch  |--|Head  |-|         |      |      |Switch    |
            +-+--+---+  |Router| |         |  +---+---+--+--+--+----+
              |__|      +--A---+ (         )  |Network|     |__|
                                  \       /   |Emulat.|
            U-turn                 \     /    |"netem"|     U-turn
            V300 to V400            `-+-'     +-------+     V100 to V200

           Implementations                  ,---.       +--------+
                               +~~~~~~~~~~~/     \~~~~~~| Remote |
            +------->-----F2->-|          /       \     |->---.  |
            | +---------+      | Tunnel  (         )    |     |  |
            | | transmit|-F1->-|   ID 1  (         )    |->.  |  |
            | | Imp 1   |      +~~~~~~~~~|         |~~~~|  |  |  |
            | | receive |-<--+           (         )    | F1  F2 |
            | +---------+    |           |Internet |    |  |  |  |
            *-------<-----+  F1          |         |    |  |  |  |
              +---------+ |  | +~~~~~~~~~|         |~~~~|  |  |  |
              | transmit|-*  *-|         |         |    |<-*  |  |
              | Imp 2   |      | Tunnel  (         )    |     |  |
              | receive |-<-F2-|   ID 2   \       /     |<----*  |
              +---------+      +~~~~~~~~~~~\     /~~~~~~| Switch |
                                            `-+-'       +--------+

   Illustrations of a test setup with a bidirectional tunnel.  The upper
   diagram emphasizes the VLAN connectivity and geographical location.
   The lower diagram shows example flows traveling between two
   measurement implementations (for simplicity, only two flows are
   shown).

                                 Figure 1

   The testing employs the Layer 2 Tunneling Protocol, version 3
   (L2TPv3) [RFC3931] tunnel between test sites on the Internet.  The
   tunnel IP and L2TPv3 headers are intended to conceal the test
   equipment addresses and ports from hash functions that would tend to
   spread different test streams across parallel network resources, with
   likely variation in performance as a result.

   At each end of the tunnel, one pair of VLANs encapsulated in the
   tunnel are looped back so that test traffic is returned to each test
   site.  Thus, test streams traverse the L2TP tunnel twice, but appear
   to be one-way tests from the test equipment point of view.

   The network emulator is a host running Fedora 14 Linux [Fedora14]
   with IP forwarding enabled and the "netem" Network emulator [netem]
   loaded and operating as part of the Fedora Kernel 2.6.35.11.
   Connectivity across the netem/Fedora host was accomplished by
   bridging Ethernet VLAN interfaces together with "brctl" commands
   (e.g., eth1.100 <-> eth2.100).  The netem emulator was activated on
   one interface (eth1) and only operates on test streams traveling in
   one direction.  In some tests, independent netem instances operated
   separately on each VLAN.

   The links between the netem emulator host and router and switch were
   found to be 100baseTx-HD (100 Mbps half duplex) when the testing was
   complete.  Use of half duplex was not intended, but probably added a
   small amount of delay variation that could have been avoided in full
   duplex mode.

   Each individual test was run with common packet rates (1 pps, 10 pps)
   Poisson/Periodic distributions, and IP packet sizes of 64, 340, and
   500 Bytes.  These sizes cover a reasonable range while avoiding
   fragmentation and the complexities it causes, thus complying with the
   notion of "standard formed packets" described in Section 15 of
   [RFC2330].

   For these tests, a stream of at least 300 packets were sent from
   Source to Destination in each implementation.  Periodic streams (as
   per [RFC3432]) with 1 second spacing were used, except as noted.

   With the L2TPv3 tunnel in use, the metric name for the testing
   configured here (with respect to the IP header exposed to Internet
   processing) is:

   Type-IP-protocol-115-One-way-Delay-<StreamType>-Stream

   With (Section 4.2 of [RFC2679]) Metric Parameters:

   + Src, the IP address of a host (12.3.167.16 or 193.159.144.8)

   + Dst, the IP address of a host (193.159.144.8 or 12.3.167.16)

   + T0, a time

   + Tf, a time

   + lambda, a rate in reciprocal seconds

   + Thresh, a maximum waiting time in seconds (see Section 3.8.2 of
   [RFC2679] and Section 4.3 of [RFC2679])

   Metric Units: A sequence of pairs; the elements of each pair are:

   + T, a time, and

   + dT, either a real number or an undefined number of seconds.

   The values of T in the sequence are monotonic increasing.  Note that
   T would be a valid parameter to Type-P-One-way-Delay and that dT
   would be a valid value of Type-P-One-way-Delay.

   Also, Section 3.8.4 of [RFC2679] recommends that the path SHOULD be
   reported.  In this test setup, most of the path details will be
   concealed from the implementations by the L2TPv3 tunnels; thus, a
   more informative path trace route can be conducted by the routers at
   each location.

   When NetProbe is used in production, a traceroute is conducted in
   parallel with, and at the outset of, measurements.

   Perfas+ does not support traceroute.

