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Internet Engineering Task Force                               L. Avramov
INTERNET-DRAFT, Intended status: Informational                    Google
Expires: December 17,2017                                        J. Rapp
June 15, 2017                                                     VMware




                  Data Center Benchmarking Terminology
                 draft-ietf-bmwg-dcbench-terminology-13

Abstract

The purpose of this informational document is to establish definitions
and describe measurement techniques for data center benchmarking, as
well as it is to introduce new terminologies applicable to data center
performance evaluations. The purpose of this document is not to define
the test methodology, but rather establish the important concepts for
benchmarking network switches and routers in the data center. Many of
these terms and methods may be applicable beyond this publication's
scope as the technologies originally applied in the data center are
deployed elsewhere.

Status of this Memo

This Internet-Draft is submitted in full conformance with the provisions
of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF). Note that other groups may also distribute working
documents as Internet-Drafts. The list of current Internet-Drafts is at
http://datatracker.ietf.org/drafts/current.

Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."



Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document
authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal Provisions
Relating to IETF Documents (http://trustee.ietf.org/license-info) in
effect on the date of publication of this document.  Please review these



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documents carefully, as they describe your rights and restrictions with
respect to this document.  Code Components extracted from this document
must include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
     1.2. Definition format . . . . . . . . . . . . . . . . . . . . .  4
   2.  Latency  . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1. Definition  . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . .  6
     2.3 Measurement Units  . . . . . . . . . . . . . . . . . . . . .  6
   3 Jitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . .  6
     3.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . .  7
     3.3 Measurement Units  . . . . . . . . . . . . . . . . . . . . .  7
   4 Physical Layer Calibration . . . . . . . . . . . . . . . . . . .  7
     4.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . .  7
     4.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.3 Measurement Units  . . . . . . . . . . . . . . . . . . . . .  8
   5 Line rate  . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.3 Measurement Units  . . . . . . . . . . . . . . . . . . . . . 10
   6  Buffering . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.1 Buffer . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
       6.1.1 Definition . . . . . . . . . . . . . . . . . . . . . . . 11
       6.1.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . 12
       6.1.3 Measurement Units  . . . . . . . . . . . . . . . . . . . 12
     6.2 Incast . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
       6.2.1 Definition . . . . . . . . . . . . . . . . . . . . . . . 13
       6.2.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . 14
       6.2.3 Measurement Units  . . . . . . . . . . . . . . . . . . . 14
   7 Application Throughput: Data Center Goodput  . . . . . . . . . . 14
     7.1. Definition  . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.2. Discussion  . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.3. Measurement Units . . . . . . . . . . . . . . . . . . . . . 14
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   9.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   10.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1.  Normative References  . . . . . . . . . . . . . . . . . . 16
     10.2.  Informative References  . . . . . . . . . . . . . . . . . 16
     10.3.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17



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1.  Introduction

   Traffic patterns in the data center are not uniform and are
   constantly changing. They are dictated by the nature and variety of
   applications utilized in the data center. It can be largely east-west
   traffic flows (server to server inside the data center) in one data
   center and north-south (outside of the data center to server) in
   another, while some may combine both. Traffic patterns can be bursty
   in nature and contain many-to-one, many-to-many, or one-to-many
   flows. Each flow may also be small and latency sensitive or large and
   throughput sensitive while containing a mix of UDP and TCP traffic.
   One or more of these may coexist in a single cluster and flow through
   a single network device simultaneously. Benchmarking of network
   devices have long used [RFC1242], [RFC2432], [RFC2544], [RFC2889] and
   [RFC3918]. These benchmarks have largely been focused around various
   latency attributes and max throughput of the Device Under Test being
   benchmarked. These standards are good at measuring theoretical max
   throughput, forwarding rates and latency under testing conditions,
   but they do not represent real traffic patterns that may affect these
   networking devices. The data center networking devices covered are
   switches and routers.


