Network Working Group A. Morton
Internet-Draft AT&T Labs
Updates: ???? (if approved) R. Geib
Intended status: Standards Track Deutsche Telekom
Expires: February 15, 2021 L. Ciavattone
AT&T Labs
August 14, 2020
Metrics and Methods for IP Capacity
draft-ietf-ippm-capacity-metric-method-03
Abstract
This memo revisits the problem of Network Capacity metrics first
examined in RFC 5136. The memo specifies a more practical Maximum
IP-layer Capacity metric definition catering for measurement
purposes, and outlines the corresponding methods of measurement.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Scope and Goals . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. General Parameters and Definitions . . . . . . . . . . . . . 5
5. IP-Layer Capacity Singleton Metric Definitions . . . . . . . 6
5.1. Formal Name . . . . . . . . . . . . . . . . . . . . . . . 6
5.2. Parameters . . . . . . . . . . . . . . . . . . . . . . . 6
5.3. Metric Definitions . . . . . . . . . . . . . . . . . . . 6
5.4. Related Round-Trip Delay and Loss Definitions . . . . . . 8
5.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . 8
5.6. Reporting the Metric . . . . . . . . . . . . . . . . . . 8
6. Maximum IP-Layer Capacity Metric Definitions (Statistic) . . 8
6.1. Formal Name . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Parameters . . . . . . . . . . . . . . . . . . . . . . . 8
6.3. Metric Definitions . . . . . . . . . . . . . . . . . . . 9
6.4. Related Round-Trip Delay and Loss Definitions . . . . . . 10
6.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . 10
6.6. Reporting the Metric . . . . . . . . . . . . . . . . . . 11
7. IP-Layer Sender Bit Rate Singleton Metric Definitions . . . . 11
7.1. Formal Name . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. Parameters . . . . . . . . . . . . . . . . . . . . . . . 12
7.3. Metric Definition . . . . . . . . . . . . . . . . . . . . 12
7.4. Discussion . . . . . . . . . . . . . . . . . . . . . . . 12
7.5. Reporting the Metric . . . . . . . . . . . . . . . . . . 12
8. Method of Measurement . . . . . . . . . . . . . . . . . . . . 13
8.1. Load Rate Adjustment Algorithm . . . . . . . . . . . . . 13
8.2. Measurement Qualification or Verification . . . . . . . . 14
8.3. Measurement Considerations . . . . . . . . . . . . . . . 15
8.4. Running Code . . . . . . . . . . . . . . . . . . . . . . 17
9. Reporting Formats . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Configuration and Reporting Data Formats . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
13.1. Normative References . . . . . . . . . . . . . . . . . . 20
13.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
The IETF's efforts to define Network and Bulk Transport Capacity have
been chartered and progressed for over twenty years. Over that time,
the performance community has seen development of Informative
definitions in [RFC3148] for Framework for Bulk Transport Capacity
(BTC), RFC 5136 for Network Capacity and Maximum IP-layer Capacity,
and the Experimental metric definitions and methods in [RFC8337],
Model-Based Metrics for BTC.
This memo revisits the problem of Network Capacity metrics examined
first in [RFC3148] and later in [RFC5136]. Maximum IP-Layer Capacity
and [RFC3148] Bulk Transfer Capacity (goodput) are different metrics.
Max IP-layer Capacity is like the theoretical goal for goodput.
There are many metrics in [RFC5136], such as Available Capacity.
Measurements depend on the network path under test and the use case.
Here, the main use case is to assess the maximum capacity of the
access network, with specific performance criteria used in the
measurement.
This memo recognizes the importance of a definition of a Maximum IP-
layer Capacity Metric at a time when access speeds have increased
dramatically; a definition that is both practical and effective for
the performance community's needs, including Internet users. The
metric definition is intended to use Active Methods of Measurement
[RFC7799], and a method of measurement is included.
The most direct active measurement of IP-layer Capacity would use IP
packets, but in practice a transport header is needed to traverse
address and port translators. UDP offers the most direct assessment
possibility, and in the [copycat][copycat] measurement study to
investigate whether UDP is viable as a general Internet transport
protocol, the authors found that a high percentage of paths tested
support UDP transport. A number of liaisons have been exchanged on
this topic [ refs to ITU-T SG12, ETSI STQ, BBF liaisons ], discussing
the laboratory and field tests that support the UDP-based approach to
IP-layer Capacity measurement.
This memo also recognizes the many updates to the IP Performance
Metrics Framework [RFC2330] published over twenty years, and makes
use of [RFC7312] for Advanced Stream and Sampling Framework, and RFC
8468 [RFC8468]IPv4, IPv6, and IPv4-IPv6 Coexistence Updates.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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14[RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Scope and Goals
The scope of this memo is to define a metric and corresponding method
to unambiguously perform Active measurements of Maximum IP-Layer
Capacity, along with related metrics and methods.
