Network Working Group                           Jerry Perser
     INTERNET-DRAFT                                  Spirent
     Expires in: December 2002 April 2003                          David Newman
                                                     Network Test
                                                     Sumit Khurana
                                                     Telcordia
                                                     Shobha Erramilli
                                                     QNetworx
                                                     Scott Poretsky
                                                     Avici Systems
                                                     June
                                                     October 2002

                 Terminology for Benchmarking Network-layer
                         Traffic Control Mechanisms

                      <draft-ietf-bmwg-dsmterm-03.txt>

                      <draft-ietf-bmwg-dsmterm-04.txt>

     Status of this Memo

     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026.

     Internet-Drafts are working documents of the Internet Engineering
     Task Force  (IETF), its areas, and its working groups.  Note that
     other groups may also distribute working documents as Internet-
     Drafts.

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

     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt

     The list of Internet-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.

     Table of Contents

        1. Introduction  .............................................. 2
        2. Existing definitions  ...................................... 3
        3. Term definitions ............................................3
        3.1 Configuration Terms
          3.1.1 Classification .........................................3
          3.1.2 Codepoint Set ..........................................4
          3.1.3 Congestion .............................................4
          3.1.4 Congestion Management ..................................5
          3.1.5 Flow ...................................................6
        3.2 Measurement Terms
                 Network-layer Traffic Control Mechanisms

          3.2.1 Channel Capacity .......................................7
          3.2.2 Conforming .............................................7
          3.2.3 Nonconforming ..........................................8
          3.2.4 Delay ..................................................8
          3.2.5 Jitter .................................................9
          3.2.6 Undifferentiated Response ................................9 .............................10
        3.3 Sequence Tracking
          3.3.1 In-sequence Packet .....................................9 ....................................10
          3.3.2 Out-of-order Packet ...................................10 ...................................11
          3.3.3 Duplicate Packet ......................................11
          3.3.4 Stream ................................................11 ................................................12
          3.3.5 Test Sequence number  .................................12
        3.4 Vectors ...................................................12 ...................................................13
          3.4.1 Intended Vector .......................................12 .......................................13
          3.4.2 Offered Vector ........................................13 ........................................14
          3.4.3 Expected Vectors
            3.4.3.1 Expected Forwarding Vector ........................13 ........................14
            3.4.3.2 Expected Loss Vector ..............................14 ..............................15
            3.4.3.3 Expected Sequence Vector ..........................14 ..........................16
            3.4.3.4 Expected Instantaneous Delay Vector ...............15 ...............16
            3.4.3.5 Expected Average Delay Vector .....................16 .....................17
            3.4.3.6 Expected Maximum Delay Vector .....................17
            3.4.3.7 Expected Minimum Delay Vector .....................17 .....................18
            3.4.3.8 Expected Instantaneous Delay Variation Jitter Vector .....18 ..............19
            3.4.3.9 Expected Average Delay Variation Jitter Vector ...........19 ....................19
            3.4.3.10 Expected Peak-to-peak Delay Variation Jitter Vector .....19 ..............20
          3.4.4 Output Vectors
            3.4.4.1 Forwarding Vector .................................20 .................................21
            3.4.4.2 Loss Vector .......................................20 .......................................21
            3.4.4.3 Sequence Vector ...................................21 ...................................22
            3.4.4.4 Instantaneous Delay Vector ........................22 ........................23
            3.4.4.5 Average Delay Vector ..............................23 ..............................24
            3.4.4.6 Maximum Delay Vector ..............................23 ..............................25
            3.4.4.7 Minimum Delay Vector ..............................24 ..............................25
            3.4.4.8 Instantaneous Delay Variation Jitter Vector ..............25 .......................26
            3.4.4.9 Average Delay Variation Jitter Vector ....................26 .............................27
            3.4.4.10 Peak-to-peak Delay Variation Jitter Vector ..............27 .......................28
        4. Security Considerations ....................................28 ....................................29
        5. References .................................................28 .................................................29
        6. Author's Address ...........................................29 ...........................................30
        7. Full Copyright Statement ...................................30 ...................................31

     1. Introduction

     This document describes terminology for the benchmarking of
     devices that implement traffic control based on IP precedence or
     diff-serv code point criteria.

     New terminology is needed because most existing measurements
     assume the absence of congestion and only a single per-hop-
                 Network-layer Traffic Control Mechanisms

     behavior. This document introduces several new terms that will
     allow measurements to be taken during periods of congestion.

