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Versions: 00 01 02 03 RFC 6798

Audio/Video Transport Working Group                              G. Hunt
Internet-Draft                                              Unaffiliated
Intended status: Standards Track                                A. Clark
Expires: June 9, 2012                                           Telchemy
                                                                   Q. Wu
                                                                  Huawei
                                                        December 7, 2011


    RTCP XR Report Block for Packet Delay Variation Metric Reporting
                 draft-ietf-xrblock-rtcp-xr-pdv-02.txt

Abstract

   This document defines an RTCP XR Report Block that allows the
   reporting of Packet Delay Variation metrics for a range of RTP
   applications.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 9, 2012.

Copyright Notice

   Copyright (c) 2011 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



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Packet Delay Variation Metrics Block . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Packet Delay Variation Metrics Block . . . . . . . . . . . . .  5
     3.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  5
     3.2.  Definition of Fields in PDV Metrics Block  . . . . . . . .  5
     3.3.  Guidance on use of PDV metrics . . . . . . . . . . . . . .  9
     3.4.  Examples of use  . . . . . . . . . . . . . . . . . . . . .  9
   4.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . . 11
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     5.1.  New RTCP XR Block Type value . . . . . . . . . . . . . . . 12
     5.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 12
     5.3.  Contact information for registrations  . . . . . . . . . . 12
     5.4.  New registry of PDV types  . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 14
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 16
     A.1.  draft-ietf-avt-rtcp-xr-pdv-03  . . . . . . . . . . . . . . 16
     A.2.  draft-ietf-xrblock-rtcp-xr-pdv-00  . . . . . . . . . . . . 16
     A.3.  draft-ietf-xrblock-rtcp-xr-pdv-01  . . . . . . . . . . . . 16
     A.4.  draft-ietf-xrblock-rtcp-xr-pdv-02  . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17



















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1.  Introduction

1.1.  Packet Delay Variation Metrics Block

   This draft 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 Packet Delay Variation
   using one of several standard metrics.

   The metrics belong to the class of transport metrics defined in
   [MONARCH] (work in progress).

1.2.  RTCP and RTCP XR Reports

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

1.3.  Performance Metrics Framework

   The Performance Metrics Framework [RFC6390] provides guidance on the
   definition and specification of performance metrics.  Metrics
   described in this draft either reference external definitions or
   define metrics generally in accordance with the guidelines in
   [RFC6390].

1.4.  Applicability

   These metrics are applicable to a range of RTP applications.




















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2.  Definitions

   This report block makes use of binary fractions.  The terminology
   used is

      Numeric formats S X:Y

         where S indicates a two's complement signed representation, X
         the number of bits prior to the decimal place and Y the number
         of bits after the decimal place.

         Hence 8:8 represents an unsigned number in the range 0.0 to
         255.996 with a granularity of 0.0039.  S7:8 would represent the
         range -127.996 to +127.996. 0:16 represents a proper binary
         fraction with range

         0.0 to 1 - 1/65536 = 0.9999847

         though note that use of flag values at the top of the numeric
         range slightly reduces this upper limit.  For example, if the
         16- bit values 0xfffe and 0xffff are used as flags for "over-
         range" and "unavailable" conditions, a 0:16 quantity has range

         0.0 to 1 - 3/65536 = 0.9999542



























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3.  Packet Delay Variation Metrics Block

   Metrics in this block report on packet delay variation in the stream
   arriving at the RTP system.  Instances of this Metrics Block refer by
   SSRC to the separate auxiliary Measurement Information block [MEASI]
   which contains measurement intervals.  This metric block relies on
   the measurement interval in the Measurement Information block
   indicating the span of the report.  If the measurement interval is
   not received for this metric block, this metric block should be
   discarded.

3.1.  Report Block Structure

   PDV metrics block

        0               1               2               3
        0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     BT=NPDV   | I |pdvtyp |Rsv|       block length=3          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        SSRC of Source                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Pos PDV Threshold/Peak     |     Pos PDV Percentile        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Neg PDV Threshold/Peak     |     Neg PDV Percentile        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |          Mean PDV             |            unused             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

3.2.  Definition of Fields in PDV Metrics Block

   Block type (BT): 8 bits

      A Packet Delay Variation Metrics Report Block is identified by the
      constant NPDV.

      [Note to RFC Editor: please replace NPDV with the IANA provided
      RTCP XR block type for this block.]


