rfc2432.txt

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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


   Issues:
      Consideration may need to be given with respect to the impact of
      different frame formats on usable bandwidth.

      Since frame size can sometimes be a factor in frame forwarding
      benchmarks, the corresponding methodology for this metric will
      need to consider frame size distribution(s).

3.3 Forwarding Latency.

   This section presents terminology relating to the characterization of
   the forwarding latency of a DUT/SUT in a multicast environment.  It
   extends the concept of latency presented in RFC 1242.

3.3.1 Multicast Latency. (ML)

   Definition:
      The set of individual latencies from a single input port on the
      DUT or SUT to all tested ports belonging to the destination
      multicast group.

   Discussion:
      This benchmark is based on the RFC 1242 definition of latency.
      While it is useful to collect latency between a pair of source and
      destination multicast ports, it may be insightful to collect the
      same type of measurements across a range of ports supporting that
      Group Class.

      A variety of statistical exercises can be applied to the set of
      latencies measurements.

   Measurement units:
      Time units with enough precision to reflect a latency measurement.

3.3.2 Min/Max Multicast Latency. (Min/Max ML)

   Definition:
      The difference between the maximum latency measurement and the
      minimum latency measurement from the set of latencies produced by
      the Multicast Latency benchmark.

   Discussion:
      This statistic may yield some insight into how a particular
      implementation handles its multicast traffic.  This may be useful
      to users of multicast synchronization types of applications.

   Measurement units:
      Time units with enough precision to reflect latency measurement.



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3.4  Overhead

   This section presents terminology relating to the characterization of
   the overhead delays associated with explicit operations found in
   multicast environments.

3.4.1 Group Join Delay. (GJD)

   Definition:
      The time duration it takes a DUT to start forwarding multicast
      packets from the time a successful IGMP group membership report
      has been issued to the DUT.

   Discussion:
      Many factors can contribute to different results, such as the
      number or type of multicast-related protocols configured on the
      device under test. Other factors are physical topology and "tree"
      configuration.

      Because of the number of variables that could impact this metric,
      the metric may be a better characterization tool for a device
      rather than a basis for comparisons with other devices.

   Issues:
      A consideration for the related methodology:  possible need to
      differentiate a specifically-forwarded multicast frame from those
      sprayed by protocols implementing a flooding tactic to solicit
      prune feedback.

      While this metric attempts to identify a simple delay, the
      underlying and contributing delay components (e.g., propagation
      delay, frame processing delay, etc.) make this a less than simple
      measurement.  The corresponding methodology will need to consider
      this and similar factors to ensure a consistent and precise metric
      result.

   Measurement units:
      Microseconds.

3.4.2 Group Leave Delay. (GLD)

   Definition:
      The time duration it takes a DUT to cease forwarding multicast
      packets after a corresponding IGMP "Leave Group" message has been
      successfully offered to the DUT.






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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


   Discussion:
      While it is important to understand how quickly a device can
      process multicast frames; it may be beneficial to understand how
      quickly that same device can stop the process as well.

      Because of the number of variables that could impact this metric,
      the metric may be a better characterization tool for a device
      rather than a basis for comparisons with other devices.

   Measurement units:
      Microseconds.

   Issues:
      The Methodology may need to consider protocol-specific timeout
      values.

      While this metric attempts to identify a simple delay, the
      underlying and contributing delay components (e.g., propagation
      delay, frame processing delay, etc.) make this a less than simple
      measurement.  Moreover, the cessation of traffic is a rather
      unobservable event (i.e., at what point is the multicast forwarded
      considered stopped on the DUT interface processing the Leave?).
      The corresponding methodology will need to consider this and
      similar factors to ensure a consistent and precise metric result.

3.5 Capacity

   This section offers terms relating to the identification of multicast
   group limits of a DUT/SUT.

3.5.1 Multicast Group Capacity. (MGC)

   Definition:
      The maximum number of multicast groups a SUT/DUT can support while
      maintaining the ability to forward multicast frames to all
      multicast groups registered to that SUT/DUT.

   Discussion:

   Measurement units:
      Multicast groups.

   Issues:
      The related methodology may have to consider the impact of
      multicast sources per group on the ability of a SUT/DUT to "scale
      up" the number of supportable multicast groups.





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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


3.6 Interaction

   Network forwarding devices are generally required to provide more
   functionality than than the forwarding of traffic.  Moreover, network
   forwarding devices may be asked to provide those functions in a
   variety of environments.  This section offers terms to assist in the
   charaterization of DUT/SUT behavior in consideration of potentially
   interacting factors.

3.6.1 Burdened Response.

   Definition:
      A measured response collected from a DUT/SUT in light of
      interacting, or potentially interacting, distinct stimulii.

