draft-ietf-bmwg-dsmterm-03.txt   draft-ietf-bmwg-dsmterm-04.txt 
Network Working Group Jerry Perser Network Working Group Jerry Perser
INTERNET-DRAFT Spirent INTERNET-DRAFT Spirent
Expires in: December 2002 David Newman Expires in: April 2003 David Newman
Network Test Network Test
Sumit Khurana Sumit Khurana
Telcordia Telcordia
Shobha Erramilli Shobha Erramilli
QNetworx QNetworx
Scott Poretsky Scott Poretsky
Avici Systems Avici Systems
June 2002 October 2002
Terminology for Benchmarking Network-layer Terminology for Benchmarking Network-layer
Traffic Control Mechanisms Traffic Control Mechanisms
<draft-ietf-bmwg-dsmterm-03.txt> <draft-ietf-bmwg-dsmterm-04.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 2, line 10 skipping to change at page 2, line 10
3.1.3 Congestion .............................................4 3.1.3 Congestion .............................................4
3.1.4 Congestion Management ..................................5 3.1.4 Congestion Management ..................................5
3.1.5 Flow ...................................................6 3.1.5 Flow ...................................................6
3.2 Measurement Terms 3.2 Measurement Terms
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
3.2.1 Channel Capacity .......................................7 3.2.1 Channel Capacity .......................................7
3.2.2 Conforming .............................................7 3.2.2 Conforming .............................................7
3.2.3 Nonconforming ..........................................8 3.2.3 Nonconforming ..........................................8
3.2.4 Delay ..................................................8 3.2.4 Delay ..................................................8
3.2.6 Undifferentiated Response ................................9 3.2.5 Jitter .................................................9
3.2.6 Undifferentiated Response .............................10
3.3 Sequence Tracking 3.3 Sequence Tracking
3.3.1 In-sequence Packet .....................................9 3.3.1 In-sequence Packet ....................................10
3.3.2 Out-of-order Packet ...................................10 3.3.2 Out-of-order Packet ...................................11
3.3.3 Duplicate Packet ......................................11 3.3.3 Duplicate Packet ......................................11
3.3.4 Stream ................................................11 3.3.4 Stream ................................................12
3.3.5 Test Sequence number .................................12 3.3.5 Test Sequence number .................................12
3.4 Vectors ...................................................12 3.4 Vectors ...................................................13
3.4.1 Intended Vector .......................................12 3.4.1 Intended Vector .......................................13
3.4.2 Offered Vector ........................................13 3.4.2 Offered Vector ........................................14
3.4.3 Expected Vectors 3.4.3 Expected Vectors
3.4.3.1 Expected Forwarding Vector ........................13 3.4.3.1 Expected Forwarding Vector ........................14
3.4.3.2 Expected Loss Vector ..............................14 3.4.3.2 Expected Loss Vector ..............................15
3.4.3.3 Expected Sequence Vector ..........................14 3.4.3.3 Expected Sequence Vector ..........................16
3.4.3.4 Expected Instantaneous Delay Vector ...............15 3.4.3.4 Expected Instantaneous Delay Vector ...............16
3.4.3.5 Expected Average Delay Vector .....................16 3.4.3.5 Expected Average Delay Vector .....................17
3.4.3.6 Expected Maximum Delay Vector .....................17 3.4.3.6 Expected Maximum Delay Vector .....................17
3.4.3.7 Expected Minimum Delay Vector .....................17 3.4.3.7 Expected Minimum Delay Vector .....................18
3.4.3.8 Expected Instantaneous Delay Variation Vector .....18 3.4.3.8 Expected Instantaneous Jitter Vector ..............19
3.4.3.9 Expected Average Delay Variation Vector ...........19 3.4.3.9 Expected Average Jitter Vector ....................19
3.4.3.10 Expected Peak-to-peak Delay Variation Vector .....19 3.4.3.10 Expected Peak-to-peak Jitter Vector ..............20
3.4.4 Output Vectors 3.4.4 Output Vectors
3.4.4.1 Forwarding Vector .................................20 3.4.4.1 Forwarding Vector .................................21
3.4.4.2 Loss Vector .......................................20 3.4.4.2 Loss Vector .......................................21
3.4.4.3 Sequence Vector ...................................21 3.4.4.3 Sequence Vector ...................................22
3.4.4.4 Instantaneous Delay Vector ........................22 3.4.4.4 Instantaneous Delay Vector ........................23
3.4.4.5 Average Delay Vector ..............................23 3.4.4.5 Average Delay Vector ..............................24
3.4.4.6 Maximum Delay Vector ..............................23 3.4.4.6 Maximum Delay Vector ..............................25
3.4.4.7 Minimum Delay Vector ..............................24 3.4.4.7 Minimum Delay Vector ..............................25
3.4.4.8 Instantaneous Delay Variation Vector ..............25 3.4.4.8 Instantaneous Jitter Vector .......................26
3.4.4.9 Average Delay Variation Vector ....................26 3.4.4.9 Average Jitter Vector .............................27
3.4.4.10 Peak-to-peak Delay Variation Vector ..............27 3.4.4.10 Peak-to-peak Jitter Vector .......................28
4. Security Considerations ....................................28 4. Security Considerations ....................................29
5. References .................................................28 5. References .................................................29
6. Author's Address ...........................................29 6. Author's Address ...........................................30
7. Full Copyright Statement ...................................30 7. Full Copyright Statement ...................................31
1. Introduction 1. Introduction
This document describes terminology for the benchmarking of This document describes terminology for the benchmarking of
devices that implement traffic control based on IP precedence or devices that implement traffic control based on IP precedence or
diff-serv code point criteria. diff-serv code point criteria.
New terminology is needed because most existing measurements New terminology is needed because most existing measurements
assume the absence of congestion and only a single per-hop- assume the absence of congestion and only a single per-hop-
Network-layer Traffic Control Mechanisms
behavior. This document introduces several new terms that will behavior. This document introduces several new terms that will
allow measurements to be taken during periods of congestion. allow measurements to be taken during periods of congestion.
