rfc2285.txt

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Network Working Group                                      R. Mandeville
Request for Comments: 2285                 European Network Laboratories
Category: Informational                                    February 1998


           Benchmarking Terminology for LAN Switching Devices

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Table of Contents

   1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2
   2. Existing definitions . . . . . . . . . . . . . . . . . . . . . . 2
   3. Term definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
      3.1 Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . 3
         3.1.1 Device under test (DUT) . . . . . . . . . . . . . . . . 3
         3.1.2 System under test (SUT) . . . . . . . . . . . . . . . . 3
      3.2 Traffic orientation. . . . . . . . . . . . . . . . . . . . . 4
         3.2.1 Unidirectional traffic. . . . . . . . . . . . . . . . . 4
         3.2.2 Bidirectional traffic . . . . . . . . . . . . . . . . . 5
      3.3 Traffic distribution . . . . . . . . . . . . . . . . . . . . 6
         3.3.1 Non-meshed traffic. . . . . . . . . . . . . . . . . . . 6
         3.3.2 Partially meshed traffic. . . . . . . . . . . . . . . . 7
         3.3.3 Fully meshed traffic. . . . . . . . . . . . . . . . . . 8
      3.4 Bursts . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
         3.4.1 Burst . . . . . . . . . . . . . . . . . . . . . . . . . 9
         3.4.2 Burst size . . . . . . . . . . . . . . . . . . . . . . 10
         3.4.3 Inter-burst gap (IBG). . . . . . . . . . . . . . . . . 10
      3.5 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
         3.5.1 Intended load (Iload)  . . . . . . . . . . . . . . . . 11
         3.5.2 Offered load (Oload) . . . . . . . . . . . . . . . . . 12
         3.5.3 Maximum offered load (MOL) . . . . . . . . . . . . . . 13
         3.5.4 Overloading  . . . . . . . . . . . . . . . . . . . . . 14
      3.6 Forwarding rates  . . . . . . . . . . . . . . . . . . . . . 15
         3.6.1 Forwarding rate (FR) . . . . . . . . . . . . . . . . . 15
         3.6.2 Forwarding rate at maximum offered load (FRMOL). . . . 16
         3.6.3 Maximum forwarding rate (MFR). . . . . . . . . . . . . 16
      3.7 Congestion control  . . . . . . . . . . . . . . . . . . . . 17
         3.7.1 Backpressure . . . . . . . . . . . . . . . . . . . . . 17
         3.7.2 Forward pressure . . . . . . . . . . . . . . . . . . . 18



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         3.7.3 Head of line blocking  . . . . . . . . . . . . . . . . 19
      3.8 Address handling  . . . . . . . . . . . . . . . . . . . . . 20
         3.8.1 Address caching capacity . . . . . . . . . . . . . . . 20
         3.8.2 Address learning rate  . . . . . . . . . . . . . . . . 20
         3.8.3 Flood count  . . . . . . . . . . . . . . . . . . . . . 21
      3.9 Errored frame filtering . . . . . . . . . . . . . . . . . . 21
         3.9.1 Errored frames . . . . . . . . . . . . . . . . . . . . 22
      3.10 Broadcasts . . . . . . . . . . . . . . . . . . . . . . . . 22
         3.10.1 Broadcast forwarding rate at maximum load . . . . . . 22
         3.10.2 Broadcast latency . . . . . . . . . . . . . . . . . . 23
   4. Security Considerations . . . . . . . . . . . . . . . . . . . . 24
   5. References. . . . . . . . . . . . . . . . . . . . . . . . . . . 24
   6. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . 24
   7. Author's Address. . . . . . . . . . . . . . . . . . . . . . . . 24
   8. Full Copyright Statement. . . . . . . . . . . . . . . . . . . . 25

1. Introduction

   This document is intended to provide terminology for the benchmarking
   of local area network (LAN) switching devices.  It extends the
   terminology already defined for benchmarking network interconnect
   devices in RFCs 1242 and 1944 to switching devices.

   Although it might be found useful to apply some of the terms defined
   here to a broader range of network interconnect devices, this RFC
   primarily deals with devices which switch frames at the Medium Access
   Control (MAC) layer.  It defines terms in relation to the traffic put
   to use when benchmarking switching devices, forwarding performance,
   congestion control, latency, address handling and filtering.

2.  Existing definitions

   RFC 1242 "Benchmarking Terminology for Network Interconnect Devices"
   should be consulted before attempting to make use of this document.
   RFC 1944 "Benchmarking Methodology for Network Interconnect Devices"
   contains discussions of a number of terms relevant to the
   benchmarking of switching devices and should also be consulted.

