Internet Engineering Task Force (IETF) L. Ciavattone
Request for Comments: 7290 AT&T Labs
Category: Informational R. Geib
ISSN: 2070-1721 Deutsche Telekom
A. Morton
AT&T Labs
M. Wieser
Technical University Darmstadt
July 2014
Test Plan and Results for Advancing RFC 2680 on the Standards Track
Abstract
This memo provides the supporting test plan and results to advance
RFC 2680, a performance metric RFC defining one-way packet loss
metrics, along the Standards Track. 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.
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/rfc7290.
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Copyright Notice
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it for publication as an RFC or to translate it into languages other
than English.
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Table of Contents
1. Introduction ....................................................3
1.1. Requirements Language ......................................4
1.2. RFC 2680 Coverage ..........................................5
2. A Definition-Centric Metric Advancement Process .................5
3. Test Configuration ..............................................5
4. Error Calibration and RFC 2680 ..................................9
4.1. Clock Synchronization Calibration ..........................9
4.2. Packet Loss Determination Error ...........................10
5. Predetermined Limits on Equivalence ............................10
6. Tests to Evaluate RFC 2680 Specifications ......................11
6.1. One-Way Loss: ADK Sample Comparison .......................11
6.1.1. 340B/Periodic Cross-Implementation Results .........12
6.1.2. 64B/Periodic Cross-Implementation Results ..........14
6.1.3. 64B/Poisson Cross-Implementation Results ...........15
6.1.4. Conclusions on the ADK Results for One-Way
Packet Loss ........................................16
6.2. One-Way Loss: Delay Threshold .............................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 .....................17
6.3. One-Way Loss with Out-of-Order Arrival ....................17
6.4. Poisson Sending Process Evaluation ........................19
6.4.1. NetProbe Results ...................................19
6.4.2. Perfas+ Results ....................................20
6.4.3. Conclusions for Goodness-of-Fit ....................22
6.5. Implementation of Statistics for One-Way Loss .............23
7. Conclusions for a Revision of RFC 2680 .........................23
8. Security Considerations ........................................24
9. Acknowledgements ...............................................24
10. Appendix - Network Configuration and Sample Commands ..........25
11. References ....................................................28
11.1. Normative References .....................................28
11.2. Informative References ...................................29
1. Introduction
The IETF IP Performance Metrics (IPPM) working group has considered
how to advance their metrics along the Standards Track since 2001.
The renewed work effort sought to investigate ways in which the
measurement variability could be reduced in order to thereby simplify
the problem of comparison for equivalence. As a result, there is
consensus (captured in [RFC6576]) that equivalent results from
independent implementations of metric specifications are sufficient
evidence that the specifications themselves are clear and
unambiguous; it is the parallel concept of protocol interoperability
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for metric specifications. The advancement process either (1)
produces confidence that the metric definitions and supporting
material are clearly worded and unambiguous or (2) identifies ways in
which the metric definitions should be revised to achieve clarity.
It is a non-goal to compare the specific implementations themselves.
The process also permits identification of options described in the
metric RFC 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] and document the results.
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 the 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
[RFC6808] for the report that accompanies the protocol action request
submitted to the Area Director, including a description of the test
setup, procedures, results for each implementation, and conclusions.
The conclusion reached is that [RFC2680], with modifications, should
be advanced on the Standards Track. The revised text of RFC 2680
[LOSS-METRIC] is ready for review but awaits work in progress to
update the IPPM Framework [RFC2330]. Therefore, this memo documents
the information to support the advancement of [RFC2680], and the
approval of a revision of RFC 2680 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].
Some of these key words were used in [RFC2680], but there are no
requirements specified in this memo.
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1.2. RFC 2680 Coverage
This plan is intended to cover all critical requirements and sections
of [RFC2680].
Note that there are only five relevant instances of the requirement
term "MUST" in [RFC2680], outside of the boilerplate and [RFC2119]
reference; the instance of "MUST" in the Security Considerations
section of [RFC2680] is not a basis for implementation equivalence
comparisons.
