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 www.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.
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.demon.co.uk) does
not, to my knowledge, service anything other than HTTP.
Proxy Trails
It is possible, but unusual, to construct URLs containing multiple proxy
servers. Thus you specify a URL such as:
http://www.demon.co.uk:8080/http://www.hensa.ac.uk/gopher://gopher.doc.ic.ac.uk
which will proxy to HENSA via Demon Internet.
Configuring ArcWebTCP
Load ArcWebTCP and click on the icon bar icon to open the configuration
window. The default state is not to proxy HTTP requests, but to proxy FTP,
gopher and WAIS to www.hensa.ac.uk on port 80. 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.
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.