   The following document defines a set of definitions, metrics and
   terminologies including congestion scenarios, switch buffer analysis
   and redefines basic definitions in order to represent a wide mix of
   traffic conditions. The test methodologies are defined in [1].
























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1.1.  Requirements Language

   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 [RFC2119].


1.2. Definition format

   Term to be defined. (e.g., Latency)

   Definition: The specific definition for the term.

   Discussion: A brief discussion about the term, its application and
   any restrictions on measurement procedures.

   Measurement Units: Methodology for the measure and units used to
   report measurements of this term, if applicable.


2.  Latency


2.1. Definition

   Latency is a the amount of time it takes a frame to transit the DUT.
   Latency is measured in units of time (seconds, milliseconds,
   microseconds and so on). The purpose of measuring latency is to
   understand the impact of adding a device in the communication path.

   The Latency interval can be assessed between different combinations
   of events, regardless of the type of switching device (bit forwarding
   aka cut-through, or store-and-forward type of device). [RFC1242]
   defined Latency differently for each of these types of devices.

   Traditionally the latency measurement definitions are:

   FILO (First In Last Out)

   The time interval starting when the end of the first bit of the input
   frame reaches the input port and ending when the last bit of the
   output frame is seen on the output port.

   FIFO (First In First Out):

   The time interval starting when the end of the first bit of the input
   frame reaches the input port and ending when the start of the first
   bit of the output frame is seen on the output port. [RFC1242] Latency



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   for bit forwarding devices uses these events.

   LILO (Last In Last Out):

   The time interval starting when the last bit of the input frame
   reaches the input port and the last bit of the output frame is seen
   on the output port.

   LIFO (Last In First Out):

   The time interval starting when the last bit of the input frame
   reaches the input port and ending when the first bit of the output
   frame is seen on the output port. [RFC1242] Latency for bit
   forwarding devices uses these events.


   Another possibility to summarize the four different definitions above
   is to refer to the bit position as they normally occur: Input to
   output.

   FILO is FL (First bit Last bit). FIFO is FF (First bit First bit).
   LILO is LL (Last bit Last bit). LIFO is LF (Last bit First bit).

   This definition explained in this section in context of data center
   switching benchmarking is in lieu of the previous definition of
   Latency defined in RFC 1242, section 3.8 and is quoted here:

   For store and forward devices: The time interval starting when the
   last bit of the input frame reaches the input port and ending when
   the first bit of the output frame is seen on the output port.

   For bit forwarding devices: The time interval starting when the end
   of the first bit of the input frame reaches the input port and ending
   when the start of the first bit of the output frame is seen on the
   output port.

   To accommodate both types of network devices and hybrids of the two
   types that have emerged, switch Latency measurements made according
   to this document MUST be measured with the FILO events. FILO will
   include the latency of the switch and the latency of the frame as
   well as the serialization delay. It is a picture of the 'whole'
   latency going through the DUT. For applications which are latency
   sensitive and can function with initial bytes of the frame, FIFO (or
   RFC 1242 Latency for bit forwarding devices) MAY be used. In all
   cases, the event combination used in Latency measurement MUST be
   reported.





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2.2 Discussion

   As mentioned in section 2.1, FILO is the most important measuring
   definition.

   Not all DUTs are exclusively cut-through or store-and-forward. Data
   Center DUTs are frequently store-and-forward for smaller packet sizes
   and then adopting a cut-through behavior. The change of behavior
   happens at specific larger packet sizes. The value of the packet size
   for the behavior to change MAY be configurable depending on the DUT
   manufacturer. FILO covers all scenarios: Store-and-forward or cut-
   through.  The threshold of behavior change  does not matter for
   benchmarking since FILO covers both possible scenarios.

   LIFO mechanism can be used with store forward type of switches but
   not with cut-through type of switches, as it will provide negative
   latency values for larger packet sizes because LIFO removes the
   serialization delay. Therefore, this mechanism MUST NOT be used when
   comparing latencies of two different DUTs.