Statements in RFC 2680 that have the character of requirements may be
included if the community reaches consensus that the wording implies
a requirement. At least one instance of an implied requirement has
been found in Section 3.6 of [RFC2680].
2. A Definition-Centric Metric Advancement Process
The process described in Section 3.5 of [RFC6576] 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. This
memo follows that process.
3. Test Configuration
One metric implementation used was NetProbe version 5.8.5 (an earlier
version is used in the WIPM system and deployed worldwide [WIPM]).
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]. 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.
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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 Layer 2 Tunneling Protocol
version 3 (L2TPv3) [RFC3931] tunnel IDs (1 and 2), based on Figure 1
of [RFC6576].
+------------+ +------------+
| Imp 1 | ,---. | Imp 2 |
+------------+ / \ +-------+ +------------+
| 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 (where "Imp #" is the sender and
receiver of implementation 1 or 2 -- either Perfas+ or
NetProbe in this test). The lower diagram shows example
flows traveling between two measurement implementations.
For simplicity, only two flows are shown, and the netem
emulator is omitted (it would appear before or after the
Internet, depending on the flow).
Figure 1
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The testing employs the 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 point of view of the test equipment.
The network emulator is a host running Fedora 14 Linux [FEDORA], with
IP forwarding enabled and the "netem" Network emulator as part of the
Fedora Kernel 2.6.35.11 [NETEM] loaded and operating. The standard
kernel is "tickless", replacing the previous periodic timer (250 Hz,
with 4 ms uncertainty) interrupts with on-demand interrupts.
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 operated on test streams traveling in
one direction. In some tests, independent netem instances operated
separately on each VLAN. See the Appendix for more details.
The links between the netem emulator host, the router, and the switch
were found to be 100BaseTX-HD (100 Mbps half duplex), as reported by
"mii-tool" [MII-TOOL] when testing was complete. The 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.
For these tests, a stream of at least 300 packets was 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 Differentiated Services Code Point (DSCP). These headers were
encapsulated according to the L2TPv3 specification [RFC3931] and were
unlikely to influence the treatment received as the packets traversed
the Internet.
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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 of [RFC2680]) 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 2.8.2 of
[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 monotonically increasing.
Note that T would be a valid parameter of *singleton*
Type-P-One-way-Packet-Loss and that L would be a valid value of
Type-P-One-way-Packet-Loss (see Section 3.3 of [RFC2680]).
Also, Section 2.8.4 of [RFC2680] 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 traceroute can be conducted by the routers at
each location.
When NetProbe is used in production, a traceroute is conducted in
parallel 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 * * *
NetProbe Traceroute
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 and RFC 2680
An implementation is required to report calibration results on clock
synchronization per 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
For NetProbe and Perfas+ clock synchronization test results, refer to
Section 4 of [RFC6808].
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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 [ADV-METRICS], NetProbe produced six
multicast streams with an aggregate bit rate over 53 Mbit/s, in order
to characterize the one-way capacity of an emulator based on NIST
Net. 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 two NetProbe implementations
was 11.5 Mbit/s divided equally among three unicast test streams. We
concluded that steady resource usage does not contribute error
(additional loss) to the measurements.
5. Predetermined 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 that the tested specification is therefore clear.
A key point is that the allowable errors, corrections, and confidence
levels only need to be sufficient to detect any misinterpretation of
the tested specification that would indicate 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) [ADK] comparisons, the required
confidence factor for the cross-implementation comparisons SHALL be
the smallest of:
o 0.95 confidence factor at 1-packet resolution, or
o the smallest confidence factor (in combination with resolution) of
the two same-implementation comparisons for the same test
conditions (if the number of streams is sufficient to allow such
comparisons).
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For Anderson-Darling Goodness-of-Fit (ADGoF) [RADGOF] comparisons,
the required level of significance for the same-implementation
Goodness-of-Fit (GoF) SHALL be 0.05 or 5%, as specified in
Section 11.4 of [RFC2330]. This is equivalent to a 95% confidence
factor.