Network-layer Traffic Control Mechanisms
Another key difference from existing terminology is the definition Another key difference from existing terminology is the definition
of measurements as observed on egress as well as ingress of a of measurements as observed on egress as well as ingress of a
device/system under test. Again, the existence of congestion device/system under test. Again, the existence of congestion
requires the addition of egress measurements as well as those requires the addition of egress measurements as well as those
taken on ingress; without observing traffic leaving a taken on ingress; without observing traffic leaving a
device/system it is not possible to say whether traffic-control device/system it is not possible to say whether traffic-control
mechanisms effectively dealt with congestion. mechanisms effectively dealt with congestion.
The principal measurements introduced in this document are vectors The principal measurements introduced in this document are vectors
for rate, delay, and jitter, all of which can be observed with or for rate, delay, and jitter, all of which can be observed with or
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"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
RFC 2119. RFC 2119.
3. Term definitions 3. Term definitions
3.1 Configuration Terms 3.1 Configuration Terms
3.1.1 Classification 3.1.1 Classification
Definition: Definition:
Selection of packets based on the contents of packet header
according to defined rules.
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
Selection of packets based on the contents of packet header
according to defined rules.
Discussion: Discussion:
Packets can be selected based on the DS field or IP Packets can be selected based on the DS field or IP
Precedence in the packet header. Classification can also be Precedence in the packet header. Classification can also be
based on Multi-Field (MF) criteria such as IP Source and based on Multi-Field (MF) criteria such as IP Source and
destination addresses, protocol and port number. destination addresses, protocol and port number.
Classification determines the per-hop behaviors and traffic Classification determines the per-hop behaviors and traffic
conditioning functions such as shaping and dropping that are conditioning functions such as shaping and dropping that are
to be applied to the packet. to be applied to the packet.
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Measurement Units: Measurement Units:
n/a n/a
See Also: See Also:
3.1.3 Congestion 3.1.3 Congestion
Definition: Definition:
A condition in which one or more egress interfaces are A condition in which one or more egress interfaces are
offered more packets than are forwarded at any given instant. offered more packets than are forwarded.
Discussion: Discussion:
This condition is a superset of the overload definition [2].
The overload definition assumes the congestion is introduced
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
This condition is a superset of the overload definition [2].
The overload definition assumes the congestion is introduced
strictly by the tester on ingress of a DUT/SUT. That may or strictly by the tester on ingress of a DUT/SUT. That may or
may not be the case here. may not be the case here.
Another difference between congestion and overload occurs Another difference between congestion and overload occurs
when the SUT comprises multiple elements, in that congestion when the SUT comprises multiple elements, in that congestion
may occur at multiple points. Consider an SUT comprising may occur at multiple points. Consider an SUT comprising
multiple edge devices exchanging traffic with a single core multiple edge devices exchanging traffic with a single core
device. Depending on traffic patterns, the edge devices may device. Depending on traffic patterns, the edge devices may
induce congestion on multiple egress interfaces on the core induce congestion on multiple egress interfaces on the core
device. In contrast, overload [1] deals only with overload on device. In contrast, overload [1] deals only with overload on
ingress. ingress.
Throughput [1] defines the lower boundary of congestion.
Throughput is the maximum offered rate with no congestion.
At offered rates above throughput, the DUT/SUT is considered
congested.
Ingress observations alone are not sufficient to cover all Ingress observations alone are not sufficient to cover all
cases in which congestion may occur. A device with an cases in which congestion may occur. A device with an
infinite amount of memory could buffer an infinite amount of infinite amount of memory could buffer an infinite amount of
packets, and eventually forward all of them. However, these packets, and eventually forward all of them. However, these
packets may or may not be forwarded during the test duration. packets may or may not be forwarded during the test duration.
Even though ingress interfaces accept all packets without Even though ingress interfaces accept all packets without
loss, this hypothetical device may still be congested. loss, this hypothetical device may still be congested.
The definition presented here explicitly defines congestion The definition presented here explicitly defines congestion
as an event observable on egress interfaces. Regardless of as an event observable on egress interfaces. Regardless of
internal architecture, any device that cannot forward packets internal architecture, any device that cannot forward packets
on one or more egress interfaces is congested. on one or more egress interfaces is congested.
Measurement units: Measurement units:
n/a none
See Also: See Also:
Gateway Congestion Control Survey [8]
3.1.4 Congestion Management 3.1.4 Congestion Management
Definition: Definition:
An implementation of one or more per-hop-behaviors to avoid An implementation of one or more per-hop-behaviors to avoid
or minimize the condition of congestion. or minimize the condition of congestion.
Discussion: Discussion:
Congestion management may seek either to control congestion Congestion management may seek either to control congestion
or avoid it altogether. Such mechanisms classify packets or avoid it altogether. Such mechanisms classify packets
based upon IP Precedence or DSCP settings in a packet's IP based upon IP Precedence or DSCP settings in a packet's IP
header. header.
Network-layer Traffic Control Mechanisms
Congestion avoidance mechanisms seek to prevent congestion Congestion avoidance mechanisms seek to prevent congestion
before it actually occurs. before it actually occurs.
Congestion control mechanisms gives one or flows (with a Congestion control mechanisms gives one or flows (with a
discrete IP Precedence or DSCP value) preferential treatment discrete IP Precedence or DSCP value) preferential treatment
over other classes during periods of congestion. over other classes during periods of congestion.
Measurement units: Measurement units:
n/a n/a
Network-layer Traffic Control Mechanisms
See Also: See Also:
3.1.5 Flow 3.1.5 Flow
Definition: Definition:
A flow is a one or more of packets sharing a common intended A flow is a one or more of packets sharing a common intended
pair of source and destination interfaces. pair of source and destination interfaces.
Discussion: Discussion:
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3.2.2 Conforming 3.2.2 Conforming
Definition: Definition:
Packets which lie within specific rate, delay, or jitter Packets which lie within specific rate, delay, or jitter
bounds. bounds.