 IPLGW#traceroute 193.159.144.8

 Type escape sequence to abort.
 Tracing the route to 193.159.144.8

   1 12.126.218.245 [AS 7018] 0 msec 0 msec 4 msec
   2 cr84.n54ny.ip.att.net (12.123.2.158) [AS 7018] 4 msec 4 msec
     cr83.n54ny.ip.att.net (12.123.2.26) [AS 7018] 4 msec
   3 cr1.n54ny.ip.att.net (12.122.105.49) [AS 7018] 4 msec
     cr2.n54ny.ip.att.net (12.122.115.93) [AS 7018] 0 msec
     cr1.n54ny.ip.att.net (12.122.105.49) [AS 7018] 0 msec
   4 n54ny02jt.ip.att.net (12.122.80.225) [AS 7018] 4 msec 0 msec
     n54ny02jt.ip.att.net (12.122.80.237) [AS 7018] 4 msec
   5 192.205.34.182 [AS 7018] 0 msec
     192.205.34.150 [AS 7018] 0 msec
     192.205.34.182 [AS 7018] 4 msec
   6 da-rg12-i.DA.DE.NET.DTAG.DE (62.154.1.30) [AS 3320] 88 msec 88 msec
 88 msec
   7 217.89.29.62 [AS 3320] 88 msec 88 msec 88 msec
   8 217.89.29.55 [AS 3320] 88 msec 88 msec 88 msec
   9  *  *  *

   It was only possible to conduct the traceroute for the measured path
   on one of the tunnel-head routers (the normal trace facilities of the
   measurement systems are confounded by the L2TPv3 tunnel
   encapsulation).

4.  Error Calibration, RFC 2679

   An implementation is required to report on its error calibration in
   Section 3.8 of [RFC2679] (also required in Section 4.8 for sample
   metrics).  Sections 3.6, 3.7, and 3.8 of [RFC2679] give the detailed
   formulation of the errors and uncertainties for calibration.  In
   summary, Section 3.7.1 of [RFC2679] describes the total time-varying
   uncertainty as:

   Esynch(t)+ Rsource + Rdest

   where:

   Esynch(t) denotes an upper bound on the magnitude of clock
   synchronization uncertainty.

   Rsource and Rdest denote the resolution of the source clock and the
   destination clock, respectively.

   Further, Section 3.7.2 of [RFC2679] describes the total wire-time
   uncertainty as:

   Hsource + Hdest

   referring to the upper bounds on host-time to wire-time for source
   and destination, respectively.

   Section 3.7.3 of [RFC2679] describes a test with small packets over
   an isolated minimal network where the results can be used to estimate
   systematic and random components of the sum of the above errors or
   uncertainties.  In a test with hundreds of singletons, the median is
   the systematic error and when the median is subtracted from all
   singletons, the remaining variability is the random error.

   The test context, or Type-P of the test packets, must also be
   reported, as required in Section 3.8 of [RFC2679] and all metrics
   defined there.  Type-P is defined in Section 13 of [RFC2330] (as are
   many terms used below).

4.1.  NetProbe Error and Type-P

   Type-P for this test was IP-UDP with Best Effort Differentiated
   Services Code Point (DSCP).  These headers were encapsulated
   according to the L2TPv3 specifications [RFC3931]; thus, they may not
   influence the treatment received as the packets traversed the
   Internet.

   In general, NetProbe error is dependent on the specific version and
   installation details.

   NetProbe operates using host-time above the UDP layer, which is
   different from the wire-time preferred in [RFC2330], but it can be
   identified as a source of error according to Section 3.7.2 of
   [RFC2679].

   Accuracy of NetProbe measurements is usually limited by NTP
   synchronization performance (which is typically taken as ~+/-1 ms
   error or greater), although the installation used in this testing
   often exhibits errors much less than typical for NTP.  The primary
   stratum 1 NTP server is closely located on a sparsely utilized
   network management LAN; thus, it avoids many concerns raised in
   Section 10 of [RFC2330] (in fact, smooth adjustment, long-term drift
   analysis and compensation, and infrequent adjustment all lead to
   stability during measurement intervals, the main concern).

   The resolution of the reported results is 1 us (us = microsecond) in
   the version of NetProbe tested here, which contributes to at least
   +/-1 us error.

   NetProbe implements a timekeeping sanity check on sending and
   receiving time-stamping processes.  When a significant process
   interruption takes place, individual test packets are flagged as
   possibly containing unusual time errors, and they are excluded from
   the sample used for all "time" metrics.

