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rfc:rfc2432

Network Working Group K. Dubray Request for Comments: 2432 IronBridge Networks Category: Informational October 1998

             Terminology for IP Multicast Benchmarking

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.

Abstract

 The purpose of this document is to define terminology specific to the
 benchmarking of multicast IP forwarding devices. It builds upon the
 tenets set forth in RFC 1242, RFC 2285, and other IETF Benchmarking
 Methodology Working Group (BMWG) efforts.  This document seeks to
 extend these efforts to the multicast paradigm.
 The BMWG produces two major classes of documents: Benchmarking
 Terminology documents and Benchmarking Methodology documents. The
 Terminology documents present the benchmarks and other related terms.
 The Methodology documents define the procedures required to collect
 the benchmarks cited in the corresponding Terminology documents.

1. Introduction

 Network forwarding devices are being required to take a single frame
 and support delivery to a number of destinations having membership to
 a particular group. As such, multicast support may place a different
 burden on the resources of these network forwarding devices than with
 unicast or broadcast traffic types.
 Such burdens may not be readily apparent at first glance - the IP
 multicast packet's Class D address may be the only noticeable
 difference from an IP unicast packet.  However, there are many
 factors that may impact the treatment of IP multicast packets.
 Consider how a device's architecture may impact the handling of a
 multicast frame.  For example, is the multicast packet subject to the
 same processing as its unicast analog?  Or is the multicast packet
 treated as an exeception and processed on a different data path?

Dubray Informational [Page 1] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 Consider, too, how a shared memory architecture may demonstrate a
 different performance profile than an architecture which explicitly
 passes each individual packet between the processing entities.
 In addition to forwarding device architecture, there are other
 factors that may impact a device's or system's multicast related
 performance.  Protocol requirements may demand that routers and
 switches consider destination and source addressing in its multicast
 forwarding decisions.  Capturing multicast source/destination
 addressing information may impact forwarding table size and lengthen
 lookups.  Topological factors such as the degree of packet
 replication, the number of multicast groups being supported by the
 system, or the placement of multicast packets in unicast wrappers to
 span non-multicast network paths may all potentially affect a
 system's multicast related performance. For an overall understanding
 of IP multicasting, the reader is directed to [Se98], [Hu95], and
 [Mt98].
 By clearly identifying IP multicast benchmarks and related
 terminology in this document, it is hoped that detailed methodologies
 can be generated in subsequent documents.  Taken in tandem, these two
 efforts endeavor to assist the clinical, empirical, and consistent
 characterization of certain aspects of multicast technologies and
 their individual implementations.  Understanding the operational
 profile of multicast forwarding devices may assist the network
 designer to better deploy multicast in his or her networking
 environment.
 Moreover, this document focuses on one source to many destinations
 profiling.  Elements of this document may require extension when
 considering multiple source to multiple destination IP multicast
 communication.

2. Definition Format

 This section cites the template suggested by RFC 1242 in the
 specification of a term to be defined.
 Term to be defined.
 Definition:
    The specific definition for the term.
 Discussion:
    A brief discussion of the term, its application, or other
    information that would build understanding.

Dubray Informational [Page 2] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 Measurement units:
    Units used to record measurements of this term, if applicable.
 [Issues:]
    List of issues or conditions that affect this term. This field can
    present items the may impact the term's related methodology or
    otherwise restrict its measurement procedures.  This field is
    optional in this document.
 [See Also:]
    List of other terms that are relevant to the discussion of this
    term. This field is optional in this document.

2.1 Existing Terminology

 This document draws on existing terminology defined in other BMWG
 work.  Examples include, but are not limited to:
 Throughput                [RFC 1242, section 3.17]
 Latency                   [RFC 1242, section 3.8]
 Constant Load             [RFC 1242, section 3.4]
 Frame Loss Rate           [RFC 1242, section 3.6]
 Overhead behavior         [RFC 1242, section 3.11]
 Forwarding Rates          [RFC 2285, section 3.6]
 Loads                     [RFC 2285, section 3.5]
 Device Under Test (DUT)   [RFC 2285, section 3.1.1]
 System Under Test (SUT)   [RFC 2285, section 3.1.2]
 Note: "DUT/SUT" refers to a metric that may be applicable to a DUT or
 SUT.

