Re: Questions out of interest

From: Henny Bekker <>
Date: Fri, 30 May 1997 01:18:33 +0200 (METDST)

Dear Noel,

> I have been visiting the official Squid site and several other related
> sites but I haven't found any real documentation such as one would find
> for INN or sendmail.
> I'm looking for something on the lines of design model, communications model,
> cacheing algorithms, etc. Am I perhaps not fully aware of all the available
> info. ?
Have a look at URL:
It's a Web caching architecture document we have written in the framework
of the Desire/Web-caching Project..

> Also, ASAIK, if you got a cache hierarchy, such as a parent and a single
> sibling, where all the clients are going through the sibling, on a miss,
> the sibling will interrogate the parent. If the parent can't deliver the
> object, the sibling establishes an Internet connection itself (pls. see
> diagram).
> client --------------------------> sibling
> ------------------------------------> Internet
> |
> |
> \ /
> parent
Your so called "sibling host" (say host A) is in fact the first-level Web
caching server for the browsers. This Web caching server can have a sibling
relation with your so called "parent host" (say host B). Host A will send
an ICP request to host B to check if the requested object is available.
If so, the parent send it imediately back (if small enough) in the ACK-ICP
packet or send a empty ACK packet so that host B can fetch it with a GET
request. If the requested object is not on host B, it will send a NACK to
Host A which will fetch the object from the originating Web server..
It's also possible
that host A is a child of host B. In this case the requested object will
be fetched from the originating Web server (or from other sibling/parent
Web caching servers) by Host B.

> Would it be possible for the parent to retrieve the object itself, and then
> forwards it to the sibling, both servers having the opporunity to cache the
> object ?
Only if Host B is the parent of host A.. A sibling host will not ever fetsh
an object for another sibling relation from the internet..

Cheers, Henny

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Received on Thu May 29 1997 - 16:21:07 MDT

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