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Network Working Group                                          Z. Sarker
Internet-Draft                                              I. Johansson
Intended status: Informational                               Ericsson AB
Expires: January 6, 2020                                          X. Zhu
                                                                   J. Fu
                                                                  W. Tan
                                                              M. Ramalho
                                                           Cisco Systems
                                                            July 5, 2019


  Evaluation Test Cases for Interactive Real-Time Media over Wireless
                                Networks
                   draft-ietf-rmcat-wireless-tests-08

Abstract

   The Real-time Transport Protocol (RTP) is a common transport choice
   for interactive multimedia communication applications.  The
   performance of such applications typically depends on a well-
   functioning congestion control algorithm.  To ensure seamless and
   robust user experience, a well-designed RTP-based congestion control
   algorithm should work well across all access network types.  This
   document describes test cases for evaluating performances of such
   congestion control algorithms over LTE and Wi-Fi networks.

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 https://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 6, 2020.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Cellular Network Specific Test Cases  . . . . . . . . . . . .   3
     3.1.  Varying Network Load  . . . . . . . . . . . . . . . . . .   6
       3.1.1.  Network Connection  . . . . . . . . . . . . . . . . .   6
       3.1.2.  Simulation Setup  . . . . . . . . . . . . . . . . . .   7
     3.2.  Bad Radio Coverage  . . . . . . . . . . . . . . . . . . .   9
       3.2.1.  Network connection  . . . . . . . . . . . . . . . . .   9
       3.2.2.  Simulation Setup  . . . . . . . . . . . . . . . . . .   9
     3.3.  Desired Evaluation Metrics for cellular test cases  . . .  10
   4.  Wi-Fi Networks Specific Test Cases  . . . . . . . . . . . . .  10
     4.1.  Bottleneck in Wired Network . . . . . . . . . . . . . . .  12
       4.1.1.  Network topology  . . . . . . . . . . . . . . . . . .  12
       4.1.2.  Test setup  . . . . . . . . . . . . . . . . . . . . .  13
       4.1.3.  Typical test scenarios  . . . . . . . . . . . . . . .  14
       4.1.4.  Expected behavior . . . . . . . . . . . . . . . . . .  15
     4.2.  Bottleneck in Wi-Fi Network . . . . . . . . . . . . . . .  15
       4.2.1.  Network topology  . . . . . . . . . . . . . . . . . .  15
       4.2.2.  Test setup  . . . . . . . . . . . . . . . . . . . . .  15
       4.2.3.  Typical test scenarios  . . . . . . . . . . . . . . .  17
       4.2.4.  Expected behavior . . . . . . . . . . . . . . . . . .  18
     4.3.  Other Potential Test Cases  . . . . . . . . . . . . . . .  19
       4.3.1.  EDCA/WMM usage  . . . . . . . . . . . . . . . . . . .  19
       4.3.2.  Effects of Legacy 802.11b Devices . . . . . . . . . .  19
   5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  19
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  20
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22







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1.  Introduction

   Wireless networks (both cellular and Wi-Fi [IEEE802.11]) are an
   integral part of the Internet.  Mobile devices connected to the
   wireless networks account for an increasingly more significant
   portion of the media traffic over the Internet.  Application
   scenarios range from video conferencing calls in a bus or train to
   media consumption by someone on a living room couch.  It is well
   known that the characteristics and technical challenges for
   supporting multimedia services over wireless are very different from
   those of providing the same service over a wired network.  Even
   though basic test cases for evaluating RTP-based congestion control
   schemes as defined in [I-D.ietf-rmcat-eval-test] have covered many
   effects of the impairments common to both wired and wireless
   networks, there remain characteristics and dynamics unique to a given
   wireless environment.  For example, in LTE networks, the base station
   maintains individual queues per radio bearer per user hence it leads
   to a different nature of interactions between traffic flows of
   different users.  This contrasts with wired networks, where traffic
   flows from all users share the same queue.  Furthermore, user
   mobility patterns in a cellular network differ from those in a Wi-Fi
   network.  Therefore, it is important to evaluate the performance of
   proposed candidate RTP-based congestion control solutions over
   cellular mobile networks and over Wi-Fi networks respectively.

   RMCAT evaluation criteria document [I-D.ietf-rmcat-eval-criteria]
   provides the guideline for evaluating candidate algorithms and
   recognizes the importance of testing over wireless access networks.
   However, it does not describe any specific test cases for performance
   evaluation of candidate algorithms.  This document describes test
   cases specifically targeting cellular networks such as LTE networks
   and Wi-Fi networks.

