





Internet Engineering Task Force (IETF)                        L. Avramov
Request for Comments: 8238                                        Google
Category: Informational                                          J. Rapp
ISSN: 2070-1721                                                   VMware
                                                             August 2017


                  Data Center Benchmarking Terminology

Abstract

   The purposes of this informational document are to establish
   definitions and describe measurement techniques for data center
   benchmarking, as well as to introduce new terminology applicable to
   performance evaluations of data center network equipment.  This
   document establishes the important concepts for benchmarking network
   switches and routers in the data center and is a prerequisite for the
   test methodology document (RFC 8239).  Many of these terms and
   methods may be applicable to network equipment beyond the scope of
   this document as the technologies originally applied in the data
   center are deployed elsewhere.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc8238.














Avramov & Rapp                Informational                     [Page 1]

RFC 8238          Data Center Benchmarking Terminology       August 2017


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 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.





































Avramov & Rapp                Informational                     [Page 2]

RFC 8238          Data Center Benchmarking Terminology       August 2017


Table of Contents

   1. Introduction ....................................................4
      1.1. Requirements Language ......................................5
      1.2. Definition Format ..........................................5
   2. Latency .........................................................5
      2.1. Definition .................................................5
      2.2. Discussion .................................................7
      2.3. Measurement Units ..........................................7
   3. Jitter ..........................................................8
      3.1. Definition .................................................8
      3.2. Discussion .................................................8
      3.3. Measurement Units ..........................................8
   4. Calibration of the Physical Layer ...............................9
      4.1. Definition .................................................9
      4.2. Discussion .................................................9
      4.3. Measurement Units ..........................................9
   5. Line Rate ......................................................10
      5.1. Definition ................................................10
      5.2. Discussion ................................................10
      5.3. Measurement Units .........................................11
   6. Buffering ......................................................12
      6.1. Buffer ....................................................12
           6.1.1. Definition .........................................12
           6.1.2. Discussion .........................................14
           6.1.3. Measurement Units ..................................14
      6.2. Incast ....................................................15
           6.2.1. Definition .........................................15
           6.2.2. Discussion .........................................15
           6.2.3. Measurement Units ..................................16
   7. Application Throughput: Data Center Goodput ....................16
      7.1. Definition ................................................16
      7.2. Discussion ................................................16
      7.3. Measurement Units .........................................16
   8. Security Considerations ........................................17
   9. IANA Considerations ............................................18
   10. References ....................................................18
      10.1. Normative References .....................................18
      10.2. Informative References ...................................19
   Acknowledgments ...................................................20
   Authors' Addresses ................................................20










Avramov & Rapp                Informational                     [Page 3]

RFC 8238          Data Center Benchmarking Terminology       August 2017


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.  They can be largely
   east-west traffic flows (server to server inside the data center) in
   one data center and north-south (from the outside of the data center
   to the 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.  All of these may coexist in a single
   cluster and flow through a single network device simultaneously.
   Benchmarking tests for 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 (DUT) 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.

   Currently, typical data center networking devices are
   characterized by:

   -  High port density (48 ports or more).

   -  High speed (currently, up to 100 GB/s per port).

   -  High throughput (line rate on all ports for Layer 2 and/or
      Layer 3).

   -  Low latency (in the microsecond or nanosecond range).

   -  Low amount of buffer (in the MB range per networking device).

   -  Layer 2 and Layer 3 forwarding capability (Layer 3 not mandatory).

   This document defines a set of definitions, metrics, and new
   terminology, including congestion scenarios and switch buffer
   analysis, and redefines basic definitions in order to represent a
   wide mix of traffic conditions.  The test methodologies are defined
   in [RFC8239].







Avramov & Rapp                Informational                     [Page 4]

RFC 8238          Data Center Benchmarking Terminology       August 2017


1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 measurements and units used to
      report measurements of the term in question, if applicable.

2.  Latency

2.1.  Definition

   Latency is 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 a store-and-forward 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.









Avramov & Rapp                Informational                     [Page 5]

RFC 8238          Data Center Benchmarking Terminology       August 2017


   -  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.
      Latency (as defined in [RFC1242]) 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.  Latency (as defined in
      [RFC1242]) for store-and-forward devices uses these events.

