IP Performance Measurement (ippm) B. Trammell
Internet-Draft ETH Zurich
Intended status: Informational October 12, 2012
Expires: April 15, 2013
Hybrid Measurement using IPPM Metrics
draft-trammell-ippm-hybrid-ps-00.txt
Abstract
Hybrid measurement is the combination of metrics derived from passive
and active measurement to produce a measurement result. This
document discusses use cases for hybrid measurement using metrics
defined within the IPPM framework
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1. Introduction
Hybrid measurement is the combination of metrics derived from passive
and active measurement to produce a measurement result. This
combination can be either spatial or temporal. For example, one way
delay to a given endpoint could be derived from passive measurements
from a sample of remote endpoints with which traffic is frequently
exchanged, and supplemented with active measurements from endpoints
with less frequent traffic, to build a "delay map" to a certain point
in the network. On the temporal side, loss or delay metrics could be
passively measured and stored over time to provide a baseline against
which actively-measured loss or delay metrics could be compared
during troubleshooting, in order to determine whether a specific path
or path segment is contributing to an observed performance problem.
The IPPM working group has produced a framework [RFC2330] for and
rich set of well-defined metrics (e.g. [RFC2679], [RFC2680]) for IP
performance measurement using active methods, and protocols for
measuring them. These metrics could form the basis of a platform for
hybrid measurement, provided that passively-derived metrics were
defined to compatible with the corresponding actively-derived
metrics; or alternately, provided that methodologies for passive
measurement can be defined for each of the existing active metrics to
be used, such that those methodologies produce values for the metrics
equivalent to the active methodology for the same metric parameters,
given some assumptions about the packet stream to be observed to
perform the passive measurement, and given tolerances for uncertainty
in the results.
2. Problem Statement
Complicating the definition of hybrid measurements is that passive
measurement must make do with the traffic that is observable, while
active measurement has some control over the traffic observed.
Measurements for some set of parameters are not possible if no
suitable traffic is observed, and the timing of the measurement
cannot be controlled. Placement of the observation points for
passive measurement along a path additionally introduces uncertainty
in the results. For example, passive one-way delay measurement could
be performed using two measurement points, one close to each
endpoint, with synchronized clocks, comparing the observation times
of packets via their hashes. This will not produce a value which is
directly comparable to a Type-P-One-way-Delay measured as specified
in section 3.6 of [RFC2679], because it will not account for the one-
way-delay from the source to the source-side observation point, or
from the destination-side observation point to the destination. Any
specification of hybrid measurement using IPPM metrics must handle
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these complications.
The proposed specification entails:
o Definition of scenarios and requirements for hybrid measurement.
o Selection of existing IPPM metrics to be used for the active side
of hybrid measurements to meet these requirements.
o Definition of equivalent passive measurement methodologies for
each selected metric, specifically addressing the assumptions
about the observed packet stream which must hold for the metric to
be valid, and with a specific allowance for the measurement and/or
estimation of uncertainty due to uncontrollable conditions or
observation point placement.
o Definition of metrics based on these passive methodologies, or
modification of the definition of existing metrics to add passive
methodologies.
o Definition of methods for comparison between active and passive
metrics allowing for estimated uncertainty.
o Definition of methods for spatial and temporal composition of
active and passive metrics together allowing for estimated
uncertainty.
3. Scenarios and Requirements
[EDITOR'S NOTE: This section will contain scenarios and requirements
for hybrid measurement. Candidate scenarios include (1) use of
passive measurement to measure delay, loss, etc. on paths on which
traffic is frequently sent, supplemented with active measurement on
low-traffic paths or during low-traffic times and (2) use of passive
measurement to establish a long-term baseline against which active
measurements can be compared to detect and isolate anomalies, as in
the introduction.]
4. Selected IPPM Metrics
[EDITOR'S NOTE: this section will contain information on the metrics
selected for passive measurement, and initial discussion of passive
measurement methodologies for them. Metric definition will
presumably be left for a future document.]
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5. Security Considerations
[EDITOR'S NOTE: this section will discuss general security
considerations of using passive measurement for performance, both on
the potential for attacks against the measurement system as well as
the potential for privacy or security threats posed by the
measurement system itself.]
6. IANA Considerations
This document contains no considerations for IANA.
7. References
7.1. Normative References
[RFC2330] Paxson, V., Almes, G., Mahdavi, J., and M. Mathis,
"Framework for IP Performance Metrics", RFC 2330,
May 1998.
7.2. Informative References
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2680] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Packet Loss Metric for IPPM", RFC 2680, September 1999.
Author's Address
Brian Trammell
Swiss Federal Institute of Technology Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Phone: +41 44 632 70 13
Email: trammell@tik.ee.ethz.ch
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