2.  Terminologies

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Cellular Network Specific Test Cases

   A cellular environment is more complicated than its wireline
   counterpart since it seeks to provide services in the context of
   variable available bandwidth, location dependencies and user
   mobilities at different speeds.  In a cellular network, the user may
   reach the cell edge which may lead to a significant amount of



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   retransmissions to deliver the data from the base station to the
   destination and vice versa.  These network links or radio links will
   often act as a bottleneck for the rest of the network and will
   eventually lead to excessive delays or packet drops.  An efficient
   retransmission or link adaptation mechanism can reduce the packet
   loss probability but there will still be some packet losses and delay
   variations.  Moreover, with increased cell load or handover to a
   congested cell, congestion in the transport network will become even
   worse.  Besides, there are certain characteristics which make the
   cellular network different from and more challenging than other types
   of access networks such as Wi-Fi and wired network.  In a cellular
   network --

   o  The bottleneck is often a shared link with relatively few users.

      *  The cost per bit over the shared link varies over time and is
         different for different users.

      *  Leftover/unused resource can be consumed by other greedy users.

   o  Queues are always per radio bearer hence each user can have many
      of such queues.

   o  Users can experience both Inter and Intra Radio Access Technology
      (RAT) handovers (see [HO-def-3GPP] for the definition of
      "handover").

   o  Handover between cells or change of serving cells (as described in
      [HO-LTE-3GPP] and [HO-UMTS-3GPP]) might cause user plane
      interruptions which can lead to bursts of packet losses, delay
      and/or jitter.  The exact behavior depends on the type of radio
      bearer.  Typically, the default best-effort bearers do not
      generate packet loss, instead, packets are queued up and
      transmitted once the handover is completed.

   o  The network part decides how much the user can transmit.

   o  The cellular network has variable link capacity per user

      *  Can vary as fast as a period of milliseconds.

      *  Depends on many factors (such as distance, speed, interference,
         different flows).

      *  Uses complex and smart link adaptation which makes the link
         behavior ever more dynamic.

      *  The scheduling priority depends on the estimated throughput.



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   o  Both Quality of Service (QoS) and non-QoS radio bearers can be
      used.

   Hence, a real-time communication application operating in such a
   cellular network needs to cope with a shared bottleneck link and
   variable link capacity, events like handover, non-congestion related
   loss, abrupt changes in bandwidth (both short term and long term) due
   to handover, network load and bad radio coverage.  Even though 3GPP
   define QoS bearers [QoS-3GPP] to ensure high-quality user experience,
   adaptive real-time applications are desired.

   Different mobile operators deploy their own cellular network with
   their own set of network functionalities and policies.  Usually, a
   mobile operator network includes 2G, EDGE, 3G and 4G radio access
   technologies.  Looking at the specifications of such radio
   technologies it is evident that only 3G and 4G radio technologies can
   support the high bandwidth requirements from real-time interactive
   video applications.  The future real-time interactive application
   will impose even greater demand on cellular network performance which
   makes 4G (and beyond radio technologies) more suitable access
   technology for such genre of application.

   The key factors to define test cases for cellular networks are

   o  Shared and varying link capacity

   o  Mobility

   o  Handover

   However, for cellular networks, it is very hard to separate such
   events from one another as these events are heavily related.  Hence
   instead of devising separate test cases for all those important
   events, we have divided the test case into two categories.  It should
   be noted that the goal of the following test cases is to evaluate the
   performance of candidate algorithms over the radio interface of the
   cellular network.  Hence it is assumed that the radio interface is
   the bottleneck link between the communicating peers and that the core
   network does not add any extra congestion in the path.  Also, the
   combination of multiple access technologies such as one user has LTE
   connection and another has Wi-Fi connection is kept out of the scope
   of this document.  However, later those additional scenarios can also
   be added in this list of test cases.  While defining the test cases
   we assumed a typical real-time telephony scenario over cellular
   networks where one real-time session consists of one voice stream and
   one video stream.





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   Even though it is possible to carry out tests over operational LTE
   (and 5G) networks, and actually such tests are already available
   today, these tests cannot in the general case be carried out in a
   deterministic fashion or to ensure repeatability.  The main reason is
   that these networks are in the control of cellular operators and
   there exist various amounts of competing traffic in the same cell(s).
   In practice, it is only in underground mines that one can carry out
   near deterministic testing.  Even there, it is not guaranteed either
   as workers in the mines may carry with them their personal mobile
   phones.  Furthermore, the underground mining setting may not reflect
   typical usage patterns in an urban setting.  We, therefore, recommend
   that an LTE network simulator is used for the test cases defined in
   this document, for example --- NS-3 LTE simulator [LTE-simulator].

3.1.  Varying Network Load

   The goal of this test is to evaluate the performance of the candidate
   congestion control algorithm under varying network load.  The network
   load variation is created by adding and removing network users a.k.a.
   User Equipments (UEs) during the simulation.  In this test case, each
   of the user/UE in the media session is an RMCAT compliant endpoint.
   The arrival of users follows a Poisson distribution proportional to
   the length of the call so as to keep the number of users per cell
   fairly constant during the evaluation period.  At the beginning of
   the simulation, there should be enough time to warm-up the network.
   This is to avoid running the evaluation in an empty network where
   network nodes are having empty buffers, low interference at the
   beginning of the simulation.  This network initialization period is
   therefore excluded from the evaluation period.