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 to those contained in Appendix A.1 of
[RFC6576] for one-way delay.
6.1. One-Way Loss: ADK Sample Comparison
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, 3, and
4 of [RFC2680].
By testing the extent to which the counts of one-way packet loss on
different test streams of two [RFC2680] implementations appear to be
from the same loss process, we reduce comparison steps because
comparing the resulting summary statistics (as defined in Section 4
of [RFC2680]) would require a redundant set of equivalence
evaluations. We can easily check whether the single statistic in
Section 4 of [RFC2680] was implemented and report on that fact.
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 two or
more implementations, using identical options and network
emulator settings (if used).
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3. Measure a sample of one-way packet loss singletons with *four or
more* instances of the *same* implementations, using identical
options, noting that connectivity differences SHOULD be the same
as for cross-implementation testing.
4. If less than ten test streams are available, skip to step 7.
5. Apply the ADK comparison procedures (see Appendix B of
[RFC6576]), and determine the resolution and confidence factor
for distribution equivalence of each same-implementation
comparison and each cross-implementation comparison.
6. 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.
7. Compare the cross-implementation ADK performance with the
equivalence threshold determined in step 5 to determine if
equivalence can be declared.
The metric parameters varied for each loss test, and they are listed
first in each sub-section below.
The cross-implementation comparison uses a simple ADK analysis
[RTOOL] [RADK], where all NetProbe loss counts are compared with all
Perfas+ loss results.
In the results analysis of this section:
o All comparisons used 1-packet resolution.
o No correction factors were applied.
o The 0.95 confidence factor (and ADK criterion for t.obs < 1.960
for cross-implementation comparison) was used.
6.1.1. 340B/Periodic Cross-Implementation Results
Tests described in this section used:
o IP header + payload = 340 octets
o Periodic sampling at 1 packet per second
o Test duration = 1200 seconds (during April 7, 2011, EDT)
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The netem emulator was set for 100 ms constant delay, with a 10% loss
ratio. 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.
=======================================
A07bps_loss <- c(114, 175, 138, 142, 181, 105) (NetProbe)
A07per_loss <- c(115, 128, 136, 127, 139, 138) (Perfas+)
> A07bps_loss <- c(114, 175, 138, 142, 181, 105)
> A07per_loss <- c(115, 128, 136, 127, 139, 138)
>
> A07cross_loss_ADK <- adk.test(A07bps_loss, A07per_loss)
> A07cross_loss_ADK
Anderson-Darling k-sample test.
Number of samples: 2
Sample sizes: 6 6
Total number of values: 12
Number of unique values: 11
Mean of Anderson Darling Criterion: 1
Standard deviation of Anderson Darling Criterion: 0.6569
T = (Anderson Darling Criterion - mean)/sigma
Null Hypothesis: All samples come from a common population.
t.obs P-value extrapolation
not adj. for ties 0.52043 0.20604 0
adj. for ties 0.62679 0.18607 0
>
=======================================
The cross-implementation comparisons pass the ADK criterion
(t.obs < 1.960).
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6.1.2. 64B/Periodic Cross-Implementation Results
Tests described in this section used:
o IP header + payload = 64 octets
o Periodic sampling at 1 packet per second
o Test duration = 300 seconds (during March 24, 2011, EDT)
The netem emulator was set for 0 ms constant delay, with a 10% loss
ratio.
=======================================
> M24per_loss <- c(42,34,35,35) (Perfas+)
> M24apd_23BC_loss <- c(27,39,29,24) (NetProbe)
> M24apd_loss23BC_ADK <- adk.test(M24apd_23BC_loss,M24per_loss)
> M24apd_loss23BC_ADK
Anderson-Darling k-sample test.
Number of samples: 2
Sample sizes: 4 4
Total number of values: 8
Number of unique values: 7
Mean of Anderson Darling Criterion: 1
Standard deviation of Anderson Darling Criterion: 0.60978
T = (Anderson Darling Criterion - mean)/sigma
Null Hypothesis: All samples come from a common population.
t.obs P-value extrapolation
not adj. for ties 0.76921 0.16200 0
adj. for ties 0.90935 0.14113 0
Warning: At least one sample size is less than 5.
p-values may not be very accurate.
