draft-ietf-ippm-tcp-throughput-tm-00.txt   draft-ietf-ippm-tcp-throughput-tm-01.txt 
Network Working Group B. Constantine, Ed. Network Working Group B. Constantine
Internet-Draft JDSU Internet-Draft JDSU
Intended status: Informational G. Forget Intended status: Informational G. Forget
Expires: November 15, 2010 Bell Canada (Ext. Consultant) Expires: November 3, 2010 Bell Canada (Ext. Consultant)
L. Jorgenson L. Jorgenson
Apparent Networks Apparent Networks
Reinhard Schrage Reinhard Schrage
Schrage Consulting Schrage Consulting
Apr 15, 2010 May 3, 2010
TCP Throughput Testing Methodology TCP Throughput Testing Methodology
draft-ietf-ippm-tcp-throughput-tm-00.txt draft-ietf-ippm-tcp-throughput-tm-01.txt
Abstract Abstract
This memo describes a methodology for measuring sustained TCP This memo describes a methodology for measuring sustained TCP
throughput performance in an end-to-end managed network environment. throughput performance in an end-to-end managed network environment.
This memo is intended to provide a practical approach to help users This memo is intended to provide a practical approach to help users
validate the TCP layer performance of a managed network, which should validate the TCP layer performance of a managed network, which should
provide a better indication of end-user application level experience. provide a better indication of end-user application level experience.
In the methodology, various TCP and network parameters are identified In the methodology, various TCP and network parameters are identified
that should be tested as part of the network verification at the TCP that should be tested as part of the network verification at the TCP
layer. layer.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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
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Drafts. Creation date Apr 15, 2010. Drafts. Creation date May 3, 2010.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
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This Internet-Draft will expire on November 15, 2010. This Internet-Draft will expire on November 3, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the BSD License. described in the BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Goals of this Methodology. . . . . . . . . . . . . . . . . . . 4 2. Goals of this Methodology. . . . . . . . . . . . . . . . . . . 4
2.1 TCP Equilibrium State Throughput . . . . . . . . . . . . . 5 2.1 TCP Equilibrium State Throughput . . . . . . . . . . . . . 5
3. TCP Throughput Testing Methodology . . . . . . . . . . . . . . 6 3. TCP Throughput Testing Methodology . . . . . . . . . . . . . . 6
3.1. Baseline Round-trip Delay and Bandwidth. . . . . . . . . . 7 3.1 Determine Network Path MTU . . . . . . . . . . . . . . . . 7
3.1.1 Techniques to Measure Round Trip Time . . . . . . . . 7 3.2. Baseline Round-trip Delay and Bandwidth. . . . . . . . . . 7
3.1.2 Techniques to Measure End-end Bandwidth . . . . . . . 8 3.2.1 Techniques to Measure Round Trip Time . . . . . . . . 8
3.2. Single TCP Connection Throughput Tests . . . . . . . . . . .9 3.2.2 Techniques to Measure End-end Bandwidth . . . . . . . 8
3.2.1 Interpretation of the Single Connection TCP 3.3. Single TCP Connection Throughput Tests . . . . . . . . . . .9
Throughput Results . . . . . . . . . . . . . . . . . . 12 3.3.1 Interpretation of the Single Connection TCP
3.3. TCP MSS Throughput Testing . . . . . . . . . . . . . . . . 12 Throughput Results . . . . . . . . . . . . . . . . . . 13
3.3.1 TCP Test for Network Path MTU . . . . . . . . . . . . 12 3.4. TCP MSS Throughput Testing . . . . . . . . . . . . . . . . 13
3.3.2 MSS Size Testing Method . . . . . . . . . . . . . . . 13 3.4.1 MSS Size Testing Method. . . . . . . . . . . . . . . 13
3.3.3 Interpretation of TCP MSS Throughput Results . . . . . 14 3.4.2 Interpretation of TCP MSS Throughput Results. . . . . 14
3.4. Multiple TCP Connection Throughput Tests. . . . . . . . . . 14 3.5. Multiple TCP Connection Throughput Tests. . . . . . . . . . 15
3.4.1 Multiple TCP Connections - below Link Capacity . . . . 14 3.5.1 Multiple TCP Connections - below Link Capacity . . . . 15
3.4.2 Multiple TCP Connections - over Link Capacity. . . . . 15 3.5.2 Multiple TCP Connections - over Link Capacity. . . . . 16
3.5.3 Interpretation of Multiple TCP Connection Results. . . 16
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
Even though RFC2544 was meant to benchmark network equipment and Even though RFC2544 was meant to benchmark network equipment and
used by network equipment manufacturers (NEMs), network providers used by network equipment manufacturers (NEMs), network providers
have used it to benchmark operational networks in order to have used it to benchmark operational networks in order to
provide SLAs (Service Level Agreements) to their business customers. verify SLAs (Service Level Agreements) before turning on a service
to their business customers. Testing an operational network prior to
customer activation is referred to as "turn-up" testing and the SLA
is generally Layer 2/3 packet throughput, delay, loss and
jitter.