The main goal is to harmonize the specified metric and method across
the industry, and this memo is the vehicle through which working
group (and eventually, IETF) consensus will be captured and
communicated to achieve broad agreement, and possibly result in
changes in the specifications of other Standards Development
Organizations (SDO) (through the SDO's normal contribution process,
or through liaison exchange).
A local goal is to aid efficient test procedures where possible, and
to recommend reporting with additional interpretation of the results.
Also, to foster the development of protocol support for this metric
and method of measurement (all active testing protocols currently
defined by the IPPM WG are UDP-based, meeting a key requirement of
these methods). The supporting protocol development to measure this
metric according to the specified method is a key future contribution
to Internet measurement.
3. Motivation
As with any problem that has been worked for many years in various
SDOs without any special attempts at coordination, various solutions
for metrics and methods have emerged.
There are five factors that have changed (or begun to change) in the
2013-2019 time frame, and the presence of any one of them on the path
requires features in the measurement design to account for the
changes:
1. Internet access is no longer the bottleneck for many users.
2. Both speed and latency are important to user's satisfaction.
3. UDP's growing role in Transport, in areas where TCP once
dominated.
4. Content and applications moving physically closer to users.
5. Less emphasis on ISP gateway measurements, possibly due to less
traffic crossing ISP gateways in future.
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4. General Parameters and Definitions
This section lists the REQUIRED input factors to specify a Sender or
Receiver metric.
o Src, the address of a host (such as the globally routable IP
address).
o Dst, the address of a host (such as the globally routable IP
address).
o i, the limit on the number of Hops a specific packet may visit as
it traverses from the host at Src to the host at Dst (such as the
TTL or Hop Limit).
o MaxHops, the maximum value of i used, (i=1,2,3,...MaxHops).
o T0, the time at the start of measurement interval, when packets
are first transmitted from the Source.
o I, the duration of a measurement interval (default 10 sec)
o dt, the duration of N equal sub-intervals in I (default 1 sec)
o Tmax, a maximum waiting time for test packets to arrive at the
destination, set sufficiently long to disambiguate packets with
long delays from packets that are discarded (lost), such that the
distribution of one-way delay is not truncated.
o F, the number of different flows synthesized by the method
(default 1 flow)
o flow, the stream of packets with the same n-tuple of designated
header fields that (when held constant) result in identical
treatment in a multi-path decision (such as the decision taken in
load balancing). Note: The IPv6 flow label MAY be included in the
flow definition when routers have complied with [RFC6438]
guidelines at the Tunnel End Points (TEP), and the source of the
measurement is a TEP.
o Type-P, the complete description of the packets for which this
assessment applies (including the flow-defining fields). Note
that the UDP transport layer is one requirement specified below.
Type-P is a parallel concept to "population of interest" defined
in ITU-T Rec. Y.1540.
o PM, a list of fundamental metrics, such as loss, delay, and
reordering, and corresponding Target performance threshold. At
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least one fundamental metric and Target performance threshold MUST
be supplied (such as One-way IP Packet Loss [RFC7680] equal to
zero).
A non-Parameter which is required for several metrics is defined
below:
o T, the host time of the *first* test packet's *arrival* as
measured at MP(Dst). There may be other packets sent between
source and destination hosts that are excluded, so this is the
time of arrival of the first packet used for measurement of the
metric.
Note that time stamps, sequnce numbers, etc. will be established by
the test protocol.
5. IP-Layer Capacity Singleton Metric Definitions
This section sets requirements for the following components to
support the Maximum IP-layer Capacity Metric.
5.1. Formal Name
Type-P-IP-Capacity, or informally called IP-layer Capacity.
Note that Type-P depends on the chosen method.
5.2. Parameters
This section lists the REQUIRED input factors to specify the metric,
beyond those listed in Section 4.
No additional Parameters are needed.
5.3. Metric Definitions
This section defines the REQUIRED aspects of the measureable IP-layer
Capacity metric (unless otherwise indicated) for measurements between
specified Source and Destination hosts:
Define the IP-layer capacity, C(T,I,PM), to be the number of IP-layer
bits (including header and data fields) in packets that can be
transmitted from the Src host and correctly received by the Dst host
during one contiguous sub-interval, dt.
The number of these IP-layer bits is designated n0[dtn,dtn+1] for a
specific dt.
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When the packet size is known and of fixed size, the packet count
during a single sub-interval dt multiplied by the total bits in IP
header and data fields is equal to n0[dtn,dtn+1].
Anticipating a Sample of Singletons, the interval dt SHOULD be set to
a natural number m so that T+I = T + m*dt with dtn+1 - dtn = dt and
with 1 <= n <= m.
Parameter PM represents other performance metrics [see section
Related Round-Trip Delay and Loss Definitions below]; their
measurement results SHALL be collected during measurement of IP-layer
Capacity and associated with the corresponding dtn for further
evaluation and reporting.