                 Network-layer Traffic Control Mechanisms

     Another key difference from existing terminology is the definition
     of measurements as observed on egress as well as ingress of a
     device/system under test. Again, the existence of congestion
     requires the addition of egress measurements as well as 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 DUT/SUT.

     This document describes only those terms relevant to measuring
     behavior of a device or a group of devices using one of these two
     mechanisms. End-to-end and service-level measurements are beyond
     the scope of this document.

     2.  Existing definitions

     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
     RFC 2119.

     3. Term definitions

     3.1 Configuration Terms

     3.1.1 Classification

        Definition:

                 Network-layer Traffic Control Mechanisms

          Selection of packets based on the contents of packet header
          according to defined rules.

                 Network-layer Traffic Control Mechanisms

        Discussion:
          Packets can be selected based on the DS field or IP
          Precedence in the packet header.  Classification can also be
          based on Multi-Field (MF) criteria such as IP Source and
          destination addresses, protocol and port number.

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

        Measurement units:
           n/a

        See Also:

     3.1.2 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:

     3.1.3 Congestion

        Definition:
          A condition in which one or more egress interfaces are
          offered more packets than are forwarded at any given instant. forwarded.

        Discussion:

                 Network-layer Traffic Control Mechanisms

          This condition is a superset of the overload definition [2].
          The overload definition assumes the congestion is introduced
                 Network-layer Traffic Control Mechanisms
          strictly by the tester on ingress of a DUT/SUT. That may or
          may not be the case here.

          Another difference between congestion and overload occurs
          when the SUT comprises multiple elements, in that 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 congestion on multiple egress interfaces on the core
          device. In contrast, overload [1] deals only with overload on
          ingress.

          Throughput [1] defines the lower boundary of congestion.
          Throughput is the maximum offered rate with no congestion.
          At offered rates above throughput, the DUT/SUT is considered
          congested.

          Ingress observations alone are not sufficient to cover all
          cases in which congestion may occur. A device with an
          infinite amount of memory could buffer an infinite amount of
          packets, and eventually forward all of them. However, these
          packets may or may not be forwarded during the test duration.
          Even though ingress interfaces accept all packets without
          loss, this hypothetical device may still be congested.

          The definition presented here explicitly defines congestion
          as an event observable on egress interfaces. Regardless of
          internal architecture, any device that cannot forward packets
          on one or more egress interfaces is congested.

        Measurement units:
           n/a
          none

        See Also:
          Gateway Congestion Control Survey [8]

     3.1.4 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. Such mechanisms classify packets
          based upon IP Precedence or DSCP settings in a packet's IP
          header.

                 Network-layer Traffic Control Mechanisms

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

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

        Measurement units:
           n/a
                 Network-layer Traffic Control Mechanisms

        See Also:

     3.1.5 Flow

        Definition:
          A flow is a one or more of packets sharing a common intended
          pair of source and destination 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 [3] are a subset of flows.  As defined in [3],
          microflows require application-to-application measurement. In
          contrast, flows use lower-layer classification criteria.
          Since this document focuses on network-layer classification
          criteria, we concentrate 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 ISO 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 [3]
          Streams
                 Network-layer Traffic Control Mechanisms

     3.2 Measurement Terms

     3.2.1 Channel Capacity

        Definition:
          The maximum forwarding rate [2] at which none of the offered
          packets are dropped by the DUT/SUT.

        Discussion:
          Channel 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 is based on the
          ingress interface(s) of the DUT/SUT.

          Ingress-based measurements do not account for congestion of
          the DUT/SUT. Channel capacity, as an egress measurement, does
          take congestion into account.

          Understanding channel capacity is a necessary precursor to
          any measurement involving congestion.  Throughput numbers can
          be higher than channel capacity because of queueing.

          This measurement differs from forwarding rate at maximum
          offered load (FRMOL) [2] in that it is intolerant of loss.

        Measurement units:
           N-octet packets per second

        See Also:
          Throughput [1]
          Forwarding Rate at Maximum Offered Load [2]

     3.2.2 Conforming

        Definition:
          Packets which 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
                 Network-layer Traffic Control Mechanisms

          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
                 Network-layer Traffic Control Mechanisms
          Forwarding Vector
          Offered Vector
          Nonconforming

     3.2.3 Nonconforming

        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

     3.2.4 Delay

        Definition:
          The time interval starting when the last bit of the input IP
          packet reaches the input port of the DUT/SUT and ending when
          the last bit of the output IP packet is seen on the output
          port of the DUT/SUT.

