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Network Working Group                                     T.  Alexander
Internet-Draft                                           VeriWave, Inc.
                                                            S.  Bradner
                                                     Harvard University
Expires October 2005                                         April 2005

           Benchmarking Methodology for Wireless LAN Devices
                   <draft-alexander-wlan-meth-01.txt>

Status of this Memo
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   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of RFC 3668.

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Copyright Notice
                Copyright (C) The Internet Society (2005).

Abstract
   This document provides a framework and methodology for performing
   stress testing and benchmarking of wireless LAN (WLAN) devices,
   including clients (i.e., host interfaces) and Access Points.  The
   document defines and discusses a number of tests and associated test
   conditions that may be used to characterize the performance of such
   devices, and also supplies the methods used to calculate the results
   of these tests.  This document also describes specific formats for
   reporting the results of the tests. It extends the methodology
   defined for benchmarking network interconnecting devices in RFC 2544
   and LAN switches in RFC 2889 to IEEE 802.11 WLAN devices.

   Table of Contents




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   1.  Introduction .................................................. 3
   2.  Existing definitions and requirements ......................... 3
   3.  Tester description and test setups ............................ 4
    3.1. Functional model of the tester .............................. 4
    3.2. Test setup .................................................. 5
     3.2.1. Test setup for Access Points ............................. 5
     3.2.2. Test setup for clients ................................... 5
    3.3. DUT setup ................................................... 6
     3.3.1. Access Point setup ....................................... 6
     3.3.2. Client setup ............................................. 7
    3.4. Wireless configuration parameters ........................... 8
     3.4.1. Channel assignment ....................................... 8
     3.4.2. Transmit power level ..................................... 8
     3.4.3. RTS threshold ............................................ 8
     3.4.4. Fragmentation threshold .................................. 9
     3.4.5. Power management mode .................................... 9
     3.4.6. Service priority ........................................ 10
    3.5. Test conditions ............................................ 10
     3.5.1. Test environment ........................................ 10
     3.5.2. Frame sizes ............................................. 11
     3.5.3. Frame formats and verification .......................... 12
     3.5.4. Half-duplex effects on calculating offered load ......... 13
     3.5.5. Retry of unacknowledged frames .......................... 14
     3.5.6. Physical layer (PHY) data rates ......................... 15
     3.5.7. Management and control frames ........................... 15
     3.5.8. Authentication and association .......................... 16
     3.5.9. Signal level and signal-to-noise ratios ................. 16
     3.5.10. Beacons and PCF access method settings ................. 17
     3.5.11. Multiple clients ....................................... 18
     3.5.12. Trial duration ......................................... 18
     3.5.13. Configuration combinations ............................. 19
     3.5.14. Basic test parameters .................................. 19
   4.  Interpreting and reporting test results ...................... 21
   5.  Benchmarking tests ........................................... 21
    5.1. Throughput related tests ................................... 22
     5.1.1. Unicast intra-BSS throughput, forwarding rate
            and frame loss .......................................... 22
     5.1.2. Unicast ESS throughput, forwarding rate and frame loss .. 24
     5.1.3. Multicast forwarding rate ............................... 26
     5.1.4. Forward pressure ........................................ 27
     5.1.5. Authentication and association rate ..................... 29
     5.1.6. Power management mode throughput, forwarding rate
            and frame loss .......................................... 32
    5.2. Latency and timing tests ................................... 33
     5.2.1. Intra-BSS latency and latency variation ................. 34
     5.2.2. ESS latency and latency variation ....................... 35
     5.2.3. Roaming and reassociation time .......................... 37
     5.2.4. Rate adaptation time .................................... 39



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     5.2.5. Beacon interval and timing .............................. 41
     5.2.6. Reset recovery time ..................................... 42
    5.3. Capacity tests ............................................. 43
     5.3.1. Burst capacity .......................................... 44
     5.3.2. Authentication and association database capacity ........ 45
     5.3.3. Power-save buffer capacity .............................. 48
   4. Security Considerations ....................................... 49
   5. IANA Considerations ........................................... 49
   6. References .................................................... 50
    6.1. Normative References ....................................... 50
    6.2. Informative References ..................................... 50
   7.  Author's Addresses ........................................... 50
   Appendix A.  Intended load computations .......................... 51
    A.1. Calculating theoretical maximum media capacity ............. 51
    A.2. Calculating constant intended load ......................... 52
    A.3. Calculating burst intended load ............................ 53
   Full Copyright Statement ......................................... 54
   Intellectual Property ............................................ 54

1.  Introduction

   This document defines and describes a specific set of tests that may
   be used by vendors and users of IEEE 802.11 Wireless LAN (WLAN)
   [802.11] devices to measure and report performance characteristics
   of such devices.  It extends the methodology that was originally
   defined for benchmarking network interconnecting devices in RFC 2544
   [RFC2544], and then subsequently extended to other types of devices
   (such as LAN switching devices in RFC 2889 [RFC2889]), to cover IEEE
   802.11 WLAN devices. Note that only IEEE 802.11 conformant devices
   are covered by this document; other technologies (e.g., Hiperlan/2)
   are not considered.

   Wireless LANs may be characterized as using a complex, rate-adaptive
   protocol designed for shared media access and subject to numerous
   environmental influences, many of which are outside the control of
   the end-user.  The tests in this document are therefore intended to
   provide a means of comparison and evaluation, rather than absolute
   measures of performance in an arbitrary end-user environment.

2.  Existing definitions and requirements

   RFC 1242, "Benchmarking Terminology for Network Interconnect Devices"
   [RFC1242] is relied upon for much of the terminology used in this
   document, and MUST be consulted before attempting to make use of this
   document.  In addition, RFC 2285, "Benchmarking Terminology for LAN
   Switching Devices" [RFC2285] SHOULD be reviewed as well.  RFC 2544,
   "Benchmarking Methodology for Network Interconnect Devices" [RFC2544]
   and RFC 2889, "Benchmarking Methodology for LAN Switching Devices"



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   [RFC2889], also provide useful background information and context.
   The WLAN-specific terms and definitions in this document are
   described in Clauses 3 and 4 of the IEEE 802.11 standard [802.11].

   For the sake of clarity and continuity this RFC adopts the general
   template for benchmarking tests set out in Section 26 of RFC 2544.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

3.  Tester description and test setups

   A common set of test setup and measurement conditions is used across
   all of the tests described in this document.  Exceptions to these
   conditions are noted, if necessary, in the descriptions of the
   individual tests.

3.1. Functional model of the tester

   For the purposes of this document, the tester is defined as a
   separate device that is used to transmit controlled test traffic to
   the physical ports of the device under test (DUT) as well as to
   receive and measure test traffic from the physical ports of the DUT.
   The tester MUST NOT be a part of the DUT, nor can the DUT provide any
   portion of the reported test results. An exception is the case of
   client devices, which MAY be required to host test software in order
   to support the requirements of one or more tests.

   The tester MUST transmit 802.11-conformant traffic to the DUT during
   the tests described herein, and MUST follow the rules of the 802.11
   protocol with respect to media access and frame exchanges. It MAY be
   configured to transmit non-conformant traffic for special purposes
   (e.g., for debug), but this is outside the scope of this document.
   The tester MUST support some means of distinguishing test traffic
   (either injected into or emitted by the DUT) from normal data,
   control and management frames that are generated by the DUT itself.
   The tester SHOULD further support means of unambiguously determining
   frame loss and frame duplication (e.g., by the use of sequence
   numbers), as well as time-stamping transmitted and received frames.

   No constraints are placed by this document on the specific
   implementation of the tester or test system, provided that it is
   capable of measuring DUT responses to the required degree of
   accuracy, establishing the required test conditions at the physical
   interfaces of the DUT, and generating test traffic with the relevant
   parameters. These parameters include frame sizes, offered load, burst
   sizes and inter-burst gap, signal output level, etc.



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3.2. Test setup

3.2.1. Test setup for Access Points

   Many of the tests performed on Access Points require that test
   traffic be injected into and/or received from both the wired and the
   wireless ports of these devices. The ideal means of implementing
   tests on Access Points is therefore to use a tester or test system
   that can interface to both types of ports on the DUT, as shown in
   Figure 1.

                               +------------+
                    Wireless   |   Access   |  Wired
                  +----------->|   Point    |<-------------+
                  | Media      |    DUT     |  Media       |
                  | Interface  +------------+  Interface   |
                  |                                        |
                  |            +------------+              |
                  |            |            |              |
                  +----------->|   tester   |<-------------+
                               |            |
                               +------------+
                                 Figure 1

   The tests in this document are also generally applicable to DUTs that
   provide multiple media interfaces, such as an Access Point that
   supports multiple wireless interfaces that are aggregated into a
   single wired interface. Section 6 of RFC 2544 [RFC2544], as well as
   Section 5.2.3 of RFC 2889 [RFC2889], may be consulted for information
   on extending the tests to multi-port devices. Test results MUST be
   reported separately for each physical port of the DUT.

3.2.2. Test setup for clients

   Due to the variety of physical configurations of client devices, a
   test setup for a client is dependent on the nature of the DUT. If the
   client is multi-homed, and can be set up to transfer traffic between
   the wireless interface being tested and some other physically
   accessible interface, then a test setup similar to Figure 1 can be
   used, as shown in Figure 2.

                               +------------+
                    Wireless   |   client   |  Secondary
                  +----------->|     DUT    |<-------------+
                  | Media      |            |  Wired or    |
                  | Interface  +------------+  Wireless    |
                  | Under Test                 Interface   |
                  |            +------------+              |



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                  |            |            |              |
                  +----------->|   tester   |<-------------+
                               |            |
                               +------------+
                                 Figure 2

   The DUT is set up to route traffic injected into the wireless
   interface under test to a secondary interface, which may be either
   wired or wireless. Also, traffic injected into this secondary
   interface by the tester is transferred to the wireless interface
   under test. The secondary interface MUST have bandwidth and delay
   characteristics that are known to be much better than that of the
   wireless media interface of the DUT that is actually being tested.

   If the DUT is not multi-homed (or lacks a suitable secondary
   interface), then some test software MAY be supported on the client
   itself in order to enable it to be tested, as shown in Figure 3.

            +--------+  Wireless  +------------+    +----------+
            |        |    Media   |   Client   |    |   Test   |
            | tester |<---------->|  Interface |<-->| Software |
            |        |  Interface |    DUT     |    |  On DUT  |
            +--------+ Under Test +------------+    +----------+
                                 Figure 3

   If the approach of Figure 3 is adopted, then it is understood that
   the DUT comprises only the physical media interface and any device
   driver and protocol stack software that is actually interposed
   between the physical interface and the test software. The entire
   device of which the physical media interface is a part MUST NOT be
   considered to be tested by this method, as the test software may have
   an impact on the remainder of the client device that is not
   characterized by the tests presented in this document.

   If a software program is executed on the DUT in order to enable
   testing, the description and version of this software MUST be
   included along with the test results.

3.3 DUT setup

   The general DUT setup MUST follow the requirements described in
   Section 7 of RFC 2544 [RFC2544].

   The specific software or firmware version being used in the DUT, as
   well as the exact DUT configuration (including any functions that
   have been disabled) MUST be reported together with the results.

3.3.1. Access Point setup



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   Access Points MUST be configured with both their wired and their
   wireless interfaces active following the instructions for normal use
   from the manufacturer. The wired interface MAY be disconnected from
   the tester for tests that do not involve traffic exchanged between
   the wired and wireless interfaces.

   A System under Test (SUT) comprising one or more Access Points
   interfaced to a dedicated management and switching device MAY be
   treated as a single complex DUT and tested as a unit. In this case,
   the wired interface(s) of the tester MUST be connected to wired
   interface(s) on the management and switching device, instead of to
   the wired interfaces of the Access Point(s) directly.

   Access Points generally operate in one or more of the following
   modes:

      Intra BSS (Basic Service Set) mode. Here, an Access Point receives
      data packets from a wireless client and forwards these packets to
      another wireless client directly, i.e., without traversing the
      wired media. Both clients must be associated with the same Access
      Point.

      ESS (Extended Service Set) mode. In this case an Access Point
      receives data packets from a wireless client and forwards these to
      a wired client (residing on its wired interface) or to another
      wireless client by means of a second Access Point and the wired
      network.