2.3 Measurement Units

   The measuring methods to use for benchmarking purposes are as
   follows:

   1) FILO MUST be used as a measuring method, as this will include the
   latency of the packet; and today the application commonly needs to
   read the whole packet to process the information and take an action.

   2) FIFO MAY be used for certain applications able to proceed the data
   as the first bits arrive (FPGA for example)

   3) LIFO MUST NOT be used, because it subtracts the latency of the
   packet; unlike all the other methods.


3 Jitter

3.1 Definition

   Jitter in the data center context is synonymous with the common term
   Delay variation. It is derived from multiple measurements of one-way
   delay, as described in RFC 3393. The mandatory definition of Delay
   Variation is the PDV form from section 4.2 of [RFC5481]. When
   considering a stream of packets, the delays of all packets are
   subtracted from the minimum delay over all packets in the stream.
   This facilitates assessment of the range of delay variation (Max -
   Min), or a high percentile of PDV (99th percentile, for robustness



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   against outliers).

   If First-bit to Last-bit timestamps are used for Delay measurement,
   then Delay Variation MUST be measured using packets or frames of the
   same size, since the definition of latency includes the serialization
   time for each packet. Otherwise if using First-bit to First-bit, the
   size restriction does not apply.

3.2 Discussion

   In addition to PDV Range and/or a high percentile of PDV, Inter-
   Packet Delay Variation (IPDV) as defined in section 4.1 of [RFC5481]
   (differences between two consecutive packets) MAY be used for the
   purpose of determining how packet spacing has changed during
   transfer, for example, to see if packet stream has become closely-
   spaced or "bursty". However, the Absolute Value of IPDV SHOULD NOT be
   used, as this collapses the "bursty" and "dispersed" sides of the
   IPDV distribution together.

3.3 Measurement Units

   The measurement of delay variation is expressed in units of seconds.
   A PDV histogram MAY be provided for the population of packets
   measured.


4 Physical Layer Calibration

4.1 Definition

   The calibration of the physical layer consists of defining and
   measuring the latency of the physical devices used to perform tests
   on the DUT.

   It includes the list of all physical layer components used as listed
   here after:

   -Type of device used to generate traffic / measure traffic

   -Type of line cards used on the traffic generator

   -Type of transceivers on traffic generator

   -Type of transceivers on DUT

   -Type of cables

   -Length of cables



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   -Software name, and version of traffic generator and DUT

   -List of enabled features on DUT MAY be provided and is recommended
   (especially the control plane protocols such as LLDP, Spanning-Tree
   etc.). A comprehensive configuration file MAY be provided to this
   effect.


4.2 Discussion

   Physical layer calibration is part of the end to end latency, which
   should be taken into acknowledgment while evaluating the DUT. Small
   variations of the physical components of the test may impact the
   latency being measured, therefore they MUST be described when
   presenting results.


4.3 Measurement Units

   It is RECOMMENDED to use all cables of: The same type, the same
   length, when possible using the same vendor. It is a MUST to document
   the cables specifications on section 4.1 along with the test results.
   The test report MUST specify if the cable latency has been removed
   from the test measures or not. The accuracy of the traffic generator
   measure MUST be provided (this is usually a value in the 20ns range
   for current test equipment).

5 Line rate

5.1 Definition

   The transmit timing, or maximum transmitted data rate is controlled
   by the "transmit clock" in the DUT.  The receive timing (maximum
   ingress data rate) is derived from the transmit clock of the
   connected interface.

   The line rate or physical layer frame rate is the maximum capacity to
   send frames of a specific size at the transmit clock frequency of the
   DUT.

   The term "nominal value of Line Rate" defines the maximum speed
   capability for the given port; for example 1GE, 10GE, 40GE, 100GE
   etc.

   The frequency ("clock rate") of the transmit clock in any two
   connected interfaces will never be precisely the same; therefore, a
   tolerance is needed. This will be expressed by Parts Per Million
   (PPM) value. The IEEE standards allow a specific +/- variance in the



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   transmit clock rate, and Ethernet is designed to allow for small,
   normal variations between the two clock rates. This results in a
   tolerance of the line rate value when traffic is generated from a
   testing equipment to a DUT.