   We performed a NetProbe calibration of the type described in Section
   3.7.3 of [RFC2679], using 64-Byte packets over a cross-connect cable.
   The results estimate systematic and random components of the sum of
   the Hsource + Hdest errors or uncertainties.  In a test with 300
   singletons conducted over 30 seconds (periodic sample with 100 ms
   spacing), the median is the systematic error and the remaining
   variability is the random error.  One set of results is tabulated
   below:

   (Results from the "R" software environment for statistical computing
   and graphics - http://www.r-project.org/ )
   > summary(XD4CAL)
         CAL1            CAL2             CAL3
    Min.   : 89.0   Min.   : 68.00   Min.   : 54.00
    1st Qu.: 99.0   1st Qu.: 77.00   1st Qu.: 63.00
    Median :110.0   Median : 79.00   Median : 65.00
    Mean   :116.8   Mean   : 83.74   Mean   : 69.65
    3rd Qu.:127.0   3rd Qu.: 88.00   3rd Qu.: 74.00
    Max.   :205.0   Max.   :177.00   Max.   :163.00
   >
   NetProbe Calibration with Cross-Connect Cable, one-way delay values
   in microseconds (us)

   The median or systematic error can be as high as 110 us, and the
   range of the random error is also on the order of 116 us for all
   streams.

   Also, anticipating the Anderson-Darling K-sample (ADK) [ADK]
   comparisons to follow, we corrected the CAL2 values for the
   difference between the means of CAL2 and CAL3 (as permitted in
   Section 3.2 of [RFC6576]), and found strong support (for the Null
   Hypothesis) that the samples are from the same distribution
   (resolution of 1 us and alpha equal 0.05 and 0.01)

   > XD4CVCAL2 <- XD4CAL$CAL2 - (mean(XD4CAL$CAL2)-mean(XD4CAL$CAL3))
   > boxplot(XD4CVCAL2,XD4CAL$CAL3)
   > XD4CV2_ADK <- adk.test(XD4CVCAL2, XD4CAL$CAL3)
   > XD4CV2_ADK
   Anderson-Darling k-sample test.

   Number of samples:  2
   Sample sizes: 300 300
   Total number of values: 600
   Number of unique values: 97

   Mean of Anderson Darling Criterion: 1
   Standard deviation of Anderson Darling Criterion: 0.75896

   T = (Anderson-Darling Criterion - mean)/sigma

   Null Hypothesis: All samples come from a common population.

                        t.obs P-value extrapolation
   not adj. for ties  0.71734 0.17042             0
   adj. for ties     -0.39553 0.44589             1
   >
   using [Rtool] and [Radk].

4.2.  Perfas+ Error and Type-P

   Perfas+ is configured to use GPS synchronization and uses NTP
   synchronization as a fall-back or default.  GPS synchronization
   worked throughout this test with the exception of the calibration
   stated here (one implementation was NTP synchronized only).  The time
   stamp accuracy typically is 0.1 ms.

   The resolution of the results reported by Perfas+ is 1 us (us =
   microsecond) in the version tested here, which contributes to at
   least +/-1 us error.

   Port    5001 5002 5003
   Min.    -227 -226  294
   Median  -169 -167  323
   Mean    -159 -157  335
   Max.       6  -52  376
   s        102  102   93
   Perfas+ Calibration with Cross-Connect Cable, one-way delay values in
   microseconds (us)

   The median or systematic error can be as high as 323 us, and the
   range of the random error is also less than 232 us for all streams.

5.  Predetermined Limits on Equivalence

   This section provides the numerical limits on comparisons between
   implementations, in order to declare that the results are equivalent
   and therefore, the tested specification is clear.  These limits have
   their basis in Section 3.1 of [RFC6576] and the Appendix of
   [RFC2330], with additional limits representing IP Performance Metrics
   (IPPM) consensus prior to publication of results.

   A key point is that the allowable errors, corrections, and confidence
   levels only need to be sufficient to detect misinterpretation of the
   tested specification resulting in diverging implementations.

   Also, the allowable error must be sufficient to compensate for
   measured path differences.  It was simply not possible to measure
   fully identical paths in the VLAN-loopback test configuration used,
   and this practical compromise must be taken into account.

   For Anderson-Darling K-sample (ADK) comparisons, the required
   confidence factor for the cross-implementation comparisons SHALL be
   the smallest of:

   o  0.95 confidence factor at 1 ms resolution, or

   o  the smallest confidence factor (in combination with resolution) of
      the two same-implementation comparisons for the same test
      conditions.

   A constant time accuracy error of as much as +/-0.5 ms MAY be removed
   from one implementation's distributions (all singletons) before the
   ADK comparison is conducted.

   A constant propagation delay error (due to use of different sub-nets
   between the switch and measurement devices at each location) of as
   much as +2 ms MAY be removed from one implementation's distributions
   (all singletons) before the ADK comparison is conducted.

   For comparisons involving the mean of a sample or other central
   statistics, the limits on both the time accuracy error and the
   propagation delay error constants given above also apply.

6.  Tests to Evaluate RFC 2679 Specifications

   This section describes some results from real-world (cross-Internet)
   tests with measurement devices implementing IPPM metrics and a
   network emulator to create relevant conditions, to determine whether
   the metric definitions were interpreted consistently by implementors.

   The procedures are slightly modified from the original procedures
   contained in Appendix A.1 of [RFC6576].  The modifications include
   the use of the mean statistic for comparisons.

   Note that there are only five instances of the requirement term
   "MUST" in [RFC2679] outside of the boilerplate and [RFC2119]
   reference.

