rfc2285.txt

RFC 的详细文档！

   See Also:

      unidirectional traffic (3.2.1)
      bidirectional traffic (3.2.2)
      non-meshed traffic (3.3.1)
      partially meshed traffic (3.3.2)
      burst (3.4.1)
      intended load (3.5.1)
      offered load (3.5.2)

3.4 Bursts

   This group of definitions applies to the intervals between frames or
   groups of frames offered to the DUT/SUT.

3.4.1 Burst

   Definition:

      A sequence of frames transmitted with the minimum legal inter-
      frame gap.

   Discussion:

      This definition follows from discussions in section 3.16 of RFC
      1242 and section 21 of RFC 1944 which describes cases where it is
      useful to consider isolated frames as single frame bursts.

   Measurement units:

      n/a

   Issues:



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   See Also:

      burst size (3.4.2)
      inter-burst gap (IBG) (3.4.3)

3.4.2 Burst size

   Definition:

      The number of frames in a burst.

   Discussion:

      Burst size can range from one to infinity.  In unidirectional
      traffic as well as in bidirectional or meshed traffic on full
      duplex interfaces there is no theoretical limit to burst length.
      When traffic is bidirectional or meshed bursts on half duplex
      media are finite since interfaces interrupt transmission
      intermittently to receive frames.

      On real networks burst size will normally increase with window
      size.  This makes it desirable to test devices with small as well
      as large burst sizes.

   Measurement units:

      number of N-octet frames

   Issues:

   See Also:

      burst (3.4.1)
      inter-burst gap (IBG) (3.4.3)

3.4.3 Inter-burst gap (IBG)

   Definition:

      The interval between two bursts.

   Discussion:

      This definition conforms to the discussion in section 20 of RFC
      1944 on bursty traffic.






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      Bidirectional and meshed traffic are inherently bursty since
      interfaces share their time between receiving and transmitting
      frames.  External sources offering bursty traffic for a given
      frame size and burst size must adjust the inter-burst gap to
      achieve a specified average rate of frame transmission.

   Measurement units:

      nanoseconds
      microseconds
      milliseconds
      seconds

   Issues:

   See Also:

      burst (3.4.1)
      burst size (3.4.2)

3.5 Loads

   This group of definitions applies to the rates at which traffic is
   offered to any DUT/SUT.

3.5.1 Intended load (Iload)

   Definition:

      The number of frames per second that an external source attempts
      to transmit to a DUT/SUT for forwarding to a specified output
      interface or interfaces.

   Discussion:

      Collisions on CSMA/CD links or the action of congestion control
      mechanisms can effect the rate at which an external source of
      traffic transmits frames to a DUT/SUT.  This makes it useful to
      distinguish the load that an external source attempts to apply to
      a DUT/SUT and the load it is observed or measured to apply.

      In the case of Ethernet an external source of traffic MUST
      implement the truncated binary exponential back-off algorithm to
      ensure that it is accessing the medium legally







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   Measurement units:

      bits per second
      N-octets per second
      (N-octets per second / media_maximum-octets per second) x 100

   Issues:

   See Also:

      burst (3.4.1)
      inter-burst gap (3.4.3)
      offered load (3.5.2)

3.5.2 Offered load (Oload)

   Definition:

      The number of frames per second that an external source can be
      observed or measured to transmit to a DUT/SUT for forwarding to a
      specified output interface or interfaces.

   Discussion:

      The load which an external device can be observed to apply to a
      DUT/SUT may be less than the intended load due to collisions on
      half duplex media or the action of congestion control mechanisms.
      This makes it important to distinguish intended and offered load
      when analyzing the results of forwarding rate measurements using
      bidirectional or fully meshed traffic.

      Frames which are not successfully transmitted by an external
      source of traffic to a DUT/SUT MUST NOT be counted as transmitted
      frames when measuring forwarding rates.

      The frame count on an interface of a DUT/SUT may exceed the rate
      at which an external device offers frames due to the presence of
      spanning tree BPDUs (Bridge Protocol Data Units) on 802.1D-
      compliant switches or SNMP frames.  Such frames should be treated
      as modifiers as described in section 11 of RFC 1944.

      Offered load MUST be indicated when reporting the results of
      forwarding rate measurements.








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   Measurement units:

      bits per second
      N-octets per second
      (N-octets per second / media_maximum-octets per second) x 100

   Issues:

      token ring

   See Also:

      bidirectional traffic (3.2.2)
      fully meshed traffic (3.3.3)
      intended load (3.5.1)
      forwarding rate (3.6.1)

3.5.3 Maximum offered load (MOL)

   Definition:

      The highest number of frames per second that an external source
      can transmit to a DUT/SUT for forwarding to a specified output
      interface or interfaces.

