RFC4689

Network Working Group S. Poretsky Request for Comments: 4689 Reef Point Systems Category: Informational J. Perser

                                                            Veriwave
                                                        S. Erramilli
                                                           Telcordia
                                                          S. Khurana
                                                            Motorola
                                                        October 2006

Terminology for Benchmarking Network-layer Traffic Control Mechanisms

Status of This Memo

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2006).

Abstract

This document describes terminology for the benchmarking of devices that implement traffic control using packet classification based on defined criteria. The terminology is to be applied to measurements made on the data plane to evaluate IP traffic control mechanisms. Rules for packet classification can be based on any field in the IP header, such as the Differentiated Services Code Point (DSCP), or any field in the packet payload, such as port number.

Introduction

New terminology is needed because most existing measurements assume the absence of congestion and only a single per-hop behavior. This document introduces several new terms that will allow measurements to be taken during periods of congestion.

Another key difference from existing terminology is the definition of measurements as observed on egress and ingress of a device/system under test. Again, the existence of congestion requires the addition of egress measurements, as well as of those taken on ingress; without observing traffic leaving a device/system, it is not possible to say whether traffic-control mechanisms effectively dealt with congestion.

The principal measurements introduced in this document are vectors for rate, delay, and jitter, all of which can be observed with or without congestion of the Device Under Test (DUT)/System Under Test (SUT). This document describes only those terms relevant to measuring behavior of a DUT or SUT at the egress during periods of congestion. End-to-end and service-level measurements are beyond the scope of this document.

Existing Definitions

RFC 1224, "Techniques for Managing Asynchronously Generated Alerts" [St91], is used for 'Time with fine enough units to distinguish between two events'.

RFC 1242, "Benchmarking Terminology for Network Interconnect Devices", and RFC 2285, "Benchmarking Terminology for LAN Switching Devices", should be consulted before attempting to make use of this document.

RFC 2474, "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", section 2, contains discussions of a number of terms relevant to network-layer traffic control mechanisms and should also be consulted.

For the sake of clarity and continuity, this RFC adopts the template for definitions set out in Section 2 of RFC 1242. Definitions are indexed and grouped together in sections for ease of reference.

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 BCP 14, RFC 2119 [Br97]. RFC 2119 defines the use of these key words to help make the intent of standards track documents as clear as possible. While this document uses these keywords, this document is not a standards track document.

Frequently Used Acronyms

DA Destination Address DS DiffServ DSCP DiffServ Code Point DUT Device Under Test IP Internet Protocol PHB Per Hop Behavior SA Source Address SUT System Under Test

Term Definitions

Configuration Terms

Classification

Definition:

  Selection of packets according to defined rules.

Discussion:

  Classification determines the per-hop behaviors and traffic
  conditioning functions, such as shaping and dropping, that are to
  be applied to the packet.

  Classification of packets can be based on the DS field or IP
  Precedence in the packet header.  Classification can be based on
  other IP header fields, such as IP Source Address (SA),
  Destination Address (DA), and protocol, or on fields in the packet
  payload, such as port number.  Classification can also be based on
  ingress interface.  It is possible to base classification on
  Multi-Field (MF) criteria such as IP source and destination
  addresses, protocol, and port number.  For further discussion of
  packet classification and its network applications, see [Bl98].

Measurement units:

  n/a

See Also:

  None

Codepoint Set

Definition:

  The set of all DS Code-points or IP precedence values used during
  the test duration.

Discussion:

  Describes all the code-point markings associated with packets that
  are input to the DUT/SUT.  For each entry in the codepoint set,
  there are associated vectors describing the rate of traffic,
  delay, loss, or jitter containing that particular DSCP or IP
  precedence value.

  The treatment that a packet belonging to a particular code-point
  gets is subject to the DUT classifying packets to map to the
  correct PHB.  Moreover, the forwarding treatment in general is
  also dependent on the complete set of offered vectors.

Measurement Units:

  n/a

See Also:

  None

Forwarding Congestion

Definition:

  A condition in which one or more egress interfaces are offered
  more packets than are forwarded.

Discussion:

  This condition is a superset of the overload definition [Ma98].
  Overload [Ma98] deals with overloading input and output interfaces
  beyond the maximum transmission allowed by the medium.  Forwarding
  congestion does not assume ingress interface overload as the only
  source of overload on output interfaces.

  Another difference between Forwarding Congestion and overload
  occurs when the SUT comprises multiple elements, in that
  Forwarding Congestion may occur at multiple points.  Consider an
  SUT comprising multiple edge devices exchanging traffic with a
  single core device.  Depending on traffic patterns, the edge
  devices may induce Forwarding Congestion on multiple egress
  interfaces on the core device.

  Throughput [Br91] defines the lower boundary of Forwarding
  Congestion.  Throughput is the maximum offered rate with no
  Forwarding Congestion.  At offered rates above throughput, the
  DUT/SUT is considered to be in a state of Forwarding Congestion.