      WDS (Wireless Distribution System) mode. This is a variant of the
      ESS mode.  Here an Access Point receives data packets from a
      wireless client associated with it, and forwards these packets to
      a second Access Point over the wireless medium. The second Access
      Point then transfers these packets to their final destination. The
      effect is similar to a wireless repeater network.

   A single Access Point is normally capable of performing data
   transfers using more than one of the above modes simultaneously.

3.3.2. Client setup

   Devices containing client DUTs SHOULD be set up using the
   manufacturer's normal instructions to match an normal user
   configuration; however, user applications and processes that are not
   part of a vendor-supplied device configuration MAY be removed or
   suspended during the tests. Vendor-supplied configuration utilities
   SHOULD be used to configure the various parameters of the wireless
   interface (e.g., fragmentation thresholds) according to the
   requirements of the test.



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   Many client devices offer one or more power-saving modes that can
   materially impact the test results. Tests SHOULD be run at different
   power-save settings, but a full suite of tests MUST be run at least
   one specific setting and the results reported. The power-save mode
   setting MUST be reported along with the test results. (See Section
   3.4.5.)

   Clients operate in one of the following modes:

      Associated with an Access Point. In this case, the client sends
      all data traffic to the Access Point, for forwarding to the
      ultimate destination.

      In Independent BSS (IBSS) mode. This is a peer-to-peer mode of
      operation, where two or more clients form an "ad hoc network" and
      forward packets amongst each other without the services of an
      Access Point.

   Clients cannot operate in both of the above modes simultaneously.

3.4. Wireless configuration parameters

   DUT setup considerations specific to WLAN devices are given below.

3.4.1. Channel assignment

   The DUT MUST be configured to use a wireless channel that a normal
   user would use at the location where the test was run.  For example,
   if the test is run in the U.S. then a standard U.S. wireless channel
   is used. The channel used MUST be reported with the test results.

3.4.2. Transmit power level

   For DUTs with adjustable transmit power levels, tests MAY be run at
   different transmit power settings, although a full suite of tests
   MUST be run at each power setting tested. The power setting used in
   each test MUST be reported with the test results.

3.4.3. RTS threshold

   The 802.11 protocol supports the use of a Request To Send (RTS) /
   Clear To Send (CTS) handshake prior to data transfer, as a means for
   interfaces to seize and reserve the medium before actually
   transferring data. This is normally expected to be used for larger
   frame sizes, where contention-based medium access may result in high
   retransmission overheads. Determination of whether to use an RTS/CTS
   handshake is based on the size of the frame to be transmitted, and is
   statically configured as a threshold on the frame size.



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   For DUTs with adjustable RTS thresholds, tests MAY be run at
   different RTS thresholds, although a full suite of tests MUST be run
   at each RTS threshold tested. The RTS threshold used in each test
   MUST be reported with the test results.

3.4.4. Fragmentation threshold

   The 802.11 protocol supports fragmentation and reassembly at the link
   layer, in order to decrease retransmission overhead under high error
   rates that may prevail in a radio frequency (RF) environment. If a
   fragment of a frame is lost due to a bit error or a collision, only
   that fragment is retransmitted. Determination of whether to fragment
   a frame before transmission is based on the size of the frame, and is
   statically configured as a threshold on the frame size.

   For DUTs with adjustable fragmentation thresholds, tests MAY be run
   at different fragmentation thresholds, although a full suite of tests
   MUST be run at each fragmentation threshold tested. The fragmentation
   threshold used in each test MUST be reported with the test results.

   The tests in this document are performed at different fixed frame
   sizes. The number of fragments produced with a given fragmentation
   threshold will be known a priori for any given frame size. The tester
   SHOULD therefore verify that the number of fragments generated by the
   DUT during a test is correct.

3.4.5. Power management mode

   The 802.11 protocol supports several power management functions, in
   order to allow client devices to reduce power by placing their
   wireless interfaces in a low-power mode during known periods of
   inactivity. (Access Points do not enter a power-saving mode, but
   support power-save by clients associated with them.) Transmission to
   a client in power-save mode is typically bursty; the Access Point
   accumulates packets destined for the client in internal buffers,
   notifies the client of these packets by means of special fields in
   its beacons, and then transfers them when the client and requests its
   outstanding data. Good time synchronization between Access Points and
   clients is essential for efficient and low-latency data transfers, as
   clients need to be awake and listening when Access Points issue
   notifications via beacons.

   Throughput and latency measurements on a client are significantly
   affected by the power management mode of the client. Therefore,
   throughput and latency tests SHOULD be run with power management
   disabled or minimized. If the DUT and tester are capable of
   supporting multiple power management modes, then tests MAY be run in
   different modes. The power management mode of the client MUST be



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   reported with the test results.

3.4.6. Service priority

   For DUTs with adjustable service priorities (QoS levels), tests MAY
   be run at different service priorities, although a full suite of
   tests SHOULD be run at least one service priority. For such DUTs, the
   service priority used in each test MUST be reported with the test
   results.

   Throughput and latency tests on Access Points involving traffic
   traversing wired interfaces can be affected by QoS settings on these
   wired interfaces.  In such situations, the QoS settings assigned to
   the wired interfaces of Access Points MUST be reported with the test
   results.

3.5. Test conditions

   Test conditions for measurements on WLAN devices are covered in this
   section.  The complexity of the wireless LAN media and protocol
   necessitate special attention to specifying and setting up these
   conditions in order to obtain repeatable results.

3.5.1. Test environment

   Wireless LAN test environments may be divided into two general
   categories: shielded environments and open-air environments.

   Shielded environments use cabling and/or RF shielding techniques to
   significantly attenuate signals and noise unrelated to the test.
   Typically, the DUT is enclosed within an RF-tight chamber and cabled
   to the tester (which is also placed in an RF-tight chamber);
   alternatively, both the DUT and the tester may be placed in the same
   chamber, such as a Faraday cage.  Unless the chamber is fairly large,
   coupling between the DUT and tester is conducted (i.e., via cables)
   and not radiated (via antennas).

   Open-air environments mimic the actual use model of a WLAN DUT. In
   this case, the DUT is placed at a specific location within some
   moderately controlled (or at least characterized) indoor or outdoor
   environment. The tester is also placed within the same environment at
   a specific position relative to the DUT and other known signal
   sources (if any). Antennas are used on both the DUT and the tester to
   enable signal transfer; coupling is hence radiated.

   The tests described in this document can be carried out in either of
   the above environments, provided that the remainder of the test
   conditions specified in this section (particularly the signal-to-



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   noise and signal-to-interference ratios, described in Section 3.5.9)
   are met. The test environment used in the tests MUST be described
   along with the results.

3.5.2. Frame sizes

   All of the described tests SHOULD be performed using several fixed
   sizes of test data frames. Frame sizes are calculated from the first
   byte of the MAC DA to the last byte of the FCS (i.e., all of the
   802.11 MAC header and trailer fields are included, but the PLCP
   header is not included). The various mode-specific encapsulations
   supported by the 802.11 protocol makes frame size calculations
   somewhat challenging. The test results MUST list the frame sizes used
   for test data frames.

   When using test data encoded using the 3-address 802.11 frame format
   without encryption, the data frame sizes that SHOULD be used during
   the tests are:

      28, 64, 128, 256, 512, 1024, 1528, 2048, 2332

   The payload length may be obtained by subtracting 28 from the frame
   size.  A frame size of 28 bytes corresponds to a null frame (i.e., an
   802.11 data frame with a zero-length payload).  A frame size of 1528
   bytes results in a payload length of exactly 1500 bytes, which is the
   maximum sized frame that can be bridged on to an Ethernet LAN.  A
   frame size of 2332 bytes corresponds to the maximum defined 802.11
   MAC Service Data Unit (upper-layer payload) of 2304 bytes.

   Test data that uses a 3-address 802.11 frame format with Wired
   Equivalent Priority (WEP) encryption SHOULD use the following frame
   sizes:

      28, 64, 128, 256, 512, 1024, 1536, 2048, 2340

   With the exception of null frames, the payload length may be obtained
   by subtracting 36 from the frame size. Null frames contain no WEP
   header and thus remain at 28 bytes.

   When using a 4-address 802.11 frame format without encryption, the
   802.11 header/trailer overhead increases to 34 bytes, and the test
   data frame sizes that SHOULD be used are:

      34, 64, 128, 256, 512, 1024, 1534, 2048, 2346

   In this case, a frame size of 34 bytes corresponds to a null frame,
   1534 bytes to a payload length of 1500 bytes, and 2346 bytes to the
   maximum defined 802.11 payload length of 2312 bytes. Note that the



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   usable 802.11 payload sizes for the other frame size values are
   smaller by 6 bytes over the 3-address case.

   Finally, when using a 4-address 802.11 test data frame format with
   WEP, the 802.11 header/trailer overhead increases to 42 bytes, and
   the frame sizes that SHOULD be used are:

      34, 64, 128, 256, 512, 1024, 1542, 2048, 2354

   As before, null frames do not contain a WEP header.

   Inclusion of additional 802.11-specific header and trailer fields for
   extended capabilities (e.g., advanced encryption, QoS support) can
   cause the frame size to change. Test data traffic that includes such
   additional header and trailer fields SHOULD use frame sizes
   consistent with those given above.

   In some cases, such as tests on clients, or ESS testing on APs (see
   Subclause 3.25 of the IEEE 802.11 standard [802.11] for a description
   of ESS), not all of the above frame sizes are practicable. For
   example, a null frame will not be processed by clients. Test
   procedures for these specific situations detail exceptions to the
   frame sizes to be used.

   Frame sizes of 802.11 management and control frames generated during
   the test MUST conform to those required by the 802.11 standard
   [802.11].

3.5.3. Frame formats and verification

   The frame formats used for test data frames (with the exception of
   null 802.11 frames) SHOULD follow the recommendations in Appendix C
   of RFC 2544 [RFC2544].  LLC/SNAP encapsulation as per RFC 1042
   [RFC1042] MUST be used to contain higher-layer payloads. Note that
   when the added overhead of the 8-byte LLC/SNAP header is taken into
   account, 64 byte WLAN frame sizes can only support link layer
   payloads ranging from 28 bytes to as little as 14 bytes, and hence
   may not be able to contain an IP header.

   With the exception of null frames, the test frame format MUST contain
   some means (such as a unique signature field, as described in Section
   4 of RFC 2544 [RFC2544]) that will enable the tester to filter out
   frames that are not part of the offered load, or are duplicated by
   the DUT. In tests on Access Points involving multiple virtual or
   physical test clients, the test frame format MAY also support means
   for distinguishing between frames originating from different clients.

   The provisions for verifying received frames in Section 10 of RFC



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   2544 [RFC2544] SHOULD be followed as well. This is particularly
   significant for 802.11, which implements retransmission at the link
   layer. The verification of received frames SHOULD be independent of
   the facilities provided by the 802.11 protocol.

3.5.4. Half-duplex effects on calculating offered load

   WLAN Access Points and clients perform medium access in half-duplex
   mode, implementing deference and backoff to minimize the probability
   of collisions.  Further, packet transmission is bidirectional, in
   that data transmission from source to destination is immediately
   followed by an acknowledgement from destination to source. This leads
   to a number of issues when attempting to impose or calculate an
   offered load during testing.

   The relevant characteristics of 802.11 media access are:
      Carrier sensing before access. Stations are required to defer to
      all ongoing transmissions before attempting to transmit. Small
      changes in relative access timing between stations may result in
      large variations in the actual access pattern.

      Random backoff after all transmission attempts. The 802.11
      protocol attempts to avoid collisions by forcing all stations to
      delay for a random interval after both successful or unsuccessful
      transmission attempts. The random backoff must be implemented even
      if only one station is attempting to transmit.

      Suspension of backoff timers when the medium is busy. To preserve
      station priority in a busy environment, the 802.11 protocol
      requires backoff timers for stations contending for the medium to
      be suspended (rather than reset) during deference periods. Hence
      stations contending for media access over more than one deference
      period will have a higher probability of access than a station
      that is contending for the first time.

