draft-ietf-ippm-loss-episode-metrics-02.txt   draft-ietf-ippm-loss-episode-metrics-03.txt 
Network Working Group N. Duffield Network Working Group N. Duffield
Internet-Draft AT&T Labs-Research Internet-Draft AT&T Labs-Research
Intended status: Standards Track A. Morton Intended status: Standards Track A. Morton
Expires: December 22, 2011 AT&T Labs Expires: April 29, 2012 AT&T Labs
J. Sommers J. Sommers
Colgate University Colgate University
June 20, 2011 October 27, 2011
Loss Episode Metrics for IPPM Loss Episode Metrics for IPPM
draft-ietf-ippm-loss-episode-metrics-02 draft-ietf-ippm-loss-episode-metrics-03
Abstract Abstract
The IETF has developed a one way packet loss metric that measures the The IETF has developed a one way packet loss metric that measures the
loss rate on a Poisson probe stream between two hosts. However, the loss rate on a Poisson probe stream between two hosts. However, the
impact of packet loss on applications is in general sensitive not impact of packet loss on applications is in general sensitive not
just to the average loss rate, but also to the way in which packet just to the average loss rate, but also to the way in which packet
losses are distributed in loss episodes (i.e., maximal sets of losses are distributed in loss episodes (i.e., maximal sets of
consecutively lost probe packets). This draft defines one-way packet consecutively lost probe packets). This draft defines one-way packet
loss episode metrics, specifically the frequency and average duration loss episode metrics, specifically the frequency and average duration
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This Internet-Draft will expire on December 22, 2011. This Internet-Draft will expire on April 29, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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3.8. Reporting the Metric . . . . . . . . . . . . . . . . . . . 11 3.8. Reporting the Metric . . . . . . . . . . . . . . . . . . . 11
4. An active probing methodology for Bi-Packet Loss . . . . . . . 11 4. An active probing methodology for Bi-Packet Loss . . . . . . . 11
4.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Metric Name . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 11 4.2. Metric Parameters . . . . . . . . . . . . . . . . . . . . 11
4.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 12 4.3. Metric Units . . . . . . . . . . . . . . . . . . . . . . . 12
4.4. Metric Definition . . . . . . . . . . . . . . . . . . . . 12 4.4. Metric Definition . . . . . . . . . . . . . . . . . . . . 12
4.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 12 4.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . . 12
4.6. Methodologies . . . . . . . . . . . . . . . . . . . . . . 12 4.6. Methodologies . . . . . . . . . . . . . . . . . . . . . . 12
4.7. Errors and Uncertainties . . . . . . . . . . . . . . . . . 13 4.7. Errors and Uncertainties . . . . . . . . . . . . . . . . . 13
4.8. Reporting the Metric . . . . . . . . . . . . . . . . . . . 13 4.8. Reporting the Metric . . . . . . . . . . . . . . . . . . . 13
5. Loss Epsiode Proto-Metrics . . . . . . . . . . . . . . . . . . 13 5. Loss Episode Proto-Metrics . . . . . . . . . . . . . . . . . . 13
5.1. Loss-Pair-Counts . . . . . . . . . . . . . . . . . . . . . 13 5.1. Loss-Pair-Counts . . . . . . . . . . . . . . . . . . . . . 13
5.2. Bi-Packet-Loss-Ratio . . . . . . . . . . . . . . . . . . . 14 5.2. Bi-Packet-Loss-Ratio . . . . . . . . . . . . . . . . . . . 14
5.3. Bi-Packet-Loss-Episode-Duration-Number . . . . . . . . . . 14 5.3. Bi-Packet-Loss-Episode-Duration-Number . . . . . . . . . . 14
5.4. Bi-Packet-Loss-Episode-Frequency-Number . . . . . . . . . 14 5.4. Bi-Packet-Loss-Episode-Frequency-Number . . . . . . . . . 14
6. Loss Episode Metrics derived from Bi-Packet Loss Probing . . . 14 6. Loss Episode Metrics derived from Bi-Packet Loss Probing . . . 14
6.1. Geometric Stream: Loss Ratio . . . . . . . . . . . . . . . 15 6.1. Geometric Stream: Loss Ratio . . . . . . . . . . . . . . . 15
6.1.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 15 6.1.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 15
6.1.2. Metric Parameters . . . . . . . . . . . . . . . . . . 15 6.1.2. Metric Parameters . . . . . . . . . . . . . . . . . . 15