   Discussion:

      The maximum load that an external device can apply to a DUT/SUT
      may not equal the maximum load allowed by the medium.  This
      will be the case  when an external source lacks the resources
      to transmit frames at the minimum legal inter-frame gap or when
      it has sufficient resources to transmit frames below the
      minimum legal inter-frame gap.  Moreover, maximum load may vary
      with respect to parameters other than a medium's maximum
      theoretical utilization.  For example, on those media employing
      tokens, maximum load may vary as a function of Token Rotation
      Time, Token Holding Time, or the ability to chain multiple
      frames to a single token.  The maximum load that an external
      device applies to a DUT/SUT MUST be specified when measuring
      forwarding rates.

   Measurement units:

      bits per second
      N-octets per second
      (N-octets per second / media_maximum-octets per second) x 100

   Issues:



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   See Also:

      offered load (3.5.2)

3.5.4 Overloading

   Definition:

      Attempting to load a DUT/SUT in excess of the maximum rate of
      transmission allowed by the medium.

   Discussion:

      Overloading can serve to exercise buffers and buffer allocation
      algorithms as well as congestion control mechanisms.  The number
      of input interfaces required to overload one or more output
      interfaces of a DUT/SUT will vary according to the media rates of
      the interfaces involved.

      An external source can also overload an interface by transmitting
      frames below the minimum inter-frame gap.  A DUT/SUT MUST forward
      such frames at intervals equal to or above the minimum gap
      specified in standards.

      A DUT/SUT using congestion control techniques such as backpressure
      or forward pressure may exhibit no frame loss when a tester
      attempts to overload one or more of its interfaces.  This should
      not be exploited to suggest that the DUT/SUT supports rates of
      transmission in excess of the maximum rate allowed by the medium
      since both techniques reduce the rate at which the tester offers
      frames to prevent overloading.  Backpressure achieves this purpose
      by jamming the transmission interfaces of the tester and forward
      pressure by hindering the tester from gaining fair access to the
      medium.  Analysis of both cases should take the distinction
      between intended load (3.5.1) and offered load (3.5.2) into
      account.

   Measurement units:

      bits per second
      N-octets per second
      (N-octets per second / media_maximum-octets per second) x 100

   Issues:







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   See Also:

      unidirectional traffic (3.2.1)
      intended load (3.5.1)
      offered load (3.5.2)
      forwarding rate (3.6.1)
      backpressure (3.7.1)
      forward pressure (3.7.2)

3.6 Forwarding rates

   This group of definitions applies to the rates at which traffic is
   forwarded by any DUT/SUT in response to a stimulus.

3.6.1 Forwarding rate (FR)

   Definition:

      The number of frames per second that a device can be observed to
      successfully transmit to the correct destination interface in
      response to a specified offered load.

   Discussion:

      Unlike throughput defined in section 3.17 of RFC 1242, forwarding
      rate makes no explicit reference to frame loss.  Forwarding rate
      refers to the number of frames per second observed on the output
      side of the interface under test and MUST be reported in relation
      to the offered load.  Forwarding rate can be measured with
      different traffic orientations and distributions.

      It should be noted that the forwarding rate of a DUT/SUT may be
      sensitive to the action of congestion control mechanisms.

   Measurement units:

      N-octet frames per second

   Issues:

   See Also:

      offered load (3.5.2)
      forwarding rate at maximum offered load (3.6.2)
      maximum forwarding rate (3.6.3)






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3.6.2 Forwarding rate at maximum offered load (FRMOL)

   Definition:

      The number of frames per second that a device can be observed to
      successfully transmit to the correct destination interface in
      response to the maximum offered load.

   Discussion:

      Forwarding rate at maximum offered load may be less than the
      maximum rate at which a device can be observed to successfully
      forward traffic.  This will be the case when the ability of a
      device to forward frames degenerates when offered traffic at
      maximum load.

      Maximum offered load MUST be cited when reporting forwarding rate
      at maximum offered load.

   Measurement units:

      N-octet frames per second

   Issues:

   See Also:

      maximum offered load (3.5.3)
      forwarding rate (3.6.1)
      maximum forwarding rate (3.6.3)

3.6.3 Maximum forwarding rate (MFR)

   Definition:

      The highest forwarding rate of a DUT/SUT taken from an iterative
      set of forwarding rate measurements.

   Discussion:

      The forwarding rate of a device may degenerate before maximum load
      is reached.  The load applied to a device must be cited when
      reporting maximum forwarding rate.








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      The following example illustrates how the terms relative to
      loading and forwarding rates are meant to be used.  In particular
      it shows how the distinction between forwarding rate at maximum
      offered load (FRMOL) and maximum forwarding rate (MFR) can be used
      to characterize a DUT/SUT.

                    (A)                          (B)
                Test Device                     DUT/SUT
                Offered Load                Forwarding Rate
                ------------                ---------------
        (1)       14,880 fps - MOL              7,400 fps - FRMOL
        (2)       13,880 fps                    8,472 fps
        (3)       12,880 fps                   12,880 fps  - MFR

   Measurement units:

      N-octet frames per second

   Issues:

   See Also:

      offered load (3.5.2)
      forwarding rates (3.6.1)
      forwarding rate at maximum load (3.6.2)

3.7 Congestion control

   This group of definitions applies to the behavior of a DUT/SUT when
   congestion or contention is present.

3.7.1 Backpressure

   Definition: