





Internet Engineering Task Force (IETF)                          A. Clark
Request for Comments: 7005                                      Telchemy
Category: Standards Track                                       V. Singh
ISSN: 2070-1721                                         Aalto University
                                                                   Q. Wu
                                                                  Huawei
                                                          September 2013


         RTP Control Protocol (RTCP) Extended Report (XR) Block
                 for De-Jitter Buffer Metric Reporting

Abstract

   This document defines an RTP Control Protocol (RTCP) Extended Report
   (XR) block that allows the reporting of de-jitter buffer metrics for
   a range of RTP applications.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7005.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  De-Jitter Buffer Metrics Block . . . . . . . . . . . . . .  3
     1.2.  RTCP and RTCP Extended Reports . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Standards Language . . . . . . . . . . . . . . . . . . . . . .  4
   3.  De-Jitter Buffer Operation . . . . . . . . . . . . . . . . . .  4
     3.1.  Idealized De-Jitter Buffer . . . . . . . . . . . . . . . .  4
     3.2.  Fixed De-Jitter Buffer . . . . . . . . . . . . . . . . . .  5
     3.3.  Adaptive De-Jitter Buffer  . . . . . . . . . . . . . . . .  5
   4.  De-Jitter Buffer Metrics Block . . . . . . . . . . . . . . . .  6
     4.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  6
     4.2.  Definition of Fields in De-Jitter Buffer Metrics Block . .  6
   5.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.1.  SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . .  9
     5.2.  Offer/Answer Usage . . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  New RTCP XR Block Type Value . . . . . . . . . . . . . . .  9
     6.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 10
     6.3.  Contact Information for Registrations  . . . . . . . . . . 10
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Metrics Represented Using the Template from
                RFC 6390  . . . . . . . . . . . . . . . . . . . . . . 12





















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1.  Introduction

1.1.  De-Jitter Buffer Metrics Block

   This document defines a new block type to augment those defined in
   [RFC3611] for use in a range of RTP applications.

   The new block type provides information on de-jitter buffer
   configuration and performance.

   The metric belongs to the class of transport-related end-system
   metrics defined in [RFC6792].

   Instances of this metrics block refer by synchronization source
   (SSRC) to the separate auxiliary Measurement Information Block
   [RFC6776], which contains information such as the SSRC of the
   measured stream, and RTP sequence numbers and time intervals
   indicating the span of the report.

1.2.  RTCP and RTCP Extended Reports

   The use of RTCP for reporting is defined in [RFC3550].  [RFC3611]
   defines an extensible structure for reporting using an RTCP Extended
   Report (XR).  This document defines a new Extended Report block for
   use with [RFC3550] and [RFC3611].

1.3.  Performance Metrics Framework

   "Guidelines for Considering New Performance Metric Development"
   [RFC6390] provides guidance on the definition and specification of
   performance metrics.  "Guidelines for Use of the RTP Monitoring
   Framework" [RFC6792] provides guidance on the reporting block format
   using RTCP XR.  Metrics described in this document are in accordance
   with the guidelines in [RFC6390]and [RFC6792].

1.4.  Applicability

   Real-time applications employ a de-jitter buffer [RFC5481] to absorb
   jitter introduced on the path from source to destination.  These
   metrics are used to report how the de-jitter buffer at the receiving
   end of the RTP stream behaves as a result of jitter in the network;
   they are applicable to a range of RTP applications.

   These metrics correspond to terminal-related factors that affect
   real-time application quality and are useful for providing a better
   end-user quality of experience (QoE) when these terminal-related
   factors are used as inputs to calculate QoE metrics [QMB].




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2.  Standards Language

   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 RFC 2119 [RFC2119].

3.  De-Jitter Buffer Operation

   A de-jitter buffer is required to absorb delay variation in the
   network delivery of media packets.  A de-jitter buffer works by
   holding media data for a period of time after it is received and
   before it is played out.  Packets that arrive early are held in the
   de-jitter buffer longer.  If packets arrive too early, they may be
   discarded if there is no available de-jitter buffer space.  If
   packets are delayed excessively by the network, they may be discarded
   if they miss their playout time.

   The de-jitter buffer can be considered a time window with the early
   edge aligned with the delay corresponding to the earliest arriving
   packet and the late edge representing the maximum permissible delay
   before a late arriving packet would be discarded.  The delay applied
   to packets that arrive on time or at their expected arrival time is
   known as the nominal delay, and this is equivalent to the time
   difference/buffer size difference between the insertion point of the
   on-time packets and the point at which the packets are read out.

