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Versions: 00 01                                                         
                    Benchmarking Methodology Working Group
                    Internet Draft - December 1995

                    Bob Mandeville
                    ENL
                    Ajay V. Shah
                    Wandel & Goltermann Technologies, Inc

                    Benchmarking Methodology for Ethernet Switches

                    <draft-ietf-bmwg-ethernet-switches-00.txt>



Status of this Document

This document is an Internet-Draft.  Internet-Drafts are working
documents of  the Internet Engineering Task Force (IETF), its areas,
and its working groups.  Note that other groups may also distribute
working documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as ``work in progress.''

To learn the current status of any Internet-Draft, please check the
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Distribution of this document is unlimited. Please send comments to
bmwg@harvard.edu or to the editors.


Abstract

This initial draft sets out to define a methodology designed
specifically for Ethernet switches.  Although the roots of these
devices are clearly to be found in bridging, switches have matured
enough in the last few years to deserve some special attention.  The
test methodology described here concentrates on four areas: throughput,
address handling, latency and behavior in abnormal conditions.  This
draft will attempt to make clear why switch specific tests are needed
in each of these four areas and will define a number of tests in each
area.  In addition to defining the tests this document also describes
specific formats for reporting the results of the tests.  Appendix A
lists the tests and conditions that we believe should be included for
specific cases and gives additional information about testing
practices.  Appendix B is a reference listing of maximum frame rates to
be used with specific frame sizes on Ethernet.

1.    Introduction
Vendors often engage in "specsmanship" in an attempt to give their
products a better position in the marketplace.  This often involves
"smoke & mirrors" to confuse the potential users of the products.
This document and follow up memos attempt to define a specific
set of tests that vendors can use to measure and report the
performance characteristics of their ethernet switch.  The results of
these tests will provide the user comparable data from different
vendors with which to evaluate these devices.

A previous document, "Benchmarking Terminology for Network
Interconnect Devices" (RFC 1242), defined many of the terms that
are used in this document.  The terminology document should be
consulted before attempting to make use of this document.

2.    Real world
Please refer to the draft on "Benchmarking Methodology for
Network Interconnect Devices".

3.    Tests to be run
Please refer to the draft on "Benchmarking Methodology for
Network Interconnect Devices".

4.    Evaluating the results
Please refer to the draft on "Benchmarking Methodology for
Network Interconnect Devices".

5.     Requirements
In this document, the words that are used to define the significance
of each particular requirement are capitalized. These words are:

    * "MUST"
    This word or the adjective "REQUIRED" means that the
item is an absolute requirement of the specification.

    * "SHOULD"
    This word or the adjective "RECOMMENDED" means that there may
exist valid reasons in particular circumstances to ignore this item,
but the full implications should be understood and the case carefully
weighed before choosing a different course.

    * "MAY"
    This word or the adjective "OPTIONAL" means that this item is
truly optional.  One vendor may choose to include the item because a
particular marketplace requires it or because it enhances the product,
for example; another vendor may omit the same item.

An implementation is not compliant if it fails to satisfy one or more
of the MUST requirements for the test it implements.  An implementation
that satisfies all the MUST and all the SHOULD requirements for the
test is said to be "unconditionally compliant"; one that satisfies all
the MUST requirements but not all the SHOULD requirements for the test
is said to be "conditionally compliant".

6.    Device set up
The device MUST be in a stable state (i.e.: the device SHOULD have
completed its initialization process) prior to the start of any tests.
Before starting to perform the tests, the device to be tested MUST be
configured following the instructions provided to the user.
Specifically, it is expected that all of the supported features will be
configured and enabled during this set up (See Appendix A).  It is
expected that all of the tests will be run without changing the
configuration or setup of the device in any way other than that
required to do the specific test.  For example, it is not acceptable to
change the size of frame handling buffers between tests of frame
handling rates when testing the throughput of the device.  It is
necessary to modify the configuration when starting a test to determine
the effect of filters on throughput, but the only change MUST be to
enable the specific filter. The device set up SHOULD include the
normally recommended configuration.  The specific version of the
software and the exact device configuration, including what device
functions are disabled, used during the tests SHOULD be included as
part of the report of the results.