6.1.  One-Way Delay, ADK Sample Comparison: Same- and Cross-
      Implementation

   This test determines if implementations produce results that appear
   to come from a common delay distribution, as an overall evaluation of
   Section 4 of [RFC2679], "A Definition for Samples of One-way Delay".
   Same-implementation comparison results help to set the threshold of
   equivalence that will be applied to cross-implementation comparisons.

   This test is intended to evaluate measurements in Sections 3 and 4 of
   [RFC2679].

   By testing the extent to which the distributions of one-way delay
   singletons from two implementations of [RFC2679] appear to be from
   the same distribution, we economize on comparisons, because comparing
   a set of individual summary statistics (as defined in Section 5 of
   [RFC2679]) would require another set of individual evaluations of
   equivalence.  Instead, we can simply check which statistics were
   implemented, and report on those facts.

   1.  Configure an L2TPv3 path between test sites, and each pair of
       measurement devices to operate tests in their designated pair of
       VLANs.

   2.  Measure a sample of one-way delay singletons with two or more
       implementations, using identical options and network emulator
       settings (if used).

   3.  Measure a sample of one-way delay singletons with *four*
       instances of the *same* implementations, using identical options,
       noting that connectivity differences SHOULD be the same as for
       the cross-implementation testing.

   4.  Apply the ADK comparison procedures (see Appendices A and B of
       [RFC6576]) and determine the resolution and confidence factor for
       distribution equivalence of each same-implementation comparison
       and each cross-implementation comparison.

   5.  Take the coarsest resolution and confidence factor for
       distribution equivalence from the same-implementation pairs, or
       the limit defined in Section 5 above, as a limit on the
       equivalence threshold for these experimental conditions.

   6.  Apply constant correction factors to all singletons of the sample
       distributions, as described and limited in Section 5 above.

   7.  Compare the cross-implementation ADK performance with the
       equivalence threshold determined in step 5 to determine if
       equivalence can be declared.

   The common parameters used for tests in this section are:

   o  IP header + payload = 64 octets

   o  Periodic sampling at 1 packet per second

   o  Test duration = 300 seconds (March 29, 2011)

   The netem emulator was set for 100 ms average delay, with uniform
   delay variation of +/-50 ms.  In this experiment, the netem emulator
   was configured to operate independently on each VLAN; thus, the
   emulator itself is a potential source of error when comparing streams
   that traverse the test path in different directions.

   In the result analysis of this section:

   o  All comparisons used 1 microsecond resolution.

   o  No correction factors were applied.

   o  The 0.95 confidence factor (1.960 for paired stream comparison)
      was used.

6.1.1.  NetProbe Same-Implementation Results

   A single same-implementation comparison fails the ADK criterion (s1
   <-> sB).  We note that these streams traversed the test path in
   opposite directions, making the live network factors a possibility to
   explain the difference.

   All other pair comparisons pass the ADK criterion.

          +------------------------------------------------------+
          |            |             |             |             |
          | ti.obs (P) |     s1      |     s2      |     sA      |
          |            |             |             |             |
          .............|.............|.............|.............|
          |            |             |             |             |
          |    s2      | 0.25 (0.28) |             |             |
          |            |             |             |             |
          ...........................|.............|.............|
          |            |             |             |             |
          |    sA      | 0.60 (0.19) |-0.80 (0.57) |             |
          |            |             |             |             |
          ...........................|.............|.............|
          |            |             |             |             |
          |    sB      | 2.64 (0.03) | 0.07 (0.31) |-0.52 (0.48) |
          |            |             |             |             |
          +------------+-------------+-------------+-------------+

               NetProbe ADK results for same-implementation

6.1.2.  Perfas+ Same-Implementation Results

   All pair comparisons pass the ADK criterion.

          +------------------------------------------------------+
          |            |             |             |             |
          | ti.obs (P) |     p1      |     p2      |     p3      |
          |            |             |             |             |
          .............|.............|.............|.............|
          |            |             |             |             |
          |    p2      | 0.06 (0.32) |             |             |
          |            |             |             |             |
          .........................................|.............|
          |            |             |             |             |
          |    p3      | 1.09 (0.12) | 0.37 (0.24) |             |
          |            |             |             |             |
          ...........................|.............|.............|
          |            |             |             |             |
          |    p4      |-0.81 (0.57) |-0.13 (0.37) | 1.36 (0.09) |
          |            |             |             |             |
          +------------+-------------+-------------+-------------+

                Perfas+ ADK results for same-implementation

6.1.3.  One-Way Delay, Cross-Implementation ADK Comparison

   The cross-implementation results are compared using a combined ADK
   analysis [Radk], where all NetProbe results are compared with all
   Perfas+ results after testing that the combined same-implementation
   results pass the ADK criterion.

   When 4 (same) samples are compared, the ADK criterion for 0.95
   confidence is 1.915, and when all 8 (cross) samples are compared it
   is 1.85.

   Combination of Anderson-Darling K-Sample Tests.