        Discussion:
          Delay is measured the same regardless of the type of DUT/SUT.
          Latency [1] require some knowledge of whether the DUT/SUT is
          a "store and forward" or a "bit forwarding" device.  The fact
          that a DUT/SUT's technology has a lower delay than another
          technology should be visible.

                 Network-layer Traffic Control Mechanisms

          By specifying the metric to be inside the Internet protocol,
          the tester is relieved from specifying the start/end for
          every data link layer protocol that IP runs on.  This avoids
          determining if the start/end delimiters are included in the
          frame.  Also heterogeneous data link protocol can be used in
          a test.

          The measurement point at the end closely simulates the way an
          internet datagram is processed.  An internet datagram is not
                 Network-layer Traffic Control Mechanisms
          passed up or down the stack unless it is complete.
          Completion occurs once the last bit of the IP packet has been
          received.

          Delay can be run at any offered load.  Recommend at or below
          the channel capacity for non-congested delay.  For congested
          delay, run the offered load above the channel capacity.

        Measurement units:
           Seconds.

        See Also:
          Latency [1]

     3.2.5 Jitter

        Definition:
          The absolute value of the difference between the arrival
          delay of two consecutive packets belonging to the same
          stream.

        Discussion:
          The delay fluctuation between two consecutive packets in a
          stream is reported as the jitter.  Jitter can be expressed as
          |D(i) - D(i-1)| where D equals the delay and i is the test
          sequence number.  The measurement does not include lost
          packets.

          Jitter can be determined by the ipdv [6] (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.

        Measurement units:
          Seconds

        See Also:
          Jitter variation [5]
          ipdv [6]
          interarrival jitter [7]
                 Network-layer Traffic Control Mechanisms

     3.2.6 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 DSCPs or IP precedence enabled
          can be compared to the undifferentiated response to determine
          the effect of differentiating traffic.

        Measurement units:
          n/a

     3.3 Sequence Tracking

     3.3.1 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 are considered in-sequence.

                 Network-layer Traffic Control Mechanisms

          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) 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
                 Network-layer Traffic Control Mechanisms

        See Also:
          Stream
          Test Sequence number

     3.3.2 Out-of-order Packet

        Definition:
          A received packet with a Test Sequence number less that
          expected.

        Discussion:
          As a stream of packets enter 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 re-
          ordered is counted as an Out-of-order Packet.

          Certain streaming protocol (such as TCP) require the packets
          to be in a certain order.  Packets outside this are dropped
          by the streaming protocols even though there 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.

          Out-of-order Packet count is based on the worst case
          streaming protocol.  It allows for no reordering.

          Packet loss does not affect the Out-of-order Packet count.
          Only packets that were not received in the order that they
          were transmitted.

        Measurement units:
          Packet count

        See Also:
          Stream
          Test Sequence number
                 Network-layer Traffic Control Mechanisms

     3.3.3 Duplicate Packet

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

        Discussion:

        Measurement units:
          Packet count
                 Network-layer Traffic Control Mechanisms

        See Also:
          Stream
          Test Sequence number

     3.3.4 Stream

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

        Discussion:
          Streams are tracked by test sequence number or "unique
          signature field" (RFC 2889).  Streams define how individual
          packet's 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 transverse 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 mulitcast stream can be forward to
          multiple destination interfaces.

        Measurement units:
           n/a

        See Also:
          Flow
          MicroFlow [3]
          Test sequence number
                 Network-layer Traffic Control Mechanisms

     3.3.6 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 and
          the traffic receiver checks the value upon receipt of the
          packet.  The traffic generator changes the value on each
                 Network-layer Traffic Control Mechanisms

          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 number of received packets,
          the traffic receiver may also report number of in-sequence
          packets, number of out-sequence packets, number of duplicate
          packets, and number of reordered packets.

          The recommended algorithm to use to change the sequence
          number on sequential packets is an incrementing value.

        Measurement units:
           n/a

        See Also:
          Stream

     3.4 Vectors
          A vector is a group of packets all containing a specific DSCP
          or IP precedence value.  Vectors are expressed as a pair of
          numbers.  The first is being the particular diff-serv value.
          The second is the metric expressed as a rate, loss
          percentage, delay, or jitter.