7.    Frame sizes
All of the described tests SHOULD be performed at a number of frame
sizes.  Specifically, the sizes SHOULD include the maximum and minimum
legitimate sizes for Ethernet and enough sizes in between to be able to
get a full characterization of the device performance.

In most cases it makes more sense to test the device with the minimum
frame size for the media since this would stress the device to its
limits and help characterize the per-frame processing overhead of the
device.  However, the latency of the device under test MUST be
evaluated using a range of different frame sizes as highlighted in
section 7.1.


7.1    Frame sizes to be used on Ethernet
64, 128, 256, 512, 1024, 1280, 1518

These sizes include the maximum and minimum frame sizes permitted by
the Ethernet standard and a selection of sizes between these extremes
with a finer granularity for the smaller frame sizes and higher frame
rates.

8. Modifiers
It might be useful to know the device performance under a number of
conditions; some of these conditions are noted below.   It is expected
that the reported results will include as many of these conditions as
the test equipment is able to generate.  The suite of tests SHOULD be
first run without any modifying conditions and then repeated under each
of the conditions separately.  To preserve the ability to compare the
results of these tests it is necessary to let the device know of the
various addresses configured on all of its ports.  A phenomenon know as
the "Learning Process" is required for this purpose.  This process MUST
send any frames that are required to generate all the addresses to be
used in the test, thus not requiring the device to learn addresses
every time the first instance of the test is run.  All of the addresses
SHOULD resolve to the same "next-hop" and it is expected that this will
be the address of the receiving side of the test equipment. This
learning process will have to be repeated at the beginning of each
test.

8.1    Broadcast frames
Please refer to the draft on "Benchmarking Methodology for Network
Interconnect Devices".

9.    Multidirectional traffic
Normal network activity is not all in a single direction.  To test the
multidirectional performance of a device, the test series SHOULD be
run with the same data rate being offered from all the directions. The
sum of the data rates should not exceed the theoretical limit for
Ethernet.

10.    Single stream path
The full suite of tests SHOULD be run along with whatever modifier
conditions that are relevant using a single input and output network
port on the device.  If the internal design of the device has multiple
distinct pathways, for example, multiple interface cards each with
multiple network ports, then it is not necessary that all possible
types of pathways SHOULD be tested separately since these tests test
the basic switching fabric of the device and is not geared towards
testing the internal hardware neither is it geared towards testing if
the interface card is properly in place in the device.

11.    Multiple frame sizes
This document does not address the issue of testing the effects of a
mixed frame size environment other than to suggest that if such tests
are wanted then frames SHOULD be distributed between all of the listed
sizes for Ethernet.  The distribution MAY approximate the conditions on
the network in which the device would be used.

12.    Maximum frame rate
The maximum frame rate that should be used when testing LAN
connections SHOULD be the listed theoretical maximum rate for the frame
size on Ethernet.  A list of maximum frame rates for LAN connections is
included in Appendix B.

13.    Bursty traffic
It is convenient to measure the device performance under steady state
load but this is an unrealistic way to gage the functioning of a device
since actual network traffic normally consists of bursts of frames.
Some of the tests described below SHOULD be performed with both steady
state traffic and with traffic consisting of repeated bursts of frames.
The frames within a burst are transmitted with the minimum legitimate
inter-frame gap.

14.    Trial description
A particular test consists of multiple trials.  Each trial returns one
piece of information, for example the loss rate at a particular input
frame rate.  Each trial consists of a number of phases:

    a)  Send the "learning frames" to the switch port and wait 2
seconds to be sure that the learning has settled. The formats of the
learning frame that should be used are shown in the Test Frame Formats
document.

    b) Run the test trial.

    c) Wait for two sec for any residual frames to be received.

    d) Wait for at least five seconds for the device to restabilize.