   This test case also includes user mobility and some competing
   traffic.  The latter includes both same kind of flows (with same
   adaptation algorithms) and different kind of flows (with different
   services and congestion control schemes).  The investigated
   congestion control algorithms should show maximum possible network
   utilization and stability in terms of rate variations, lowest
   possible end to end frame latency, network latency and Packet Loss
   Rate (PLR) at different cell load level.

3.1.1.  Network Connection

   Each mobile user is connected to a fixed user.  The connection
   between the mobile user and fixed user consists of an LTE radio
   access, an Evolved Packet Core (EPC) and an Internet connection.  The
   mobile user is connected to the EPC using LTE radio access technology
   which is further connected to the Internet.  The fixed user is
   connected to the Internet via wired connection with sufficiently high
   bandwidth, for instance, 10 Gbps, so that the system is resource-



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   limited on the wireless interface.  The wired connection to the
   Internet in this setup does not introduce any network impairments to
   the test; it only adds 10 ms of one-way propagation delay.

   The path from the fixed user to the mobile users is defined as
   "Downlink" and the path from the mobile users to the fixed user is
   defined as "Uplink".  We assume that only uplink or downlink is
   congested for mobile users.  Hence, we recommend that the uplink and
   downlink simulations are run separately.


                             uplink
            ++)))        +-------------------------->
            ++-+      ((o))
            |  |       / \     +-------+     +------+    +---+
            +--+      /   \----+       +-----+      +----+   |
                     /     \   +-------+     +------+    +---+
             UE         BS        EPC        Internet    fixed
                         <--------------------------+
                                  downlink

                       Figure 1: Simulation Topology

3.1.2.  Simulation Setup

   The values enclosed within "[ ]" for the following simulation
   attributes follow the same notion as in [I-D.ietf-rmcat-eval-test].
   The desired simulation setup is as follows --

   1.  Radio environment:

       A.  Deployment and propagation model: 3GPP case 1 [Deployment]

       B.  Antenna: Multiple-Input and Multiple-Output (MIMO), [2D, 3D]

       C.  Mobility: [3km/h, 30km/h]

       D.  Transmission bandwidth: 10Mhz

       E.  Number of cells: multi-cell deployment (3 Cells per Base
           Station (BS) * 7 BS) = 21 cells

       F.  Cell radius: 166.666 Meters

       G.  Scheduler: Proportional fair with no priority

       H.  Bearer: Default bearer for all traffic.




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       I.  Active Queue Management (AQM) settings: AQM [on,off]

   2.  End to end Round Trip Time (RTT): [40, 150]

   3.  User arrival model: Poisson arrival model

   4.  User intensity:

       *  Downlink user intensity: {0.7, 1.4, 2.1, 2.8, 3.5, 4.2, 4.9,
          5.6, 6.3, 7.0, 7.7, 8.4, 9,1, 9.8, 10.5}

       *  Uplink user intensity : {0.7, 1.4, 2.1, 2.8, 3.5, 4.2, 4.9,
          5.6, 6.3, 7.0}

   5.  Simulation duration: 91s

   6.  Evaluation period: 30s-60s

   7.  Media traffic:

       1.  Media type: Video

           a.  Media direction: [Uplink, Downlink]

           b.  Number of Media source per user: One (1)

           c.  Media duration per user: 30s

           d.  Media source: same as defined in Section 4.3 of
               [I-D.ietf-rmcat-eval-test]

       2.  Media Type: Audio

           a.  Media direction: Uplink and Downlink

           b.  Number of Media source per user: One (1)

           c.  Media duration per user: 30s

           d.  Media codec: Constant Bit Rate (CBR)

           e.  Media bitrate: 20 Kbps

           f.  Adaptation: off

   8.  Other traffic models:





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       *  Downlink simulation: Maximum of 4Mbps/cell (web browsing or
          FTP traffic following default TCP congestion control
          [RFC5681])

       *  Unlink simulation: Maximum of 2Mbps/cell (web browsing or FTP
          traffic following default TCP congestion control [RFC5681])

3.2.  Bad Radio Coverage

   The goal of this test is to evaluate the performance of candidate
   congestion control algorithm when users visit part of the network
   with bad radio coverage.  The scenario is created by using a larger
   cell radius than that in the previous test case.  In this test case,
   each of the user/UE in the media session is an RMCAT compliant
   endpoint.  The arrival of users follows a Poisson distribution
   proportional to the length of the call, so as to keep the number of
   users per cell fairly constant during the evaluation period.  At the
   beginning of the simulation, there should be enough amount of time to
   warm-up the network.  This is to avoid running the evaluation in an
   empty network where network nodes are having empty buffers, low
   interference at the beginning of the simulation.  This network
   initialization period is therefore excluded from the evaluation
   period.