>
=======================================
The cross-implementation comparisons pass the ADK criterion.
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6.1.3. 64B/Poisson Cross-Implementation Results
Tests described in this section used:
o IP header + payload = 64 octets
o Poisson sampling at lambda = 1 packet per second
o Test duration = 1200 seconds (during April 27, 2011, EDT)
The netem configuration was 0 ms delay and 10% loss, but there were
two passes through an emulator for each stream, and loss emulation
was present for 18 minutes of the 20-minute (1200-second) test.
=======================================
A27aps_loss <- c(91,110,113,102,111,109,112,113) (NetProbe)
A27per_loss <- c(95,123,126,114) (Perfas+)
A27cross_loss_ADK <- adk.test(A27aps_loss, A27per_loss)
> A27cross_loss_ADK
Anderson-Darling k-sample test.
Number of samples: 2
Sample sizes: 8 4
Total number of values: 12
Number of unique values: 11
Mean of Anderson Darling Criterion: 1
Standard deviation of Anderson Darling Criterion: 0.65642
T = (Anderson Darling Criterion - mean)/sigma
Null Hypothesis: All samples come from a common population.
t.obs P-value extrapolation
not adj. for ties 2.15099 0.04145 0
adj. for ties 1.93129 0.05125 0
Warning: At least one sample size is less than 5.
p-values may not be very accurate.
>
=======================================
The cross-implementation comparisons barely pass the ADK criterion at
95% = 1.960 when adjusting for ties.
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6.1.4. Conclusions on the ADK Results for One-Way Packet Loss
We conclude that the two implementations are capable of producing
equivalent one-way packet loss measurements based on their
interpretation of [RFC2680].
6.2. One-Way Loss: Delay Threshold
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 second of 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 seconds of one-way
constant delay in one direction of transmission equivalent to
2 seconds of additional one-way delay (or change the path delay
while the 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 seconds of 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 EDT)
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The netem emulator settings added constant delays as specified in the
procedure above.
6.2.1. NetProbe Results for Loss Threshold
In NetProbe, the loss threshold was 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 were 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).
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
Section 2.8.2 of [RFC2680]). We take the position that the
assumption of post-processing is compliant and that the text of the
revision of RFC 2680 should be revised slightly to include this
point.
6.3. One-Way Loss with Out-of-Order Arrival
Section 3.6 of [RFC2680] indicates, with a lowercase "must" in the
text, that implementations need to ensure that reordered packets are
handled correctly. In essence, this is an implied requirement
because the correct packet must be identified as lost if it fails to
arrive before its delay threshold under all circumstances, and
reordering is always a possibility on IP network paths. See
[RFC4737] for the definition of reordering used in IETF
standard-compliant measurements.
The netem emulator can produce packet reordering because each
packet's delay is drawn from an independent distribution. Here,
significant delay (2000 ms) and delay variation (1000 ms) were
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sufficient to produce packet reordering. Using the procedure
described in Section 6.1, the netem emulator was set to introduce 10%
loss while reordering was present.
The tests described in this section used:
o IP header + payload = 64 octets
o Periodic sampling = 1 packet per second
o Test duration = 600 seconds (during May 2, 2011, EDT)
=======================================
> Y02aps_loss <- c(53,45,67,55) (NetProbe)
> Y02per_loss <- c(59,62,67,69) (Perfas+)
> Y02cross_loss_ADK <- adk.test(Y02aps_loss, Y02per_loss)
> Y02cross_loss_ADK
Anderson-Darling k-sample test.
Number of samples: 2
Sample sizes: 4 4
Total number of values: 8
Number of unique values: 7
Mean of Anderson Darling Criterion: 1
Standard deviation of Anderson Darling Criterion: 0.60978
T = (Anderson Darling Criterion - mean)/sigma
Null Hypothesis: All samples come from a common population.
t.obs P-value extrapolation
not adj. for ties 1.11282 0.11531 0
adj. for ties 1.19571 0.10616 0
Warning: At least one sample size is less than 5.
p-values may not be very accurate.
