Network Working Group Jerry Perser
INTERNET-DRAFT
Expires in: October 2005 Scott Poretsky
Quarry Technologies
Shobha Erramilli
Qnetworx
Sumit Khurana
Telcordia
February 2005
Terminology for Benchmarking Network-layer
Traffic Control Mechanisms
<draft-ietf-bmwg-dsmterm-10.txt>
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Abstract
This document describes terminology for the benchmarking of
devices that implement traffic control based on IP precedence or
diff-serv code point criteria. The terminology is to be applied
to measurements made on the data plane to evaluate IP traffic
control meachanisms.
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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...................................................7
3.2 Measurement Terms
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
3.3.1 In-sequence Packet....................................12
3.3.2 Out-of-order Packet...................................12
3.3.3 Duplicate Packet......................................13
3.3.4 Stream................................................14
3.3.5 Test Sequence number .................................15
3.4 Vectors...................................................15
3.4.1 Intended Vector.......................................15
3.4.2 Offered Vector........................................16
3.4.3 Expected Vectors
3.4.3.1 Expected Forwarding Vector........................16
3.4.3.2 Expected Loss Vector..............................17
3.4.3.3 Expected Sequence Vector..........................18
3.4.3.4 Expected Instantaneous Delay Vector...............18
3.4.3.5 Expected Average Delay Vector.....................19
3.4.3.6 Expected Maximum Delay Vector.....................10
3.4.3.7 Expected Minimum Delay Vector.....................20
3.4.3.8 Expected Instantaneous Jitter Vector..............21
3.4.3.9 Expected Average Jitter Vector....................22
3.4.3.10 Expected Peak-to-peak Jitter Vector..............22
3.4.4 Output Vectors
3.4.4.1 Forwarding Vector.................................23
3.4.4.2 Loss Vector.......................................24
3.4.4.3 Sequence Vector...................................24
3.4.4.4 Instantaneous Delay Vector........................25
3.4.4.5 Average Delay Vector..............................26
3.4.4.6 Maximum Delay Vector..............................27
3.4.4.7 Minimum Delay Vector..............................28
3.4.4.8 Instantaneous Jitter Vector.......................28
3.4.4.9 Average Jitter Vector.............................29
3.4.4.10 Peak-to-peak Jitter Vector.......................30
4. Acknowledgments............................................31
5. Security Considerations....................................31
6. Normative References.......................................31
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7. Informative References.....................................32
8. Author's Address...........................................33
9. Full Copyright Statement...................................34
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 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 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.
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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: None
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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]. 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.
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] implies that it is impractical to build a black-box
test to externally observe Incipient Congestion indicated by
increased delay in a router. [Ra99] introduces Explicit
Congestion Notification (ECN) as the externally observable,
deterministic method for indicating Incipient Congestion.
Because [Ra99] is an Experimental RFC with limited
deployment, ECN is not used for this particular methodology.
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 to be in a state of Forwarding
Congestion.
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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. Even though ingress interfaces accept all
packets without loss, Forwarding Congestion is present in
this hypothetical device.
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 packets IP
header.
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:
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3.1.5 Flow
Definition:
A flow is a one or more of packets sharing a common intended
pair of source and destination interfaces.
Discussion:
Packets are grouped by the ingress and egress interfaces they
use on a given DUT/SUT.
A flow can contain multiple source IP addresses and/or
destination IP addresses. All packets in a flow MUST enter
on the same ingress interface and exit on the same egress
interface, and have some common network layer content.
Microflows [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 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 successfully transmit to the correct destination
interface in response to a specified offered load while the
device drops none of the offered packets.
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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 frame 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 queuing. 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 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 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
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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.
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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 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 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:
Seconds.
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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 received packets belonging to the
same stream.
Discussion:
The 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 delay and i
is the order the packets were received.
Under loss, jitter can be measured between non-consecutive
test sequence numbers. When Traffic Control Mechanisms are
losing packets, the Forwarding Delay may fluctuate as a
response. Jitter MUST be able to benchmark the delay
variation with or with out 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.
