Here are my definitions; in fact, I consider that caches and mirrors aim at
reaching the same goals...
Cache :
An intermediary equipment or program between the client and the server
aiming at reducing network bandwidth and improving the quality of service
from the user point of view by storing web objects closer to the end-user.
The user requests not satisfied by the cache MUST be forwarded to the server
or upper level cache in a cache mesh.
The cache MUST freshen the stored data according to server information.
It SHOULD contain its own internal algorithms to freshen the data if no
particular server information is given.
Mirror :
A copy of a Web server aiming at reducing network bandwidth and improving
the quality of service from the user point of view by storing all or part of
the content of the origin server closer to the end-user.
The user requests not satisfied by the mirror MUST result in the sending of
the appropriate HTTP error code.
A complemental system, either installed on the origin server or on the
mirror, SHOULD freshen the copied data when necessary.
> From owner-wrec@cs.utk.edu Fri Aug 27 15:02 EDT 1999
>
> Hello WREC'ers.
>
> We've had a great deal of discussion these past two weeks concerning
caching and replication. I propose that we work on getting our core
definitions completed now. From these, we can move onto finishing up the
taxonomic implementation and deployments based upon these definitions.
>
> First I suggest we break the defintions up into a small base set that are
the most fundamental. From the base set come the first and second
derivatives that form all the core terms necessary to describe repliacation
and caching implementations. Included are a starting point for discussion.
>
> As we move from the terminology to the taxonimc discussions, please keep
in mind the following:
>
> Implementation and deployment that is broadly (or hopelessly depended
upon) in the Internet today belongs in the taxonomy draft.
>
> Current research and needed research belongs in the research draft. (Joe
Touch Editor)
>
> Known problems and implementation shortcomings of current
implementation/deployment belong in the known issues draft (John Dilley
Editor)
>
> Here are the core terms as they stand today. Feel free to add/subtract
the core set.
>
>
> Base Terms:
> Client
> Exactly adopted from RFC2616. Editors View - Consensus
> "A program that establishes connections for the purpose of sending
requests."
>
> Proxy
> A derived definition for RFC2616. Editors View - Consensus
> Editors Note: The term has been heavily debated within the WG. Consensus
> is to override the definition in RFC2616.
> "An intermediary system which acts as both a server and a
> client for the purpose of making requests on behalf of
> other clients. Requests are serviced internally or by
> passing them on, with possible translation, to other
> servers. A proxy MUST implement both the client and server
> requirements of this specification. A "transparent proxy"
> is a proxy that does not modify the request or response
> beyond what is required for proxy authentication and
> identification. A "non-transparent proxy" is a proxy that
> modifies the request or response in order to provide some
> added service to the user agent, such as group annotation
> services, media type transformation, protocol reduction,
> or anonymity filtering. Except where either transparent or
> non-transparent behavior is explicitly stated, the HTTP
> proxy requirements apply to both types of proxies.
>
> Note: The term "transparent proxy" given in [6] has different
> meaning within the Web caching community. Further
> unspecified references in this document (including the
> following paragraph) are to the Web caching community
> definition, which is given later.
>
> The condition requiring implementation of both server and
> client requirements of HTTP/1.1 is only appropriate for a
> non-transparent proxy."
>
> Replication
> Not defined. Editors View - Open Disucssion
> Editors Note: Amazingly enough, we can't find any definition for
replication
> in any on-line RFC or draft. Is it really intuitive. We think not,
since
> there so much debate in the working group surrounding what is
replication.
>
> Server
> Exactly adopted from RFC2616. Editors View - Consensus
> "An application program that accepts connections in order to
> service requests by sending back responses. Any given program may
> be capable of being both a client and a server; our use of these
> terms refers only to the role being performed by the program for a
> particular connection, rather than to the program's capabilities
> in general. Likewise, any server may act as an origin server,
> proxy, gateway, or tunnel, switching behavior based on the nature
> of each request."
>
> Surrogate
> Not defined Editors View - Open Discussion
> Editors-Note: A fundemental concept to the web. Surrogates act in
behalf of
> content publishers. Examples of surrogates within the taxonomy are:
Mirrors
> and accelerators.
>
> First Derivative Terms: (Build upon base terms)
> Cache
> A derived definition for RFC2616. Editors View - Open Disuccsion
> Editor-Notes: The most controversial term in the taxonomy. Is it
dervived
> from replication or is it a base term? 3 variants proposed need
> rationalization. There has been so many comments on each of the variant
> definitions, we would like the individuals to supply thier current
concise
> definitions for dicussion.
> Current taxonomy definition
> "A program's local store of response messages and the
> subsystem that controls its message storage, retrieval, and
> deletion. A cache stores cacheable responses in order to
> reduce the response time, server load and network
> bandwidth consumption on future, equivalent requests. Any
> client or server may include a cache, though a cache
> cannot be used by a server while it is acting as a tunnel."
>
> Joe Touch's definition
> Joe can you supply your current definition?
>
> Wojtek Sylwestrzak's definition
> Wojtek can you supply your current definition?
>
> Misha Rabinovich's definition
> Misha can you supply your current definition?
>
> Ivan Lovric's definition
> Ivan can you supply your current definition?
>
>
> Mirror
> Not defined. Editors View - Nees Discussion
> Editors-Note: An attempt at taxonomy has been made. It is clear
> from discussion that a definition is in order. The taxonomic variants
> can then be defined from it.
>
> Origin Server
> Exactly adopted from RFC2616. Editors View - Consensus
> "The server on which a given resource resides or is to be created."
>
> Reverse Proxy
> A new defintion. Editors View - Open Discussion
> Editors-Note: Differentiation from proxy is needed.
> "An intermediary system which acts as both a server and a
> client for the purpose of serving requests on behalf of
> origin servers. Requests are serviced internally or by
> passing them on to the origin server they are representing.
> A reverse proxy must interpret and, if necessary, rewrite a
> request message before forwarding it. Reverse proxies are
> often used as server-side portals through network firewalls
> and as helper applications for off loading requests from
> origin servers."
>
> Second Derivative Terms: (Build upon first derivative terms)
> Caching Proxy
> A new defintion. Editors View - Consensus
> "A proxy with a cache, acting as server to clients, and
> a client to servers"
>
> Caching Reverse Proxy (Accelerator)
> Not Defined. Editors View - Needs Discussion
> Editors-Note: Do we need it? Suggested definition
> "A reverse proxy with a cache, acting as server to clients, and
> a client to servers"
>
> Replica Origin Server
> New definition. Editors View - Open Disussion
> Editors-Note: In light of the recent disuccsion, the authoritative
> attribute is quiestionable.
> "origin server storing a persistent replica of a data set
> stored at the authoritative reference"
>
> Surrogate Cache
> Not Defined. Editors View - Needs Discussion
> Editors-Node: Do we need it, or is it a role that is provided by
proxies,
> reverse proxies and replica origin servers?
>
> - Gary
>
>
>
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