Network providers are coming to the realization that RFC2544 testing Network providers are coming to the realization that RFC2544 testing
and TCP layer testing are required to more adequately ensure end-user and TCP layer testing are required to more adequately ensure end-user
satisfaction. satisfaction. Therefore, the network provider community desires to
measure network throughput performance at the TCP layer. Measuring
Therefore, the network provider community desires to measure network TCP throughput provides a meaningful measure with respect to the end
throughput performance at the TCP layer. Measuring TCP throughput user's application SLA (and ultimately reach some level of TCP
provides a meaningful measure with respect to the end user's testing interoperability which does not exist today).
application SLA (and ultimately reach some level of TCP testing
interoperability which does not exist today).
The complexity of the network grows and the various queuing The complexity of the network grows and the various queuing
mechanisms in the network greatly affect TCP layer performance (i.e. mechanisms in the network greatly affect TCP layer performance (i.e.
improper default router settings for queuing, etc.) and devices such improper default router settings for queuing, etc.) and devices such
as firewalls, proxies, load-balancers can actively alter the TCP as firewalls, proxies, load-balancers can actively alter the TCP
settings as a TCP session traverses the network (such as window size, settings as a TCP session traverses the network (such as window size,
MSS, etc.). Network providers (and NEMs) are wrestling with end-end MSS, etc.). Network providers (and NEMs) are wrestling with end-end
complexities of the above and there is a strong interest in the complexities of the above and there is a strong interest in the
standardization of a test methodology to validate end-to-end TCP standardization of a test methodology to validate end-to-end TCP
performance (as this is the precursor to acceptable end-user performance (as this is the precursor to acceptable end-user
application performance). application performance).
Before RFC2544 testing existed, network providers and NEMs deployed
a variety of ad hoc test techniques to verify the Layer 2/3
performance of the network. RFC2544 was a huge step forward in the
network test world, standardizing the Layer 2/3 test methodology
which greatly improved the quality of the network and reduced
operational test expenses. These managed networks are intended to be
predictable, but therein lies the problem. It is difficult if not
impossible, to extrapolate end user application layer performance
from RFC2544 results and the goal of RFC2544 was never intended
to do so.
So the intent behind this draft TCP throughput work is to define So the intent behind this draft TCP throughput work is to define
a methodology for testing sustained TCP layer performance. In this a methodology for testing sustained TCP layer performance. In this
document, sustained TCP throughput is that amount of data per unit document, sustained TCP throughput is that amount of data per unit
time that TCP transports during equilibrium (steady state), i.e. time that TCP transports during equilibrium (steady state), i.e.
after the initial slow start phase. We refer to this state as TCP after the initial slow start phase. We refer to this state as TCP
Equilibrium, and that the equalibrium throughput is the maximum Equilibrium, and that the equalibrium throughput is the maximum
achievable for the TCP connection(s). achievable for the TCP connection(s).
One other important note; the precursor to conducting the TCP tests One other important note; the precursor to conducting the TCP tests
test methodlogy is to perform RFC2544 related Layer 2/3 tests. It test methodlogy is to perform "network stress tests" such as RFC2544
is highly recommended to run traditional RFC2544 type test to verify Layer 2/3 tests or other conventional tests (OWAMP, etc.). It is
highly recommended to run traditional Layer 2/3 type test to verify
the integrity of the network before conducting TCP testing. the integrity of the network before conducting TCP testing.
2. Goals of this Methodology 2. Goals of this Methodology
Before defining the goals of this methodology, it is important to Before defining the goals of this methodology, it is important to
clearly define the areas that are not intended to be measured or clearly define the areas that are not intended to be measured or
analyzed by such a methodology. analyzed by such a methodology.
- The methodology is not intended to predict TCP throughput - The methodology is not intended to predict TCP throughput
behavior during the transient stages of a TCP connection, such behavior during the transient stages of a TCP connection, such
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practices" that an engineer should apply when validating the practices" that an engineer should apply when validating the
ability of a managed network to carry end-user TCP applications. ability of a managed network to carry end-user TCP applications.
Some specific goals are to: Some specific goals are to:
- Provide a practical test approach that specifies the more well - Provide a practical test approach that specifies the more well
understood (and end-user configurable) TCP parameters such as Window understood (and end-user configurable) TCP parameters such as Window
size, MSS, # connections, and how these affect the outcome of TCP size, MSS, # connections, and how these affect the outcome of TCP
performance over a network performance over a network
- Provide specific test conditions (link speed, RTD, window size, - Provide specific test conditions (link speed, RTT, window size,
etc.) and maximum achievable TCP throughput under TCP Equilbrium etc.) and maximum achievable TCP throughput under TCP Equilbrium
conditions. For guideline purposes, provide examples of these test conditions. For guideline purposes, provide examples of these test
conditions and the maximum achievable TCP throughput during the conditions and the maximum achievable TCP throughput during the
equilbrium state. Section 2.1 provides specific details concerning equilbrium state. Section 2.1 provides specific details concerning
the definition of TCP Equilibrium within the context of this draft. the definition of TCP Equilibrium within the context of this draft.