Mathematically, this definition can be represented as:
( n0[dtn,dtn+1] )
C(T,I,PM) = -------------------------
dt
Equation for IP-Layer Capacity
and:
o n0 is the total number of IP-layer header and payload bits that
can be transmitted in Standard Formed packets from the Src host
and correctly received by the Dst host during one contiguous sub-
interval, dt in length, during the interval [T, T+I],
o C(T,I,PM) the IP-Layer Capacity, corresponds to the value of n0
measured in any sub-interval ending at dtn (meaning T + n*dt),
divided by the length of sub-interval, dt.
o all sub-intervals SHOULD be of equal duration. Choosing dt as
non-overlapping consecutive time intervals allows for a simple
implementation.
o The bit rate of the physical interface of the measurement device
must be higher than that of the link whose C(T,I,PM) is to be
measured.
Measurements according to these definitions SHALL use UDP transport
layer.
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5.4. Related Round-Trip Delay and Loss Definitions
RTD[dtn-1,dtn] is defined as a sample of the [RFC2681] Round-trip
Delay between the Src host and the Dst host over the interval
[T,T+I]. The statistics used to to summarize RTD[dtn-1,dtn] MAY
include the minimum, maximum, and mean.
RTL[dtn-1,dtn] is defined as a sample of the [RFC6673] Round-trip
Loss between the Src host and the Dst host over the interval [T,T+I].
The statistics used to to summarize RTL[dtn-1,dtn] MAY include the
lost packet count and the lost packet ratio.
5.5. Discussion
See the corresponding section for Maximum IP-Layer Capacity.
5.6. Reporting the Metric
The IP-Layer Capacity SHALL be reported with meaningful resolution,
in units of Megabits per second (Mbps).
The Related Round Trip Delay and/or Loss metric measurements for the
same Singleton SHALL be reported, also with meaningful resolution for
the values measured.
Individual Capacity measurements MAY be reported in a manner
consistent with the Maximum IP-Layer Capacity, see Section 9.
6. Maximum IP-Layer Capacity Metric Definitions (Statistic)
This section sets requirements for the following components to
support the Maximum IP-layer Capacity Metric.
6.1. Formal Name
Type-P-Max-IP-Capacity, or informally called Maximum IP-layer
Capacity.
Note that Type-P depends on the chosen method.
6.2. Parameters
This section lists the REQUIRED input factors to specify the metric,
beyond those listed in Section 4.
No additional Parameters or definitions are needed.
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6.3. Metric Definitions
This section defines the REQUIRED aspects of the Maximum IP-layer
Capacity metric (unless otherwise indicated) for measurements between
specified Source and Destination hosts:
Define the Maximum IP-layer capacity, Maximum_C(T,I,PM), to be the
maximum number of IP-layer bits n0[dtn,dtn+1] that can be transmitted
in packets from the Src host and correctly received by the Dst host,
over all dt length intervals in [T, T+I], and meeting the PM
criteria. Equivalently the Maximum of a Sample of size m of
C(T,I,PM) collected during the interval [T, T+I] and meeting the PM
criteria.
The interval dt SHOULD be set to a natural number m so that T+I = T +
m*dt with dtn+1 - dtn = dt and with 1 <= n <= m.
Parameter PM represents the other performance metrics [see section
Related Round-Trip Delay and Loss Definitions below] and their
measurement results for the maximum IP-layer capacity. At least one
target performance threshold (PM criterion) MUST be defined. If more
than one target performance threshold is defined, then the sub-
interval with maximum number of bits transmitted MUST meet all the
target performance thresholds.
Mathematically, this definition can be represented as:
max ( n0[dtn,dtn+1] )
[T,T+I]
Maximum_C(T,I,PM) = -------------------------
dt
where:
T T+I
_________________________________________
| | | | | | | | | | |
dtn=1 2 3 4 5 6 7 8 9 10 n+1
n=m
Equation for Maximum Capacity
and:
o n0 is the total number of IP-layer header and payload bits that
can be transmitted in Standard Formed packets from the Src host
and correctly received by the Dst host during one contiguous sub-
interval, dt in length, during the interval [T, T+I],
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o Maximum _C(T,I,PM) the Maximum IP-Layer Capacity, corresponds to
the maximum value of n0 measured in any sub-interval ending at dtn
(meaning T + n*dt), divided by the constant length of all sub-
intervals, dt.
o all sub-intervals SHOULD be of equal duration. Choosing dt as
non-overlapping consecutive time intervals allows for a simple
implementation.
o The bit rate of the physical interface of the measurement systems
must be higher than that of the link whose Maximum _C(T,I,PM) is
to be measured (the bottleneck link).