   Discussion:
      Many metrics provide a one dimensional view into an operating
      characteristic of a tested system.  For example, the forwarding
      rate metric may yield information about the packet processing
      ability of a device.  Collecting that same metric in view of
      another control variable can oftentimes be very insightful. Taking
      that same forwarding rate measurement, for instance, while the
      device's address table is injected with an additional 50,000
      entries may yield a different perspective.

   Measurement units:
      A burdened response is a type of metric.  Metrics of this this
      type must follow guidelines when reporting results.

      The metric's principal result MUST be reported in conjunction with
      the contributing factors.

      For example, in reporting a Forwarding Burdened Latency, the
      latency measurement should be reported with respect to
      corresponding Offered Load and Forwarding Rates.

   Issues: A Burdened response may be very illuminating when trying to
      characterize a single device or system.  Extreme care must be
      exercised when attempting to use that characterization as a basis
      of comparison with other devices or systems.  Test agents must
      ensure that the measured response is a function of the controlled
      stimulii, and not secondary factors.  An example of of such an
      interfering factor would be configuration mismatch of a timer
      impacting a response process.







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3.6.2 Forwarding Burdened Multicast Latency. (FBML)

   Definition:
      A multicast latency taken from a DUT/SUT in the presence of a
      traffic forwarding requirement.

   Discussion:
      This burdened response metric builds on the Multicast Latency
      definition offered in section 3.3.1.  It mandates that the DUT be
      subjected to an additional measure of traffic not required by the
      non-burdened metric.

      This metric attempts to provide a means by which to evaluate how
      traffic load may or may not impact a device's or system's packet
      processing delay.

   Measurement units:
      Time units with enough precision to reflect the latencies
      measurements.

      Latency measurements MUST be reported with the corresponding
      sustained Forwarding Rate and associated Offered Load.

3.6.3 Forwarding Burdened Group Join Delay. (FBGJD)

   Definition:
      A multicast Group Join Delay taken from a DUT in the presence of a
      traffic forwarding requirement.

   Discussion:
      This burdened response metric builds on the Group Join Delay
      definition offered in section 3.4.1.  It mandates that the DUT be
      subjected to an additional measure of traffic not required by the
      non-burdened metric.

      Many factors can contribute to different results, such as the
      number or type of multicast-related protocols configured on the
      device under test. Other factors could be physical topology or the
      logical multicast "tree" configuration.

      Because of the number of variables that could impact this metric,
      the metric may be a better characterization tool for a device
      rather than a basis for comparisons with other devices.

   Measurement units:
      Time units with enough precision to reflect the delay
      measurements.




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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


      Delay measurements MUST be reported with the corresponding
      sustained Forwarding Rate and associated Offered Load.

   Issues:
      While this metric attempts to identify a simple delay, the
      underlying and contributing delay components (e.g., propagation
      delay, frame processing delay, etc.) make this a less than simple
      measurement.  The corresponding methodology will need to consider
      this and similar factors to ensure a consistent and precise metric
      result.

4. Security Considerations

   This document addresses metrics and terminology relating to the
   performance benchmarking of IP Multicast forwarding devices.  The
   information contained in this document does not impact the security
   of the Internet.

   Methodologies regarding the collection of the metrics described
   within this document may need to cite security considerations.  This
   document does not address methodological issues.

5. Acknowledgments

   The IETF BMWG participants have made several comments and suggestions
   regarding this work.  Particular thanks goes to Harald Alvestrand,
   Scott Bradner, Brad Cain, Eric Crawley, Bob Mandeville, David Newman,
   Shuching Sheih, Dave Thaler, Chuck Winter, Zhaohui Zhang, and John
   Galgay for their insightful review and assistance.






















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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


6. References

   [Br91] Bradner, S., "Benchmarking Terminology for Network
          Interconnection Devices", RFC 1242, July 1991.

   [Br96] Bradner, S., and J. McQuaid, "Benchmarking Methodology for
          Network Interconnect Devices", RFC 1944, May 1996.

   [Hu95] Huitema, C.  "Routing in the Internet."  Prentice-Hall, 1995.

   [Se98] Semeria, C. and Maufer, T.  "Introduction to IP Multicast
          Routing."  http://www.3com.com/nsc/501303.html  3Com Corp.,
          1998.

   [Ma98] Mandeville, R., "Benchmarking Terminology for LAN Switching
          Devices", RFC 2285, February 1998.

   [Mt98] Maufer, T.  "Deploying IP Multicast in the Enterprise."
          Prentice-Hall, 1998.

7. Author's Address

   Kevin Dubray
   IronBridge Networks
   55 Hayden Avenue
   Lexington, MA 02421
   USA

   Phone: [phone]
   EMail: [e-mail]





















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RFC 2432       Terminology for IP Multicast Benchmarking    October 1998


8.  Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
























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