draft-ietf-tsvwg-rtcweb-qos-10.txt   draft-ietf-tsvwg-rtcweb-qos-11.txt 
Network Working Group S. Dhesikan Network Working Group P. Jones
Internet-Draft C. Jennings Internet-Draft S. Dhesikan
Intended status: Standards Track Cisco Systems Intended status: Standards Track C. Jennings
Expires: July 27, 2016 D. Druta, Ed. Expires: July 30, 2016 Cisco Systems
D. Druta
AT&T AT&T
P. Jones January 27, 2016
Cisco Systems
January 24, 2016
DSCP and other packet markings for WebRTC QoS DSCP and other packet markings for WebRTC QoS
draft-ietf-tsvwg-rtcweb-qos-10 draft-ietf-tsvwg-rtcweb-qos-11
Abstract Abstract
Many networks, such as service provider and enterprise networks, can Many networks, such as service provider and enterprise networks, can
provide treatment for individual packets based on Differentiated provide different forwarding treatments for individual packets based
Services Code Point (DSCP) values on a per-hop basis. This document on Differentiated Services Code Point (DSCP) values on a per-hop
provides the recommended DSCP values for web browsers to use for basis. This document provides the recommended DSCP values for web
various classes of WebRTC traffic. browsers to use for various classes of WebRTC traffic.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 July 27, 2016. This Internet-Draft will expire on July 30, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the Copyright (c) 2016 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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9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. Dedication . . . . . . . . . . . . . . . . . . . . . . . . . 7 10. Dedication . . . . . . . . . . . . . . . . . . . . . . . . . 7
11. Document History . . . . . . . . . . . . . . . . . . . . . . 8 11. Document History . . . . . . . . . . . . . . . . . . . . . . 8
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
12.1. Normative References . . . . . . . . . . . . . . . . . . 8 12.1. Normative References . . . . . . . . . . . . . . . . . . 8
12.2. Informative References . . . . . . . . . . . . . . . . . 9 12.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
Differentiated Services Code Points (DSCP) [RFC2474] packet marking Differentiated Services Code Point (DSCP) [RFC2474] packet marking
can help provide QoS in some environments. This specification can help provide QoS in some environments. This specification
proposes how WebRTC applications can mark packets, but does not provides default packet marking for browsers that support WebRTC
contradict or redefine any advice from previous IETF RFCs. Rather, applications, but does not change any advice or requirements in
it merely provides a simple set of recommendations for implementers existing IETF RFCs. The contents of this specification are intended
based on the previous RFCs. to be a simple set of implementation recommendations based on the
previous RFCs.
There are many use cases where such marking does not help, but it There are many use cases where such marking does not help, but it
seldom makes things worse if packets are marked appropriately. As seldom makes things worse if packets are marked appropriately. There
one example of where it does not help, if too many packets, say all are some environments where DSCP markings frequently help, though.
audio or all audio and video, are marked for a given network
condition then it can prevent desirable results. Either too much
other traffic will be starved, or there is not enough capacity for
the preferentially marked packets (i.e., audio and/or video).
There are some environments where DSCP markings frequently help.
These include: These include:
1. Private, wide-area networks. 1. Private, wide-area networks.
2. Residential Networks. If the congested link is the broadband 2. Residential Networks. If the congested link is the broadband
uplink in a cable or DSL scenario, often residential routers/NAT uplink in a cable or DSL scenario, often residential routers/NAT
support preferential treatment based on DSCP. support preferential treatment based on DSCP.
3. Wireless Networks. If the congested link is a local wireless 3. Wireless Networks. If the congested link is a local wireless
network, marking may help. network, marking may help.
Traditionally DSCP values have been thought of as being site Traditionally, DSCP values have been thought of as being site
specific, with each site selecting its own code points for specific, with each site selecting its own code points for
controlling per-hop-behavior to influence the QoS for transport-layer controlling per-hop-behavior to influence the QoS for transport-layer
flows. However in the WebRTC use cases, the browsers need to set flows. However in the WebRTC use cases, the browsers need to set
them to something when there is no site specific information. In them to something when there is no site specific information. In
this document, "browsers" is used synonymously with "Interactive User this document, "browsers" is used synonymously with "Interactive User
Agent" as defined in the HTML specification, Agent" as defined in the HTML specification,
[W3C.REC-html5-20141028]. This document describes a subset of DSCP [W3C.REC-html5-20141028]. This document describes a subset of DSCP
code point values drawn from existing RFCs and common usage for use code point values drawn from existing RFCs and common usage for use
with WebRTC applications. These code points are solely defaults. with WebRTC applications. These code points are solely defaults.