15.    Trial duration
The aim of these tests is to determine the rate continuously
supportable by the device.  The actual duration of the test trials must
be a compromise between this aim and the duration of the benchmarking
test suite.  The duration of the test portion of each trial SHOULD be
at least 10 seconds.

16.    Benchmarking tests:
Note: The notation "type of data stream" refers to the above
modifications to a frame stream with a constant inter-frame gap, for
example, the addition of traffic filters to the configuration of the
device under test.

16.1    Switch Throughput Test

Objective:
To determine the throughput of the switching device under test.

Typically Ethernet switches are equipped with a large number of
10 Mbit/s  ports.   Smaller devices often have 8 or 12 ports while
larger devices  equipped with special internal buses are equipped with
over a hundred  dedicated 10 Mbit/s ports.   Such switching devices are
built to forward  Ethernet frames from their source to their
destination addresses by  establishing a connection between appropriate
incoming and outgoing ports of the switching device.  Since the source
and destination ports through which traffic is forwarded are not
predictable, it seems most appropriate to test the throughput of
Ethernet switching devices by creating multiple streams of  traffic
with all of the ports on the device both sending and receiving  frames
at the same time.   It also seems appropriate to call this kind of
throughput as switching throughput.  Closer examination of the types of
multiple streams of traffic that might be created to test the switching
throughput of a device makes it obvious that choices have to be made in
order to make the testing process as efficient and pertinent as
possible.  These choices pertain to:

a) the pattern of traffic to be created between the ports under test,
b) the load of the test traffic,
c) the inter-frame gap and the interval between bursts of the test
   traffic,
d) the frame sizes used for the test traffic and
e) the address learning process.

We will now look at each of these in turn.


a) The pattern of traffic to be created between the switching ports
under test.

Almost all Ethernet switching devices can assign a large number of
MAC  addresses to each one of their ports.  Test frames can therefore
contain a  large number of source addresses and destination addresses.
This makes the number of connections that a switch can be required to
set up during a test very large.   A switch with just six ports and
eight MAC addresses assigned to each would have to establish 1,920
(5x8x8x6) separate connections in order to forward frames
between all of the source and destination addresses.   It is necessary
to keep in mind that the order in which individual connections between
source and destination addresses need to be set up by  the device under
test will have a direct effect on the way in which the load of the test
traffic is distributed over a devices ports.  Consequently, in order to
keep tight control over the distribution of the load presented to the
ports under test it is desirable to create a pattern of
multi-directional traffic which makes it possible to guarantee the
exact  loads that will result from traffic being generated in a
multi-directional traffic pattern.

Summary:
It is desirable to create a multi-directional traffic pattern to test
the throughput of Ethernet switching devices to ensure that the device
under test creates switched connections on a frame-by-frame basis
between all of the learned source and destination addresses on all of
the tested ports.  The multi-directional pattern of traffic has to be
designed so that traffic switched in and out of the ports under test
equals whatever target load is set.

Procedure:
The multi-directional traffic pattern can be achieved on a
frame-by-frame basis simply as follows:

The first frame sent to port 1 from the test  instrument SHOULD carry a
destination address assigned to port 2. The second frame sent to port 1
SHOULD carry a destination address assigned to port 3 and so on until
the highest port number is reached.  This pattern will then be repeated
until the end of the test.  Traffic will be sent to all of the  ports
under test in similar fashion. In this way all of the ports are both
sending and receiving frames for the duration of the test.  The same
number of MAC addresses SHOULD be learned by each port for any one
test.  Naturally each port SHOULD learn a different set of such
addresses.   If  the device allows and the test concentrates on
switching throughput and not address handling then eight MAC addresses
per port appears to be a good  number to work with.  If eight addresses
are listed as belonging to a given port then the MAC addresses assigned
to frames sent to that port can be  picked randomly from the list for
the duration of the test.  The same can  hold for the destination
addresses that belong to each of the ports under test.  The frames
generated for the switching throughput test repeatatively rotate
through the source and destination ports in an ascending order but the
source and destination addresses behind each port can be chosen
randomly.  For example, the first frame will be sent to port 1 and
forwarded to port 2.  It will carry any one of the source addresses
assigned to port  1 in its source address field and any one of the
destination addresses assigned to port 2 in its destination field.

b) The load of the test traffic.