   This test case also includes user mobility and some competing
   traffic.  The latter includes the same kind of flows (with same
   adaptation algorithms).  The investigated congestion control
   algorithms should result in maximum possible network utilization and
   stability in terms of rate variations, lowest possible end to end
   frame latency, network latency and Packet Loss Rate (PLR) at
   different cell load levels.

3.2.1.  Network connection

   Same as defined in Section 3.1.1

3.2.2.  Simulation Setup

   The desired simulation setup is the same as the Varying Network Load
   test case defined in Section 3.1 except the following changes:

   1.  Radio environment: Same as defined in Section 3.1.2 except the
       following:

       A.  Deployment and propagation model: 3GPP case 3 [Deployment]

       B.  Cell radius: 577.3333 Meters




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       C.  Mobility: 3km/h

   2.  User intensity = {0.7, 1.4, 2.1, 2.8, 3.5, 4.2, 4.9, 5.6, 6.3,
       7.0}

   3.  Media traffic model: Same as defined in Section 3.1.2

   4.  Other traffic models:

       *  Downlink simulation: Maximum of 2Mbps/cell (web browsing or
          FTP traffic following default TCP congestion control
          [RFC5681])

       *  Unlink simulation: Maximum of 1Mbps/cell (web browsing or FTP
          traffic following default TCP congestion control [RFC5681])

3.3.  Desired Evaluation Metrics for cellular test cases

   RMCAT evaluation criteria document [I-D.ietf-rmcat-eval-criteria]
   defines the metrics to be used to evaluate candidate algorithms.
   However, looking at the nature and distinction of cellular networks
   we recommend that at least the following metrics be used to evaluate
   the performance of the candidate algorithms for the test cases
   defined in this document.

   The desired metrics are --

   o  Average cell throughput (for all cells), shows cell utilizations.

   o  Application sending and receiving bitrate, goodput.

   o  Packet Loss Rate (PLR).

   o  End to end Media frame delay.  For video, this means the delay
      from capture to display.

   o  Transport delay.

   o  Algorithm stability in terms of rate variation.

4.  Wi-Fi Networks Specific Test Cases

   Given the prevalence of Internet access links over Wi-Fi, it is
   important to evaluate candidate RMCAT congestion control solutions
   over test cases that include Wi-Fi access lines.  Such evaluations
   should also highlight the inherently different characteristics of Wi-
   Fi networks in contrast to wired networks:




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   o  The wireless radio channel is subject to interference from nearby
      transmitters, multipath fading, and shadowing, causing
      fluctuations in link throughput and sometimes an error-prone
      communication environment

   o  Available network bandwidth is not only shared over the air
      between concurrent users but also between uplink and downlink
      traffic due to the half-duplex nature of wireless transmission
      medium.

   o  Packet transmissions over Wi-Fi are susceptible to contentions and
      collisions over the air.  Consequently, traffic load beyond a
      certain utilization level over a Wi-Fi network can introduce
      frequent collisions over the air and significant network overhead,
      as well as packet drops due to buffer overflow at the
      transmitters.  This, in turn, leads to excessive delay,
      retransmissions, packet losses and lower effective bandwidth for
      applications.  Note, however, that the consequent delay and loss
      patterns caused by collisions are qualitatively different from
      those induced by congestion over a wired connection.

   o  The IEEE 802.11 standard (i.e., Wi-Fi) supports multi-rate
      transmission capabilities by dynamically choosing the most
      appropriate modulation scheme for the given received signal
      strength.  A different choice of physical-layer rate leads to
      different application-layer throughput.

   o  Presence of legacy 802.11b networks can significantly slow down
      the rest of a modern Wi-Fi network.  As discussed in [Heusse2003],
      the main reason for such abnomaly is that it takes longer to
      transmit the same packet over a slower link than over a faster
      link.

   o  Handover from one Wi-Fi Access Point (AP) to another may lead to
      packet delay and losses during the process.

   o  IEEE 802.11e defined EDCA/WMM (Enhanced DCF Channel Access/Wi-Fi
      Multi-Media) to give voice and video streams higher priority over
      pure data applications (e.g., file transfers).

   In summary, the presence of Wi-Fi access links in different network
   topologies can exert different impact on the network performance in
   terms of application-layer effective throughput, packet loss rate,
   and packet delivery delay.  These, in turn, influence the behavior of
   end-to-end real-time multimedia congestion control.

   Unless otherwise mentioned, test cases in this section are described
   using the underlying PHY- and MAC-layer parameters based on the IEEE



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   802.11n Standard.  Statistics collected from enterprise Wi-Fi
   networks show that the two dominant physical modes are 802.11n and
   802.11ac, accounting for 41% and 58% of connected devices.  As Wi-Fi
   standards evolve over time -- for instance, with the introduction of
   the emerging Wi-Fi 6 (802.11ax) products -- the PHY- and MAC-layer
   test case specifications need to be updated accordingly to reflect
   such changes.

