Network Working Group Jerry Perser
INTERNET-DRAFT Spirent
Expires in: August 2003 David Newman
Network Test
Sumit Khurana
Telcordia
Shobha Erramilli
QNetworx
Scott Poretsky
Avici Systems
February 2002
Terminology for Benchmarking Network-layer
Traffic Control Mechanisms
<draft-ietf-bmwg-dsmterm-05.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 .............................................. 3
2. Existing definitions ...................................... 3
3. Term definitions ............................................4
3.1 Configuration Terms
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 ...................................................6
3.2 Measurement Terms
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3.2.1 Channel Capacity .......................................7
3.2.2 Conforming .............................................8
3.2.3 Nonconforming ..........................................8
3.2.4 Delay ..................................................9
3.2.5 Jitter ................................................10
3.2.6 Undifferentiated Response .............................11
3.3 Sequence Tracking
3.3.1 In-sequence Packet ....................................11
3.3.2 Out-of-order Packet ...................................12
3.3.3 Duplicate Packet ......................................12
3.3.4 Stream ................................................13
3.3.5 Test Sequence number .................................13
3.4 Vectors ...................................................14
3.4.1 Intended Vector .......................................14
3.4.2 Offered Vector ........................................15
3.4.3 Expected Vectors
3.4.3.1 Expected Forwarding Vector ........................15
3.4.3.2 Expected Loss Vector ..............................16
3.4.3.3 Expected Sequence Vector ..........................16
3.4.3.4 Expected Instantaneous Delay Vector ...............17
3.4.3.5 Expected Average Delay Vector .....................18
3.4.3.6 Expected Maximum Delay Vector .....................18
3.4.3.7 Expected Minimum Delay Vector .....................19
3.4.3.8 Expected Instantaneous Jitter Vector ..............20
3.4.3.9 Expected Average Jitter Vector ....................21
3.4.3.10 Expected Peak-to-peak Jitter Vector ..............21
3.4.4 Output Vectors
3.4.4.1 Forwarding Vector .................................22
3.4.4.2 Loss Vector .......................................22
3.4.4.3 Sequence Vector ...................................23
3.4.4.4 Instantaneous Delay Vector ........................24
3.4.4.5 Average Delay Vector ..............................25
3.4.4.6 Maximum Delay Vector ..............................26
3.4.4.7 Minimum Delay Vector ..............................26
3.4.4.8 Instantaneous Jitter Vector .......................27
3.4.4.9 Average Jitter Vector .............................28
3.4.4.10 Peak-to-peak Jitter Vector .......................29
4. Security Considerations ....................................30
5. Normative References .......................................30
6. Informative References .....................................31
7. Author's Address ...........................................32
8. Full Copyright Statement ...................................33
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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-
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 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.
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3. Term definitions
3.1 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:
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:
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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]. The overload definition assumes the congestion is
introduced strictly by the tester on ingress of a DUT/SUT.
That may or may not be the case here.
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 congestion on multiple egress
interfaces on the core device. In contrast, overload [Br91]
deals only with overload on ingress.
Packet Loss, not increased Delay, is the metric to indicate
the condition of Forwarding Congestion. Packet Loss is a
deterministic indicator of Forwarding Congestion. While
increased delay may be an indicator of Forwarding Congestion,
it is a non-deterministic indicator of Forwarding Congestion.
External observation of increased delay to indicate
congestion is in effect external observation of Incipient
Congestion. [Ra99] states that it is impractical to build a
black-box test to externally observe Incipient Congestion in
a router. For the purpose of "black-box" testing a DUT/SUT,
Packet Loss as the indicator of Forwarding Congestion is
used.
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 congested.
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 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.
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Forwarding Congestion, indicated by occurrence of packet
loss, is one type of congestion for a DUT/SUT. Congestion
Collapse [Na84] is defined as the state in which buffers are
full and all arriving packets must be dropped across the
network. Incipient Congestion [Ra99] is defined as
congestion that produces increased delay without packet loss.
The definition presented here explicitly defines Forwarding
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 under
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. Such mechanisms classify packets
based upon IP Precedence or DSCP settings in a packet's IP
header.
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
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.
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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, 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 [Ni98]
Streams
3.2 Measurement Terms
3.2.1 Channel Capacity
Definition:
The maximum forwarding rate [Ma98] 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.
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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) [Ma98] in that it is intolerant of loss.
Measurement units:
N-octet packets per second
See Also:
Throughput [Br91]
Forwarding Rate at Maximum Offered Load [Ma98]
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
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
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.
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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 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.
Delay is delay, regardless of the technology being measured.
2. 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. 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.
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4. Delay can be measured at any offered load, whereas latency
[Br99] is measured only at the throughput level.
For example, non-congested delay may be measured with an
offered load that does not exceed the channel capacity, while
congested delay may involve an offered load that exceeds
channel capacity.
5. Delay SHOULD NOT be used as an absolute indicator of
DUT/SUT Forwarding Congestion. While delay may rise when
offered load nears or exceeds channel capacity, there is no
universal point at which delay can be said to indicate the
presence or absence of Forwarding Congestion.
Measurement units:
Seconds.
See Also:
Latency [Br91]
Latency [Al99]
One-way Delay [Br99]
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 [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.
Measurement units:
Seconds
See Also:
Jitter variation [Ja99]
ipdv [De02]
interarrival jitter [Sc96]
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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 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) 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
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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
3.3.3 Duplicate Packet
Definition:
A received packet with a Test Sequence number matching a
previously received packet.
Discussion:
Measurement units:
Packet count
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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 [Ni98]
Test sequence number
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
packet transmitted based on an algorithm agreed to by the
traffic receiver.
