Network Working Group                                      K. Dubray
INTERNET-DRAFT                                          Bay Networks
Expiration Date:  January  September 1998                          March 1998                             July 1997

                 Terminology for IP Multicast Benchmarking
                     <draft-ietf-bmwg-mcast-02.txt>
                     <draft-ietf-bmwg-mcast-03.txt>

Status of this Memo

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   This memo provides information for the Internet community.  This memo
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Abstract

   The purpose of this draft is to add terminology specific to the
   benchmarking of multicast IP forwarding devices. It builds upon the
   tenets set forth in RFC 1242, RFC 1944, and other IETF Benchmarking
   Methodology Working Group (BMWG) effort and extends them to the
   multicast paradigm.

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.

   By clearly identifying 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.

   [While primarily directed towards intermediate IP multicast
   forwarding devices on LANs, elements of this text may or may not be
   applicable to other media as well.]

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 and any
      restrictions on measurement procedures.

   Measurement units:
      Units used to record measurements of this term, if applicable.

   [Issues:]
      List of issues or conditions that effect this term. This
      field is optional in this draft.

   [See Also:]
      List of other terms that are relevant to the discussion
      of this term. This field is optional in this draft.

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  ([4], section 3.6)
   Loads             ([4], section 3.5)
   Devices           ([4], section 3.1)

3. Table of Defined Terms

   3.1 General Nomenclature
     3.1.1 Traffic Class.
     3.1.2 Group Class.
     3.1.3 Service Class.

   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 Translational Encapsulation Throughput (ET)
     3.2.5 Decapsulation Throughput (TT) (DT)
     3.2.6 Re-encapsulation Throughput (RET)

   3.3 Fairness

   3.4 Forwarding Latency
     3.4.1
     3.3.1 Multicast Latency
     3.4.2
     3.3.2 Min/Max Multicast Latency

   3.5

   3.4 Overhead
     3.5.1
     3.4.1 Group Join Delay.
     3.5.2
     3.4.2 Group Leave Delay.

   3.6

   3.5 Capacity
     3.5.1 Multicast Group Capacity.

   3.6 Interaction
     3.6.1 Burdened Response
     3.6.2 Forwarding Burdened Multicast Latency
     3.6.3 Forwarding Burdened Join Delay
     3.6.4 Forwarding Burdened Multicast Group Capacity.

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

3.1.1 Traffic Class.

   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.

3.1.2 Group Class.

   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.

   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 relating 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.

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. device across a fixed number of ports.

   Discussion:
     Often times, throughput is collected on a homogenous traffic
     type - though the packets' destinations may vary, the packets
     follow the same packet forwarding path through the DUT.

     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.

   Measurement units:
     Frames per second

   Issues:
     Related methodology may have to address the ratio of unicast packets
     to multicast packets.

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 (or even the definition itself) may
     have to reflect the impact that the pairing (source, group) has on
     many multicast routing protocols.

     Refers to the concept of Forwarding Rate originally defined in
     this document.  The definition of Forwarding Rate has been
     moved to [4].

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.

   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.

3.2.4 Translational Encapsulation Throughput (TT) (ET)

   Definition:
     The maximum rate at which none of the frames offered in an
     transitional format to the SUT a DUT are dropped in the process of
     converting those frames to their appropriate, final format encapsulated
     and
     subsequent correct delivery. correctly forwarded by the DUT without loss.

   Discussion:
     A popular technique in presenting frames a frame to devices 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
     transitional translational process.

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

   Measurement units:
     Frames per second.

3.3 Fairness.

3.2.5 Decapsulation Throughput (DT)

   Definition:
     The ability of maximum rate at which frames offered a SUT to fulfill DUT are decapsulated
     and correctly forwarded by the requirements of a Traffic
     Class DUT without compromising the requirements, if any, of other
     Classes. loss.

   Discussion:

   Measurement units:
     Not applicable.

3.4 Forwarding Latency.

   This section presents terminology relating
     A popular technique in presenting a frame to the characterization of
   the forwarding latency of a DUT/SUT in device that may
     not support a multicast environment.
   It extends protocol feature is to encapsulate, or tunnel,
     the concept of latency presented packet containing the unsupported feature in RFC 1242.

3.4.1 Multicast Latency.

   Definition:
     The set of individual latencies from a single input port on format that
     is supported by that device. At some point, the DUT or SUT to all tested ports belonging frame may be required
     to be returned its orginal format from its encapsulation wrapper for
     use by the destination
     multicast group.

   Discussion:
     This benchmark is based on frame's next destination.