   Typically, a Wi-Fi access network connects to a wired infrastructure.
   Either the wired or the Wi-Fi segment of the network could be the
   bottleneck.  In the following sections, we describe basic test cases
   for both scenarios separately.  The same set of performance metrics
   as in [I-D.ietf-rmcat-eval-test]) should be collected for each test
   case.

   All test cases described below can be carried out using simulations,
   e.g. based on [ns-2] or [ns-3].  When feasible, it is also encouraged
   to perform testbed-based evaluations using Wi-Fi access points and
   endpoints running up-to-date IEEE 802.11 protocols, such as 802.11ac
   and the emerging Wi-Fi 6, to verify the viability of the candidate
   schemes.

4.1.  Bottleneck in Wired Network

   The test scenarios below are intended to mimic the setup of video
   conferencing over Wi-Fi connections from the home.  Typically, the
   Wi-Fi home network is not congested and the bottleneck is present
   over the wired home access link.  Although it is expected that test
   evaluation results from this section are similar to those from test
   cases defined for wired networks (see [I-D.ietf-rmcat-eval-test]), it
   is still worthwhile to run through these tests as sanity checks.

4.1.1.  Network topology

   Figure 2 shows the network topology of Wi-Fi test cases.  The test
   contains multiple mobile nodes (MNs) connected to a common Wi-Fi
   access point (AP) and their corresponding wired clients on fixed
   nodes (FNs).  Each connection carries either a RMCAT or a TCP traffic
   flow.  Directions of the flows can be uplink, downlink, or bi-
   directional.











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                                   Uplink
                             +----------------->+
            +------+                                       +------+
            | MN_1 |))))                             /=====| FN_1 |
            +------+    ))                          //     +------+
                .        ))                        //         .
                .         ))                      //          .
                .          ))                    //           .
            +------+         +----+         +-----+        +------+
            | MN_N | ))))))) |    |         |     |========| FN_N |
            +------+         |    |         |     |        +------+
                             | AP |=========| FN0 |
           +----------+      |    |         |     |      +----------+
           | MN_tcp_1 | )))) |    |         |     |======| MN_tcp_1 |
           +----------+      +----+         +-----+      +----------+
                 .          ))                 \\             .
                 .         ))                   \\            .
                 .        ))                     \\           .
           +----------+  ))                       \\     +----------+
           | MN_tcp_M |)))                         \=====| MN_tcp_M |
           +----------+                                  +----------+
                            +<-----------------+
                                    Downlink

              Figure 2: Network topology for Wi-Fi test cases

4.1.2.  Test setup

   o  Test duration: 120s

   o  Wi-Fi network characteristics:

      *  Radio propagation model: Log-distance path loss propagation
         model [NS3WiFi]

      *  PHY- and MAC-layer configuration: IEEE 802.11n

      *  MCS Index at 11: 16-QAM 1/2, Raw Data Rate@52Mbps

   o  Wired path characteristics:

      *  Path capacity: 1Mbps

      *  One-Way propagation delay: 50ms.

      *  Maximum end-to-end jitter: 30ms

      *  Bottleneck queue type: Drop tail.



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      *  Bottleneck queue size: 300ms.

      *  Path loss ratio: 0%.

   o  Application characteristics:

      *  Media Traffic:

         +  Media type: Video

         +  Media direction: See Section 4.1.3

         +  Number of media sources (N): See Section 4.1.3

         +  Media timeline:

            -  Start time: 0s.

            -  End time: 119s.

      *  Competing traffic:

         +  Type of sources: long-lived TCP or CBR over UDP

         +  Traffic direction: See Section 4.1.3

         +  Number of sources (M): See Section 4.1.3

         +  Congestion control: Default TCP congestion control [RFC5681]
            or constant-bit-rate (CBR) traffic over UDP.

         +  Traffic timeline: See Section 4.1.3

4.1.3.  Typical test scenarios

   o  Single uplink RMCAT flow: N=1 with uplink direction and M=0.

   o  One pair of bi-directional RMCAT flows: N=2 (with one uplink flow
      and one downlink flow); M=0.

   o  One pair of bi-directional RMCAT flows, one on-off CBR over UDP
      flow on uplink: N=2 (with one uplink flow and one downlink flow);
      M=1 (uplink).  CBR flow ON time at 0s-60s, OFF time at 60s-119s.

   o  One pair of bi-directional RMCAT flows, one off-on CBR over UDP
      flow on uplink: N=2 (with one uplink flow and one downlink flow);
      M=1 (uplink).  OFF time for UDP flow: 0s-60s; ON time: 60s-119s.




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   o  One RMCAT flow competing against one long-live TCP flow over
      uplink: N=1 (uplink) and M = 1(uplink), TCP start time at 0s and
      end time at 119s.