>
=======================================
The test results indicate that extensive reordering was present.
Both implementations capture the extensive delay variation between
adjacent packets. In NetProbe, packet arrival order is preserved in
the raw measurement files, so an examination of arrival packet
sequence numbers also reveals reordering.
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Despite extensive continuous packet reordering present in the
transmission path, the distributions of loss counts from the two
implementations pass the ADK criterion at 95% = 1.960.
6.4. Poisson Sending Process Evaluation
Section 3.7 of [RFC2680] indicates that implementations need to
ensure that their sending process is reasonably close to a classic
Poisson distribution when used. Much more detail on sample
distribution generation and Goodness-of-Fit testing is specified in
Section 11.4 of [RFC2330] and the Appendix of [RFC2330].
In this section, each implementation's Poisson distribution is
compared with an idealistic version of the distribution available in
the base functionality of the R-tool for Statistical Analysis [RTOOL]
and performed using the Anderson-Darling Goodness-of-Fit test package
(ADGofTest) [RADGOF]. The Goodness-of-Fit criterion derived from
[RFC2330] requires a test statistic value AD <= 2.492 for 5%
significance. The Appendix of [RFC2330] also notes that there may be
difficulty satisfying the ADGofTest when the sample includes many
packets (when 8192 were used, the test always failed, but smaller
sets of the stream passed).
Both implementations were configured to produce Poisson distributions
with lambda = 1 packet per second and to assign received packet
timestamps in the measurement application (above the UDP layer; see
the calibration results in Section 4 of [RFC6808] for error
assessment).
6.4.1. NetProbe Results
Section 11.4 of [RFC2330] suggests three possible measurement points
to evaluate the Poisson distribution. The NetProbe analysis uses
"user-level timestamps made just before or after the system call for
transmitting the packet".
The statistical summary for two NetProbe streams is below:
=======================================
> summary(a27ms$s1[2:1152])
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.0100 0.2900 0.6600 0.9846 1.3800 8.6390
> summary(a27ms$s2[2:1152])
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.010 0.280 0.670 0.979 1.365 8.829
=======================================
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We see that both of the means are near the specified lambda = 1.
The results of ADGoF tests for these two streams are shown below:
=======================================
> ad.test( a27ms$s1[2:101], pexp, 1)
Anderson-Darling GoF Test
data: a27ms$s1[2:101] and pexp
AD = 0.8908, p-value = 0.4197
alternative hypothesis: NA
> ad.test( a27ms$s1[2:1001], pexp, 1)
Anderson-Darling GoF Test
data: a27ms$s1[2:1001] and pexp
AD = 0.9284, p-value = 0.3971
alternative hypothesis: NA
> ad.test( a27ms$s2[2:101], pexp, 1)
Anderson-Darling GoF Test
data: a27ms$s2[2:101] and pexp
AD = 0.3597, p-value = 0.8873
alternative hypothesis: NA
> ad.test( a27ms$s2[2:1001], pexp, 1)
Anderson-Darling GoF Test
data: a27ms$s2[2:1001] and pexp
AD = 0.6913, p-value = 0.5661
alternative hypothesis: NA
=======================================
We see that both sets of 100 packets and 1000 packets from two
different streams (s1 and s2) all passed the AD <= 2.492 criterion.
6.4.2. Perfas+ Results
Section 11.4 of [RFC2330] suggests three possible measurement points
to evaluate the Poisson distribution. The Perfas+ analysis uses
"wire times for the packets as recorded using a packet filter".
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However, due to limited access at the Perfas+ side of the test setup,
the captures were made after the Perfas+ streams traversed the
production network, adding a small amount of unwanted delay variation
to the wire times (and possibly error due to packet loss).
The statistical summary for two Perfas+ streams is below:
=======================================
> summary(a27pe$p1)
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.004 0.347 0.788 1.054 1.548 4.231
> summary(a27pe$p2)
Min. 1st Qu. Median Mean 3rd Qu. Max.