     3.4.1 Intended Vector

        Definition:

          A vector describing the rate at which packets having a
          specific code-point (or IP precedence) that an external
          source attempts to transmit to a DUT/SUT.

        Discussion:
          Intended loads across the different code-point classes
          determine the metrics associated with a specific code-point
          traffic class.

                 Network-layer Traffic Control Mechanisms

        Measurement Units:
          N-octets packets per second

        See Also:
          Offered Vector
          Expected Forwarding Vector
          Expected Loss Vector
          Expected Sequence Vector
          Expected Delay Vector
          Expected Jitter Vector
          Forwarding Vector
                 Network-layer Traffic Control Mechanisms

          Loss Vector

     3.4.2 Offered Vector

        Definition:
          A vector describing the measured rate at which packets having
          a specific DSCP or IP precedence value are offered to the
          DUT/SUT.

        Discussion:
          Offered loads across the different code-point classes,
          constituting a code-point set, determine the metrics
          associated with a specific code-point traffic class.

        Measurement Units:
          N-octets packets per second

        See Also:
          Expected Forwarding Vector
          Expected Loss Vector
          Expected Sequence Vector
          Expected Delay Vector
          Expected Jitter Vector
          Forwarding Vector
          Codepoint Set

     3.4.3 Expected Vectors

     3.4.3.1 Expected Forwarding Vector

        Definition:
          A vector describing the expected output rate of packets
          having a specific DSCP or IP precedence value.  The value is
          dependent on the set of offered vectors and configuration of
          the DUT.

        Discussion:

                 Network-layer Traffic Control Mechanisms
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected forwarding vector.

        Measurement units:
          N-octet packets per second
                 Network-layer Traffic Control Mechanisms

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Sequence Vector
          Expected Delay Vector
          Expected Jitter Vector

     3.4.3.2 Expected Loss Vector

        Definition:
          A vector describing the percentage of packets, having a
          specific DSCP or IP precedence value, that should not be
          forwarded.  The value is dependent on the set of offered
          vectors and configuration of the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected loss vector.

        Measurement Units:
          Percentage of intended packets that are expected to be
          dropped.

        See Also:
          Intended Vector
          Offered Vector
          Expected Forwarding Vector
                 Network-layer Traffic Control Mechanisms
          Expected Sequence Vector
          Expected Delay Vector
          Expected Jitter Vector

     3.2.3.3 Expected Sequence Vector

        Definition:

                 Network-layer Traffic Control Mechanisms

          A vector describing the expected in-sequence packets having a
          specific DSCP or IP precedence value. The value is dependent
          on the set of offered vectors and configuration of the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected sequence vector.

        Measurement Units:
          N-octet packets per second

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Forwarding Vector
          Expected Delay Vector
          Expected Jitter Vector

     3.4.3.4 Expected Instantaneous Delay Vector

        Definition:
          A vector describing the expected delay for packets having a
          specific DSCP or IP precedence value. The value is dependent
          on the set of offered vectors and configuration of the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

                 Network-layer Traffic Control Mechanisms

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected delay vector.

        Measurement units:
          Seconds.

        See Also:

                 Network-layer Traffic Control Mechanisms

          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Sequence Vector
          Expected Forwarding Vector
          Expected Jitter Vector

     3.4.3.5 Expected Average Delay Vector

        Definition:
          A vector describing the expected average delay for packets
          having a specific DSCP or IP precedence value. The value is
          dependent on the set of offered vectors and configuration of
          the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected average delay vector.

        Measurement units:
          Seconds.

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Sequence Vector
          Expected Forwarding Vector
          Expected Jitter Vector
                 Network-layer Traffic Control Mechanisms

     3.4.3.6 Expected Maximum Delay Vector

        Definition:
          A vector describing the expected maximum delay for packets
          having a specific DSCP or IP precedence value. The value is
          dependent on the set of offered vectors and configuration of
          the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
                 Network-layer Traffic Control Mechanisms

          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected maximum delay vector.

        Measurement units:
          Seconds.

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Sequence Vector
          Expected Forwarding Vector
          Expected Jitter Vector

     3.4.3.7 Expected Minimum Delay Vector

        Definition:
          A vector describing the expected minimum delay for packets
          having a specific DSCP or IP precedence value. The value is
          dependent on the set of offered vectors and configuration of
          the DUT.

