Internet DRAFT - draft-zheng-ippm-framework-passive
draft-zheng-ippm-framework-passive
Network Working Group L. Zheng
Internet-Draft Huawei Technologies
Intended status: Informational N. Elkins
Expires: August 15, 2015 Inside Products, Inc.
L. Deng
China Mobile
M. Ackermann
Blue Cross Blue Shield of Michigan
G. Mirsky
Ericsson
February 11, 2015
Framework for IP Passive Performance Measurements
draft-zheng-ippm-framework-passive-03
Abstract
This document describes the framework for passive measurement. In
particular, the differences between passive and active measurements
are analyzed, general considerations for both metric definition and
measurement methodology are discussed, and requirements for various
entities performing a given passive measurement task are described
according to a reference model.
Status of This Memo
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Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Measurement Methods . . . . . . . . . . . . . . . . . . . . . 3
3.1. Active Measurement Method . . . . . . . . . . . . . . . . 3
3.2. Passive Measurement Method . . . . . . . . . . . . . . . 3
3.3. Hybrid Measurement Method . . . . . . . . . . . . . . . . 4
4. Measured Metrics . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Active Metrics . . . . . . . . . . . . . . . . . . . . . 4
4.2. Passive Metrics . . . . . . . . . . . . . . . . . . . . . 4
4.2.1. Passive Measurement Metric Elements . . . . . . . . . 6
5. Reference Model . . . . . . . . . . . . . . . . . . . . . . . 8
6. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Discussion of Errors / Unintended Consequences . . . . . 10
6.2. Control Protocol . . . . . . . . . . . . . . . . . . . . 10
6.3. Measurement Session Management . . . . . . . . . . . . . 10
6.4. Data Collected Correlation . . . . . . . . . . . . . . . 11
6.5. Measurement Configuration . . . . . . . . . . . . . . . . 11
6.6. Scalability and Robustness . . . . . . . . . . . . . . . 11
6.7. Privacy Issues . . . . . . . . . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informational References . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
This document describes the framework for passive measurement. In
particular, the differences between passive and active measurements
are analyzed, general considerations for both metric definition and
measurement methodology are discussed, and requirements for various
entities performing a given passive measurement task are described
according to a reference model.
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The IETF IP Performance Metrics (IPPM) working group first created a
framework for metric development in [RFC2330], which enabled
development of many fundamental metrics. [RFC2330] has been updated
once by [RFC5835], which describes a detailed framework for composing
and aggregating metrics originally defined in [RFC2330].
2. Terminology
TBD
3. Measurement Methods
3.1. Active Measurement Method
Active Measurement Method: The process of measuring performance or
reliability parameters by the examination of traffic (IP Packets)
injected into the network, expressly for the purpose of measurement
by intended Measurement Point(s).
The packets in an Active Measurement Stream typically have fields
which are dedicated to and customized for measurement purposes. As
an example, a sequence number is a common information field used for
dedicated measurements, potentially at multiple measurement points.
Packet stream characteristics (e.g. Protocol Type) and specific
field information (e.g. IP Address), are known at the source and
usually communicated to the measurement point(s) as well.
Because traffic stream characteristics (e.g. number of packets), and
traffic type (e.g. protocol) are known to the Active Measurement
Point receivers, more efficient and focused operations are possible.
3.2. Passive Measurement Method
Passive Measurement Method: The process of measuring some performance
or reliability parameter associated with the existing traffic
(packets) on the network.
[Note: There are definitions for both active and passive measurement
methods in [I-D.ietf-ippm-metric-registry]. Further discussion and
coordination may be needed.]
Some passive methods observe and collect information on all packets
that pass the observation or Measurement Point(s), while other
Passive Methods filter the packets as a first step and only process
information on packets that match the filter criteria.
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Passive Methods may be conducted at one or more Measurement Points.
Certain Metrics (e.g. latency across a particular network path),
require multiple Measurement Points and observed packets must include
sufficient information (e.g. sequence number), to correlate packets
from different observation points.
Passive traffic may be observed/measured at any point in an IP
session path, including source host, destination host and
middleboxes. Passive traffic may also be observed/measured by ""Out
of band"" devices, which do not participate in processing the actual
session traffic. This parallel approach typically has the least
effect upon network conditions and the session traffic being
measured.
3.3. Hybrid Measurement Method
Hybrid Measurement Method: Methods of Measurement which use a
combination of Active Methods and Passive Methods.
Hybrid Methods are not fully defined or delineated at this time.
