| IP Performance Measurement (ippm) | B. Trammell |
| Internet-Draft | ETH Zurich |
| Intended status: Informational | October 12, 2012 |
| Expires: April 13, 2013 |
Hybrid Measurement using IPPM Metrics
draft-trammell-ippm-hybrid-ps-00.txt
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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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.
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 these complications.
The proposed specification entails:
[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.]
[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.]
[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.]
This document contains no considerations for IANA.
| [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. |
| [RFC2680] | Almes, G., Kalidindi, S. and M. Zekauskas, "A One-way Packet Loss Metric for IPPM", RFC 2680, September 1999. |