   Sample sizes within each data set:
   Data set 1 :  299 297 298 300 (NetProbe)
   Data set 2 :  300 300 298 300 (Perfas+)
   Total sample size per data set: 1194 1198
   Number of unique values per data set: 1188 1192
   ...
   Null Hypothesis:
   All samples within a data set come from a common distribution.
   The common distribution may change between data sets.

   NetProbe           ti.obs P-value extrapolation
   not adj. for ties 0.64999 0.21355             0
   adj. for ties     0.64833 0.21392             0
   Perfas+
   not adj. for ties 0.55968 0.23442             0
   adj. for ties     0.55840 0.23473             0

   Combined Anderson-Darling Criterion:
                      tc.obs P-value extrapolation
   not adj. for ties 0.85537 0.17967             0
   adj. for ties     0.85329 0.18010             0

   The combined same-implementation samples and the combined cross-
   implementation comparison all pass the ADK criterion at P>=0.18 and
   support the Null Hypothesis (both data sets come from a common
   distribution).

   We also see that the paired ADK comparisons are rather critical.
   Although the NetProbe s1-sB comparison failed, the combined data set
   from four streams passed the ADK criterion easily.

6.1.4.  Conclusions on the ADK Results for One-Way Delay

   Similar testing was repeated many times in the months of March and
   April 2011.  There were many experiments where a single test stream
   from NetProbe or Perfas+ proved to be different from the others in
   paired comparisons (even same-implementation comparisons).  When the
   outlier stream was removed from the comparison, the remaining streams
   passed combined ADK criterion.  Also, the application of correction
   factors resulted in higher comparison success.

   We conclude that the two implementations are capable of producing
   equivalent one-way delay distributions based on their interpretation
   of [RFC2679].

6.1.5.  Additional Investigations

   On the final day of testing, we performed a series of measurements to
   evaluate the amount of emulated delay variation necessary to achieve
   successful ADK comparisons.  The need for correction factors (as
   permitted by Section 5) and the size of the measurement sample
   (obtained as sub-sets of the complete measurement sample) were also
   evaluated.

   The common parameters used for tests in this section are:

   o  IP header + payload = 64 octets

   o  Periodic sampling at 1 packet per second

   o  Test duration = 300 seconds at each delay variation setting, for a
      total of 1200 seconds (May 2, 2011 at 1720 UTC)

   The netem emulator was set for 100 ms average delay, with (emulated)
   uniform delay variation of:

   o  +/-7.5 ms

   o  +/-5.0 ms

   o  +/-2.5 ms

   o  0 ms

   In this experiment, the netem emulator was configured to operate
   independently on each VLAN; thus, the emulator itself is a potential
   source of error when comparing streams that traverse the test path in
   different directions.

   In the result analysis of this section:

   o  All comparisons used 1 microsecond resolution.

   o  Correction factors *were* applied as noted (under column heading
      "mean adj").  The difference between each sample mean and the
      lowest mean of the NetProbe or Perfas+ stream samples was
      subtracted from all values in the sample. ("raw" indicates no
      correction factors were used.)  All correction factors applied met
      the limits described in Section 5.

   o  The 0.95 confidence factor (1.960 for paired stream comparison)
      was used.

   When 8 (cross) samples are compared, the ADK criterion for 0.95
   confidence is 1.85.  The Combined ADK test statistic ("TC observed")
   must be less than 1.85 to accept the Null Hypothesis (all samples in
   the data set are from a common distribution).

   Emulated Delay                        Sub-Sample size
   Variation     0ms
   adk.combined (all)           300 values             75 values
   Adj. for ties           raw         mean adj    raw        mean adj
   TC observed             226.6563    67.51559    54.01359   21.56513
   P-value                         0          0           0          0
   Mean std dev (all),us         719                    635
   Mean diff of means,us         649          0         606          0

   Variation +/- 2.5ms
   adk.combined (all)           300 values             75 values
   Adj. for ties            raw        mean adj     raw       mean adj
   TC observed              14.50436   -1.60196     3.15935   -1.72104
   P-value                         0     0.873      0.00799    0.89038
   Mean std dev (all),us        1655                   1702
   Mean diff of means,us         471          0         513          0

   Variation +/- 5ms
   adk.combined (all)           300 values             75 values
   Adj. for ties            raw        mean adj     raw       mean adj
   TC observed               8.29921   -1.28927     0.37878   -1.81881
   P-value                         0    0.81601     0.29984    0.90305
   Mean std dev (all),us        3023                   2991
   Mean diff of means,us         582          0         513          0

   Variation +/- 7.5ms
   adk.combined (all)           300 values             75 values
   Adj. for ties            raw        mean adj     raw       mean adj
   TC observed              2.53759    -0.72985     0.29241   -1.15840
   P-value                  0.01950     0.66942     0.32585    0.78686
   Mean std dev (all),us        4449                   4506
   Mean diff of means,us         426          0         856          0

   From the table above, we conclude the following:

   1.  None of the raw or mean adjusted results pass the ADK criterion
       with 0 ms emulated delay variation.  Use of the 75 value sub-
       sample yielded the same conclusion.  (We note the same results
       when comparing same-implementation samples for both NetProbe and
       Perfas+.)

