Network Working Group Jerry Perser
INTERNET-DRAFT Spirent
Expires in: December 2001 May 2002 David Newman
Network Test
Sumit Khurana
Telcordia
Shobha Erramilli
Telcordia
QNetworx
Scott Poretsky
Avici Systems
June
November 2001
Terminology for Benchmarking Network-layer
Traffic Control Mechanisms
<draft-ietf-bmwg-dsmterm-01.txt>
<draft-ietf-bmwg-dsmterm-02.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
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Internet-Drafts are draft documents valid for a maximum of six
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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 definitions ............................................3
3.1 Channel Capacity..........................................3
3.2 Classification............................................4
3.3 Configuration Terms
3.1.1 Classification .........................................3
3.1.2 Codepoint Set.............................................4
3.4 Conforming................................................5
3.5 Congestion................................................5
3.6 Set ..........................................4
3.1.3 Congestion Management.....................................6
3.7 Delay.....................................................7
3.8 Expected Vector...........................................7 .............................................4
3.1.4 Congestion Management ..................................5
3.2 Vectors ....................................................6
3.2.1 Intended Vector ........................................6
Network-layer Traffic Control Mechanisms
3.9 Flow......................................................8
3.10
3.2.2 Offered Vector .........................................6
3.2.3 Expected Vectors
3.2.3.1 Expected Forwarding Vector .......................................9
3.11 Jitter...................................................9
3.12 Nonconforming...........................................10
3.13 Offered Vector..........................................11
3.14 Stream..................................................11
3.15 Tail dropping...........................................12
3.16 ...........................7
3.2.3.2 Expected Loss Vector .................................8
3.2.3.3 Expected Sequence Vector .............................8
3.2.3.4 Expected Delay Vector ................................9
3.2.3.5 Expected Jitter Vector ..............................10
3.2.4 Output Vectors
3.2.4.1 Forwarding Vector ...................................11
3.2.4.2 Loss Vector .........................................11
3.2.4.3 Sequence Vector .....................................12
3.2.4.4 Delay Vector ........................................13
3.2.4.5 Jitter Vector .......................................14
3.3 Measurement Terms
3.3.1 Channel Capacity ......................................15
3.3.2 Conforming ............................................15
3.3.3 Nonconforming .........................................16
3.3.4 Delay .................................................16
3.3.5 Flow ..................................................17
3.3.6 Stream ................................................18
3.3.7 Test Sequence number....................................12
3.17 Unburdened Response.....................................13 number ..................................19
3.3.8 Undifferentiated Response .............................19
4. Security Considerations.....................................13 Considerations ....................................20
5. References..................................................14 References .................................................20
6. Author's Address............................................14 Address ...........................................21
7. Full Copyright Statement....................................15 Statement ...................................22
1. Introduction
Driven by Internet economics, service providers and enterprises
alike have shown strong interest in adding traffic-control
capabilities to network devices. These capabilities would enable
network operators to define and deliver minimum or maximum levels of
bandwidth, delay, and jitter for multiple classes of traffic.
Perhaps more importantly, network operators would be able to set
pricing according to the level of service delivered.
Networking device manufacturers have responded with a wide variety
of approaches for controlling network traffic. While there are
numerous ôpolicy managementö and ôquality of serviceö frameworks,
many of them rely on one of two network-layer mechanisms for the
actual control of forwarding rate, delay, and jitter. These two
mechanisms are the IP precedence setting in the IP header and the
diff-serv code point (DSCP) defined in [3].
This document describes terminology for the various terms to be used in benchmarking of
devices that implement traffic control based on IP precedence or
DSCP
diff-serv code point criteria. This document
New terminology is narrowly focused, in that it
describes only terms for measuring behavior of a device or a group
of devices using one of these two mechanisms. End-to-end and
service-level needed because most existing measurements are beyond
assume the scope absence of this document. 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. New
terminology is needed because most existing benchmarking terms
assume the absence of congestion. For example, throughput is one of
the most widely used measurements û- yet RFC 1242 defines throughput
as a rate in the absence of loss. As a result, throughput is not a
meaningful measurement where congestion exists.