4.1.4.  Expected behavior

   o  Single uplink RMCAT flow: the candidate algorithm is expected to
      detect the path capacity constraint, to converge to bottleneck
      link capacity and to adapt the flow to avoid unwanted oscillation
      when the sending bit rate is approaching the bottleneck link
      capacity.  No excessive oscillations in the media rate should be
      present.

   o  Bi-directional RMCAT flows: It is expected that the candidate
      algorithm is able to converge to the bottleneck capacity of the
      wired path on both directions despite the presence of measurement
      noise over the Wi-Fi connection.  In the presence of background
      TCP or CBR over UDP traffic, the rate of RMCAT flows should adapt
      in a timely manner to changes in the available bottleneck
      bandwidth.

   o  One RMCAT flow competing with long-live TCP flow over uplink: the
      candidate algorithm should be able to avoid congestion collapse,
      and to stabilize at a fair share of the bottleneck link capacity.

4.2.  Bottleneck in Wi-Fi Network

   These test cases assume that the wired portion along the media path
   is well-provisioned whereas the bottleneck exists over the Wi-Fi
   access network.  This is to mimic the application scenarios typically
   encountered by users in an enterprise environment or at a coffee
   house.

4.2.1.  Network topology

   Same as defined in Section 4.1.1

4.2.2.  Test setup

   o  Test duration: 120s

   o  Wi-Fi network characteristics:

      *  Radio propagation model: Log-distance path loss propagation
         model [NS3WiFi]

      *  PHY- and MAC-layer configuration: IEEE 802.11n




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      *  MCS Index at 11: 16-QAM 1/2, Raw Data Rate at 52Mbps

   o  Wired path characteristics:

      *  Path capacity: 100Mbps.

      *  One-Way propagation delay: 50ms.

      *  Maximum end-to-end jitter: 30ms.

      *  Bottleneck queue type: Drop tail.

      *  Bottleneck queue size: 300ms.

      *  Path loss ratio: 0%.

   o  Application characteristics:

      *  Media Traffic:

         +  Media type: Video

         +  Media direction: See Section 4.2.3.

         +  Number of media sources (N): See Section 4.2.3.

         +  Media timeline:

            -  Start time: 0s.

            -  End time: 119s.

      *  Competing traffic:

         +  Type of sources: long-lived TCP or CBR over UDP.

         +  Number of sources (M): See Section 4.2.3.

         +  Traffic direction: See Section 4.2.3.

         +  Congestion control: Default TCP congestion control [RFC5681]
            or constant-bit-rate (CBR) traffic over UDP.

         +  Traffic timeline: See Section 4.2.3.







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4.2.3.  Typical test scenarios

   This section describes a few test scenarios that are deemed as
   important for understanding the behavior of a candidate RMCAT
   solution over a Wi-Fi network.

   a.  Multiple RMCAT Flows Sharing the Wireless Downlink: N=16 (all
       downlink); M = 0.  This test case is for studying the impact of
       contention on the multiple concurrent RMCAT flows.  For an
       802.11n network, given the MCS Index of 11 and the corresponding
       raw data rate of 52Mbps, the total application-layer throughput
       (assuming reasonable distance, low interference and infrequent
       contentions caused by competing streams) is around 20Mbps.
       Consequently, a total of N=16 RMCAT flows are needed to saturate
       the wireless interface in this experiment.  Evaluation of a given
       candidate solution should focus on whether downlink RMCAT flows
       can stabilize at a fair share of total application-layer
       throughput.

   b.  Multiple RMCAT Flows Sharing the Wireless Uplink: N = 16 (all
       downlink); M = 0.  When multiple clients attempt to transmit
       video packets uplink over the wireless interface, they introduce
       more frequent contentions and potential collisions.  Per-flow
       throughput is expected to be lower than that in the previous
       downlink-only scenario.  Evaluation of a given candidate solution
       should focus on whether uplink flows can stabilize at a fair
       share of application-layer throughput.

   c.  Multiple Bi-directional RMCAT Flows: N = 16 (8 uplink and 8
       downlink); M = 0.  The goal of this test is to evaluate the
       performance of the candidate solution in terms of bandwidth
       fairness between uplink and downlink flows.

   d.  Multiple Bi-directional RMCAT Flows with on-off CBR traffic: N =
       16 (8 uplink and 8 downlink); M = 5(uplink).  The goal of this
       test is to evaluate the adaptation behavior of the candidate
       solution when its available bandwidth changes due to the
       departure of background traffic.  The background traffic consists
       of several (e.g., M=5) CBR flows transported over UDP.  These
       background flows are ON at times t=0-60s and are OFF at times
       t=61-120s.

   e.  Multiple Bi-directional RMCAT Flows with off-on CBR traffic: N =
       16 (8 uplink and 8 downlink); M = 5(uplink).  The goal of this
       test is to evaluate the adaptation behavior of the candidate
       solution when its available bandwidth changes due to the arrival
       of background traffic.  The background traffic consists of
       several (e.g., M=5) parallel CBR flows transported over UDP.