   Line rate SHOULD be measured in frames per second.


5.2 Discussion

   For a transmit clock source, most Ethernet switches use "clock
   modules" (also called "oscillator modules") that are sealed,
   internally temperature-compensated, and very accurate. The output
   frequency of these modules is not adjustable because it is not
   necessary.  Many test sets, however, offer a software-controlled
   adjustment of the transmit clock rate. These adjustments SHOULD be
   used to compensate the test equipment in order to not send more than
   the line rate of the DUT.

   To allow for the minor variations typically found in the clock rate
   of commercially-available clock modules and other crystal-based
   oscillators, Ethernet standards specify the maximum transmit clock
   rate variation to be not more than +/- 100 PPM (parts per million)
   from a calculated center frequency. Therefore a DUT must be able to
   accept frames at a rate within +/- 100 PPM to comply with the
   standards.

   Very few clock circuits are precisely +/- 0.0 PPM because:

   1.The Ethernet standards allow a maximum of +/- 100 PPM (parts per
   million) variance over time. Therefore it is normal for the frequency
   of the oscillator circuits to experience variation over time and over
   a wide temperature range, among external factors.

   2.The crystals, or clock modules, usually have a specific  +/- PPM
   variance that is significantly better than +/- 100 PPM. Often times
   this is +/- 30 PPM or better in order to be considered a
   "certification instrument".

   When testing an Ethernet switch throughput at "line rate", any
   specific switch will have a clock rate variance. If a test set is
   running +1 PPM faster than a switch under test, and a sustained line
   rate test is performed,  a gradual increase in latency and eventually
   packet drops as buffers fill and overflow in the switch can be
   observed. Depending on how much clock variance there is between the
   two connected systems, the effect may be seen after the traffic
   stream has been running for a few hundred microseconds, a few
   milliseconds, or seconds. The same low latency and no-packet-loss can



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   be demonstrated by setting the test set link occupancy to slightly
   less than 100 percent link occupancy. Typically 99 percent link
   occupancy produces excellent low-latency and no packet loss. No
   Ethernet switch or router will have a transmit clock rate of exactly
   +/- 0.0 PPM. Very few (if any) test sets have a clock rate that is
   precisely +/- 0.0 PPM.

   Test set equipment manufacturers are well-aware of the standards, and
   allow a software-controlled +/- 100 PPM "offset" (clock-rate
   adjustment) to compensate for normal variations in the clock speed of
   DUTs. This offset adjustment allows engineers to determine the
   approximate speed the connected device is operating, and verify that
   it is within parameters allowed by standards.



5.3 Measurement Units

   "Line Rate" can be measured in terms of "Frame Rate":

   Frame Rate = Transmit-Clock-Frequency / (Frame-Length*8 + Minimum_Gap
   + Preamble + Start-Frame Delimiter)

   Minimum_Gap represents the inter frame gap. This formula "scales up"
   or "scales down" to represent 1 GB Ethernet, or 10 GB Ethernet and so
   on.

   Example for 1 GB Ethernet speed with 64-byte frames: Frame Rate =
   1,000,000,000 /(64*8 + 96 + 56 + 8) Frame Rate = 1,000,000,000 / 672
   Frame Rate = 1,488,095.2 frames per second.

   Considering the allowance of +/- 100 PPM, a switch may "legally"
   transmit traffic at a frame rate between 1,487,946.4 FPS and
   1,488,244 FPS.  Each 1 PPM variation in clock rate will translate to
   a 1.488 frame-per-second frame rate increase or decrease.

   In a production network, it is very unlikely to see precise line rate
   over a very brief period. There is no observable difference between
   dropping packets at 99% of line rate and 100% of line rate.

   Line rate can be measured at 100% of line rate with a -100PPM
   adjustment.