Another key difference from existing benchmarking 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
Network-layer Traffic Control Mechanisms on ingress; without observing traffic leaving a device
device/system it is not possible to say whether traffic-control
mechanisms effectively dealt with congestion.
The principal measurements introduced in this document are rate
vectors, vectors
for rate, delay, and jitter, all of which can be observed with or
without congestion of the DUT/SUT.
2. Existing definitions
RFC 1242
Network-layer Traffic Control Mechanisms
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 Channel Capacity
Definition:
The maximum forwarding rate of a link or set of aggregated
links at which none of the offered packets are dropped by the
DUT/SUT.
Discussion:
Channel capacity measures the data rate at the egress
interface(s) of the DUT/SUT. In contrast, throughput as defined
in RFC 1242 measures the data 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.
Network-layer Traffic Control Mechanisms
Measurement units:
N-octet packets per second
Issues:
See Also:
Throughput [1]
3.2 Configuration Terms
3.1.1 Classification
Definition:
Selection of packets based on the contents of packet header
according to defined rules.
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:
Network-layer Traffic Control Mechanisms
n/a
Issues:
See Also:
Rules
3.3
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 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
Network-layer Traffic Control Mechanisms 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:
3.4 Conforming
Definition:
Packets that lie within the bounds specified by a traffic
profile.
Discussion:
Rules may be configured that allow a given traffic class to
consume only X bit/s of channel capacity and no more. All
additional packets are dropped. All packets that constitute
the first X bits/s measured over a period of time specified by
the traffic profile, are then said to be conforming whereas
those exceeding the bound are non conforming.
In particular in a congestion scenario, some individual packets
will be conforming and others will not.
Measurement units:
n/a
Issues:
See Also:
Expected Vector
Forwarding Vector
Offered Vector
3.5
3.1.3 Congestion
Definition:
A condition in which one or more egress interfaces are
offered more packets than can be are forwarded at any given instant.
Discussion:
This condition is a superset of the overload definition [2].
That
The overload definition assumes the overload congestion is introduced
strictly by the tester on ingress of a DUT/SUT. That may or
may not be the case here.
Network-layer Traffic Control Mechanisms
Another difference is that with multiple-DUT measurements,
congestion may occur at multiple points. For example,
multiple edge devices collectively may congest a core device.
In contrast, overload [1] deals only with overload on
ingress.
Network-layer Traffic Control Mechanisms
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
Issues:
See Also:
3.6
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 packetÆs packet's IP
header.
Congestion avoidance mechanisms seek to prevent congestion
before it actually occurs.
Congestion control mechanisms gives one or more service
classes preferential treatment over other classes during
periods of congestion.
Measurement units:
n/a
Issues:
See Also:
Network-layer Traffic Control Mechanisms
3.7 Delay
Definition:
The time interval starting when the last bit of the input IP
packets reaches the input port of the DUT/SUT and ending when
the last bit of the output IP packets is seen on the output
port of the DUT/SUT.
Discussion:
Delay
3.2 Vectors
A vector is measured the same regardless of the type of DUT/SUT.
Latency [1] require some knowledge a group of whether the DUT/SUT is packets all containing a
"store and forward" specific DSCP
or IP precedence value. Vectors are expressed as a "bit forwarding" device. The fact
that a DUT/SUT's technology has a lower delay than another
technology should be visible. pair of
numbers. The measurement point at the end is more like the way an
internet datagram is processed. An internet datagram first is not
passed up or down being the stack unless it particular diff-serv value.
The second 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 metric expressed as a rate, loss
percentage, delay, run the offered load above the channel capacity.
Measurement units:
Seconds.