  Packet Loss, not increased Forwarding Delay, is the external
  observable metric used to indicate the condition of Forwarding
  Congestion.  Packet Loss is a deterministic indicator of
  Forwarding Congestion.  The condition of increased Forwarding
  Delay without Packet Loss is an indicator of Forwarding Congestion
  known as Incipient Congestion.  Incipient Congestion is a non-
  deterministic indicator of Forwarding Congestion [Fl93].  As
  stated in [Ec98], RED [Br98] detects incipient congestion before
  the buffer overflows, but the current Internet environment is
  limited to packet loss as the mechanism for indicating congestion
  to the end-nodes.  [Ra99] implies that it is impractical to build
  a black-box test to observe Incipient Congestion.  [Ra99] instead
  introduces Explicit Congestion Notification (ECN) as a
  deterministic Black-Box method for observing Incipient Congestion.
  [Ra99] is an Experimental RFC with limited deployment, so ECN is
  not used for this particular methodology.  For the purpose of

  "black-box" testing a DUT/SUT, this methodology uses Packet Loss
  as the indicator of Forwarding Congestion.

  Ingress observations alone are not sufficient to cover all cases
  in which Forwarding Congestion may occur.  A device with an
  infinite amount of memory could buffer an infinite number of
  packets and eventually forward all of them.  However, these
  packets may or may not be forwarded during the test duration.
  Congestion Collapse [Na84] is defined as the state in which
  buffers are full and all arriving packets MUST be dropped across
  the network.  Even though ingress interfaces accept all packets
  without loss, Forwarding Congestion is present in this
  hypothetical device.

  The definition presented here explicitly defines Forwarding
  Congestion as an event observable on egress interfaces.
  Regardless of internal architecture, any device exhibiting Packet
  Loss on one or more egress interfaces is experiencing Forwarding
  Congestion.

Measurement units:

  None

See Also:

  Gateway Congestion Control Survey [Ma91]

Congestion Management

Definition:

  An implementation of one or more per-hop behaviors to avoid or
  minimize the condition of congestion.

Discussion:

  Congestion management may seek either to control congestion or
  avoid it altogether through Classification.

  Congestion avoidance mechanisms seek to prevent congestion before
  it actually occurs.

  Congestion control mechanisms give one or more flows (with a
  discrete IP Precedence or DSCP value) preferential treatment over
  other classes during periods of congestion.

Measurement units:

  n/a

See Also:

  Classification

Flow

Definition:

  A flow is one or more packets sharing a common intended pair of
  ingress and egress interfaces.

Discussion:

  Packets are grouped by the ingress and egress interfaces they use
  on a given DUT/SUT.

  A flow can contain multiple source IP addresses and/or destination
  IP addresses.  All packets in a flow MUST enter on the same
  ingress interface and exit on the same egress interface and have
  some common network layer content.

  Microflows [Ni98] are a subset of flows.  As defined in [Ni98],
  microflows require application-to-application measurement.  In
  contrast, flows use lower-layer classification criteria.  Since
  this document focuses on network-layer classification criteria, it
  concentrates here on the use of network-layer identifiers in
  describing a flow.  Flow identifiers also may reside at the data-
  link, transport, or application layers of the OSI model.  However,
  identifiers other than those at the network layer are out of scope
  for this document.

  A flow may contain a single code point/IP precedence value or may
  contain multiple values destined for a single egress interface.
  This is determined by the test methodology.

Measurement units:

  n/a

See Also:

  Microflow [Ni98]
  Streams

Measurement Terms

Forwarding Capacity

Definition:

  The number of packets per second that a device can be observed to
  transmit successfully to the correct egress interface in response
  to a specified offered load while the device drops none of the
  offered packets.

Discussion:

  Forwarding Capacity measures the packet rate at the egress
  interface(s) of the DUT/SUT.  In contrast, throughput (as defined
  in RFC 1242) measures the packet rate at the ingress interface(s)
  of the DUT/SUT.

  Ingress-based measurements do not account for queuing of the
  DUT/SUT.  Throughput rates can be higher than the Forwarding
  Capacity because of queueing.  The difference is dependent upon
  test duration, packet rate, and queue size.  Forwarding Capacity,
  as an egress measurement, does take queuing into account.

  Understanding Forwarding Capacity is a necessary precursor to any
  measurement involving Traffic Control Mechanisms.  The
  accompanying methodology document MUST take into consideration
  Forwarding Capacity when determining the expected forwarding
  vectors.  When the sum of the expected forwarding vectors on an
  interface exceeds the Forwarding Capacity, the Forwarding Capacity
  will govern the forwarding rate.

  This measurement differs from forwarding rate at maximum offered
  load (FRMOL) [Ma98] in that the Forwarding Capacity requires zero
  loss.