   The last two characteristics above are peculiar to 802.11, and not
   usually found in other half-duplex media access methods such as
   Ethernet. Further, 802.11 media access uses an acknowledged transfer
   (thus leading to inherently bidirectional packet flow, even though
   the intended test data traffic is unidirectional); imposes further
   delays when acknowledgement frames are lost; and cause stations to
   emit a much higher proportion of management and control packets
   during data transfer. All of these conspire to render data traffic in
   a WLAN inherently bursty, as interfaces are forced to insert gaps in
   otherwise steady flows when packets are being received or when
   backoffs occur. Care must therefore be taken when measuring
   throughput or computing offered load, especially for bidirectional
   data transfers.



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   In particular, as noted in RFC 2285 [RFC2285], special attention must
   be paid towards ensuring that the actual offered load on the DUT is
   measured, instead of (or as well as) the intended load.  The offered
   load may be less than the intended load due to contention effects for
   the wireless medium.  The tester MUST adjust the inter-frame spacing
   according to the target intended load (i.e., to achieve the desired
   rate of frame transmission), and then MUST measure and report the
   actual offered load at the end of the trial.

   See Appendix A of this document for notes about generating the
   intended load for these tests.  Either the frame-based or the time-
   based method described in Appendix B of RFC 2889 [RFC2889] MAY be
   used for these tests but, in either case, the method used MUST be
   reported with the results. Most of the tests in this document use a
   constant (non-bursty) load, and the Iload calculations in Section A.2
   apply. Burst loads use the calculations in Section A.3.

   The tester MUST follow the normal 802.11 protocol requirements when
   transferring test data frames to the DUT, unless the DUT is to be
   oversubscribed, or the burst capacity of the DUT is to be measured.
   The tester SHOULD also note attempts by the DUT to violate the timing
   requirements of the 802.11 protocol by not conforming to the backoff
   rules, or by reducing its inter-frame spacing to less than the legal
   minimum.

   For bidirectional test data traffic, any offered load beyond 50% of
   the theoretical maximum (computed as per Appendix A) MUST be
   considered to oversubscribe the DUT. Oversubscription of the DUT MUST
   be recorded as part of the test results.

3.5.5. Retry of unacknowledged frames

   Recovery from frame errors and collisions is performed by 802.11
   stations using a simple stop-and-wait acknowledgement handshake. If a
   sending station does not receive a valid acknowledgement frame within
   a short time delay after it transmits a unicast data or management
   frame, it is required to perform a backoff and retry. Sequence
   numbers and flag bits are used to distinguish between retries and new
   frames.

   The tester MUST follow the backoff and retry rules of the 802.11
   protocol. When performing tests involving multiple virtual stations
   sending to a single DUT, the tester SHOULD maintain a separate
   backoff timer for each individual virtual station. In the case of
   throughput tests, however, the tester MAY perform retransmissions
   with a reduced or zero backoff period, in order to maintain a
   reasonably high offered load in spite of the high error rates found
   in WLAN media. If this is done, the actual backoff period used MUST



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   be reported with the test results.

   The number of retries performed by the tester when conducting
   throughput and forwarding rate tests SHOULD be at least 7.

   Note that tests involving reduced (non-standard) backoff periods -
   and the consequently high offered loads - could expose catastrophic
   behavior on the part of the DUT, which in turn could be indicative of
   mysterious field failures.  Also, an aggregate of stations sending
   packets to a single DUT, such as an Access Point in a LAN, could
   result in the DUT receiving bursts of packets at the minimum
   interframe gap, even though each client individually conforms to the
   prescribed backoff rules.

3.5.6. Physical layer (PHY) data rates

   The physical layer of the 802.11 WLAN protocol supports data transfer
   at a number of different data rates, such as 1, 2, 5.5, 6, 9, 11, 12,
   etc. Mb/s.  Further, the receiver and transmitter in a data exchange
   may use different PHY data rates. These data rates are achieved with
   different modulation formats, generally resulting in different packet
   error ratios and/or signal-to-noise ratios at the receiver. Tests
   performed at one data rate may not correlate with tests performed at
   another rate. The test results MUST therefore record the data rate
   used by both the DUT and the tester.

   Rate adaptation is supported by 802.11 devices in order to maintain
   data transfer under changing noise and interference environments
   (although at different throughputs). Devices may automatically fall
   back to lower PHY data rates in order to cope with decreasing signal
   strength or increasing noise levels, as the lower PHY data rates
   provide better signal-to-noise ratios.  This can make test results
   impossible to reproduce or interpret in the case of measurements
   needing constant PHY data rates. A given trial MUST maintain a
   constant PHY data rate for all test data packets, unless otherwise
   specified.

3.5.7. Management and control frames

   Unlike most other LAN link layer protocols, 802.11 involves the
   exchange of a substantial number of management and control frames
   during and in between data transfers. Control frames are typically
   used for acknowledgement, medium reservation, and polling. Management
   frames are required for discovery, connection setup and teardown, and
   other signaling. Note that every unicast data frame that is
   successfully transferred requires an acknowledgement control frame to
   be transmitted by the receiver.




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   To emulate the conditions occurring in a real 802.11 WLAN, therefore,
   tests SHOULD include some (small) amount of management and control
   frames in addition to acknowledgement frames. The proportion of
   management and control frames, including beacons, MAY be kept under
   5% of all frames transferred.

3.5.8. Authentication and association

   Transfer of data between stations on an 802.11 WLAN is permitted to
   begin only after a successful connection setup, as indicated by an
   authentication handshake followed by an association handshake. (See
   Clause 8 and Subclause 11.3, respectively, of the 802.11 standard
   [802.11].) Also, it is illegal to transfer data after a connection
   has been terminated.

   The tester MUST be authenticated and associated with the DUT prior to
   the start of a trial. It SHOULD perform an authentication and
   association handshake with the DUT at the start of each trial, and a
   deauthentication handshake at the conclusion; however, it MAY elect
   to remain authenticated with the DUT across multiple trials. In the
   case of throughput, forwarding rate, latency and burst capacity
   tests, disassociation by the DUT during the test data transfer
   portion of a trial MUST be reported and SHOULD cause the trial to be
   terminated.

   The tester MUST NOT accept any unicast data frames from the DUT until
   after the successful completion of the authentication and association
   handshake, and MUST NOT accept any data frames, whether valid or not,
   after receiving an acknowledgement for a disassociation or
   deauthentication frame transmitted to the DUT.

3.5.9. Signal level and signal-to-noise ratios

   The 802.11 WLAN protocol is fundamentally based on a shared-medium RF
   physical layer, and is therefore significantly affected by:

      The absolute signal level received by the PHY;

      The signal-to-noise ratio, as measured at the input of the PHY;
      and

      The carrier-to-interference (C/I) or signal-to-interference ratio,
      also as measured at the input of the PHY. This parameter includes
      both co-channel interference (CCI) and adjacent-channel
      interference (ACI).

   The above parameters impact key attributes of the link between two
   stations, such as packet error rate, retries and backoffs, deference



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   to ongoing transmissions, etc. These parameters MUST be measured and
   maintained within known limits during every trial. Measurements are
   usually performed in one of three ways:

      Directly from the DUT, assuming that the DUT is capable of
      accurately measuring these parameters and providing them to the
      tester upon request.

      Directly from the tester, assuming that the tester is provided
      with the requisite measurement capabilities and the path between
      the DUT and tester is controlled and well characterized.

      Using a passive listening device (which MAY be part of the tester
      or test system) that is co-located with the DUT.

   Unless otherwise specified, the tester MUST ensure that the signal-
   to-noise and carrier-to-interference ratios are at least 10 dB above
   the minimum and 10 dB below the maximum specified levels for a 10%
   Packet Error Ratio (PER) as measured at the DUT. Further, the tester
   MUST ensure that the absolute signal level received by the DUT is
   held constant to within +/- 5 dB over the duration of the trial. The
   signal level MUST be reported with the test results.

   In order to evaluate the performance of the DUT at various signal
   levels, the tests described in this document MAY be run with various
   values of power output by the tester. If this is done, the power
   output SHOULD be varied in steps of 10 dB.

   Note that the specific method used to control the received signal and
   the signal-to-interference ratios is implementation-specific and is
   outside the scope of this document.

3.5.10. Beacons and PCF access method settings

   IEEE 802.11 networks use special management frames, referred to as
   beacons, to enable discovery of Access Points by clients and
   synchronize protocol timers within a group of stations. Beacons are
   typically emitted every 100 Time Units (a Time Unit is 1024
   microseconds, so the usual inter-beacon period is 102.4
   milliseconds).

   As beacons are key elements of the 802.11 discovery and connection
   maintenance protocol, the tester MUST generate beacons with the
   correct contents and at accurate intervals when performing tests on
   clients. Beacons generated by the tester MUST support a timing
   accuracy of at least 1% relative to the advertised beacon period. In
   the case of tests on Access Points, the tester MUST follow the
   standard 802.11 deference rules in order to allow the Access Point to



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   transmit its beacons. The DUT MUST be configured with the correct
   parameters necessary to generate beacons with the required contents.

   Beacons are also used to define the starting points of contention-
   free periods (CFPs), where the 802.11 Point Coordination Function
   (PCF) access rules apply and a polling mode of data transfer is
   performed under the control of an Access Point. This document does
   not address tests performed during CFPs. In the case of tests on
   Access Points, PCF mode SHOULD be disabled or turned off if possible.
   If PCF mode cannot be disabled, it MUST be minimized as far as
   possible, and traffic SHOULD NOT be transmitted to the DUT by the
   tester using PCF mode.

3.5.11. Multiple clients

   In the case of tests on Access Points, measurements of frame loss,
   throughput, forwarding rate, latency and burst capacity SHOULD be
   performed with multiple clients concurrently transmitting to the same
   DUT.  This simulates the situation in an actual network, where
   multiple clients connect to a single Access Point and contribute to
   the total offered load.  Each client is represented by a different
   MAC address.  The MAC addresses SHOULD be chosen randomly to exercise
   the DUT's ability to perform lookups.

   The number of clients used in the test MUST be reported.  For
   throughput, frame loss, forwarding rate and burst capacity tests, the
   aggregate results for all of the clients combined MUST be reported.
   For latency tests, the worst-case latency and latency variation among
   all of the clients MUST be reported.

3.5.12. Trial duration

   The duration of each trial SHOULD be selected using the guidelines of
   Section 24 of RFC 2544 [RFC2544]. Further, it SHOULD be long enough
   to minimize any connection setup and startup effects, such as
   authentication and association, that can affect the test results. It
   SHOULD also be long enough to make the random fluctuations of the
   CSMA/CA access method statistically insignificant.

   The recommended duration of each trial is 30 seconds. The trial
   duration SHOULD be adjustable between 1 second and 300 seconds. The
   tester MUST transmit all test data frames within the trial duration.
   To eliminate the case where a device possessing large frame buffers
   can appear to be faster than it actually is, the tester MUST NOT
   accept received test data frames for more than 1% beyond the end of
   the trial duration, or 1 second, whichever is larger. (Thus a 30
   second trial duration causes the tester to receive frames for no more
   than 31 seconds, starting from the beginning of the trial.) Frames



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   received outside of these limits are not counted as part of the
   results.

3.5.13. Configuration combinations

   WLAN DUTs typically offer a number of orthogonal configuration
   parameters.  For instance, the setting of fragmentation is
   independent of RTS/CTS usage, and both are independent of the
   security mode employed.  This leads to a potentially enormous number
   of combinations of configuration parameters, and consequently a very
   large number of possible tests.

   To reduce the amount of test time and effort, each test defines a
   baseline configuration that MUST be set up and tested.  The baseline
   configuration is then modified by altering a single parameter at a
   time (holding all others at the baseline), and the test repeated.
   This process reduces the total number of tests to be performed, while
   still providing useful information regarding the influence of user-
   configurable parameters on DUT performance.

3.5.14.  Basic test parameters

   Unless otherwise specified, the following are the defaults for test
   parameters.  The specific parameters to be used are listed for each
   test.

      Burst size - Tests that measure the burst capacity of the DUT
      SHOULD be run with burst sizes between 1 (constant load) and 930
      frames.