        Discussion:
          The DUT is configured in a certain way in order that service
          differentiation occurs for a particular DSCP or IP precedence
          value when a specific traffic mix consisting of multiple
          DSCPs or IP precedence values are applied. This term attempts
          to capture the expected forwarding behavior when subjected to
          a certain offered vectors.

          The actual algorithm or mechanism the DUT uses to achieve
          service differentiation is not important in describing the
          expected minimum delay vector.

                 Network-layer Traffic Control Mechanisms

        Measurement units:
          Seconds.

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Loss Vector
          Expected Sequence Vector
          Expected Forwarding Vector
                 Network-layer Traffic Control Mechanisms

          Expected Jitter Vector

     3.2.3.8 Expected Instantaneous Delay Variation Jitter Vector

        Definition:
          A vector describing the expected variation in the delay of jitter between two
          consecutive packets' arrival times having a specific DSCP or
          IP precedence value. The value is dependent on the set of
          offered vectors and configuration of the DUT.

        Discussion:
          Instantaneous Delay Variation Jitter is the absolute value of the difference
          between the delay measurement of two packets belonging to the
          same stream.

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

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

        Measurement units:
          Seconds

        See Also:
          Delay
          Jitter
          Offered Vector
          Output Vectors
          Expected Average Delay Variation Jitter Vector
          Expected Peak-to-peak Delay Variation Jitter Vector
          Stream
                 Network-layer Traffic Control Mechanisms

     3.2.3.9 Expected Average Delay Variation Jitter Vector

        Definition:
          A vector describing the expected average variation jitter in the
          delay of packet arrival
          times for packets having specific DSCP or IP precedence
          value. The value is dependent on the set of offered vectors
          and configuration of the DUT.

        Discussion:
          Average Delay Variation Jitter Vector is the average of all the Instantaneous Delay Variation
          Jitter Vectors measured during the test duration. duration for the same
          DSCP or IP precedence value.

                 Network-layer Traffic Control Mechanisms

        Measurement units:
          Seconds

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Instantaneous Delay Variation Jitter Vector
          Expected Peak-to-peak Delay Variation Jitter Vector

     3.2.3.10 Expected Peak-to-peak Delay Variation Jitter Vector

        Definition:
          A vector describing the expected maximum variation in the
          delay of packet arrival times for packets having specific
          DSCP or IP precedence value. The value is dependent on the
          set of offered vectors and configuration of the DUT.

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

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

        Measurement units:
          Seconds

        See Also:
          Intended Vector
          Offered Vector
          Output Vectors
          Expected Instantaneous Delay Variation Jitter Vector
          Expected Average Delay Variation Jitter Vector
                 Network-layer Traffic Control Mechanisms

     3.4.4 Output Vectors

     3.4.4.1 Forwarding Vector
                 Network-layer Traffic Control Mechanisms

        Definition:
          The number of packets per second for all packets containing a
          specific DSCP or IP precedence value that a device can be
          observed to successfully forward to the correct destination
          interface in response to an offered vector.

        Discussion:
          Forwarding Vector is expressed as pair of numbers.  Both the
          specific DSCP (or IP precedence) value AND the packets per
          second value combine to make a vector.

          The Forwarding Vector represents packet rate based on its
          specific DSCP (or IP precedence) value.  It is not
          necessarily based on a stream or flow.  The Forwarding Vector
          may be expressed as per port of the DUT/SUT. However, it must
          be consistent with the Expected Forwarding Vector.

          Forwarding Vector is a per-hop measurement.  The DUT/SUT may
          change the specific DSCP (or IP precedence) value for a
          multiple-hop measurement.

        Measurement units:
          N-octet packets per second

        See Also:
          Intended Vector
          Offered Vector
          Expected Vectors
          Loss Vector
          Sequence Vector
          Delay Vectors

     3.4.4.2 Loss Vector

        Definition:
          The percentage of packets containing specific DSCP or IP
          precedence value that a DUT/SUT did not transmit to the
          correct destination interface in response to an offered
          vector.

        Discussion:
          Loss Vector is expressed as pair of numbers.  Both the
          specific DSCP (or IP precedence) value AND the percentage
          value combine to make a vector.

