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Network Working Group                                            X. Ding
Internet-Draft                                                     Q. Wu
Intended status: Standards Track                                  Huawei
Expires: January 4, 2018                                           R. Gu
                                                            China Mobile
                                                            July 3, 2017


          An Enhanced Media Delivery Index (eMDI) based on TCP
                         draft-ding-tcp-emdi-00

Abstract

   This document introduces an Enhanced Media Delivery Index (eMDI) that
   can be used as a diagnostic tool or a quality indicator for
   monitoring a network intended to deliver streaming media over TCP
   transport.  It aims to address the problems that RFC4445 has when
   measuring in environments where TCP traffic is dominated as a
   transport for streaming media.

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 January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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



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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Measurement Setup . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Measurement Method  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Use Examples  . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Network Troubleshooting in VoD scenario . . . . . . . . .   5
     5.2.  WiFi Anomaly Analysis in the Home Network . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   TCP is one major transport protocol in use in most IP networks, and
   supports the transfer of over 80 percent of all traffic (e.g.,OTT
   traffic, IPTV VOD traffic) across the public Internet today.  Packet
   loss ratio and latency are two major characteristics in the network
   to affect the behavior of TCP.  The bad TCP performance might also
   indicate the unacceptable end-user-perceived quality level.

   Media Delivery Index (MDI)[RFC4445] is a method widely used in the
   network as a diagnostic tool to measure both the instantaneous and
   longer-term behavior of networks carrying streaming media in the
   media layer.  However the limitation of MDI measurement is mostly
   applicable to streaming media and protocol over UDP, it falls short
   when monitoring a network intended to deliver multimedia applications
   over TCP Transport, i.e., the traditional MDI metrics especially
   Media Loss Rate (MLR) deployed in the network devices is difficult to
   infer the packet loss if the missing packets were retransmitted when
   the packet loss was detected by the TCP sender.  On the other hand,
   TCP sender will adjust the sending data rate to reduce the
   probability of further packet loss, which means throughput is
   declining when extra delay is incurred by retransmitting lost
   packets.  Therefore, throughput can be regarded as a quality
   indication for network monitoring and diagnosis.

   This document introduces a new measurement method and associated
   metrics,i.e.,downstream/upstream/end to end throughput, to complement
   methods defined in [RFC4445].  This new method can quickly identify
   the root cause of the QoS related problem, improve efficiency of
   network monitoring and troubleshooting.




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2.  Terminologies

   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].

   This document uses the following terms:

   Measurement point (MP):   A measurement point is the logical or
      physical location defined in the TCP that acts as a source of
      information gathered for monitoring purposes.

   Upstream packet lost ratio (UPLR):   UPLR is the ratio of the number
      of packets lost to the total number of packets sent from server to
      measurement point during predefined measurement interval.

   Downstream packet lost ratio (DPLR):   DPLR is the ratio of the
      number of packets lost to the total number of packets sent from
      measurement point to client during a predefined measurement
      interval.

   Upstream average RTT (URTT):   URTT is the average RTT at the path
      from server to measurement point during a predefined measurement
      interval.

   Downstream average RTT (DRTT):   DRTT is the average RTT at the path
      from measurement point to client during a predefined measurement
      interval.

   End to end Throughput (E2ET):  E2ET is the rate of successful packet
      delivery over an end-end network path during a predefined
      measurement interval.

   Downstream throughput (DT):  DT is measured by the number of packets
      received per second at the downstream of measurement point during
      a predefined measurement interval.

   Upstream throughput (UT):  UT is measured by the number of packets
      received per second at the upstream of measurement point during a
      predefined measurement interval.

3.  Measurement Setup

   A stream of packets sent by streaming media Server passes through MP
   (MP can be bridge, router or gateway), and finally reach the client
   (destination endpoint).  If a node A is placed between the server and
   MP in the network , then A is upstream node of MP.  Otherwise, A is
   downstream node of MP.



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     +--------+                MP |                    +--------+
     | Server |------Upstream---->|-----Downstream---->| client |
     +--------+                   |                    +--- ----+

4.  Measurement Method

   The rationale of the measurement is to compare DT/UT/E2ET with data
   packet rate.  If DT is less than data packet rate and UT is greater
   than data packet rate, there is something wrong with the downstream
   network.  Otherwise, the upstream network has some problems.

   When the packet loss occurs in the network, an additional limit(i.e.,
   packet loss probability) is imposed on the throughput besides TCP
   recieve window.  In case of light or moderate packet loss when the
   TCP rate is adjusted by the congestion avoidance algorithm, DT can be
   calculated according to the following formula:

   DT = MSS/(DRTT+URTT)(DPLR)(1/2);

   Where MSS is the maximum segment size.  Assuming the number of lost
   packets at the downstream during a predefined measurement interval is
   a, and the number of total packets sent by MP is x, then DPLR is then
   calculated as following:

   DPLR = a/x.

