One document matched: draft-ietf-ippm-rate-problem-02.xml
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<rfc category="info" docName="draft-ietf-ippm-rate-problem-02"
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<front>
<title abbrev="Rate Problem Statement">Rate Measurement Test Protocol
Problem Statement</title>
<author fullname="Al Morton" initials="A." surname="Morton">
<organization>AT&T Labs</organization>
<address>
<postal>
<street>200 Laurel Avenue South</street>
<city>Middletown,</city>
<region>NJ</region>
<code>07748</code>
<country>USA</country>
</postal>
<phone>+1 732 420 1571</phone>
<facsimile>+1 732 368 1192</facsimile>
<email>acmorton@att.com</email>
<uri>http://home.comcast.net/~acmacm/</uri>
</address>
</author>
<date day="1" month="February" year="2013"/>
<abstract>
<t>There is a rate measurement scenario which has wide-spread attention
of Internet access subscribers and seemingly all industry players,
including regulators. This memo presents an access rate-measurement
problem statement for test protocols to measure IP Performance Metrics.
Key test protocol aspects require the ability to control packet size on
the tested path and enable asymmetrical packet size testing in a
controller-responder architecture.</t>
</abstract>
<note title="Requirements Language">
<t>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 <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>There are many possible rate measurement scenarios. This memo
describes one rate measurement problem and presents a rate-measurement
problem statement for test protocols to measure IP Performance Metrics
(IPPM).</t>
<t>The access-rate scenario or use case has wide-spread attention of
Internet access subscribers and seemingly all Internet industry players,
including regulators. This problem is being approached with many
different measurement methods. This memo</t>
</section>
<section title="Purpose and Scope">
<t>The scope and purpose of this memo is to define the measurement
problem statement for test protocols conducting access rate measurement
on production networks. Relevant test protocols include <xref
target="RFC4656"/> and <xref target="RFC5357"/>), but the problem is
stated in a general way so that it can be addressed by any existing test
protocol, such as <xref target="RFC6812"/>. </t>
<t>This memo discusses possibilities for methods of measurement, but
does not specify exact methods which would normally be part of the
solution, not the problem.</t>
<t>We characterize the access rate measurement scenario as follows:<list
style="symbols">
<t>The Access portion of the network is the focus of this problem
statement. The user typically subscribes to a service with
bi-directional access partly described by rates in bits per second.
The rates may be expressed as raw capacity or restricted capacity as
described in <xref target="RFC6703"/>. These are the quantities that
must be measured according to one or more standard metrics for which
methods must also be agreed as a part of the solution.</t>
<t>Referring to the reference path defined in <xref
target="I-D.morton-ippm-lmap-path"/>, possible measurement points
include a Subscriber's host (mp000), the access service demarcation
point (mp100), Intra IP access where a globally routable address is
present (mp150), or the gateway between the measured access network
and other networks (mp190).</t>
<t>Rates at the edge of the network are several orders of magnitude
less than aggregation and core portions.</t>
<t>Asymmetrical ingress and egress rates are prevalent.</t>
<t>Extremely large scale of access services requires low complexity
devices participating at the user end of the path.</t>
</list></t>
<t>Today, the majority of widely deployed access services achieve rates
less than 100 Mbit/s, and this is the order of magnitude for which a
solution is sought now.</t>
<t>This problem statement assumes that the most-likely bottleneck device
or link is adjacent to the remote (user-end) measurement device, or is
within one or two router/switch hops of the remote measurement
device.</t>
<t>Other use cases for rate measurement involve situations where the
packet switching and transport facilities are leased by one operator
from another and the actual capacity available cannot be directly
determined (e.g., from device interface utilization). These scenarios
could include mobile backhaul, Ethernet Service access networks, and/or
extensions of layer 2 or layer 3 networks. The results of rate
measurements in such cases could be employed to select alternate
routing, investigate whether capacity meets some previous agreement,
and/or adapt the rate of traffic sources if a capacity bottleneck is
found via the rate measurement. In the case of aggregated leased
networks, available capacity may also be asymmetric. In these cases, the
tester is assumed to have a sender and receiver location under their
control. We refer to this scenario below as the aggregated leased
network case.</t>
<t>Support of active measurement methods will be addressed here,
consistent with the IPPM working group's traditional charter. Active
measurements require synthetic traffic dedicated to testing, and do not
use user traffic.</t>
<t>The actual path used by traffic may influence the rate measurement
results for some forms of access, as it may differ between user and test
traffic if the test traffic has different characteristics, primarily in
terms of the packets themselves (the Type-P described in <xref
target="RFC2330"/>).</t>
<t>There are several aspects of Type-P where user traffic may be
examined and directed to special treatment that may affect transmission
rates. The possibilities include:</t>
<t><list style="symbols">
<t>Packet length</t>
<t>IP addresses used</t>
<t>Transport protocol used (where TCP packets may be routed
differently from UDP)</t>
<t>Transport Protocol port numbers used</t>
</list></t>
<t>This issue requires further discussion when specific
solutions/methods of measurement are proposed, but for this problem
statement it is sufficient to Identify the problem and indicate that the
solution may require an extremely close emulation of user traffic, in
terms of the factors above.</t>
<t>Although the user may have multiple instances of network access
available to them, the primary problem scope is to measure one form of
access at a time. It is plausible that a solution for the single access
problem will be applicable to simultaneous measurement of multiple
access instances, but discussion of this is beyond the current
scope.</t>
<t>A key consideration is whether active measurements will be conducted
with user traffic present (In-Service testing), or not present
(Out-of-Service testing), such as during pre-service testing or
maintenance that interrupts service temporarily. Out-of-Service testing
includes activities described as "service commissioning", "service
activation", and "planned maintenance". Opportunistic In-Service testing
when there is no user traffic present throughout the test interval is
essentially equivalent to Out-of-Service testing. Both In-Service and
Out-of-Service testing are within the scope of this problem.</t>
<t>It is a non-goal to solve the measurement protocol specification
problem in this memo.</t>
<t>It is a non-goal to standardize methods of measurement in this memo.