Discussion: Discussion:
A DUT/SUT may be configured to allow a given traffic class to A DUT/SUT may be configured to allow a given traffic class to
consume a given amount of bandwidth, or to fall within consume a given amount of bandwidth, or to fall within
Network-layer Traffic Control Mechanisms
predefined delay or jitter boundaries. All packets that lie predefined delay or jitter boundaries. All packets that lie
within specified bounds are then said to be conforming, within specified bounds are then said to be conforming,
whereas those outside the bounds are nonconforming. whereas those outside the bounds are nonconforming.
Measurement units: Measurement units:
n/a n/a
See Also: See Also:
Expected Vector Expected Vector
Network-layer Traffic Control Mechanisms
Forwarding Vector Forwarding Vector
Offered Vector Offered Vector
Nonconforming Nonconforming
3.2.3 Nonconforming 3.2.3 Nonconforming
Definition: Definition:
Packets that do not lie within specific rate, delay, or Packets that do not lie within specific rate, delay, or
jitter bounds. jitter bounds.
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the last bit of the output IP packet is seen on the output the last bit of the output IP packet is seen on the output
port of the DUT/SUT. port of the DUT/SUT.
Discussion: Discussion:
Delay is measured the same regardless of the type of DUT/SUT. Delay is measured the same regardless of the type of DUT/SUT.
Latency [1] require some knowledge of whether the DUT/SUT is Latency [1] require some knowledge of whether the DUT/SUT is
a "store and forward" or a "bit forwarding" device. The fact a "store and forward" or a "bit forwarding" device. The fact
that a DUT/SUT's technology has a lower delay than another that a DUT/SUT's technology has a lower delay than another
technology should be visible. technology should be visible.
Network-layer Traffic Control Mechanisms
By specifying the metric to be inside the Internet protocol, By specifying the metric to be inside the Internet protocol,
the tester is relieved from specifying the start/end for the tester is relieved from specifying the start/end for
every data link layer protocol that IP runs on. This avoids every data link layer protocol that IP runs on. This avoids
determining if the start/end delimiters are included in the determining if the start/end delimiters are included in the
frame. Also heterogeneous data link protocol can be used in frame. Also heterogeneous data link protocol can be used in
a test. a test.
The measurement point at the end closely simulates the way an The measurement point at the end closely simulates the way an
internet datagram is processed. An internet datagram is not internet datagram is processed. An internet datagram is not
Network-layer Traffic Control Mechanisms
passed up or down the stack unless it is complete. passed up or down the stack unless it is complete.
Completion occurs once the last bit of the IP packet has been Completion occurs once the last bit of the IP packet has been
received. received.
Delay can be run at any offered load. Recommend at or below Delay can be run at any offered load. Recommend at or below
the channel capacity for non-congested delay. For congested the channel capacity for non-congested delay. For congested
delay, run the offered load above the channel capacity. delay, run the offered load above the channel capacity.
Measurement units: Measurement units:
Seconds. Seconds.
See Also: See Also:
Latency [1] Latency [1]
3.2.5 Jitter
Definition:
The absolute value of the difference between the arrival
delay of two consecutive packets belonging to the same
stream.
Discussion:
The delay fluctuation between two consecutive packets in a
stream is reported as the jitter. Jitter can be expressed as
|D(i) - D(i-1)| where D equals the delay and i is the test
sequence number. The measurement does not include lost
packets.
Jitter can be determined by the ipdv [6] (IP Delay Variation)
by taking the absolute value of the ipdv. The two metrics
will produce different mean values. _Mean Jitter_ will
produce a positive value, where the _mean ipdv_ is typically
zero.
Measurement units:
Seconds
See Also:
Jitter variation [5]
ipdv [6]
interarrival jitter [7]
Network-layer Traffic Control Mechanisms
3.2.6 Undifferentiated Response 3.2.6 Undifferentiated Response
Definition: Definition:
The vector(s) obtained when mechanisms used to support diff- The vector(s) obtained when mechanisms used to support diff-
serv or IP precedence are disabled. serv or IP precedence are disabled.
Discussion: Discussion:
Enabling diff-serv or IP precedence mechanisms may impose Enabling diff-serv or IP precedence mechanisms may impose
additional processing overhead for packets. This overhead may additional processing overhead for packets. This overhead may
degrade performance even when traffic belonging to only one degrade performance even when traffic belonging to only one
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Definition: Definition:
A received packet with the expected Test Sequence number. A received packet with the expected Test Sequence number.
Discussion: Discussion:
In-sequence is done on a stream level. As packets are In-sequence is done on a stream level. As packets are
received on a stream, each packet's Test Sequence number is received on a stream, each packet's Test Sequence number is
compared with the previous packet. Only packets that match compared with the previous packet. Only packets that match
the expected are considered in-sequence. the expected are considered in-sequence.
Network-layer Traffic Control Mechanisms
Packets that do not match the expected Test Sequence number Packets that do not match the expected Test Sequence number
are counted as _not in-sequence_ or out-of-sequence. Every are counted as _not in-sequence_ or out-of-sequence. Every
packet that is received is either in-sequence or out-of- packet that is received is either in-sequence or out-of-
sequence. Subtracting the in-sequence from the received sequence. Subtracting the in-sequence from the received
packets (for that stream) can derive the out-of-sequence packets (for that stream) can derive the out-of-sequence
count. count.
Two types of events will prevent the in-sequence from Two types of events will prevent the in-sequence from
incrementing: packet loss and reordered packets. incrementing: packet loss and reordered packets.
Measurement units: Measurement units:
Packet count Packet count
Network-layer Traffic Control Mechanisms
See Also: See Also:
Stream Stream
Test Sequence number Test Sequence number
3.3.2 Out-of-order Packet 3.3.2 Out-of-order Packet
Definition: Definition:
A received packet with a Test Sequence number less that A received packet with a Test Sequence number less that
expected. expected.
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Packet loss does not affect the Out-of-order Packet count. Packet loss does not affect the Out-of-order Packet count.
Only packets that were not received in the order that they Only packets that were not received in the order that they
were transmitted. were transmitted.
Measurement units: Measurement units:
Packet count Packet count
See Also: See Also:
Stream Stream
Test Sequence number Test Sequence number
Network-layer Traffic Control Mechanisms
3.3.3 Duplicate Packet 3.3.3 Duplicate Packet
Definition: Definition:
A received packet with a Test Sequence number matching a A received packet with a Test Sequence number matching a
previously received packet. previously received packet.