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       These background flows are OFF at times t=0-60s and are ON at
       times t=61-120s.

   f.  Multiple Bi-directional RMCAT flows in the presence of background
       TCP traffic: N=16 (8 uplink and 8 downlink); M = 5 (uplink).  The
       goal of this test is to evaluate how RMCAT flows compete against
       TCP over a congested Wi-Fi network for a given candidate
       solution.  TCP start time: 40s, end time: 80s.

   g.  Varying number of RMCAT flows: A series of tests can be carried
       out for the above test cases with different values of N, e.g., N
       = [4, 8, 12, 16, 20].  The goal of this test is to evaluate how a
       candidate RMCAT solution responds to varying traffic load/demand
       over a congested Wi-Fi network.  The start time of these RMCAT
       flows is randomly distributed within a window of t=0-10s, whereas
       their end times are randomly distributed within a window of
       t=110-120s.

4.2.4.  Expected behavior

   o  Multiple downlink RMCAT flows: each RMCAT flow should get its fair
      share of the total bottleneck link bandwidth.  Overall bandwidth
      usage should not be significantly lower than that experienced by
      the same number of concurrent downlink TCP flows.  In other words,
      the performance of multiple concurrent TCP flows will be used as a
      performance benchmark for this test scenario.  The end-to-end
      delay and packet loss ratio experienced by each flow should be
      within an acceptable range for real-time multimedia applications.

   o  Multiple uplink RMCAT flows: overall bandwidth usage shared by all
      RMCAT flows should not be significantly lower than that
      experienced by the same number of concurrent uplink TCP flows.  In
      other words, the performance of multiple concurrent TCP flows will
      be used as a performance benchmark for this test scenario.

   o  Multiple bi-directional RMCAT flows with dynamic background
      traffic carrying CBR flows over UDP: RMCAT flows should adapt in a
      timely fashion to the resulting changes in available bandwidth.

   o  Multiple bi-directional RMCAT flows with dynamic background
      traffic over TCP: during the presence of TCP background flows, the
      overall bandwidth usage shared by all RMCAT flows should not be
      significantly lower than those achieved by the same number of bi-
      directional TCP flows.  In other words, the performance of
      multiple concurrent TCP flows will be used as a performance
      benchmark for this test scenario.  All downlink RMCAT flows are
      expected to obtain similar bandwidth with respect to each other.
      The throughput of RMCAT flows should decrease upon the arrival of



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      TCP background traffic and increase upon their departure, both
      reactions should occur in a timely fashion (e.g., within 10s of
      seconds).

   o  Varying number of bi-directional RMCAT flows: the test results for
      varying values of N -- while keeping all other parameters constant
      -- is expected to show steady and stable per-flow throughput for
      each value of N.  The average throughput of all RMCAT flows is
      expected to stay constant around the maximum rate when N is small,
      then gradually decrease with increasing number of RMCAT flows till
      it reaches the minimum allowed rate, beyond which the offered load
      to the Wi-Fi network (with a large value of N) is exceeding its
      capacity.

4.3.  Other Potential Test Cases

4.3.1.  EDCA/WMM usage

   EDCA/WMM is prioritized QoS with four traffic classes (or Access
   Categories) with differing priorities.  RMCAT flows should achieve
   better performance (i.e., lower delay, fewer packet losses) with
   EDCA/WMM enabled when competing against non-interactive background
   traffic (e.g., file transfers).  When most of the traffic over Wi-Fi
   is dominated by media, however, turning on WMM may actually degrade
   performance since all media flows now attempt to access the wireless
   transmission medium more aggressively, thereby causing more frequent
   collisions and collision-induced losses.  This is a topic worthy of
   further investigation.

4.3.2.  Effects of Legacy 802.11b Devices

   When there exist 802.11b devices connected to a modern 802.11
   network, they may affect the performance of the whole network.
   Additional test cases can be added to evaluate the impacts of legacy
   devices on the performance of the candidate congestion control
   algorithm.

5.  Conclusion

   This document defines a collection of test cases that are considered
   important for cellular and Wi-Fi networks.  Moreover, this document
   also provides a framework for defining additional test cases over
   wireless cellular/Wi-Fi networks.








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6.  IANA Considerations

   This memo includes no request to IANA.

7.  Security Considerations

   The security considerations in [I-D.ietf-rmcat-eval-criteria] and the
   relevant congestion control algorithms apply.  The principles for
   congestion control are described in [RFC2914], and in particular, any
   new method MUST implement safeguards to avoid congestion collapse of
   the Internet.

   The evaluations of the test cases are intended to carry out in a
   controlled lab environment.  Hence, the applications, simulators and
   network nodes ought to be well-behaved and should not impact the
   desired results.  It is important to take appropriate caution to
   avoid leaking non-responsive traffic from unproven congestion
   avoidance techniques onto the open Internet.