   For the sake of clarity and continuity this RFC adopts the template
   for definitions set out in Section 2 of RFC 1242.  Definitions are
   indexed and grouped together in sections for ease of reference.

   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.






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3. Term definitions

3.1 Devices

   This group of definitions applies to all types of networking devices.

3.1.1 Device under test (DUT)

   Definition:

      The network forwarding device to which stimulus is offered and
      response measured.

   Discussion:

      A single stand-alone or modular unit which receives frames on one
      or more of its interfaces and then forwards them to one or more
      interfaces according to the addressing information contained in
      the frame.

   Measurement units:

      n/a

   Issues:

   See Also:

      system under test (SUT) (3.1.2)

3.1.2 System Under Test (SUT)

   Definition:

      The collective set of network devices to which stimulus is offered
      as a single entity and response measured.

   Discussion:

      A system under test may be comprised of a variety of networking
      devices.  Some devices may be active in the forwarding decision-
      making process, such as routers or switches; other devices may be
      passive such as a CSU/DSU.  Regardless of constituent components,
      the system is treated as a singular entity to which stimulus is
      offered and response measured.






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   Measurement units:

      n/a

   Issues:

   See Also:

      device under test (DUT) (3.1.1)

3.2 Traffic orientation

   This group of definitions applies to the traffic presented to the
   interfaces of a DUT/SUT and indicates whether the interfaces are
   receiving only, transmitting only, or both receiving and
   transmitting.

3.2.1 Unidirectional traffic

   Definition:

      When all frames presented to the input interfaces of a DUT/SUT are
      addressed to output interfaces which do not themselves receive any
      frames.

   Discussion:

      This definition conforms to the discussion in section 16 of RFC
      1944 which describes how unidirectional traffic can be offered to
      a DUT/SUT to measure throughput.  Unidirectional traffic is also
      appropriate for:

      -the measurement of the minimum inter-frame gap -the creation of
      many-to-one or one-to-many interface overload -the detection of
      head of line blocking -the measurement of forwarding rates and
      throughput when congestion control mechanisms are active.

      When a tester offers unidirectional traffic to a DUT/SUT reception
      and transmission are handled by different interfaces or sets of
      interfaces of the DUT/SUT.  All frames received from the tester by
      the DUT/SUT are transmitted back to the tester from interfaces
      which do not themselves receive any frames.

      It is useful to distinguish traffic orientation and traffic
      distribution when considering traffic patterns used in device
      testing.  Unidirectional traffic, for example, is traffic
      orientated in a single direction between mutually exclusive sets
      of source and destination interfaces of a DUT/SUT.  Such traffic,



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      however, can be distributed between interfaces in different ways.
      When traffic is sent to two or more interfaces from an external
      source and then forwarded by the DUT/SUT to a single output
      interface the traffic orientation is unidirectional and the
      traffic distribution between interfaces is many-to-one.  Traffic
      can also be sent to a single input interface and forwarded by the
      DUT/SUT to two or more output interfaces to achieve a one-to-many
      distribution of traffic.

      Such traffic distributions can also be combined to test for head
      of line blocking or to measure forwarding rates and throughput
      when congestion control mechanisms are active.

      When a DUT/SUT is equipped with interfaces running at different
      media rates the number of input interfaces required to load or
      overload an output interface or interfaces will vary.

      It should be noted that measurement of the minimum inter-frame gap
      serves to detect violations of the IEEE 802.3 standard.

   Issues:

      half duplex / full duplex

   Measurement units:

      n/a

   See Also:

      bidirectional traffic (3.2.2)
      non-meshed traffic (3.3.1)
      partially meshed traffic (3.3.2)
      fully meshed traffic (3.3.3)
      congestion control (3.7)
      head of line blocking (3.7.3)

3.2.2 Bidirectional traffic

   Definition:

      Frames presented to a DUT/SUT such that every receiving interface
      also transmits.

   Discussion:

      This definition conforms to the discussion in section 14 of RFC
      1944.



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      When a tester offers bidirectional traffic to a DUT/SUT all the
      interfaces which receive frames from the tester also transmit
      frames back to the tester.

      Bidirectional traffic MUST be offered when measuring the
      throughput or forwarding rate of full duplex interfaces of a
      switching device.