                 Network-layer Traffic Control Mechanisms

          The Loss Vector represents percentage based on a specific
          DSCP or IP precedence value.  It is not necessarily based on
          a stream or flow.  The Loss Vector may be expressed as per
          port of the DUT/SUT. However, it must be consistent with the
          Expected Loss Vector
                 Network-layer Traffic Control Mechanisms

          Loss Vector is a per-hop measurement.  The DUT/SUT may change
          the specific DSCP or IP precedence value for a multiple-hop
          measurement.

        Measurement Units:
          Percentage of offered packets that are not forwarded.

        See Also:
          Intended Vector
          Offered Vector
          Expected Vectors
          Forwarding Vector
          Sequence Vector
          Delay Vectors

     3.4.4.3 Sequence Vector

        Definition:
          The number of packets per second for all packets containing a
          specific DSCP or IP precedence value that a device can be
          observed to transmit in sequence to the correct destination
          interface in response to an offered vector.

        Discussion:
          Sequence Vector is expressed as pair of numbers.  Both the
          specific DSCP (or IP precedence) value AND the packets per
          second value combine to make a vector.

          The Sequence Vector represents packet rate based on its
          specific DSCP or IP precedence value.  It is not necessarily
          based on a stream or flow.  The Sequence Vector may be
          expressed as per port of the DUT/SUT.  However, it must be
          consistent with the Expected Sequence Vector.

          Sequence Vector is a per-hop measurement.  The DUT/SUT may
          change the specific DSCP or IP precedence value for a
          multiple-hop measurement.

        Measurement Units:
          N-octet packets per second

        Issues:

        See Also:
          In-sequence Packet
                 Network-layer Traffic Control Mechanisms
          Intended Vector
          Offered Vector
          Expected Vectors
          Loss Vector
          Forwarding Vector
                 Network-layer Traffic Control Mechanisms

          Delay Vectors

     3.4.4.4 Instantaneous Delay Vector

        Definition:
          The delay for a packet containing specific DSCP or IP
          precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:
          Instantaneous Delay vector is expressed as pair of numbers.
          Both the specific DSCP (or IP precedence) value AND delay
          value combine to make a vector.

          The Instantaneous Delay Vector represents delay on its
          specific DSCP or IP precedence value.  It is not necessarily
          based on a stream or flow.  The Delay vector may be expressed
          as per port of the DUT/SUT.  However, it must be consistent
          with the Expected Delay vectors.

          Instantaneous Delay Vector is a per-hop measurement.  The
          DUT/SUT may change the specific DSCP or IP precedence value
          for a multiple-hop measurement.

          Instantaneous Delay vector can be obtained at any offered
          load.  Recommend at or below the channel capacity in the
          absence of congestion.  For congested delay, run the offered
          load above the channel capacity.

          Forwarding Vector may contain several Instantaneous Delay
          Vectors.  For every packet received in a Forwarding Vector,
          there is a corresponding Instantaneous Delay Vector.

        Measurement Units:
          Seconds

        See Also:
          Delay
          Intended Vector
          Offered Vector
          Expected Delay Vectors
          Average Delay Vector
          Maximum Delay Vector
          Minimum Delay Vector
                 Network-layer Traffic Control Mechanisms

     3.4.4.5 Average Delay Vector

        Definition:

                 Network-layer Traffic Control Mechanisms

          The average delay for packets containing specific DSCP or IP
          precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:
          Average Delay vector is expressed as pair of numbers.  Both
          the specific DSCP (or IP precedence) value AND delay value
          combine to make a vector.

          The Delay Vector represents delay on its specific DSCP or IP
          precedence value.  It is not necessarily based on a stream or
          flow.  The Delay vector may be expressed as per port of the
          DUT/SUT.  However, it must be consistent with the Expected
          Delay vector.

          The Average Delay Vector is computed by averaging all the
          Instantaneous Delay Vectors for a given vector.

          Average Delay Vector is a per-hop measurement.  The DUT/SUT
          may change the specific DSCP or IP precedence value for a
          multiple-hop measurement.

          Average Delay vector can be obtained at any offered load.
          Recommend at or below the channel capacity in the absence of
          congestion.  For congested delay, run the offered load above
          the channel capacity.