- In test situations where the recommended procedure does not yield - In test situations where the recommended procedure does not yield
the maximum achievable TCP throughput result, this draft provides some the maximum achievable TCP throughput result, this draft provides some
possible areas within the end host or network that should be possible areas within the end host or network that should be
considered for investigation (although again, this draft is not considered for investigation (although again, this draft is not
intended to provide a detailed diagnosis of these issues) intended to provide a detailed diagnosis of these issues)
2.1 TCP Equilibrium State Throughput 2.1 TCP Equilibrium State Throughput
TCP connections have three (3) fundamental congestion window phases TCP connections have three (3) fundamental congestion window phases
as documented in RFC-TBD. These states are: as documented in RFC2581. These states are:
- Slow Start, which occurs during the beginning of a TCP transmission - Slow Start, which occurs during the beginning of a TCP transmission
or after a retransmission time out event or after a retransmission time out event
- Congestion avoidance, which is the phase during which TCP ramps up - Congestion avoidance, which is the phase during which TCP ramps up
to establish the maximum attainable throughput on an end-end network to establish the maximum attainable throughput on an end-end network
path. Retransmissions are a natural by-product of the TCP congestion path. Retransmissions are a natural by-product of the TCP congestion
avoidance algorithm as it seeks to achieve maximum throughput on avoidance algorithm as it seeks to achieve maximum throughput on
the network path. the network path.
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cause the state change from congestion avoidance to a retransmission cause the state change from congestion avoidance to a retransmission
phase). All maximum achievable throughputs specified in Section 3 are phase). All maximum achievable throughputs specified in Section 3 are
with respect to this Equilibrium state. with respect to this Equilibrium state.
3. TCP Throughput Testing Methodology 3. TCP Throughput Testing Methodology
This section summarizes the specific test methodology to achieve the This section summarizes the specific test methodology to achieve the
goals listed in Section 2. goals listed in Section 2.
As stated in Section 1, it is considered best practice to verify As stated in Section 1, it is considered best practice to verify
the integrity of the network from a Layer2/3 perspective by first the integrity of the network by conducting Layer2/3 stress tests
conducting RFC2544 type testing. If the network is not performing such as RFC2544 or other methods of network stress tests. If the
properly in terms of packet loss, jitter, etc. when running RFC2544 network is not performing properly in terms of packet loss, jitter,
tests, then the TCP layer testing will not be meaningful since the etc. then the TCP layer testing will not be meaningful since the
equalibrium throughput would be very difficult to achieve (in a equalibrium throughput would be very difficult to achieve (in a
"dysfunctional" network). "dysfunctional" network).
The following provides the sequential order of steps to conduct the The following provides the sequential order of steps to conduct the
TCP throughput testing methodology: TCP throughput testing methodology:
1. Baseline Round-trip Delay and Bandwidth. These measurements provide 1. Identify the Path MTU. Packetization Layer Path MTU Discovery
or PLPMTUD (RFC4821) should be conducted to verify the minimum network
path MTU. Conducting PLPMTUD establishes the upper limit for the MSS
to be used in subsequent steps.
2. Baseline Round-trip Delay and Bandwidth. These measurements provide
estimates of the ideal TCP window size, which will be used in estimates of the ideal TCP window size, which will be used in
subsequent test steps. subsequent test steps.
2. Single TCP Connection Throughput Tests. With baseline measurements 3. Single TCP Connection Throughput Tests. With baseline measurements
of round trip delay and bandwidth, a series of single connection TCP of round trip delay and bandwidth, a series of single connection TCP
throughput tests can be conducted to baseline the performance of the throughput tests can be conducted to baseline the performance of the
network against expectations. network against expectations.
3. TCP MSS Throughput Testing. By varying the MSS size of the TCP 4. TCP MSS Throughput Testing. By varying the MSS size of the TCP
connection, the ability of the network to sustain expected TCP connection, the ability of the network to sustain expected TCP
throughput can be verified. throughput can be verified.
4. Multiple TCP Connection Throughput Tests. Single connection TCP 5. Multiple TCP Connection Throughput Tests. Single connection TCP
testing is a useful first step to measure expected versus actual TCP testing is a useful first step to measure expected versus actual TCP
performance. The multiple connection test more closely emulates performance. The multiple connection test more closely emulates
customer traffic, which comprise many TCP connections over a network customer traffic, which comprise many TCP connections over a network
link. link.
Important to note are some of the key characteristics and Important to note are some of the key characteristics and
considerations for the TCP test instrument. The test host may be a considerations for the TCP test instrument. The test host may be a
standard computer or dedicated communications test instrument standard computer or dedicated communications test instrument
and these TCP test hosts be capable of emulating both a client and a and these TCP test hosts be capable of emulating both a client and a
server. server. As a general rule of thumb, testing TCP throughput at rates
greater than 250-500 Mbit/sec generally requires high performance
server hardware or dedicated hardware based test tools.
Whether the TCP test host is a standard computer or dedicated test Whether the TCP test host is a standard computer or dedicated test
instrument, the following areas should be considered when selecting instrument, the following areas should be considered when selecting
a test host: a test host:
- TCP implementation used by the test host OS, i.e. Linux OS kernel - TCP implementation used by the test host OS, i.e. Linux OS kernel
using TCP Reno, TCP options supported, etc. This will obviously be using TCP Reno, TCP options supported, etc. This will obviously be
more important when using custom test equipment where the TCP more important when using custom test equipment where the TCP
implementation may be customized or tuned to run in higher implementation may be customized or tuned to run in higher
performance hardware performance hardware
- Most importantly, the TCP test host must be capable of generating - Most importantly, the TCP test host must be capable of generating
and receiving stateful TCP test traffic at the full link speed of the and receiving stateful TCP test traffic at the full link speed of the
network under test. This requirement is very serious and may require network under test. This requirement is very serious and may require
custom test equipment, especially on 1 GigE and 10 GigE networks. custom test equipment, especially on 1 GigE and 10 GigE networks.