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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.
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
Loss Vector
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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:
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
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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
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
One-way Packet Loss Metric [Ka99]
3.2.3.3 Expected Sequence Vector
Definition:
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.
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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.
The actual algorithm or mechanism the DUT uses to achieve
service differentiation is not important in describing the
expected delay vector.
Measurement units:
Seconds.
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See Also:
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
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.
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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 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.
Measurement units:
Seconds.
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See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Loss Vector
Expected Sequence Vector
Expected Forwarding Vector
Expected Jitter Vector
3.2.3.8 Expected Instantaneous Jitter Vector
Definition:
A vector describing the expected 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 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 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 measurement.
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:
Seconds
See Also:
Delay
Jitter
Offered Vector
Output Vectors
Expected Average Jitter Vector
Expected Peak-to-peak Jitter Vector
Stream
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3.2.3.9 Expected Average Jitter Vector
Definition:
A vector describing the expected jitter in 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 Jitter Vector is the average of all the Instantaneous
Jitter Vectors measured during the test duration for the same
DSCP or IP precedence value.
Measurement units:
Seconds
See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Instantaneous Jitter Vector
Expected Peak-to-peak Jitter Vector
3.2.3.10 Expected Peak-to-peak 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 Jitter Vector is the maximum delay minus the
minimum 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.
Measurement units:
Seconds
See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Instantaneous Jitter Vector
Expected Average Jitter Vector
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3.4.4 Output Vectors
3.4.4.1 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 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.
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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.
See Also:
Intended Vector
Offered Vector
Expected Vectors
Forwarding Vector
Sequence Vector
Delay Vectors
One-way Packet Loss Metric [Ka99]
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:
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See Also:
In-sequence Packet
Intended Vector
Offered Vector
Expected Vectors
Loss Vector
Forwarding Vector
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
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3.4.4.5 Average Delay Vector
Definition:
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
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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:
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.
Perser, Newman, Khurana, Erramilli, Poretsky [Page 26]
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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.
Minimum Delay Vector is based upon the minimum Instantaneous
Delay Vector of all packets in a Forwarding Vector.
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 Jitter Vector
Definition:
The 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 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.
Perser, Newman, Khurana, Erramilli, Poretsky [Page 27]
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The 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 delay and i is the test sequence
number. Packets lost are not counted in the measurement.
Instantaneous Jitter Vector is a per-hop measurement. The
DUT/SUT may change the specific DSCP or IP precedence value
for a multiple-hop measurement.
Forwarding Vector may contain several Instantaneous Jitter
Vectors. For n packets received in a Forwarding Vector,
there are exactly (n-1) Instantaneous Jitter Vectors.
Measurement units:
Seconds
See Also:
Delay
Jitter
Forwarding Vector
Stream
Expected Vectors
Average Jitter Vector
Peak-to-peak Jitter Vector
3.4.4.9 Average Jitter Vector
Definition:
The average 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 Jitter Vector is the average of all the Instantaneous
Jitter Vectors of the same DSCP or IP precedence value,
measured during the test duration.
Average 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 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
Perser, Newman, Khurana, Erramilli, Poretsky [Page 28]
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See Also:
Jitter
Forwarding Vector
Stream
Expected Vectors
Instantaneous Jitter Vector
Peak-to-peak Jitter Vector
3.4.4.10 Peak-to-peak Jitter 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 Jitter Vector is the maximum delay minus the
minimum delay of the packets (in a vector) forwarded by the
DUT/SUT.
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 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:
Seconds
See Also:
Jitter
Forwarding Vector
Stream
Expected Vectors
Average Jitter Vector
Peak-to-peak Jitter Vector
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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. Normative References
[Br91] Bradner, S., Editor, "Benchmarking Terminology for
Network Interconnection Devices", RFC 1242, July 1991.
[Ma98] Mandeville, R., "Benchmarking Terminology for LAN
Switching Devices", RFC 2285, February 1998.
[Ni98] 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.
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6. Informative References
[Al99] Almes, G., Kalidindi, S., Zekauskas, M., _A One-way Delay
Metric for IPPM_, RFC 2679, September 1999
[Bl98] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W.
Weiss, "An Architecture for Differentiated Services",
RFC 2475, December 1998.
[Br99] Bradner, S., McQuaid, J. _Benchmarking Methodology for
Network Interconnect Devices_, RFC 2544, March 1999
[De02] C. Demichelis, P. Chimento, _IP Packet Delay Variation
Metric for IPPM_, RFC 3393, November 2002
[Ja99] V. Jacobson, K. Nichols, K. Poduri, _An Expedited
Forwarding PHB_, RFC 2598, June 1999
[Ka99] Almes, G., Kalidindi, S., Zekauskas, M., _A One-way
Packet Loss Metric for IPPM_, RFC 2680, September 1999
[Ma91] A. Mankin, K. Ramakrishnan, _Gateway Congestion Control
Survey_, RFC 1254, August 1991
[Na84] Nagle, John, "Congestion Control in IP/TCP
Internetworks", RFC 896, January 1984.
[Ra99] Ramakrishnan, K. and Floyd, S., "A Proposal to add
Explicit Congestion Notification (ECN) to IP", RFC 2481,
January 1999.
[Sc96] H. Schulzrinne, GMD Fokus, S. Casner, R. Frederick,
V. Jacobson, _RTP: A Transport Protocol for Real-Time
Applications_, RFC 1889, January 1996
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7. 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
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8. 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.
Perser, Newman, Khurana, Erramilli, Poretsky [Page 33]