Measurement units:
Seconds
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.
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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 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 packets 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
See Also:
Stream
Test Sequence number
3.3.2 Out-of-order Packet
Definition:
A received packet with a Test Sequence number less than
expected.
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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 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
Packet Reordering Metric for IPPM [Mo03]
3.3.3 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.
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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 offered packet to the
DUT/SUT MUST contain a unique packet-by-packet identifier.
Measurement units:
Packet count
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" [Ma00]. Streams define how individual
packets statistic 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 multicast stream can be forward to
multiple destination interfaces.
Measurement units:
n/a
See Also:
Flow
Microflow [Ni98]
Test sequence number
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3.3.5 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.
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-of-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 attempted rate at which packets
having a specific code-point (or IP precedence) are
transmitted to a DUT/SUT by an external source.
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
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See Also:
Offered Vector
Expected Forwarding Vector
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
Forwarding Vector
Loss Vector
3.4.2 Offered Vector
Definition:
A vector describing the measured rate at which packets having
a specific DSCP or IP precedence value are offered to the
DUT/SUT.
Discussion:
Offered loads across the different code-point classes,
constituting a code-point set, determine the metrics
associated with a specific code-point traffic class.
Measurement Units:
N-octets packets per second
See Also:
Expected Forwarding Vector
Expected Loss Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
Forwarding Vector
Codepoint Set
3.4.3 Expected Vectors
3.4.3.1 Expected Forwarding Vector
Definition:
A vector describing the expected output rate of packets
having a specific DSCP or IP precedence value. The value is
dependent on the set of offered vectors and configuration of
the DUT.
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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 forwarding vector.
Measurement units:
N-octet packets per second
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 vector.
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 is expected to be
dropped.
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See Also:
Intended Vector
Offered Vector
Expected Forwarding Vector
Expected Sequence Vector
Expected Delay Vector
Expected Jitter Vector
One-way Packet Loss Metric [Ka99]
3.4.3.3 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.
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.
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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 delay vector.
Measurement units:
Seconds.
See Also:
Forwarding Delay
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.
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See Also:
Intended Vector
Offered Vector
Output Vectors
Expected Loss Vector
Expected Sequence Vector
Expected Forwarding Vector
Expected Jitter Vector
3.4.3.6 Expected Maximum Delay Vector
Definition:
A vector describing the expected maximum delay for packets
having a specific DSCP or IP precedence value. The value is
dependent on the set of offered vectors and configuration of
the DUT.
Discussion:
The DUT is configured in a certain way in order that service
differentiation occurs for a particular DSCP or IP precedence
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.
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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 minimum 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
3.4.3.8 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 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
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See Also:
Delay
Jitter
Offered Vector
Output Vectors
Expected Average Jitter Vector
Expected Peak-to-peak Jitter Vector
Stream
3.4.3.9 Expected Average Jitter Vector
Definition:
A vector describing the expected jitter in packet arrival
times 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:
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
3.4.3.10 Expected Peak-to-peak Jitter Vector
Definition:
A vector describing the expected maximum variation in the
delay of packet arrival times for packets having a 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.
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Measurement units:
Seconds
See Also:
Intended Vector
Offered Vector
Output Vectors
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 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
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3.4.4.2 Loss Vector
Definition:
The percentage of packets containing a 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.
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 is 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.
Perser, Erramilli, Poretsky, Khurana [Page 24]
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The Sequence Vector represents packet rate based on its
specific DSCP or IP precedence value. It is not necessarily
based on a stream or flow. The Sequence Vector may be
expressed as per port of the DUT/SUT. However, it MUST be
consistent with the Expected Sequence Vector.
Sequence Vector is a per-hop measurement. The DUT/SUT may
change the specific DSCP or IP precedence value for a
multiple-hop measurement.
Measurement Units:
N-octet packets per second
Issues:
See Also:
In-sequence Packet
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 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:
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 Forwarding Capacity in the
absence of forwarding congestion. For congested delay, run
the offered load above the Forwarding Capacity.