   Another possible way to summarize the four definitions above is to
   refer to the bit positions 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, as explained in this section in the context of
   data center switch benchmarking, is in lieu of the previous
   definition of "latency" as provided in RFC 1242, Section 3.8 and
   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.






Avramov & Rapp                Informational                     [Page 6]

RFC 8238          Data Center Benchmarking Terminology       August 2017


   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 that are latency
   sensitive and can function with initial bytes of the frame, FIFO
   (or, for bit-forwarding devices, latency per RFC 1242) MAY be used.
   In all cases, the event combinations used in latency measurements
   MUST be reported.

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 change to cut-through behavior at specific larger
   packet sizes.  The value of the packet size at which the behavior
   changes MAY be configurable, depending on the DUT manufacturer.  FILO
   covers both scenarios: store-and-forward and cut-through.  The
   threshold for the change in behavior does not matter for
   benchmarking, since FILO covers both possible scenarios.

   The LIFO mechanism can be used with store-and-forward switches
   but not with cut-through 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 the 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; 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 process the data
      as the first bits arrive -- for example, with a Field-Programmable
      Gate Array (FPGA).

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




Avramov & Rapp                Informational                     [Page 7]

RFC 8238          Data Center Benchmarking Terminology       August 2017


3.  Jitter

3.1.  Definition

   In the context of the data center, jitter 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 Packet Delay
   Variation (PDV) as defined in 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 the assessment of the range of delay variation
   (Max - Min) or a high percentile of PDV (99th percentile, for
   robustness against outliers).

   When 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 a 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 a 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.














Avramov & Rapp                Informational                     [Page 8]

RFC 8238          Data Center Benchmarking Terminology       August 2017


4.  Calibration of the Physical Layer

4.1.  Definition

   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
   specified here:

   -  Type of device used to generate traffic / measure traffic.

   -  Type of line cards used on the traffic generator.

   -  Type of transceivers on the traffic generator.

   -  Type of transceivers on the DUT.

   -  Type of cables.

   -  Length of cables.

   -  Software name and version of the traffic generator and DUT.

   -  A list of enabled features on the DUT MAY be provided and is
      recommended (especially in the case of control-plane protocols,
      such as the Link Layer Discovery Protocol and Spanning Tree).  A
      comprehensive configuration file MAY be provided to this effect.

4.2.  Discussion

   Calibration of the physical layer contributes to end-to-end latency
   and should be taken into account when evaluating the DUT.  Small
   variations in 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 that all cables used for testing (1) be of the same
   type and length and (2) come from the same vendor whenever possible.
   It is a MUST to document the cable specifications listed in
   Section 4.1, along with the test results.  The test report MUST
   specify whether or not the cable latency has been subtracted from the
   test measurements.  The accuracy of the traffic-generator
   measurements MUST be provided (for current test equipment, this is
   usually a value within a range of 20 ns).




Avramov & Rapp                Informational                     [Page 9]

RFC 8238          Data Center Benchmarking Terminology       August 2017


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 (expressed as Gigabit
   Ethernet), 1 GE, 10 GE, 40 GE, 100 GE.

   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 a Parts Per Million
   (PPM) value.  The IEEE standards allow a specific +/- variance in the
   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 test
   equipment to a DUT.

   Line rate SHOULD be measured in frames per second (FPS).

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 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.






Avramov & Rapp                Informational                    [Page 10]

RFC 8238          Data Center Benchmarking Terminology       August 2017


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

   1. The Ethernet standards allow a maximum variance of +/- 100 PPM
      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 other external factors.

   2. The crystals, or clock modules, usually have a specific +/- PPM
      variance that is significantly better than +/- 100 PPM.
      Oftentimes, 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 be demonstrated by setting the test set's 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 at which 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 interframe gap.  This formula "scales up"
   or "scales down" to represent 1 GB Ethernet, 10 GB Ethernet, and
   so on.






Avramov & Rapp                Informational                    [Page 11]

RFC 8238          Data Center Benchmarking Terminology       August 2017


   Example for 1 GB Ethernet speed with 64-byte frames:

      Frame Rate = 1,000,000,000 / (64*8 + 96 + 56 + 8)

                 = 1,000,000,000 / 672

                 = 1,488,095.2 FPS

   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 frame-rate increase or decrease of 1.488 FPS.

   In a production network, it is very unlikely that one would 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 -100 PPM
   adjustment.

   Line rate SHOULD be measured at 99.98% with a 0 PPM adjustment.