   The reference for the expected arrival time may be, for example, the
   first packet in the session or the running average delay.  If all
   packets arrived at their expected arrival time, then every packet
   would be held in the de-jitter buffer exactly the nominal delay.

   The de-jitter buffer maximum delay is the delay that is applied to
   the earliest arriving packet that is not discarded and corresponds to
   the early edge of the de-jitter buffer time window.

3.1.  Idealized De-Jitter Buffer

   In practice, de-jitter buffer implementations vary considerably;
   however, they should behave in a manner conceptually consistent with
   an idealized de-jitter buffer, which is described as follows:











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   (i)    Receive the first packet and delay playout by D ms.  Keep the
          RTP timestamp (TS) and receive time as a reference.

          RTP TS[1]

          receive time[1]

          Assume that both are normalized in ticks (there are 10,000
          ticks in a millisecond).

   (ii)   Receive the next packet.

   (iii)  Calculate r = RTP TS[n] - RTP TS[1] and t = receive time[n] -
          receive time[1].  If r == t, then the packet arrived on time.
          If r < t, then the packet arrived late, and if r > t, then the
          packet arrived early.

   (iv)   Delay playout of packet by D + (r-t).

   (v)    Go back to (ii).

   Note that this idealized implementation assumes that the sender's RTP
   clock is synchronized to the clock in the receiver, which is used to
   timestamp packet arrivals.  If there is no such inherent
   synchronization, the system may need to use an adaptive de-jitter
   buffer or other techniques to ensure reliable reception.

3.2.  Fixed De-Jitter Buffer

   A fixed de-jitter buffer lacks provision to track the condition of
   the network and has a fixed size, and packets leaving the de-jitter
   buffer have a constant delay.  For fixed de-jitter buffer
   implementation, the nominal delay is set to a constant value
   corresponding to the packets that arrive at their expected arrival
   time, while the maximum delay is set to a constant value
   corresponding to the fixed size of the de-jitter buffer.

3.3.  Adaptive De-Jitter Buffer

   An adaptive de-jitter buffer can adapt to the change in the network's
   delay and has variable size or variable delay.  It allows the nominal
   delay to be set to a low value initially to minimize user perceived
   delay; however, it can automatically extend the late edge (and
   possibly also retract the early edge) of a buffer window if a
   significant proportion of the packets are arriving late (and hence
   being discarded).





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4.  De-Jitter Buffer Metrics Block

   This block describes the configuration and operating parameters of
   the de-jitter buffer in the receiver of the RTP end system or RTP
   mixer that sends the report.  Instances of this metrics block use the
   SSRC to refer to the separate auxiliary Measurement Information Block
   [RFC6776], which describes the measurement periods in use (see
   [RFC6776], Section 4.2).  This metrics block relies on the
   measurement interval in the Measurement Information Block indicating
   the span of the report and MUST be sent in the same compound RTCP
   packet as the Measurement Information Block.  If the measurement
   interval is not received in the same compound RTCP packet as this
   metrics block, this metrics block MUST be discarded.

4.1.  Report Block Structure

   De-Jitter Buffer (DJB) Metrics Block

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     BT=23    | I |C|  resv    |       Block Length=3          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SSRC of Source                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          DJB nominal          |        DJB maximum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     DJB high-water mark       |      DJB low-water mark       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

4.2.  Definition of Fields in De-Jitter Buffer Metrics Block

   Block Type (BT): 8 bits

      A De-Jitter Buffer Metrics Report Block is identified by the
      constant 23.

   Interval Metric flag (I): 2 bits

      This field is used to indicate whether the de-jitter buffer
      metrics are Sampled, Interval, or Cumulative metrics:

         I=01: Sampled Value - the reported value is a sampled
         instantaneous value.





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         I=10: Interval Duration - the reported value applies to the
         most recent measurement interval duration between successive
         metrics reports.

         I=11: Cumulative Duration - the reported value applies to the
         accumulation period characteristic of cumulative measurements.

      In this document, de-jitter buffer metrics can only be sampled and
      cannot be measured over definite intervals.  Also, the value I=00
      is reserved for future use.  Senders MUST NOT use the values I=00,
      I=10, or I=11.  If a block is received with I=00, I=10, or I=11,
      the receiver MUST discard the block.

   Jitter Buffer Configuration (C): 1 bit

      This field is used to identify the de-jitter buffer method in use
      at the receiver, according to the following code:

         0 = Fixed de-jitter buffer

         1 = Adaptive de-jitter buffer

   Reserved (resv): 5 bits

      These bits are reserved.  They MUST be set to zero by senders and
      ignored by receivers (see [RFC6709], Section 4.2).