6.1.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 16 6.1.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 16
6.1.4. Metric Definition . . . . . . . . . . . . . . . . . . 16 6.1.4. Metric Definition . . . . . . . . . . . . . . . . . . 16
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6.2.4. Metric Definition . . . . . . . . . . . . . . . . . . 17 6.2.4. Metric Definition . . . . . . . . . . . . . . . . . . 17
6.2.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 17 6.2.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 17
6.2.6. Methodologies . . . . . . . . . . . . . . . . . . . . 17 6.2.6. Methodologies . . . . . . . . . . . . . . . . . . . . 17
6.2.7. Errors and Uncertainties . . . . . . . . . . . . . . . 17 6.2.7. Errors and Uncertainties . . . . . . . . . . . . . . . 17
6.2.8. Reporting the Metric . . . . . . . . . . . . . . . . . 18 6.2.8. Reporting the Metric . . . . . . . . . . . . . . . . . 18
6.3. Geometric Stream: Loss Episode Frequency . . . . . . . . . 18 6.3. Geometric Stream: Loss Episode Frequency . . . . . . . . . 18
6.3.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 18 6.3.1. Metric Name . . . . . . . . . . . . . . . . . . . . . 18
6.3.2. Metric Parameters . . . . . . . . . . . . . . . . . . 18 6.3.2. Metric Parameters . . . . . . . . . . . . . . . . . . 18
6.3.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 18 6.3.3. Metric Units . . . . . . . . . . . . . . . . . . . . . 18
6.3.4. Metric Definition . . . . . . . . . . . . . . . . . . 18 6.3.4. Metric Definition . . . . . . . . . . . . . . . . . . 18
6.3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 18 6.3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . 19
6.3.6. Methodologies . . . . . . . . . . . . . . . . . . . . 19 6.3.6. Methodologies . . . . . . . . . . . . . . . . . . . . 19
6.3.7. Errors and Uncertainties . . . . . . . . . . . . . . . 19 6.3.7. Errors and Uncertainties . . . . . . . . . . . . . . . 19
6.3.8. Reporting the Metric . . . . . . . . . . . . . . . . . 19 6.3.8. Reporting the Metric . . . . . . . . . . . . . . . . . 19
7. Applicability of Loss Episode Metrics . . . . . . . . . . . . 19 7. Applicability of Loss Episode Metrics . . . . . . . . . . . . 19
7.1. Relation to Gilbert Model . . . . . . . . . . . . . . . . 19 7.1. Relation to Gilbert Model . . . . . . . . . . . . . . . . 19
8. IPR Considerations . . . . . . . . . . . . . . . . . . . . . . 20 8. IPR Considerations . . . . . . . . . . . . . . . . . . . . . . 20
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
12.1. Normative References . . . . . . . . . . . . . . . . . . . 21 12.1. Normative References . . . . . . . . . . . . . . . . . . . 21
12.2. Informative References . . . . . . . . . . . . . . . . . . 21 12.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction 1. Introduction
1.1. Background and Motivation 1.1. Background and Motivation
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characterizing the statistics of the patterns of packet loss within characterizing the statistics of the patterns of packet loss within
the stream of probes. This is useful information in understanding the stream of probes. This is useful information in understanding
the effect of packet losses on application performance, since the effect of packet losses on application performance, since
different applications can have different sensitivities to patterns different applications can have different sensitivities to patterns
of loss, being sensitive not only to the long term average loss rate, of loss, being sensitive not only to the long term average loss rate,
but how losses are distributed in time. As an example: MPEG video but how losses are distributed in time. As an example: MPEG video
traffic may be sensitive to loss involving the I-frame in a group of traffic may be sensitive to loss involving the I-frame in a group of
pictures, but further losses within an episode of sufficiently short pictures, but further losses within an episode of sufficiently short
duration have no further impact; the damage is already done. duration have no further impact; the damage is already done.