Discussion: Discussion:
Measurement units: Measurement units:
Packet count Packet count
Network-layer Traffic Control Mechanisms
See Also: See Also:
Stream Stream
Test Sequence number Test Sequence number
3.3.4 Stream 3.3.4 Stream
Definition: Definition:
A group of packets tracked as a single entity by the traffic A group of packets tracked as a single entity by the traffic
receiver. A stream may share a common content such as type receiver. A stream may share a common content such as type
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a single entity. A mulitcast stream can be forward to a single entity. A mulitcast stream can be forward to
multiple destination interfaces. multiple destination interfaces.
Measurement units: Measurement units:
n/a n/a
See Also: See Also:
Flow Flow
MicroFlow [3] MicroFlow [3]
Test sequence number Test sequence number
Network-layer Traffic Control Mechanisms
3.3.6 Test Sequence number 3.3.6 Test Sequence number
Definition: Definition:
A field in the IP payload portion of the packet that is used 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 to verify the order of the packets on the egress of the
DUT/SUT. DUT/SUT.
Discussion: Discussion:
The traffic generator sets the test sequence number value and The traffic generator sets the test sequence number value and
the traffic receiver checks the value upon receipt of the the traffic receiver checks the value upon receipt of the
packet. The traffic generator changes the value on each packet. The traffic generator changes the value on each
Network-layer Traffic Control Mechanisms
packet transmitted based on an algorithm agreed to by the packet transmitted based on an algorithm agreed to by the
traffic receiver. traffic receiver.
The traffic receiver keeps track of the sequence numbers on a The traffic receiver keeps track of the sequence numbers on a
per stream basis. In addition to number of received packets, per stream basis. In addition to number of received packets,
the traffic receiver may also report number of in-sequence the traffic receiver may also report number of in-sequence
packets, number of out-sequence packets, number of duplicate packets, number of out-sequence packets, number of duplicate
packets, and number of reordered packets. packets, and number of reordered packets.
The recommended algorithm to use to change the sequence The recommended algorithm to use to change the sequence
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A vector describing the rate at which packets having a A vector describing the rate at which packets having a
specific code-point (or IP precedence) that an external specific code-point (or IP precedence) that an external
source attempts to transmit to a DUT/SUT. source attempts to transmit to a DUT/SUT.
Discussion: Discussion:
Intended loads across the different code-point classes Intended loads across the different code-point classes
determine the metrics associated with a specific code-point determine the metrics associated with a specific code-point
traffic class. traffic class.
Network-layer Traffic Control Mechanisms
Measurement Units: Measurement Units:
N-octets packets per second N-octets packets per second
See Also: See Also:
Offered Vector Offered Vector
Expected Forwarding Vector Expected Forwarding Vector
Expected Loss Vector Expected Loss Vector
Expected Sequence Vector Expected Sequence Vector
Expected Delay Vector Expected Delay Vector
Expected Jitter Vector Expected Jitter Vector
Forwarding Vector Forwarding Vector
Network-layer Traffic Control Mechanisms
Loss Vector Loss Vector
3.4.2 Offered Vector 3.4.2 Offered Vector
Definition: Definition:
A vector describing the measured rate at which packets having A vector describing the measured rate at which packets having
a specific DSCP or IP precedence value are offered to the a specific DSCP or IP precedence value are offered to the
DUT/SUT. DUT/SUT.
Discussion: Discussion:
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3.4.3.1 Expected Forwarding Vector 3.4.3.1 Expected Forwarding Vector
Definition: Definition:
A vector describing the expected output rate of packets A vector describing the expected output rate of packets
having a specific DSCP or IP precedence value. The value is having a specific DSCP or IP precedence value. The value is
dependent on the set of offered vectors and configuration of dependent on the set of offered vectors and configuration of
the DUT. the DUT.
Discussion: Discussion:
Network-layer Traffic Control Mechanisms
The DUT is configured in a certain way in order that service The DUT is configured in a certain way in order that service
differentiation occurs for a particular DSCP or IP precedence differentiation occurs for a particular DSCP or IP precedence
value when a specific traffic mix consisting of multiple value when a specific traffic mix consisting of multiple
DSCPs or IP precedence values are applied. This term attempts DSCPs or IP precedence values are applied. This term attempts
to capture the expected forwarding behavior when subjected to to capture the expected forwarding behavior when subjected to
a certain offered vectors. a certain offered vectors.
The actual algorithm or mechanism the DUT uses to achieve The actual algorithm or mechanism the DUT uses to achieve
service differentiation is not important in describing the service differentiation is not important in describing the
expected forwarding vector. expected forwarding vector.
Measurement units: Measurement units:
N-octet packets per second N-octet packets per second
Network-layer Traffic Control Mechanisms
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Loss Vector Expected Loss Vector
Expected Sequence Vector Expected Sequence Vector
Expected Delay Vector Expected Delay Vector
Expected Jitter Vector Expected Jitter Vector
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expected loss vector. expected loss vector.
Measurement Units: Measurement Units:
Percentage of intended packets that are expected to be Percentage of intended packets that are expected to be
dropped. dropped.
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Expected Forwarding Vector Expected Forwarding Vector
Network-layer Traffic Control Mechanisms
Expected Sequence Vector Expected Sequence Vector
Expected Delay Vector Expected Delay Vector
Expected Jitter Vector Expected Jitter Vector
3.2.3.3 Expected Sequence Vector 3.2.3.3 Expected Sequence Vector
Definition: Definition:
Network-layer Traffic Control Mechanisms
A vector describing the expected in-sequence packets having a A vector describing the expected in-sequence packets having a
specific DSCP or IP precedence value. The value is dependent specific DSCP or IP precedence value. The value is dependent
on the set of offered vectors and configuration of the DUT. on the set of offered vectors and configuration of the DUT.