      Fragmentation - Tests MAY be performed with fragmentation enabled
      as well as disabled.  The results MUST be reported separately.  If
      fragmentation is enabled, the DUT and tester MUST be configured to
      produce at least two fragments per data frame.

      Frame sizes - The frame sizes listed in Section 3.2.3 above MUST
      be used for data traffic in the tests described in this document,
      with the exception of tests on clients, where the 28 byte frame
      size MAY be omitted, and tests on Access Points requiring
      transfers between wired and wireless media, in which case frame
      sizes greater than 1542 bytes MAY be omitted. The actual frame
      sizes used MUST be reported.

      Frame spacing - For tests involving constant loads, the spacing
      between frames MUST be computed from the intended load according
      to the calculations in Section A.2. When performing tests
      involving bursts of frames generated by the tester, the spacing
      between frames within a burst MUST be set to the DIFS value for



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      the PHY data rate and type for the test, and the spacing between
      bursts MUST be computed from the intended load according to the
      calculations in Section A.3. The tester MAY additionally perform
      tests with an IFS within the burst being larger than the DIFS
      value; these results MUST be reported separately. A maximum
      offered load exceeding 50% of the theoretical capacity of the
      wireless medium will oversubscribe the DUT, resulting in frame
      loss.

      Nominal beacon interval - In the case of tests on Access Points,
      if the DUT enables the beacon period to be adjusted, it SHOULD be
      set to 102.4 milliseconds. (See Section 3.5.10 above.) The nominal
      beacon period of the DUT MUST be reported.

      Number of STAs - In the case of tests on Access Points, the
      minimum number of test clients is 2; however, the test SHOULD be
      carried out with 64 or more concurrent clients.  Each client
      SHOULD make up an equal fraction of the total offered load.  The
      number of virtual or physical clients that are used in the test
      MUST be reported.

      RTS/CTS usage - Tests MAY be performed with the RTS/CTS handshake
      enabled as well as disabled.  The results MUST be reported
      separately.

      Security usage - If the DUT can be configured to implement one or
      more security modes, such as WEP [802.11], tests SHOULD be
      performed using each of the security modes as well as with
      security disabled.  The results MUST be reported separately.

      Signal level - Tests SHOULD be performed using multiple signal
      levels as generated by the tester and measured at the DUT.  The
      average signal level recorded at the DUT, as well as the signal
      level being generated by the tester, MUST be reported for each
      trial.

      Test Access Point beacon period - The beacon period of the Access
      Points used to test a client MUST be the same (to within 1%) and
      MUST be reported with the test results.

      Uni-directional transfer - Each trial causes test data to flow in
      only one direction; i.e., from the wired to the wireless media, or
      vice versa, but not both.  No test data frames are to be directed
      between clients on the wireless medium during tests involving uni-
      directional transfers. As explained in Sections 3.5.4 and 3.5.5,
      acknowledgement frames MUST NOT cause test data traffic to be
      interpreted as bidirectional.




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      Bi-directional transfer - Each trial causes test data frames to
      flow in both directions (for example, from the wired to the
      wireless media and from the wireless to the wired media). This
      also covers the case where test data traffic is directed between
      clients on the wireless medium.

      Wireless Distribution System (WDS) - Tests MAY be performed on
      Access Points supporting the Wireless Distribution System (WDS)
      mode of operation [802.11]. (See Section 3.3.1 above.) The results
      of tests performed in this mode MUST be reported separately.

      Power management mode - As noted in Section 3.4.5, tests on
      clients SHOULD be run with a baseline configuration that disables
      power management.

4.  Interpreting and reporting test results

   Test results SHOULD be reported in a common format to aid the reader
   in interpreting results and comparing them across DUTs. Results from
   a set of trials involving the variation of one or more test
   parameters described in Section 3.5.14 above SHOULD be presented as
   graphs, with the x coordinate being the parameter value and the y
   coordinate being the test results.

   The following test conditions MUST be reported with the results of
   all trials:

      PHY type (e.g., 802.11g), bit rate and channel used

      Signal power level, signal-to-noise ratio and signal-to-
      interference ratio of signals from tester, measured at or near the
      DUT

      PLCP layer options (short slot time, short preamble, etc.)
      configured for the DUT and the tester

      PCF mode settings if PCF mode is not disabled

5.  Benchmarking tests

   The following tests are divided into three categories. Throughput
   related tests deal with the rates at which the DUT can perform
   various functions, such as forwarding data traffic or performing
   authentications and associations.  Latency and timing tests measure
   the time taken by the DUT to carry out specific tasks, such as
   forwarding a frame, adapting to a new rate, or recovering from a
   reset. Finally, capacity tests quantify the storage capacity of a DUT
   for different functions, such as dealing with bursts of data traffic.



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   Objectives, test parameters, procedures and reporting formats are
   described for each test.

5.1. Throughput related tests

   Throughput related tests measure the rates at which the DUT can
   perform its tasks.  For an Access Point, this includes the rates at
   which it can forward data within the BSS or between the BSS and the
   DS, as well as the rate at which new clients can establish
   associations with it.  For a client, this measures the rate at which
   it can accept and transmit data.

   For throughput and forwarding rate tests, either the Frame Based or
   Time Based modes of testing may be used, as described in Appendix B
   of RFC 2889 [RFC2889].  The DUT is initially set up according to the
   baseline configuration, using a starting combination of test
   parameters.  Packets are then sent to the DUT by the tester at a
   specific offered load for the duration of the trial, and the number
   of frames received from the DUT are counted.  The process MUST be
   iterated at different offered loads, using a search algorithm, until
   the desired measurement (throughput or maximum forwarding rate) has
   been made.  Additional trials are then performed in the same manner
   using different DUT configurations until all configurations have been
   exhausted.

   The tester MUST count, as valid received test frames, those which it
   receives without error and with the proper signature (i.e., the right
   combination of source and destination addresses, frame length and
   frame payload).  In addition, on the wireless medium the tester must
   only count as valid those unique data frames for which it sent an
   802.11 ACK frame to the DUT in response.  It MUST NOT count duplicate
   frames, frames originating from the DUT, data frames that it did not
   acknowledge, or management and control frames as part of the
   measurements.  Such frames MAY be counted separately, or not counted
   at all.

   For the purposes of computing the actual offered load, the tester
   MUST count as valid transmitted frames only those test frames that
   were acknowledged by the DUT on the wireless medium (i.e., with an
   802.11 ACK frame), or transferred to the DUT without a locally
   detected error on the wired medium.  All other frames MUST NOT be
   counted as part of the offered load.

5.1.1. Unicast intra-BSS throughput, forwarding rate and frame loss

5.1.1.1. Objective

   To determine the throughput of the DUT when handling unicast WLAN



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   data frames that are confined to the wireless medium (and, in the
   case of clients, internally to the client).  This test is applicable
   to both clients and Access Points.  In the case of clients, this test
   provides the basic measure of their ability to transmit and receive
   frames without loss across their wireless interface.  In the case of
   Access Points, this test measures their ability to forward frames
   from one wireless client to another on the wireless medium.

   This test is applicable to IBSS (Independent BSS) as well as
   infrastructure BSS client configurations.  If an IBSS client is being
   tested, the results determine the ability of the client to exchange
   data traffic with another IBSS client.  In infrastructure mode, the
   results determine the ability of the client to exchange data with an
   Access Point.

5.1.1.2. Test parameters

   The following parameters are relevant to this test. See Section
   3.5.14.

      Frame sizes, Signal level, Number of STAs, Fragmentation, RTS/CTS
      usage, Security usage and Wireless Distribution System (WDS).

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, security and WDS not used.

5.1.1.3. Procedure

   The DUT is initially set up according to the baseline configuration,
   using a starting combination of frame size and tester signal level.
   The frame spacing required for a given offered load is computed per
   Appendix A.  The tester MUST follow the half-duplex test conditions
   described in Section 3.5.4.  The throughput, maximum forwarding rate
   and frame loss rate are then found as described below.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 3 plus the number of
   security modes.

   When testing Access Points with multiple physical or virtual clients,
   consecutive frames transmitted by the tester to the DUT MUST have
   different combinations of source and destination addresses, and all
   possible such combinations of addresses MUST be represented equally
   within each trial.  This distributes the load of transmission and
   reception uniformly among the clients.  Failure to ensure this can
   lead to inconsistent results.



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5.1.1.4. Analysis and reporting

   The throughput of the DUT is computed and reported (per Section 26.1
   of RFC 2544 [2544]) as the maximum offered load, in frames per
   second, resulting in zero frame loss rate [RFC1242].

   The maximum forwarding rate of the DUT is computed and reported as
   the maximum number of test frames per second that the DUT is observed
   to successfully forward, irrespective of frame loss, at some value of
   offered load.  The offered load applied to the DUT at the maximum
   forwarding rate MUST be reported as well.

   The frame loss rate MUST be reported with the maximum forwarding
   rate.  In this context, "rate" refers to the percentage of frames
   that were successfully injected into the DUT by the tester, but not
   forwarded by the DUT to the tester for any reason.

   The test results SHOULD be reported as graphs of throughput and
   maximum forwarding rate versus each of: frame size and signal level.
   Separate results MUST be reported per configuration.

5.1.2. Unicast ESS throughput, forwarding rate and frame loss

5.1.2.1. Objective

   To determine the throughput of the DUT when forwarding unicast data
   frames between the wireless and the wired media (i.e., between the
   BSS and the DS, as described in 5.2.2 of [802.11]).  This test is
   only applicable to Access Points.  The results of this test can be
   used to determine the ability of an Access Point to support multiple
   wireless clients transferring data to a wired LAN segment.

   The general setup for the test comprises two or more virtual or
   physical clients on the wireless side of the DUT that transfer data
   to or from two or more virtual clients on the wired side.

5.1.2.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Frame Spacing, Signal level, Number of STAs,
      Fragmentation, RTS/CTS usage, Security usage and Wireless
      Distribution System (WDS).

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, and security not used.




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5.1.2.3. Procedure

   The DUT is first set up according to the baseline configuration,
   using the initial combination of transfer direction, frame size and
   tester signal level.  The required frame spacing is computed per
   Appendix A.  For bidirectional tests, the tester MUST follow the
   half-duplex test conditions described in Section 3.5.4 on the
   wireless medium.  The throughput, maximum forwarding rate and frame
   loss rate are then measured as described below.  The measurements are
   repeated for each combination of transfer direction, frame size and
   tester signal level.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 2 plus the number of
   security modes.

   Consecutive frames transmitted by the tester to the DUT MUST have
   different combinations of source and destination addresses,
   representing conversations between different sets of clients on the
   wired and wireless media.  All possible such combinations of
   addresses MUST be represented equally within each trial.  This
   distributes the load of transmission and reception uniformly among
   the clients.  Failure to ensure this can lead to inconsistent
   results.

5.1.2.4. Analysis and reporting

   The throughput of the DUT is computed and reported (per Section 26.1
   of RFC 2544 [RFC2544]) as the maximum offered load, in frames per
   second, resulting in zero frame loss rate [RFC1242].

   The maximum forwarding rate of the DUT is computed and reported as
   the maximum number of test frames per second that the DUT is observed
   to successfully forward, irrespective of frame loss, at some value of
   offered load.  The offered load applied to the DUT at the maximum
   forwarding rate MUST be reported as well.

   The frame loss rate MUST be reported with the maximum forwarding
   rate.  In this context, "rate" refers to the percentage of frames
   that were successfully injected into the DUT by the tester, but not
   forwarded by the DUT to the tester for any reason.

   The test results SHOULD be reported as graphs of throughput and
   maximum forwarding rate versus each of: frame size and signal level.
   Separate results MUST be reported per configuration.




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   Note that the wired interfaces of Access Points are often capable of
   much higher link rates than the wireless interfaces, potentially
   leading to extremely high frame loss rates when transferring frames
   from the wired to the wireless media.  Care should be taken to allow
   enough time for the DUT to recover and return to a normal state
   between trials.

5.1.3. Multicast forwarding rate

5.1.3.1. Objective

   To determine the maximum rate at which the DUT can forward multicast
   data frames between the wireless and the wired media (i.e., between
   the BSS and the DS, as described in 5.2.2 of [802.11]).  This test is
   only applicable to Access Points.  As multicast or broadcast traffic
   is dealt with differently from unicast traffic by the 802.11
   protocol, this test therefore determines the ability of an Access
   Point to handle such traffic.

