Network Working Group Z. Sarker
Internet-Draft I. Johansson
Intended status: Informational Ericsson AB
Expires: June 25, 2019 X. Zhu
J. Fu
W. Tan
M. Ramalho
Cisco Systems
December 22, 2018

Evaluation Test Cases for Interactive Real-Time Media over Wireless Networks
draft-ietf-rmcat-wireless-tests-06

Abstract

The Real-time Transport Protocol (RTP) is used for interactive multimedia communication applications. These applications are typically required to implement congestion control. 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

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This Internet-Draft will expire on June 25, 2019.

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Table of Contents

1. Introduction

Wireless networks (both cellular and Wi-Fi [IEEE802.11] local area network) are an integral part of the Internet. Mobile devices connected to the wireless networks generate huge amount of media traffic in the Internet. Application scenarios range from users having a video call in the bus to media consumption by someone sitting on a living room couch. It is well known that the characteristics and technical challenges for offering multimedia services over wireless are very different from those of providing the same service over a wired network. Even though RMCAT basic test cases as defined in [I-D.ietf-rmcat-eval-test] have covered many effects of the impairments also visible in wireless networks, there remains characteristics and dynamics unique to a given wireless environment. For example, in LTE networks the base station maintains queues per radio bearer per user hence it leads to a different nature of interaction from that over the wired network, where traffic from all users share the same queue. Furthermore, user mobility in a cellular network is different than user mobility in a Wi-Fi network. Therefore, It is important to evaluate performance of the proposed RMCAT candidate solutions separately over cellular mobile networks and over Wi-Fi local networks (i.e., IEEE 802.11xx protocol family ).

RMCAT evaluation criteria [I-D.ietf-rmcat-eval-criteria] document 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 evaluating performance of the candidate algorithm. This document describes test cases specifically targeting cellular networks such as LTE networks and Wi-Fi local 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 a wireline ditto 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 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 which 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 transport network will become even worse. Besides, there are certain characteristics which make the cellular network different and challenging than other types of access network such as Wi-Fi and wired network. In a cellular network -

[QoS-3GPP] to ensure high quality user experience, adaptive real-time applications are desired.

Hence, a real-time communication application operating in such a cellular network need to cope with shared bottleneck link and variable link capacity, event likes handover, non-congestion related loss, abrupt change in bandwidth (both short term and long term) due to handover, network load and bad radio coverage. Even though 3GPP define QoS bearers

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 network are

However, for cellular network 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 in two categories. It should be noted that in the following test cases the goal is to evaluate the performance of candidate algorithms over 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. We 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, which is proportional to the length of the call, so that the number of users per cell is kept 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 competing traffic. The competing traffics includes both same kind of flows (with same adaptation algorithms) and different kind of flows (with different service and congestion control). 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 a 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 no bottleneck (practically infinite bandwidth). The Internet and wired connection in this setup does not add any network impairments to the test, it only adds 10ms of one-way transport propagation delay.

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

Figure 1: Simulation Topology

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

3.1.2. Simulation Setup

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

  1. Radio environment
    1. Deployment and propagation model : 3GPP case 1[Deployment]
    2. Antenna: Multiple-Input and Multiple-Output (MIMO), [2D, 3D]
    3. Mobility: [3km/h, 30km/h]
    4. Transmission bandwidth: 10Mhz
    5. Number of cells: multi cell deployment (3 Cells per Base Station (BS) * 7 BS) = 21 cells
    6. Cell radius: 166.666 Meters
    7. Scheduler: Proportional fair with no priority
    8. Bearer: Default bearer for all traffic.
    9. 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:
  5. Simulation duration: 91s
  6. Evaluation period : 30s-60s
  7. Media traffic
    1. Media type: Video
      1. Media direction: [Uplink, Downlink]
      2. Number of Media source per user: One (1)
      3. Media duration per user: 30s
      4. Media source: same as define in section 4.3 of [I-D.ietf-rmcat-eval-test]
    2. Media Type : Audio
      1. Media direction: Uplink and Downlink
      2. Number of Media source per user: One (1)
      3. Media duration per user: 30s
      4. Media codec: Constant BitRate (CBR)
      5. Media bitrate : 20 Kbps
      6. Adaptation: off
  8. Other traffic model:

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 larger cell radius than 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, which is proportional to the length of the call, so that the number of users per cell is kept 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 competing traffic. The competing traffics includes same kind of flows (with same adaptation algorithms) . 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.