        Measurement Units:
          Seconds

        See Also:
          Delay
          Intended Vector
          Offered Vector
          Expected Delay Vectors
          Instantaneous Delay Vector
          Maximum Delay Vector
          Minimum Delay Vector

     3.4.4.6 Maximum Delay Vector

        Definition:
          The maximum delay from all packets containing specific DSCP
          or IP precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:

                 Network-layer Traffic Control Mechanisms

        Discussion:

          Maximum Delay vector is expressed as pair of numbers.  Both
          the specific DSCP (or IP precedence) value AND delay value
          combine to make a vector.

          The Maximum Delay Vector represents delay on its specific
          DSCP or IP precedence value.  It is not necessarily based on
          a stream or flow.  The Maximum Delay vector may be expressed
          as per port of the DUT/SUT.  However, it must be consistent
          with the Expected Delay vector.

          Maximum Delay Vector is based upon the maximum Instantaneous
          Delay Vector of all packets in a Forwarding Vector.

          Maximum Delay Vector is a per-hop measurement.  The DUT/SUT
          may change the specific DSCP or IP precedence value for a
          multiple-hop measurement.

        Measurement Units:
          Seconds

        See Also:
          Delay
          Intended Vector
          Offered Vector
          Expected Delay Vectors
          Instantaneous Delay Vector
          Forwarding Vector
          Average Delay Vector
          Minimum Delay Vector

     3.4.4.7 Minimum Delay Vector

        Definition:
          The minimum delay from all packets containing specific DSCP
          or IP precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:
          Delay vector is expressed as pair of numbers.  Both the
          specific DSCP (or IP precedence) value AND delay value
          combine to make a vector.

          The Minimum Delay Vector represents delay on its specific
          DSCP or IP precedence value.  It is not necessarily based on
          a stream or flow.  The Minimum Delay vector may be expressed
          as per port of the DUT/SUT.  However, it must be consistent
          with the Expected Delay vector.

                 Network-layer Traffic Control Mechanisms

          Minimum Delay Vector is based upon the minimum Instantaneous
          Delay Vector of all packets in a Forwarding Vector.

                 Network-layer Traffic Control Mechanisms

          Minimum Delay Vector is a per-hop measurement.  The DUT/SUT
          may change the specific DSCP or IP precedence value for a
          multiple-hop measurement.

          Minimum Delay vector can be obtained at any offered load.
          Recommend at or below the channel capacity in the absence of
          congestion.  For congested delay, run the offered load above
          the channel capacity.

        Measurement Units:
          Seconds

        See Also:
          Delay
          Intended Vector
          Offered Vector
          Expected Delay Vectors
          Instantaneous Delay Vector
          Forwarding Vector
          Average Delay Vector
          Maximum Delay Vector

     3.4.4.8 Instantaneous Delay Variation Jitter Vector

        Definition:
          The variation in the delay jitter for two consecutive packets containing specific
          DSCP or IP precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:
          Instantaneous Delay Variation Jitter is the absolute value of the difference
          between the delay measurement of two packets belonging to the
          same stream.

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

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

                 Network-layer Traffic Control Mechanisms

          Instantaneous Delay Variation Jitter Vector is a per-hop measurement.  The
          DUT/SUT may change the specific DSCP or IP precedence value
          for a multiple-hop measurement.

                 Network-layer Traffic Control Mechanisms

          Forwarding Vector may contain several Instantaneous Delay
          Variation Jitter
          Vectors.  For n packets received in a Forwarding Vector,
          there is n-1 several are exactly (n-1) Instantaneous Delay Variation Jitter Vectors.

        Measurement units:
          Seconds

        See Also:
          Delay
          Jitter
          Forwarding Vector
          Stream
          Expected Vectors
          Average Delay Variation Jitter Vector
          Peak-to-peak Delay Variation Jitter Vector

     3.4.4.9 Average Delay Variation Jitter Vector

        Definition:
          The average variation in the delay jitter for packets containing specific DSCP or IP
          precedence value that a device can be observed to
          successfully transmit to the correct destination interface in
          response to an offered vector.

        Discussion:
          Average Delay Variation Jitter Vector is the average of all the Instantaneous Delay Variation
          Jitter Vectors of the same DSCP or IP precedence value,
          measured during the test duration.

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

          Average Delay Variation Jitter vector is a per-hop measurement.  The DUT/SUT
          may change the specific DSCP or IP precedence value for a
          multiple-hop measurement.