   The general setup for the test comprises one virtual or physical
   client on the wireless side of the DUT that injects multicast data
   destined for the wireless side, as well as one virtual or physical
   client on the wired side that injects multicast data in the reverse
   direction.

   Note that the 802.11 protocol does not make special provisions for
   multicast versus broadcast traffic.  A single test is hence used to
   measure the ability of DUTs to handle both.

5.1.3.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Frame Spacing, Signal level, Number of STAs, RTS/CTS
      usage, Security usage, and Uni-directional transfer.

   The baseline DUT configuration for performing this test consists of:
   RTS/CTS disabled and security not used.

5.1.3.3. Procedure

   The DUT is first set up according to the baseline configuration,
   using an initial combination of transfer direction, frame size and
   tester signal level.  The required frame spacing is computed per
   Appendix A.  The throughput, maximum forwarding rate and frame loss
   rate are then measured as described below.  The measurements are
   repeated for each combination of transfer direction, frame size and



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   tester signal level.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 1 plus the number of
   security modes.

   Either broadcast addresses, random multicast addresses, or a mixture
   of the two MAY be used as destination addresses for the test data.
   The addresses used MUST be reported with the results.

5.1.3.4. Analysis and reporting

   The maximum multicast forwarding rate of the DUT is computed and
   reported as the maximum number of test frames per second that the DUT
   is observed to successfully forward, irrespective of frame loss, at
   some value of offered load.  The offered load applied to the DUT at
   the maximum forwarding rate MUST be reported as well.

   The frame loss rate MUST be reported with the maximum forwarding
   rate.  In this context, "rate" refers to the percentage of frames
   that were successfully injected into the DUT by the tester, but not
   forwarded by the DUT to the tester for any reason.

   The test results SHOULD be reported as a graph of maximum forwarding
   rate versus each of: frame size and signal level.  Separate results
   MUST be reported per configuration.

   Note that the wired interfaces of Access Points are often capable of
   much higher link rates than the wireless interfaces, potentially
   leading to extremely high frame loss rates when transferring
   multicast frames to the wireless media.  Care should be taken to
   allow enough time for the DUT to recover and return to a normal state
   between trials.

5.1.4. Forward pressure

   This test measures forward pressure, as defined in Section 3.7.2 of
   RFC 2285 [RFC2285] and described in Section 5.6 of RFC 2889
   [RFC2889].

5.1.4.1. Objective

   The objective of the forward pressure test is to determine if a DUT
   has been configured to transmit on the wireless medium at less than
   the minimum interframe spacing, or to transmit without adhering to
   the backoff rules of the 802.11 protocol.  Such DUT configurations



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   will enable the DUT to obtain an unfair share of the available
   capacity of the medium.  The test overloads the wireless port of the
   DUT, by injecting traffic into its wired interface, and measures the
   minimum and average interframe spacing used by the DUT to access the
   wireless medium.

   As this test requires a minimum of two ports on the DUT, it is
   performed only on Access Points.  Further, it cannot be performed if
   the aggregate bandwidth of the wired interface(s) of the DUT does not
   exceed that of the wireless interface.

5.1.4.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Frame Spacing, Number of STAs, RTS/CTS usage and Uni-
      directional transfer.

   The baseline DUT configuration for performing this test consists of
   RTS/CTS disabled.

5.1.4.3. Procedure

   The DUT is set up according to the baseline configuration, using an
   initial value for frame size.  A continuous stream of test frames is
   injected into the wired port(s) of the DUT, directed at a test client
   located on the wireless side.  Initially, the IFS between injected
   frames is set according to the following equation:

      IFS1 = ACKtime + SIFS + DIFS + 0.5 * CWmin * slotTime

   where
      IFS1 = starting IFS
      ACKtime = time required to transmit 1 ACK frame on the wireless
         medium
      SIFS = short interframe spacing for 802.11 PHY type
      DIFS = DCF interframe spacing for 802.11 PHY type
      CWmin = minimum value of contention window parameter for PHY
      slotTime = slot time for PHY

   All times are measured in microseconds.  This initial value of IFS is
   selected to enable the DUT to forward all frames on to the wireless
   medium without forward pressure.  The tester MUST acknowledge all
   frames transmitted by the DUT on the wireless medium strictly
   according to the 802.11 medium access rules.

   The IFS between frames injected into the wired interface is then



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   iteratively reduced, in steps of 5 microseconds, until it reaches:

      IFS2 = ACKtime + SIFS + 0.5 * DIFS

      where the notation is as above.

   At each iteration, the minimum and average spacing used by the DUT
   between the end of an ACK frame and the start of a data frame is
   measured by the tester.

   The above process MAY be repeated with the RTS/CTS handshake enabled
   on the wireless side of the DUT.  In this case, IFS1 and IFS2 are
   computed as follows:

      IFS1 = RTStime + CTStime + ACKtime + 3 * SIFS + DIFS + 0.5 * CWmin
      * slotTime IFS2 = RTStime + CTStime + ACKtime + 3 * SIFS + 0.5 *
      DIFS

   where
      RTStime = time required to transmit 1 RTS frame on the wireless
         medium
      CTStime = time required to transmit 1 CTS frame on the wireless
         medium

      and the rest of the notation is as before.

5.1.4.4. Analysis and reporting

   Forward pressure is occurring if:

      - the minimum spacing between an ACK frame sent to the DUT by the
      tester and an immediately succeeding RTS or data frame is less
      than one DIFS time for the 802.11 PHY type, or

      - the average spacing between the ACK frame and the immediately
      succeeding RTS or data frame is less than (DIFS + 0.5 * CWmin *
      slotTime) for the 802.11 PHY type.

   If this condition is detected, the test results MUST indicate that
   forward pressure is occurring.  The test results MAY also be reported
   as a graph of minimum and average interframe spacing (between an ACK
   frame and the following RTS or data frame) as a function of offered
   load on the wired interface of the DUT.

5.1.5. Authentication and association rate

5.1.5.1. Objective




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   The 802.11 protocol requires that a station wishing to transmit data
   to another station must authenticate itself with that station, and
   also establish a connection (i.e., associate with that station).  The
   rate at which these functions can be carried out directly impacts the
   time taken for a wireless LAN to recover from faults and transient
   conditions, such as an Access Point being reset, a group of clients
   being turned on concurrently, or a client roaming from one Access
   Point to another.  The objective of this test is hence to determine
   the rate at which a DUT can perform the authentication and
   association functions.  This test is only applicable to Access
   Points.

5.1.5.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Signal level, Number of STAs, and Security usage.

   In addition, the following test parameters MUST be configured to be
   the same for all trials:

      Association Timeout - The tester MUST wait a predetermined amount
      of time for the DUT to respond to an association request with an
      association response. If the DUT fails to respond within this
      time, the association attempt MUST be considered to have failed,
      and a timeout error SHOULD be reported for that client. The
      minimum value of the association timeout MUST be at least 10
      milliseconds, and MUST NOT exceed 100 milliseconds.

   The association timeout used by the tester MUST be reported with the
   test results.

   The baseline DUT configuration for performing this test consists of:
   security not used.

5.1.5.3. Procedure

   The DUT is first set up according to the baseline configuration.  The
   tester then causes the required number of virtual or physical test
   clients to authenticate and associate themselves with the DUT, and
   measures the rate at which the DUT successfully completes
   authentications and associations. Each client is authenticated and
   associated in turn; the tester MUST NOT present a new client to the
   DUT until the authentication and association for the previous client
   has been completed. The DUT therefore determines the maximum rate at
   which clients can associate.




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   It is recommended that the authentication and association database
   capacity test in Section 5.3.2 be performed first to determine the
   maximum number of clients that can successfully associate with the
   DUT. The number of virtual clients presented to the DUT SHOULD be
   kept below this number. An authentication failure for a client SHOULD
   keep the tester from attempting an association for that client.
   Failure of the DUT to respond to an association request within the
   specified timeout MUST be counted as an association failure.

   After the test clients successfully authenticate and associate with
   the DUT, the tester MUST verify that these clients have indeed been
   associated by causing the test clients to transmit data frames to one
   another, and ensure that these data frames are correctly forwarded by
   the DUT. The rate at which verification data frames are transmitted
   to the DUT MUST be well below the intra-BSS throughput supported by
   the DUT. The tester MUST ensure that at least one data frame
   originating from each client is forwarded.

   If the DUT deauthenticates one or more clients during the data
   transfer phase, these MUST be counted as authentication failures. If
   the DUT disassociates one or more clients during this phase, these
   MUST be counted as association failures.  If none of the test data
   frames transmitted by a physical or virtual client are forwarded
   successfully, this MUST be treated as a verification failure. If
   failures do occur, the tester MAY attempt to find a lower rate of
   authentication and association for which no verification failures are
   found for all of the test clients.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is equal to the number of
   security modes.  Additional tests MAY be performed to determine
   authentication and association rates with different numbers of STAs,
   but the number MUST remain constant for each test run.

   After each trial has been completed, the tester MUST remove the test
   client authentications and associations from the DUT database by
   performing the 802.11 deauthentication procedure for each client.

5.1.5.4. Analysis and reporting

   The authentication and association rate of the DUT is computed and
   reported as the maximum number of authentications and associations
   that can be successfully performed per second. Authentication,
   association and verification failures MUST be reported along with the
   test results.




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   If the test is performed at different signal levels, the test results
   SHOULD be reported as a table of signal level versus the
   authentication and association rate for each DUT configuration.  If
   the test is done for different numbers of STAs, the results MAY be
   presented as graphs of authentication rate versus number of test
   clients.

5.1.6 Power management mode throughput, forwarding rate and frame loss

5.1.6.1. Objective

   To determine the throughput of the DUT when operating in power
   management mode. This test is applicable to clients only, and
   measures their ability to receive and transmit frames without loss
   while they attempt to conserve power.

   This test is applicable to IBSS (Independent BSS) as well as
   infrastructure BSS client configurations. It is generally conducted
   using a process similar to that for the unicast intra-BSS throughput,
   forwarding rate and frame loss test described in Section 5.1.1 above.

5.1.6.2. Test parameters

   The following parameters are relevant to this test. See Section
   3.5.14.

      Power Management Mode, Frame sizes, Frame Spacing, Signal level,
      Fragmentation, RTS/CTS usage and Security usage.

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, and security not used.

5.1.6.3. Procedure

   The DUT is initially set up according to the baseline configuration,
   using a starting combination of frame size, frame spacing and tester
   signal level. In addition, the DUT is placed into power-save or power
   management mode, such that it attempts to conserve power by shutting
   down its 802.11 interface when it is not transferring data. (If
   necessary the DUT MAY be run on batteries in order to ensure that
   power management mode is enabled.)

   The test traffic used consists of unicast WLAN data frames that are
   confined to the wireless medium (and internally to the client).  Test
   traffic is then exchanged with the DUT by the tester. The required
   frame spacing is computed per Appendix A.  The tester MUST follow the
   half-duplex test conditions described in Section 3.5.4, and the
   client setup and test conditions described in Section 3.2.2 and



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   3.3.2. The throughput, forwarding rate and frame loss rate are then
   found as described below.  The test SHOULD be repeated with different
   frame sizes and signal levels.

   The tester MUST verify that the client enters power management mode,
   and SHOULD also verify that the client uses the PS Poll mechanism
   specified in 11.2 of the IEEE 802.11 standard [802.11] to transfer
   data. Failure to enter power management mode MUST be reported along
   with the test results.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 2 plus the number of
   security modes.

5.1.6.4. Analysis and reporting

   The throughput of the DUT is computed and reported (per Section 26.1
   of RFC 2544 [2544]) as the maximum offered load, in frames per
   second, resulting in zero frame loss rate [RFC1242].

   The maximum forwarding rate of the DUT is computed and reported as
   the maximum number of test frames per second that the DUT is observed
   to successfully forward, irrespective of frame loss, at some value of
   offered load.  The offered load applied to the DUT at the maximum
   forwarding rate MUST be reported as well.