However, the problem statement will mandate that support for one or more
categories of rate measurement methods and adequate control features for
the methods in the test protocol.</t>
</section>
<section title="Active Rate Measurement">
<t>This section lists features of active measurement methods needed to
measure access rates in production networks.</t>
<t>Test coordination between source and destination devices through
control messages and other basic capabilities described in the methods
of IPPM RFCs <xref target="RFC2679"/><xref target="RFC2680"/> are taken
as given (these could be listed later, if desired).</t>
<t>Most forms of active testing intrude on user performance to some
degree. One key tenet of IPPM methods is to minimize test traffic
effects on user traffic in the production network. Section 5 of <xref
target="RFC2680"/> lists the problems with high measurement traffic
rates, and the most relevant for rate measurement is the tendency for
measurement traffic to skew the results, followed by the possibility of
introducing congestion on the access link. Obviously, categories of rate
measurement methods that use less active test traffic than others with
similar accuracy SHALL be preferred for In-Service testing.</t>
<t>On the other hand, Out-of-Service tests where the test path shares no
links with In-Service user traffic have none of the congestion or skew
concerns, but these tests must address other practical concerns such as
conducting measurements within a reasonable time from the tester's point
of view. Out-of-Service tests where some part of the test path is shared
with In-Service traffic MUST respect the In-Service constraints.</t>
<t>The **intended metrics to be measured** have strong influence over
the categories of measurement methods required. For example, using the
terminology of <xref target="RFC5136"/>, a it may be possible to measure
a Path Capacity Metric while In-Service if the level of background
(user) traffic can be assessed and included in the reported result.</t>
<t>The measurement *architecture* MAY be either of one-way (e.g., <xref
target="RFC4656"/>) or two-way (e.g., <xref target="RFC5357"/>), but the
scale and complexity aspects of end-user or aggregated access
measurement clearly favor two-way (with low-complexity user-end device
and round-trip results collection, as found in <xref
target="RFC5357"/>). However, the asymmetric rates of many access
services mean that the measurement system MUST be able to evaluate
performance in each direction of transmission. In the two-way
architecture, it is expected that both end devices MUST include the
ability to launch test streams and collect the results of measurements
in both (one-way) directions of transmission (this requirement is
consistent with previous protocol specifications, and it is not a unique
problem for rate measurements).</t>
<t>The following paragraphs describe features for the roles of test
packet SENDER, RECEIVER, and results REPORTER.</t>
<t>SENDER:</t>
<t>Generate streams of test packets with various characteristics as
desired (see Section 4). The SENDER may be located at the user end of
the access path, or may be located elsewhere in the production network,
such as at one end of an aggregated leased network segment.</t>
<t>RECEIVER:</t>
<t>Collect streams of test packets with various characteristics (as
described above), and make the measurements necessary to support rate
measurement at the other end of an end-user access or aggregated leased
network segment.</t>
<t>REPORTER:</t>
<t>Use information from test packets and local processes to measure
delivered packet rates.</t>
</section>
<section title="Measurement Method Categories">
<t>The design of rate measurement methods can be divided into two
phases: test stream design and measurement (SENDER and RECEIVER), and a
follow-up phase for analysis of the measurement to produce results
(REPORTER). The measurement protocol that addresses this problem MUST
only serve the test stream generation and measurement functions.</t>
<t>For the purposes of this problem statement, we categorize the many
possibilities for rate measurement stream generation as follows;<list
style="numbers">
<t>Packet pairs, with fixed intra-pair packet spacing and fixed or
random time intervals between pairs in a test stream.</t>
<t>Multiple streams of packet pairs, with a range of intra-pair
spacing and inter-pair intervals.</t>
<t>One or more packet ensembles in a test stream, using a fixed
ensemble size in packets and one or more fixed intra-ensemble packet
spacings (including zero spacing).</t>
<t>One or more packet chirps, where intra-packet spacing typically
decreases between adjacent packets in the same chirp and each pair
of packets represents a rate for testing purposes.</t>
</list></t>
<t>For all categories, the test protocol MUST support:</t>
<t><list style="numbers">