Measurement units:

  N-octet packets per second

See Also:

  Throughput [Br91]
  Forwarding Rate at Maximum Offered Load [Ma98]

Conforming Packet

Definition:

  Packets that lie within specific rate, delay, or jitter bounds.

Discussion:

  A DUT/SUT may be configured to allow a given traffic class to
  consume a given amount of bandwidth, or to fall within predefined
  delay or jitter boundaries.  All packets that lie within specified
  bounds are then said to be conforming, whereas those outside the
  bounds are nonconforming.

Measurement units:

  n/a

See Also:

  Expected Vector
  Forwarding Vector
  Offered Vector
  Nonconforming

Nonconforming Packet

Definition:

  Packets that do not lie within specific rate, delay, or jitter
  bounds.

Discussion:

  A DUT/SUT may be configured to allow a given traffic class to
  consume a given amount of bandwidth, or to fall within predefined
  delay or jitter boundaries.  All packets that do not lie within
  these bounds are then said to be nonconforming.

Measurement units:

  n/a

See Also:

  Expected Vector
  Forwarding Vector
  Offered Vector
  Conforming

Forwarding Delay

Definition:

  The time interval starting when the last bit of the input IP
  packet is offered to the input port of the DUT/SUT and ending when
  the last bit of the output IP packet is received from the output
  port of the DUT/SUT.

Discussion:

  The delay time interval MUST be externally observed.  The delay
  measurement MUST NOT include delays added by test bed components
  other than the DUT/SUT, such as propagation time introduced by
  cabling or non-zero delay added by the test instrument.
  Forwarding Delay differs from latency [Br91] and one-way delay
  [Al99] in several key regards:

  1. Latency [Br91] assumes knowledge of whether the DUT/SUT uses
     "store and forward" or "bit forwarding" technology.  Forwarding
     Delay is the same metric, measured the same way, regardless of
     the architecture of the DUT/SUT.

  2. Forwarding Delay is a last-in, last-out (LILO) measurement,
     unlike the last-in, first-out method [Br91] or the first-in,
     last-out method [Al99].

     The LILO method most closely simulates the way a network-layer
     device actually processes an IP datagram.  IP datagrams are not
     passed up and down the stack unless they are complete, and
     processing begins only once the last bit of the IP datagram has
     been received.

     Further, the LILO method has an additive property, where the
     sum of the parts MUST equal the whole.  This is a key
     difference from [Br91] and [Al99].  For example, the delay
     added by two DUTs MUST equal the sum of the delay of the DUTs.
     This may or may not be the case with [Br91] and [Al99].

  3. Forwarding Delay measures the IP datagram only, unlike [Br91],
     which also includes link-layer overhead.

     A metric focused exclusively on the Internet protocol relieves
     the tester from specifying the start/end for every link-layer
     protocol that IP runs on.  This avoids the need to determine
     whether the start/stop delimiters are included.  It also allows
     the use of heterogeneous link-layer protocols in a test.

  4. Forwarding Delay can be measured at any offered load, whereas
     the latency methodology [Br99] recommends measurement at, and
     only at, the throughput level.  Comparing the Forwarding Delay
     below the throughput to Forwarding Delay above the Forwarding
     Capacity will give insight to the traffic control mechanisms.

     For example, non-congested delay may be measured with an
     offered load that does not exceed the Forwarding Capacity,
     while congested delay may involve an offered load that exceeds
     the Forwarding Capacity.

     Note: Forwarding Delay SHOULD NOT be used as an absolute
     indicator of DUT/SUT Forwarding Congestion.  While Forwarding
     Delay may rise when offered load nears or exceeds the
     Forwarding Capacity, there is no universal point at which
     Forwarding Delay can be said to indicate the presence or
     absence of Forwarding Congestion.

Measurement units:

  milliseconds

See Also:

  Latency [Br91]
  Latency [Al99]
  One-way Delay [Br99]

Jitter

Definition:

  The absolute value of the difference between the Forwarding Delay
  of two consecutive received packets belonging to the same stream.

Discussion:

  The Forwarding Delay fluctuation between two consecutive received
  packets in a stream is reported as the jitter.  Jitter can be
  expressed as |D(i) - D(i-1)|, where D equals the Forwarding Delay
  and i is the order the packets were received.

  Under loss, jitter can be measured between non-consecutive test
  sequence numbers.  When IP Traffic Control Mechanisms are dropping
  packets, fluctuating Forwarding Delay may be observed.  Jitter
  MUST be able to benchmark the delay variation independently of
  packet loss.

  Jitter is related to the IPDV [De02] (IP Delay Variation) by
  taking the absolute value of the ipdv.  The two metrics will
  produce different mean values.  Mean Jitter will produce a
  positive value, where the mean ipdv is typically zero.  Also, IPDV
  is undefined when one packet from a pair is lost.