Discussion: Discussion:
The DUT is configured in a certain way in order that service The DUT is configured in a certain way in order that service
differentiation occurs for a particular DSCP or IP precedence differentiation occurs for a particular DSCP or IP precedence
value when a specific traffic mix consisting of multiple value when a specific traffic mix consisting of multiple
DSCPs or IP precedence values are applied. This term attempts DSCPs or IP precedence values are applied. This term attempts
to capture the expected forwarding behavior when subjected to to capture the expected forwarding behavior when subjected to
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on the set of offered vectors and configuration of the DUT. on the set of offered vectors and configuration of the DUT.
Discussion: Discussion:
The DUT is configured in a certain way in order that service The DUT is configured in a certain way in order that service
differentiation occurs for a particular DSCP or IP precedence differentiation occurs for a particular DSCP or IP precedence
value when a specific traffic mix consisting of multiple value when a specific traffic mix consisting of multiple
DSCPs or IP precedence values are applied. This term attempts DSCPs or IP precedence values are applied. This term attempts
to capture the expected forwarding behavior when subjected to to capture the expected forwarding behavior when subjected to
a certain offered vectors. a certain offered vectors.
Network-layer Traffic Control Mechanisms
The actual algorithm or mechanism the DUT uses to achieve The actual algorithm or mechanism the DUT uses to achieve
service differentiation is not important in describing the service differentiation is not important in describing the
expected delay vector. expected delay vector.
Measurement units: Measurement units:
Seconds. Seconds.
See Also: See Also:
Network-layer Traffic Control Mechanisms
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Loss Vector Expected Loss Vector
Expected Sequence Vector Expected Sequence Vector
Expected Forwarding Vector Expected Forwarding Vector
Expected Jitter Vector Expected Jitter Vector
3.4.3.5 Expected Average Delay Vector 3.4.3.5 Expected Average Delay Vector
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Seconds. Seconds.
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Loss Vector Expected Loss Vector
Expected Sequence Vector Expected Sequence Vector
Expected Forwarding Vector Expected Forwarding Vector
Expected Jitter Vector Expected Jitter Vector
Network-layer Traffic Control Mechanisms
3.4.3.6 Expected Maximum Delay Vector 3.4.3.6 Expected Maximum Delay Vector
Definition: Definition:
A vector describing the expected maximum delay for packets A vector describing the expected maximum delay for packets
having a specific DSCP or IP precedence value. The value is having a specific DSCP or IP precedence value. The value is
dependent on the set of offered vectors and configuration of dependent on the set of offered vectors and configuration of
the DUT. the DUT.
Discussion: Discussion:
The DUT is configured in a certain way in order that service The DUT is configured in a certain way in order that service
differentiation occurs for a particular DSCP or IP precedence differentiation occurs for a particular DSCP or IP precedence
Network-layer Traffic Control Mechanisms
value when a specific traffic mix consisting of multiple value when a specific traffic mix consisting of multiple
DSCPs or IP precedence values are applied. This term attempts DSCPs or IP precedence values are applied. This term attempts
to capture the expected forwarding behavior when subjected to to capture the expected forwarding behavior when subjected to
a certain offered vectors. a certain offered vectors.
The actual algorithm or mechanism the DUT uses to achieve The actual algorithm or mechanism the DUT uses to achieve
service differentiation is not important in describing the service differentiation is not important in describing the
expected maximum delay vector. expected maximum delay vector.
Measurement units: Measurement units:
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differentiation occurs for a particular DSCP or IP precedence differentiation occurs for a particular DSCP or IP precedence
value when a specific traffic mix consisting of multiple value when a specific traffic mix consisting of multiple
DSCPs or IP precedence values are applied. This term attempts DSCPs or IP precedence values are applied. This term attempts
to capture the expected forwarding behavior when subjected to to capture the expected forwarding behavior when subjected to
a certain offered vectors. a certain offered vectors.
The actual algorithm or mechanism the DUT uses to achieve The actual algorithm or mechanism the DUT uses to achieve
service differentiation is not important in describing the service differentiation is not important in describing the
expected minimum delay vector. expected minimum delay vector.
Network-layer Traffic Control Mechanisms
Measurement units: Measurement units:
Seconds. Seconds.
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Loss Vector Expected Loss Vector
Expected Sequence Vector Expected Sequence Vector
Expected Forwarding Vector Expected Forwarding Vector
Network-layer Traffic Control Mechanisms
Expected Jitter Vector Expected Jitter Vector
3.2.3.8 Expected Instantaneous Delay Variation Vector 3.2.3.8 Expected Instantaneous Jitter Vector
Definition: Definition:
A vector describing the expected variation in the delay of A vector describing the expected jitter between two
two consecutive packets' arrival times having a specific DSCP consecutive packets' arrival times having a specific DSCP or
or IP precedence value. The value is dependent on the set of IP precedence value. The value is dependent on the set of
offered vectors and configuration of the DUT. offered vectors and configuration of the DUT.
Discussion: Discussion:
Instantaneous Delay Variation is the absolute value of the Instantaneous Jitter is the absolute value of the difference
difference between the delay measurement of two packets between the delay measurement of two packets belonging to the
belonging to the same stream. same stream.
The delay fluctuation between two consecutive packets in a The delay fluctuation between two consecutive packets in a
stream is reported as the "Instantaneous Delay Variation". stream is reported as the "Instantaneous Jitter".
Instantaneous Delay Variation can be expressed as |D(i) - Instantaneous Jitter can be expressed as |D(i) - D(i-1)|
D(i-1)| where D equals the delay and i is the test sequence where D equals the delay and i is the test sequence number.
number. Packets lost are not counted in the measurement. Packets lost are not counted in the measurement.
Forwarding Vector may contain several Instantaneous Delay Forwarding Vector may contain several Jitter Vectors. For n
Variation Vectors. For n packets received in a Forwarding packets received in a Forwarding Vector, there is a total of
Vector, there is n-1 several Instantaneous Delay Variation (n-1) Instantaneous Jitter Vectors.
Vectors.