   2.  When the smallest emulated delay variation was inserted (+/-2.5
       ms), the mean adjusted samples pass the ADK criterion and the
       high P-value supports the result.  The raw results do not pass.

   3.  At higher values of emulated delay variation (+/-5.0 ms and
       +/-7.5 ms), again the mean adjusted values pass ADK.  We also see
       that the 75-value sub-sample passed the ADK in both raw and mean
       adjusted cases.  This indicates that sample size may have played
       a role in our results, as noted in the Appendix of [RFC2330] for
       Goodness-of-Fit testing.

   We note that 150 value sub-samples were also evaluated, with ADK
   conclusions that followed the results for 300 values.  Also, same-
   implementation analysis was conducted with results similar to the
   above, except that more of the "raw" or uncorrected samples passed
   the ADK criterion.

6.2.  One-Way Delay, Loss Threshold, RFC 2679

   This test determines if implementations use the same configured
   maximum waiting time delay from one measurement to another under
   different delay conditions, and correctly declare packets arriving in
   excess of the waiting time threshold as lost.

   See the requirements of Section 3.5 of [RFC2679], third bullet point,
   and also Section 3.8.2 of [RFC2679].

   1.  configure an L2TPv3 path between test sites, and each pair of
       measurement devices to operate tests in their designated pair of
       VLANs.

   2.  configure the network emulator to add 1.0 sec. one-way constant
       delay in one direction of transmission.

   3.  measure (average) one-way delay with two or more implementations,
       using identical waiting time thresholds (Thresh) for loss set at
       3 seconds.

   4.  configure the network emulator to add 3 sec. one-way constant
       delay in one direction of transmission equivalent to 2 seconds of
       additional one-way delay (or change the path delay while test is
       in progress, when there are sufficient packets at the first delay
       setting).

   5.  repeat/continue measurements.

   6.  observe that the increase measured in step 5 caused all packets
       with 2 sec. additional delay to be declared lost, and that all
       packets that arrive successfully in step 3 are assigned a valid
       one-way delay.

   The common parameters used for tests in this section are:

   o  IP header + payload = 64 octets

   o  Poisson sampling at lambda = 1 packet per second

   o  Test duration = 900 seconds total (March 21, 2011)

   The netem emulator was set to add constant delays as specified in the
   procedure above.

6.2.1.  NetProbe Results for Loss Threshold

   In NetProbe, the Loss Threshold is implemented uniformly over all
   packets as a post-processing routine.  With the Loss Threshold set at
   3 seconds, all packets with one-way delay >3 seconds are marked
   "Lost" and included in the Lost Packet list with their transmission
   time (as required in Section 3.3 of [RFC2680]).  This resulted in 342
   packets designated as lost in one of the test streams (with average
   delay = 3.091 sec.).

6.2.2.  Perfas+ Results for Loss Threshold

   Perfas+ uses a fixed Loss Threshold that was not adjustable during
   this study.  The Loss Threshold is approximately one minute, and
   emulation of a delay of this size was not attempted.  However, it is
   possible to implement any delay threshold desired with a post-
   processing routine and subsequent analysis.  Using this method, 195
   packets would be declared lost (with average delay = 3.091 sec.).

6.2.3.  Conclusions for Loss Threshold

   Both implementations assume that any constant delay value desired can
   be used as the Loss Threshold, since all delays are stored as a pair
   <Time, Delay> as required in [RFC2679].  This is a simple way to
   enforce the constant loss threshold envisioned in [RFC2679] (see
   specific section references above).  We take the position that the
   assumption of post-processing is compliant and that the text of the
   RFC should be revised slightly to include this point.

6.3.  One-Way Delay, First Bit to Last Bit, RFC 2679

   This test determines if implementations register the same relative
   change in delay from one packet size to another, indicating that the
   first-to-last time-stamping convention has been followed.  This test
   tends to cancel the sources of error that may be present in an
   implementation.

   See the requirements of Section 3.7.2 of [RFC2679], and Section 10.2
   of [RFC2330].

   1.  configure an L2TPv3 path between test sites, and each pair of
       measurement devices to operate tests in their designated pair of
       VLANs, and ideally including a low-speed link (it was not
       possible to change the link configuration during testing, so the
       lowest speed link present was the basis for serialization time
       comparisons).

   2.  measure (average) one-way delay with two or more implementations,
       using identical options and equal size small packets (64-octet IP
       header and payload).

   3.  maintain the same path with additional emulated 100 ms one-way
       delay.

   4.  measure (average) one-way delay with two or more implementations,
       using identical options and equal size large packets (500 octet
       IP header and payload).

   5.  observe that the increase measured between steps 2 and 4 is
       equivalent to the increase in ms expected due to the larger
       serialization time for each implementation.  Most of the
       measurement errors in each system should cancel, if they are
       stationary.