Perser, Erramilli, Poretsky, Khurana [Page 25]
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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
3.4.4.5 Average Delay Vector
Definition:
The average delay for 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:
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 Forwarding Capacity in the absence
of congestion. For congested delay, run the offered load
above the Forwarding Capacity.
Measurement Units:
Seconds
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See Also:
Delay
Intended Vector
Offered Vector
Expected Delay Vectors
Instantaneous Delay Vector
Maximum Delay Vector
Minimum Delay Vector
3.4.4.6 Maximum Delay Vector
Definition:
The maximum delay from all packets containing 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:
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
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3.4.4.7 Minimum Delay Vector
Definition:
The minimum delay from 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:
Delay vector is expressed as pair of numbers. Both the
specific DSCP (or IP precedence) value AND delay value
combine to make a vector.
The Minimum Delay Vector represents delay on its specific
DSCP or IP precedence value. It is not necessarily based on
a stream or flow. The Minimum Delay vector may be expressed
as per port of the DUT/SUT. However, it MUST be consistent
with the Expected Delay vector.
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 Forwarding Capacity in the absence
of congestion. For congested delay, run the offered load
above the Forwarding 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 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.
Perser, Erramilli, Poretsky, Khurana [Page 28]
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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.
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 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:
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.
Perser, Erramilli, Poretsky, Khurana [Page 29]
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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
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 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:
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. Acknowledgments
The authors gratefully acknowledge the contributions of the
IETF's benchmarking 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 following
individuals also made noteworthy contributions to the
editors' understanding of the subject matter: John Dawson,
Kevin Dubray, and Kathleen Nichols.
5. 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.
6. 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", RFC 2119, March 1997
[Ma98] Mandeville, R., "Benchmarking Terminology for LAN
Switching Devices", RFC 2285, February 1998.
[Ni98] Nichols, K., Blake, S., Baker, F., Black, D., "Definition
of the Differentiated Services Field (DS Field) in the
IPv4 and IPv6 Headers", RFC 2474, December 1998.
Perser, Erramilli, Poretsky, Khurana [Page 31]
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7. Informative References
[Al99] Almes, G., Kalidindi, S., Zekauskas, M., "A One-way Delay
Metric for IPPM", RFC 2679, September 1999
[Bl98] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
Weiss, W., "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] Demichelis, C., Chimento, P., "IP Packet Delay Variation
Metric for IPPM", RFC 3393, November 2002
[Ja99] Jacobson, V., Nichols, K., Poduri, K., "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] Mankin, A., Ramakrishnan, K., "Gateway Congestion Control
Survey", RFC 1254, August 1991
[Ma00] Mandeville, R., Perser, J., "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. and Floyd, S., "A Proposal to add
Explicit Congestion Notification (ECN) to IP", RFC 2481,
January 1999.
[Sc96] Schulzrinne, H., Casner, S., Frederick, R., Jacobson, V.,
"RTP: A Transport Protocol for Real-Time Applications",
RFC 1889, January 1996
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8. Authors' Addresses
Jerry Perser
USA
Phone:
EMail: jerry@perser.org
Scott Poretsky
Quarry Technologies
8 New England Executive Park
Burlington, MA 01803
USA
Phone: + 1 508 439 9008
EMail: sporetsky@quarrytech.com
Shobha Erramilli
QNetworx Inc
1119 Campus Drive West
Morganville, NJ 07751
USA
Phone:
EMail: shobha@qnetworx.com
Sumit Khurana
Telcordia Technologies
445 South Street
Morristown, NJ 07960
USA
Phone: + 1 973 829 3170
EMail: sumit@research.telcordia.com
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The IETF invites any interested party to bring to its attention any
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dard. Please address the information to the IETF at ietf-ipr@ietf.org.
Disclaimer of Warranty
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMA-
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Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and except as
set forth therein, the authors retain all their rights.
Perser, Erramilli, Poretsky, Khurana [Page 34]