Issues:
See Also:
3.8 Expected or jitter.
3.2.1 Intended Vector
Definition:
A vector describing the expected output rate of at which packets having a
specific code-point. The value is dependent on code-point (or IP precedence) that an external
source attempts to transmit to a DUT/SUT.
Discussion:
Intended loads across the set of
offered vectors and configuration of different code-point classes
determine the DUT.
Discussion:
The DUT is configured in metrics associated with a certain way in order that service
discrimination happens specific code-point
traffic class.
Measurement Units:
N-octets packets per second
Issues:
See Also:
Offered Vector
Expected Forwarding Vector
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
Forwarding Vector
Loss Vector
3.2.2 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
Network-layer Traffic Control Mechanisms
Issues:
Packet size.
See Also:
Expected Forwarding Vector
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
Forwarding Vector
Codepoint Set
3.2.3 Expected Vectors
3.2.3.1 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:
The DUT is configured in a certain way in order that service
differentiation occurs for behavior aggregates when a
specific traffic mix consisting of multiple behavior
aggregates is applied. This term attempts to capture the
expected forwarding behavior, for which the device is
configured, when subjected to a certain offered load.
Network-layer Traffic Control Mechanisms
The actual algorithms or mechanism, that the DUT uses to
achieve service discrimination, differentiation, is not important in
describing the expected vector.
Measurement units:
N-octets
N-octet packets per second
Issues:
See Also:
Forwarding
Intended Vector
Offered Vector
Codepoint Set
3.9 Flow
Output Vectors
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
Network-layer Traffic Control Mechanisms
3.2.3.2 Expected Loss Vector
Definition:
A flow is a one or more vector describing the percentage of packets sharing packets, having a common intended
pair
specific DSCP or IP precedence value, that should not be
forwarded. The value is dependent on the set of source offered
vectors and destination interfaces.
Discussion:
Packets are groups by configuration of the ingress and egress interfaces they
use on DUT.
Discussion:
The DUT is configured in a given DUT/SUT.
A flow can contain certain way in order that service
differentiation occurs for behavior aggregates when a
specific traffic mix consisting of multiple source behavior
aggregates is applied. This term attempts to capture the
expected loss behavior, for which the device is configured,
when subjected to a certain offered load.
The actual algorithms or mechanism, that 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.
Issues:
See Also:
Intended Vector
Offered Vector
Expected Forwarding Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
3.2.3.3 Expected Sequence Vector
Definition:
A vector describing the expected sequencing 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:
The DUT is configured in a certain way in order that service
differentiation occurs for behavior aggregates when a
specific traffic mix consisting of multiple behavior
aggregates is applied. This term attempts to capture the
expected sequence behavior, for which the device is
configured, when subjected to a certain offered load.
Network-layer Traffic Control Mechanisms
The actual algorithms or mechanism, that the DUT uses to
achieve service differentiation, is not important in
describing the expected vector.
Measurement Units:
N-octet packets per second
Issues:
See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Loss Vector
Expected Forwarding Vector
Expected Delay Vector
Expected Jitter Vector
3.2.3.4 Expected 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 behavior aggregates when a
specific traffic mix consisting of multiple behavior
aggregates is applied. This term attempts to capture the
expected delay behavior, for which the device is configured,
when subjected to a certain offered load.
The actual algorithms or mechanism, that the DUT uses to
achieve service differentiation, is not important in
describing the expected delay vector.
Measurement units:
Seconds.
Issues:
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
3.2.3.5 Expected Jitter Vector
Definition:
A vector describing the expected 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:
Jitter is the absolute value of the difference between the
delay measurement of two packets belonging to the same
stream.
The jitter 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 delay
and i is the test sequence number. Packets lost are not
counted in the jitter measurement.
Average Jitter is the average of the instantaneous jitter
measured during the test duration.
Peak-to-peak jitter is the maximum delay minus the minimum
delay of the packets forwarded by the DUT/SUT.