The loss episode metrics presented here represent have the following The loss episode metrics presented here have the following useful
useful properties: properties:
1. the metrics are empirical and do not depend on an underlying 1. the metrics are empirical and do not depend on an underlying
model; e.g., the loss process is not assumed to be Markovian. On model; e.g., the loss process is not assumed to be Markovian. On
the other hand, it turns out that the metrics of this memo can be the other hand, it turns out that the metrics of this memo can be
related to the special case of the Gilbert Model parameters; see related to the special case of the Gilbert Model parameters; see
Section 7. Section 7.
2. the metric units can be directly compared with applications or 2. the metric units can be directly compared with applications or
user requirements or tolerance for network loss performance, in user requirements or tolerance for network loss performance, in
the frequency and duration of loss episodes, as well as the usual the frequency and duration of loss episodes, as well as the usual
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o P, the specification of the packet type, over and above the source o P, the specification of the packet type, over and above the source
and destination addresses and destination addresses
2.3. Metric Units 2.3. Metric Units
A Loss Pair is pair (l1, l2) where each of l1 and l2 is a binary A Loss Pair is pair (l1, l2) where each of l1 and l2 is a binary
value 0 or 1, where 0 signifies successful transmission of a packet value 0 or 1, where 0 signifies successful transmission of a packet
and 1 signifies loss. and 1 signifies loss.
The metric unit for Type-P-One-way-Bi-Packet-Loss takes is a Loss The metric unit of Type-P-One-way-Bi-Packet-Loss is a Loss Pair.
Pair
2.4. Metric Definition 2.4. Metric Definition
1. "The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, 1. "The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1,
T2, F, P) is (1,1)" means that Src sent the first bit of a Type-P T2, F, P) is (1,1)" means that Src sent the first bit of a Type-P
packet to Dst at wire-time T1 and the first bit of a Type-P packet to Dst at wire-time T1 and the first bit of a Type-P
packet to Dst a wire-time T2>T1, and that neither packet was packet to Dst a wire-time T2>T1, and that neither packet was
received at Dst. received at Dst.
2. The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1, 2. The Type-P-One-way-Bi-Packet-Loss with parameters (Src, Dst, T1,
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The metric definition of Type-P-One-way-Bi-Packet-Loss-Stream is The metric definition of Type-P-One-way-Bi-Packet-Loss-Stream is
sufficiently general to describe the case where packets are sampled sufficiently general to describe the case where packets are sampled
from a pre-existing stream. This is useful in the case that there is from a pre-existing stream. This is useful in the case that there is
a general purpose measurement stream setup between two hosts, and we a general purpose measurement stream setup between two hosts, and we
which to select a substream from it for the purposes of loss episode which to select a substream from it for the purposes of loss episode
measurement. In the next section we specialize this somewhat to more measurement. In the next section we specialize this somewhat to more
concretely describe a purpose built packet stream for loss episode concretely describe a purpose built packet stream for loss episode
measurement. measurement.
3.6. Methodologies 3.6. Methodologies
The methodologies related to the Type-P-One-way-Packet-Loss metric in
Section 2.6 of [RFC2680] are similar for the Type-P-One-way-Bi-
Packet-Loss-Stream metric described above. In particular, the
methodologies described in RFC 2680 apply to both packets of each
pair.
3.7. Errors and Uncertainties 3.7. Errors and Uncertainties
Sources of error for the Type-P-One-way-Packet-Loss metric in Section
2.7 of [RFC2680] apply to each packet of each pair for the Type-P-
One-way-Bi-Packet-Loss-Stream metric.
3.8. Reporting the Metric 3.8. Reporting the Metric
Refer to Section 2.8 of [RFC2680].