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

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 (gigabytes).
      When the buffer size is expressed, an indication of the frame MTU
      (Maximum Transmission Unit) used for that measurement is also
      necessary, as well as the CoS (Class of Service) or DSCP
      (Differentiated Services Code Point) value set, as oftentimes the
      buffers are carved by a quality-of-service implementation.  Please
      refer to Section 3 of [RFC8239] for further details.

      Example: The Buffer Size of the DUT when sending 1518-byte frames
      is 18 MB.

   Port Buffer Size: The port buffer size is the amount of buffer for
      a single ingress port, a single egress port, or a combination of
      ingress and egress buffering locations for a single port.  We
      mention the three locations for the port buffer because the DUT's



Avramov & Rapp                Informational                    [Page 12]

RFC 8238          Data Center Benchmarking Terminology       August 2017


      buffering scheme can be unknown or untested, 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 by 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 a certain type of 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 (bytes), KB (kilobytes), MB (megabytes), or GB
      (gigabytes).  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 3 KB of port buffer for
      1518-byte frames, and a total of 4.7 MB of maximum port buffer for
      1518-byte frames and a CoS of 0.

   Maximum DUT Buffer Size: This is the total buffer size that a DUT can
      be measured to have.  It is most likely different 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
      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 3 KB of port buffer for
      1518-byte frames and a total of 4.7 MB of maximum port buffer for
      1518-byte frames.  The DUT has a Maximum Buffer Size of 18 MB at
      1500 B and a CoS of 0.

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

   Microburst: A microburst is a type of burst where packet drops occur
      when there is not sustained or noticeable congestion on a link or
      device.  One characteristic of a microburst is when the burst
      is not evenly distributed over T and is less than the constant C
      (C = the average time between two evenly spaced consecutive
      packets).





Avramov & Rapp                Informational                    [Page 13]

RFC 8238          Data Center Benchmarking Terminology       August 2017


   Intensity of Microburst: This is a percentage and represents the
      level, between 1 and 100%, of the microburst.  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 but rather on how to measure it.  A larger buffer is not
   necessarily better and can cause issues with bufferbloat.

6.1.2.  Discussion

   When measuring buffering on a DUT, it is important to understand the
   behavior of each and every port.  This provides data for the total
   amount of buffering available on the switch.  The terms of buffer
   efficiency help 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 comprehensive data center
   device-buffering benchmarking.

6.1.3.  Measurement Units

   When the DUT buffer is measured:

   -  The buffer size MUST be measured.

   -  The port buffer size MAY be provided for each port.

   -  The maximum port buffer size MUST be measured.

   -  The maximum DUT buffer size MUST be measured.

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

   -  The CoS or DSCP value set during the test SHOULD be provided.













Avramov & Rapp                Informational                    [Page 14]

RFC 8238          Data Center Benchmarking Terminology       August 2017


6.2.  Incast

6.2.1.  Definition

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

   Synchronous arrival time: When two or more frames of sizes L1 and L2
      arrive at their respective ingress port or multiple ingress ports
      and there is an overlap of arrival times for any of the bits on
      the DUT, then the L1 and L2 frames have synchronous arrival times.
      This is called "Incast", regardless of whether the pattern is
      many-to-one (simpler) or many-to-many.

   Asynchronous arrival time: This is any condition not defined by
      "synchronous arrival time".

   Percentage of synchronization: This defines the level of overlap
      (amount of bits) between frames of sizes L1,L2..Ln.

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

   Stateful traffic: Stateful traffic is packets exchanged with a
      stateful protocol, such as TCP.

   Stateless traffic: Stateless traffic is packets exchanged with a
      stateless protocol, such as UDP.

6.2.2.  Discussion

   In this scenario, buffers are used on the DUT.  In an ingress
   buffering mechanism, the ingress port buffers would be used along
   with virtual output queues, when available, whereas in an egress
   buffering mechanism, the egress buffer of the one outgoing port would
   be used.





Avramov & Rapp                Informational                    [Page 15]

RFC 8238          Data Center Benchmarking Terminology       August 2017


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

   When one or more frames have synchronous arrival times at the DUT,
   they are considered to be 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
   captured by the Goodput [TCP-INCAST].  Goodput is the
   application-level throughput.  For standard TCP applications, a very
   small loss can have a dramatic effect on application throughput.
   [RFC2647] provides a definition of Goodput; the definition in this
   document is a variant of that definition.