0.0010 0.2710 0.7080 0.9696 1.3740 7.1160
=======================================
We see that both of the means are near the specified lambda = 1.
The results of ADGoF tests for these two streams are shown below:
=======================================
> ad.test(a27pe$p1, pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p1 and pexp
AD = 1.1364, p-value = 0.2930
alternative hypothesis: NA
> ad.test(a27pe$p2, pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p2 and pexp
AD = 0.5041, p-value = 0.7424
alternative hypothesis: NA
> ad.test(a27pe$p1[1:100], pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p1[1:100] and pexp
AD = 0.7202, p-value = 0.5419
alternative hypothesis: NA
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> ad.test(a27pe$p1[101:193], pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p1[101:193] and pexp
AD = 1.4046, p-value = 0.201
alternative hypothesis: NA
> ad.test(a27pe$p2[1:100], pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p2[1:100] and pexp
AD = 0.4758, p-value = 0.7712
alternative hypothesis: NA
> ad.test(a27pe$p2[101:193], pexp, 1 )
Anderson-Darling GoF Test
data: a27pe$p2[101:193] and pexp
AD = 0.3381, p-value = 0.9068
alternative hypothesis: NA
>
=======================================
We see that sets of 193, 100, and 93 packets from two different
streams (p1 and p2) all passed the AD <= 2.492 criterion.
6.4.3. Conclusions for Goodness-of-Fit
Both NetProbe and Perfas+ implementations produce adequate Poisson
distributions according to the Anderson-Darling Goodness-of-Fit at
the 5% significance (1-alpha = 0.05, or 95% confidence level).
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6.5. Implementation of Statistics for One-Way Loss
We check to see which statistics were implemented and report on those
facts, noting that Section 4 of [RFC2680] does not specify the
calculations exactly and only gives some illustrative examples.
NetProbe Perfas+
Type-P-One-way-Packet-Loss-Average yes yes
(this is more commonly referred
to as "loss ratio")
Implementation of RFC 2680 Section 4 Statistics
We note that implementations refer to this metric as a loss ratio,
and this is an area for likely revision of the text to make it more
consistent with widespread usage.
7. Conclusions for a Revision of RFC 2680
This memo concludes that [RFC2680] should be advanced on the
Standards Track and recommends the following edits to improve the
text (which are not deemed significant enough to affect maturity).
o Revise Type-P-One-way-Packet-Loss-Ave to
Type-P-One-way-Delay-Packet-Loss-Ratio.
o Regarding implementation of the loss delay threshold
(Section 6.2), the assumption of post-processing is compliant, and
the text of the revision of RFC 2680 should be revised slightly to
include this point.
o The IETF has reached consensus on guidance for reporting metrics
[RFC6703], and this memo should be referenced in a revision of
RFC 2680 to incorporate recent experience where appropriate.
We note that there are at least two errata for [RFC2680], and it
appears that these minor revisions should be incorporated in a
revision of RFC 2680.
The authors that revise [RFC2680] 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.
We recognize the existence of BCP 170 [RFC6390], which provides
guidelines for development of documents describing new performance
metrics. However, the advancement of [RFC2680] represents fine-
tuning of long-standing specifications based on experience that
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helped to formulate BCP 170, and material that satisfies some of the
requirements of [RFC6390] can be found in other RFCs, such as the
IPPM Framework [RFC2330]. Thus, no specific changes to address
BCP 170 guidelines are recommended for a revision of RFC 2680.
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 Customer Premises Equipment (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 on
statistical interpretation with Ganga Maguluri.
Constructive comments and helpful reviews were also provided by Bill
Cerveny, Joachim Fabini, and Ann Cerveny.
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10. Appendix - Network Configuration and Sample Commands
This Appendix provides some background information on the host
configuration and sample tc commands for the "netem" network
emulator, as described in Section 3 and Figure 1 of this memo. These
details are also applicable to the test plan in [RFC6808].
