Terminology for Benchmarking Network-layer Traffic Control Mechanisms

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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 © 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.

Table of Contents

   1. Introduction ....................................................2
   2. Existing Definitions ............................................3
   3. Term Definitions ................................................4
      3.1. Configuration Terms ........................................4
           3.1.1. Classification ......................................4
           3.1.2. Codepoint Set .......................................4
           3.1.3. Forwarding Congestion ...............................5
           3.1.4. Congestion Management ...............................6
           3.1.5. Flow ................................................7
      3.2. Measurement Terms ..........................................7
           3.2.1. Forwarding Capacity .................................7
           3.2.2. Conforming Packet ...................................8
           3.2.3. Nonconforming Packet ................................9
           3.2.4. Forwarding Delay ....................................9
           3.2.5. Jitter .............................................11
           3.2.6. Undifferentiated Response ..........................11
      3.3. Sequence Tracking .........................................12
           3.3.1. Test Sequence Number ...............................12
           3.3.2. Stream .............................................12
           3.3.3. In-Sequence Packet .................................13
           3.3.4. Out-of-Order Packet ................................14
           3.3.5. Duplicate Packet ...................................14
      3.4. Vectors ...................................................15
           3.4.1. Intended Vector ....................................15
           3.4.2. Offered Vector .....................................16
           3.4.3. Expected Vectors ...................................16
           3.4.4. Output Vectors .....................................23
   4. Security Considerations ........................................30
   5. Acknowledgements ...............................................30
   6. References .....................................................31
      6.1. Normative References ......................................31
      6.2. Informative References ....................................31

1. 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.

2. 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.

2.1. 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

3. Term Definitions

3.1. Configuration Terms

3.1.1. 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

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:

      None

3.1.3. 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]

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 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

3.1.5. 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

3.2. Measurement Terms

3.2.1. 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]

3.2.2. 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

3.2.3. 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

3.2.4. 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]

3.2.5. 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]

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 DSCP 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. 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

3.3.2. 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

3.3.3. 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

3.3.4. 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]

3.3.5. 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

3.4. 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.

3.4.1. 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

3.4.2. 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

3.4.3. Expected Vectors

3.4.3.1. 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

3.4.3.2. 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]

3.4.3.3. 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

3.4.3.4. 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

3.4.3.5. 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

3.4.3.6. 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

3.4.3.7. 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

3.4.3.8. 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

3.4.3.9. 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

3.4.4. Output Vectors

3.4.4.1. 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

3.4.4.2. 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]

3.4.4.3. 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

3.4.4.4. 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

3.4.4.5. 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

3.4.4.6. 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

3.4.4.7. 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

3.4.4.8. 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

3.4.4.9. 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

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. 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.

6. References

6.1. 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.

6.2. 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: jerry@perser.org

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

   Phone: + 1 508 439 9008
   EMail: sporetsky@reefpoint.com

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

   EMail: shobha@research.telcordia.com

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

   Phone: +1 512 996 6604
   Email: skhurana@motorola.com

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