Measurement units:

  milliseconds

See Also:

  Forwarding Delay
  Jitter variation [Ja99]
  ipdv [De02]
  interarrival jitter [Sc96]

Undifferentiated Response

Definition:

  The vector(s) obtained when mechanisms used to support diff-serv
  or IP precedence are disabled.

Discussion:

  Enabling diff-serv or IP precedence mechanisms may impose
  additional processing overhead for packets.  This overhead may
  degrade performance even when traffic belonging to only one class,

  the best-effort class, is offered to the device.  Measurements
  with "undifferentiated response" SHOULD be made to establish a
  baseline.

  The vector(s) obtained with DSCP or IP precedence enabled can be
  compared to the undifferentiated response to determine the effect
  of differentiating traffic.

Measurement units:

  n/a

Sequence Tracking

Test Sequence Number

Definition:

  A field in the IP payload portion of the packet that is used to
  verify the order of the packets on the egress of the DUT/SUT.

Discussion:

  The traffic generator sets the test sequence number value.  Upon
  receipt of the packet,  the traffic receiver checks the value.
  The traffic generator changes the value on each packet transmitted
  based on an algorithm agreed to by the traffic receiver.

  The traffic receiver keeps track of the sequence numbers on a
  per-stream basis.  In addition to the number of received packets,
  the traffic receiver may also report the number of in-sequence
  packets, the number of out-of-sequence packets, the number of
  duplicate packets, and the number of reordered packets.  The
  RECOMMENDED algorithm to change the sequence number on sequential
  packets is an incrementing value.

Measurement units:

  n/a

See Also:

  Stream

Stream

Definition:

  A group of packets tracked as a single entity by the traffic
  receiver.  A stream MUST share common content, such as type (IP,
  UDP), IP SA/DA, packet size, or payload.

Discussion:

  Streams are tracked by test sequence number or "unique signature
  field" [Ma00].  Streams define how individual packet statistics
  are grouped together to form an intelligible summary.

  Common stream groupings would be by egress interface, destination
  address, source address, DSCP, or IP precedence.  A stream using
  test sequence numbers can track the ordering of packets as they
  traverse the DUT/SUT.

  Streams are not restricted to a pair of source and destination
  interfaces as long as all packets are tracked as a single entity.
  A multicast stream can be forwarded to multiple destination
  interfaces.

Measurement units:

  n/a

See Also:

  Flow
  Microflow [Ni98]
  Test sequence number

In-Sequence Packet

Definition:

  A received packet with the expected Test Sequence number.

Discussion:

  In-sequence is done on a stream level.  As packets are received on
  a stream, each packet's Test Sequence number is compared with the
  previous packet.  Only packets that match the expected Test
  Sequence number are considered in-sequence.

  Packets that do not match the expected Test Sequence number are
  counted as "not in-sequence" or out-of-sequence.  Every packet
  that is received is either in-sequence or out-of-sequence.
  Subtracting the in-sequence from the received packets (for that
  stream), the tester can derive the out-of-sequence count.

  Two types of events will prevent the in-sequence from
  incrementing: packet loss and reordered packets.

Measurement units:

  Packet count

See Also:

  Stream
  Test Sequence number

Out-of-Order Packet

Definition:

  A received packet with a sequence number less than the sequence
  number of any previously arriving packet.

Discussion:

  As a stream of packets enters a DUT/SUT, they include a Stream
  Test Sequence number indicating the order the packets were sent to
  the DUT/SUT.  On exiting the DUT/SUT, these packets may arrive in
  a different order.  Each packet that was reordered is counted as
  an Out-of-Order Packet.

  Certain streaming protocols (such as TCP) require the packets to
  be in a certain order.  Packets outside this are dropped by the
  streaming protocols even though they were properly received by the
  IP layer.  The type of reordering tolerated by a streaming
  protocol varies from protocol to protocol, and also by
  implementation.

  Packet loss does not affect the Out-of-Order Packet count.  The
  Out-of-Order Packet count is impacted only by packets that were
  not received in the order that they were transmitted.

Measurement units:

  packets

See Also:

  Stream
  Test Sequence number
  Packet Reordering Metric for IPPM [Mo03]

Duplicate Packet

Definition:

  A received packet with a Test Sequence number matching a
  previously received packet.

Discussion:

  A Duplicate Packet is a packet that the DUT/SUT has successfully
  transmitted out an egress interface more than once.  The egress
  interface has previously forwarded this packet.

  A Duplicate Packet SHOULD be a bit-for-bit copy of an already
  transmitted packet (including Test Sequence number).  If the
  Duplicate Packet traversed different paths through the DUT/SUT,
  some fields (such as TTL or checksum) may have changed.

