Network Working Group L. Ciavattone
Internet-Draft AT&T Labs
Intended status: Informational R. Geib
Expires: April 23, 2012 Deutsche Telekom
A. Morton
AT&T Labs
M. Wieser
University of Applied Sciences
Darmstadt
October 21, 2011
Test Plan and Results for Advancing RFC 2680 on the Standards Track
draft-morton-ippm-testplan-rfc2680-00
Abstract
This memo proposes to advance a performance metric RFC along the
standards track, specifically RFC 2680 on One-way Loss Metrics.
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 2680.
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].
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 http://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 April 23, 2012.
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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it for publication as an RFC or to translate it into languages other
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. RFC 2680 Coverage . . . . . . . . . . . . . . . . . . . . 4
2. A Definition-centric metric advancement process . . . . . . . 5
3. Test configuration . . . . . . . . . . . . . . . . . . . . . . 5
4. Error Calibration, RFC 2679 . . . . . . . . . . . . . . . . . 9
4.1. Clock Synchronization Calibration . . . . . . . . . . . . 9
4.1.1. NetProbe Clock Error . . . . . . . . . . . . . . . . . 10
4.1.2. Perfas Clock Error . . . . . . . . . . . . . . . . . . 12
4.2. Packet Loss Determination Error . . . . . . . . . . . . . 13
5. Pre-determined Limits on Equivalence . . . . . . . . . . . . . 13
6. Tests to evaluate RFC 2680 Specifications . . . . . . . . . . 14
6.1. One-way Packet Loss, ADK Sample Comparison - Same &
Cross Implementation . . . . . . . . . . . . . . . . . . . 14
6.1.1. NetProbe Same-implementation results . . . . . . . . . 16
6.1.2. Perfas Same-implementation results . . . . . . . . . . 16
6.1.3. One-way Packet Loss, Cross-Implementation ADK
Comparison . . . . . . . . . . . . . . . . . . . . . . 16
6.1.4. Conclusions on the ADK Results for One-way Packet
Loss . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.2. One-way Packet Loss, Loss threshold, RFC 2680 . . . . . . 16
6.2.1. NetProbe results for Loss Threshold . . . . . . . . . 17
6.2.2. Perfas Results for Loss Threshold . . . . . . . . . . 17
6.2.3. Conclusions for Loss Threshold . . . . . . . . . . . . 18
6.3. Implementation of Statistics for One-way Delay . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.1. Normative References . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The IETF (IP Performance Metrics working group, IPPM) has considered
how to advance their metrics along the standards track since 2001.
A renewed work effort sought to investigate ways in which the
measurement variability could be reduced and thereby simplify the
problem of comparison for equivalence.
There is consensus [I-D.ietf-ippm-metrictest] that the metric
definitions should be the primary focus of evaluation rather than the
implementations of metrics, and equivalent results are deemed to be
evidence that the metric specifications are clear and unambiguous.
This is the metric specification equivalent of protocol
interoperability. The advancement process either produces confidence
that the metric definitions and supporting material are clearly
worded and unambiguous, OR, identifies ways in which the metric
definitions should be revised to achieve clarity.
The process should also permit identification of options that were
not implemented, so that they can be removed from the advancing
specification (this is an aspect more typical of protocol advancement
along the standards track).
This memo's purpose is to implement the current approach for
[RFC2680].
In particular, this memo documents consensus on the extent of
tolerable errors when assessing equivalence in the results. In
discussions, the IPPM working group agreed that test plan and
procedures should include the threshold for determining equivalence,
and this information should be available in advance of cross-
implementation comparisons. This memo includes procedures for same-
implementation comparisons to help set the equivalence threshold.
Another aspect of the metric RFC advancement process is the
requirement to document the work and results. The procedures of
[RFC2026] are expanded in[RFC5657], including sample implementation
and interoperability reports. This memo follows the template in
[I-D.morton-ippm-advance-metrics] for the report that accompanies the
protocol action request submitted to the Area Director, including
description of the test set-up, procedures, results for each
implementation and conclusions.
1.1. RFC 2680 Coverage
This plan, in its first draft version, does not cover all critical
requirements and sections of [RFC2680]. Material will be added as it
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is "discovered" (not all requirements use requirements language).
2. A Definition-centric metric advancement process
The process described in Section 3.5 of [I-D.ietf-ippm-metrictest]
takes as a first principle 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.
IF two implementations do not measure an equivalent singleton or
sample, or produce the an equivalent statistic,
AND sources of measurement error do not adequately explain the lack
of agreement,
THEN the details of each implementation should be audited along with
the exact definition text, to determine if there is a lack of clarity
that has caused the implementations to vary in a way that affects the
correspondence of the results.