Ethernet is a half-duplex technology.  Consequently the maximum load of
10  Mbit/s that a port can handle includes both the frames transmitted
and the frames received by that port.  Since the multi-directional
pattern of traffic described above requires ports to send and receive
frames at the same time, the only way to fully load all ports is to
send exactly half the maximum  number of frames per second that a port
can legally handle to each of the  ports under test.  The load on each
port is to be calculated in frames per  second.  The maximum number of
frames per second that a 10 Mbit/s port can  handle is a function of
frame length (see Appendix B).  For the multi-directional traffic
pattern if the frame size is 64 bytes, the minimum legal length for
Ethernet frames, then the total number of frames transmitted by any one
port MUST not exceed 14880/2 frames.  Because each port transmits in a
round-robin fashion to all of the other ports the maximum number of
frames received by any port will be (14880/2/number of ports) x the
number of ports or 7440 frames.  At maximum load therefore each port
under test will see 7440 64-byte frames in and 7440 64-byte frames
out.  For loads inferior to 100% the same formula applies and
guarantees that the load is evenly distributed over all of the ports
under test.  For example to achieve a 80% load on all switching ports
under test the test instrument MUST send 40% of the maximum legal load
for the frame length used for the test to each of the ports.  The
switch test SHOULD be run at different loads.  Experience shows that
loads of 70%, 80%, 90% and 100% provide significant results.


Overload Condition

Loads exceeding 100% can readily be created by this testing methodology
since at the full line rate on short frames for example, a port is said
to be loaded at 100% when it is transmitting at 50% of the line rate or
7440  frames per second and receiving at 50% of the line rate.   Since
ports can  transmit at more than 50% of the full line rate, it is
relatively easy to  create loads well in excess of the Ethernet legal
limit.  It is important to build such overloads into the test
methodology since they can occur on switched Ethernet networks when
many ports send frames to a single receiving port at high rates.

Overloads SHOULD be part of the test methodology since they allow the
tester to discover if the device under test implements some sort of
back-pressure mechanism and also allows the tester to appreciate the
size and efficiency of the buffers of device under test.

Overloads where the ports under test are required to process frames
in  excess of the legal maximum defined for each frame length of 10%,
20% and 30% provide significant results.

c) The inter-frame gap and the interval between bursts of the test
traffic.

Experience demonstrates that real LAN traffic is often bursty in nature
that is frames are mostly transmitted in dense packs with pauses
occurring between successive packs.  This makes it particularly
desirable to construct a test pattern with bursty traffic where the
number of frames in each burst and the time between bursts can be
treated as variables.  It SHOULD be noted that because ports both send
and receive frames during  the switching throughput test the test
instrument cannot send sustained  bursts of frames with minimum
inter-frame gap that last the entire duration of the test as would be
the case if the traffic was uni-directional and  frames were sent from
ports whose only job it is to transmit frames to ports whose only job
it is to receive frames.

Procedure:
Traffic sent to ports SHOULD send frames in bursts such that the
inter-frame gap between frames within a burst is set to the legal
minimum of 9.6  microseconds and the interval between bursts is set
according to the target load.  This test methodology makes frequent
reference to the interval between bursts which will from here on in be
called the inter-burst gap or IBG.