3. Table of Defined Terms

 3.1 General Nomenclature
   3.1.1 Traffic Class. (TC)
   3.1.2 Group Class. (GC)
   3.1.3 Service Class. (SC)
 3.2 Forwarding and Throughput
   3.2.1 Mixed Class Throughput (MCT).
   3.2.2 Scaled Group Forwarding Matrix (SGFM).
   3.2.3 Aggregated Multicast Throughput (AMT)
   3.2.4 Encapsulation Throughput (ET)
   3.2.5 Decapsulation Throughput (DT)
   3.2.6 Re-encapsulation Throughput (RET)

Dubray Informational [Page 3] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 3.3 Forwarding Latency
   3.3.1 Multicast Latency (ML)
   3.3.2 Min/Max Multicast Latency (Min/Max ML)
 3.4 Overhead
   3.4.1 Group Join Delay. (GJD)
   3.4.2 Group Leave Delay. (GLD)
 3.5 Capacity
   3.5.1 Multicast Group Capacity. (MGC)
 3.6 Interaction
   3.6.1 Burdened Response
   3.6.2 Forwarding Burdened Multicast Latency (FBML)
   3.6.3 Forwarding Burdened Join Delay (FBJD)

3.1 General Nomenclature

 This section will present general terminology to be used in this and
 other documents.

3.1.1 Traffic Class. (TC)

 Definition:
    An equivalence class of packets comprising one or more data
    streams.
 Discussion:
    In the scope of this document, Traffic Class will be considered a
    logical identifier used to discriminate between a set or sets of
    packets offered the DUT.
    For example, one Traffic Class may identify a set of unicast
    packets offered to the DUT.  Another Traffic Class may
    differentiate the multicast packets destined to multicast group X.
    Yet another Class may distinguish the set of multicast packets
    destined to multicast group Y.
    Unless otherwise qualified, the usage of the word "Class" in this
    document will refer simply to a Traffic Class.
 Measurement units:
    Not applicable.

Dubray Informational [Page 4] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

3.1.2 Group Class. (GC)

 Definition:
    A specific type of Traffic Class where the packets comprising the
    Class are destined to a particular multicast group.
 Discussion:
 Measurement units:
    Not applicable.

3.1.3 Service Class. (SC)

 Definition:
    A specific type of Traffic Class where the packets comprising the
    Class require particular treatment or treatments by the network
    forwarding devices along the path to the packets' destination(s).
 Discussion:
 Measurement units:
    Not applicable.

3.2 Forwarding and Throughput.

 This section presents terminology related to the characterization of
 the packet forwarding ability of a DUT/SUT in a multicast
 environment.  Some metrics extend the concept of throughput presented
 in RFC 1242.  The notion of Forwarding Rate is cited in RFC 2285.

3.2.1 Mixed Class Throughput (MCT).

 Definition:
    The maximum rate at which none of the offered frames, comprised
    from a unicast Class and a multicast Class, to be forwarded are
    dropped by the device across a fixed number of ports.
 Discussion:
    Often times, throughput is collected on a homogenous traffic class
    - the offered load to the DUT is either singularly unicast or
    singularly multicast.  In most networking environments, the
    traffic mix is seldom so uniformly distributed.
    Based on the RFC 1242 definition for throughput, the Mixed Class
    Throughput benchmark attempts to characterize the DUT's ability to
    process both unicast and multicast frames in the same aggregated
    traffic stream.

Dubray Informational [Page 5] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 Measurement units:
    Frames per second
 Issues:
    Related methodology may have to address the ratio of unicast
    packets to multicast packets.
    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).