In this definition, the m sub-intervals can be viewed as trials when
the Src host varies the transmitted packet rate, searching for the
maximum n0 that meets the PM criteria measured at the Dst host in a
test of duration, I. When the transmitted packet rate is held
constant at the Src host, the m sub-intervals may also be viewed as
trials to evaluate the stability of n0 and metric(s) in the PM list
over all dt-length intervals in I.
Measurements according to these definitions SHALL use UDP transport
layer.
6.4. Related Round-Trip Delay and Loss Definitions
RTD[dtn,dtn+1] is defined as a sample of the [RFC2681] Round-trip
Delay between the Src host and the Dst host over the interval
[T,T+I], and corresponds to the dt interval containing
Maximum_C(T,I,PM). The statistics used to to summarize
RTD[dtn,dtn+1] MAY include the minimum, maximum, and mean.
RTL[dtn,dtn+1] is defined as a sample of the [RFC6673] Round-trip
Loss between the Src host and the Dst host over the interval [T,T+I]
and corresponds to the dt interval containing Maximum_C(T,I,PM). The
statistics used to to summarize RTL[dtn-1,dtn] MAY include the lost
packet count and the lost packet ratio.
6.5. Discussion
If traffic conditioning applies along a path for which Maximum
_C(T,I,PM) is to be determined, different values for dt SHOULD be
picked and measurements be executed during multiple intervals [T,
T+I]. Any single interval dt SHOULD be chosen so that is an integer
multiple of increasing values k times serialisation delay of a path
MTU at the physical interface speed where traffic conditioning is
expected. This should avoid taking configured burst tolerance
singletons as a valid Maximum _C(T,I,PM) result.
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A Maximum_C(T,I,PM) without any indication of bottleneck congestion,
be that an increasing latency, packet loss or ECN marks during a
measurement interval I, is likely to underestimate Maximum_C(T,I,PM).
6.6. Reporting the Metric
The Maximum IP-Layer Capacity SHALL be reported with meaningful
resolution, in units of Megabits per second.
The Related Round Trip Delay and/or Loss metric measurements for the
same Singleton SHALL be reported, also with meaningful resolution for
the values measured.
When there are demonstrated and repeatable Capacity modes in the
Sample, then the Maximum IP-Layer Capacity SHALL be reported for each
mode, along with the relative time from the beginning of the stream
that the mode was observed to be present. Bimodal Maxima have been
observed with some services, sometimes called a "turbo mode"
intending to deliver short transfers more quickly, or reduce the
initial buffering time for some video streams. Note that modes
lasting less than dt duration will not be detected.
Some transmission technologies have multiple methods of operation
that may be activated when channel conditions degrade or improve, and
these transmission methods may determine the Maximum IP-Layer
Capacity. Examples include line-of-sight microwave modulator
constellations, or cellular modem technologies where the changes may
be initiated by a user moving from one coverage area to another.
Operation in the different transmission methods may be observed over
time, but the modes of Maximum IP-Layer Capacity will not be
activated deterministically as with the "turbo mode" described in the
paragraph above.
7. IP-Layer Sender Bit Rate Singleton Metric Definitions
This section sets requirements for the following components to
support the IP-layer Sender Bitrate Metric.
7.1. Formal Name
Type-P-IP-Sender-Bit-Rate, or informally called IP-layer Sender
Bitrate.
Note that Type-P depends on the chosen method.
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7.2. Parameters
This section lists the REQUIRED input factors to specify the metric,
beyond those listed in Section 4.
o S, the duration of the measurement interval at the Source
o st, the nominal duration of N sub-intervals in S (default = 0.05
seconds)
S SHALL be longer than I, primarily to account for on-demand
activation of the path, or any preamble to testing required.
st SHOULD be much smaller than the sub-interval dt. The st parameter
does not have relevance when the Source is transmitting at a fixed
rate throughout S.
7.3. Metric Definition
This section defines the REQUIRED aspects of the IP-layer Sender
Bitrate metric (unless otherwise indicated) for measurements at the
specified Source on packets addressed for the intended Destination
host and matching the required Type-P:
Define the IP-layer Sender Bit Rate, B(S,st), to be the number of IP-
layer bits (including header and data fields) that are transmitted
from the Source during one contiguous sub-interval, st, during the
test interval S (where S SHALL be longer than I), and where the
fixed-size packet count during that single sub-interval st also
provides the number of IP-layer bits in any interval: n0[stn-1,stn].
Measurements according to these definitions SHALL use UDP transport
layer. Any feedback from Dst host to Src host received by Src host
during an interval [stn-1,stn] MUST NOT result in an adaptation of
the Src host traffic conditioning during this interval.
7.4. Discussion
Both the Sender and Receiver or (source and destination) bit rates
SHOULD be assessed as part of a measurement.
7.5. Reporting the Metric
The IP-Layer Sender Bit Rate SHALL be reported with meaningful
resolution, in units of Megabits per second.