   Line rate SHOULD be measured at 99,98% with 0 PPM adjustment.

   The PPM adjustment SHOULD only be used for a line rate type of
   measurement.




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6  Buffering

6.1 Buffer

6.1.1 Definition

   Buffer Size: The term buffer size represents the total amount of
   frame buffering memory available on a DUT. This size is expressed in
   B (bytes); KB (kilobytes), MB (megabytes) or GB (gigabyte). When the
   buffer size is expressed it SHOULD be defined by a size metric stated
   above. When the buffer size is expressed, an indication of the frame
   MTU used for that measurement is also necessary as well as the cos
   (class of service) or dscp (differentiated services code point) value
   set; as often times the buffers are carved by quality of service
   implementation. Please refer to the buffer efficiency section for
   further details.

   Example: Buffer Size of DUT when sending 1518 bytes frames is 18 MB.

   Port Buffer Size: The port buffer size is the amount of buffer for a
   single ingress port, egress port or combination of ingress and egress
   buffering location for a single port. The reason for mentioning the
   three locations for the port buffer is because the DUT buffering
   scheme can be unknown or untested, and so knowing the buffer location
   helps clarify the buffer architecture and consequently the total
   buffer size. The Port Buffer Size is an informational value that MAY
   be provided from the DUT vendor. It is not a value that is tested by
   benchmarking. Benchmarking will be done using the Maximum Port Buffer
   Size or Maximum Buffer Size methodology.

   Maximum Port Buffer Size: In most cases, this is the same as the Port
   Buffer Size. In certain switch architecture called SoC (switch on
   chip), there is a port buffer and a shared buffer pool available for
   all ports. The Maximum Port Buffer Size , in terms of an SoC buffer,
   represents the sum of the port buffer and the maximum value of shared
   buffer allowed for this port, defined in terms of B (byte), KB
   (kilobyte), MB (megabyte), or GB (gigabyte). The Maximum Port Buffer
   Size needs to be expressed along with the frame MTU used for the
   measurement and the cos or dscp bit value set for the test.

   Example: A DUT has been measured to have 3KB of port buffer for 1518
   frame size packets and a total of 4.7 MB of maximum port buffer for
   1518 frame size packets and a cos of 0.

   Maximum DUT Buffer Size: This is the total size of Buffer a DUT can
   be measured to have. It is, most likely, different than than the
   Maximum Port Buffer Size. It can also be different from the sum of
   Maximum Port Buffer Size. The Maximum Buffer Size needs to be



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   expressed along with the frame MTU used for the measurement and along
   with the cos or dscp value set during the test.

   Example: A DUT has been measured to have 3KB of port buffer for 1518
   frame size packets and a total of 4.7 MB of maximum port buffer for
   1518 B frame size packets. The DUT has a Maximum Buffer Size of 18 MB
   at 1500 B and a cos of 0.

   Burst: The burst is a fixed number of packets sent over a percentage
   of linerate of a defined port speed. The amount of frames sent are
   evenly distributed across the interval, T. A constant, C, can be
   defined to provide the average time between two consecutive packets
   evenly spaced.

   Microburst: It is a burst. A microburst is when packet drops occur
   when there is not sustained or noticeable congestion upon a link or
   device. A characterization of microburst is when the Burst is not
   evenly distributed over T, and is less than the constant C [C=
   average time between two consecutive packets evenly spaced out].

   Intensity of Microburst: This is a percentage, representing the level
   of microburst between 1 and 100%. The higher the number the higher
   the microburst is. I=[1-[ (TP2-Tp1)+(Tp3-Tp2)+....(TpN-Tp(n-1) ] /
   Sum(packets)]]*100

   The above definitions are not meant to comment on the ideal sizing of
   a buffer, rather on how to measure it. A larger buffer is not
   necessarily better and can cause issues with buffer bloat.