   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 loss.

7.3.  Measurement Units

   The Goodput, G, is then measured by the following formula:

      G = (S/F) x V bytes per second

      -  S represents the payload bytes, not including packet or
         TCP headers.

      -  F is the frame size.

      -  V is the speed of the media in bytes per second.



Avramov & Rapp                Informational                    [Page 16]

RFC 8238          Data Center Benchmarking Terminology       August 2017


      Example: A TCP file transfer over HTTP on 10 GB/s media.

      The file cannot be transferred over Ethernet as a single
      continuous stream.  It must be broken down into individual frames
      of 1500 B when the standard MTU is used.  Each packet requires
      20 B of IP header information and 20 B of TCP header information;
      therefore, 1460 B are available per packet for the file transfer.
      Linux-based systems are further limited to 1448 B, as they also
      carry a 12 B timestamp.  Finally, in this example the date is
      transmitted over Ethernet, which adds 26 B of overhead per packet
      to 1500 B, increasing it to 1526 B.

      G = 1460/1526 x 10 Gbit/s, which is 9.567 Gbit/s or 1.196 GB/s.

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

   When conducting Goodput measurements, please document, in addition to
   the items listed in Section 4.1, the following information:

   -  The TCP stack used.

   -  OS versions.

   -  Network Interface Card (NIC) firmware version and model.

   For example, Windows TCP stacks and different Linux versions can
   influence TCP-based test 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.

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






Avramov & Rapp                Informational                    [Page 17]

RFC 8238          Data Center Benchmarking Terminology       August 2017


   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

   This document does not require any IANA actions.

10.  References

10.1.  Normative References

   [RFC1242]  Bradner, S., "Benchmarking Terminology for Network
              Interconnection Devices", RFC 1242, DOI 10.17487/RFC1242,
              July 1991, <https://www.rfc-editor.org/info/rfc1242>.

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

   [RFC2544]  Bradner, S. and J. McQuaid, "Benchmarking Methodology for
              Network Interconnect Devices", RFC 2544,
              DOI 10.17487/RFC2544, March 1999,
              <https://www.rfc-editor.org/info/rfc2544>.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
              March 2009, <https://www.rfc-editor.org/info/rfc5481>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in
              RFC 2119 Key Words", BCP 14, RFC 8174,
              DOI 10.17487/RFC8174, May 2017,
              <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8239]  Avramov, L. and J. Rapp, "Data Center Benchmarking
              Methodology", RFC 8239, DOI 10.17487/RFC8239, August 2017,
              <https://www.rfc-editor.org/info/rfc8239>.












Avramov & Rapp                Informational                    [Page 18]

RFC 8238          Data Center Benchmarking Terminology       August 2017


10.2.  Informative References

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

   [RFC2647]  Newman, D., "Benchmarking Terminology for Firewall
              Performance", RFC 2647, DOI 10.17487/RFC2647, August 1999,
              <https://www.rfc-editor.org/info/rfc2647>.

   [RFC2889]  Mandeville, R. and J. Perser, "Benchmarking Methodology
              for LAN Switching Devices", RFC 2889,
              DOI 10.17487/RFC2889, August 2000,
              <https://www.rfc-editor.org/info/rfc2889>.

   [RFC3918]  Stopp, D. and B. Hickman, "Methodology for IP Multicast
              Benchmarking", RFC 3918, DOI 10.17487/RFC3918,
              October 2004, <https://www.rfc-editor.org/info/rfc3918>.

   [TCP-INCAST]
              Chen, Y., Griffith, R., Zats, D., Joseph, A., and R. Katz,
              "Understanding TCP Incast and Its Implications for Big
              Data Workloads", April 2012, <http://yanpeichen.com/
              professional/usenixLoginIncastReady.pdf>.



























Avramov & Rapp                Informational                    [Page 19]

RFC 8238          Data Center Benchmarking Terminology       August 2017


Acknowledgments

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

Authors' Addresses

   Lucien Avramov
   Google
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   United States of America

   Email: lucien.avramov@gmail.com


   Jacob Rapp
   VMware
   3401 Hillview Ave.
   Palo Alto, CA  94304
   United States of America

   Email: jhrapp@gmail.com




























Avramov & Rapp                Informational                    [Page 20]