   Block Length: 16 bits

      The length of this report block in 32-bit words, minus one, in
      accordance with the definition in [RFC3611].  This field MUST be
      set to 3 to match the fixed length of the report block.

   SSRC of Source: 32 bits

      As defined in Section 4.1 of [RFC3611].

   De-jitter buffer nominal delay (DJB nominal): 16 bits

      This is the current nominal de-jitter buffer delay (in
      milliseconds) that corresponds to the nominal de-jitter buffer
      delay for packets that arrive exactly on time.  It is calculated
      based on the time spent in the de-jitter buffer for the packet
      that arrives exactly on time.  This parameter MUST be provided for
      both fixed and adaptive de-jitter buffer implementations.






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      The measured value is an unsigned value.  If the measured value
      exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
      over-range measurement.  If the measurement is unavailable, the
      value 0xFFFF MUST be reported.

   De-jitter buffer maximum delay (DJB maximum): 16 bits

      This is the current maximum de-jitter buffer delay (in
      milliseconds) that corresponds to the earliest arriving packet
      that would not be discarded.  It is calculated based on the time
      spent in the de-jitter buffer for the earliest arriving packet.
      In simple queue implementations, this may correspond to the size
      of the de-jitter buffer.  In adaptive de-jitter buffer
      implementations, this value may vary dynamically.  This parameter
      MUST be provided for both fixed and adaptive de-jitter buffer
      implementations.

      The measured value is an unsigned value.  If the measured value
      exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
      over-range measurement.  If the measurement is unavailable, the
      value 0xFFFF MUST be reported.

   De-jitter buffer high-water mark (DJB high-water mark): 16 bits

      This is the highest value of the de-jitter buffer nominal delay
      (in milliseconds) that occurred at any time during the reporting
      interval.  This parameter MUST be provided for adaptive de-jitter
      buffer implementations, and its value MUST be set to DJB maximum
      for fixed de-jitter buffer implementations.

      The measured value is an unsigned value.  If the measured value
      exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
      over-range measurement.  If the measurement is unavailable, the
      value 0xFFFF MUST be reported.

   De-jitter buffer low-water mark (DJB low-water mark): 16 bits

      This is the lowest value of the de-jitter buffer nominal delay (in
      milliseconds) that occurred at any time during the reporting
      interval.  This parameter MUST be provided for adaptive de-jitter
      buffer implementations, and its value MUST be set to DJB maximum
      for fixed de-jitter buffer implementations.

      The measured value is an unsigned value.  If the measured value
      exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
      over-range measurement.  If the measurement is unavailable, the
      value 0xFFFF MUST be reported.




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5.  SDP Signaling

   [RFC3611] defines the use of the Session Description Protocol (SDP)
   [RFC4566] for signaling the use of XR blocks.  However, XR blocks MAY
   be used without prior signaling (see Section 5 of RFC 3611).

5.1.  SDP rtcp-xr-attrib Attribute Extension

   This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
   in [RFC3611] by providing an additional value of "xr-format" to
   signal the use of the report block defined in this document.

   xr-format =/ xr-djb-block

   xr-djb-block = "de-jitter-buffer"

5.2.  Offer/Answer Usage

   When SDP is used in Offer/Answer context [RFC3264], the SDP Offer/
   Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute
   parameters applies.  For detailed usage of Offer/Answer for
   unilateral parameters, refer to Section 5.2 of [RFC3611].

6.  IANA Considerations

   New block types for RTCP XR are subject to IANA registration.  For
   general guidelines on IANA considerations for RTCP XR, refer to
   [RFC3611].

6.1.  New RTCP XR Block Type Value

   This document assigns the block type value 23 in the IANA "RTP
   Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
   the "De-Jitter Buffer Metrics Block".

6.2.  New RTCP XR SDP Parameter

   This document also registers a new parameter "de-jitter-buffer" in
   the "RTP Control Protocol Extended Reports (RTCP XR) Session
   Description Protocol (SDP) Parameters Registry".











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6.3.  Contact Information for Registrations

   The contact information for registrations is:

   Qin Wu (sunseawq@huawei.com)
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

7.  Security Considerations

   It is believed that this RTCP XR block introduces no new security
   considerations beyond those described in [RFC3611].  This block does
   not provide per-packet statistics, so the risk to confidentiality
   documented in Section 7, paragraph 3 of [RFC3611] does not apply.