3.1. Baseline Round-trip Delay and Bandwidth 3.1. Determine Network Path MTU
TCP implementations should use Path MTU Discovery techniques (PMTUD),
but this technique does not always prove reliable in real world
situations. Since PMTUD relies on ICMP messages (to inform the host
that unfragmented transmission cannot occur), PMTUD is not always
reliable since many network managers completely disable ICMP.
Increasingly network providers and enterprises are instituting fixed
MTU sizes on the hosts to eliminate TCP fragmentation issues in the
application.
Packetization Layer Path MTU Discovery or PLPMTUD (RFC4821) should
be conducted to verify the minimum network path MTU. Conducting
the PLPMTUD test establishes the upper limit upon the MTU, which
establishes the upper limit for the MSS in the subsequent test steps.
3.2. Baseline Round-trip Delay and Bandwidth
Before stateful TCP testing can begin, it is important to baseline Before stateful TCP testing can begin, it is important to baseline
the round trip delay and bandwidth of the network to be tested. the round trip delay and bandwidth of the network to be tested.
These measurements provide estimates of the ideal TCP window size, These measurements provide estimates of the ideal TCP window size,
which will be used in subsequent test steps. which will be used in subsequent test steps.
These latency and bandwidth tests should be run over a long enough These latency and bandwidth tests should be run over a long enough
period of time to characterize the performance of the network over period of time to characterize the performance of the network over
the course of a meaningful time period. One example would the course of a meaningful time period. One example would
be to take samples during various times of the work day. The goal be to take samples during various times of the work day. The goal
would be to determine a representative minimum, average, and maximum would be to determine a representative minimum, average, and maximum
RTD and bandwidth for the network under test. Topology changes are RTD and bandwidth for the network under test. Topology changes are
to be avoided during this time of initial convergence (e.g. in to be avoided during this time of initial convergence (e.g. in
crossing BGP4 boundaries). crossing BGP4 boundaries).
In some cases, baselining bandwidth may not be required, since a In some cases, baselining bandwidth may not be required, since a
network provider's end-to-end topology may be well enough defined. network provider's end-to-end topology may be well enough defined.
3.1.1 Techniques to Measure Round Trip Time 3.2.1 Techniques to Measure Round Trip Time
We follow in the definitions used in the references of the appendix; We follow in the definitions used in the references of the appendix;
hence Round Trip Time (RTT) is the time elapsed between the clocking hence Round Trip Time (RTT) is the time elapsed between the clocking
in of the first bit of a payload packet to the receipt of the last in of the first bit of a payload packet to the receipt of the last
bit of the corresponding acknowledgement. Round Trip Delay (RTD) bit of the corresponding acknowledgement. Round Trip Delay (RTD)
is used synonymously to twice the Link Latency. is used synonymously to twice the Link Latency.
In any method used to baseline round trip delay between network In any method used to baseline round trip delay between network
end-points, it is important to realize that network latency is the end-points, it is important to realize that network latency is the
sum of inherent network delay and congestion. The RTT should be sum of inherent network delay and congestion. The RTT should be
baselined during "off-peak" hours to obtain a reliable figure for baselined during "off-peak" hours to obtain a reliable figure for
network latency (versus additional delay caused by congestion). network latency (versus additional delay caused by congestion).
During the actual sustained TCP throughput tests, it is critical During the actual sustained TCP throughput tests, it is critical
to measure RTT along with measured TCP throughput. Congestive to measure RTT along with measured TCP throughput. Congestive
effects can be isolated if RTT is concurrently measured. effects can be isolated if RTT is concurrently measured
This is not meant to provide an exhaustive list, but summarizes some This is not meant to provide an exhaustive list, but summarizes some
of the more common ways to determine round trip time (RTT) through of the more common ways to determine round trip time (RTT) through
the network. The desired resolution of the measurement (i.e. msec the network. The desired resolution of the measurement (i.e. msec
versus usec) may dictate whether the RTT measurement can be achieved versus usec) may dictate whether the RTT measurement can be achieved
with standard tools such as ICMP ping techniques or whether with standard tools such as ICMP ping techniques or whether
specialized test equipment would be required with high precision specialized test equipment would be required with high precision
timers. The objective in this section is to list several techniques timers. The objective in this section is to list several techniques
in order of decreasing accuracy. in order of decreasing accuracy.
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test equipment RTT measurement may be compatible with delay test equipment RTT measurement may be compatible with delay
measurement protocols specified in RFC5357. measurement protocols specified in RFC5357.
- Conduct packet captures of TCP test applications using for example - Conduct packet captures of TCP test applications using for example
"iperf" or FTP, etc. By running multiple experiments, the packet "iperf" or FTP, etc. By running multiple experiments, the packet
captures can be studied to estimate RTT based upon the SYN -> SYN-ACK captures can be studied to estimate RTT based upon the SYN -> SYN-ACK
handshakes within the TCP connection set-up. handshakes within the TCP connection set-up.
- ICMP Pings may also be adequate to provide round trip time - ICMP Pings may also be adequate to provide round trip time
estimations. Some limitations of ICMP Ping are the msec resolution estimations. Some limitations of ICMP Ping are the msec resolution
and whether the network elements / end points respond to pings (or and whether the network elements respond to pings (or block them).
block them).