Details and examples will be forthcoming. As this occurs, this
section will be expanded upon accordingly.
4. Measured Metrics
The de facto focus of RFC2330 is on active measurement. Although
many of the concepts discussed in RFC2330, metrics, measurement
methodology, errors with time apply to both passive and active
methods of measurement techniques, there are considerable differences
in terms of metric definition and measurement methodology for passive
measurement.
4.1. Active Metrics
Active Metrics: A set of standard measurements for evaluating network
performance or reliability, based upon the results of active traffic
(IP Packets), injected into the network by a source node, expressly
for the purpose of measurement and examined by one or more
Measurement Points.
Examples of Active Metrics include: Latency, Throughput, errors, etc.
4.2. Passive Metrics
Passive Metrics: A set of standard measurements for evaluating
network performance or reliability, based upon the results of Passive
traffic (IP Packets), existing on the network and examined by one or
more Measurement Points.
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[Editor Note]: While Active and Passive Methods differ considerably,
the Metrics requirements and definitions for Active and Passive are
similar if not identical. Both can be described as defined reference
events, as packets pass defined reference points. These concepts are
consistent with and further elucidated by ITU-T Recommendation Y.1540
[Y.1540.2011].
Therefore it makes sense to be agnostic to the distinction between
active and passive, with respect to Metrics. Distinctions or
different definitions for Active and Passive Metrics, should only be
created as needed, consistent with the IPPM Metric Registry
[I-D.ietf-ippm-metric-registry].
Passive measurements may be used in scenarios where active
measurement alone is not enough or applicable. Since no extra in-
band traffic which may alter service and performance behavior is
introduced, passive measurement may be done during peak traffic.
Passive measurement is not without cost. In the best scenario, the
passive measurement point is external to the devices participating in
the network traffic. For example, a passive network TAP may be
placed at a switch to capture traffic. This would create very
little, if any, interference with in-band traffic. Alternatively,
care must be taken if a passive measurement technique creates load on
a participant in the network. For example, a packet trace taken at
one of the end host points may add load to the device thus
potentially changing the environment which it is measuring. The
benefits of this method for measurement and diagnostics must be
weighed with the costs.
For networks where charges are based on the amount of data sent,
passive measurement may be the first choice for end-to-end
measurement, as it does not introduce any extra expense to the
subscriber. In terms of Quality of Experience (QoE) measurement,
passive measurement is expected to be more accurate and helpful in
troubleshooting as it reflects the status of real application
traffic.
For passive measurement, the concepts of singleton, sample and
statistical, as defined in [RFC2330], also apply. However, there are
some differences. The singleton, sample, and statistical
measurements are those taken within the boundaries of captured
traffic.
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4.2.1. Passive Measurement Metric Elements
In passive measurement, the most important aspects have to do with
the portion of reality which is actually measured at any point in
time. So, it may be useful to define some terms for passive
measurement. These are as follows:
1. Capture content: this is the type(s) of packet or metric found.
2. Capture distribution: this is the actual pattern of data in the
collected packets. The pattern or distribution may be Poisson
but it may also be bimodal, uniform, or skewed. For example, one
might see an FTP transfer as a relatively uniform distribution, a
TCP connection with a windowing issue may display a skewed
distribution, etc.
3. Capture limits: this is the way the set of packets or metrics are
selected. For example, one may decide to take a trace that
consists of 1,000 packets. Alternatively, one might take a
packet capture for 5 minutes with no regard to how many packets
are found.
4. Capture methodology: this is the area in which passive differs
most greatly from active methods. For example, [RFC2679],
section 3.6. Methodologies discusses the various techniques of
injecting test packets into the network. This is not applicable
to passive measurement. Passive measurement simply collects that
which exists.
5. Unruly Nature of Capture: With reality, there are no guarantees.
That is, if one imagines a passive sample to be a packet trace
taken at a host. If the metric one is looking for is IP/TCP
connectivity measured by a TCP three way handshake, then in
active measurement, one can be guaranteed to find that metric
because one has injected packets of that type into the stream.
In passive measurement, the capture may contain anywhere from
zero occurrences of the desired metric to many instances of the
desired metric.
6. Capture Selection: With active measurement, one may create 500
packets of a certain type and pick according to the sampling
distribution desired.
For example, [RFC2330] in the discussion of generating Poisson
distributions (11.1.3), discusses a method:
Method 1 is to proceed as follows:
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1. Generate E1 and wait that long.
