RFC 2227 (rfc2227) - Page 2 of 37
Simple Hit-Metering and Usage-Limiting for HTTP
Alternative Format: Original Text Document
RFC 2227 Hit-Metering and Usage-Limiting October 1997
4 Analysis 17
4.1 Approximation accuracy for counting users 18
4.2 What about "Network Computers"? 19
4.3 Critical-path delay analysis 19
5 Specification 20
5.1 Specification of Meter header and directives 20
5.2 Abbreviations for Meter directives 23
5.3 Counting rules 24
5.3.1 Counting rules for hit-metering 24
5.3.2 Counting rules for usage-limiting 25
5.3.3 Equivalent algorithms are allowed 26
5.4 Counting rules: interaction with Range requests 27
5.5 Implementation by non-caching proxies 27
5.6 Implementation by cooperating caches 28
6 Examples 28
6.1 Example of a complete set of exchanges 28
6.2 Protecting against HTTP/1.0 proxies 30
6.3 More elaborate examples 30
7 Interactions with content negotiation 31
7.1 Treatment of responses carrying a Vary header 31
7.2 Interaction with Transparent Content Negotiation 32
8 A Note on Capturing Referrals 32
9 Alternative proposals 33
10 Security Considerations 34
11 Acknowledgments 35
12 References 35
13 Authors' Addresses 36
14 Full Copyright Statement 37
1 Introduction
For a variety of reasons, content providers want to be able to
collect information on the frequency with which their content is
accessed. This desire leads to some of the "cache-busting" done by
existing servers. ("Cache-busting" is the use by servers of
techniques intended to prevent caching of responses; it is unknown
exactly how common this is.) This kind of cache-busting is done not
for the purpose of maintaining transparency or security properties,
but simply to collect demographic information. Some cache-busting is
also done to provide different advertising images to appear on the
same page (i.e., each retrieval of the page sees a different ad).
This proposal supports a model similar to that of publishers of
hard-copy publications: such publishers (try to) report to their
advertisers how many people read an issue of a publication at least
once; they don't (try to) report how many times a reader re-reads an
issue. They do this by counting copies published, and then try to
estimate, for their publication, on average how many people read a
Mogul & Leach Standards Track