Measurement units:
Seconds (instantaneous)
Seconds P-P (peak to peak)
Seconds Avg (average)
Issues:
See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Forwarding Vector
3.2.4 Output Vectors
Network-layer Traffic Control Mechanisms
3.2.4.1 Forwarding 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 successfully transmit 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
Issues:
See Also:
Intended Vector
Offered Vector
Expected Vectors
Loss Vector
Sequence Vector
Delay Vector
Jitter Vector
3.2.4.2 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
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.
Issues:
See Also:
Intended Vector
Offered Vector
Expected Vectors
Forwarding Vector
Sequence Vector
Delay Vector
Jitter Vector
3.2.4.3 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 out of 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:
Network-layer Traffic Control Mechanisms
See Also:
Intended Vector
Offered Vector
Expected Vectors
Loss Vector
Forwarding Vector
Delay Vector
Jitter Vector
3.2.4.4 Delay Vector
Definition:
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:
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.
Delay vector is measured similarly 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.
Delay Vector is a per-hop measurement. The DUT/SUT may
change the specific DSCP or IP addresses and/or precedence value for a
multiple-hop measurement.
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
Issues:
See Also:
Delay
Network-layer Traffic Control Mechanisms
Intended Vector
Offered Vector
Expected Delay Vector
Loss Vector
Forwarding Vector
Jitter Vector
3.2.4.5 Jitter Vector
Definition:
The 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:
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 addresses. All precedence) value AND jitter value
combine to make a vector.
The jitter 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 delay
and i is the test sequence number. Packets lost are not
counted in the jitter measurement.
Jitter vector is a per-hop measurement. The DUT/SUT may
change the specific DSCP or IP precedence value for a
multiple-hop measurement.
Average Jitter is the average of the instantaneous jitter
measured during the test duration.
Peak-to-peak Jitter is the maximum delay minus the minimum
delay of the packets in a flow must enter on forwarded by the same ingress interface and exit on DUT/SUT.
Measurement units:
Seconds (instantaneous)
Seconds P-P (peak to peak)
Seconds Avg (average)
Issues:
See Also:
Intended Vector
Offered Vector
Expected Vectors
Network-layer Traffic Control Mechanisms
Loss Vector
Sequence Vector
Delay Vector
Forwarding Vector
3.3 Measurement Terms
3.3.1 Channel Capacity
Definition:
The maximum forwarding rate [2] at which none of the same egress
interface, and have some common network layer content.
Microflows [3] offered
packets are a subset dropped by the DUT/SUT.
Discussion:
Channel capacity measures the packet rate at the egress
interface(s) of flows. As defined in [3],
microflows require application-to-application measurement. the DUT/SUT. In contrast, flows use lower-layer classification criteria. Since
this document focuses on network-layer classification criteria,
we concentrate here throughput as
defined in RFC 1242 measures the packet rate is based on the use
ingress interface(s) of network-layer identifiers in
describing a flow. Flow identifiers also may reside at the
data-link, transport, or application layers DUT/SUT.
Ingress-based measurements do not account for congestion of
the ISO model.
However, identifiers other 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 those channel capacity because of queueing.
This measurement differs from forwarding rate at the network layer are
out maximum
offered load (FRMOL) [2] in that it is intolerant of scope for this document. loss.
Measurement units:
N-octet packets per second
Issues:
See Also:
Throughput [1]
Forwarding Rate at Maximum Offered Load [2]
3.3.2 Conforming
Definition:
Packets which lie within specific rate, delay, or jitter
bounds.
Discussion:
A flow DUT/SUT may contain be configured to allow a single code point/IP precedence value or
may contain multiple values destined for given traffic class to
consume a single egress
interface. This is determined by 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 test methodology. bounds are nonconforming.
Measurement units:
n/a
Issues:
See Also:
Microflow [3]
Network-layer Traffic Control Mechanisms
Streams
3.10
Expected Vector
Forwarding Vector
Offered Vector
Nonconforming
3.3.3 Nonconforming
Definition:
The number of packets per second for all packets containing a
single DSCP (or IP precedence)
Packets that a device can do not lie within specific rate, delay, or
jitter bounds.