2. Perform a measurement.
3. Generate E2 and wait that long.
4. Perform a measurement.
5. Generate E3 and wait that long.
6. Perform a measurement ...
With passive measurement, one has no way of knowing if a particular
desired packet or packet sequence exists at all in the set of packets
captured.
Having said that, if there do exist many such packets, one may use a
random (or another) sampling method to pick the instances desired.
That is, if one has 100,000 instances of TCP three-way handshakes,
one may decide to randomly choose 50 to examine more closely.
Inherent Inequality of Active and Passive Measurements: due to the
nature of data traffic, depending on what metric is measured, it is
unlikely that it will have a random or Poisson distribution. Hence,
metrics created using Active methods and those generated using
Passive methods are likely to differ. It is not known at this point
whether that difference is significant or not.
[TBD: More discussion here on distributions and inequality]
. Point of View: In passive measurement, it matters greatly where
the measurement is being done. Point of view is critical. Passive
measurement only knows what it sees from its own perspective.
In troubleshooting problems using passive measurement, it is often
necessary to get multiple points of view. Let us take a simple case
of diagnosing packet loss from an end user perspective. If one takes
a packet trace at the client host, one sees that certain packets are
not being received. If one takes two packet traces at the same time
at the server and client, one sees that the server sends these
packets yet the client does not receive them. Hence, the problem
must be at a middle box. So, then, one must start taking traces at
client, server, and a trace point after the first middle box, etc.
The measurement techniques for passive measurement must accommodate
and facilitate such tasks.
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Active measurement techniques know clearly the measurement point and
path because that is a part of the definition of the Active
measurement task.
5. Reference Model
This section describes the main functional components of the passive
measurement system, and the interactions between the components.
Some new terms are defined in this document and some are borrowed
from the LMAP Framework [I-D.ietf-lmap-framework].
+---------------+ +---------------+
| Measurement | Coordination | Measurement |
| Agent A |--------------| Agent B |
+---------------+ +---------------+
^ | ^ |
Control | | Report Control | | Report
| | +-----------------+ |
| +-----|-------------------+ |
| | | |
v v v v
+------------+ +------------+
| Controller |---------| Collector |
+------------+ +------------+
Figure 1: Passive Measurement Reference Model
Although there are considerable similarities between the proposed
reference model and the LMAP framework [I-D.ietf-lmap-framework], it
should be noted that the above architecture is provided as a more
general outline of an integral collection of functional components
collaborating in performing a specific instance of passive
measurement method. Various functions from LMAP framework in
performing a passive measurement task represent a specific way of
realizing the general model.
Controller: A entity that exchanges the Control of the Measurement
Task with the Measurement Entity, receives the Report from the
Collector and conducts the value calculation/derivation for the
metrics measured of the Measurement Task. When multiple Measurement
Entities are involved for a certain Measurement Task, Controller may
only have Control exchanged with one or some of the Measurement
Entities.
Collector: A entity that receives a Report from a Measurement Entity
and provides the Report to the Controller for metric calculation /
derivation.
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Measurement Agent: An entity that exchanges the Control of the
Measurement Task with the Controller, performs Measurement Tasks and
sends the Report to Collector. When multiple Measurement Agents are
involved for a certain Measurement Task, Coordination may be required
between Measurement Entities.
Control: The collective description of information exchanged between
Controller and Measurement Agent, i.e. configurations, instructions,
states, etc. for a Measurement Agent to perform and Report
Measurement Tasks.
Coordination: [TBD. Discuss coordination with MAs and Controller]
Report: The set of Measurement Results and other associated
information as defined by the Control.
[Measurement Task]: The act that consists of the single operation of
the Measurement Method at a particular time and with all its Input
Parameters set to specific values.
[Measurement Result]: The output of a single Measurement Task (the
value obtained for the parameter of interest or Metric).
[Note: further discussion and clarifications regarding these borrowed
terms from LMAP framework are to be expected, with coordination with
[I-D.ietf-lmap-framework].]
6. Methodology
For a given set of well-defined metrics, a number of distinct
measurement methodologies may exist. Let us take One-way Packet Loss
as example. Packet loss over a path is the difference between the
number of packets transmitted at the starting interface of the path
and received at the ending interface of this path. In order to
perform packet loss measurements on a live traffic flow, different
methodologies exist. A partial list includes:
1. observation, e.g. Sequence Number, pros and cons
2. inserting a delimiting packet: Y.1731, RFC6374, pros and cons
3. altering the packet:
Note: This list is by no means exhaustive. The purpose is to point
out the variety of measurement techniques.