Individual IP-Layer Sender Bit Rate measurements are discussed
further in Section 9.
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8. Method of Measurement
The duration of a test, I, MUST be constrained in a production
network, since this is an active test method and it will likely cause
congestion on the Src to Dst host path during a test.
Additional Test methods and configurations may be provided in this
section, after review and further testing.
8.1. Load Rate Adjustment Algorithm
A table SHALL be pre-built defining all the offered load rates that
will be supported (R1 - Rn, in ascending order). Each rate is
defined as datagrams of size S, sent as a burst of count C, every
time interval T. While it is advantageous to use datagrams of as
large a size as possible, it may be prudent to use a slightly smaller
maximum that allows for secondary protocol headers and/or tunneling
without resulting in IP-layer fragmentation.
At the beginning of a test, the sender begins sending at rate R1 and
the receiver starts a feedback timer at interval F (while awaiting
inbound datagrams). As datagrams are received they are checked for
sequence number anomalies (loss, out-of-order, duplication, etc.) and
the delay variation is measured (one-way or round-trip). This
information is accumulated until the feedback timer F expires and a
status feedback message is sent from the receiver back to the sender,
to communicate this information. The accumulated statistics are then
reset by the receiver for the next feedback interval. As feedback
messages are received back at the sender, they are evaluated to
determine how to adjust the current offered load rate (Rx).
If the feedback indicates that there were no sequence number
anomalies AND the delay variation was below the lower threshold, the
offered load rate is increased. If congestion has not been confirmed
up to this point, the offered load rate is increased by more than one
rate (e.g., Rx+10). This allows the offered load to quickly reach a
near-maximum rate. Conversely, if congestion has been previously
confirmed, the offered load rate is only increased by one (Rx+1).
If the feedback indicates that sequence number anomalies were
detected OR the delay variation was above the upper threshold, the
offered load rate is decreased. If congestion is confirmed by the
current feedback message being processed, the offered load rate is
decreased by more than one rate (e.g., Rx-30). This one-time
reduction is intended to compensate for the fast initial ramp-up. In
all other cases, the offered load rate is only decreased by one (Rx-
1).
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If the feedback indicates that there were no sequence number
anomalies AND the delay variation was above the lower threshold, but
below the upper threshold, the offered load rate is not changed.
This allows time for recent changes in the offered load rate to
stabilize, and the feedback to represent current conditions more
accurately.
Lastly, the method for confirming congestion is that there were
sequence number anomalies OR the delay variation was above the upper
threshold for two consecutive feedback intervals. The algorithm
described above is also presented in ITU-T Rec. Y.1540, 2020
version[Y.1540], in Annexes A and B, and implemented in the reference
for Section 8.4, Running Code.
8.2. Measurement Qualification or Verification
When assessing a Maximum rate as the metric specifies, artificially
high (optimistic) values might be measured until some buffer on the
path is filled. Other causes include bursts of back-to-back packets
with idle intervals delivered by a path, while the measurement
interval (dt) is small and aligned with the bursts. The artificial
values might result in an un-sustainable Maximum Capacity observed
when the method of measurement is searching for the Maximum, and that
would not do. This situation is different from the bi-modal service
rates (discussed under Reporting), which are characterized by a
multi-second duration (much longer than the measured RTT) and
repeatable behavior.
There are many ways that the Method of Measurement could handle this
false-max issue. The default value for measurement of singletons (dt
= 1 second) has proven to a be of practical value during tests of
this method, allows the bimodal service rates to be characterized,
and it has an obvious alignment with the reporting units (Mbps).
Another approach comes from Section 24 of RFC 2544[RFC2544] and its
discussion of Trial duration, where relatively short trials conducted
as part of the search are followed by longer trials to make the final
determination. In the production network, measurements of singletons
and samples (the terms for trials and tests of Lab Benchmarking) must
be limited in duration because they may be service-affecting. But
there is sufficient value in repeating a sample with a fixed sending
rate determined by the previous search for the Max IP-layer Capacity,
to qualify the result in terms of the other performance metrics
measured at the same time.
A qualification measurement for the search result is a subsequent
measurement, sending at a fixed 99.x % of the Max IP-layer Capacity
for I, or an indefinite period. The same Max Capacity Metric is
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applied, and the Qualification for the result is a sample without
packet loss or a growing minimum delay trend in subsequent singletons
(or each dt of the measurement interval, I). Samples exhibiting
losses or increasing queue occupation require a repeated search and/
or test at reduced fixed sender rate for qualification.
Here, as with any Active Capacity test, the test duration must be
kept short. 10 second tests for each direction of transmission are
common today. The default measurement interval specified here is I =
10 seconds). In combination with a fast search method and user-
network coordination, the concerns raised in RFC 6815[RFC6815] are
alleviated. The method for assessing Max IP Capacity is different
from classic [RFC2544] methods: they use short term load adjustment
and are sensitive to loss and delay, like other congestion control
algorithms used on the Internet every day.