3.1.2 Techniques to Measure End-end Bandwidth 3.2.2 Techniques to Measure End-end Bandwidth
There are many well established techniques available to provide There are many well established techniques available to provide
estimated measures of bandwidth over a network. This measurement estimated measures of bandwidth over a network. This measurement
should be conducted in both directions of the network, especially for should be conducted in both directions of the network, especially for
access networks which are inherently asymmetrical. Some of the access networks which are inherently asymmetrical. Some of the
asymmetric implications to TCP performance are documented in RFC-3449 asymmetric implications to TCP performance are documented in RFC-3449
and the results of this work will be further studied to determine and the results of this work will be further studied to determine
relevance to this draft. relevance to this draft.
The bandwidth measurement test must be run with stateless IP streams The bandwidth measurement test must be run with stateless IP streams
(not stateful TCP) in order to determine the available bandwidth in (not stateful TCP) in order to determine the available bandwidth in
each direction. And this test should obviously be performed at each direction. And this test should obviously be performed at
various intervals throughout a business day (or even across a week). various intervals throughout a business day (or even across a week).
Ideally, the bandwidth test should produce a log output of the Ideally, the bandwidth test should produce a log output of the
bandwidth achieved across the test interval AND the round trip delay. bandwidth achieved across the test interval AND the round trip delay.
And during the actual TCP level performance measurements (Sections And during the actual TCP level performance measurements (Sections
3.2 - 3.5), the test tool must be able to track round trip time 3.3 - 3.5), the test tool must be able to track round trip time
of the TCP connection(s) during the test. Measuring round trip time of the TCP connection(s) during the test. Measuring round trip time
variation (aka "jitter") provides insight into effects of congestive variation (aka "jitter") provides insight into effects of congestive
delay on the sustained throughput achieved for the TCP layer test. delay on the sustained throughput achieved for the TCP layer test.
3.2. Single TCP Connection Throughput Tests 3.3. Single TCP Connection Throughput Tests
This draft specifically defines TCP throughput techniques to verify This draft specifically defines TCP throughput techniques to verify
sustained TCP performance in a managed business network. Defined sustained TCP performance in a managed business network. Defined
in section 2.1, the equalibrium throughput reflects the maximum in section 2.1, the equalibrium throughput reflects the maximum
rate achieved by a TCP connection within the congestion avoidance rate achieved by a TCP connection within the congestion avoidance
phase on a end-end network path. This section and others will define phase on a end-end network path. This section and others will define
the method to conduct these sustained throughput tests and guidelines the method to conduct these sustained throughput tests and guidelines
of the predicted results. of the predicted results.
With baseline measurements of round trip time and bandwidth With baseline measurements of round trip time and bandwidth
from section 3.1, a series of single connection TCP throughput tests from section 3.2, a series of single connection TCP throughput tests
can be conducted to baseline the performance of the network against can be conducted to baseline the performance of the network against
expectations. The optimum TCP window size can be calculated from expectations. The optimum TCP window size can be calculated from
the bandwidth delay product (BDP), which is: the bandwidth delay product (BDP), which is:
BDP = RTT x Bandwidth BDP = RTT x Bandwidth
By dividing the BDP by 8, the "ideal" TCP window size is calculated. By dividing the BDP by 8, the "ideal" TCP window size is calculated.
An example would be a T3 link with 25 msec RTT. The BDP would equal An example would be a T3 link with 25 msec RTT. The BDP would equal
~1,105,000 bits and the ideal TCP window would equal ~138,000 bytes. ~1,105,000 bits and the ideal TCP window would equal ~138,000 bytes.
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This correlation of retransmissions and RTT over the course of the This correlation of retransmissions and RTT over the course of the
test will clearly identify which portions of the transfer reached test will clearly identify which portions of the transfer reached
TCP Equilbrium state and to what effect increased RTT (congestive TCP Equilbrium state and to what effect increased RTT (congestive
effects) may have been the cause of reduced equilibrium performance. effects) may have been the cause of reduced equilibrium performance.
Host hardware performance must be well understood before conducting Host hardware performance must be well understood before conducting
this TCP single connection test and other tests in this section. this TCP single connection test and other tests in this section.
Dedicated test equipment may be required, especially for line rates Dedicated test equipment may be required, especially for line rates
of GigE and 10 GigE. of GigE and 10 GigE.
3.2.1 Interpretation of the Single Connection TCP Throughput Results 3.3.1 Interpretation of the Single Connection TCP Throughput Results
At the end of this step, the user will document the theoretical BDP At the end of this step, the user will document the theoretical BDP
and a set of Window size experiments with measured TCP throughput for and a set of Window size experiments with measured TCP throughput for
each TCP window size setting. For cases where the sustained TCP each TCP window size setting. For cases where the sustained TCP
throughput does not equal the predicted value, some possible causes throughput does not equal the predicted value, some possible causes
are listed: are listed:
- Network congestion causing packet loss - Network congestion causing packet loss
- Network congestion not causing packet loss, but effectively - Network congestion not causing packet loss, but effectively
increasing the size of the required TCP window during the transfer increasing the size of the required TCP window during the transfer
- Network fragmentation at the IP layer
- Intermediate network devices which actively regenerate the TCP - Intermediate network devices which actively regenerate the TCP
connection and can alter window size, MSS, etc. connection and can alter window size, MSS, etc.