   The frame loss rate MUST be reported with the maximum forwarding
   rate.  In this context, "rate" refers to the percentage of frames
   that were injected into the DUT by the tester, but not forwarded by
   the DUT to the tester for any reason.

   The test results SHOULD be reported as graphs of throughput and
   maximum forwarding rate versus each of: frame size and signal level.
   Separate results MUST be reported per configuration.

5.2. Latency and timing tests

   Latency and timing tests measure the delays encountered when the DUT
   forwards traffic, or performs other essential tasks.  These delays
   have significant impact on delay-sensitive protocols (such as those
   handling voice and video), as well as system responsiveness and
   network stability.

   RFC 1242 [RFC1242] provides two possible definitions of latency
   (either the delay from last bit in to first bit out, or the delay
   from first bit in to first bit out).  The test results MUST indicate



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   which definition is applicable.

5.2.1. Intra-BSS latency and latency variation

5.2.1.1. Objective

   To determine the latency and latency variation (a.k.a. jitter)
   exhibited by the DUT when forwarding unicast WLAN data frames that
   are confined to the wireless medium.  This test is only applicable to
   Access Points.

5.2.1.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Frame Spacing, Signal level, Number of STAs,
      Fragmentation, RTS/CTS usage, Security usage and Wireless
      Distribution System (WDS).

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, security and WDS not used.

5.2.1.3. Procedure

   The DUT is initially set up according to the baseline configuration.
   The tester MUST follow the half-duplex test conditions described in
   Section 3.5.4.  The latency and latency variation of the DUT are
   measured over a 1 second interval located in the middle of the trial
   duration, as described below.  An identifying tag or signature MUST
   be placed in each data frame sent to the DUT during the measurement
   interval, so that it can be correlated with the frames received from
   the DUT.  Note that frames transmitted to the DUT during the
   measurement interval can continue to be received beyond the end of
   the measurement interval; these frames MUST be included in the
   results.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 3 plus the number of
   security modes.

   When testing Access Points with multiple physical or virtual clients,
   consecutive frames transmitted by the tester to the DUT MUST have
   different combinations of source and destination addresses, and all
   possible such combinations of addresses MUST be represented equally
   within each trial.  This distributes the load of transmission and



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   reception uniformly among the clients.  Failure to ensure this can
   lead to inconsistent results.

5.2.1.4. Analysis and reporting

   The instantaneous latency of the DUT is measured (per Section 26.2 of
   RFC 2544 [RFC2544]) as the difference, in seconds, between the
   timestamps assigned to a frame transmitted to the DUT and the
   corresponding frame received from the DUT.  The mean of these
   differences in timestamps over all the data frames received from the
   DUT in a 1 second interval is computed and reported as the average
   latency of the DUT.

   The latency variation of the DUT is measured and reported as the
   difference between the maximum and minimum instantaneous latency of
   all the frames received from the DUT in the same 1 second interval.

   The offered load and the observed frame loss rate over this 1 second
   interval MUST be reported as well.  In this context, "frame loss
   rate" refers to the percentage of frames that were injected into the
   DUT by the tester, but not forwarded by the DUT to the tester for any
   reason.

   The test results SHOULD be reported as graphs of latency and latency
   variation versus each of: frame size and signal level.  Separate
   results MUST be reported per configuration and direction of traffic
   flow.

5.2.2. ESS latency and latency variation

5.2.2.1. Objective

   To determine the latency and latency variation (a.k.a. jitter)
   exhibited by the DUT when forwarding unicast data frames between the
   wired and wireless media (i.e., between the BSS and the DS, as
   described in 5.2.2 of [802.11]).  This test is only applicable to
   Access Points.  The results of this test can be used to estimate the
   latency and latency variation introduced by an Access Point on delay-
   sensitive traffic to or from a client.

   The general setup for the test comprises one or more virtual or
   physical clients on the wireless side of the DUT that transfers data
   to or from one or more virtual clients on the wired side.

5.2.2.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:



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      Frame sizes, Frame Spacing, Signal level, Number of STAs,
      Fragmentation, RTS/CTS usage, Security usage and Uni-directional
      transfer.

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, and security not used.

5.2.2.3. Procedure

   The DUT is initially set up according to the baseline configuration.
   and data are transmitted to it by the tester at a constant load for
   the duration of the trial.  The latency and latency variation of the
   DUT are measured over a 1 second interval located in the middle of
   the trial duration, as described below.  An identifying tag or
   signature MUST be placed in each data frame sent to the DUT during
   the measurement interval, so that it can be correlated with the
   frames received from the DUT.  Note that frames transmitted to the
   DUT during the measurement interval can continue to be received
   beyond the end of the measurement interval; these frames MUST be
   included in the results.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is 2 plus the number of
   security modes.

   When testing Access Points with multiple physical or virtual clients,
   consecutive frames transmitted by the tester to the DUT MUST have
   different combinations of source and destination addresses, and all
   possible such combinations of addresses MUST be represented equally
   within each trial.  This distributes the load of transmission and
   reception uniformly among the clients.  Failure to ensure this can
   lead to inconsistent results.

5.2.2.4. Analysis and reporting

   The instantaneous latency of the DUT is measured (per Section 26.2 of
   RFC 2544 [RFC2544]) as the difference, in seconds, between the
   timestamps assigned to a frame transmitted to the DUT and the
   corresponding frame received from the DUT.  The mean of these
   differences in timestamps over all the data frames received from the
   DUT in a 1 second interval is computed and reported as the average
   latency of the DUT.

   The latency variation of the DUT is measured and reported as the
   difference between the maximum and minimum instantaneous latency of
   all the frames received from the DUT in the same 1 second interval.



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   The offered load and the observed frame loss rate over this 1 second
   interval MUST be reported as well.  In this context, "frame loss
   rate" refers to the percentage of frames that were injected into the
   DUT by the tester, but not forwarded by the DUT to the tester for any
   reason.

   The test results SHOULD be reported as graphs of latency and latency
   variation versus each of: frame size and signal level.  Separate
   results MUST be reported per configuration and per direction of
   traffic flow.

5.2.3. Roaming and reassociation time

5.2.3.1. Objective

   The 802.11 protocol enables a client to dynamically disassociate
   itself from one Access Point and reassociate with another Access
   Point in the same ESS.  This is done to facilitate the mobility (or
   roaming) of clients within an extended region that constitutes a
   single logical network covered by more than one Access Points.  The
   rate at which clients can transition from one Access Point to the
   next hence plays a large part in the quality and reliability of the
   mobile system; long roaming times can result in lost data and dropped
   connections.  This test seeks to determine the rate at which WLAN
   clients and Access Points can support roaming functions.

   In 802.11 networks, clients are the primary drivers of roaming
   behavior.  A client is responsible for detecting when a roaming
   operation is required - for instance, because the signal from its
   Access Point has fallen below some threshold of acceptability - and
   also for locating some other Access Point and associating with it.
   Access Points are a contributing factor to the total roaming delay,
   in terms of the time required for them to accept and complete an
   association or reassociation with a roaming client.  Client and
   Access Point roaming time contributions are measured separately.

5.2.3.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Number of STAs, RTS/CTS usage, RTS/CTS usage and Test
      Access Point beacon period.

   The baseline DUT configuration for performing this test consists of:
   RTS/CTS disabled and security not used.

5.2.3.3. Procedure



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   When performed on a client, this test MUST utilize two separately
   controllable physical or virtual Access Points belonging to the same
   service set (i.e., with the same SSID).  Both test Access Points MAY
   be simulated by the same physical device, but both MUST be of similar
   signal strength as measured at the DUT location.

   During the test, both Access Points are started simultaneously, and
   the DUT is allowed to authenticate with one or both of them, and then
   associate with one or the other of them.  The association with the
   specific test Access Point MUST be verified by causing the DUT to
   transfer one or more frames of test data to it.  The test Access
   Point with which the DUT is associated is disabled or otherwise
   prevented from transmitting beacons to the DUT and responding to DUT
   frames.  The DUT should then discover that it is unable to
   communicate with the first test Access Point and associate with the
   second test Access Point.  The association with the second test
   Access Point MUST be verified by causing the DUT to transfer one or
   more frames of test data to it.

   When performed on an Access Point, the tester authenticates a single
   virtual or physical client with the DUT, and then measures the time
   required to perform an association procedure of the test client with
   the DUT (as per subclause 11.3 of IEEE 802.11 [802.11]).  It then
   measures the time required to perform a reassociation procedure of
   the test client with the DUT.  An authentication failure of the test
   client MUST keep the tester from attempting an association for the
   client.

   In both cases, the DUT is initially set up and tested according to
   the baseline configuration.  After the baseline configuration has
   been tested, the tester MAY repeat the process with a new
   configuration, until the desired number of different configurations
   have been exercised.  The maximum number of such additional test
   configurations is 1 plus the number of security modes.

   In the case of Access Points, the test MAY be repeated with one or
   more additional clients associated with the DUT, in order to measure
   the ability of the DUT to handle associations and reassociations at
   various database capacities.

5.2.3.4. Analysis and reporting

   In the case of a client, the roaming time of the DUT is measured as
   the time, in seconds, from the Target Beacon Transmission Time (see
   11.1.2.1 of IEEE 802.11 [802.11]) of the first missing beacon from
   the first test Access Point after it has been disabled, to the last
   bit of the Association or Reassociation Request frame transmitted to
   the second test Access Point by the DUT.  The beacon period used or



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   observed for both test Access Points MUST be reported as well.

   In the case of an Access Point, the association response time of the
   DUT is measured as the time, in seconds, from the last bit of the
   Association Request frame transmitted by the tester to the last bit
   of the Association Response frame transmitted to the tester by the
   DUT.  The reassociation response time of the DUT is measured as the
   time, in seconds, from the last bit of the Reassociation Request
   frame transmitted by the tester to the last bit of the Reassociation
   Response frame transmitted to the tester by the DUT.

   Separate results MUST be reported per DUT configuration.  If
   additional clients are used for Access Point testing, the number of
   additional clients used in each trial MUST be reported.

5.2.4. Rate adaptation time

5.2.4.1. Objective

   Rate adaptation is used by 802.11 devices to maintain connectivity
   and continue to transfer data successfully (at lower rates) in spite
   of a decreasing signal-to-noise ratio, as may happen when mobile
   stations roam from one location to another. The slower rates employ
   more robust and error tolerant modulation formats that require less
   signal-to-noise ratios. This test determines the signal levels at
   which an 802.11 device switch from one rate to another, and also
   measures the time taken for the device to detect and perform the rate
   change.

   This test can be performed on both Access Points and clients.

5.2.4.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame size, Offered load, Number of STAs (in the case of Access
      Points), RTS/CTS usage, Fragmentation, and Security.

   The baseline DUT configuration for performing this test consists of:
   RTS/CTS disabled, fragmentation and security not used

5.2.4.3. Procedure

   When performed on an Access Point, this test MUST utilize a one or
   more controllable physical or virtual clients to generate test
   traffic to and from the DUT. When performed on a client, the test
   MUST utilize a controllable physical or virtual Access Point with a



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   traffic generator capable of causing the DUT to send and receive
   traffic. The signal strength at the DUT location MUST be controllable
   in steps of 3 dB or better.

   The test is performed in two parts. The first part establishes the
   signal levels at which the DUT switches from one PHY data rate to
   another. The second part uses these results to further determine the
   time taken for the DUT to perform these data rate steps.

   At the start of the first part of the test, the necessary
   authentication and association procedures are used to establish a
   connection with the DUT (one per physical or virtual client, in the
   case of tests on Access Points).  Data are then exchanged with the
   DUT at the maximum data rate corresponding to the DUT PHY type, and
   at the highest signal level that will not overload the DUT.  Data
   transfer MUST be verified as taking place both from and to the DUT.
   The tester progressively reduces its transmitted signal level by
   steps of 3 dB or less while transferring data to and from the DUT,
   and records the PHY data rate of the frames received from the DUT for
   each signal level. At least 1 second of data transfer (at the
   configured offered load) MUST be performed at each signal level
   before stepping to the next. The process is continued until the DUT
   is found to be operating at the minimum data rate for the DUT PHY
   type, or until the tester has reached the lower limit of its transmit
   power range. The range of signal levels used MUST be reported along
   with the test results. The signal levels reported MUST be referenced
   to the DUT receiver.

