Network Working Group                                          K. Dubray
INTERNET-DRAFT                                       IronBridge Networks
Expiration Date:  January  Febuary 1999                                 July                               August 1998

               Terminology for IP Multicast Benchmarking
                     <draft-ietf-bmwg-mcast-04.txt>
                     <Draft-ietf-bmwg-mcast-05.txt>

Status of this Memo

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Abstract

   The purpose of this draft 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?
   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.

   This work is primarily directed  towards  intermediate  IP  multicast
   forwarding  devices (e.g., routers or switches) on LANs.  Elements of
   this text may or may not  be  applicable  to  other  media  as  well.
   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 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. document.

   [See Also:]
      List of other terms that are relevant to the discussion
      of this term. This field is optional in this draft. 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)
   Devices           (RFC 2285, 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 Encapsulation Throughput (ET)
     3.2.5 Decapsulation Throughput (DT)
     3.2.6 Re-encapsulation Throughput (RET)

   3.3 Forwarding Latency
     3.3.1 Multicast Latency
     3.3.2 Min/Max Multicast Latency

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

   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

3.1 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 pack-
     ets 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 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.

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

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 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.

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

   Measurement units:
     Frames per second.

3.2.5 Decapsulation Throughput (DT)

   Definition:
     The maximum rate at which frames offered a DUT are decapsulated
     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 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.

     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 the set of
     latencies measurements.

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

   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.

   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.

     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.

   Measurement units:
     Microseconds.

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

   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.  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.

     The Methodology may also need to consider protocol-specific timeout
     values as well.

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
     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.

3.6.2 Forwarding Burdened Multicast Latency.

   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.

   Definition:
     A multicast Group Join Delay taken from a DUT/SUT 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 system 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 or
     system rather than a basis for comparisons with other devices.

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

     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.

6. References

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

   [Br96] Bradner, S., McQuaid, J.  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,
       Prentice-Hall, 1998.

7. Author's Address

      Kevin Dubray
      IronBridge Networks
      55 Hayden Avenue
      Lexington, MA 02421
      USA
      Phone: 781 402 8018
      EMail: kdubray@ironbridgenetworks.com