3.3. TCP MSS Throughput Testing 3.4. TCP MSS Throughput Testing
This test setup should be conducted as a single TCP connection test. This test setup should be conducted as a single TCP connection test.
By varying the MSS size of the TCP connection, the ability of the By varying the MSS size of the TCP connection, the ability of the
network to sustain expected TCP throughput can be verified. This is network to sustain expected TCP throughput can be verified. This is
similar to frame and packet size techniques within RFC2-2544, which similar to frame and packet size techniques within RFC2-2544, which
aim to determine the ability of the routing/switching devices to aim to determine the ability of the routing/switching devices to
handle loads in term of packets/frames per second at various frame handle loads in term of packets/frames per second at various frame
and packet sizes. This test can also further characterize the and packet sizes. This test can also further characterize the
performance of a network in the presence of active TCP elements performance of a network in the presence of active TCP elements
(proxies, etc.), devices that fragment IP packets, and the actual (proxies, etc.), devices that fragment IP packets, and the actual
end hosts themselves (servers, etc.). end hosts themselves (servers, etc.).
3.3.1 TCP Test for Network Path MTU 3.4.1 MSS Size Testing Method
TCP implementations should use Path MTU Discovery techniques (PMTUD),
but this technique does not always prove reliable in real world
situations. Since PMTUD relies on ICMP messages (to inform the host
that unfragmented transmission cannot occur), PMTUD is not always
reliable since many network managers completely disable ICMP.
Increasingly network providers and enterprises are instituting fixed
MTU sizes on the hosts to eliminate TCP fragmentation issues in the
application.
Packetization Layer Path MTU Discovery or PLPMTUD (RFC4821) should
be conducted to verify the minimum network path MTU. Conducting
the PLPMTUD test establishes the upper limit upon the MTU, which in
turn establishes the upper limit for the MSS testing of section 3.3.2.
MSS refers specifically to the payload size of the TCP packet and does
not include TCP or IP headers.
3.3.2 MSS Size Testing Method
The single connection testing listed in Section 3.2 should be The single connection testing listed in Section 3.3 should be
repeated, using the appropriate window size and collecting repeated, using the appropriate window size and collecting
throughput measurements per various MSS sizes. throughput measurements per various MSS sizes.
The following are the typical sizes of MSS settings for various The following are the typical sizes of MSS settings for various
link speeds: link speeds:
- 256 bytes for very low speed links such as 9.6Kbps (per RFC1144). - 256 bytes for very low speed links such as 9.6Kbps (per RFC1144).
- 536 bytes for low speed links (per RFC879) . - 536 bytes for low speed links (per RFC879) .
- 966 bytes for SLIP high speed (per RFC1055). - 966 bytes for SLIP high speed (per RFC1055).
- 1380 bytes for IPSec VPN Tunnel testing - 1380 bytes for IPSec VPN Tunnel testing
- 1452 bytes for PPPoE connectivity (per RFC2516) - 1452 bytes for PPPoE connectivity (per RFC2516)
- 1460 for Ethernet and Fast Ethernet (per RFC895). - 1460 for Ethernet and Fast Ethernet (per RFC895).
- 8960 byte jumbo frames for GigE - 8960 byte jumbo frames for GigE
Using the optimum window size determined by conducting steps 3.1 and Using the optimum window size determined by conducting steps 3.2 and
3.2, a variety of window sizes should be tested according to the link 3.3, a variety of window sizes should be tested according to the link
speed under test. Using Fast Ethernet with 5 msec RTT as an example, speed under test. Using Fast Ethernet with 5 msec RTT as an example,
the optimum TCP window size would be 62.5 kbytes and the recommended the optimum TCP window size would be 62.5 kbytes and the recommended
MSS for Fast Ethernet is 1460 bytes. MSS for Fast Ethernet is 1460 bytes.
Link Achievable TCP Throughput (Mbps) for Link Achievable TCP Throughput (Mbps) for
Speed RTT(ms) MSS=1000 MSS=1260 MSS=1300 MSS=1380 MSS=1420 MSS=1460 Speed RTT(ms) MSS=1000 MSS=1260 MSS=1300 MSS=1380 MSS=1420 MSS=1460
---------------------------------------------------------------------- ----------------------------------------------------------------------
T1 20 | 1.20 1.008 1.040 1.104 1.136 1.168 T1 20 | 1.20 1.008 1.040 1.104 1.136 1.168
T1 50 | 1.44 1.411 1.456 1.335 1.363 1.402 T1 50 | 1.44 1.411 1.456 1.335 1.363 1.402
T1 100 | 1.44 1.512 1.456 1.435 1.477 1.402 T1 100 | 1.44 1.512 1.456 1.435 1.477 1.402
skipping to change at page 14, line 18 skipping to change at page 14, line 35
Link Achievable TCP Throughput (Mbps) for Link Achievable TCP Throughput (Mbps) for
Speed RTT(ms) MSS=1260 MSS=1300 MSS=1380 MSS=1420 MSS=1460 MSS=8960 Speed RTT(ms) MSS=1260 MSS=1300 MSS=1380 MSS=1420 MSS=1460 MSS=8960
---------------------------------------------------------------------- ----------------------------------------------------------------------
1Gig 0.1 | 924.812 926.966 882.495 894.240 919.819 713.786 1Gig 0.1 | 924.812 926.966 882.495 894.240 919.819 713.786
1Gig 0.5 | 924.812 926.966 930.922 932.743 934.467 856.543 1Gig 0.5 | 924.812 926.966 930.922 932.743 934.467 856.543
1Gig 1.0 | 924.812 926.966 930.922 932.743 934.467 927.922 1Gig 1.0 | 924.812 926.966 930.922 932.743 934.467 927.922
10Gig 0.05| 9248.125 9269.655 9309.218 9839.790 9344.671 8565.435 10Gig 0.05| 9248.125 9269.655 9309.218 9839.790 9344.671 8565.435
10Gig 0.3 | 9248.125 9269.655 9309.218 9839.790 9344.671 9755.079 10Gig 0.3 | 9248.125 9269.655 9309.218 9839.790 9344.671 9755.079
Each row in the table is a separate test that should be conducted Each row in the table is a separate test that should be conducted
over a predetermined test interval and the throughput, retransmissions, over a predetermined test interval and the throughput,retransmissions,
and RTT logged during the entire test interval. and RTT logged during the entire test interval.