8.  Acknowledgments

   The authors would like to thank Tomas Frankkila, Magnus Westerlund,
   Kristofer Sandlund, and Sergio Mena de la Cruz for their valuable
   input and review comments regarding this draft.

9.  References

9.1.  Normative References

   [Deployment]
              TS 25.814, 3GPP., "Physical layer aspects for evolved
              Universal Terrestrial Radio Access (UTRA)", October 2006,
              <http://www.3gpp.org/ftp/specs/
              archive/25_series/25.814/25814-710.zip>.

   [HO-def-3GPP]
              TR 21.905, 3GPP., "Vocabulary for 3GPP Specifications",
              December 2009, <http://www.3gpp.org/ftp/specs/
              archive/21_series/21.905/21905-940.zip>.

   [HO-LTE-3GPP]
              TS 36.331, 3GPP., "E-UTRA- Radio Resource Control (RRC);
              Protocol specification", December 2011,
              <http://www.3gpp.org/ftp/specs/
              archive/36_series/36.331/36331-990.zip>.






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   [HO-UMTS-3GPP]
              TS 25.331, 3GPP., "Radio Resource Control (RRC); Protocol
              specification", December 2011,
              <http://www.3gpp.org/ftp/specs/
              archive/25_series/25.331/25331-990.zip>.

   [I-D.ietf-rmcat-eval-criteria]
              Singh, V., Ott, J., and S. Holmer, "Evaluating Congestion
              Control for Interactive Real-time Media", draft-ietf-
              rmcat-eval-criteria-08 (work in progress), November 2018.

   [NS3WiFi]  "Wi-Fi Channel Model in NS3 Simulator",
              <https://www.nsnam.org/doxygen/
              classns3_1_1_yans_wifi_channel.html>.

   [QoS-3GPP]
              TS 23.203, 3GPP., "Policy and charging control
              architecture", June 2011, <http://www.3gpp.org/ftp/specs/
              archive/23_series/23.203/23203-990.zip>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
              RFC 2914, DOI 10.17487/RFC2914, September 2000,
              <https://www.rfc-editor.org/info/rfc2914>.

   [RFC5681]  Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
              Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
              <https://www.rfc-editor.org/info/rfc5681>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

9.2.  Informative References

   [Heusse2003]
              Heusse, M., Rousseau, F., Berger-Sabbatel, G., and A.
              Duda, "Performance anomaly of 802.11b", in Proc. 23th
              Annual Joint Conference of the IEEE Computer and
              Communications Societies, (INFOCOM'03), March 2003.







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   [I-D.ietf-rmcat-cc-requirements]
              Jesup, R. and Z. Sarker, "Congestion Control Requirements
              for Interactive Real-Time Media", draft-ietf-rmcat-cc-
              requirements-09 (work in progress), December 2014.

   [I-D.ietf-rmcat-eval-test]
              Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test
              Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat-
              eval-test-10 (work in progress), May 2019.

   [IEEE802.11]
              IEEE, "Standard for Information technology--
              Telecommunications and information exchange between
              systems Local and metropolitan area networks--Specific
              requirements Part 11: Wireless LAN Medium Access Control
              (MAC) and Physical Layer (PHY) Specifications", 2012.

   [LTE-simulator]
              "NS-3, A discrete-Event Network Simulator",
              <https://www.nsnam.org/docs/release/3.23/manual/html/
              index.html>.

   [ns-2]     "The Network Simulator - ns-2",
              <http://www.isi.edu/nsnam/ns/>.

   [ns-3]     "The Network Simulator - ns-3", <https://www.nsnam.org/>.

Authors' Addresses

   Zaheduzzaman Sarker
   Ericsson AB
   Laboratoriegraend 11
   Luleae  97753
   Sweden

   Phone: +46 107173743
   Email: zaheduzzaman.sarker@ericsson.com


   Ingemar Johansson
   Ericsson AB
   Laboratoriegraend 11
   Luleae  97753
   Sweden

   Phone: +46 10 7143042
   Email: ingemar.s.johansson@ericsson.com




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   Xiaoqing Zhu
   Cisco Systems
   12515 Research Blvd., Building 4
   Austin, TX  78759
   USA

   Email: xiaoqzhu@cisco.com


   Jiantao Fu
   Cisco Systems
   707 Tasman Drive
   Milpitas, CA  95035
   USA

   Email: jianfu@cisco.com


   Wei-Tian Tan
   Cisco Systems
   725 Alder Drive
   Milpitas, CA  95035
   USA

   Email: dtan2@cisco.com


   Michael A. Ramalho
   Cisco Systems, Inc.
   8000 Hawkins Road
   Sarasota, FL  34241
   USA

   Phone: +1 919 476 2038
   Email: mramalho@cisco.com
















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