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Delay Delay
Jitter
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Average Delay Variation Vector Expected Average Jitter Vector
Expected Peak-to-peak Delay Variation Vector Expected Peak-to-peak Jitter Vector
Stream Stream
Network-layer Traffic Control Mechanisms
3.2.3.9 Expected Average Delay Variation Vector 3.2.3.9 Expected Average Jitter Vector
Definition: Definition:
A vector describing the expected average variation in the A vector describing the expected jitter in packet arrival
delay of packet arrival times for packets having specific times for packets having specific DSCP or IP precedence
DSCP or IP precedence value. The value is dependent on the value. The value is dependent on the set of offered vectors
set of offered vectors and configuration of the DUT. and configuration of the DUT.
Discussion: Discussion:
Average Delay Variation is the average of all the Average Jitter Vector is the average of all the Instantaneous
Instantaneous Delay Variation Vectors measured during the Jitter Vectors measured during the test duration for the same
test duration. DSCP or IP precedence value.
Network-layer Traffic Control Mechanisms
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Instantaneous Delay Variation Vector Expected Instantaneous Jitter Vector
Expected Peak-to-peak Delay Variation Vector Expected Peak-to-peak Jitter Vector
3.2.3.10 Expected Peak-to-peak Delay Variation Vector 3.2.3.10 Expected Peak-to-peak Jitter Vector
Definition: Definition:
A vector describing the expected maximum variation in the A vector describing the expected maximum variation in the
delay of packet arrival times for packets having specific delay of packet arrival times for packets having specific
DSCP or IP precedence value. The value is dependent on the DSCP or IP precedence value. The value is dependent on the
set of offered vectors and configuration of the DUT. set of offered vectors and configuration of the DUT.
Discussion: Discussion:
Peak-to-peak Delay Variation Vector is the maximum delay Peak-to-peak Jitter Vector is the maximum delay minus the
minus the minimum delay of the packets (in a vector) minimum delay of the packets (in a vector) forwarded by the
forwarded by the DUT/SUT. DUT/SUT.
Peak-to-peak Delay Variation is not derived from the Peak-to-peak Jitter is not derived from the Instantaneous
Instantaneous Delay Variation Vector. Peak-to-peak Delay Jitter Vector. Peak-to-peak Jitter is based upon all the
Variation is based upon all the packets during the test packets during the test duration, not just two consecutive
duration, not just two consecutive packets. packets.
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Intended Vector Intended Vector
Offered Vector Offered Vector
Output Vectors Output Vectors
Expected Instantaneous Delay Variation Vector Expected Instantaneous Jitter Vector
Expected Average Delay Variation Vector Expected Average Jitter Vector
Network-layer Traffic Control Mechanisms
3.4.4 Output Vectors 3.4.4 Output Vectors
3.4.4.1 Forwarding Vector 3.4.4.1 Forwarding Vector
Network-layer Traffic Control Mechanisms
Definition: Definition:
The number of packets per second for all packets containing a The number of packets per second for all packets containing a
specific DSCP or IP precedence value that a device can be specific DSCP or IP precedence value that a device can be
observed to successfully forward to the correct destination observed to successfully forward to the correct destination
interface in response to an offered vector. interface in response to an offered vector.
Discussion: Discussion:
Forwarding Vector is expressed as pair of numbers. Both the Forwarding Vector is expressed as pair of numbers. Both the
specific DSCP (or IP precedence) value AND the packets per specific DSCP (or IP precedence) value AND the packets per
skipping to change at page 21, line 5 skipping to change at page 21, line 51
The percentage of packets containing specific DSCP or IP The percentage of packets containing specific DSCP or IP
precedence value that a DUT/SUT did not transmit to the precedence value that a DUT/SUT did not transmit to the
correct destination interface in response to an offered correct destination interface in response to an offered
vector. vector.
Discussion: Discussion:
Loss Vector is expressed as pair of numbers. Both the Loss Vector is expressed as pair of numbers. Both the
specific DSCP (or IP precedence) value AND the percentage specific DSCP (or IP precedence) value AND the percentage
value combine to make a vector. value combine to make a vector.
Network-layer Traffic Control Mechanisms
The Loss Vector represents percentage based on a specific The Loss Vector represents percentage based on a specific
DSCP or IP precedence value. It is not necessarily based on DSCP or IP precedence value. It is not necessarily based on
a stream or flow. The Loss Vector may be expressed as per a stream or flow. The Loss Vector may be expressed as per
port of the DUT/SUT. However, it must be consistent with the port of the DUT/SUT. However, it must be consistent with the
Expected Loss Vector Expected Loss Vector
Network-layer Traffic Control Mechanisms
Loss Vector is a per-hop measurement. The DUT/SUT may change Loss Vector is a per-hop measurement. The DUT/SUT may change
the specific DSCP or IP precedence value for a multiple-hop the specific DSCP or IP precedence value for a multiple-hop
measurement. measurement.
Measurement Units: Measurement Units:
Percentage of offered packets that are not forwarded. Percentage of offered packets that are not forwarded.
See Also: See Also:
Intended Vector Intended Vector
skipping to change at page 22, line 4 skipping to change at page 22, line 51
change the specific DSCP or IP precedence value for a change the specific DSCP or IP precedence value for a
multiple-hop measurement. multiple-hop measurement.
Measurement Units: Measurement Units:
N-octet packets per second N-octet packets per second
Issues: Issues:
See Also: See Also:
In-sequence Packet In-sequence Packet
Network-layer Traffic Control Mechanisms
Intended Vector Intended Vector
Offered Vector Offered Vector
Expected Vectors Expected Vectors
Loss Vector Loss Vector
Forwarding Vector Forwarding Vector
Network-layer Traffic Control Mechanisms
Delay Vectors Delay Vectors
3.4.4.4 Instantaneous Delay Vector 3.4.4.4 Instantaneous Delay Vector
Definition: Definition:
The delay for a packet containing specific DSCP or IP The delay for a packet containing specific DSCP or IP
precedence value that a device can be observed to precedence value that a device can be observed to
successfully transmit to the correct destination interface in successfully transmit to the correct destination interface in
response to an offered vector. response to an offered vector.
skipping to change at page 23, line 4 skipping to change at page 23, line 51
Seconds Seconds
See Also: See Also:
Delay Delay
Intended Vector Intended Vector
Offered Vector Offered Vector
Expected Delay Vectors Expected Delay Vectors
Average Delay Vector Average Delay Vector
Maximum Delay Vector Maximum Delay Vector
Minimum Delay Vector Minimum Delay Vector
Network-layer Traffic Control Mechanisms
3.4.4.5 Average Delay Vector 3.4.4.5 Average Delay Vector
Definition: Definition:
Network-layer Traffic Control Mechanisms
The average delay for packets containing specific DSCP or IP The average delay for packets containing specific DSCP or IP
precedence value that a device can be observed to precedence value that a device can be observed to
successfully transmit to the correct destination interface in successfully transmit to the correct destination interface in
response to an offered vector. response to an offered vector.