     More specifically, decapsulation refers to the RFC 1242 definition act of latency.
     While it is useful to collect latency between taking a pair
     frame or part of source a frame embedded as a payload of another frame and destination multicast ports,
     returning it may be insightful to collect the same type of measurements across a range of ports supporting
     that Group Class.

     A variety of payload's appropriate format. This benchmark
     attempts to characterize the overhead behavior associated with that
     translational process.

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

   Measurement units:
     Frames per second.

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.

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

   Measurement units:
     Frames per second.

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.

   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 applied to the set of
     latencies measurements.

Dubray, K.             Expires September 1998                  [Page 7]^L
   Measurement units:
     Time units with enough precision to reflect measurement.

3.3.2 Min/Max Multicast Latency.

   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 measurement.

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.

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

   Discussion:
     Many factors can contribute to different results, such as
     the number or type of multicast-related protocols configured
     on the system 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 or
     system rather than a basis for comparisons with other devices.

     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.

   Measurement units:
     Microseconds.

3.4.2 Group Leave Delay.

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

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

   Measurement units:
     Microseconds.

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

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.

   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.

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 set of
     latencies measurements. device's address
     table is injected with an additional 50,000 entries may yield a
     different perspective.

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

3.4.2 Min/Max Multicast Latency.

   Definition:
     While burdened response is not a specific metric, metrics of this
     this type must follow guidelines when reporting results.

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

     For example, in reporting a Forwarding Burdened Latency, the maximum
     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
     minimum 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.

3.6.2 Forwarding Burdened Multicast Latency.

   Definition:
     A multicast latency measurement taken from a DUT/SUT in the set presence of latencies produced by
     a traffic forwarding requirement.

   Discussion:
     This burdened response metric builds on the Multicast Latency benchmark.

   Discussion:
     This statistic may yield some insight into how a particular
     implementation handles its multicast traffic.  This may definition
     offered in section 3.3.1.  It mandates that the DUT be useful subjected to users of multicast synchronization types
     an additional measure of applications. traffic not required by the non-burdened
     metric.

     It attempts to provide a means 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 measurement.

3.5  Overhead

   This section presents terminology relating to the characterization of latencies measurements.

     Latency measurements MUST be reported with the overhead delays corresponding sustained
     Forwarding Rate and associated with explicit operations found in
   multicast environments.

3.5.1 Offered Load.

3.6.3 Forwarding Burdened Group Join Delay.

   Definition:
     The time duration it takes a DUT/SUT to start forwarding
     A multicast
     packets Group Join Delay taken from a DUT/SUT in the time presence of
     a successful IGMP group membership report has
     been issued 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 DUT/SUT.

   Discussion: non-burdened
     metric.

     Many different factors can contribute to different results, such as
     the number or type of multicast-related protocols configured
     on the system under test.

     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.

   Measurement units:
     Microseconds.

3.5.2 Group Leave Delay.

   Definition:
     The time duration it takes a DUT/SUT to cease forwarding multicast
     packets after a corresponding IGMP "Leave Group" message has been
     successfully offered to Other factors are physical topology and
     "tree" configuration.

     Because of the DUT/SUT.

   Discussion:
     While it is important to understand how quickly a system can
     process multicast frames; it may be beneficial to understand
     how quickly number of variables that same system can stop could impact this metric,
     the process as well.

   Measurement units:
     Microseconds.

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

3.6 Capacity

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

3.6.1 Multicast Group Capacity.

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

   Discussion: device or
     system rather than a basis for comparisons with other devices.

   Measurement units:
     Multicast groups.

   Issues:
     The related methodology may have
     Time units with enough precision to consider the impact of multicast
     sources per group on reflect the ability of a SUT/DUT to "scale up" delay measurements.

     Delay measurements MUST be reported with the
     number of supportable multicast groups. corresponding sustained
     Forwarding Rate and associated Offered Load.

4. Security Considerations

   Security issues are not addressed in this memo.

5. References

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

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

   [3] Craig, R.  Terminology for Cell/Call Benchmarking. <draft-ietf-
       bmwg-call-01.txt> March, 1997. Work in progress.

   [4] Mandeville, R.  Benchmarking Terminology for LAN Switching Devices. <draft-ietf-bmwg-lanswitch-06.txt> July, 1997.
       Work in progress.
       RFC 2285.  February, 1998.

5. Author's Address

   Kevin Dubray
   Bay Networks, Inc.
   2 Federal Street
   600 Technology Park Drive
   M/S BL60-301
   Billerica, MA 01984
   (508) 01981
   (978) 916-3862
   kdubray@baynetworks.com

   or direct discussion to the Benchmarking Methodology Working Group:
   bmwg@harvard.edu