Note: A methodology for a metric should have the property that it is
repeatable: if the methodology is used multiple times under identical
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conditions, it should result in consistent measurements. A
methodology for a metric should be scalable, robust and secured.
Following sections list the functional requirements and design
considerations of any passive measurement methodology.
6.1. Discussion of Errors / Unintended Consequences
As discussed in Section 6.3 Measurements, Uncertainties and Errors of
RFC2330, the measurement technique itself can introduce errors.
"consider the timing error due to measurement overheads within the
computer making the measurement, as opposed to delays due to the
Internet component being measured. The former is a measurement
error, while the latter reflects the metric of interest. Note that
one technique that can help avoid this overhead is the use of a
packet filter/sniffer, running on a separate computer that records
network packets and timestamps them accurately."
With some types of passive measurement, changing the packet may
create extra load on the network, change the characteristics of
network traffic, or change the nature of the problem itself.
Obviously, the benefits of the measurement must be such as to offset
the potential unintended consequences.
6.2. Control Protocol
As depicted by the reference model, there are different functional
components residing along an end-to-end path or within an ISP's
domain that cooperate to perform a specific passive measurement task.
This section describes the high level function requirements for the
control protocol between these collaborating components.
Note: LMAP is developing the control protocol between MA and
controller, here will be the discussion for control protocol between
measurement parties, i.e. MA to MA or MA to MP.
6.3. Measurement Session Management
A measurement session refers to the period of time in which
measurement for certain performance metrics is enabled over a
forwarding path. A measurement session may be started either
proactively or on demand. The methodology must indicate how the
measurement session is to be started.
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6.4. Data Collected Correlation
When there is no coordination between MAs during a measurement
session, data collected on the upstream MA and downstream MA, e.g.
packet counts or timestamps, may be periodically report to the
Controller. And the value of the performance metrics are calculated/
derived on the Controller. Certain synchronization mechanism is
required to ensure the data collected on upstream and downstream are
correlated. This may further require that the upstream and
downstream MEs have a certain time synchronization capability (e.g.,
supporting the Network Time Protocol (NTP) [RFC5905], or the IEEE
1588 Precision Time Protocol (PTP) [IEEE.1588.2008].)
6.5. Measurement Configuration
A measurement session can be configured statically or dynamically.
The methods must be discussed.
6.6. Scalability and Robustness
[TBD]
6.7. Privacy Issues
[TBD]
7. Security Considerations
This document does not bring new security issues to IPPM.
8. Acknowledgements
The authors would like to thank Al Morton, Brian Trammell and Robert
Hamilton for their valuable comments.
9. References
9.1. Normative References
[I-D.li-mpls-seamless-mpls-mbb]
Li, Z., Li, L., Morillo, M., and T. Yang, "Seamless MPLS
for Mobile Backhaul", draft-li-mpls-seamless-mpls-mbb-01
(work in progress), February 2014.
[IEEE.1588.2008]
"Standard for a Precision Clock Synchronization Protocol
for Networked Measurement and Control Systems", IEEE
Standard 1588, March 2008.
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[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330, May
1998.
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC5835] Morton, A. and S. Van den Berghe, "Framework for Metric
Composition", RFC 5835, April 2010.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
9.2. Informational References
[I-D.ietf-ippm-metric-registry]
Bagnulo, M., Claise, B., Eardley, P., Morton, A., and A.
Akhter, "Registry for Performance Metrics", draft-ietf-
ippm-metric-registry-01 (work in progress), September
2014.
[I-D.ietf-lmap-framework]
Eardley, P., Morton, A., Bagnulo, M., Burbridge, T.,
Aitken, P., and A. Akhter, "A framework for large-scale
measurement platforms (LMAP)", draft-ietf-lmap-
framework-10 (work in progress), January 2015.
[Y.1540.2011]
"Internet protocol data communication service - IP packet
transfer and availability performance parameters", ITU-T
Y.1540, March 2011.
Authors' Addresses
Lianshu Zheng
Huawei Technologies
China
Email: vero.zheng@huawei.com
Nalini Elkins
Inside Products, Inc.
USA
Email: nalini.elkins@insidethestack.com
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Lingli Deng
China Mobile
China
Email: denglingli@chinamobile.com
Michael Ackermann
Blue Cross Blue Shield of Michigan
USA
Email: mike.ackermann@bcbsmi.com
Greg Mirsky
Ericsson
USA
Email: gregory.mirsky@ericsson.com
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