  A multicast packet is not a Duplicate Packet by definition.  For a
  given IP multicast group, a DUT/SUT SHOULD forward a packet once
  on a given egress interface provided the path to one or more
  multicast receivers is through that interface.  Several egress
  interfaces will transmit the same packet, but only once per
  interface.

  To detect a Duplicate Packet, each packet offered to the DUT/SUT
  MUST contain a unique packet-by-packet identifier.

Measurement units:

  Packet count

See Also:

  Stream
  Test Sequence number

Vectors

A vector is a group of packets all matching a specific classification criteria, such as DSCP. Vectors are identified by the classification criteria and benchmarking metrics, such as a Forwarding Capacity, Forwarding Delay, or Jitter.

Intended Vector

Definition:

  A description of the configuration on an external source
  for the attempted rate of a stream transmitted to a DUT/SUT
  matching specific classification rules.

Discussion:

  The Intended Vector of a stream influences the benchmark
  measurements.  The Intended Vector is described by the
  classification criteria and attempted rate.

Measurement Units:

  N-bytes packets per second

See Also:

  Stream
  Offered Vector
  Forwarding Vector

Offered Vector

Definition:

  A description for the attempted rate of a stream offered to
  a DUT/SUT matching specific classification rules.

Discussion:

  The Offered Vector of a stream influences the benchmark
  measurements.  The Offered Vector is described by the
  classification criteria and offered rate.

Measurement Units:

  N-bytes packets per second

See Also:

  Stream
  Intended Vector
  Forwarding Vector

Expected Vectors

Expected Forwarding Vector

Definition:

  A description of the expected output rate of packets matching a
  specific classification, such as DSCP.

Discussion:

  The value of the Expected Forwarding Vector is dependent on the
  set of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Forwarding Vector.

Measurement units:

  N-octet packets per second

See Also:

  Classification
  Stream
  Intended Vector
  Offered Vector

Expected Loss Vector

Definition:

  A description of the percentage of packets having a specific
  classification that should not be forwarded.

Discussion:

  The value of the Expected Loss Vector is dependent on the set of
  offered vectors and Classification configuration on the DUT/SUT.
  The DUT is configured in a certain way so that classification
  occurs when a traffic mix consisting of multiple streams is
  applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Loss Vector.

Measurement Units:

  Percentage of intended packets expected to be dropped.

See Also:

  Classification
  Stream
  Intended Vector
  Offered Vector
  One-way Packet Loss Metric [Ka99]

Expected Sequence Vector

Definition:

  A description of the expected in-sequence packets matching a
  specific classification, such as DSCP.

Discussion:

  The value of the Expected Sequence Vector is dependent on the set
  of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Sequence Vector.

Measurement Units:

  N-octet packets per second

See Also:

  Classification
  Stream
  In-Sequence Packet
  Intended Vector
  Offered Vector

Expected Delay Vector

Definition:

  A description of the expected instantaneous Forwarding Delay for
  packets matching a specific classification, such as DSCP.

Discussion:

  The value of the Expected Delay Vector is dependent on the set of
  offered vectors and Classification configuration on the DUT/SUT.
  The DUT is configured in a certain way so that classification
  occurs when a traffic mix consisting of multiple streams is
  applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Delay Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Delay
  Intended Vector
  Offered Vector

Expected Average Delay Vector

Definition:

  A description of the expected average Forwarding Delay for packets
  matching a specific classification, such as DSCP.

Discussion:

  The value of the Expected Average Delay Vector is dependent on the
  set of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Average Delay Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector

Expected Maximum Delay Vector

Definition:

  A description of the expected maximum Forwarding Delay for packets
  matching a specific classification, such as DSCP.

Discussion:

  The value of the Expected Maximum Delay Vector is dependent on the
  set of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Maximum Delay Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector

Expected Minimum Delay Vector

Definition:

  A description of the expected minimum Forwarding Delay for packets
  matching a specific classification, such as DSCP.

Discussion:

  The value of the Expected Minimum Delay Vector is dependent on the
  set of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Minimum Delay Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector

Expected Instantaneous Jitter Vector

Definition:

  A description of the expected Instantaneous Jitter between two
  consecutive packets arrival times matching a specific
  classification, such as DSCP.

Discussion:

  Instantaneous Jitter is the absolute value of the difference
  between the Forwarding Delay measurement of two packets belonging
  to the same stream.

  The Forwarding Delay fluctuation between two consecutive packets
  in a stream is reported as the "Instantaneous Jitter".
  Instantaneous Jitter can be expressed as |D(i) - D(i-1)|, where D
  equals the Forwarding Delay and i is the test sequence number.
  Packets lost are not counted in the measurement.

  The Forwarding Vector may contain several Jitter Vectors.  For n
  packets received in a Forwarding Vector, there is a total of (n-1)
  Instantaneous Jitter Vectors.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Jitter
  Intended Vector
  Offered Vector

Expected Average Jitter Vector

Definition:

  A description of the expected average jitter for packets arriving
  in a stream matching a specific classification, such as DSCP.