   Interval Metric flag (I): 2 bit

      This field is used to indicate whether the Basic Loss/Discard
      metrics are Sampled, Interval or Cumulative metrics, that is,
      whether the reported values applies to the most recent measurement
      interval duration between successive metrics reports (I=10) (the



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      Interval Duration) or to the accumulation period characteristic of
      cumulative measurements (I=11) (the Cumulative Duration) or to the
      value of a continuously measured or calculated that has been
      sampled at end of the interval (I=01) (Sampled Value).


   Packet Delay Variation Metric Type (pdvtyp): 4 bits

      This field is used to identify the Packet Delay Variation Metric
      Type used in this report block, according to the following code:


         bits 014-017

            0: interarrival jitter, Section 6.4.1 of [RFC3550],

            1: MAPDV2, Clause 6.2.3.2 of [G.1020],

            2: 2-point PDV, Clause 6.2.4 of [Y.1540].


   Rsv.: 2 bits

      This field is reserved for future definition.  In the absence of
      such a definition, the bits in this field MUST be set to zero and
      MUST be ignored by the receiver.


   Block Length: 16 bits

      The length of this report block in 32-bit words, minus one.  For
      the Packet Delay Variation Metrics block, the block length is
      equal to 3.


   SSRC of source: 32 bits

      As defined in Section 4.1 of [RFC3611].


   Positive PDV Threshold/Peak: 16 bits

      This field is associated with the Positive PDV percentile and
      expressed in Milliseconds with numeric format S11:4.  The term
      Positive represents that the packets are arriving later than the
      expected time.

      If the measured value is more negative than -2047.9375 (the value



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      which would be coded as 0x8001), the value 0x8000 SHOULD be
      reported to indicate an over-range negative measurement.  If the
      measured value is more positive than +2047.8125 (the value which
      would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to
      indicate an over-range positive measurement.  If the measurement
      is unavailable, the value 0x7FFF SHOULD be reported.


   Positive PDV Percentile: 16 bits

      The percentages of packets in the RTP stream for which individual
      packet delays were less than the Positive PDV Threshold.  It is
      expressed in numeric format 8:8 with values from 0 to 100th
      percentile.

      If the measurement is unavailable, the value 0xFFFF SHOULD be
      reported.


   Negative PDV Threshold/Peak: 16 bits

      This field is associated with the Negative PDV percentile and
      expressed in Milliseconds with numeric format S11:4.  The term
      Negative represents that the packets are arriving earlier than the
      expected time.

      If the measured value is more negative than -2047.9375 (the value
      which would be coded as 0x8001), the value 0x8000 SHOULD be
      reported to indicate an over-range negative measurement.  If the
      measured value is more positive than +2047.8125 (the value which
      would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to
      indicate an over-range positive measurement.  If the measurement
      is unavailable, the value 0x7FFF SHOULD be reported.


   Negative PDV Percentile: 16 bits

      The percentages of packets in the RTP stream for which individual
      packet delays were more than the Negative PDV Threshold.  It is
      expressed in numeric format 8:8 with values from 0 to 100th
      percentile.

      If the measurement is unavailable, the value 0xFFFF SHOULD be
      reported.

      If the PDV Type indicated is 2-point PDV and the Positive and
      Negative PDV Percentiles are set to 100.0 then the Positive and
      Negative Threshold/Peak PDV values are the peak values measured



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      during the reporting interval (which may be from the start of the
      call for cumulative reports).  In this case, the difference
      between the Positive and Negative Threshold/Peak values defines
      the range of 2-point PDV.


   Mean PDV: 16 bits

      The mean PDV value of data packets is expressed in milliseconds
      with Numeric format S11:4 format.

      For MAPDV2 this value is generated according to Clause 6.2.3.2 of
      [G.1020].  For interval reports the MAPDV2 value is reset at the
      start of the interval.

      For interarrival jitter, the value reported is the value of J(i)
      calculated according to [RFC3550] at the time the report is
      generated.

      For 2-point PDV, the value reported is the mean of per-packet
      2-point PDV values.  This metric indicates the arrival time of the
      first media packet of the session with respect to the mean of the
      arrival times of every packet of the session.  A single value of
      the metric (for a single session) may not be useful by itself, but
      its average over a number of sessions may be useful in diagnosing
      media delay at session startup.  For example, this might occur if
      media packets are often delayed behind signalling packets due to
      head-of-line blocking.

      If the measured value is more negative than -2047.9375 (the value
      which would be coded as 0x8001), the value 0x8000 SHOULD be
      reported to indicate an over-range negative measurement.  If the
      measured value is more positive than +2047.8125 (the value which
      would be coded as 0x7FFD), the value 0x7FFE SHOULD be reported to
      indicate an over-range positive measurement.  If the measurement
      is unavailable, the value 0x7FFF SHOULD be reported.