Discussion:
A DUT/SUT may be observed to
successfully transmit configured to the correct destination interface in
response allow a given traffic class to an offered vector.
Discussion:
Forwarding Vector is expressed as pair
consume a given amount of numbers. Both the
codepoint (or IP precedence) value AND the packets per second
value combine bandwidth, or to make a vector.
The forwarding vector represents packet rate based on their
codepoint fall within
predefined delay or IP precedence value. It is jitter boundaries. All packets that do
not necessary based on
stream or flow. The forwarding vector may lie within these bounds are then said to be expresses as ôper
portö or ôof the DUT/SUTö.
nonconforming.
Measurement units:
n/a
Issues:
See Also:
Expected Vector
Forwarding Vector is a per-hop measurement.
Offered Vector
Conforming
3.3.4 Delay
Definition:
The time interval starting when the last bit of the input IP
packets reaches the input port of the DUT/SUT may
change and ending when
the codepoint or last bit of the output IP precedence value for a multiple-hop
measurement.
Measurement units:
N-octet packets per second
Issues:
See Also:
Codepoint Set
Expected Vector
Offered Vector.
3.11 Jitter
Definition:
Variation in a stream's delay.
Discussion:
Jitter is seen on the absolute value output
port of the difference between DUT/SUT.
Discussion:
Network-layer Traffic Control Mechanisms
Delay is measured the
delay measurement same regardless of two packets belonging to the same stream. 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 jitter between two consecutive packets in fact
that a stream is
reported as DUT/SUT's technology has a lower delay than another
technology should be visible.
By specifying the "instantaneous jitter". Instantaneous jitter
can metric to be expressed as |D(i) û D(i+1)| where D equals inside the delay
and i Internet protocol,
the tester is relieved from specifying the test sequence number. Packets lost start/end for
every data link layer protocol that IP runs on. This avoids
determining if the start/end delimiter are not
counted included in the jitter measurement.
Network-layer Traffic Control Mechanisms
Average Jitter is the average of
frame. Also heterogeneous data link protocol can be used in
a test.
The measurement point at the instantaneous jitter
measured during end is closely simulates the test duration.
Peak-to-peak jitter way
an internet datagram is processed. An internet datagram is
not passed up or down the maximum delay minus stack unless it is complete.
Completion occurs once the minimum
delay last bit of the packets forwarded by IP packet has been
received.
Delay can be run at any offered load. Recommend at or below
the DUT/SUT.
Measurement units:
Seconds (instantaneous)
Seconds P-P (peak to peak)
Seconds avg (average) channel capacity for non-congested delay. For congested
delay, run the offered load above the channel capacity.
Measurement units:
Seconds.
Issues:
Mean
Standard Deviation
Median
90th percentile
Inter Quartile Range
See Also:
Stream
3.12 Nonconforming
Latency [1]
3.3.5 Flow
Definition:
Packets that lie outside the parameter bounds
A flow is a one or more of packets sharing a given
traffic profile. common intended
pair of source and destination interfaces.
Discussion:
Rules may be configured for
Packets are grouped by the ingress and egress interfaces they
use on a given traffic class based on
parameters, such as an upper bound on the rate of packet
arrivals. DUT/SUT.
A flow can contain multiple source IP addresses and/or
destination IP addresses. All packets that lie outside in a flow must enter
on the bounds specified by same ingress interface and exit on the traffic profile, measured over same egress
interface, and have some common network layer content.
Microflows [3] are a period subset of time specified flows. As defined in the traffic profile, are said to be nonconforming.
Measurement units:
n/a
Issues:
See Also:
Conforming
3.13 Offered Vector
Definition: [3],
microflows require application-to-application measurement. In
contrast, flows use lower-layer classification criteria.