The host interface and configuration are shown below. Due to the
limit of 72 characters per line, line breaks were added to the "tc"
commands in the output below.
[system@dell4-4 ~]$ su
Password:
[root@dell4-4 system]# service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[ OK ]
[root@dell4-4 system]# service iptables stop
iptables: Flushing firewall rules: [ OK ]
iptables: Setting chains to policy ACCEPT: nat filter [ OK ]
iptables: Unloading modules: [ OK ]
[root@dell4-4 system]# brctl show
bridge name bridge id STP enabled interfaces
virbr0 8000.000000000000 yes
[root@dell4-4 system]# ifconfig eth1.300 0.0.0.0 promisc up
[root@dell4-4 system]# ifconfig eth1.400 0.0.0.0 promisc up
[root@dell4-4 system]# ifconfig eth2.400 0.0.0.0 promisc up
[root@dell4-4 system]# ifconfig eth2.300 0.0.0.0 promisc up
[root@dell4-4 system]# brctl addbr br300
[root@dell4-4 system]# brctl addif br300 eth1.300
[root@dell4-4 system]# brctl addif br300 eth2.300
[root@dell4-4 system]# ifconfig br300 up
[root@dell4-4 system]# brctl addbr br400
[root@dell4-4 system]# brctl addif br400 eth1.400
[root@dell4-4 system]# brctl addif br400 eth2.400
[root@dell4-4 system]# ifconfig br400 up
[root@dell4-4 system]# brctl show
bridge name bridge id STP enabled interfaces
br300 8000.0002b3109b8a no eth1.300
eth2.300
br400 8000.0002b3109b8a no eth1.400
eth2.400
virbr0 8000.000000000000 yes
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[root@dell4-4 system]# brctl showmacs br300
port no mac addr is local? ageing timer
2 00:02:b3:10:9b:8a yes 0.00
1 00:02:b3:10:9b:99 yes 0.00
1 00:02:b3:c4:c9:7a no 0.52
2 00:02:b3:cf:02:c6 no 0.52
2 00:0b:5f:54:de:81 no 0.01
[root@dell4-4 system]# brctl showmacs br400
port no mac addr is local? ageing timer
2 00:02:b3:10:9b:8a yes 0.00
1 00:02:b3:10:9b:99 yes 0.00
2 00:02:b3:c4:c9:7a no 0.60
1 00:02:b3:cf:02:c6 no 0.42
2 00:0b:5f:54:de:81 no 0.33
[root@dell4-4 system]# tc qdisc add dev eth1.300 root netem
delay 100ms
[root@dell4-4 system]# ifconfig eth1.200 0.0.0.0 promisc up
[root@dell4-4 system]# vconfig add eth1 100
Added VLAN with VID == 100 to IF -:eth1:-
[root@dell4-4 system]# ifconfig eth1.100 0.0.0.0 promisc up
[root@dell4-4 system]# vconfig add eth2 100
Added VLAN with VID == 100 to IF -:eth2:-
[root@dell4-4 system]# ifconfig eth2.100 0.0.0.0 promisc up
[root@dell4-4 system]# ifconfig eth2.200 0.0.0.0 promisc up
[root@dell4-4 system]# brctl addbr br100
[root@dell4-4 system]# brctl addif br100 eth1.100
[root@dell4-4 system]# brctl addif br100 eth2.100
[root@dell4-4 system]# ifconfig br100 up
[root@dell4-4 system]# brctl addbr br200
[root@dell4-4 system]# brctl addif br200 eth1.200
[root@dell4-4 system]# brctl addif br200 eth2.200
[root@dell4-4 system]# ifconfig br200 up
[root@dell4-4 system]# brctl show
bridge name bridge id STP enabled interfaces
br100 8000.0002b3109b8a no eth1.100
eth2.100
br200 8000.0002b3109b8a no eth1.200
eth2.200
br300 8000.0002b3109b8a no eth1.300
eth2.300
br400 8000.0002b3109b8a no eth1.400
eth2.400
virbr0 8000.000000000000 yes
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[root@dell4-4 system]# brctl showmacs br100
port no mac addr is local? ageing timer
2 00:02:b3:10:9b:8a yes 0.00
1 00:02:b3:10:9b:99 yes 0.00
1 00:0a:e4:83:89:07 no 0.19
2 00:0b:5f:54:de:81 no 0.91
2 00:e0:ed:0f:72:86 no 1.28
[root@dell4-4 system]# brctl showmacs br200
port no mac addr is local? ageing timer
2 00:02:b3:10:9b:8a yes 0.00
1 00:02:b3:10:9b:99 yes 0.00
2 00:0a:e4:83:89:07 no 1.14
2 00:0b:5f:54:de:81 no 1.87
1 00:e0:ed:0f:72:86 no 0.24
[root@dell4-4 system]# tc qdisc add dev eth1.100 root netem
delay 100ms
[root@dell4-4 system]#
=====================================================================
Some sample tc command lines controlling netem and its impairments
are given below.