IF there was a lack of clarity or multiple legitimate interpretations
of the definition text,
THEN the text should be modified and the resulting memo proposed for
consensus and advancement along the standards track.
Finally, all the findings MUST be documented in a report that can
support advancement on the standards track, similar to those
described in [RFC5657]. The list of measurement devices used in
testing satisfies the implementation requirement, while the test
results provide information on the quality of each specification in
the metric RFC (the surrogate for feature interoperability).
3. Test configuration
One metric implementation used was NetProbe version 5.8.5, (an
earlier version is used in the WIPM system and deployed world-wide).
NetProbe uses UDP packets of variable size, and 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+ uses UDP unicast packets of
variable size (but supports also TCP and multicast). Test streams
with periodic, Poisson or uniform sample distributions may be used.
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Figure 1 shows a view of the test path as each Implementation's test
flows pass through the Internet and the L2TPv3 tunnel IDs (1 and 2),
based on Figure 1 of [I-D.ietf-ippm-metrictest].
+----+ +----+ +----+ +----+
|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 bi-directional 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 Tunnel 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
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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
[http://fedoraproject.org/] with IP forwarding enabled and the
"netem" Network emulator as part of the Fedora Kernel 2.6.35.11 [http
://www.linuxfoundation.org/collaborate/workgroups/networking/netem]
loaded and operating. 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 (100Mbps half duplex) as reported by "mii-
tool"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, 10pps)
Poisson/Periodic distributions, and IP packet sizes of 64, 340, and
500 Bytes.
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.
As required in Section 2.8.1 of [RFC2680], packet Type-P must be
reported. The packet Type-P for this test was IP-UDP with Best
Effort DCSP. These headers were encapsulated according to the L2TPv3
specifications [RFC3931], and thus may not influence the treatment
received as the packets traversed the Internet.
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-Packet-Loss-<StreamType>-Stream
With (Section 3.2. [RFC2680]) Metric Parameters:
+ Src, the IP address of a host (12.3.167.16 or 193.159.144.8)
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+ 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 2.8.2 of
[RFC2680]) and (Section 3.8. [RFC2680])
Metric Units: A sequence of pairs; the elements of each pair are:
+ T, a time, and
+ L, either a zero or a one
The values of T in the sequence are monotonic increasing. Note that
T would be a valid parameter to the *singleton* Type-P-One-way-
Packet-Loss, and that L would be a valid value of Type-P-One-way-
Packet Loss (see Section 2 of [RFC2680]).
Also, Section 2.8.4 of [RFC2680] recommends that the path SHOULD be
reported. In this test set-up, 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.
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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 calibration results on clock
synchronization in Section 2.8.3 of [RFC2680] (also required in
Section 3.7 of [RFC2680] for sample metrics).
Also, it is recommended to report the probability that a packet
successfully arriving at the destination network interface is
incorrectly designated as lost due to resource exhaustion in Section
2.8.3 of [RFC2680].
4.1. Clock Synchronization Calibration
First, we look at clock synchronization. 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
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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).
4.1.1. NetProbe Clock Error
In general, NetProbe clock 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 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 ~+/-1ms
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).
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The resolution of the reported results is 1us (us = microsecond) in
the version of NetProbe tested here, which contributes to at least
+/-1us error.
NetProbe implements a time-keeping sanity check on sending and
receiving time-stamping processes. When the significant process
interruption takes place, individual test packets are flagged as
possibly containing unusual time errors, and 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 100ms
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) comparisons to
follow, we corrected the CAL2 values for the difference between means
between CAL2 and CAL3 (as specified in [I-D.ietf-ippm-metrictest]),
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)
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> 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
>
4.1.2. Perfas Clock Error
Perfas+ is configured to use GPS synchronisation and uses NTP
synchronization as a fall-back or default. GPS synchronisation
worked throughout this test with the exception of the calibration
stated here (one implementation was NTP synchronised only). The time
stamp accuracy typically is 0.1 ms.
The resolution of the results reported by Perfas+ is 1us (us =
microsecond) in the version tested here, which contributes to at
least +/-1us 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.
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4.2. Packet Loss Determination Error
Since both measurement implementations have resource limitations, it
is theoretically possible that these limits could be exceeded and a
packet that arrived at the destination successfully might be
discarded in error.
In previous test efforts [I-D.morton-ippm-advance-metrics], NetProbe
produced 6 multicast streams with an aggregate bit rate over 53
Mbit/s, in order to characterize the 1-way capacity of a NISTNet-
based emulator. Neither the emulator nor the pair of NetProbe
implementations used in this testing dropped any packets in these
streams.
