IMIX Genome: Specification of variable packet
sizes for additional testing
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Benchmarking Methodologies have always relied on test conditions with
constant packet sizes, with the goal of understanding what network
device capability has been tested. Tests with constant packet size
reveal device capabilities but differ significantly from the conditions
encountered in operational deployment, and so additional tests are
sometimes conducted with a mixture of packet sizes, or "IMIX". The
mixture of sizes a networking device will encounter is highly variable
and depends on many factors. An IMIX suited for one networking device
and deployment will not be appropriate for another. However, the mix of
sizes may be known and the tester may be asked to augment the fixed size
tests. To address this need, and the perpetual goal of specifying
repeatable test conditions, this draft defines a way to specify the
exact repeating sequence of packet sizes from the usual set of fixed
sizes, and other forms of mixed size specification.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
This memo defines a method to unambiguously specify the sequence of
packet sizes used in a load test.
Benchmarking Methodologies have always
relied on test conditions with constant packet sizes, with the goal of
understanding what network device capability has been tested. Tests with
the smallest size stress the header processing capacity, and tests with
the largest size stress the overall bit processing capacity. Tests with
sizes in-between may determine the transition between these two
capacities.
Streams of constant packet size differ significantly from the
conditions encountered in operational deployment, and so additional
tests are sometimes conducted with a mixture of packet sizes. The set of
sizes used is often called an Internet Mix, or "IMIX" , , .
The mixture of sizes a networking device will encounter is highly
variable and depends on many factors. An IMIX suited for one networking
device and deployment will not be appropriate for another. However, the
mix of sizes may be known and the tester may be asked to augment the
fixed size tests. The references above cite the original studies and
their methodologies - similar methods can be used to determine new size
mixes.
To address this need, and the perpetual goal of specifying repeatable
test conditions, this draft proposes a way to specify the exact
repeating sequence of packet sizes from the usual set of fixed sizes:
the IMIX Genome. Other, less exact forms of size specification are also
recommended for extremely complicated or customized size mixes.
This memo takes the position that it cannot be proven for all
circumstances that the sequence of packet sizes does not affect the test
result, thus a standardized specification of sequence is valuable.
This memo defines a method to unambiguously specify the sequence of
packet sizes that have been used in a load test, assuming that a
relevant mix of sizes is known to the tester and the length of the
repeating sequence is not very long (<100 packets).
The IMIX Genome will allow an exact sequence of packet sizes to be
communicated as a single-line name, resolving the current ambiguity with
results that simply refer to "IMIX".
While documentation of the exact sequence is ideal, the memo also
covers the case where the sequence of sizes is very long or may be
generated by a pseudo-random process.
It is a colossal non-goal to standardize one or more versions of the
IMIX. This topic has been discussed on many occasions on the
bmwg-list. The goal is to enable
customization with minimal constraints while fostering repeatable
testing once the fixed size testing is complete.
The IMIX Genome is specified in the following format:
IMIX - 123456...x
where each number is replaced by the letter corresponding to the size
of the packet at that position in the sequence. The following table
gives the letter encoding for the
standard sizes (64, 128, 256, 512, 1024, 1280, and 1518 bytes) and
"jumbo" sizes (2112, 9000, 16000). Note that the 4 octet Ethernet frame
check sequence may fail to detect bit errors in the larger jumbo frames,
see .
Size, bytes
Genome Code Letter
64
a
128
b
256
c
512
d
1024
e
1280
f
1518
g
2112
h
9000
i
16000
j
MTU
z
For example: a five packet sequence with sizes 64,64,64,1280,1518
would be designated:
IMIX - aaafg
While this approach allows some flexibility, there are also
constraints.
Non-RFC2544 packet sizes would need to be approximated by those
available in the table.
The Genome for very long sequences can become undecipherable by
humans.
z=MTU is seen as valuable, so MTU MUST be specified if used.
Whether more tabulated packet sizes would be useful is TBD, and
"jumbo" sizes were added in this version.
Some questions testers must ask and answer when using the IMIX
Genome are:
Multiple Source-Destination Address Pairs: is the IMIX sequence
applicable to each pair, across multiple pairs in sets, or across
all pairs?
Multiple Tester Ports: is the IMIX sequence applicable to each
port, across multiple ports in sets, or across all ports?
The chosen configuration would be expressed the following
general form:
Source Address/Port/Blade
Destination Address/Port/Blade
Corresponding IMIX
x.x.x.x Blade2
y.y.y.y Blade3
IMIX - aaafg
where testers can specify the IMIX used between any two entities in
the test architecture.
The Custom IMIX is specified in the following format:
CUSTOM IMIX - 123456...x
where each number is replaced by the letter corresponding to the size
of the packet at that position in the sequence. The tester MUST complete
the following table, giving the letter encoding for each size used,
where each set of three lower-case letters would be replaced by the
integer size in octets.
Size, bytes
Custom Code Letter
aaa
A
bbb
B
ccc
C
ddd
D
eee
E
fff
F
ggg
G
etc.
up to Z
For example: a five packet sequence with sizes aaa,aaa,aaa,ggg,ggg
would be designated:
CUSTOM IMIX - AAAGG
When the IMIX-Genome cannot be used (when the sheer length of the
sequence would make the genome unmanageable), two options are possible.
When a sequence can be decomposed into a series of short repeating
sequences, then a run-length encoding approach MAY be used as shown
below:
Count of Repeating Sequences
Packet Size Sequence
20
abcd
5
ggga
10
dcba
When the sequence is designed to vary within some proportional
constraints, a table simply giving the proportions of each size MAY be
used instead.
IP Length
Percentage of Total
Other Length(s)
64
23
82
128
67
146
1000
10
1018
Note that the table of proportions also allows non-standard packet
sizes, but trades the short genome specification and ability to specify
the exact sequence for other flexibilities.
Benchmarking activities as described in this memo are limited to
technology characterization using controlled stimuli in a laboratory
environment, with dedicated address space and the other constraints
.
The benchmarking network topology will be an independent test setup
and MUST NOT be connected to devices that may forward the test traffic
into a production network, or misroute traffic to the test management
network.
Further, benchmarking is performed on a "black-box" basis, relying
solely on measurements observable external to the DUT/SUT.
Special capabilities SHOULD NOT exist in the DUT/SUT specifically for
benchmarking purposes. Any implications for network security arising
from the DUT/SUT SHOULD be identical in the lab and in production
networks.
This memo makes no requests of IANA, and hopes that IANA will leave
it alone as well.
Thanks to Sarah Banks, Aamer Akhter, and Steve Maxwell for their
review and comments. Ilya Varlashkin suggested the run-length coding
approach in Section 5.
Test Methodology Journal: IMIX (Internet Mix) Journal
http://gospirent.com/whitepaper/IMIX%20Test%20Methodolgy%20Journal.pdf
Library: Test Plans
http://www.ixiacom.com/library/test_plans/display?skey=testing_pppox
The Journal of Internet Test Methodologies
http://www.ixiacom.com/pdfs/test_plans/agilent_journal_of_internet_test_methodologies.pdf
Discussion on IMIX
http://www.ietf.org/mail-archive/web/bmwg/current/msg00691.html
Discussion of Jumbo Packets and FCS Failure, see
http://sd.wareonearth.com/~phil/jumbo.html and
http://staff.psc.edu/mathis/MTU/arguments.html#crc
http://www.ietf.org/mail-archive/web/bmwg/current/msg00691.html