This specification defines some inputs that the browser in a WebRTC This specification defines inputs that are provided by the WebRTC
application can consider to aid in determining how to set the various application hosted in the browser that aid the browser in determining
packet markings and defines the mapping from abstract QoS policies how to set the various packet markings. The specification also
(flow type, priority level) to those packet markings. defines the mapping from abstract QoS policies (flow type, priority
level) to those packet markings.
2. Relation to Other Standards 2. Relation to Other Standards
This document exists as a complement to [RFC7657], which describes This document is a complement to [RFC7657], which describes the
the interaction between DSCP and real-time communications. It covers interaction between DSCP and real-time communications. That RFC
the implications of using various DSCP values, particularly focusing covers the implications of using various DSCP values, particularly
on Real-time Transport Protocol (RTP) [RFC3550] streams that are focusing on Real-time Transport Protocol (RTP) [RFC3550] streams that
multiplexed onto a single transport-layer flow. are multiplexed onto a single transport-layer flow.
There are a number of guidelines specified in [RFC7657] that should There are a number of guidelines specified in [RFC7657] that apply to
be followed when marking traffic sent by WebRTC applications, as it marking traffic sent by WebRTC applications, as it is common for
is common for multiple RTP streams to be multiplexed on the same multiple RTP streams to be multiplexed on the same transport-layer
transport-layer flow. Generally, the RTP streams would be marked flow. Generally, the RTP streams would be marked with a value as
with a value as appropriate from Table 1. A WebRTC application might appropriate from Table 1. A WebRTC application might also multiplex
also multiplex data channel [I-D.ietf-rtcweb-data-channel] traffic data channel [I-D.ietf-rtcweb-data-channel] traffic over the same
over the same 5-tuple as RTP streams, which would also be marked as 5-tuple as RTP streams, which would also be marked as per that table.
per that table. The guidance in [RFC7657] says that all data channel The guidance in [RFC7657] says that all data channel traffic would be
traffic would be marked with a single value that is typically marked with a single value that is typically different than the
different than the value(s) used for RTP streams multiplexed with the value(s) used for RTP streams multiplexed with the data channel
data channel traffic over the same 5-tuple, assuming RTP streams are traffic over the same 5-tuple, assuming RTP streams are marked with a
marked with a value other than default forwarding (DF). This is value other than default forwarding (DF). This is expanded upon
expanded upon further in the next section. further in the next section.
This specification does not change or override the advice in any This specification does not change or override the advice in any
other standards about setting packet markings. It simply selects a other standards about setting packet markings. Rather, it simply
subset of DSCP values that is relevant in the WebRTC context. This selects a subset of DSCP values that is relevant in the WebRTC
document also specifies the inputs that are needed by the browser to context.
provide to the media engine.
The DSCP value set by the endpoint is not always trusted by the The DSCP value set by the endpoint is not trusted by the network. In
network. Therefore, the DSCP value may be remarked at any place in addition, the DSCP value may be remarked at any place in the network
the network for a variety of reasons to any other DSCP value, for a variety of reasons to any other DSCP value, including default
including default forwarding (DF) value to provide basic best effort forwarding (DF) value to provide basic best effort service. The
service. The mitigation for such action is through an authorization mitigation for such action is through an authorization mechanism.
mechanism. Such authorization mechanism is outside the scope of this Such authorization mechanism is outside the scope of this document.
document. There is benefit in marking traffic even if it only
benefits the first few hops. There is benefit in marking traffic even if it only benefits the
first few hops.
3. Terminology 3. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
4. Inputs 4. Inputs
WebRTC entities transmit and receive two types of flows of WebRTC applications transmit and receive two types of flows of
significance to this document: significance to this document:
o media flows which are RTP streams [I-D.ietf-rtcweb-rtp-usage] o media flows which are RTP streams [I-D.ietf-rtcweb-rtp-usage]
o data flows which are data channels [I-D.ietf-rtcweb-data-channel] o data flows which are data channels [I-D.ietf-rtcweb-data-channel]
Each of the RTP streams and distinct data channels consists of all of Each of the RTP streams and distinct data channels consists of all of
the packets associated with an independent media entity and are not the packets associated with an independent media entity, so an RTP
always equivalent to a transport-layer flow defined by a 5-tuple stream or distinct data channel is not always equivalent to a
(source address, destination address, source port, destination port, transport-layer flow defined by a 5-tuple (source address,
and protocol). There may be multiple RTP streams and data channels destination address, source port, destination port, and protocol).