3.3.3 Interpretation of TCP MSS Throughput Results 3.4.2 Interpretation of TCP MSS Throughput Results
For cases where the predicted TCP throughput does not equal the For cases where the predicted TCP throughput does not equal the
predicted throughput predicted for a given MSS, some possible causes predicted throughput predicted for a given MSS, some possible causes
are listed: are listed:
- TBD - TBD
3.4. Multiple TCP Connection Throughput Tests 3.5. Multiple TCP Connection Throughput Tests
After baselining the network under test with a single TCP connection After baselining the network under test with a single TCP connection
(Section 3.2), the nominal capacity of the network has been (Section 3.3), the nominal capacity of the network has been
determined. The capacity measured in section 3.2 may be a capacity determined. The capacity measured in section 3.3 may be a capacity
range and it is reasonable that some level of tuning may have been range and it is reasonable that some level of tuning may have been
required (i.e. router shaping techniques employed, intermediary required (i.e. router shaping techniques employed, intermediary
proxy like devices tuned, etc.). proxy like devices tuned, etc.).
Single connection TCP testing is a useful first step to measure Single connection TCP testing is a useful first step to measure
expected versus actual TCP performance and as a means to diagnose expected versus actual TCP performance and as a means to diagnose
/ tune issues in the network and active elements. However, the / tune issues in the network and active elements. However, the
ultimate goal of this methodology is to more closely emulate customer ultimate goal of this methodology is to more closely emulate customer
traffic, which comprise many TCP connections over a network link. traffic, which comprise many TCP connections over a network link.
This methodology inevitably seeks to provide the framework for This methodology inevitably seeks to provide the framework for
testing stateful TCP connections in concurrence with stateless testing stateful TCP connections in concurrence with stateless
traffic streams, and this is described in Section 3.5. traffic streams, and this is described in Section 3.5.
3.4.1 Multiple TCP Connections - below Link Capacity 3.5.1 Multiple TCP Connections - below Link Capacity
First, the ability of the network to carry multiple TCP connections First, the ability of the network to carry multiple TCP connections
to full network capacity should be tested. Prioritization and QoS to full network capacity should be tested. Prioritization and QoS
settings are not considered during this step, since the network settings are not considered during this step, since the network
capacity is not to be exceeded by the test traffic (section 3.3.2 capacity is not to be exceeded by the test traffic (section 3.5.2
covers the over capacity test case). covers the over capacity test case).
For this multiple connection TCP throughput test, the number of For this multiple connection TCP throughput test, the number of
connections will more than likely be limited by the test tool (host connections will more than likely be limited by the test tool (host
vs. dedicated test equipment). As an example, for a GigE link with vs. dedicated test equipment). As an example, for a GigE link with
1 msec RTT, the optimum TCP window would equal ~128 KBytes. So under 1 msec RTT, the optimum TCP window would equal ~128 KBytes. So under
this condition, 8 concurrent connections with window size equal to this condition, 8 concurrent connections with window size equal to
16KB would fill the GigE link. For 10G, 80 connections would be 16KB would fill the GigE link. For 10G, 80 connections would be
required to accomplish the same. required to accomplish the same.
Just as in section 3.2, the end host or test tool can not be the Just as in section 3.3, the end host or test tool can not be the
processing bottleneck or the throughput measurements will not be processing bottleneck or the throughput measurements will not be
valid. The test tool must be benchmarked in ideal lab conditions to valid. The test tool must be benchmarked in ideal lab conditions to
verify it's ability to transfer stateful TCP traffic at the given verify it's ability to transfer stateful TCP traffic at the given
network line rate. network line rate.
For this test step, it should be conducted over a reasonable test For this test step, it should be conducted over a reasonable test
duration and results should be logged per interval such as throughput duration and results should be logged per interval such as throughput
per connection, RTT, and retransmissions. per connection, RTT, and retransmissions.
Since the network is not to be driven into over capacity (by nature Since the network is not to be driven into over capacity (by nature
of the BDP allocated evenly to each connection), this test verifies of the BDP allocated evenly to each connection), this test verifies
the ability of the network to carry multiple TCP connections up to the ability of the network to carry multiple TCP connections up to
the link speed of the network. the link speed of the network.