Discussion:

  Average Jitter Vector is the average of all the Instantaneous
  Jitter Vectors measured during the test duration for the same
  stream.

  The value of the Expected Average Jitter Vector is dependent on
  the set of offered vectors and Classification configuration on the
  DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Average Jitter Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Jitter
  Intended Vector
  Offered Vector
  Expected Instantaneous Jitter Vector

3.4.3.10. Expected Peak-to-peak Jitter Vector

Definition:

  A description of the expected maximum variation in the Forwarding
  Delay of packet arrival times for packets arriving in a stream
  matching a specific classification, such as DSCP.

Discussion:

  Peak-to-peak Jitter Vector is the maximum Forwarding Delay minus
  the minimum Forwarding Delay of the packets (in a vector)
  forwarded by the DUT/SUT.

  Peak-to-peak Jitter is not derived from the Instantaneous Jitter
  Vector.  Peak-to-peak Jitter is based upon all the packets during
  the test duration, not just two consecutive packets.

  The value of the Expected Peak-to-peak Jitter Vector is dependent
  on the set of offered vectors and Classification configuration on
  the DUT/SUT.  The DUT is configured in a certain way so that
  classification occurs when a traffic mix consisting of multiple
  streams is applied.

  This term captures the expected forwarding behavior from the DUT
  receiving multiple Offered Vectors.  The actual algorithm or
  mechanism the DUT uses to achieve service differentiation is
  implementation specific and is not important when describing the
  Expected Peak-to-peak Jitter Vector.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Jitter
  Intended Vector
  Offered Vector
  Expected Instantaneous Jitter Vector
  Expected Average Jitter Vector

Output Vectors

Forwarding Vector

Definition:

  The number of packets per second for a stream matching a specific
  classification, such as DSCP, that a DUT/SUT is measured to
  forward to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Forwarding Vector is expressed as a combination of values: the
  classification rules AND the measured packets per second for the
  stream matching the classification rules.  Forwarding Vector is a
  per-hop measurement.  The DUT/SUT MAY remark the specific DSCP (or
  IP precedence) value for a multi-hop measurement.  The stream
  remains the same.

Measurement units:

  N-octet packets per second

See Also:

  Classification
  Stream
  Forwarding Capacity
  Intended Vector
  Offered Vector
  Expected Vector

Loss Vector

Definition:

  The percentage of packets per second for a stream matching a
  specific classification, such as DSCP, that a DUT/SUT is measured
  not to transmit to the correct destination interface in response
  to an offered vector.

Discussion:

  Loss Vector is expressed as a combination of values: the
  classification rules AND the measured percentage value of packet
  loss.  Loss Vector is a per-hop measurement.  The DUT/SUT MAY
  remark the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

Measurement Units:

  Percentage of packets

See Also:

  Classification
  Stream
  Intended Vector
  Offered Vector
  Expected Vector
  One-way Packet Loss Metric [Ka99]

Sequence Vector

Definition:

  The number of packets per second for all packets in a stream
  matching a specific classification, such as DSCP, that a DUT/SUT
  is measured to transmit in sequence to the correct destination
  interface in response to an offered vector.

Discussion:

  Sequence Vector is expressed as a combination of values: the
  classification rules AND the number of packets per second that are
  in-sequence.

  Sequence Vector is a per-hop measurement.  The DUT/SUT MAY remark
  the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

Measurement Units:

  N-octet packets per second

See Also:

  Classification
  Stream
  In-sequence Packet
  Intended Vector
  Offered Vector
  Expected Vector

Instantaneous Delay Vector

Definition:

  The instantaneous Forwarding Delay for a packet in a stream
  matching a specific classification, such as DSCP, that a DUT/SUT
  is measured to transmit to the correct destination interface
  successfully in response to an offered vector.

Discussion:

  Instantaneous Delay Vector is expressed as a combination of
  values: the classification rules AND Forwarding Delay.  For every
  packet received in a Forwarding Vector, there is a corresponding
  Instantaneous Delay Vector.

  Instantaneous Delay Vector is a per-hop measurement.  The DUT/SUT
  MAY remark the specific DSCP or IP precedence value for a multi-
  hop measurement.  The stream remains the same.

  Instantaneous Delay Vector can be obtained at any offered load.
  It is RECOMMENDED that this vector be obtained at or below the
  Forwarding Capacity in the absence of Forwarding Congestion.  For
  congested Forwarding Delay, run the offered load above the
  Forwarding Capacity.

Measurement Units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Capacity
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector

Average Delay Vector

Definition:

  The average Forwarding Delay for packets in a stream matching a
  specific classification, such as DSCP, that a DUT/SUT is measured
  to transmit to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Average Delay Vector is expressed as combination of values: the
  classification rules AND average Forwarding Delay.