8.3. Measurement Considerations
In general, the wide-spread measurements that this memo encourages
will encounter wide-spread behaviors. The bimodal IP Capacity
behaviors already discussed in Section 6.6 are good examples.
In general, it is RECOMMENDED to locate test endpoints as close to
the intended measured link(s) as practical (this is not always
possible for reasons of scale; there is a limit on number of test
endpoints coming from many perspecitves, management and measurement
traffic for example).
The path measured may be state-full based on many factors, and the
Parameter "Time of day" when a test starts may not be enough
information. Repeatable testing may require the time from the
beginning of a measured flow, and how the flow is constructed
including how much traffic has already been sent on that flow when a
state-change is observed, because the state-change may be based on
time or bytes sent or both.
Many different traffic shapers and on-demand access technologies may
be encountered, as anticipated in [RFC7312], and play a key role in
measurement results. Methods MUST be prepared to provide a short
preamble transmission to activate on-demand access, and to discard
the preamble from subsequent test results.
Conditions which might be encountered during measurement, where
packet losses may occur independently from the measurement sending
rate:
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1. Congestion of an interconnection or backbone interface may appear
as packet losses distributed over time in the test stream, due to
much higher rate interfaces in the backbone.
2. Packet loss due to use of Random Early Detection (RED) or other
active queue management.
3. There may be only small delay variation independent of sending
rate under these conditions, too.
4. Persistent competing traffic on measurement paths that include
shared media may cause random packet losses in the test stream.
It is possible to mitigate these conditions using the flexibility of
the load-rate adjusting algorithm described in Section 8.1 above
(tuning specific parameters).
In general, results depend on the sending stream characteristics; the
measurement community has known this for a long time, and needs to
keep it front of mind. Although the default is a single flow (F=1)
for testing, use of multiple flows may be advantageous for the
following reasons:
1. the test hosts may be able to create higher load than with a
single flow, or parallel test hosts may be used to generate 1
flow each.
2. there may be link aggregation present (flow-based load balancing)
and multiple flows are needed to occupy each member of the
aggregate.
3. access policies may limit the IP-Layer Capacity depending on the
Type-P of packets, possibly reserving capacity for various stream
types.
Each flow would be controlled using its own implementation of the
Load Adjustment (Search) Algorithm.
As testing continues, implementers should expect some evolution in
the methods. The ITU-T has published a Supplement (60) to the
Y-series of Recommendations, "Interpreting ITU-T Y.1540 maximum IP-
layer capacity measurements", [Y.Sup60], which is the result of
continued testing with the metric and method described here.
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8.4. Running Code
Much of the development of the method and comparisons with existing
methods conducted at IETF Hackathons and elsewhere have been based on
the example udpst Linux measurement tool (which is a working
reference for further development) [udpst]. The current project:
o is a utility that can function as a client or server daemon
o is written in C, and built with gcc (release 9.3) and its standard
run-time libraries
o allows configuration of most of the parameters described in
Sections 4 and 7.
o Supports IPv4 and IPv6 address families.
o
9. Reporting Formats
The singleton IP-Layer Capacity results SHOULD be accompanied by the
context under which they were measured.
o timestamp (especially the time when the maximum was observed in
dtn)
o source and destination (by IP or other meaningful ID)
o other inner parameters of the test case (Section 4)
o outer parameters, such as "done in motion" or other factors
belonging to the context of the measurement
o result validity (indicating cases where the process was somehow
interrupted or the attempt failed)
o a field where unusual circumstances could be documented, and
another one for "ignore/mask out" purposes in further processing
The Maximum IP-Layer Capacity results SHOULD be reported in the
format of a table with a row for each of the test Phases and Number
of Flows. There SHOULD be columns for the phases with number of
flows, and for the resultant Maximum IP-Layer Capacity results for
the aggregate and each flow tested.
As mentioned in Section 6.6, bi-modal (or multi-modal) maxima SHALL
be reported for each mode separately.
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+--------------+----------------------+-----------+-----------------+
| Phase, # | Max IP-Layer | Loss | RTT min, max, |
| Flows | Capacity, Mbps | Ratio | msec |
+--------------+----------------------+-----------+-----------------+
| Search,1 | 967.31 | 0.0002 | 30, 58 |
| Verify,1 | 966.00 | 0.0000 | 30, 38 |
+--------------+----------------------+-----------+-----------------+
Maximum IP-layer Capacity Results
Static and configuration parameters:
The sub-interval time, dt, MUST accompany a report of Maximum IP-
Layer Capacity results, and the remaining Parameters from Section 4,
General Parameters.