Discussion: Discussion:
Average Delay vector is expressed as pair of numbers. Both Average Delay vector is expressed as pair of numbers. Both
the specific DSCP (or IP precedence) value AND delay value the specific DSCP (or IP precedence) value AND delay value
combine to make a vector. combine to make a vector.
skipping to change at page 24, line 5 skipping to change at page 24, line 55
Minimum Delay Vector Minimum Delay Vector
3.4.4.6 Maximum Delay Vector 3.4.4.6 Maximum Delay Vector
Definition: Definition:
The maximum delay from all packets containing specific DSCP The maximum delay from all packets containing specific DSCP
or IP precedence value that a device can be observed to or IP precedence value that a device can be observed to
successfully transmit to the correct destination interface in successfully transmit to the correct destination interface in
response to an offered vector. response to an offered vector.
Discussion:
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
Discussion:
Maximum Delay vector is expressed as pair of numbers. Both Maximum Delay vector is expressed as pair of numbers. Both
the specific DSCP (or IP precedence) value AND delay value the specific DSCP (or IP precedence) value AND delay value
combine to make a vector. combine to make a vector.
The Maximum Delay Vector represents delay on its specific The Maximum Delay Vector represents delay on its specific
DSCP or IP precedence value. It is not necessarily based on DSCP or IP precedence value. It is not necessarily based on
a stream or flow. The Maximum Delay vector may be expressed a stream or flow. The Maximum Delay vector may be expressed
as per port of the DUT/SUT. However, it must be consistent as per port of the DUT/SUT. However, it must be consistent
with the Expected Delay vector. with the Expected Delay vector.
skipping to change at page 25, line 5 skipping to change at page 25, line 56
Delay vector is expressed as pair of numbers. Both the Delay vector is expressed as pair of numbers. Both the
specific DSCP (or IP precedence) value AND delay value specific DSCP (or IP precedence) value AND delay value
combine to make a vector. combine to make a vector.
The Minimum Delay Vector represents delay on its specific The Minimum Delay Vector represents delay on its specific
DSCP or IP precedence value. It is not necessarily based on DSCP or IP precedence value. It is not necessarily based on
a stream or flow. The Minimum Delay vector may be expressed a stream or flow. The Minimum Delay vector may be expressed
as per port of the DUT/SUT. However, it must be consistent as per port of the DUT/SUT. However, it must be consistent
with the Expected Delay vector. with the Expected Delay vector.
Network-layer Traffic Control Mechanisms
Minimum Delay Vector is based upon the minimum Instantaneous Minimum Delay Vector is based upon the minimum Instantaneous
Delay Vector of all packets in a Forwarding Vector. Delay Vector of all packets in a Forwarding Vector.
Network-layer Traffic Control Mechanisms
Minimum Delay Vector is a per-hop measurement. The DUT/SUT Minimum Delay Vector is a per-hop measurement. The DUT/SUT
may change the specific DSCP or IP precedence value for a may change the specific DSCP or IP precedence value for a
multiple-hop measurement. multiple-hop measurement.
Minimum Delay vector can be obtained at any offered load. Minimum Delay vector can be obtained at any offered load.
Recommend at or below the channel capacity in the absence of Recommend at or below the channel capacity in the absence of
congestion. For congested delay, run the offered load above congestion. For congested delay, run the offered load above
the channel capacity. the channel capacity.
Measurement Units: Measurement Units:
skipping to change at page 25, line 32 skipping to change at page 26, line 29
See Also: See Also:
Delay Delay
Intended Vector Intended Vector
Offered Vector Offered Vector
Expected Delay Vectors Expected Delay Vectors
Instantaneous Delay Vector Instantaneous Delay Vector
Forwarding Vector Forwarding Vector
Average Delay Vector Average Delay Vector
Maximum Delay Vector Maximum Delay Vector
3.4.4.8 Instantaneous Delay Variation Vector 3.4.4.8 Instantaneous Jitter Vector
Definition: Definition:
The variation in the delay for two consecutive packets The jitter for two consecutive packets containing specific
containing specific DSCP or IP precedence value that a device DSCP or IP precedence value that a device can be observed to
can be observed to successfully transmit to the correct successfully transmit to the correct destination interface in
destination interface in response to an offered vector. response to an offered vector.
Discussion: Discussion:
Instantaneous Delay Variation is the absolute value of the Instantaneous Jitter is the absolute value of the difference
difference between the delay measurement of two packets between the delay measurement of two packets belonging to the
belonging to the same stream. same stream.
Jitter vector is expressed as pair of numbers. Both the Jitter vector is expressed as pair of numbers. Both the
specific DSCP (or IP precedence) value AND jitter value specific DSCP (or IP precedence) value AND jitter value
combine to make a vector. combine to make a vector.
The delay fluctuation between two consecutive packets in a The delay fluctuation between two consecutive packets in a
stream is reported as the "Instantaneous Delay Variation". stream is reported as the "Instantaneous Jitter".
Instantaneous Delay Variation can be expressed as |D(i) - Instantaneous Jitter Vector can be expressed as |D(i) - D(i-
D(i-1)| where D equals the delay and i is the test sequence 1)| where D equals the delay and i is the test sequence
number. Packets lost are not counted in the measurement. number. Packets lost are not counted in the measurement.
Network-layer Traffic Control Mechanisms 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.
Instantaneous Delay Variation Vector is a per-hop Network-layer Traffic Control Mechanisms
measurement. The DUT/SUT may change the specific DSCP or IP
precedence value for a multiple-hop measurement.
