Framework for IP Passive Performance Measurements
draft-zheng-ippm-framework-passive-01

Network Working Group                                           L. Zheng
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                 N. Elkins
Expires: December 26, 2014                               Inside Products
                                                                 L. Deng
                                                            China Mobile
                                                            M. Ackermann
                                                           BCBS Michigan
                                                               G. Mirsky
                                                                Ericsson
                                                           June 24, 2014

           Framework for IP Passive Performance Measurements
                 draft-zheng-ippm-framework-passive-01

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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   This Internet-Draft will expire on December 26, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
 

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   Provisions Relating to IETF Documents
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Table of Contents

   1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2 Terminology  . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3 Passive Metric Definition  . . . . . . . . . . . . . . . . . . .  5
   4 Reference Model  . . . . . . . . . . . . . . . . . . . . . . . .  8
   5 Methodology  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6 Methodology Design Considerations  . . . . . . . . . . . . . . . 10
     6.1 Discussion of Errors / Unintended Consequences . . . . . . . 10
     6.2 Control Protocol . . . . . . . . . . . . . . . . . . . . . . 10
     6.3 Measurement Session Management . . . . . . . . . . . . . . . 11
     6.4 Data Collected Correlation . . . . . . . . . . . . . . . . . 11
     6.5 Measurement Configuration  . . . . . . . . . . . . . . . . . 11
     6.6 Scalability and Robustness . . . . . . . . . . . . . . . . . 11
   7 Security Considerations  . . . . . . . . . . . . . . . . . . . . 11
   8 IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 11
   9 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
   10 References  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     10.1 Normative References  . . . . . . . . . . . . . . . . . . . 12
     10.2 Informative References  . . . . . . . . . . . . . . . . . . 13

 

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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.

   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].

   The first task of this document will be to define active and passive
   measurement methods.

   Active Measurement Method: The process of measuring some performance
   or reliability parameter associated with the transfer of traffic by
   generating and/or receiving packets injected into the network.

   In contrast, passive measurement is defined as:

   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.manyfolks-ippm-metric-registry]. Further discussion
   and coordination may be needed.]

   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.

   It should be noted that there can be different ways of how one
   conducts a "passive" measurement task (without injecting packets) as
   well as pure observation.

   Examples include:

   1. adding a dedicated packet header[draft-PDM]

   2. changes to an existing header for marking[draft-coloring]
 

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   Terminology used in the above examples will be defined in Section 2:
   Terminology.

   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 who charge for 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.

2 Terminology

   In this sections, we will define some terms and acronyms which will
   be referred to in this document.

   Coloring : A scheme for modifying a field in the IP header for
   purposes of measurement.  A description of this scheme for IPv4 may
   be found at [draft-coloring].

   PDM : Performance and Diagnostic Metrics (PDM) header.  An IP header
   which is appended to packets for the purposes of measurement. A
   description of the IPv6 version of this header may be found at
   [draft-PDM].

3 Passive Metric Definition

   In RFC2330, singleton, sample, and statistics are defined as follows:

   "By a 'singleton' metric, we refer to metrics that are, in a sense,
   atomic.  For example, a single instance of "bulk throughput capacity"
 

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   from one host to another might be defined as a singleton metric, even
   though the instance involves measuring the timing of a number of
   Internet packets.

   By a 'sample' metric, we refer to metrics derived from a given
   singleton metric by taking a number of distinct instances together.
   For example, we might define a sample metric of one-way delays from
   one host to another as an hour's worth of measurements, each made at
   Poisson intervals with a mean spacing of one second.

   By a 'statistical' metric, we refer to metrics derived from a given
   sample metric by computing some statistic of the values defined by
   the singleton metric on the sample.  For example, the mean of all the
   one-way delay values on the sample given above might be defined as a
   statistical metric."

   For passive measurement, the concepts of singleton, sample and
   statistical also apply.   However, there are some differences. The
   singleton, sample, and statistical measurements are those taken
   within the boundaries of captured traffic.

   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
 

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   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:

         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.

   7.  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]

   8.  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
 

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   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.

   Active measurement techniques know clearly the measurement point and
   path because that is a part of the definition of the Active
   measurement task.

4 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] (indicated by brackets).

        +---------------+                +---------------+
        |  Measurement  |  Coordination  |  Measurement  |
        |   Agent A     |<-------------->|   Agent B     |
        +---------------+                +---------------+
                  ^  |                       ^    |
         Control  |  | Report        Control |    | Report
                  |  |     +-----------------+    |
                  |  +-----|-------------------+  |
                  |        |                   |  |
                  v        v                   v  v
                +------------+           +------------+
                | Controller |<--------->|  Collector |
                +------------+           +------------+

   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
 

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   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.

   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].]

5 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:

 

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   1.Observation, e.g. Sequence Number, pros and cons

   2.inserting a delimiting packet: Y.1731, RFC6374, pros and cons

   3.altering the packet: Coloring/PDM

   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
   conditions, it should result in consistent measurements.  A
   methodology for a metric should be scalable, robust and secured.

6 Methodology Design Considerations

   This section gives 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
 

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   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.

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) [IEEE1588].)

6.5 Measurement Configuration

   A measurement session can be configured statically or dynamically.
   The methods must be discussed.

6.6 Scalability and Robustness

7 Security Considerations

   This document does not bring new security issues to IPPM.

8 IANA Considerations

   This document has no actions for IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC

9 Acknowledgements

   The authors would like to thank Al Morton, Brian Trammell and Robert
   Hamilton for their valuable comments.

 

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10 References

10.1 Normative References

   [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., Ed., Burbank, J., and W. Kasch,
            "Network Time Protocol Version 4: Protocol and Algorithms
            Specification", RFC 5905, June 2010.

   [IEEE1588]  IEEE 1588-2002 standard, "Standard for a Precision Clock
            Synchronization Protocol for Networked Measurement and      
                 Control Systems"

 

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10.2 Informative References

   [draft-PDM] Elkins, N., et al, "IPPM Considerations for the IPv6 PDM
   Extension Header", draft-elkins-ippm-pdm-metrics-04 (work in
   progress),  April 2014

   [I-D.manyfolks-ippm-metric-registry] Bagnulo, M., Claise, B.,
   Eardley, P., and A. Morton, "Registry for Performance Metrics",
   draft-manyfolks-ippm-metric-registry-00 (work in progress), February
   2014.

   [draft-coloring] Chen, M, et al, "Coloring based IP Flow Performance
   Measurement Framework", draft-chen-ippm-coloring-based-ipfpm-
   framework-01 (work in progress), November, 2013.

   [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-07
   (work in progress), May 2014.

Authors' Addresses

   Lianshu Zheng
   Huawei Technologies
   China
   Email: vero.zheng@huawei.com

   Nalini Elkins
   Inside Products, Inc.
   USA
   Email: nalini.elkins@insidethestack.com

   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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