6.1.2 Discussion

   When measuring buffering on a DUT, it is important to understand the
   behavior for each and all ports. This provides data for the total
   amount of buffering available on the switch. The terms of buffer
   efficiency here helps one understand the optimum packet size for the
   buffer, or the real volume of the buffer available for a specific
   packet size. This section does not discuss how to conduct the test
   methodology; instead, it explains the buffer definitions and what
   metrics should be provided for a comprehensive data center device
   buffering benchmarking.

6.1.3 Measurement Units

   When Buffer is measured:

   -The buffer size MUST be measured

   -The port buffer size MAY be provided for each port



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   -The maximum port buffer size MUST be measured

   -The maximum DUT buffer size MUST be measured

   -The intensity of microburst MAY be mentioned when a microburst test
   is performed

   -The cos or dscp value set during the test SHOULD be provided



6.2 Incast
6.2.1 Definition

   The term Incast, very commonly utilized in the data center, refers to
   the traffic pattern of many-to-one or many-to-many conversations. It
   measures the number of ingress and egress ports and the level of
   synchronization attributed, as defined in this section. Typically in
   the data center it would refer to many different ingress server ports
   (many), sending traffic to a common uplink (one), or multiple uplinks
   (many). This pattern is generalized for any network as many incoming
   ports sending traffic to one or few uplinks. It can also be found in
   many-to-many traffic patterns.

   Synchronous arrival time: When two, or more, frames of respective
   sizes L1 and L2 arrive at their respective one or multiple ingress
   ports, and there is an overlap of the arrival time for any of the
   bits on the Device Under Test (DUT), then the frames L1 and L2 have a
   synchronous arrival times. This is called incast.

   Asynchronous arrival time: Any condition not defined by synchronous
   arrival time.

   Percentage of synchronization: This defines the level of overlap
   [amount of bits] between the frames L1,L2..Ln.

   Example: Two 64 bytes frames, of length L1 and L2, arrive to ingress
   port 1 and port 2 of the DUT. There is an overlap of 6.4 bytes
   between the two where L1 and L2 were at the same time on the
   respective ingress ports. Therefore the percentage of synchronization
   is 10%.

   Stateful type traffic defines packets exchanged with a stateful
   protocol such as TCP.

   Stateless type traffic defines packets exchanged with a stateless
   protocol such as UDP.




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6.2.2 Discussion


   In this scenario, buffers are solicited on the DUT. In an ingress
   buffering mechanism, the ingress port buffers would be solicited
   along with Virtual Output Queues, when available; whereas in an
   egress buffer mechanism, the egress buffer of the one outgoing port
   would be used.

   In either case, regardless of where the buffer memory is located on
   the switch architecture, the Incast creates buffer utilization.

   When one or more frames having synchronous arrival times at the DUT
   they are considered forming an Incast.



6.2.3 Measurement Units

   It is a MUST to measure the number of ingress and egress ports. It is
   a MUST to have a non-null percentage of synchronization, which MUST
   be specified.



7 Application Throughput: Data Center Goodput

7.1. Definition

   In Data Center Networking, a balanced network is a function of
   maximal throughput 'and' minimal loss at any given time. This is
   defined by the Goodput [4]. Goodput is the application-level
   throughput. The definition used is a variance of the definition in
   [RFC2647].

   Goodput is the number of bits per unit of time forwarded to the
   correct destination interface of the DUT, minus any bits
   retransmitted.


7.2. Discussion

   In data center benchmarking, the goodput is a value that SHOULD be
   measured. It provides a realistic idea of the usage of the available
   bandwidth. A goal in data center environments is to maximize the
   goodput while minimizing the loss.