   Issues:

      truncated binary exponential back-off algorithm

   Measurement units:

      n/a

   See Also:

      unidirectional traffic (3.2.1)
      non-meshed traffic (3.3.1)
      partially meshed traffic (3.3.2)
      fully meshed traffic (3.3.3)

3.3 Traffic distribution

   This group of definitions applies to the distribution of frames
   forwarded by a DUT/SUT.

3.3.1 Non-meshed traffic

   Definition:

      Frames offered to a single input interface and addressed to a
      single output interface of a DUT/SUT where input and output
      interfaces are grouped in mutually exclusive pairs.

   Discussion:

      In the simplest instance of non-meshed traffic all frames are
      offered to a single input interface and addressed to a single
      output interface.  The one-to-one mapping of input to output
      interfaces required by non-meshed traffic can be extended to
      multiple mutually exclusive pairs of input and output interfaces.

   Measurement units:

      n/a




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   Issues:

      half duplex / full duplex

   See Also:

      unidirectional traffic (3.2.1)
      bidirectional traffic (3.2.2)
      partially meshed traffic (3.3.2.)
      fully meshed traffic (3.3.3)
      burst (3.4.1)

3.3.2 Partially meshed traffic

   Definition:

      Frames offered to one or more input interfaces of a DUT/SUT and
      addressed to one or more output interfaces where input and output
      interfaces are mutually exclusive and mapped one-to-many, many-
      to-one or many-to-many.

   Discussion:

      This definition follows from the discussion in section 16 of RFC
      1944 on multi-port testing.  Partially meshed traffic allows for
      one-to-many, many-to-one or many-to-many mappings of input to
      output interfaces and readily extends to configurations with
      multiple switching devices linked together over backbone
      connections.

      It should be noted that partially meshed traffic can load backbone
      connections linking together two switching devices or systems more
      than fully meshed traffic.  When offered partially meshed traffic
      devices or systems can be set up to forward all of the frames they
      receive to the opposite side of the backbone connection whereas
      fully meshed traffic requires at least some of the offered frames
      to be forwarded locally, that is to the interfaces of the DUT/SUT
      receiving them.  Such frames will not traverse the backbone
      connection.

   Measurement units:

      n/a

   Issues:

      half duplex / full duplex




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   See Also:

      unidirectional traffic (3.2.1)
      bidirectional traffic (3.2.2)
      non-meshed traffic (3.3.1)
      fully meshed traffic (3.3.3)
      burst (3.4.1)

3.3.3 Fully meshed traffic

   Definition:

      Frames offered to a designated number of interfaces of a DUT/SUT
      such that each one of the interfaces under test receives frames
      addressed to all of the other interfaces under test.

   Discussion:

      As with bidirectional partially meshed traffic, fully meshed
      traffic requires each one the interfaces of a DUT/SUT to both
      receive and transmit frames.  But since the interfaces are not
      divided into groups as with partially meshed traffic every
      interface forwards frames to and receives frames from every other
      interface.  The total number of individual input/output interface
      pairs when traffic is fully meshed over n switched interfaces
      equals n x (n - 1).  This compares with n x (n / 2) such interface
      pairs when traffic is partially meshed.

      Fully meshed traffic on half duplex interfaces is inherently
      bursty since interfaces must interrupt transmission whenever they
      receive frames.  This kind of bursty meshed traffic is
      characteristic of real network traffic and can be advantageously
      used to diagnose a DUT/SUT by exercising many of its component
      parts simultaneously.  Additional inspection may be warranted to
      correlate the frame forwarding capacity of a DUT/SUT when offered
      meshed traffic and the behavior of individual elements such as
      input or output buffers, buffer allocation mechanisms, aggregate
      switching capacity, processing speed or medium access control.

      The analysis of forwarding rate measurements presents a challenge
      when offering bidirectional or fully meshed traffic since the rate
      at which the tester can be observed to transmit frames to the
      DUT/SUT may be smaller than the rate at which it intends to
      transmit due to collisions on half duplex media or the action of
      congestion control mechanisms.  This makes it important to take
      account of both the intended and offered loads defined in sections
      3.5.1.and 3.5.2 below when reporting the results of such
      forwarding rate measurements.



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      When offering bursty meshed traffic to a DUT/SUT a number of
      variables have to be considered.  These include frame size, the
      number of frames within bursts, the interval between bursts as
      well as the distribution of load between incoming and outgoing
      traffic.  Terms related to bursts are defined in section 3.4
      below.

   Measurement units:

      n/a

   Issues:

      half duplex / full duplex