The PM list metrics corresponding to the sub-interval where the
Maximum Capacity occurred MUST accompany a report of Maximum IP-Layer
Capacity results, for each test phase.
The IP-Layer Sender Bit rate results SHOULD be reported in the format
of a table with a row for each of the test Phases, sub-intervals (st)
and Number of Flows. There SHOULD be columns for the phases with
number of flows, and for the resultant IP-Layer Sender Bit rate
results for the aggregate and each flow tested.
+------------------------+-------------+-----------------------+----+
| Phase, Flow or | st, sec | Sender Bit Rate, Mbps | ?? |
| Aggregate | | | |
+------------------------+-------------+-----------------------+----+
| Search,1 | 0.00 - 0.05 | 345 | __ |
| Search,2 | 0.00 - 0.05 | 289 | __ |
| Search,Agg | 0.00 - 0.05 | 634 | __ |
+------------------------+-------------+-----------------------+----+
IP-layer Sender Bit Rate Results
Static and configuration parameters:
The subinterval time, st, MUST accompany a report of Sender IP-Layer
Bit Rate results.
Also, the values of the remaining Parameters from Section 4, General
Parameters, MUST be reported.
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9.1. Configuration and Reporting Data Formats
As a part of the multi-Standards Development Organization (SDO)
harmonization of this metric and method of measurement, one of the
areas where the Broadband Forum (BBF) contributed its expertise was
in the definition of an information model and data model for
configuration and reporting. These models are consistent with the
metric parameters and default values specified as lists is this memo.
[TR-471] provides the Information model that was used to prepare a
full data model in related BBF work. The BBF has als carefully
considered topics within its purvue, such as placement of measurement
systems within the access archtecture.
10. Security Considerations
Active metrics and measurements have a long history of security
considerations. The security considerations that apply to any active
measurement of live paths are relevant here. See [RFC4656] and
[RFC5357].
When considering privacy of those involved in measurement or those
whose traffic is measured, the sensitive information available to
potential observers is greatly reduced when using active techniques
which are within this scope of work. Passive observations of user
traffic for measurement purposes raise many privacy issues. We refer
the reader to the privacy considerations described in the Large Scale
Measurement of Broadband Performance (LMAP) Framework [RFC7594],
which covers active and passive techniques.
There are some new considerations for Capacity measurement as
described in this memo.
1. Cooperating Source and Destination hosts and agreements to test
the path between the hosts are REQUIRED.
2. Integrity protection for feedback messages conveying measurements
is RECOMMENDED.
3. Hosts SHOULD limit the number of simultaneous tests to avoid
resource exhaust and inaccuate results.
4. Senders MUST be rate-limited. This can be accomplished using the
pre-built table defining all the offered load rates that will be
supported (Section 8.1). The recommended load-control search
algorithm results in "ramp up" from the lowest rate in the table.
5. Service subscribers with limited data volumes who conduct
extensive capacity testing might experience the effects of
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Service Provider controls on their service. Testing with the
Service Provider's measurement hosts SHOULD be limited in
frequency and/or overall volume of test traffic.
The exact specification of these features is left for the future
protocol development.
11. IANA Considerations
This memo makes no requests of IANA.
12. Acknowledgements
Thanks to Joachim Fabini, Matt Mathis, Ignacio Alvarez-Hamelin, and
Wolfgang Balzer for their extensive comments on the memo and related
topics.
13. References
13.1. Normative References
[RFC1242] Bradner, S., "Benchmarking Terminology for Network
Interconnection Devices", RFC 1242, DOI 10.17487/RFC1242,
July 1991, <https://www.rfc-editor.org/info/rfc1242>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
DOI 10.17487/RFC2330, May 1998,
<https://www.rfc-editor.org/info/rfc2330>.
[RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544,
DOI 10.17487/RFC2544, March 1999,
<https://www.rfc-editor.org/info/rfc2544>.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, DOI 10.17487/RFC2681,
September 1999, <https://www.rfc-editor.org/info/rfc2681>.
[RFC2889] Mandeville, R. and J. Perser, "Benchmarking Methodology
for LAN Switching Devices", RFC 2889,
DOI 10.17487/RFC2889, August 2000,
<https://www.rfc-editor.org/info/rfc2889>.
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[RFC3148] Mathis, M. and M. Allman, "A Framework for Defining
Empirical Bulk Transfer Capacity Metrics", RFC 3148,
DOI 10.17487/RFC3148, July 2001,
<https://www.rfc-editor.org/info/rfc3148>.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
<https://www.rfc-editor.org/info/rfc4656>.
[RFC5136] Chimento, P. and J. Ishac, "Defining Network Capacity",
RFC 5136, DOI 10.17487/RFC5136, February 2008,
<https://www.rfc-editor.org/info/rfc5136>.
[RFC5180] Popoviciu, C., Hamza, A., Van de Velde, G., and D.
