draft-ietf-ippm-model-based-metrics-09.txt   draft-ietf-ippm-model-based-metrics-10.txt 
IP Performance Working Group M. Mathis IP Performance Working Group M. Mathis
Internet-Draft Google, Inc Internet-Draft Google, Inc
Intended status: Experimental A. Morton Intended status: Experimental A. Morton
Expires: August 31, 2017 AT&T Labs Expires: September 1, 2017 AT&T Labs
February 27, 2017 February 28, 2017
Model Based Metrics for Bulk Transport Capacity Model Based Metrics for Bulk Transport Capacity
draft-ietf-ippm-model-based-metrics-09.txt draft-ietf-ippm-model-based-metrics-10.txt
Abstract Abstract
We introduce a new class of Model Based Metrics designed to assess if We introduce a new class of Model Based Metrics designed to assess if
a complete Internet path can be expected to meet a predefined Target a complete Internet path can be expected to meet a predefined Target
Transport Performance by applying a suite of IP diagnostic tests to Transport Performance by applying a suite of IP diagnostic tests to
successive subpaths. The subpath-at-a-time tests can be robustly successive subpaths. The subpath-at-a-time tests can be robustly
applied to critical infrastructure, such as network interconnections applied to critical infrastructure, such as network interconnections
or even individual devices, to accurately detect if any part of the or even individual devices, to accurately detect if any part of the
infrastructure will prevent paths traversing it from meeting the infrastructure will prevent paths traversing it from meeting the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 31, 2017. This Internet-Draft will expire on September 1, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1.1. Version Control 1.1. Version Control
RFC Editor: Please remove this entire subsection prior to RFC Editor: Please remove this entire subsection prior to
publication. publication.
Please send comments about this draft to ippm@ietf.org. See Please send comments about this draft to ippm@ietf.org. See
http://goo.gl/02tkD for more information including: interim drafts, http://goo.gl/02tkD for more information including: interim drafts,
an up to date todo list and information on contributing. an up to date todo list and information on contributing.
Formatted: Mon Feb 27 13:49:06 PST 2017 Formatted: Tue Feb 28 14:24:28 PST 2017
Changes since -09 draft:
o Five last minute editing nits.
Changes since -08 draft: Changes since -08 draft:
o Language, spelling and usage nits. o Language, spelling and usage nits.
o Expanded the abstract describe the models. o Expanded the abstract describe the models.
o Remove superfluous standards like language o Remove superfluous standards like language
o Remove superfluous "future technology" language. o Remove superfluous "future technology" language.
o Interconnects -> network interconnections. o Interconnects -> network interconnections.
o Added more labels to Figure 1. o Added more labels to Figure 1.
o Defined Bulk Transport. o Defined Bulk Transport.
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traffic. traffic.
Section 7 describes packet transfer statistics and methods to test Section 7 describes packet transfer statistics and methods to test
them against the statistical criteria provided by the mathematical them against the statistical criteria provided by the mathematical
models. Since the statistical criteria typically apply to the models. Since the statistical criteria typically apply to the
complete path (a composition of subpaths) [RFC6049], in situ testing complete path (a composition of subpaths) [RFC6049], in situ testing
requires that the end-to-end statistical criteria be apportioned as requires that the end-to-end statistical criteria be apportioned as
separate criteria for each subpath. Subpaths that are expected to be separate criteria for each subpath. Subpaths that are expected to be
bottlenecks would then be permitted to contribute a larger fraction bottlenecks would then be permitted to contribute a larger fraction
of the end-to-end packet loss budget. In compensation, subpaths that of the end-to-end packet loss budget. In compensation, subpaths that
to not exhibit bottlenecks have must be constrained to contribute to not expected exhibit bottlenecks must be constrained to contribute
less packet loss. Thus the statistical criteria for each subpath in less packet loss. Thus the statistical criteria for each subpath in
each test of a TIDS is an apportioned share of the end-to-end each test of a TIDS is an apportioned share of the end-to-end
statistical criteria for the complete path which was determined by statistical criteria for the complete path which was determined by
the mathematical model. the mathematical model.
Section 8 describes the suite of individual tests needed to verify Section 8 describes the suite of individual tests needed to verify
all of required IP delivery properties. A subpath passes if and only all of required IP delivery properties. A subpath passes if and only
if all of the individual IP diagnostic tests pass. Any subpath that if all of the individual IP diagnostic tests pass. Any subpath that
fails any test indicates that some users are likely to fail to attain fails any test indicates that some users are likely to fail to attain
their Target Transport Performance under some conditions. In their Target Transport Performance under some conditions. In
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test paths, even when some subpath has a flaw. test paths, even when some subpath has a flaw.
The definitions in Section 3 are sufficient for most test streams. The definitions in Section 3 are sufficient for most test streams.
We describe the slowstart and standing queue test streams in more We describe the slowstart and standing queue test streams in more
detail. detail.
In conventional measurement practice stochastic processes are used to In conventional measurement practice stochastic processes are used to
eliminate many unintended correlations and sample biases. However eliminate many unintended correlations and sample biases. However
MBM tests are designed to explicitly mimic temporal correlations MBM tests are designed to explicitly mimic temporal correlations
caused by network or protocol elements themselves. Some portions of caused by network or protocol elements themselves. Some portions of
these system, such as traffic arrival (test scheduling) are naturally these systems, such as traffic arrival (test scheduling) are
stochastic. Other behaviors, such as back-to-back packet naturally stochastic. Other behaviors, such as back-to-back packet
transmissions, are dominated by implementation specific deterministic transmissions, are dominated by implementation specific deterministic
effects. Although these behaviors always contain non-deterministic effects. Although these behaviors always contain non-deterministic
elements and might be modeled stochastically, these details typically elements and might be modeled stochastically, these details typically
do not contribute significantly to the overall system behavior. do not contribute significantly to the overall system behavior.
