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RFC2432 - Terminology for IP Multicast Benchmarking

王朝other·作者佚名  2008-05-31
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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 RFC1242, RFC2285, 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.

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 RFC1242 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.

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 [RFC1242, section 3.17]

Latency [RFC1242, section 3.8]

Constant Load [RFC1242, section 3.4]

Frame Loss Rate [RFC1242, section 3.6]

Overhead behavior [RFC1242, section 3.11]

Forwarding Rates [RFC2285, section 3.6]

Loads [RFC2285, section 3.5]

Device Under Test (DUT) [RFC2285, section 3.1.1]

System Under Test (SUT) [RFC2285, 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)

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.

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 RFC1242. The notion of Forwarding Rate is cited in RFC2285.

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 RFC1242 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.

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.

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.

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.

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 RFC1242.

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 RFC1242 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.

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.

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.

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. (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.

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", RFC1242, July 1991.

[Br96] Bradner, S., and J. McQuaid, "Benchmarking Methodology for

Network Interconnect Devices", RFC1944, 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", RFC2285, 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

8. Full Copyright Statement

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

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING

BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION

HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

 
 
 
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