  The average Forwarding Delay is computed by averaging all the
  Instantaneous Delay Vectors for a given stream.

  Average Delay Vector is a per-hop measurement.  The DUT/SUT MAY
  remark the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

  Average Delay Vector can be obtained at any offered load.  It is
  recommended that the offered load be at or below the Forwarding
  Capacity in the absence of congestion.  For congested Forwarding
  Delay, run the offered load above the Forwarding Capacity.

Measurement Units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Capacity
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector
  Instantaneous Delay Vector

Maximum Delay Vector

Definition:

  The maximum Forwarding Delay for packets in a stream matching a
  specific classification, such as DSCP, that a DUT/SUT is measured
  to transmit to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Maximum Delay Vector is expressed as combination of values: the
  classification rules AND maximum Forwarding Delay.

  The maximum Forwarding Delay is computed by selecting the highest
  value from the Instantaneous Delay Vectors for a given stream.

  Maximum Delay Vector is a per-hop measurement.  The DUT/SUT MAY
  remark the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

  Maximum Delay Vector can be obtained at any offered load.  It is
  recommended that the offered load be at or below the Forwarding
  Capacity in the absence of congestion.  For congested Forwarding
  Delay, run the offered load above the Forwarding Capacity.

Measurement Units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Capacity
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector
  Instantaneous Delay Vector

Minimum Delay Vector

Definition:

  The minimum Forwarding Delay for packets in a stream matching a
  specific classification, such as DSCP, that a DUT/SUT is measured
  to transmit to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Minimum Delay Vector is expressed as a combination of values: the
  classification rules AND minimum Forwarding Delay.  The minimum
  Forwarding Delay is computed by selecting the lowest value from
  the Instantaneous Delay Vectors for a given stream.

  Minimum Delay Vector is a per-hop measurement.  The DUT/SUT MAY
  remark the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

  Minimum Delay Vector can be obtained at any offered load.  It is
  recommended that the offered load be at or below the Forwarding
  Capacity in the absence of congestion.  For congested Forwarding
  Delay, run the offered load above the Forwarding Capacity.

Measurement Units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Capacity
  Forwarding Delay
  Intended Vector
  Offered Vector
  Expected Delay Vector

Instantaneous Jitter Vector

Definition:

  The jitter for two consecutive packets in a stream matching a
  specific classification, such as DSCP, that a DUT/SUT is measured
  to transmit to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Instantaneous Jitter is the absolute value of the difference
  between the Forwarding Delay measurement of two packets belonging
  to the same stream.

  The Instantaneous Jitter vector is expressed as a pair of numbers.
  Both the specific DSCP (or IP precedence) value AND jitter value
  combine to make a vector.

  The Forwarding Delay fluctuation between two consecutive packets
  in a stream is reported as the "Instantaneous Jitter".
  Instantaneous Jitter Vector can be expressed as |D(i) - D(i-1)|,
  where D equals the Forwarding Delay and i is the test sequence
  number.  Packets lost are not counted in the measurement.

  The Instantaneous Jitter Vector is a per-hop measurement.  The
  DUT/SUT MAY remark the specific DSCP or IP precedence value for a
  multi-hop measurement.  The stream remains the same.

  There may be several Instantaneous Jitter Vectors for a single
  stream.  For n packets measured, there may be (n-1) Instantaneous
  Jitter Vectors.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Forwarding Delay
  Jitter
  Forwarding Vector
  Expected Vectors

Average Jitter Vector

Definition:

  The average jitter for packets in a stream matching a specific
  classification, such as DSCP, that a DUT/SUT is measured to
  transmit to the correct destination interface successfully in
  response to an offered vector.

Discussion:

  Average jitter is calculated by the average of all the
  Instantaneous Jitter Vectors of the same stream measured during
  the test duration.  Average Jitter Vector is expressed as a
  combination of values:  the classification rules AND average
  Jitter.

  Average Jitter Vector is a per-hop measurement.  The DUT/SUT MAY
  remark the specific DSCP or IP precedence value for a multi-hop
  measurement.  The stream remains the same.

Measurement units:

  milliseconds

See Also:

  Classification
  Stream
  Jitter
  Forwarding Vector
  Expected Vector
  Instantaneous Jitter Vector

3.4.4.10. Peak-to-peak Jitter Vector

Definition:

  The maximum possible variation in the Forwarding Delay for packets
  in a stream matching a specific classification, such as DSCP, that
  a DUT/SUT is measured to transmit to the correct destination
  interface successfully in response to an offered vector.

Discussion:

  Peak-to-peak Jitter Vector is calculated by subtracting the
  maximum Forwarding Delay from the minimum Forwarding Delay of the
  packets forwarded by the DUT/SUT.  Jitter vector is expressed as a
  combination of values:  the classification rules AND peak-to-peak
  Jitter.