3.4.2 Multiple TCP Connections - over Link Capacity 3.5.2 Multiple TCP Connections - over Link Capacity
In this step, the network bandwidth is intentionally exceeded with In this step, the network bandwidth is intentionally exceeded with
multiple TCP connections to test expected prioritization and queuing multiple TCP connections to test expected prioritization and queuing
within the network. within the network.
All conditions related to Section 3.3 set-up apply, especially the All conditions related to Section 3.3 set-up apply, especially the
ability of the test hosts to transfer stateful TCP traffic at network ability of the test hosts to transfer stateful TCP traffic at network
line rates. line rates.
Using the same example from Section 3.2, a GigE link with 1 msec Using the same example from Section 3.3, a GigE link with 1 msec
RTT would require a window size of 128 KB to fill the link (with RTT would require a window size of 128 KB to fill the link (with
one TCP connection). Assuming a 16KB window, 8 concurrent one TCP connection). Assuming a 16KB window, 8 concurrent
connections would fill the GigE link capacity and values higher than connections would fill the GigE link capacity and values higher than
8 would over-subscribe the network capacity. The user would select 8 would over-subscribe the network capacity. The user would select
values to over-subscribe the network (i.e. possibly 10 15, 20, etc.) values to over-subscribe the network (i.e. possibly 10 15, 20, etc.)
to conduct experiments to verify proper prioritization and queuing to conduct experiments to verify proper prioritization and queuing
within the network. within the network.
3.5.3 Interpretation of Multiple TCP Connection Test Restults
Without any prioritization in the network, the over subscribed test Without any prioritization in the network, the over subscribed test
results could assist in the queuing studies. With proper queuing, results could assist in the queuing studies. With proper queuing,
the bandwidth should be shared in a reasonable manner. The author the bandwidth should be shared in a reasonable manner. The author
understands that the term "reasonable" is too wide open, and future understands that the term "reasonable" is too wide open, and future
draft versions of this memo would attempt to quantify this sharing draft versions of this memo would attempt to quantify this sharing
in more tangible terms. It is known that if a network element in more tangible terms. It is known that if a network element
is not set for proper queuing (i.e. FIFO), then an oversubscribed is not set for proper queuing (i.e. FIFO), then an oversubscribed
TCP connection test will generally show a very uneven distribution of TCP connection test will generally show a very uneven distribution of
bandwidth. bandwidth.
skipping to change at page 17, line 18 skipping to change at page 17, line 18
and Reinhard Schrage for technical review and contributions to this and Reinhard Schrage for technical review and contributions to this
draft-00 memo. draft-00 memo.
Also thanks to Matt Mathis and Matt Zekauskas for many good comments Also thanks to Matt Mathis and Matt Zekauskas for many good comments
through email exchange and for pointing me to great sources of through email exchange and for pointing me to great sources of
information pertaining to past works in the TCP capacity area. information pertaining to past works in the TCP capacity area.
5. References 5. References
[RFC2581] Allman, M., Paxson, V., Stevens W., "TCP Congestion [RFC2581] Allman, M., Paxson, V., Stevens W., "TCP Congestion
Control", RFC 2581, April 1999. Control", RFC 2581, May 1999.
[RFC3148] Mathis M., Allman, M., "A Framework for Defining [RFC3148] Mathis M., Allman, M., "A Framework for Defining
Empirical Bulk Transfer Capacity Metrics", RFC 3148, July Empirical Bulk Transfer Capacity Metrics", RFC 3148, July
2001. 2001.
[RFC2544] Bradner, S., McQuaid, J., "Benchmarking Methodology for [RFC2544] Bradner, S., McQuaid, J., "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544, April 1999 Network Interconnect Devices", RFC 2544, May 1999
[RFC3449] Balakrishnan, H., Padmanabhan, V. N., Fairhurst, G., [RFC3449] Balakrishnan, H., Padmanabhan, V. N., Fairhurst, G.,
Sooriyabandara, M., "TCP Performance Implications of Sooriyabandara, M., "TCP Performance Implications of
Network Path Asymmetry", RFC 3449, December 2002 Network Path Asymmetry", RFC 3449, December 2002
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., Babiarz, [RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., Babiarz,
J., "A Two-Way Active Measurement Protocol (TWAMP)", J., "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008 RFC 5357, October 2008
[RFC4821] Mathis, M., Heffner, J., "Packetization Layer Path MTU [RFC4821] Mathis, M., Heffner, J., "Packetization Layer Path MTU
Discovery", RFC 4821, April 2007 Discovery", RFC 4821, May 2007
draft-ietf-ippm-btc-cap-00.txt Allman, M., "A Bulk draft-ietf-ippm-btc-cap-00.txt Allman, M., "A Bulk
Transfer Capacity Methodology for Cooperating Hosts", Transfer Capacity Methodology for Cooperating Hosts",
August 2001 August 2001
[MSMO] The Macroscopic Behavior of the TCP Congestion Avoidance [MSMO] The Macroscopic Behavior of the TCP Congestion Avoidance
Algorithm Mathis, M.,Semke, J, Mahdavi, J, Ott, T Algorithm Mathis, M.,Semke, J, Mahdavi, J, Ott, T
July 1997 SIGCOMM Computer Communication Review, July 1997 SIGCOMM Computer Communication Review,
Volume 27 Issue 3 Volume 27 Issue 3
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