We will assume that bursts contain frames of a single length and that
the number of frames per burst is constant for any one test.  IBG is a
function of the line speed, which for Ethernet is 10 Mbit/s, the
length of the frames in the bursts, the number of frames in the bursts,
the length of the preamble and the inter-frame gap.  If the target load
is known the IBG can be calculated as follows:


mmax (mediamaximum)
= maximum number of bits per second supported by the media which for
Ethernet is 10 000 000 bits per second.  The media transmits one bit
every 1 / 10 000 000 seconds.  We will call this one bit time.


ifg (inter-frame gap)
= 96 bits for frames within a burst or 9.6 microseconds or 96 bit times.

pre (preamble)
= 64 bits or the time required to transmit a 64 bit Ethernet preamble
on the media which equals 6.4 microseconds or 64 bit times.

frt (frame time)
= the time required to transmit one Ethernet frame of a given length on
the media.  A 64-byte frame is made up of 64 x 8 bytes or 512 bits and
therefore requires 51.2 microseconds or 512 bit times to be transmitted
on the 10 000 000 bit per second Ethernet media.

For simplicity let FRT = pre + ifg + frt expressed in bit times.

mfr (maximum frame rate)
= maximum number of frames per second supported by the media which is
a  function of mmax and FRT: mfr = mmax / FRT. mfr is expressed in
seconds.

tload (target load)
= the target load expressed as a percentage of the maximum number of
frames the media can handle for a given frame length.

For simplicity let mfr x tload/2 be designated as the sendrate, that
is the number of frames per second that the test instrument SHOULD send
to each one of the ports under test.

bsize (burst size)
= the number of frames contained in a single burst

Using this notation and knowing what the target load is we can
calculate the inter-burst gap as:

IBG = (1 - (sendrate x FRT ))  /  ((sendrate / bsize)  - 1)

Here are two examples to illustrate.

Example 1.
To calculate the IBG required to generate a target load of 100% on all
ports using 64-byte frames with 20 frames per burst we have:
mmax = 10 000 000

tload = 100%.

We know that:
ifg = 96 bit times
pre = 64 bit times
frt = 512 bit times
which add up to an FRT of 672 bit times.  Substituting these values
into mfr = mmax / FRT we get 10 000 000 / 672 = 14 880 so that the
sendrate of mfr x tload/2 = 14 880 x 100%/2 = 7440.
Furthermore, 7440 x FRT = 5 000 000 bit times or 0.5 seconds.


Since each burst contains 20 frames and 7440 frames per second are sent
to each port the number of bursts per second will equal 7440 / 20 = 372
bursts and the number of intervals between bursts will be equal the
number of  bursts minus one or 371.

So we have:
IBG =  (1 - 0.5) /( 372 - 1)  =  0.5 / 371  =  0.0013477 seconds or
1.3477 milliseconds.  Checking we find that 372 bursts of 20 frame
transmissions taking 67.2 microseconds each add up to 0.5 seconds while
371 inter-burst gaps of 1.3477 milliseconds account for the remaining
0.5 seconds.

Example 2.
To calculate the IBG for a target load of 80% with 512-byte frames we
first find the sendrate = 940 and the FRT = 4256 bit times.
Then IBG = (1s - (940 x 425.6)) / ((940/128) - 1)  =  94.58
milliseconds.  Checking we have 940 frames transmitted with a
transmission time of 425.6 equal to 0.4 seconds and 6.34375 inter-burst
gaps of 94.58 milliseconds  equal to 0.06 seconds.

The examples above show that not all combinations of frame size, burst
size and load make a perfect fit because they fill each second of
transmission time with fractions of the desired IBG.  Given frame size
and desired load it is however possible to calculate the characteristic
values of the burst sizes which allow a perfect fit.  The
characteristic values for burst sizes less than 1000 which allow a
perfect fit of the calculated IBG into every second of transmission
time for 64-byte frames and for loads of 50% to 130% by 10% steps are:
1, 2, 3, 4, 5, 6, 8,12, 24,31, 62, 93, 124, 186, 248, 372, 744, 930.