multiplexed over the same 5-tuple, with each having a different level There may be multiple RTP streams and data channels multiplexed over
of importance to the application and, therefore, potentially marked the same 5-tuple, with each having a different level of importance to
using different DSCP values than another RTP stream or data channel the application and, therefore, potentially marked using different
within the same transport-layer flow. (Note that there are DSCP values than another RTP stream or data channel within the same
restrictions with respect to marking different data channels carried transport-layer flow. (Note that there are restrictions with respect
within the same SCTP association as outlined in Section 5.) to marking different data channels carried within the same SCTP
association as outlined in Section 5.)
The following are the inputs that the browser provides to the media The following are the inputs provided by the WebRTC application to
engine: the browser:
o Flow Type: The browser provides this input as it knows if the flow o Flow Type: The browser provides this input as it knows if the flow
is audio, interactive video with or without audio, non-interactive is audio, interactive video with or without audio, non-interactive
video with or without audio, or data. video with or without audio, or data.
o Application Priority: Another input is the relative importance of o Application Priority: Another input is the relative importance of
an RTP stream or data channel. Many applications have multiple an RTP stream or data channel. Many applications have multiple
flows of the same Flow Type and often some flows are more flows of the same Flow Type and often some flows are more
important than others. For example, in a video conference where important than others. For example, in a video conference where
there are usually audio and video flows, the audio flow may be there are usually audio and video flows, the audio flow may be
more important than the video flow. JavaScript applications can more important than the video flow. JavaScript applications can
tell the browser whether a particular flow is high, medium, low or tell the browser whether a particular flow is high, medium, low or
very low importance to the application. very low importance to the application.
[I-D.ietf-rtcweb-transports] defines in more detail what an [I-D.ietf-rtcweb-transports] defines in more detail what an
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o Application Priority: Another input is the relative importance of o Application Priority: Another input is the relative importance of
an RTP stream or data channel. Many applications have multiple an RTP stream or data channel. Many applications have multiple
flows of the same Flow Type and often some flows are more flows of the same Flow Type and often some flows are more
important than others. For example, in a video conference where important than others. For example, in a video conference where
there are usually audio and video flows, the audio flow may be there are usually audio and video flows, the audio flow may be
more important than the video flow. JavaScript applications can more important than the video flow. JavaScript applications can
tell the browser whether a particular flow is high, medium, low or tell the browser whether a particular flow is high, medium, low or
very low importance to the application. very low importance to the application.
[I-D.ietf-rtcweb-transports] defines in more detail what an [I-D.ietf-rtcweb-transports] defines in more detail what an
individual flow is within the WebRTC context. individual flow is within the WebRTC context and priorities for media
and data flows.
5. DSCP Mappings 5. DSCP Mappings
The DSCP markings for each flow type of interest to WebRTC given the The DSCP values for each flow type of interest to WebRTC based on
application priority is shown in the following table. The DSCP application priority are shown in the following table. These values
values for each flow type listed are a reasonable subset of code are based on the framework and recommended values in [RFC4594]. A
point values taken from [RFC4594]. A web browser SHOULD use these web browser SHOULD use these values to mark the appropriate media
values to mark the appropriate media packets. More information on EF packets. More information on EF can be found in [RFC3246]. More
can be found in [RFC3246]. More information on AF can be found in information on AF can be found in [RFC2597]. DF is default
[RFC2597]. DF is default forwarding which provides the basic best forwarding which provides the basic best effort service [RFC2474].
effort service.
+------------------------+-------+------+-------------+-------------+ +------------------------+-------+------+-------------+-------------+
| Flow Type | Very | Low | Medium | High | | Flow Type | Very | Low | Medium | High |
| | Low | | | | | | Low | | | |
+------------------------+-------+------+-------------+-------------+ +------------------------+-------+------+-------------+-------------+
| Audio | CS1 | DF | EF (46) | EF (46) | | Audio | CS1 | DF | EF (46) | EF (46) |
| | (8) | (0) | | | | | (8) | (0) | | |
| | | | | | | | | | | |
| Interactive Video with | CS1 | DF | AF42, AF43 | AF41, AF42 | | Interactive Video with | CS1 | DF | AF42, AF43 | AF41, AF42 |
| or without audio | (8) | (0) | (36, 38) | (34, 36) | | or without audio | (8) | (0) | (36, 38) | (34, 36) |
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within the application. It is an input that the browser receives to within the application. It is an input that the browser receives to
assist it in selecting the DSCP value. Application priority does not assist it in selecting the DSCP value. Application priority does not
refer to priority in the network transport. refer to priority in the network transport.