4. An active probing methodology for Bi-Packet Loss 4. An active probing methodology for Bi-Packet Loss
This section specializes the preceding section for an active probing This section specializes the preceding section for an active probing
methodology. The basic idea is a follows. We set up a sequence of methodology. The basic idea is a follows. We set up a sequence of
evenly spaced times T1 < T2 < ... < Tn. Each time Ti is potentially evenly spaced times T1 < T2 < ... < Tn. Each time Ti is potentially
the first packet time for a packet pair measurement. We make an the first packet time for a packet pair measurement. We make an
independent random decision at each time, whether to initiate such a independent random decision at each time, whether to initiate such a
measurement. Hence the interval count between successive times at measurement. Hence the interval count between successive times at
which a pair is initiated follows a geometric distribution. We also which a pair is initiated follows a geometric distribution. We also
specify that the spacing between successive times Ti is the same as specify that the spacing between successive times Ti is the same as
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schedule. Note that the choice of time spacing directly affects the schedule. Note that the choice of time spacing directly affects the
ability of the host CPU to meet the required schedule (e.g., consider ability of the host CPU to meet the required schedule (e.g., consider
a 100 microsecond spacing versus a 100 millisecond spacing). a 100 microsecond spacing versus a 100 millisecond spacing).
For other considerations, refer to Section 3.7. [RFC2680]. For other considerations, refer to Section 3.7. [RFC2680].
4.8. Reporting the Metric 4.8. Reporting the Metric
Refer to Section 3.8. of [RFC2680]. Refer to Section 3.8. of [RFC2680].
5. Loss Epsiode Proto-Metrics 5. Loss Episode Proto-Metrics
This section describes four generic proto-metric quantities This section describes four generic proto-metric quantities
associated with an arbitrary set of loss pairs. These are the Loss- associated with an arbitrary set of loss pairs. These are the Loss-
Pair-Counts, Bi-Packet-Loss-Ratio, Bi-Packet-Loss-Episode-Duration- Pair-Counts, Bi-Packet-Loss-Ratio, Bi-Packet-Loss-Episode-Duration-
Number, Bi-Packet-Loss-Episode-Frequency-Number. Specific loss Number, Bi-Packet-Loss-Episode-Frequency-Number. Specific loss
episode metrics can then be constructed when these proto metrics take episode metrics can then be constructed when these proto metrics take
as their input, sets of loss pairs samples generated by the Type-P- as their input, sets of loss pairs samples generated by the Type-P-
One-way-Bi-Packet-Loss-Stream and Type-P-One-way-Bi-Packet-Loss- One-way-Bi-Packet-Loss-Stream and Type-P-One-way-Bi-Packet-Loss-
Geometric Stream. The second of these is described in Section 4. It Geometric Stream. The second of these is described in Section 4. It
is not expected that these proto-metrics would be reported is not expected that these proto-metrics would be reported
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and destination address and destination address
6.3.3. Metric Units 6.3.3. Metric Units
A positive number. A positive number.
6.3.4. Metric Definition 6.3.4. Metric Definition
The result obtained by computing the Bi-Packet-Loss-Episode-Frequency The result obtained by computing the Bi-Packet-Loss-Episode-Frequency
over a Type-P-One-way-Bi-Packet-Loss-Geometric-Stream sample with the over a Type-P-One-way-Bi-Packet-Loss-Geometric-Stream sample with the
metric parameters, then dividing he result by the launch spacing metric parameters, then dividing the result by the launch spacing
parameter d. parameter d.
6.3.5. Discussion 6.3.5. Discussion
Type-P-One-way-Bi-Packet-Loss-Geometric-Stream-Episode-Frequency Type-P-One-way-Bi-Packet-Loss-Geometric-Stream-Episode-Frequency
estimates the average frequency per unit time with which loss estimates the average frequency per unit time with which loss
episodes start (or finish). The frequency relative to the count of episodes start (or finish). The frequency relative to the count of
potential probe launches is obtained by multiplying the metric value potential probe launches is obtained by multiplying the metric value
by the packet launch spacing parameter d. by the packet launch spacing parameter d.