  Peak-to-peak Jitter is not derived from the Instantaneous Jitter
  Vector.  Peak-to-peak Jitter is based upon all the packets during
  the test duration, not just two consecutive packets.

Measurement units:

  milliseconds

See Also:

  Jitter
  Forwarding Vector
  Stream
  Expected Vectors
  Instantaneous Jitter Vector
  Average Jitter Vector

Security Considerations

Documents of this type do not directly affect the security of the Internet or of corporate networks as long as benchmarking is not performed on devices or systems connected to production networks.

Packets with unintended and/or unauthorized DSCP or IP precedence values may present security issues. Determining the security consequences of such packets is out of scope for this document.

Acknowledgements

The authors gratefully acknowledge the contributions of the IETF's Benchmarking Methodology Working Group members in reviewing this document. The authors would like to express our thanks to David Newman for his consistent and valuable assistance throughout the development of this document. The authors would also like to thank Al Morton and Kevin Dubray for their ideas and support.

References

Normative References

[Br91] Bradner, S., "Benchmarking terminology for network

      interconnection devices", RFC 1242, July 1991.

[Br97] Bradner, S., "Key words for use in RFCs to Indicate

      Requirement Levels", BCP 14, RFC 2119, March 1997.

[Br98] Braden, B., Clark, D., Crowcroft, J., Davie, B., Deering, S.,

      Estrin, D., Floyd, S., Jacobson, V., Minshall, G., Partridge,
      C., Peterson, L., Ramakrishnan, K., Shenker, S., Wroclawski,
      J., and L. Zhang, "Recommendations on Queue Management and
      Congestion Avoidance in the Internet", RFC 2309, April 1998.

[Ma98] Mandeville, R., "Benchmarking Terminology for LAN Switching

      Devices", RFC 2285, February 1998.

[Ni98] Nichols, K., Blake, S., Baker, F., and D. Black, "Definition

      of the Differentiated Services Field (DS Field) in the IPv4
      and IPv6 Headers", RFC 2474, December 1998.

[St91] Steinberg, L., "Techniques for managing asynchronously

      generated alerts", RFC 1224, May 1991.

Informative References

[Al99] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way Delay

      Metric for IPPM", RFC 2679, September 1999.

[Bl98] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z., and

      W. Weiss, "An Architecture for Differentiated Service", RFC
      2475, December 1998.

[Br99] Bradner, S. and J. McQuaid, "Benchmarking Methodology for

      Network Interconnect Devices", RFC 2544, March 1999.

[De02] Demichelis, C. and P. Chimento, "IP Packet Delay Variation

      Metric for IP Performance Metrics (IPPM)", RFC 3393, November
      2002.

[Ec98] http://www3.ietf.org/proceedings/98mar/98mar-edited-135.htm

[Fl93] Floyd, S., and Jacobson, V., "Random Early Detection gateways

      for Congestion Avoidance", IEEE/ACM Transactions on
      Networking, V.1 N.4, August 1993, p. 397-413.  URL
      "ftp://ftp.ee.lbl.gov/papers/early.pdf".

[Ja99] Davie, B., Charny, A., Bennet, J.C., Benson, K., Le Boudec,

      J., Courtney, W., Davari, S., Firoiu, V., and D. Stiliadis,
      "An Expedited Forwarding PHB (Per-Hop Behavior)", RFC 3246,
      March 2002.

[Ka99] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way Packet

      Loss Metric for IPPM", RFC 2680, September 1999.

[Ma91] Mankin, A. and K. Ramakrishnan, "Gateway Congestion Control

      Survey", RFC 1254, August 1991.

[Ma00] Mandeville, R. and J. Perser, "Benchmarking Methodology for

      LAN Switching Devices", RFC 2889, August 2000.

[Mo03] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, S.,

      Perser, J., "Packet Reordering Metric for IPPM", Work in
      Progress.

[Na84] Nagle, J., "Congestion control in IP/TCP internetworks", RFC

      896, January 1984.

[Ra99] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of

      Explicit Congestion Notification (ECN) to IP", RFC 3168,
      September 2001.

[Sc96] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,

      "RTP: A Transport Protocol for Real-Time Applications", STD
      64, RFC 3550, July 2003.

Authors' Addresses

Jerry Perser Veriwave 8770 SW Nimbus Ave. Suite B Beaverton, OR 97008 USA USA

Phone: + 1 818 338 4112 EMail: [email protected]

Scott Poretsky Reef Point Systems 8 New England Executive Park Burlington, MA 01803 USA

Phone: + 1 508 439 9008 EMail: [email protected]

Shobha Erramilli Telcordia Technologies 331 Newman Springs Road Red Bank, New Jersey 07701 USA

EMail: [email protected]

Sumit Khurana Motorola 7700 West Parmer Ln. Austin, TX 78729 USA

Phone: +1 512 996 6604 Email: [email protected]

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