The above table assumes that packets marked with CS1 are treated as The above table assumes that packets marked with CS1 are treated as
"less than best effort". However, the treatment of CS1 is "less than best effort". However, the treatment of CS1 is
implementation dependent. If an implementation treats CS1 as other implementation dependent. If an implementation treats CS1 as other
than "less than best effort", then the actual priority (or, more than "less than best effort", then the actual priority (or, more
precisely, the per-hop-behavior) of the packets may be changed from precisely, the per-hop-behavior) of the packets may be changed from
what is intended. It is common for CS1 to be treated the same as DF, what is intended. It is common for CS1 to be treated the same as DF,
so anyone using CS1 cannot assume that CS1 will be treated so applications and browsers using CS1 cannot assume that CS1 will be
differently than DF. Implementers should also note that excess EF treated differently than DF [RFC7657]. Implementers should also note
traffic is dropped. This could mean that a packet marked as EF may that excess EF traffic is dropped. This could mean that a packet
not get through as opposed to a packet marked with a different DSCP marked as EF may not get through as opposed to a packet marked with a
value. different DSCP value.
The browser SHOULD first select the flow type of the flow. Within The browser SHOULD first select the flow type of the flow. Within
the flow type, the relative importance of the flow SHOULD be used to the flow type, the relative importance of the flow SHOULD be used to
select the appropriate DSCP value. select the appropriate DSCP value.
The combination of flow type and application priority provides The combination of flow type and application priority provides
specificity and helps in selecting the right DSCP value for the flow. specificity and helps in selecting the right DSCP value for the flow.
All packets within a flow SHOULD have the same application priority. All packets within a flow SHOULD have the same application priority.
In some cases, the selected application priority cell may have In some cases, the selected application priority cell may have
multiple DSCP values, such as AF41 and AF42. These offer different multiple DSCP values, such as AF41 and AF42. These offer different
drop precedences. The different drop precedence values provides drop precedences. The different drop precedence values provides
additional granularity in classifying packets within a flow. For additional granularity in classifying packets within a flow. For
example, in a video conference, the video flow may have medium example, in a video conference, the video flow may have medium
application priority. If so, either AF42 or AF43 may be selected. application priority. If so, either AF42 or AF43 may be selected.
If the I-frames in the stream are more important than the P-frames, If the I-frames in the stream are more important than the P-frames,
then the I-frames can be marked with AF42 and the P-frames marked then the I-frames can be marked with AF42 and the P-frames marked
with AF43. with AF43.
It is worth noting that the application priority is utilized by the
SCTP scheduler for data channel traffic per
[I-D.ietf-rtcweb-data-channel]. Further, the scheduler functionality
is viewed as more important than the DSCP marking.
For reasons discussed in Section 6 of [RFC7657], if multiple flows For reasons discussed in Section 6 of [RFC7657], if multiple flows
are multiplexed using a reliable transport (e.g., TCP) then all of are multiplexed using a reliable transport (e.g., TCP) then all of
the packets for all flows multiplexed over that transport-layer flow the packets for all flows multiplexed over that transport-layer flow
MUST be marked using the same DSCP value. Likewise, all WebRTC data MUST be marked using the same DSCP value. Likewise, all WebRTC data
channel packets transmitted over an SCTP association MUST be marked channel packets transmitted over an SCTP association MUST be marked
using the same DSCP value, regardless of how many data channels using the same DSCP value, regardless of how many data channels
(streams) exist or what kind of traffic is carried over the various (streams) exist or what kind of traffic is carried over the various
SCTP streams. In the event that the browser wishes to change the SCTP streams. In the event that the browser wishes to change the
DSCP value in use for an SCTP association, it MUST reset the SCTP DSCP value in use for an SCTP association, it MUST reset the SCTP
congestion controller after changing values. Frequent changes in the congestion controller after changing values. Frequent changes in the
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performance. performance.
For the data channel traffic multiplexed over an SCTP association, it For the data channel traffic multiplexed over an SCTP association, it
is RECOMMENDED that the DSCP value selected be the one associated is RECOMMENDED that the DSCP value selected be the one associated
with the highest priority requested for all data channels multiplexed with the highest priority requested for all data channels multiplexed
over the SCTP association. Likewise, when multiplexing multiple over the SCTP association. Likewise, when multiplexing multiple
flows over a TCP connection, the DCSP value selected should be the flows over a TCP connection, the DCSP value selected should be the
one associated with the highest priority requested for all one associated with the highest priority requested for all
multiplexed flows. multiplexed flows.