3.2.2 Scaled Group Forwarding Matrix (SGFM).

 Definition:
    A table that demonstrates Forwarding Rate as a function of tested
    multicast groups for a fixed number of tested DUT/SUT ports.
 Discussion:
    A desirable attribute of many Internet mechanisms is the ability
    to "scale." This benchmark seeks to demonstrate the ability of a
    SUT to forward as the number of multicast groups is scaled
    upwards.
 Measurement units:
    Packets per second, with corresponding tested multicast group and
    port configurations.
 Issues:
    The corresponding methodology may have to reflect the impact that
    the pairing (source, group) has on many multicast routing
    protocols.
    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).

3.2.3 Aggregated Multicast Throughput (AMT)

 Definition:
    The maximum rate at which none of the offered frames to be
    forwarded through N destination interfaces of the same multicast
    group are dropped.
 Discussion:
    Another "scaling" type of exercise, designed to identify the
    DUT/SUT's ability to handle traffic as a function of the multicast
    destination ports it is required to support.

Dubray Informational [Page 6] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 Measurement units:
    The ordered pair (N,t) where,
       N = the number of destination ports of the multicast group.
       t = the throughput, in frames per second, relative to the
       source stream.
 Issues:
    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).

3.2.4 Encapsulation Throughput (ET)

 Definition:
    The maximum rate at which frames offered a DUT are encapsulated
    and correctly forwarded by the DUT without loss.
 Discussion:
    A popular technique in presenting a frame to a device that may not
    support a protocol feature is to encapsulate, or tunnel, the
    packet containing the unsupported feature in a format that is
    supported by that device.
    More specifically, encapsulation refers to the act of taking a
    frame or part of a frame and embedding it as a payload of another
    frame. This benchmark attempts to characterize the overhead
    behavior associated with that translational process.
 Measurement units:
    Frames per second.
 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).

3.2.5 Decapsulation Throughput (DT)

 Definition:
    The maximum rate at which frames offered a DUT are decapsulated
    and correctly forwarded by the DUT without loss.

Dubray Informational [Page 7] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

 Discussion:
    A popular technique in presenting a frame to a device that may not
    support a protocol feature is to encapsulate, or tunnel, the
    packet containing the unsupported feature in a format that is
    supported by that device. At some point, the frame may be required
    to be returned its orginal format from its encapsulation wrapper
    for use by the frame's next destination.
    More specifically, decapsulation refers to the act of taking a
    frame or part of a frame embedded as a payload of another frame
    and returning it to the payload's appropriate format. This
    benchmark attempts to characterize the overhead behavior
    associated with that translational process.
 Measurement units:
    Frames per second.
 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).

3.2.6 Re-encapsulation Throughput (RET)

 Definition:
    The maximum rate at which frames of one encapsulated format
    offered a DUT are converted to another encapsulated format and
    correctly forwarded by the DUT without loss.
 Discussion:
    A popular technique in presenting a frame to a device that may not
    support a protocol feature is to encapsulate, or tunnel, the
    packet containing the unsupported feature in a format that is
    supported by that device. At some point, the frame may be required
    to be converted from one encapsulation format to another
    encapsulation format.
    More specifically, re-encapsulation refers to the act of taking an
    encapsulated payload of one format and replacing it with another
    encapsulated format - all the while preserving the original
    payload's contents.  This benchmark attempts to characterize the
    overhead behavior associated with that translational process.
 Measurement units:
    Frames per second.

Dubray Informational [Page 8] 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.

Dubray Informational [Page 9] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

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.

Dubray Informational [Page 10] 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.

Dubray Informational [Page 11] 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.

Dubray Informational [Page 12] RFC 2432 Terminology for IP Multicast Benchmarking October 1998

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.

Dubray Informational [Page 13] 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.

Dubray Informational [Page 14] 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: 781 372 8118
 EMail: kdubray@ironbridgenetworks.com

Dubray Informational [Page 15] 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.

Dubray Informational [Page 16]

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