Forwarding Vector may contain several Instantaneous Delay Forwarding Vector may contain several Instantaneous Jitter
Variation Vectors. For n packets received in a Forwarding Vectors. For n packets received in a Forwarding Vector,
Vector, there is n-1 several Instantaneous Delay Variation there are exactly (n-1) Instantaneous Jitter Vectors.
Vectors.
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Delay Delay
Jitter
Forwarding Vector Forwarding Vector
Stream Stream
Expected Vectors Expected Vectors
Average Delay Variation Vector Average Jitter Vector
Peak-to-peak Delay Variation Vector Peak-to-peak Jitter Vector
3.4.4.9 Average Delay Variation Vector 3.4.4.9 Average Jitter Vector
Definition: Definition:
The average variation in the delay for packets containing The average jitter for packets containing specific DSCP or IP
specific DSCP or IP precedence value that a device can be precedence value that a device can be observed to
observed to successfully transmit to the correct destination successfully transmit to the correct destination interface in
interface in response to an offered vector. response to an offered vector.
Discussion: Discussion:
Average Delay Variation is the average of all the Average Jitter Vector is the average of all the Instantaneous
Instantaneous Delay Variation Vectors measured during the Jitter Vectors of the same DSCP or IP precedence value,
test duration. measured during the test duration.
Average Delay Variation vector is expressed as pair of Average Jitter vector is expressed as pair of numbers. Both
numbers. Both the specific DSCP (or IP precedence) value AND the specific DSCP (or IP precedence) value AND jitter value
jitter value combine to make a vector. combine to make a vector.
Average Delay Variation vector is a per-hop measurement. The Average Jitter vector is a per-hop measurement. The DUT/SUT
DUT/SUT may change the specific DSCP or IP precedence value may change the specific DSCP or IP precedence value for a
for a multiple-hop measurement. multiple-hop measurement.
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Delay Jitter
Forwarding Vector Forwarding Vector
Stream Stream
Expected Vectors Expected Vectors
Instantaneous Delay Variation Vector Instantaneous Jitter Vector
Peak-to-peak Delay Variation Vector Peak-to-peak Jitter Vector
Network-layer Traffic Control Mechanisms
3.4.4.10 Peak-to-peak Delay Variation Vector 3.4.4.10 Peak-to-peak Jitter Vector
Network-layer Traffic Control Mechanisms
Definition: Definition:
The maximum possible variation in the delay for packets The maximum possible variation in the delay for packets
containing specific DSCP or IP precedence value that a device containing specific DSCP or IP precedence value that a device
can be observed to successfully transmit to the correct can be observed to successfully transmit to the correct
destination interface in response to an offered vector. destination interface in response to an offered vector.
Discussion: Discussion:
Peak-to-peak Delay Variation Vector is the maximum delay Peak-to-peak Jitter Vector is the maximum delay minus the
minus the minimum delay of the packets (in a vector) minimum delay of the packets (in a vector) forwarded by the
forwarded by the DUT/SUT. DUT/SUT.
Delay Variation vector is expressed as pair of numbers. Both Jitter vector is expressed as pair of numbers. Both the
the specific DSCP (or IP precedence) value AND jitter value specific DSCP (or IP precedence) value AND jitter value
combine to make a vector. combine to make a vector.
Peak-to-peak Delay Variation is not derived from the Peak-to-peak Jitter is not derived from the Instantaneous
Instantaneous Delay Variation Vector. Peak-to-peak Delay Jitter Vector. Peak-to-peak Jitter is based upon all the
Variation is based upon all the packets during the test packets during the test duration, not just two consecutive
duration, not just two consecutive packets. packets.
Measurement units: Measurement units:
Seconds Seconds
See Also: See Also:
Delay Jitter
Forwarding Vector Forwarding Vector
Stream Stream
Expected Vectors Expected Vectors
Average Delay Variation Vector Average Jitter Vector
Peak-to-peak Delay Variation Vector Peak-to-peak Jitter Vector
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
4. Security Considerations 4. Security Considerations
Documents of this type do not directly affect the security of Documents of this type do not directly affect the security of
the Internet or of corporate networks as long as benchmarking the Internet or of corporate networks as long as benchmarking
is not performed on devices or systems connected to is not performed on devices or systems connected to
production networks. production networks.
Packets with unintended and/or unauthorized DSCP or IP Packets with unintended and/or unauthorized DSCP or IP
skipping to change at page 29, line 5 skipping to change at page 29, line 34
Switching Devices", RFC 2285, February 1998. Switching Devices", RFC 2285, February 1998.
[3] K. Nichols, S. Blake, F. Baker, D. Black,"Definition of [3] K. Nichols, S. Blake, F. Baker, D. Black,"Definition of
the Differentiated Services Field (DS Field) in the IPv4 the Differentiated Services Field (DS Field) in the IPv4
and IPv6 Headers", RFC 2474, December 1998. and IPv6 Headers", RFC 2474, December 1998.
[4] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. [4] S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W.
Weiss, "An Architecture for Differentiated Services", RFC Weiss, "An Architecture for Differentiated Services", RFC
2475, December 1998. 2475, December 1998.
[5] V. Jacobson, K. Nichols, K. Poduri, _An Expedited
Forwarding PHB_, RFC 2598, June 1999
[6] C. Demichelis, P. Chimento, _IP Packet Delay Variation
Metric for IPPM_, draft-ietf-ippm-ipdv-10.txt
[7] H. Schulzrinne, GMD Fokus, S. Casner, R. Frederick,
V. Jacobson, _RTP: A Transport Protocol for Real-Time
Applications_, RFC 1889, January 1996
[8] A. Mankin, K. Ramakrishnan, _Gateway Congestion Control
Survey_, RFC 1254, August 1991
Network-layer Traffic Control Mechanisms Network-layer Traffic Control Mechanisms
6. Authors' Address 6. Authors' Address
Jerry Perser Jerry Perser
Spirent Communications Spirent Communications
26750 Agoura Road 26750 Agoura Road
Calabasas, CA 91302 Calabasas, CA 91302
USA USA
 End of changes. 

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