Since this document focuses on network-layer classification
Network-layer Traffic Control Mechanisms
A vector describing
criteria, we concentrate here on the rate at which packets having use of network-layer
identifiers in describing a specific
code-point are offered to flow. Flow identifiers also may
reside at the DUT/SUT.
Discussion:
Offered loads across data-link, transport, or application layers of
the different code-point classes,
constituting a code-point set, determine ISO model. However, identifiers other than those at the metrics associated
with
network layer are out of scope for this document.
A flow may contain a specific code-point traffic class. 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-octets packets per second units:
n/a
Issues:
Packet size.
See Also:
Expected Vector
Forwarding Vector
Codepoint Set
3.14
Microflow [3]
Streams
3.3.6 Stream
Definition:
A group of packets tracked as a single entity by the traffic
receiver. A stream shares may share a common content such as type
(IP, UDP), frame packet size, or payload.
Discussion:
Streams are tracked by "sequence number" 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
Issues:
Network-layer Traffic Control Mechanisms
See Also:
Flow
MicroFlow [3]
Network-layer Traffic Control Mechanisms
Test sequence number
3.15 Tail dropping
Definition:
The condition in which a congested DUT/SUT discards newly
arriving packets.
Discussion:
Every DUT/SUT has a finite amount of traffic it can forward,
beyond which congestion occurs. Once the offered load crosses
the congestion threshold, the device may discard any additional
traffic that arrives until congestion clears.
Tail dropping is typically a function of offered load exceeding
a DUT/SUTÆs buffer capacity, but other factors internal to the
DUT/SUT may also come into play. In terms of what is externally
observable, tail dropping can be said to occur only when
offered load exceeds channel capacity. Since a DUT/SUT may
buffer traffic on ingress, the actual threshold for tail
dropping may be higher than channel capacity.
Measurement units:
n/a
Issues:
Some congestion management mechanisms seek to avoid tail
dropping by discarding packets before offered load exceeds
channel capacity. In the presence of such mechanisms, neither
congestion nor tail dropping should occur.
See Also:
Channel capacity
Congestion
3.16
3.3.7 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
packet transmitted based on an algorithm agreed to by the
traffic receiver.
Network-layer Traffic Control Mechanisms
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 and 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
Issues:
See Also:
Stream
3.17 Unburdened
3.3.8 Undifferentiated Response
Definition:
A performance measure
The vector(s) obtained when mechanisms used to support diff-
serv or IP precedence and DiffServ are disabled.
Discussion:
Enabling Diffserv diff-serv or IP precedence mechanisms such as scheduling algorithms may impose an
additional processing overhead for packets, which packets. This overhead may
cause the aggregate response to suffer
degrade performance even when traffic belonging to only one
class, the best effort best-effort class, is offered to the device. Comparisons
Network-layer Traffic Control Mechanisms
Measurements with "unburdened performance" may
thus "undifferentiated response" should be in order when obtaining metrics made
to ensure that enabling
Diffserv mechanisms doesn't impose an excessive performance
penalty. 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
4. Security Considerations
Documents of this type do not directly effect affect the security of
the Internet or of corporate networks as long as benchmarking
is not performed on devices or systems connected to operating
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
Network-layer Traffic Control Mechanisms 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.
Network-layer Traffic Control Mechanisms
6. Author's 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
Telcordia Technologies
331 Newman Springs Road,
Navesink,
QNetworx Inc
1119 Campus Drive West
Morganville NJ 07701 07751
USA
Network-layer Traffic Control Mechanisms
Phone: + 1 732 758 5508
EMail: shobha@research.telcordia.com shobha@qnetworx.com
Scott Poretsky
Avici Systems
101 Billerica AveùBuilding Ave_Building #6
N. Billerica, MA 01862
USA
Phone: + 1 978 964 2287
EMail: sporetsky@avici.com
Network-layer Traffic Control Mechanisms
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Reserved.
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The limited permissions granted above are perpetual and will
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