tc qdisc add dev eth1.100 root netem loss 0%
tc qdisc add dev eth1.200 root netem loss 0%
tc qdisc add dev eth1.300 root netem loss 0%
tc qdisc add dev eth1.400 root netem loss 0%
Add delay and delay variation:
tc qdisc change dev eth1.100 root netem delay 100ms 50ms
tc qdisc change dev eth1.200 root netem delay 100ms 50ms
tc qdisc change dev eth1.300 root netem delay 100ms 50ms
tc qdisc change dev eth1.400 root netem delay 100ms 50ms
Add delay, delay variation, and loss:
tc qdisc change dev eth1 root netem delay 2000ms 1000ms loss 10%
=====================================================================
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11. References
11.1. 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.
[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.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
November 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.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[RFC6576] Geib, R., Morton, A., Fardid, R., and A. Steinmitz, "IP
Performance Metrics (IPPM) Standard Advancement Testing",
BCP 176, RFC 6576, March 2012.
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[RFC6703] Morton, A., Ramachandran, G., and G. Maguluri, "Reporting
IP Network Performance Metrics: Different Points of View",
RFC 6703, August 2012.
[RFC6808] Ciavattone, L., Geib, R., Morton, A., and M. Wieser, "Test
Plan and Results Supporting Advancement of RFC 2679 on the
Standards Track", RFC 6808, December 2012.
11.2. 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.
[FEDORA] "Fedora", <http://fedoraproject.org/>.
[LOSS-METRIC]
Almes, G., Kalidindi, S., Zekauskas, M., and A. Morton,
Ed., "A One-Way Loss Metric for IPPM", Work in Progress,
July 2014.
[MII-TOOL]
Hinds, D., Becker, D., and B. Eckenfels, "Linux System
Administrator's Manual", February 2013,
<http://man7.org/linux/man-pages/man8/mii-tool.8.html>.
[NETEM] Linux Foundation, "netem",
<http://www.linuxfoundation.org/collaborate/workgroups/
networking/netem>.
[Perfas] Heidemann, C., "Qualitaet in IP-Netzen Messverfahren",
published by ITG Fachgruppe, 2nd meeting 5.2.3,
November 2001, <www.itg523.de/oeffentlich/01nov/
Heidemann_QOS_Messverfahren.pdf>.
[RADGOF] Bellosta, C., "ADGofTest: Anderson-Darling Goodness-of-Fit
Test. R package version 0.3.", R-Package Version 0.3,
December 2011, <http://cran.r-project.org/web/packages/
ADGofTest/index.html>.
[RADK] Scholz, F., "ADK: Anderson-Darling K-Sample Test and
Combinations of Such Tests. R package version 1.0.", 2008.
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[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RTOOL] R Development Core Team, "R: A Language and Environment
for Statistical Computing", ISBN 3-900051-07-0, 2014,
<http://www.R-project.org/>.
[WIPM] AT&T, "AT&T Global IP Network", 2014,
<http://ipnetwork.bgtmo.ip.att.net/pws/index.html>.
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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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