8.  Contributors

   Geoff Hunt wrote the initial draft of this document.

9.  Acknowledgments

   The authors gratefully acknowledge reviews and feedback provided by
   Bruce Adams, Philip Arden, Amit Arora, Claire Bi, Bob Biskner, Benoit
   Claise, Kevin Connor, Claus Dahm, Spencer Dawkins, Randy Ethier, Roni
   Even, Jim Frauenthal, Kevin Gross, Albert Higashi, Tom Hock, Shane
   Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Mohamed Mostafa, Amy
   Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Dan Romascanu,
   Albrecht Schwarz, Tom Taylor, Hideaki Yamada, and Glen Zorn.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3264]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
              with Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control
              Protocol Extended Reports (RTCP XR)", RFC 3611,
              November 2003.



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   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC6776]  Clark, A. and Q. Wu, "Measurement Identity and Information
              Reporting Using a Source Description (SDES) Item and an
              RTCP Extended Report (XR) Block", RFC 6776, October 2012.

10.2.  Informative References

   [QMB]      Clark, A., "RTP Control Protocol (RTCP) Extended Report
              (XR) Blocks for QoE Metric Reporting", Work in Progress,
              May 2013.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, March 2009.

   [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development", BCP 170, RFC 6390,
              October 2011.

   [RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
              Considerations for Protocol Extensions", RFC 6709,
              September 2012.

   [RFC6792]  Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
              RTP Monitoring Framework", RFC 6792, November 2012.

























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Appendix A.  Metrics Represented Using the Template from RFC 6390

   a.  De-Jitter Buffer Nominal Delay Metric

       *  Metric Name: De-jitter buffer nominal delay in RTP

       *  Metric Description: The "expected arrival time" is the time
          that an RTP packet would arrive if there was no delay
          variation.  The delay applied to packets that arrive at their
          expected time is known as the Nominal Delay.

       *  Method of Measurement or Calculation: See Section 4.2,
          de-jitter buffer nominal delay definition.

       *  Units of Measurement: See Section 4.2, de-jitter buffer
          nominal delay definition.

       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 4.

       *  Measurement Timing: See Section 4 for measurement timing and
          Section 4.2 for Interval Metric flag.

       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

   b.  De-Jitter Buffer Maximum Delay Metric

       *  Metric Name: De-jitter buffer maximum delay in RTP.

       *  Metric Description: It is the current maximum de-jitter buffer
          delay for RTP traffic that corresponds to the earliest
          arriving packet that would not be discarded.

       *  Method of Measurement or Calculation: See Section 4.2,
          de-jitter buffer maximum delay definition and Section 3, the
          last paragraph.

       *  Units of Measurement: See Section 4.2, de-jitter buffer
          maximum delay definition.

       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 4.

       *  Measurement Timing: See Section 4 for measurement timing and
          Section 4.2 for Interval Metric flag.




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       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

   c.  De-Jitter Buffer High-Water Mark Metric

       *  Metric Name: De-jitter buffer high-water mark in RTP.

       *  Metric Description: It is the highest value of the de-jitter
          buffer nominal delay for RTP traffic which occurred at any
          time during the reporting interval.

       *  Method of Measurement or Calculation: See Section 4.2,
          de-jitter buffer high-water mark definition.

       *  Units of Measurement: See Section 4.2, de-jitter buffer
          nominal delay definition.

       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 4.

       *  Measurement Timing: See Section 4 for measurement timing and
          Section 4.2 for Interval Metric flag.

       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

   d.  De-Jitter Buffer Low-Water Mark Metric

       *  Metric Name: De-jitter buffer low-water mark in RTP.

       *  Metric Description: It is the lowest value of the de-jitter
          buffer nominal delay (for RTP traffic) that occurred at any
          time during the reporting interval.

       *  Method of Measurement or Calculation: See Section 4.2,
          de-jitter buffer low-water mark definition.

       *  Units of Measurement: See Section 4.2, de-jitter buffer low
          water mark definition.

       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 4, 1st paragraph.

       *  Measurement Timing: See Section 4 for measurement timing and
          Section 4.2 for Interval Metric flag.




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       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

Authors' Addresses

   Alan Clark
   Telchemy Incorporated
   2905 Premiere Parkway, Suite 280
   Duluth, GA  30097
   USA

   EMail: alan.d.clark@telchemy.com


   Varun Singh
   Aalto University
   School of Electrical Engineering
   Otakaari 5 A
   Espoo, FIN  02150
   Finland

   EMail: varun@comnet.tkk.fi


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: sunseawq@huawei.com



















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