IPPM Metrics for Measuring Connectivity
RFC 2678
Document | Type |
RFC - Proposed Standard
(September 1999; No errata)
Obsoletes RFC 2498
|
|
---|---|---|---|
Authors | Jamshid Mahdavi , Vern Paxson | ||
Last updated | 2013-03-02 | ||
Stream | Legacy | ||
Formats | plain text html pdf htmlized bibtex | ||
Stream | Legacy state | (None) | |
Consensus Boilerplate | Unknown | ||
RFC Editor Note | (None) | ||
IESG | IESG state | RFC 2678 (Proposed Standard) | |
Telechat date | |||
Responsible AD | (None) | ||
Send notices to | (None) |
Network Working Group J. Mahdavi Request for Comments: 2678 Pittsburgh Supercomputing Center Obsoletes: 2498 V. Paxson Category: Standards Track Lawrence Berkeley National Laboratory September 1999 IPPM Metrics for Measuring Connectivity Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1999). All Rights Reserved. 1. Introduction Connectivity is the basic stuff from which the Internet is made. Therefore, metrics determining whether pairs of hosts (IP addresses) can reach each other must form the base of a measurement suite. We define several such metrics, some of which serve mainly as building blocks for the others. This memo defines a series of metrics for connectivity between a pair of Internet hosts. It builds on notions introduced and discussed in RFC 2330, the IPPM framework document. The reader is assumed to be familiar with that document. The structure of the memo is as follows: + An analytic metric, called Type-P-Instantaneous-Unidirectional- Connectivity, will be introduced to define one-way connectivity at one moment in time. + Using this metric, another analytic metric, called Type-P- Instantaneous-Bidirectional-Connectivity, will be introduced to define two-way connectivity at one moment in time. + Using these metrics, corresponding one- and two-way analytic metrics are defined for connectivity over an interval of time. Mahdavi & Paxson Standards Track [Page 1] RFC 2678 IPPM Metrics for Measuring Connectivity September 1999 + Using these metrics, an analytic metric, called Type-P1-P2- Interval-Temporal-Connectivity, will be introduced to define a useful notion of two-way connectivity between two hosts over an interval of time. + Methodologies are then presented and discussed for estimating Type-P1-P2-Interval-Temporal-Connectivity in a variety of settings. Careful definition of Type-P1-P2-Interval-Temporal-Connectivity and the discussion of the metric and the methodologies for estimating it are the two chief contributions of the memo. 2. Instantaneous One-way Connectivity 2.1. Metric Name: Type-P-Instantaneous-Unidirectional-Connectivity 2.2. Metric Parameters: + Src, the IP address of a host + Dst, the IP address of a host + T, a time 2.3. Metric Units: Boolean. 2.4. Definition: Src has *Type-P-Instantaneous-Unidirectional-Connectivity* to Dst at time T if a type-P packet transmitted from Src to Dst at time T will arrive at Dst. 2.5. Discussion: For most applications (e.g., any TCP connection) bidirectional connectivity is considerably more germane than unidirectional connectivity, although unidirectional connectivity can be of interest for some security applications (e.g., testing whether a firewall correctly filters out a "ping of death"). Most applications also require connectivity over an interval, while this metric is instantaneous, though, again, for some security applications instantaneous connectivity remains of interest. Finally, one might not have instantaneous connectivity due to a transient event such as a full queue at a router, even if at nearby instants in time one does have connectivity. These points are addressed below, with this metric serving as a building block. Mahdavi & Paxson Standards Track [Page 2] RFC 2678 IPPM Metrics for Measuring Connectivity September 1999 Note also that we have not explicitly defined *when* the packet arrives at Dst. The TTL field in IP packets is meant to limit IP packet lifetimes to 255 seconds (RFC 791). In practice the TTL field can be strictly a hop count (RFC 1812), with most Internet hops being much shorter than one second. This means that most packets will have nowhere near the 255 second lifetime. In principle, however, it is also possible that packets might survive longer than 255 seconds. Consideration of packet lifetimes must be taken into account in attempts to measure the value of this metric. Finally, one might assume that unidirectional connectivity is difficult to measure in the absence of connectivity in the reverse direction. Consider, however, the possibility that a process on Dst's host notes when it receives packets from Src and reports thisShow full document text