<t>Variable payload lengths among packet streams</t>
<t>Variable length (in packets) among packet streams or
ensembles</t>
<t>Variable IP header markings among packet streams</t>
<t>Choice of UDP transport and variable port numbers, OR, choice of
TCP transport and variable port numbers for two-way architectures
only, OR BOTH.</t>
<t>Variable number of packets-pairs, ensembles, or streams used in a
test session</t>
</list>The items above are additional variables that the test protocol
MUST be able to identify and control.</t>
<t>The test protocol SHALL support test packet ensemble generation
(category 3), as this appears to minimize the demands on measurement
accuracy. Other stream generation categories are OPTIONAL.</t>
<t>>>>>>></t>
<t>Note: For measurement systems employing TCP Transport protocol, the
ability to generate specific stream characteristics requires a sender
with the ability to establish and prime the connection such that the
desired stream characteristics are allowed. See Mathis' work in progress
for more background <xref
target="I-D.mathis-ippm-model-based-metrics"/>. The general requirement
statements needed to describe an "open-loop" TCP sender require some
additional discussion.</t>
<t>It may also be useful to specify a control for Bulk Transfer Capacity
measurement with fully-specified TCP senders and receivers, as
envisioned in <xref target="RFC3148"/>, but this would be a brute-force
assessment which does not follow the conservative tenets of IPPM
measurement <xref target="RFC2330"/>.</t>
<t>>>>>>></t>
<t>Measurements for each test packet transferred between SENDER and
RECEIVER MUST be compliant with the singleton measurement methods
described in IPPM RFCs <xref target="RFC2679"/><xref target="RFC2680"/>
(these could be listed later, if desired). The time-stamp information or
loss/arrival status for each packet MUST be available for communication
to the protocol entity that collects results.</t>
</section>
<section title="Test Protocol Control & Generation Requirements">
<t>Essentially, the test protocol MUST support the measurement features
described in the sections above. This requires:</t>
<t><list style="numbers">
<t>Communicating all test variables to the Sender and Receiver</t>
<t>Results collection in a one-way architecture</t>
<t>Remote device control for both one-way and two-way
architectures</t>
<t>Asymmetric and/or pseudo-one-way test capability in a two-way
measurement architecture</t>
</list></t>
<t>The ability to control packet size on the tested path and enable
asymmetrical packet size testing in a two-way architecture are
REQUIRED.</t>
<t>The test protocol SHOULD enable measurement of the <xref
target="RFC5136"/> Capacity metric, either Out-of-Service, In-Service,
or both. Other <xref target="RFC5136"/> metrics are OPTIONAL.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>The security considerations that apply to any active measurement of
live networks are relevant here as well. See <xref target="RFC4656"/>
and <xref target="RFC5357"/>.</t>
<t>There may be a serious issue if a proprietary Service Level Agreement
involved with the access network segment provider were somehow leaked in
the process of rate measurement. To address this, test protocols SHOULD
NOT convey this information in a way that could be discovered by
unauthorized parties.</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This memo makes no requests of IANA.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>Dave McDysan provided comments and text for the aggregated leased use
case. Yaakov Stein suggested many considerations to address, including
the In-Service vs. Out-of-Service distinction and its implication on
test traffic limits and protocols. Bill Cerveny and Marcelo Bagnulo have
contributed insightful, clarifying comments that made this a better
draft.</t>
</section>
<section title="Appendix">
<t>This Appendix was proposed to briefly summarize previous rate
measurement experience. (There is a large body of research on rate
measurement, so there is a question of what to include and what to omit.
Suggestions are welcome.)</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include='reference.RFC.2330'?>
<?rfc include='reference.RFC.2679'?>
<?rfc include='reference.RFC.2680'?>
<?rfc include='reference.RFC.4656'?>
<?rfc include='reference.RFC.5357'?>
<?rfc include='reference.RFC.1305'?>
<?rfc include='reference.RFC.5618'?>
<?rfc include='reference.RFC.5938'?>
<?rfc include='reference.RFC.6038'?>
<?rfc include='reference.RFC.6703'?>
</references>
<references title="Informative References">
<?rfc include='reference.RFC.3148'?>
<?rfc include='reference.RFC.6812'?>
<?rfc include='reference.RFC.5136'?>
<?rfc include='reference.I-D.morton-ippm-lmap-path'?>
<?rfc include='reference.I-D.mathis-ippm-model-based-metrics'?>
</references>
</back>
</rfc>
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