Network Working Group K. Dubray
INTERNET-DRAFT Bay Networks
Expiration Date: September 1998 March 1998
Terminology for IP Multicast Benchmarking
<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.]
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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.
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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
3.6.4 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.
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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 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.
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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.
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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.
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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.
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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.
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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.
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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:
While burdened response is not a specific 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.
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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 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 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.
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.
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.
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[3] Craig, R. Terminology for Cell/Call Benchmarking. <draft-ietf-
bmwg-call-01.txt> March, 1997.
[4] Mandeville, R. Benchmarking Terminology for LAN Switching Devices.
RFC 2285. February, 1998.
5. Author's Address
Kevin Dubray
Bay Networks, Inc.
600 Technology Park Drive
M/S BL60-301
Billerica, MA 01981
(978) 916-3862
kdubray@baynetworks.com
or direct discussion to the Benchmarking Methodology Working Group:
bmwg@harvard.edu
Dubray, K. Expires January 1998 [Page 12]