If a packet enters a QoS domain that has no support for the above If a packet enters a network that has no support for a flow type-
defined flow types/application priority (service class), then the application priority combination specified in Table 1 (above), then
network node at the edge will remark the DSCP value based on the network node at the edge will remark the DSCP value based on
policies. This could result in the flow not getting the network policies. This could result in the flow not getting the network
treatment it expects based on the original DSCP value in the packet. treatment it expects based on the original DSCP value in the packet.
Subsequently, if the packet enters a QoS domain that supports a Subsequently, if the packet enters a network that supports a larger
larger number of service classes, there may not be sufficient number of these combinations, there may not be sufficient information
information in the packet to restore the original markings. in the packet to restore the original markings. Mechanisms for
Mechanisms for restoring such original DSCP is outside the scope of restoring such original DSCP is outside the scope of this document.
this document.
In summary, there are no guarantees or promised level of service with In summary, DSCP marking provides neither guarantees nor promised
the use of DSCP. The service provided to a packet is dependent upon levels of service. The service provided to a packet is dependent
the network design along the path, as well as the congestion levels upon the network design along the path, as well as the network
at every hop. conditions at every hop.
6. Security Considerations 6. Security Considerations
This specification does not add any additional security implication This specification does not add any additional security implication
other than the normal application use of DSCP. For security other than the normal application use of DSCP not already addressed
implications on use of DSCP, please refer to Section 6 of [RFC4594]. by the following specifications. For security implications on use of
Please also see [I-D.ietf-rtcweb-security] as an additional DSCP, please refer to Section 7 of [RFC7657] and Section 6 of
reference. [RFC4594]. Please also see [I-D.ietf-rtcweb-security] as an
additional reference.
7. IANA Considerations 7. IANA Considerations
This specification does not require any actions from IANA. This specification does not require any actions from IANA.
8. Downward References 8. Downward References
This specification contains a downwards reference to [RFC4594]. This specification contains a downwards reference to [RFC4594].
However, the parts of that RFC used by this specification are However, the parts of that RFC used by this specification are
sufficiently stable for this downward reference. sufficiently stable for this downward reference.
9. Acknowledgements 9. Acknowledgements
Thanks To David Black, Magnus Westerland, Paolo Severini, Jim Thanks to David Black, Magnus Westerland, Paolo Severini, Jim
Hasselbrook, Joe Marcus, Erik Nordmark, and Michael Tuexen for their Hasselbrook, Joe Marcus, Erik Nordmark, and Michael Tuexen for their
invaluable input. invaluable input.
10. Dedication 10. Dedication
This document is dedicated to the memory of James Polk, a long-time This document is dedicated to the memory of James Polk, a long-time
friend and colleague. James made important contributions to this friend and colleague. James made important contributions to this
specification, including being one of its primary authors. The IETF specification, including being one of its primary authors. The IETF
global community mourns his loss and he will be missed dearly. global community mourns his loss and he will be missed dearly.
skipping to change at page 9, line 38 skipping to change at page 9, line 43
[W3C.REC-html5-20141028] [W3C.REC-html5-20141028]
Hickson, I., Berjon, R., Faulkner, S., Leithead, T., Hickson, I., Berjon, R., Faulkner, S., Leithead, T.,
Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5", Navara, E., O'Connor, E., and S. Pfeiffer, "HTML5",
World Wide Web Consortium Recommendation REC- World Wide Web Consortium Recommendation REC-
html5-20141028, October 2014, html5-20141028, October 2014,
<http://www.w3.org/TR/2014/REC-html5-20141028>. <http://www.w3.org/TR/2014/REC-html5-20141028>.
Authors' Addresses Authors' Addresses
Paul E. Jones
Cisco Systems
Email: paulej@packetizer.com
Subha Dhesikan Subha Dhesikan
Cisco Systems Cisco Systems
Email: sdhesika@cisco.com Email: sdhesika@cisco.com
Cullen Jennings Cullen Jennings
Cisco Systems Cisco Systems
Email: fluffy@cisco.com Email: fluffy@cisco.com
Dan Druta (editor)
Dan Druta
AT&T AT&T
Email: dd5826@att.com Email: dd5826@att.com
Paul E. Jones
Cisco Systems
Email: paulej@packetizer.com
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