   Unused: 16 bits

      These bits are unused.  They SHOULD be set to zero by the sender
      and MUST be ignored by the receiver.









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3.3.  Guidance on use of PDV metrics

   This subsection provides informative guidance on when it might be
   appropriate to use each of the PDV metric types.

   Interarrival jitter (Section 6.4.1 of [RFC3550]) allows comparison of
   results with those from RTP end systems which support only RTCP as
   defined in [RFC3550].

   MAPDV2 (Clause 6.2.3.2 of [G.1020]) compares instantaneous (per-
   packet) delay variation against a moving average delay variation.
   This metric could be useful in determining residual impairment when
   an RTP end system uses an adaptive de-jitter buffer which tracks the
   average delay variation, provided the adaptive de-jitter buffer have
   similar averaging behaviour as the MAPDV2 algorithm.

   2-point PDV (Clause 6.2.4 of [Y.1540]) reports absolute packet delay
   variation with respect to the time of arrival of the first packet of
   the connection.  In an RTP context, the two "points" are at the
   sender (the synchronization source which applies RTP timestamps) and
   at the receiver.  The value of this metric for the packet with index
   j is identical to the quantity D(i,j) defined in Section 6.4.1 of
   [RFC3550] if the packet index i is set equal to 1, that is, the
   reference packet for the metric is the first packet of the
   connection.  The metric includes the effect of the frequency offsets
   of clocks in both the sender and receiver end systems, so it is
   useful mainly in network where synchronisation is distributed.  As
   well as measuring packet delay variation in such networks, it may be
   used to ensure that synchronisation is effective, for example where
   the network carries ISDN data traffic over RTP [RFC4040].  The metric
   is likely to be useful in networks which use fixed de-jitter
   buffering, because it may be used to determine the length of the
   required de-jitter buffer, or to determine if network performance has
   deteriorated such that existing de-jitter buffers are too small to
   accommodate the observed delay variation.

3.4.  Examples of use

      (a) To report interarrival jitter [RFC3550]:

         PDV Threshold = FFFF (Undefined); PDV Percentile = FFFF
         (Undefined); PDV type = 0 (interarrival jitter)

         causes interarrival jitter to be reported in the Mean PDV
         field.






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      (b) To report MAPDV2 [G.1020]:

         Pos PDV Threshold = 50.0; Pos PDV Percentile = 95.3; Neg PDV
         Threshold = 50.0 (note this implies -50ms); Neg PDV Percentile
         = 98.4; PDV type = 1 (MAPDV2)

         causes average MAPDV2 to be reported in the Mean PDV field.

         Note that implementations may either fix the reported
         percentile and calculate the associated PDV level or may fix a
         threshold PDV level and calculate the associated percentile.
         From a practical implementation perspective it is simpler to
         use the second of these approaches (except of course in the
         extreme case of a 100% percentile).

         2-point PDV, according to [Y.1540] is the difference in delay
         between the current packet and the first packet of the stream.
         If the sending and receiving clocks are not synchronized, this
         metric includes the effect of relative timing drift.
































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4.  SDP Signaling

   [RFC3611] defines the use of SDP (Session Description Protocol)
   [RFC4566] for signaling the use of XR blocks.  XR blocks MAY be used
   without prior signaling.

   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.

   rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF

   (defined in [RFC3611])

   xr-format =/ xr-pdv-block

   xr-pdv-block  = "pkt-dly-var" [ "," pdvtype ] [ "," nspec "," pspec ]


        pdvtype     = "pdv="    0      ; interarrival jitter  RFC 3550
                              / 1      ; MAPDV2 ITU-T G.1020
                              / 2      ; 2-point PDV ITU-T Y.1540
        nspec       = "nthr=" fixpoint     ; negative PDV threshold (ms)
                    / "npc=" fixpoint    ; negative PDV percentile
        pspec       = "pthr=" fixpoint     ; positive PDV threshold (ms)
                    / "ppc=" fixpoint    ; positive PDV percentile


        fixpoint       = 1*DIGIT "." 1*DIGIT  ; fixed point decimal
        DIGIT          = %x30-39

   When SDP is used in offer-answer, a system sending SDP may request a
   specific type of PDV measurement.  In addition, they may state a
   specific percentile or threshold value, and expect to receive the
   corresponding threshold or percentile metric, respectively.  The
   system receiving the SDP SHOULD send the PDV metrics requested, but
   if the metric is not available, the system receiving the SDP SHOULD
   send the metric block with the flag value indicating that the metric
   is unavailable.












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5.  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].