   Average RTT of some packets (d1..dm) at the downstream direction are
   used to compute DRTT:

   DRTT= sum (RTTdi)/m, i= 1..m
   Where RTTdi indicates the RTT of packet di at downstream.

   Similarly, average RTT of some packets (u1..un) at the upstream
   direction are used to compute URTT:

   URTT= sum (RTTui)/n, i= 1..n
   Where RTTui indicates the RTT of packet ui at the upstream.

   And, UT can be calculated according to the formula:

   UT = MSS/(DRTT+URTT)(UPLR)(1/2);

   Assuming the number of lost packets at the upstream during a
   predefined measurement interval is b, and the number of total packets
   sent by Server is y, then UPLR is then calculated as following:

   UPLR = b/y.




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   And E2ET can be calculated according to the formula:

   E2ET = MSS/(DRTT+URTT)(UPLR+DPLR)(1/2).

5.  Use Examples

5.1.  Network Troubleshooting in VoD scenario

                         +--------+
           IPTV Platform +--------+----------^--------------
            /OTT/CDN     +--------+          |
                         +----+---+          |
                              |              |
                        //----+---\\         |
                    |///            \\\|     |
                   |                    |    |URTT
                    |\\\            ///|     |
                        \\----+---//         |
                              |              |
                              |              |
                         +--------+          |
                   CR    +--------+          |
                              |              |
                              ---------------V------------------
                              |                      ^
                  BRAS  +-----+---+                  |
                        +---/---\-+                  | Downstream
                          //     \\                  |   Fixed
                        //         \                 |   Network
          OLT  +---------+        +-\------+         |    Latency
               +---------+        +--------+    DRTT |
                                                     |
             ----     ----         ----     ----  --------------
            /----\   /----\       /----\   /----\    |
            |    |   |    |       |    |   |    |    |Home Network
       Home |    |   |    |       |    |   |    |    |  Latency
      Network    |   |    |       |    |   |    |    |
            +----+   +----+       +----+   +----+----V------

                            Figure 1: Figure 1

   The proposed measurement method can be applied when VoD streaming
   media running over TCP is delivered as unicast stream from VoD server
   in the operator network to end users in home network.  In some cases,
   the fault occurs in the home network which cause user experience
   downgrading, in some other cases, fault occurs in the operator
   network.




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   To pinpoint the location of the fault , MP can be deployed on ONT
   device of the home network.  The home network is refer to the
   downstream of the MP and the operator network is refer to the
   upstream of the MP.  Suppose the rate of the media rate is v, we can
   compare DT/UT/E2ET with v.  If DT<v and UT>v, the home network is the
   root cause for streaming media quality downgrading.  If DT>v and
   UT<v, the operator network is the root cause.  If DT>v, UT>v, and
   E2E<v, both home network and operator network should be responsible
   for streaming media quality downgrading.

5.2.  WiFi Anomaly Analysis in the Home Network

   WiFi latency is a key factor impacting the user experience of home
   network application.  [WIFI] shows WiFi latency follows a long tail
   distribution: its 50th, 90th and 99th percentile are around 3ms, 20ms
   and 250ms.  If the WiFi network get congested, the quality degrades
   proportionally with WiFi lantency.  To analyse WIFi Anomaly degree in
   the home network, See figure 1, we can calculate cumulative
   distribution of WiFi latency based on measured values:

   WiFi Latency = DRTT - Downstream Fixed Network Latency

   and determine threshold value for WiFi Latency based on periodically
   collected dataset,e.g.,

   Threshold = UBV + coef *(UBV-LBV)

   Where UBV is the 75th percentile value, LBV is the 25th Percentile
   value, coef is coefficiency value which can be set to 1.5.

   By Comparing WiFi latency measured value with the threshold value, we
   can decide if WiFi Anomaly is the root cause of network quality
   degrading.

6.  Security Considerations

   This document does not introduce security issues beyond those
   discussed in [[RFC4445].

7.  Normative References

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

   [RFC4445]  Welch, J. and J. Clark, "A Proposed Media Delivery Index
              (MDI)", RFC 4445, DOI 10.17487/RFC4445, April 2006,
              <http://www.rfc-editor.org/info/rfc4445>.




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   [WIFI]     MobiSys'16, 2016, Singapore, ACM ISBN
              978-1-4503-4269-8/16/06, "Characterizing and Improving
              WiFi Latency in Large-Scale Operational Networks", 2016.

Authors' Addresses

   Xiaojian Ding
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: dingxiaojian1@huawei.com


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

   Email: bill.wu@huawei.com


   Rong Gu
   China Mobile
   32 Xuanwumen West Ave, Xicheng District
   Beijing  100053
   China

   Email: gurong_cmcc@outlook.com




















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