Furthermore, it is known that real protocols are subject to failures Furthermore, it is known that real protocols are subject to failures
caused by network property estimators suffering from bias due to caused by network property estimators suffering from bias due to
correlation in their own traffic. For example TCP's RTT estimator correlation in their own traffic. For example TCP's RTT estimator
used to determine the Retransmit Time Out (RTO), can be fooled by used to determine the Retransmit Time Out (RTO), can be fooled by
periodic cross traffic or start-stop applications. For these reasons periodic cross traffic or start-stop applications. For these reasons
many details of the test streams are specified deterministically. many details of the test streams are specified deterministically.
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loss recovery problematic for the transport protocol. Non-linear, loss recovery problematic for the transport protocol. Non-linear,
erratic or excessive RTT increases suggest poor interactions between erratic or excessive RTT increases suggest poor interactions between
the channel acquisition algorithms and the transport self clock. All the channel acquisition algorithms and the transport self clock. All
of the tests in this section use the same basic scanning algorithm, of the tests in this section use the same basic scanning algorithm,
described here, but score the link or subpath on the basis of how described here, but score the link or subpath on the basis of how
well it avoids each of these problems. well it avoids each of these problems.
Some network technologies rely on virtual queues or other techniques Some network technologies rely on virtual queues or other techniques
to meter traffic without adding any queuing delay, in which case the to meter traffic without adding any queuing delay, in which case the
data rate will vary with the window size all the way up to the onset data rate will vary with the window size all the way up to the onset
of load induced packet loss or ECN CE marks. For theses of load induced packet loss or ECN CE marks. For these technologies,
technologies, the discussion of queuing in Section 6.3 does not the discussion of queuing in Section 6.3 does not apply, but it is
apply, but it is still necessary to confirm that the onset of losses still necessary to confirm that the onset of losses or ECN CE marks
or ECN CE marks be at an appropriate point and progressive. If the be at an appropriate point and progressive. If the network
network bottleneck does not introduce significant queuing delay, bottleneck does not introduce significant queuing delay, modify the
modify the procedure described in Section 6.3 to start scan at a procedure described in Section 6.3 to start scan at a window equal to
window equal to or slightly smaller than the test_window. or slightly smaller than the test_window.
Use the procedure in Section 6.3 to sweep the window across the onset Use the procedure in Section 6.3 to sweep the window across the onset
of queuing and the onset of loss. The tests below all assume that of queuing and the onset of loss. The tests below all assume that
the scan emulates standard additive increase and delayed ACK by the scan emulates standard additive increase and delayed ACK by
incrementing the window by one packet for every 2*target_window_size incrementing the window by one packet for every 2*target_window_size
packets delivered. A scan can typically be divided into three packets delivered. A scan can typically be divided into three
regions: below the onset of queuing, a standing queue, and at or regions: below the onset of queuing, a standing queue, and at or
beyond the onset of loss. beyond the onset of loss.
Below the onset of queuing the RTT is typically fairly constant, and Below the onset of queuing the RTT is typically fairly constant, and
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Some historical half duplex technologies had the property that each Some historical half duplex technologies had the property that each
direction held the channel until it completely drained its queue. direction held the channel until it completely drained its queue.
When a self clocked transport protocol, such as TCP, has data and When a self clocked transport protocol, such as TCP, has data and
ACKs passing in opposite directions through such a link, the behavior ACKs passing in opposite directions through such a link, the behavior
often reverts to stop-and-wait. Each additional packet added to the often reverts to stop-and-wait. Each additional packet added to the
window raises the observed RTT by two packet times, once as it passes window raises the observed RTT by two packet times, once as it passes
through the data path, and once for the additional delay incurred by through the data path, and once for the additional delay incurred by
the ACK waiting on the return path. the ACK waiting on the return path.
The duplex self interference test fails if the RTT rises by more than The duplex self interference test fails if the RTT rises by more than
a fixed bound above the expected queugit staing time computed from a fixed bound above the expected queuing time computed from the
trom the excess window divided by the subpath IP Capacity. This excess window divided by the subpath IP Capacity. This bound must be
bound must be smaller than target_RTT/2 to avoid reverting to stop smaller than target_RTT/2 to avoid reverting to stop and wait
and wait behavior. (e.g. Data packets and ACKs both have to be behavior. (e.g. Data packets and ACKs both have to be released at
released at least twice per RTT.) least twice per RTT.)
8.3. Slowstart tests 8.3. Slowstart tests
These tests mimic slowstart: data is sent at twice the effective These tests mimic slowstart: data is sent at twice the effective
bottleneck rate to exercise the queue at the dominant bottleneck. bottleneck rate to exercise the queue at the dominant bottleneck.
8.3.1. Full Window slowstart test 8.3.1. Full Window slowstart test
This is a capacity test to confirm that slowstart is not likely to This is a capacity test to confirm that slowstart is not likely to
exit prematurely. Send slowstart bursts that are target_window_size exit prematurely. Send slowstart bursts that are target_window_size
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