Dugatkin, "IPv6 Benchmarking Methodology for Network
Interconnect Devices", RFC 5180, DOI 10.17487/RFC5180, May
2008, <https://www.rfc-editor.org/info/rfc5180>.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/info/rfc5357>.
[RFC6201] Asati, R., Pignataro, C., Calabria, F., and C. Olvera,
"Device Reset Characterization", RFC 6201,
DOI 10.17487/RFC6201, March 2011,
<https://www.rfc-editor.org/info/rfc6201>.
[RFC6412] Poretsky, S., Imhoff, B., and K. Michielsen, "Terminology
for Benchmarking Link-State IGP Data-Plane Route
Convergence", RFC 6412, DOI 10.17487/RFC6412, November
2011, <https://www.rfc-editor.org/info/rfc6412>.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC6673] Morton, A., "Round-Trip Packet Loss Metrics", RFC 6673,
DOI 10.17487/RFC6673, August 2012,
<https://www.rfc-editor.org/info/rfc6673>.
[RFC6815] Bradner, S., Dubray, K., McQuaid, J., and A. Morton,
"Applicability Statement for RFC 2544: Use on Production
Networks Considered Harmful", RFC 6815,
DOI 10.17487/RFC6815, November 2012,
<https://www.rfc-editor.org/info/rfc6815>.
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[RFC6985] Morton, A., "IMIX Genome: Specification of Variable Packet
Sizes for Additional Testing", RFC 6985,
DOI 10.17487/RFC6985, July 2013,
<https://www.rfc-editor.org/info/rfc6985>.
[RFC7312] Fabini, J. and A. Morton, "Advanced Stream and Sampling
Framework for IP Performance Metrics (IPPM)", RFC 7312,
DOI 10.17487/RFC7312, August 2014,
<https://www.rfc-editor.org/info/rfc7312>.
[RFC7594] Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A Framework for Large-Scale
Measurement of Broadband Performance (LMAP)", RFC 7594,
DOI 10.17487/RFC7594, September 2015,
<https://www.rfc-editor.org/info/rfc7594>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8337] Mathis, M. and A. Morton, "Model-Based Metrics for Bulk
Transport Capacity", RFC 8337, DOI 10.17487/RFC8337, March
2018, <https://www.rfc-editor.org/info/rfc8337>.
[RFC8468] Morton, A., Fabini, J., Elkins, N., Ackermann, M., and V.
Hegde, "IPv4, IPv6, and IPv4-IPv6 Coexistence: Updates for
the IP Performance Metrics (IPPM) Framework", RFC 8468,
DOI 10.17487/RFC8468, November 2018,
<https://www.rfc-editor.org/info/rfc8468>.
13.2. Informative References
[copycat] Edleine, K., Kuhlewind, K., Trammell, B., and B. Donnet,
"copycat: Testing Differential Treatment of New Transport
Protocols in the Wild (ANRW '17)", July 2017,
<https://irtf.org/anrw/2017/anrw17-final5.pdf>.
[RFC8239] Avramov, L. and J. Rapp, "Data Center Benchmarking
Methodology", RFC 8239, DOI 10.17487/RFC8239, August 2017,
<https://www.rfc-editor.org/info/rfc8239>.
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[TR-471] Morton, A., "Broadband Forum TR-471: IP Layer Capacity
Metrics and Measurement", July 2020,
<https://www.broadband-forum.org/technical/download/TR-
471.pdf>.
[TST009] Morton, R. A., "ETSI GS NFV-TST 009 V3.1.1 (2018-10),
"Network Functions Virtualisation (NFV) Release 3;
Testing; Specification of Networking Benchmarks and
Measurement Methods for NFVI"", October 2018,
<https://www.etsi.org/deliver/etsi_gs/NFV-
TST/001_099/009/03.01.01_60/gs_NFV-TST009v030101p.pdf>.
[udpst] AT&T, "UDP Speed Test Open Broadband project", August
2020, <https://github.com/BroadbandForum <TBD>>.
[Y.1540] Y.1540, I. R., "Internet protocol data communication
service - IP packet transfer and availability performance
parameters", December 2019,
<https://www.itu.int/rec/T-REC-Y.1540-201912-I/en>.
[Y.Sup60] Morton, A., "Recommendation Y.Sup60, (04/20) Interpreting
ITU-T Y.1540 maximum IP-layer capacity measurements", June
2020, <https://www.itu.int/rec/T-REC-Y.Sup60/en>.
Authors' Addresses
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown,, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
Email: acm@research.att.com
Ruediger Geib
Deutsche Telekom
Heinrich Hertz Str. 3-7
Darmstadt 64295
Germany
Phone: +49 6151 5812747
Email: Ruediger.Geib@telekom.de
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Len Ciavattone
AT&T Labs
200 Laurel Avenue South
Middletown,, NJ 07748
USA
Email: lencia@att.com
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