   The common parameters used for tests in this section are:

   o  IP header + payload = 64 octets

   o  Periodic sampling at l packet per second

   o  Test duration = 300 seconds total (April 12)

   The netem emulator was set to add constant 100 ms delay.

6.3.1.  NetProbe and Perfas+ Results for Serialization

   When the IP header + payload size was increased from 64 octets to 500
   octets, there was a delay increase observed.

   Mean Delays in us
   NetProbe
   Payload    s1      s2      sA      sB
   500    190893  191179  190892  190971
    64    189642  189785  189747  189467
   Diff     1251    1394    1145    1505

   Perfas
   Payload    p1      p2      p3      p4
   500    190908  190911  191126  190709
    64    189706  189752  189763  190220
   Diff     1202   1159    1363      489

   Serialization tests, all values in microseconds

   The typical delay increase when the larger packets were used was 1.1
   to 1.5 ms (with one outlier).  The typical measurements indicate that
   a link with approximately 3 Mbit/s capacity is present on the path.

   Through investigation of the facilities involved, it was determined
   that the lowest speed link was approximately 45 Mbit/s, and therefore
   the estimated difference should be about 0.077 ms.  The observed
   differences are much higher.

   The unexpected large delay difference was also the outcome when
   testing serialization times in a lab environment, using the NIST Net
   Emulator and NetProbe [ADV-METRICS].

6.3.2.  Conclusions for Serialization

   Since it was not possible to confirm the estimated serialization time
   increases in field tests, we resort to examination of the
   implementations to determine compliance.

   NetProbe performs all time stamping above the IP layer, accepting
   that some compromises must be made to achieve extreme portability and
   measurement scale.  Therefore, the first-to-last bit convention is
   supported because the serialization time is included in the one-way
   delay measurement, enabling comparison with other implementations.

   Perfas+ is optimized for its purpose and performs all time stamping
   close to the interface hardware.  The first-to-last bit convention is
   supported because the serialization time is included in the one-way
   delay measurement, enabling comparison with other implementations.

6.4.  One-Way Delay, Difference Sample Metric

   This test determines if implementations register the same relative
   increase in delay from one measurement to another under different
   delay conditions.  This test tends to cancel the sources of error
   that may be present in an implementation.

   This test is intended to evaluate measurements in Sections 3 and 4 of
   [RFC2679].

   1.  configure an L2TPv3 path between test sites, and each pair of
       measurement devices to operate tests in their designated pair of
       VLANs.

   2.  measure (average) one-way delay with two or more implementations,
       using identical options.

   3.  configure the path with X+Y ms one-way delay.

   4.  repeat measurements.

   5.  observe that the (average) increase measured in steps 2 and 4 is
       ~Y ms for each implementation.  Most of the measurement errors in
       each system should cancel, if they are stationary.

   In this test, X = 1000 ms and Y = 1000 ms.

   The common parameters used for tests in this section are:

   o  IP header + payload = 64 octets

   o  Poisson sampling at lambda = 1 packet per second

   o  Test duration = 900 seconds total (March 21, 2011)

   The netem emulator was set to add constant delays as specified in the
   procedure above.

6.4.1.  NetProbe Results for Differential Delay

         Average pre-increase delay, microseconds        1089868.0
         Average post 1 s additional, microseconds        2089686.0
         Difference (should be ~= Y = 1 s)                 999818.0

               Average delays before/after 1 second increase

   The NetProbe implementation observed a 1 second increase with a 182
   microsecond error (assuming that the netem emulated delay difference
   is exact).

   We note that this differential delay test has been run under lab
   conditions and published in prior work [ADV-METRICS].  The error was
   6 microseconds.

6.4.2.  Perfas+ Results for Differential Delay

         Average pre-increase delay, microseconds        1089794.0
         Average post 1 s additional, microseconds        2089801.0
         Difference (should be ~= Y = 1 s)                1000007.0

               Average delays before/after 1 second increase

   The Perfas+ implementation observed a 1 second increase with a 7
   microsecond error.

6.4.3.  Conclusions for Differential Delay

   Again, the live network conditions appear to have influenced the
   results, but both implementations measured the same delay increase
   within their calibration accuracy.

6.5.  Implementation of Statistics for One-Way Delay

   The ADK tests the extent to which the sample distributions of one-way
   delay singletons from two implementations of [RFC2679] appear to be
   from the same overall distribution.  By testing this way, we
   economize on the number of comparisons, because comparing a set of
   individual summary statistics (as defined in Section 5 of [RFC2679])
   would require another set of individual evaluations of equivalence.
   Instead, we can simply check which statistics were implemented, and
   report on those facts, noting that Section 5 of [RFC2679] does not
   specify the calculations exactly, and gives only some illustrative
   examples.