6.3.6. Methodologies 6.3.6. Methodologies
Refer toSection 4.6 Refer to Section 4.6
6.3.7. Errors and Uncertainties 6.3.7. Errors and Uncertainties
Because Type-P-One-way-Bi-Packet-Loss-Geometric-Stream is sampled in Because Type-P-One-way-Bi-Packet-Loss-Geometric-Stream is sampled in
general (when the launch probability q <1) the metrics described in general (when the launch probability q <1) the metrics described in
this Section can be regarded as statistical estimators of the this Section can be regarded as statistical estimators of the
corresponding idealized version corresponding to q = 1. Estimation corresponding idealized version corresponding to q = 1. Estimation
variance as it applies to Type-P-One-way-Bi-Packet-Loss-Geometric- variance as it applies to Type-P-One-way-Bi-Packet-Loss-Geometric-
Stream-Episode-Frequency is described in [SBDR08]. Stream-Episode-Frequency is described in [SBDR08].
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r = P(b|g)/(P(b|g) + P(g|b)) and m/d = 1/P(g|b). r = P(b|g)/(P(b|g) + P(g|b)) and m/d = 1/P(g|b).
These relationships can be inverted in order to recover the Gilbert These relationships can be inverted in order to recover the Gilbert
model parameters: model parameters:
P(g|b) = d/m and P(b|g)=d/m/(1/r - 1) P(g|b) = d/m and P(b|g)=d/m/(1/r - 1)
8. IPR Considerations 8. IPR Considerations
IPR disclosures concerning some of the material covered in this draft An IPR disclosure concerning some of the material covered in this
has been made to the IETF: see https://datatracker.ietf.org/ipr/1009/ draft has been made to the IETF: see
, https://datatracker.ietf.org/ipr/1010/ , and https://datatracker.ietf.org/ipr/1354/
https://datatracker.ietf.org/ipr/1126/
9. Security Considerations 9. Security Considerations
Conducting Internet measurements raises both security and privacy Conducting Internet measurements raises both security and privacy
concerns. This memo does not specify an implementation of the concerns. This memo does not specify an implementation of the
metrics, so it does not directly affect the security of the Internet metrics, so it does not directly affect the security of the Internet
nor of applications which run on the Internet. nor of applications which run on the Internet.
However,implementations of these metrics must be mindful of security However,implementations of these metrics must be mindful of security
and privacy concerns. and privacy concerns.
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artificially lowered. Therefore, the measurement methodologies artificially lowered. Therefore, the measurement methodologies
SHOULD include appropriate techniques to reduce the probability that SHOULD include appropriate techniques to reduce the probability that
measurement traffic can be distinguished from "normal" traffic. measurement traffic can be distinguished from "normal" traffic.
Authentication techniques, such as digital signatures, may be used Authentication techniques, such as digital signatures, may be used
where appropriate to guard against injected traffic attacks. The where appropriate to guard against injected traffic attacks. The
privacy concerns of network measurement are limited by the active privacy concerns of network measurement are limited by the active
measurements described in this memo: they involve no release of user measurements described in this memo: they involve no release of user
data. data.
10. IANA Considerations 10. IANA Considerations
11. Acknowledgements 11. Acknowledgements
12. References 12. References
12.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999. Packet Loss Metric for IPPM", RFC 2680, September 1999.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, Metric for IP Performance Metrics (IPPM)", RFC 3393,
November 2002. November 2002.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611, Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003. November 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3432] Raisanen, V., Grotefeld, G., and A. Morton, "Network
performance measurement with periodic streams", RFC 3432,
November 2002.
12.2. Informative References 12.2. Informative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis, [RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, "Framework for IP Performance Metrics", RFC 2330,
May 1998. May 1998.
[RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample [RFC3357] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample
Metrics", RFC 3357, August 2002. Metrics", RFC 3357, August 2002.
[SBDR08] IEEE/ACM Transactions on Networking, 16(2): 307-320, "A [SBDR08] IEEE/ACM Transactions on Networking, 16(2): 307-320, "A
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