        Measurement units:
          Seconds

        See Also:
          Delay
          Jitter
          Forwarding Vector
          Stream
          Expected Vectors
          Instantaneous Delay Variation Jitter Vector
          Peak-to-peak Delay Variation Jitter Vector

     3.4.4.10 Peak-to-peak Jitter Vector
                 Network-layer Traffic Control Mechanisms

     3.4.4.10 Peak-to-peak Delay Variation Vector

        Definition:
          The maximum possible variation in the delay for packets
          containing specific DSCP or IP precedence value that a device
          can be observed to successfully transmit to the correct
          destination interface in response to an offered vector.

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

          Delay Variation

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

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

        Measurement units:
          Seconds

        See Also:
          Delay
          Jitter
          Forwarding Vector
          Stream
          Expected Vectors
          Average Delay Variation Jitter Vector
          Peak-to-peak Delay Variation Jitter Vector
                 Network-layer Traffic Control Mechanisms

     4. 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.

     5. References

        [1]   Bradner, S., Editor, "Benchmarking Terminology for
              Network Interconnection Devices", RFC 1242, July 1991.

        [2]   Mandeville, R., "Benchmarking Terminology for LAN
              Switching Devices", RFC 2285, February 1998.

        [3]   K. Nichols, S. Blake, F. Baker, D. Black,"Definition of
              the Differentiated Services Field (DS Field) in the IPv4
              and IPv6 Headers", RFC 2474, December 1998.

        [4]   S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W.
              Weiss, "An Architecture for Differentiated Services", RFC
              2475, December 1998.

        [5]   V. Jacobson, K. Nichols, K. Poduri, _An Expedited
              Forwarding PHB_, RFC 2598, June 1999

        [6]   C. Demichelis, P. Chimento, _IP Packet Delay Variation
              Metric for IPPM_, draft-ietf-ippm-ipdv-10.txt

        [7]   H. Schulzrinne, GMD Fokus, S. Casner, R. Frederick,
              V. Jacobson, _RTP: A Transport Protocol for Real-Time
              Applications_, RFC 1889, January 1996

        [8]   A. Mankin, K. Ramakrishnan, _Gateway Congestion Control
              Survey_, RFC 1254, August 1991
                 Network-layer Traffic Control Mechanisms

     6. Authors' Address

          Jerry Perser
          Spirent Communications
          26750 Agoura Road
          Calabasas, CA 91302
          USA

          Phone: + 1 818 676 2300
          EMail: jerry.perser@spirentcom.com

          David Newman
          Network Test
          31324 Via Colinas, Suite 113
          Westlake Village, CA 91362
          USA

          Phone: + 1 818 889 0011, x10
          EMail: dnewman@networktest.com

          Sumit Khurana
          Telcordia Technologies
          445 South Street
          Morristown, NJ 07960
          USA

          Phone: + 1 973 829 3170
          EMail: sumit@research.telcordia.com

          Shobha Erramilli
          QNetworx Inc
          1119 Campus Drive West
          Morganville NJ 07751
          USA

          Phone:
          EMail: shobha@qnetworx.com

          Scott Poretsky
          Avici Systems
          101 Billerica Ave_Building #6
          N. Billerica, MA 01862
          USA

          Phone: + 1 978 964 2287
          EMail: sporetsky@avici.com
                 Network-layer Traffic Control Mechanisms

     7.  Full Copyright Statement

          Copyright (C) The Internet Society (1998).  All Rights
          Reserved.

          This document and translations of it may be copied and
          furnished to others, and derivative works that comment on or
          otherwise explain it or assist in its implementation may be
          prepared, copied, published and distributed, in whole or in
          part, without restriction of any kind, provided that the
          above copyright notice and this paragraph are included on all
          such copies and derivative works.  However, this document
          itself may not be modified in any way, such as by removing
          the copyright notice or references to the Internet Society or
          other Internet organizations, except as needed for the
          purpose of developing Internet standards in which case the
          procedures for copyrights defined in the Internet Standards
          process must be followed, or as required to translate it into
          languages other than English.

          The limited permissions granted above are perpetual and will
          not be revoked by the Internet Society or its successors or
          assigns.  This document and the information contained herein
          is provided on an "AS IS" basis and THE INTERNET SOCIETY AND
          THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES,
          EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY
          THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY
          RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR
          FITNESS FOR A PARTICULAR PURPOSE.