7.3. Measurement Units



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   When S represents the payload bytes, which does not include packet or
   TCP headers, and Ft is the Finishing Time of the last sender, the
   Goodput, G, is then measured by the following formula:

   G=S/Ft bytes per second

   Example: A TCP file transfer over HTTP protocol on a 10Gb/s media.
   The file cannot be transferred over Ethernet as a single continuous
   stream. It must be broken down into individual frames of 1500 bytes
   when the standard MTU [Maximum Transmission Unit] is used. Each
   packet requires 20 bytes of IP header information and 20 bytes of TCP
   header information; therefore 1460 byte are available per packet for
   the file transfer. Linux based systems are further limited to 1448
   bytes as they also carry a 12 byte timestamp. Finally, the date is
   transmitted in this example over Ethernet which adds a 26 byte
   overhead per packet.

   G= 1460/1526 x 10 Gbit/s which is 9.567 Gbit/s or 1.196 Gigabytes per
   second.

   Please note: This example does not take into consideration additional
   Ethernet overhead, such as the interframe gap (a minimum of 96 bit
   times), nor collisions (which have a variable impact, depending on
   the network load).

   When conducting Goodput measurements please document in addition to
   the 4.1 section:

   -The TCP Stack used

   -OS Versions

   -NIC firmware version and model

   For example, Windows TCP stacks and different Linux versions can
   influence TCP based tests results.

8.  Security Considerations

   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 constraints
   specified in the sections above.

   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.



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   Further, benchmarking is performed on a "black-box" basis, relying
   solely on measurements observable external to the DUT.

   Special capabilities SHOULD NOT exist in the DUT specifically for
   benchmarking purposes. Any implications for network security arising
   from the DUT SHOULD be identical in the lab and in production
   networks.

9.  IANA Considerations

   NO IANA Action is requested at this time.

10.  References

10.1.  Normative References

   [1]  Avramov L. and Rapp J., "Data Center Benchmarking Methodology",
         April 2017.

         [RFC1242]   Bradner, S. "Benchmarking Terminology for Network
         Interconnection Devices", RFC 1242, July 1991, <http://www.rfc-
         editor.org/info/rfc1242>

   [RFC2544]   Bradner, S. and J. McQuaid, "Benchmarking Methodology for
         Network Interconnect Devices", RFC 2544, March 1999,
         <http://www.rfc-editor.org/info/rfc2554>

         [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119,
         March 1997, <http://www.rfc-editor.org/info/rfc2119>

         [RFC5841] , Hay, R., "TCP Option to Denote Packet Mood", BCP
         14, RFC 5841, April 2010, <http://www.rfc-
         editor.org/info/rfc5841>

10.2.  Informative References


         [RFC2889]  Mandeville R. and Perser J., "Benchmarking
         Methodology for LAN Switching Devices", RFC 2889, August 2000,
         <http://www.rfc-editor.org/info/rfc2889>

   [RFC3918]  Stopp D. and Hickman B., "Methodology for IP Multicast
         Benchmarking", RFC 3918, October 2004, <http://www.rfc-
         editor.org/info/rfc3918>

   [4]  Yanpei Chen, Rean Griffith, Junda Liu, Randy H. Katz, Anthony D.
         Joseph, "Understanding TCP Incast Throughput Collapse in



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         Datacenter Networks,
         "http://yanpeichen.com/professional/usenixLoginIncastReady.pdf"

         [RFC2432] Dubray, K., "Terminology for IP Multicast
         Benchmarking", BCP 14, RFC 2432, DOI 10.17487/RFC2432, October
         1998, <http://www.rfc-editor.org/info/rfc2432>

         [RFC2647] Newman D. ,"Benchmarking Terminology for Firewall
         Performance" BCP 14, RFC 2647, August 1999, <http://www.rfc-
         editor.org/info/rfc2647>



10.3.  Acknowledgments

         The authors would like to thank Alfred Morton, Scott Bradner,
         Ian Cox, Tim Stevenson for their reviews and feedback.



Authors' Addresses

         Lucien Avramov
         Google
         1600 Amphitheatre Parkway
         Mountain View, CA 94043
         United States
         Email: lucienav@google.com

         Jacob Rapp
         VMware
         3401 Hillview Ave
         Palo Alto, CA 94304
         United States
         Phone: +1 650 857 3367
         Email: jrapp@vmware.com















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