3.2.1. Network connection

Same as defined in Section 3.1.1

3.2.2. Simulation Setup

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

  1. Radio environment : Same as defined in Section 3.1.2 except followings
    1. Deployment and propagation model : 3GPP case 3[Deployment]
    2. Cell radius: 577.3333 Meters
    3. 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 model: None

3.3. Desired Evaluation Metrics for cellular test cases

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

The desired metrics are-

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 inherent different characteristics of Wi-Fi networks in contrast to wired networks:

In summary, 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.

Throughout this draft, unless otherwise mentioned, test cases are described using 802.11n due to its wide availability in real-world networks. Statistics collected from enterprise Wi-Fi networks show that the dominant physical modes are 802.11n and 802.11ac, accounting for 73.6% and 22.5% of enterprise network users, respectively.

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.

While all test cases described below can be carried out using simulations, e.g. based on [ns-2] or [ns-3], it is also recommended to perform testbed-based evaluations using Wi-Fi access points and endpoints running up-to-date IEEE 802.11 protocols. [Editor's Note: need to add some more discussions on the pros and cons of simulation-based vs. testbed-based evaluations. Will be good to provide recommended testbed configurations. ]

4.1. Bottleneck in Wired Network

The test scenarios below are intended to mimic the set up 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 worthwhile to run through these tests as sanity checks.

4.1.1. Network topology

                             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

Figure 2 shows topology of the network for 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 RMCAT or TCP traffic flow. Directions of the flows can be uplink, downlink, or bi-directional.

4.1.2. Test setup

4.1.3. Typical test scenarios

4.1.4. Expected behavior

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

4.2.3. Typical test scenarios

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

4.2.4. Expected behavior

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 is 802.11b devices connected to modern 802.11 network, it may affect the performance of the whole network. Additional test cases can be added to evaluate the affects of legancy devices on the performance of RMCAT 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.

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 evaluation of the test cases are intended to be run 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. Acknowledgements

We would like to thank Tomas Frankkila, Magnus Westerlund, Kristofer Sandlund for their valuable comments while writing 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.
[HO-def-3GPP] TR 21.905, 3GPP., "Vocabulary for 3GPP Specifications", December 2009.
[HO-LTE-3GPP] TS 36.331, 3GPP., "E-UTRA- Radio Resource Control (RRC); Protocol specification", December 2011.
[HO-UMTS-3GPP] TS 25.331, 3GPP., "Radio Resource Control (RRC); Protocol specification", December 2011.
[I-D.ietf-rmcat-eval-criteria] Singh, V., Ott, J. and S. Holmer, "Evaluating Congestion Control for Interactive Real-time Media", Internet-Draft draft-ietf-rmcat-eval-criteria-08, November 2018.
[NS3WiFi] "Wi-Fi Channel Model in NS3 Simulator"
[QoS-3GPP] TS 23.203, 3GPP., "Policy and charging control architecture", June 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC 2914, DOI 10.17487/RFC2914, September 2000.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.

9.2. Informative References

[I-D.ietf-rmcat-cc-requirements] Jesup, R. and Z. Sarker, "Congestion Control Requirements for Interactive Real-Time Media", Internet-Draft draft-ietf-rmcat-cc-requirements-09, December 2014.
[I-D.ietf-rmcat-eval-test] Sarker, Z., Singh, V., Zhu, X. and M. Ramalho, "Test Cases for Evaluating RMCAT Proposals", Internet-Draft draft-ietf-rmcat-eval-test-08, November 2018.
[IEEE802.11] "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"
[ns-2] "The Network Simulator - ns-2"
[ns-3] "The Network Simulator - ns-3"

Authors' Addresses

Zaheduzzaman Sarker Ericsson AB Laboratoriegränd 11 Luleå, 97753 Sweden Phone: +46 107173743 EMail: zaheduzzaman.sarker@ericsson.com
Ingemar Johansson Ericsson AB Laboratoriegränd 11 Luleå, 97753 Sweden Phone: +46 10 7143042 EMail: ingemar.s.johansson@ericsson.com
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