What is Proxying
In terms of the World-Wide Web, a proxy server is an agent program which
carries out transactions on behalf of a client (ie. ArcWeb). The
proxy server is willing to fetch documents from within certain namespaces
and return them to the client. Usually, proxies cache the documents that
they have fetched to reduce network loading. Hence, if you are in the UK
and you fetch a page from the USA, it will be at least as quick to fetch it
via a proxy such as that at wwwcache.hensa.ac.uk. If the proxy already
has a copy of the page cached, it will return it directly, otherwise it will
fetch it from the source.
A bit plainer ..
Try looking at Demon Internet's description
of proxying.
And now in plain English ...
Instead of asking the machine which has a document (the target machine) to send
it to you, you can
ask another machine (the proxy) to do it on your behalf. There are
advantanges of this scheme because:
- you only ever need to talk to the proxy machine, which will usually be very
close to you (in network terms) eg. Demon customers can use www-cache.demon.co.uk.
Your link to the proxy machine will be at the highest speed that your machine
can manage.
- the proxy machine can talk to the target machine over its highest speed links
which are going to be at least as fast (in Demon's case, very much faster) as your
link. (However, the loading on the link may make it slower).
- the proxy remembers the pages it has been asked to fetch for people. If it
gets another request for the same page, it just sends you its copy. It doesn't
matter who asked for it. So if you happen to be in the UK, and you
ask for a page in the USA, the proxy may not have to bother to talk to the
machine in the USA at all. This is obviously going to be faster than you having
to connect to the machine in the USA, as the link to the USA is usually heavily
loaded.
Proxy Namespaces
The HTTP proxy servers will always respond to http URLs. The HENSA proxy
also serves gopher, WAIS and FTP URLs. Since only the HTTP protocol is used
by the client, effectively you get these methods without requiring special
software. The Demon Internet proxy (on port 8080 of www-cache.demon.co.uk) does
now appear to service FTP, gopher and WAIS in addition to HTTP.
Configuring ArcWeb to use Proxies
Choose the Network option from the Configure menu which you
will find on ArcWeb's icon bar menu, and the configuration window will be opened.
The default state is to proxy HTTP requests and to proxy FTP,
gopher and WAIS to wwwcache.hensa.ac.uk on port 8080, 8080 & 80 respectively.
To change the proxy server,
you need to know the hostname and the port number. Enter the host name in
the large box and the port number in the small box next to the protocol. If
you wish, enable HTTP proxying. The No Proxy icon chooses domains
which should be excluding permanently from proxying. It is usual to set
this to at least your own domain. For me, ac.uk is sensible, as
Southampton University is a SuperJANET site anyway and access to the other
academic sites will probably be more efficient if done directly. You can
specify several comma seperated domain names here to exclude all of those from
proxying.
Finally, to save your choices permanently, click Save Choices, to cancel all
changes, click Cancel, and to set the choices, but not save them to disc,
click OK.