Recommendations:
The size of the bursts SHOULD range from a small number of frames, 10,
to a large number of frames, 500, or more. The perfect fit values for
burst size are:
1, 2, 3, 4, 5, 6, 8,12, 24,31, 62, 93, 124, 186, 248, 372, 744, 930
frames.  Experience tends to show that tests run along the lines of
the above description do not require a large number of ports on a
device to be put to test.  The reason for this is that the switch
specific test tends to power out the buffering schemes and
transmission and receive engines of the devices under test long before
putting any strain of the internal high speed buses that are built into
this family of devices.  The pattern of traffic created in the switch
test obviously results in a large number of collisions being produced
during the test since ports are sending and receiving frames in all
directions simultaneously.  It is absolutely necessary to use a test
generator which implements the Ethernet back-off algorithm.  Even so as
ports contend for access to the media they will be forced to buffer
frames which could not be transmitted because of collisions.  This puts
the buffering mechanisms of the devices under test to work in the same
way they would on real networks although the test methodology described
here allows the tester to create full line loads and lengthy bursts
which would only occur on a real network in extreme instances.

A note on the the back-off algorithm:
We have already pointed out the necessity for the test instrument
sending traffic to the ports of switching devices under test to
implement the Ethernet back-off algorithm.  It SHOULD ne noted in
addition that this algorithm uses the formula 2(**n) -1 where n ranges
from 1 to 10 to calculate the number of 51.2 periods the transmitter
SHOULD hold off before attempting a retransmission.  It would appear
some that Ethernet controllers limit the range of n to values
less than 10.  This results in a more aggressive back-off algorithm
and has a direct consequence on the number of collision battles a
device will win.  It is therefore desirable to ascertain the relative
aggressivity of the test instruments and of the devices under test when
performing the multi-directional traffic test since many collisions
occur during this kind of test.

d) The frame sizes used for the test traffic SHOULD conform to the
frame sizes defined in RFC 1242.

e) The address learning process SHOULD conform to the process described
in RFC 1242.

Reporting format:
Since the test devices and the devices under test MAY implement
different back-off algorithms, it is impossible to determine how many
frames will actually be sent to the ports of the device under test in
advance.  This makes it necessary to count the number of frames
actually sent to each of  the ports under test.  This count MUST NOT
include the number of collisions that occurred during the test.  The
number of frames received by each of the ports MUST also be counted.
Using these two counts it becomes possible to  determine the total
percentage of frames transmitted without loss as follows:

100 - ((total frames sent to all ports - total frames received on all
        ports) x 100) /
        total frames sent to all ports.

Values calculated in this way can be reported in a table with lines
representing different loads and rows representing different burst
sizes:

burst sizes
20 40 128 256 500

loads
70%
80%
90%
100%
110%
120%
130%

16.2    Behavior Test

Objective:
To determine the behavior of the switching device under abnormal frame
conditions.

Summary:
It is imperative to determine how an Ethernet switch would behave when
it encounters frames which are defined to be illegal according to the
Ethernet specifications.  Such frames could be:

    Runts
    Jabbers
    Bad FCS

As a special case, it MAY be worthwhile to determine how the switch
behaves when it has to handle broadcasts as well as various sized Bad
FCS frames.

Procedure:
Any one port on the switch MAY be chosen as the transmitter of such
illegal frames and any other port MAY be selected as the receiver.
Traffic containing these illegal frames MUST be sent from the
transmitter and the traffic received by the receiver MUST be noted.  If
the receiver receives over 90% the illegal frames, we can qualify the
switch to be forwarding the illegal frames otherwise the switch MAY be
deemed as blocking or filtering the illegal frames.

Reporting Format:
The results generated would be whether the switch is forwarding these
illegal frames or filtering them.

16.3    Latency tests

Objective:
To measure the time it takes a frame to go through a switching device.

Summary:
A large proportion of switching devices do not store frames sent to
them before retransmiiting them onto the media.  This significantly
reduces the amount of time frames take to go through the device under
test and makes it desirable to have a test procedure which makes it
easy to recognize whether a switch stores frames before forwarding
them onto the media or not.  This is also important since devices
which store frames will have significantly greater latencies as frame
lengths increase than devices which do not.  Since there is no standard
way for switches to process broadcast frames it is also very desirable
to measure latency on broadcast frames.