5.1.  New RTCP XR Block Type value

   This document assigns the block type value NPDV in the IANA "RTCP XR
   Block Type Registry" to the "Packet Delay Variation Metrics Block".

   [Note to RFC Editor: please replace NPDV with the IANA provided RTCP
   XR block type for this block.]

5.2.  New RTCP XR SDP Parameter

   This document also registers a new parameter "pkt-dly-var" in the
   "RTCP XR SDP Parameters Registry".

5.3.  Contact information for registrations


      The contact information for the registrations is:

      Qin Wu (sunseawq@huawei.com)

      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China



5.4.  New registry of PDV types

   This document creates a new registry to be called "RTCP XR PDV block
   - PDV type" as a sub-registry of the "RTP Control Protocol Extended
   Reports (RTCP XR) Block Type Registry".  Policies for this new
   registry are as follows:

   o  The information required to support an assignment is an
      unambiguous definition of the new metric, covering the base
      measurements and how they are processed to generate the reported
      metric.  This should include the units of measurement, how values
      of the metric are reported in the three 16-bit fields "Pos PDV
      Threshold/Peak", "Neg PDV Threshold/Peak" and "Mean PDV" within
      the report block, and how the metric uses the two 16-bit fields
      "Pos PDV Percentile" and "Neg PDV Percentile".




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   o  The review process for the registry is "Specification Required" as
      described in Section 4.1 of [RFC5226].

   o  Entries in the registry are integers.  The valid range is 0 to 15
      corresponding to the 4-bit field "pdvtyp" in the block.  Values
      are to be recorded in decimal.

   o  Initial assignments are as follows:

      1.  interarrival jitter, Section 6.4.1 of [RFC3550],

      2.  MAPDV2, Clause 6.2.3.2 of [G.1020],

      3.  2-point PDV, Clause 6.2.4 of [Y.1540]





































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6.  Security Considerations

   It is believed that this proposed RTCP XR report 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.












































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7.  References

7.1.  Normative References

   [G.1020]   ITU-T, "ITU-T Rec. G.1020, Performance parameter
              definitions for quality of speech and other voiceband
              applications utilizing IP networks", July 2006.

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

   [RFC3550]  Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
              Applications", RFC 3550, July 2003.

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

   [RFC4040]  Kreuter, R., "RTP Payload Format for a 64 kbit/s
              Transparent Call", April 2005.

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

   [RFC5226]  Narten, T., "Guidelines for Writing an IANA Considerations
              Section in RFCs", May 2008.

              BCP 26

   [Y.1540]   ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and
              availability performance parameters", November 2007.

7.2.  Informative References

   [MEASI]    Hunt, G., "Measurement Identity and information Reporting
              using SDES item and XR Block",
              ID draft-ietf-xrblock-rtcp-xr-measu-identity-01,
              October 2011.

   [MONARCH]  Hunt, G., "Monitoring Architectures for RTP",
              ID draft-ietf-avtcore-monarch-04, August 2011.

   [RFC6390]  Clark, A. and B. Claise, "Framework for Performance Metric
              Development", RFC 6390, October 2011.








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Appendix A.  Change Log

   Note to the RFC-Editor: please remove this section prior to
   publication as an RFC.

A.1.  draft-ietf-avt-rtcp-xr-pdv-03

   The following are the major changes to previous version :

   o  Changed BNF for SDP following Christian Groves' and Tom Taylor's
      comments (4th and 5th May 2009).

   o  Updated references.

A.2.  draft-ietf-xrblock-rtcp-xr-pdv-00

   The following are the major changes to previous version
   draft-ietf-avt-rtcp-xr-pdv-03 :

   o  Updated references.

A.3.  draft-ietf-xrblock-rtcp-xr-pdv-01

   The following are the major changes to previous version
   draft-ietf-xrblock-rtcp-xr-pdv-00 :

   o  Fix typos or nits in the definition of Negative PDV Threshold/
      Peak.

   o  Fix nits in Numeric format S7:8.

   o  remove the text that is relevant to tag field.

   o  Add text in SDP signaling section to clarify indicationof metric
      unavailable.

A.4.  draft-ietf-xrblock-rtcp-xr-pdv-02

   The following are the major changes to previous version
   draft-ietf-xrblock-rtcp-xr-pdv-00 :

   o  Updated references.

   o  Allocate one more bit for Interval metric flag to indicate sampled
      metric can be used.

   o  Add a few clarification text for failure mode.




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Authors' Addresses

   Geoff Hunt
   Unaffiliated

   Email: r.geoff.hunt@gmail.com


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

   Email: alan.d.clark@telchemy.com


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

   Email: sunseawq@huawei.com



























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