   During the second part of the test, the same authentication and
   association process is used to establish a connection with the DUT.
   Data are then exchanged with the DUT at the maximum data rate
   corresponding to the PHY type of the DUT, and at the highest signal
   level that will not overload the DUT. The signal level of the traffic
   output by the tester is then reduced to a value that is known (from
   the preceding part) to cause the DUT to reduce its PHY data rate to a
   lower value, and the time required for the DUT to detect and respond
   is measured.  The tester SHOULD continue this process for each of the
   rates supported by the DUT. At least 1 second of data transfer MUST
   be performed at each signal level before stepping to the next. The
   range of signal levels used MUST be referenced to the DUT receiver
   and MUST be reported along with the test results.

   The DUT is initially set up and tested according to the baseline
   configuration.  After this configuration has been tested, the tester
   MAY repeat the test process with a new configuration, until the
   desired number of configurations has been exercised. The connection
   with the DUT SHOULD be broken (i.e., the tester disassociates and
   deauthenticates) and then re-established prior to starting the next



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   trial. The maximum number of additional test configurations is 2 plus
   the number of security modes.

5.2.4.4. Analysis and reporting

   The rate adaptation levels of the DUT are reported as the average
   signal levels, in dBm referenced to the DUT receiver input, that
   cause the DUT to change its PHY data rate from a given value to the
   next lower value. For example, a DUT having an 802.11b PHY (Clause 18
   of IEEE 802.11 [802.11]) will have three values reported, namely, the
   received signal levels that cause a transition from 11 Mb/s to 5.5
   Mb/s, from 5.5 Mb/s to 2 Mb/s, and from 2 Mb/s to 1 Mb/s,
   respectively.

   The rate adaptation times of the DUT MUST be measured from the first
   packet transmitted by the tester at the lower signal level to the
   first packet received from the DUT at the lower rate. Taking the same
   example, these times would be measured at the 11 Mb/s - 5.5 Mb/s, 5.5
   Mb/s - 2 Mb/s and 2 Mb/s - 1 Mb/s transition points, respectively.

   As the process of rate adaptation is heavily influenced by RF and
   analog effects, this test SHOULD be performed multiple times and the
   results averaged, the standard deviation of the results SHOULD also
   be reported.

5.2.5. Beacon interval and timing

5.2.5.1. Objective

   To determine the rate at which beacons are transmitted, as well as
   the accuracy with which the actual transmission time of beacons
   matches the advertised transmission time as indicated by the DUT.  A
   number of 802.11 network functions are affected by the rate and
   accuracy of beacon generation.  For instance, clients in power-save
   mode are expected to wake up just prior to the expected transmission
   of a beacon from an Access Point, and remain awake until the beacon
   has been received and indicates that no data is pending for them.  If
   beacons are irregular or absent, this would cause clients to either
   miss beacons (increasing response time) or remain awake for excessive
   periods (wasting power).

   This test may be performed on both Access Points and clients.  In the
   case of clients, this test is performed only if the client supports
   the IBSS (ad-hoc) mode of operation, as clients operating in
   infrastructure BSS mode do not transmit beacons.

5.2.5.2. Test parameters




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   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Nominal beacon interval.

5.2.5.3. Procedure

   The DUT is configured to generate beacons at the nominal beacon
   interval.  The tester then measures the beacon inter-arrival time and
   the variation in inter-arrival time over the duration of the trial,
   as and also captures the Beacon Interval field from the received
   beacon frames for comparison with the measured times.

   Care MUST be taken to ensure that extraneous traffic does not occur
   at or near the nominal Target Beacon Transmission Times (i.e., the
   expected arrival time of beacons), as beacon frames are required to
   defer to ongoing traffic.

   In the case of Access Points, the test MAY be repeated with one or
   more virtual or physical clients associated with the DUT, in order to
   measure the ability of the DUT to properly generate beacons at
   various database capacities.

5.2.5.4. Analysis and reporting

   The average beacon interval of the DUT is measured and reported as
   the average time, in seconds, between the first bit of consecutive
   beacon frames received by the tester.  It MUST be computed over the
   duration of the trial.

   The beacon interval variation is measured and reported as the
   difference, in seconds, between the minimum and maximum time between
   the first bit of consecutive beacon frames received by the tester.
   It MUST be computed over the duration of the trial.

   The beacon interval accuracy of the DUT is measured and reported as
   the difference between the measured average beacon interval and the
   value of the Beacon Interval field of the beacon frames from the DUT,
   expressed as a percentage of the measured average beacon interval.
   The Beacon Interval field MUST be converted to seconds prior to
   performing the computation.  If the value of the Beacon Interval
   field is modified by the DUT during the trial, this MUST be reported
   with the test results.

5.2.6. Reset recovery time

5.2.6.1. Objective




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   To determine the speed with which a DUT recovers from a device or
   software reset.  This test is only applicable to Access Points.

   The rapidity with which an Access Point recovers from a reset
   condition affects the perceived availability and stability of a
   wireless network.  For example, an excessive time required to recover
   from a reset can force clients to roam to other Access Points, cause
   higher-layer connections to be dropped, and so on.

5.2.6.2. Test parameters

   The following parameter MUST be configured prior to each trial:

      Reset duration - The test SHOULD be carried out with a reset
      duration of at least 10 seconds.

5.2.6.3. Procedure

   The DUT is set up according to its baseline configuration.  The
   tester first sets up a single virtual or physical client to serve as
   a test client and probe the DUT.  The test client is caused to send a
   continuous stream of broadcast Probe Request frames to the DUT over
   the duration of the trial period, with a nominal interval between
   Probe Request frames of 5 milliseconds.  The Probe Response frames
   from the DUT are identified and timestamped.

   During the middle of the trial period, the DUT is reset.  The time
   stamps associated with the last received Probe Response frame just
   prior to the reset, and the first received Probe Response frame just
   following the reset, are recorded.  The tester MUST verify that the
   Probe Response frames are generated by the DUT (e.g., by comparing
   the BSSID of the Probe Response frames with the MAC address of the
   DUT).

   A power-interruption reset test MUST be performed.  If the DUT is
   capable of a software reset and/or a hardware reset, then the test
   SHOULD be repeated with the software and hardware resets.  The
   results MUST be reported separately.

5.2.6.4. Analysis and reporting

   The reset recovery time MUST be measured and reported as the time, in
   seconds, between the last received Probe Response frame just prior to
   the reset and the first received Probe Response frame just following
   the reset.

5.3. Capacity tests




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   The tests described in this section measure frame storage and
   database related characteristics of the DUT. These tests are
   significant in that they quantify the ability of the DUT to handle
   the bursty traffic loads and large number of clients that are
   expected to be found in enterprise LANs. These tests are applicable
   only to Access Points.

5.3.1. Burst capacity

5.3.1.1. Objective

   To determine the ability of the DUT to forward bursts of back-to-back
   data frames typically seen in heavily loaded networks, especially
   when multiple clients are sending data to a single Access Point. The
   results are indicative of the efficiency, performance and capacity of
   the frame buffering functions implemented within the DUT under high
   load conditions.

5.3.1.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Frame sizes, Frame spacing, Burst size, Inter-burst gap, Signal
      level, Number of STAs, Fragmentation, RTS/CTS usage and security
      settings.

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, security not used.

5.3.1.3. Procedure

   The DUT is initially set up according to the baseline configuration,
   using a starting combination of frame size, frame spacing, burst size
   and inter-burst gap (IBG). For a given offered load and burst size,
   the required IBG is computed per Appendix A. In order to assure a
   reasonable distribution of traffic amongst multiple sources, the
   number of virtual or physical test clients used in this test SHOULD
   be at least 8.  The test SHOULD be performed with three traffic
   configurations: traffic flow from the wireless to the wired interface
   of the DUT, traffic flow from the wired to the wireless interface,
   and traffic flow from the wireless to the wireless interface (intra-
   BSS).

   The tester then transmits traffic to the DUT with the configured
   burst characteristics, which MUST be held constant over the duration
   of the trial, and measures the frame loss. If the frame loss is zero,
   the burst size is increased, keeping the offered load constant, and



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   the trial is repeated. If frame loss is found, the burst size is
   decreased (again keeping the offered load constant) and the trial is
   repeated. The process continues until the maximum burst length is
   found that the DUT can forward without loss at a given offered load
   and frame size.

   The tester SHOULD then repeat the test with different combinations of
   offered load and frame size, but with the same baseline
   configuration. After the baseline configuration has been tested, the
   tester MAY repeat the process with a new configuration, until the
   desired number of different configurations have been exercised. The
   maximum number of such additional configurations is 2 plus the number
   of security modes. In addition, the tester MAY repeat the test with
   different signal levels.

   The traffic generated by the tester MUST be such that consecutive
   frames are generated with different combinations of source and
   destination addresses, and all possible such combinations of
   addresses MUST be represented equally within each trial. Further, the
   tester SHOULD ensure that consecutive frames within a burst originate
   from different physical or virtual clients. This distributes the load
   uniformly among the physical or virtual clients.

5.3.1.4. Analysis and reporting

   The burst capacity of the DUT at a given offered load is computed and
   reported as the maximum number of back-to-back frames that the DUT
   will handle without the loss of any frames. (See Section 26.4 of RFC
   2544 [RFC2544].) The results SHOULD be reported as graphs of burst
   capacity versus each of: offered load, frame size, and signal level.
   Separate results MUST be reported per configuration.

5.3.2. Authentication and association database capacity

5.3.2.1. Objective

   To determine the number of clients that a DUT can successfully
   support at one time. This test is only applicable to Access Points.

   IEEE 802.11 WLANs implement a connection-oriented protocol with
   authentication and connection setup (association) being performed at
   the link layer. The number of clients that can be supported within
   the coverage area of an Access Point is thus ultimately limited by
   the capacity of the association database within the Access Point,
   even if the bandwidth requirements of the clients are well within the
   capacity of the device. This test therefore measures the ability of a
   DUT to support high concentrations of clients in a small region, such
   as within a conference room.



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5.3.2.2. Test parameters

   The following parameters MUST be configured prior to each trial as
   specified in Section 3.5.14:

      Security settings and Number of STAs.

   In addition, the following test parameters MUST be configured to be
   the same for all trials:

      Association Timeout - The tester MUST wait a predetermined amount
      of time for the DUT to respond to an association request with an
      association response. If the DUT fails to respond within this
      time, that association attempt MUST be considered to have failed,
      and a timeout error SHOULD be reported for that association
      attempt. The minimum value of the association timeout MUST be at
      least 10 milliseconds, and MUST NOT exceed 100 milliseconds.

      Association Retry Limit - The tester SHOULD retry a failed
      association attempt (i.e., where the DUT accepts the association
      request but fails to respond with an association response within
      the specified timeout). The number of retries performed by any
      physical or virtual client MUST NOT exceed the pre-set association
      retry limit. If the number of retries reaches this limit, a retry
      limit error SHOULD be reported for that client.

   Both the association timeout and the association retry limit MUST be
   reported with the test results.

   The baseline DUT configuration for performing this test consists of:
   security not used.

5.3.2.3. Procedure

   The DUT is first set up according to the baseline configuration.  The
   tester then causes the specified number of virtual or physical test
   clients to authenticate and associate themselves with the DUT, one
   client at a time, and measures the number of clients that the DUT can
   successfully associate. Each client is authenticated and associated
   in turn; the tester MUST NOT present a new client to the DUT until
   the authentication and association for the previous client has been
   completed. An authentication or association failure for a given
   client SHOULD not cause the tester to stop the trial. Note that the
   number of clients that can associate with the DUT need not equal the
   number of clients that can authenticate with it.

   After the authentication and association of test clients with the
   DUT, the tester MUST verify the associations by causing the



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   successfully associated test clients to transmit data frames to one
   another, and ensure that these data frames are properly forwarded by
   the DUT. The rate at which verification data frames are transmitted
   to the DUT MUST be well below the intra-BSS throughput supported by
   the DUT. The tester MUST ensure that at least one data frame
   originating from each client is forwarded.