The maximum load used here between any 2 NetProbe implementations was
be 11.5 Mbit/s divided equally among 3 unicast test streams. We
conclude that steady resource usage does not contribute error
(additional loss) to the measurements.
5. Pre-determined Limits on Equivalence
In this section, we provide the numerical limits on comparisons
between implementations, in order to declare that the results are
equivalent and therefore, the tested specification is clear.
A key point is that the allowable errors, corrections, and confidence
levels only need to be sufficient to detect mis-interpretation 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 1ms 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 +/-0.5ms MAY be removed
from one implementation's distributions (all singletons) before the
ADK comparison is conducted.
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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 +2ms 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 2680 Specifications
This section describes some results from production network (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 similar contained in Appendix A.1 of
[I-D.ietf-ippm-metrictest] for One-way Delay.
Note that there are only five instances of the requirement term
"MUST" in [RFC2680] outside of the boilerplate and [RFC2119]
reference.
6.1. One-way Packet Loss, ADK Sample Comparison - Same & Cross
Implementation
This test determines if implementations produce results that appear
to come from a common packet loss distribution, as an overall
evaluation of Section 3 of [RFC2680], "A Definition for Samples of
One-way Packet Loss". 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 2 and 3 of
[RFC2680].
By testing the extent to which the distributions of one-way packet
loss ratios 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.
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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 packet loss singletons with 2 or more
implementations, using identical options and network emulator
settings (if used).
3. Measure a sample of one-way packet loss 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 Appendix C of
[I-D.ietf-ippm-metrictest]) 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)
The netem emulator was set for 100ms average delay, with uniform
delay variation of +/-50ms. In this experiment, the netem emulator
was configured to operate independently on each VLAN and 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:
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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
6.1.2. Perfas Same-implementation results
All pair comparisons pass the ADK criterion.
6.1.3. One-way Packet Loss, Cross-Implementation ADK Comparison
The cross-implementation results are compared using a combined ADK
analysis [ref], where all NetProbe results are compared with all
Perfas results after testing that the combined same-implementation
results pass the ADK criterion.
6.1.4. Conclusions on the ADK Results for One-way Packet Loss
Similar testing was repeated many times ...
We conclude that the two implementations are capable of producing
equivalent one-way packet loss distributions based on their
interpretation of [RFC2680] .
6.2. One-way Packet Loss, Loss threshold, RFC 2680
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 Section 2.8.2 of [RFC2680].
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 2 or more implementations,
using identical waiting time thresholds (Thresh) for loss set at
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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)
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 which 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).
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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 [RFC2680]. This is a simple way to
enforce the constant loss threshold envisioned in [RFC2680] (see
specific section reference 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. Implementation of Statistics for One-way Delay
We check which statistics were implemented, and report on those
facts, noting that Section 4 of [RFC2680] does not specify the
calculations exactly, and gives only some illustrative examples.
NetProbe Perfas
4.1. Type-P-One-way-Delay-Packet-Loss-Ave yes yes
(this is more commonly referred to as loss ratio)
Implementation of Section 4 Statistics
7. Security Considerations
The security considerations that apply to any active measurement of
live networks are relevant here as well. See [RFC4656] and
[RFC5357].
8. IANA Considerations
This memo makes no requests of IANA, and the authos hope that IANA
will be able to use their time in other worthwhile pursuits.
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 set-up, 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
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Ganga Maguluri.
10. References
10.1. Normative References
[I-D.ietf-ippm-metrictest]
Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IPPM
standard advancement testing",
draft-ietf-ippm-metrictest-03 (work in progress),
June 2011.
[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.
[RFC4814] Newman, D. and T. Player, "Hash and Stuffing: Overlooked
Factors in Network Device Benchmarking", RFC 4814,
March 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
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[RFC5657] Dusseault, L. and R. Sparks, "Guidance on Interoperation
and Implementation Reports for Advancement to Draft
Standard", BCP 9, RFC 5657, September 2009.
10.2. Informative References
[I-D.morton-ippm-advance-metrics]
Morton, A., "Lab Test Results for Advancing Metrics on the
Standards Track", draft-morton-ippm-advance-metrics-02
(work in progress), October 2010.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
Authors' Addresses
Len Ciavattone
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1239
Fax:
Email: lencia@att.com
URI:
Ruediger Geib
Deutsche Telekom
Heinrich Hertz Str. 3-7
Darmstadt, 64295
Germany
Phone: +49 6151 58 12747
Email: Ruediger.Geib@telekom.de
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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
University of Applied Sciences Darmstadt
Birkenweg 8 Department EIT
Darmstadt, 64295
Germany
Phone:
Email: matthias.wieser@stud.h-da.de
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