Procedure:
The measurement of latency requires test instruments to place a
time-stamp on the frames sent to the device under test.  The time stamp
or tag must be placed at the head of a frame when the frame is sent to
a port of the switching device under test.  The test instrument must
also be able to record the time at which the head of the frame
containing the time tag is received inbound on the test instrument once
it has been retransmitted by the device under test back to the test
instrument.  Latency is calculated by subtracting this recorded receive
time from the recorded send time on the time tag.  This simple delta
is used to express the latency of the device under test.  Latency
should be measured for unicast frames of standard test lengths, for
broadcast frames and should be measured with different external loads
applied to the device under test.

Reporting format:
The latency measurements are to be reported in microseconds in a table.

16.4    Address handling test

Objective:
To determine how many addresses can be assigned to the ports of an
Ethernet switching device.

Summary:
It is necessary to verify how many MAC addresses can be assigned to
each port of a switching device before the device begins to drop
frames.

Procedure:
The test must be set up to isolate the address handling capacity of
the devices under test from their switching performance.  In order to
achieve this a simple uni-directional pattern of traffic with parallel
streams of traffic is created.  Half of the ports under test transmit
frames to the other half of the ports which receive them.  The test
procedure is in two steps.  In step 1 a small number of addresses is
assigned to each port and in step 2 a stream of frames is sent
back-to-back to the sending ports of the test and the number of frames
received on the receiving ports counted.  Steps 1 and 2 should be
repeated until the receive count indicates that the device has dropped
frames.

Reporting format:
The number of addresses assigned to each port in the step before the
first frames were dropped in step 2 of the test is to be presented as
the number of addresses the switching device under test supports.

17.    Editor's Addresses

Bob Mandeville
ENL Labs                            Phone: +33 1 4761 3057
ENL                                 Fax:   +33 1 4278 3671
Paris, France                       Email: bob.mandeville@eunet.fr

Ajay V. Shah
Wandel & Goltermann, Inc            Phone: +1 919 941 5740
P. O. Box 13585                     Fax:   +1 919 941 5751
Research Triangle Park, NC 27709    Email: shah@wg.com
                                    Compuserve: 102755,712


Appendix A: Testing Considerations

A.1    Scope Of This Appendix
This appendix discusses certain issues in the ethernet switch testing
methodology where experience or judgment may play a role in the tests
selected to be run or in the approach to constructing the test with a
particular device.  As such, this appendix MUST not be read as an
amendment to the methodology described in the body of this document but
as a guide to testing practice.


1.    Typical testing practice has been to wait till the device under
test stabilizes after "boot-up", otherwise the switch may be generating
frames like routing updates etc which may interfere with the test
frames.  It is also necessary to turn off the SNMP feature (if the
switch has one) to make sure that the management frames don't interfere
with the test frames.

2.    The device under test MUST be configured before starting any test
and the configuration MUST remain the same through out the testing
phase.

3.    Architectural considerations may need to be considered.  For
example, first perform the tests with the stream going between ports
on the same interface card and the repeat the tests with the stream
going into a port on one interface card and out of a port on a second
interface card. There will almost always be a best case and worst case
configuration for a given device under test architecture.

4.    Testing done using traffic streams consisting of the smallest
allowable frame size for the media has shown to be the most stressful
on the devices under test.


Appendix B: Maximum frame rates reference

Ethernet Size    Ethernet
    (bytes)        (pps)

    64       14880
    128       8445
    256       4528
    512       2349
    768       1586
    1024       1197
    1280       961
    1518       812

Ethernet size
    Preamble   64 bits
    Frame      8 x N bits
    Gap        96 bits


Benchmarking Methodology Working Group
Internet Draft - December 1995

Bob Mandeville
ENL
Ajay V. Shah
Wandel & Goltermann Technologies, Inc

B. Mandeville, A. V. Shah        [Page 13]

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