   If the DUT deauthenticates one or more clients during the data
   transfer phase, these MUST be counted as authentication failures. If
   the DUT disassociates one or more clients during this phase, these
   MUST be counted as association failures.  If none of the test data
   frames transmitted by a physical or virtual client are forwarded
   successfully, this MUST be treated as a verification failure. Clients
   for which authentication, association or verification failures have
   been detected MUST NOT be included in the count of successfully
   associated clients.

   The tester SHOULD track the association identifiers (AIDs) returned
   by the DUT and SHOULD detect the situation where the same AID is
   issued to two different clients that are associated with the DUT.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised.  The maximum number
   of such additional test configurations is equal to the number of
   security modes.

   The tester MUST remove the test client authentications and
   associations from the DUT database after the completion of each trial
   by performing the 802.11 deauthentication procedure for each
   associated client.

5.3.2.4. Analysis and reporting

   The authentication database capacity of the DUT is computed and
   reported as the maximum number of clients that can be simultaneously
   authenticated with it. A client that initially authenticates, but is
   subsequently deauthenticated by the DUT prior to the end of the
   trial, MUST NOT be counted towards the authentication database
   capacity.

   The association database capacity of the DUT is computed and reported
   as the maximum number of clients that can simultaneously associate
   with it.  (The association database capacity is always less than or
   equal to the authentication database capacity.) A client for which
   authentication, association or verification failures are detected
   during the trial MUST not be counted towards the association database
   capacity.



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   Verification failures MUST be reported along with the test results.
   Duplicate AIDs, if found, SHOULD be reported along with the results.

5.3.3. Power-save buffer capacity

5.3.3.1. Objective

   To measure the buffer capacity of the DUT when supporting clients in
   power management mode. This test is only applicable to Access Points.

   Access Points that support clients in power management mode (i.e.,
   sleeping clients) are required to accept and buffer frames on behalf
   of these clients, and forward them when the clients wake up. This
   test measures the power management mode storage capacity of the DUT,
   and hence its ability to support a large number of associated but
   sleeping clients.

5.3.3.2. Test parameters

   The following parameters are relevant to this test, and MUST be
   configured as specified in Section 3.5.14:

      Frame sizes, Number of STAs, Fragmentation, RTS/CTS usage and
      Security usage.

   In addition, the following test parameter MUST be configured prior to
   each trial:

      Power-Save Poll Delay - this is the delay interposed between the
      announcement by the DUT that data are available for a given client
      and the retrieval of data by that client by means of a PS-Poll
      frame (see subclause 7.2.1.4 of IEEE 802.11 [802.11]) or other
      means. This delay should not exceed the frame aging time of the
      DUT. It SHOULD be kept the same for all trials.

   The baseline DUT configuration for performing this test consists of:
   fragmentation off, RTS/CTS disabled, and security not used.

5.3.3.3. Procedure

   The DUT is initially set up according to the baseline configuration.
   The tester associates the required number of virtual or physical
   clients with the DUT, and causes these clients to enter power-save
   (sleep) mode. The tester MUST verify that the clients have entered
   power-save mode successfully and that the DUT is no longer
   transmitting data to the sleeping clients. The tester then transmits
   a predetermined number of test data frames to the DUT for forwarding
   to each of the sleeping clients. After all of the test data frames



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   have been sent to the DUT, the tester MUST wait for the power-save
   poll delay and then MUST cause each of the sleeping clients to wake
   up and retrieve their data. The number of frames received by each
   client from the DUT is counted.

   The same number of frames MUST be transmitted to each sleeping client
   during a particular trial. The tester MAY associate another virtual
   or physical client with the DUT to serve as a means of injecting test
   data frames, or MAY forward test data frames via the wired interface
   of the DUT. The tester SHOULD verify that the DUT signals (by means
   of its beacons) the presence of data for a given test client before
   causing the client to wake up and obtain the buffered data.  The
   tester MUST ensure that the test clients continue to poll for and
   retrieve buffered data from the DUT until the DUT signals (again via
   its beacons) that no more data are present for the clients.

   The test SHOULD be repeated with different frame sizes and numbers of
   clients.

   After the baseline configuration has been tested, the tester MAY
   repeat the process with a new configuration, until the desired number
   of different configurations have been exercised. The maximum number
   of such additional test configurations is 2 plus the number of
   security modes.

5.3.3.4. Analysis and reporting

   The power save buffer capacity of the DUT, for a given frame size and
   number of clients, is computed and reported as the total number of
   frames received by all of the virtual or physical clients from the
   DUT after they have woken up and requested their data. The results
   SHOULD be reported as graphs of power save buffer capacity versus
   each of: frame size, and number of clients. The test results MAY
   report the results for individual clients as well as the total for
   all of the clients. Separate results MUST be reported per
   configuration.

4.  Security Considerations
   Documents of this type do not directly affect the security of the
   Internet or of corporate networks as long as benchmarking is not
   performed on devices or systems connected to operating networks.

   Note that performance tests SHOULD be done on with adequate isolation
   between the DUT and the remainder of the network, or with security
   systems enabled, to avoid the possibility of compromising the
   performance of operating networks in some manner.

5. IANA Considerations



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   There are no IANA actions requested in this memo. (Note to RFC
   Editor: This section may be removed upon publication as a RFC.)

6.  References

6.1. Normative References

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

   [RFC2544] Bradner, S.  and McQuaid, J., "Benchmarking Methodology for
      Network Interconnect Devices", RFC 2544, March 1999.

   [RFC2889] Mandeville, R.  and Perser, J., "Benchmarking Methodology
      for LAN Switching Devices", RFC 2889, August 2000.

   [RFC1242] Bradner, S., Editor, "Benchmarking Terminology for Network
      Interconnection Devices", RFC 1242, July 1991.

   [RFC2285] Mandeville, R., "Benchmarking Terminology for LAN Switching
      Devices", RFC 2285, June 1998.

6.2.  Informative References

   [802.11] ANSI/IEEE Std 802.11, "Part 11: Wireless LAN Medium Access
      Control (MAC) and Physical Layer (PHY) Specifications," ISO/IEC
      8802-11:1999(E), ISBN 0-7381-1658-0, 1999.

   [RFC1042] Postel, J. and Reynolds, J., "A Standard for the
      Transmission of IP Datagrams over IEEE 802 Networks," RFC 1042,
      February 1988.

7.  Author's Addresses

   Tom Alexander
   VeriWave, Inc.
   9600 Oak Street
   Portland, OR, 97223
   email: tom@veriwave.com
   phone: +1 503 473 8358


   Scott Bradner
   Harvard University
   29 Oxford St.
   Cambridge, MA, 02138
   email: sob@harvard.edu
   phone: +1 617 495 3864



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Appendix A.  Intended load computations

   Calculating intended load for 802.11 media access is complicated by
   the number of different parameters that need to be accounted for as
   well as the random effect of backoff and management overhead. This
   appendix provides formulas for the theoretical maximum capacity of
   the media, actual intended load, and inter-burst gap.

   Note that the instantaneous capacity of the 802.11 medium changes
   from transmission to transmission due to the effects of random
   backoff after each transmission. The formulas presented here are
   therefore expected to be applied over a large volume of traffic,
   rather than individual frames or bursts of frames.  In addition, the
   parameters used in the formulas change for different 802.11 physical
   layers and also different data rates used within a particular
   physical layer.

A.1 Calculating theoretical maximum media capacity

   The theoretical maximum media capacity is calculated assuming
   constant-size data frames, transmitted with the minimum frame spacing
   according to the 802.11 protocol, with no collisions or retries
   occurring.

   The following input parameters are defined:

      LENGTH - MAC Data frame size in bytes, including FCS. For
      fragmented transfers, this is the size of each fragment.

      SPEED - PHY data rate for the MAC portion of a DATA frame, in
      bits/second.

      PLCPTIME - Time required to transmit the PLCP header for the given
      802.11 PHY type and data rate, in seconds.

      SLOTTIME - The slot time for the given 802.11 PHY type and data
      rate, in seconds.

      DIFS - The Distributed Interframe Space (see subclause 9.2.10 of
      IEEE 802.11 [802.11]), in seconds.

      SIFS - The Short Interframe Space (see subclause 9.2.10 of IEEE
      802.11 [802.11]), in seconds.

      CWmin - The minimum contention window duration (see subclause
      9.2.4 of IEEE 802.11 [802.11]), in slot times.

   The following intermediate values are calculated first:



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      TXTIME - Time required to transmit a single Data frame or
      fragment.  For transfers that do not involve an RTS/CTS exchange,
      this is the time taken to transmit the Data frame plus an
      immediately following ACK frame (see 9.2.8 of IEEE 802.11
      [802.11]). For transfers involving an RTS/CTS exchange, this is
      the time taken to transmit an RTS, CTS, Data and ACK frame.

      For RTS/CTS based transfers:

         TXTIME = (PLCPTIME * 4) + (SIFS * 3) + (((LENGTH + 48) * 8) /
      SPEED)

      For transfers not involving RTS/CTS:

         TXTIME = (PLCPTIME * 2) + SIFS + (((LENGTH + 14) * 8) / SPEED)

      AMFI - Average Minimum Frame Interval. This is the minimum legal
      interval between the start of a Data frame and the start of the
      immediately following Data frame, averaged over a large number of
      Data frames.

         AMFI = TXTIME + DIFS + ((CWmin * SLOTTIME) / 2)


   The theoretical maximum capacity of the medium (abbreviated as CAP),
   in bits/second, is then given by:

      CAP = (LENGTH * 8) / AMFI

   The above formula does not take into account overhead due to
   management frames such as beacons and probe requests/responses. The
   tester SHOULD separately account for management frame overhead during
   a trial and subtract this overhead from the calculated theoretical
   capacity in order compensate for the capacity loss due to these
   frames.

A.2 Calculating constant intended load

   The calculations in this section deal with a constant (steady) load
   generated by the tester (i.e., a constant frame pattern). Burst loads
   are covered in the next section.

   If the DUT is not to be overloaded, the intended unidirectional
   traffic load can range from 0 to 100% of the theoretical maximum
   media capacity previously calculated (0 to 50% in the case of
   bidirectional traffic streams).  See Section 3.5.1 of RFC 2285
   [RFC2285] for a full definition of Iload.  For the purposes of this
   document, the intended load is expressed as a percentage of the



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   theoretical maximum media capacity, and calculated as Iload using the
   following formula:

      Iload = (LOAD / CAP) * 100

   where LOAD is the load in bits/second, and CAP is calculated as in
   Section A.1.

   In order to actually generate traffic at Iload values less than 100%,
   the tester must insert extra spacing between frames to reduce the
   traffic load.  This extra spacing is referred to here as EFG (Excess
   Frame Gap), and is calculated as follows:

      EFG = AMFI * ((100 / Iload) - 1)

   The actual frame interval therefore becomes (AMFI + EFG). The traffic
   pattern generated by the tester hence consists of a Data frame, the
   corresponding ACK frame (from the DUT), a gap equal to the DIFS plus
   the average minimum backoff time, and a further gap equal to EFG.

   Generating Iload values greater than 100% requires that the tester
   violate the backoff rules of the 802.11 protocol. The tests in this
   document do not require Iload values greater than 100%.

A.3 Calculating burst intended load

   This section deals with the computation of intended load when the
   traffic pattern is bursty. A bursty pattern comprises a series of
   back-to-back Data/ACK exchanges separated by a DIFS, followed by a
   gap, followed by another series of back-to-back exchanges, and so on.
   The gap between bursts (referred to as the IBG) is selected based on
   the intended load. In addition, the IBG is calculated such that the
   Iload for bursty and constant traffic are directly comparable. (See
   Section 3.4.3 of RFC 2285 [RFC2285] for a discussion of IBG.)

   The following input parameters are defined, in addition to those
   defined above:

      BURST - Length of burst in frames.

   For a given Iload, the IBG is calculated as:

      IBG = DIFS + (AMFI * BURST * ((100 / Iload) - 1))

   Note that the IBG is measured from the last bit of the ACK frame of
   the last data frame in a burst to the first bit of the preamble of
   the first data frame in the next burst.




Alexander & Bradner                                            [Page 53]


Internet-Draft       WLAN Benchmarking Methodology           April 2005


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Alexander & Bradner                                            [Page 54]


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