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INFORMATIONAL
Internet Engineering Task Force (IETF)                        L. AvramovRequest for Comments: 8238                                        GoogleCategory: Informational                                          J. RappISSN: 2070-1721                                                   VMware                                                             August 2017Data Center Benchmarking TerminologyAbstract   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; seeSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8238.Avramov & Rapp                Informational                     [Page 1]

RFC 8238          Data Center Benchmarking Terminology       August 2017Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 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 2017Table of Contents1. Introduction ....................................................41.1. Requirements Language ......................................51.2. Definition Format ..........................................52. Latency .........................................................52.1. Definition .................................................52.2. Discussion .................................................72.3. Measurement Units ..........................................73. Jitter ..........................................................83.1. Definition .................................................83.2. Discussion .................................................83.3. Measurement Units ..........................................84. Calibration of the Physical Layer ...............................94.1. Definition .................................................94.2. Discussion .................................................94.3. Measurement Units ..........................................95. Line Rate ......................................................105.1. Definition ................................................105.2. Discussion ................................................105.3. Measurement Units .........................................116. Buffering ......................................................126.1. Buffer ....................................................126.1.1. Definition .........................................126.1.2. Discussion .........................................146.1.3. Measurement Units ..................................146.2. Incast ....................................................156.2.1. Definition .........................................156.2.2. Discussion .........................................156.2.3. Measurement Units ..................................167. Application Throughput: Data Center Goodput ....................167.1. Definition ................................................167.2. Discussion ................................................167.3. Measurement Units .........................................168. Security Considerations ........................................179. IANA Considerations ............................................1810. References ....................................................1810.1. Normative References .....................................1810.2. Informative References ...................................19   Acknowledgments ...................................................20   Authors' Addresses ................................................20Avramov & Rapp                Informational                     [Page 3]

RFC 8238          Data Center Benchmarking Terminology       August 20171.  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 20171.1.  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 inBCP 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.  Latency2.1.  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 inRFC 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 perRFC 1242) MAY be used.   In all cases, the event combinations used in latency measurements   MUST be reported.2.2.  Discussion   As mentioned inSection 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 20173.  Jitter3.1.  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 inRFC 3393.  The   mandatory definition of "delay variation" is the Packet Delay   Variation (PDV) as defined inSection 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 inSection 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 20174.  Calibration of the Physical Layer4.1.  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 inSection 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 20175.  Line Rate5.1.  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.  Buffering6.1.  Buffer6.1.1.  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 toSection 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'sAvramov & 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 20176.2.  Incast6.2.1.  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 Goodput7.1.  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 inSection 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.  References10.1.  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 inRFC 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 201710.2.  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 2017Acknowledgments   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.comAvramov & Rapp                Informational                    [Page 20]

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