Dr. Mark Humphrys

School of Computing. Dublin City University.

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  URI schemes

DCU proxy servers

The Web

HTTP client

Web browser

Uses MIME types.
(a) Plug-in - Runs inside browser process.
(b) Helper application - Separate process.

HTTP server

Some issues to keep servers running fast:


For high-demand sites: Multiple copies of entire site - "server farm" - front end routes requests to different CPUs.

Problem: OK to have all (small size) requests come in through one front end and get routed to searching nodes.
Not OK to have all (large size) replies go back through one front end - bottleneck.
Solution: TCP handoff - trick to have the searching node reply directly in a manner that is invisible to client.
The reply load is therefore distributed over all the nodes.

Server logs

HTTP servers can log all accesses. Can have separate log for errors.

Typical web server logs.
(Apart from being colour-coded. Normal logs are not colour-coded.)
From askapache.com.

URI schemes

Some URL formats.

URI schemes listed above:

Others (media): Others (phone): Others:

Keeping state

Relating one client-server stateless request with other client-server requests.

Identify user (pay-to-view, register, personalisation).
Shopping carts.

Performance (client-side)


DCU proxy servers

In DCU, some machines communicate with the outside world through a proxy server.
Some communicate directly (not through a proxy).

  1. wwwproxy.computing.dcu.ie = (forwards requests through
    • port: 8000

  2. proxy.dcu.ie alternates between different IP addresses (for load balancing)
    • port: 8080 or 3128
    • lookup shows it alternates randomly between:

To set proxy, something like:
  1. Firefox - Tools - Options - Advanced - Network - Settings
  2. IE - Tools - Options - Connections - LAN settings

You may use a proxy auto-config (PAC) file:

  1. http://www.computing.dcu.ie/proxy.pac
  2. http://proxy.dcu.ie/proxy.pac

Test the IP address other sites see:

Feeds      w2mind.org

On Internet since 1987.