                                                 NetProbe  Perfas+

   5.1. Type-P-One-way-Delay-Percentile            yes       no

   5.2. Type-P-One-way-Delay-Median                yes       no

   5.3. Type-P-One-way-Delay-Minimum               yes       yes

   5.4. Type-P-One-way-Delay-Inverse-Percentile    no        no

                  Implementation of Section 5 Statistics

   Only the Type-P-One-way-Delay-Inverse-Percentile has been ignored in
   both implementations, so it is a candidate for removal or deprecation
   in a revision of RFC 2679 (this small discrepancy does not affect
   candidacy for advancement).

7.  Conclusions and RFC 2679 Errata

   The conclusions throughout Section 6 support the advancement of
   [RFC2679] to the next step of the Standards Track, because its
   requirements are deemed to be clear and unambiguous based on
   evaluation of the test results for two implementations.  The results
   indicate that these implementations produced statistically equivalent
   results under network conditions that were configured to be as close
   to identical as possible.

   Sections 6.2.3 and 6.5 indicate areas where minor revisions are
   warranted in RFC 2679.  The IETF has reached consensus on guidance
   for reporting metrics in [RFC6703], and this memo should be
   referenced in the revision to RFC 2679 to incorporate recent
   experience where appropriate.

   We note that there is currently one erratum with status "Held for
   Document Update" for [RFC2679], and it appears this minor revision
   and additional text should be incorporated in a revision of RFC 2679.

   The authors that revise [RFC2679] should review all errata filed at
   the time the document is being written.  They should not rely upon
   this document to indicate all relevant errata updates.

8.  Security Considerations

   The security considerations that apply to any active measurement of
   live networks are relevant here as well.  See [RFC4656] and
   [RFC5357].

9.  Acknowledgements

   The authors thank Lars Eggert for his continued encouragement to
   advance the IPPM metrics during his tenure as AD Advisor.

   Nicole Kowalski supplied the needed CPE router for the NetProbe side
   of the test setup, and graciously managed her testing in spite of
   issues caused by dual-use of the router.  Thanks Nicole!

   The "NetProbe Team" also acknowledges many useful discussions with
   Ganga Maguluri.

10.  References

10.1.  Normative References

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2330]  Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
              "Framework for IP Performance Metrics", RFC 2330,
              May 1998.

   [RFC2679]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Delay Metric for IPPM", RFC 2679, September 1999.

   [RFC2680]  Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
              Packet Loss Metric for IPPM", RFC 2680, September 1999.

   [RFC3432]  Raisanen, V., Grotefeld, G., and A. Morton, "Network
              performance measurement with periodic streams", RFC 3432,
              November 2002.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5657]  Dusseault, L. and R. Sparks, "Guidance on Interoperation
              and Implementation Reports for Advancement to Draft
              Standard", BCP 9, RFC 5657, September 2009.

   [RFC6576]  Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP
              Performance Metrics (IPPM) Standard Advancement Testing",
              BCP 176, RFC 6576, March 2012.

   [RFC6703]  Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
              IP Network Performance Metrics: Different Points of View",
              RFC 6703, August 2012.

10.2.  Informative References

   [ADK]      Scholz, F. and M. Stephens, "K-sample Anderson-Darling
              Tests of fit, for continuous and discrete cases",
              University of Washington, Technical Report No. 81,
              May 1986.

   [ADV-METRICS]
              Morton, A., "Lab Test Results for Advancing Metrics on the
              Standards Track", Work in Progress, October 2010.

   [Fedora14] Fedora Project, "Fedora Project Home Page", 2012,
              <http://fedoraproject.org/>.

   [METRICS-TEST]
              Bradner, S. and V. Paxson, "Advancement of metrics
              specifications on the IETF Standards Track", Work
              in Progress, August 2007.

   [Perfas]   Heidemann, C., "Qualitaet in IP-Netzen Messverfahren",
              published by ITG Fachgruppe, 2nd meeting 5.2.3 (NGN),
              November 2001, <http://www.itg523.de/oeffentlich/01nov/
              Heidemann_QOS_Messverfahren.pdf>.

   [RFC3931]  Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
              Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.

   [Radk]     Scholz, F., "adk: Anderson-Darling K-Sample Test and
              Combinations of Such Tests. R package version 1.0.", 2008.

   [Rtool]    R Development Core Team, "R: A language and environment
              for statistical computing. R Foundation for Statistical
              Computing, Vienna, Austria. ISBN 3-900051-07-0", 2011,
              <http://www.R-project.org/>.

   [WIPM]     AT&T, "AT&T Global IP Network", 2012,
              <http://ipnetwork.bgtmo.ip.att.net/pws/index.html>.

   [netem]    The Linux Foundation, "netem", 2009,
              <http://www.linuxfoundation.org/collaborate/workgroups/
              networking/netem>.

Authors' Addresses

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

   Phone: +1 732 420 1239
   EMail: lencia@att.com

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

   Phone: +49 6151 58 12747
   EMail: Ruediger.Geib@telekom.de

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

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   EMail: acmorton@att.com
   URI:   http://home.comcast.net/~acmacm/

   Matthias Wieser
   Technical University Darmstadt
   Darmstadt,
   Germany

   EMail: matthias_michael.wieser@stud.tu-darmstadt.de

 

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