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