 The magazine of the Melbourne PC User Group How does the Melb PC Internet Service work? George Skarbek gskarbek@melbpc.org.au |
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Many Internet users have very little idea of how the Internet actually works. Even fewer understand how Melb PC's Internet service is configured. This article gives you a simple description of the Internet and a brief explanation of how our service operates. It is aimed at a relatively new user.
What is the Internet?
The Internet is a collection of many thousands of linked computers, connected using a portion of the total resources of the currently existing public telecommunication networks. Perhaps the best known element of the Internet is the World Wide Web (WWW or simply the Web). The Web is used primarily for activities that use browser software and the Hypertext Transport Protocol (HTTP). Other portions of the Web include mail, news and FTP servers, and other computers performing various tasks, all over the world.
This global computer network provides many services. Although most of the servers are running under the UNIX operating system, users with computers running Windows, Mac, UNIX and other operating systems, can access them. One interesting fact is that there is no governing body over this global computer communications network. This shows what cooperation at a technical level can achieve with virtually no government intervention or regulation.
How does Melb PC fit in?
The diagram shows the main hardware used at Melb PC. The first photo shows some of the computers mentioned in the schematic diagram. Note that not all have a monitor connected. They can all be administered via another computer. The second photo shows various boxes mounted in racks. The bank of lights on the left hand side corresponds to the old Dataplex 33.6 Kbps modems. The new bank of 120 modems are in two very small grey boxes without any lights on the front. Some of the other items are computers, hubs, uninterruptible power supplies (UPSs), tape drives and of course a Cisco router (another nondescript small box).
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Despite its appearance, a router is a very fast intelligent electronic
switch that creates (or maintains) a table of available routes, from this table, the router determines the
best route for a given packet of information to reach its destination.
If you are a subscriber to Melb PC's Internet service, you can dial one of our Internet phone numbers. Upon
making a connection, the system verifies your user name and password. Once your identity has been
established, you can read your mail and messages in the newsgroups Melb PC receives, or you can surf the net.
"Surfing" refers to looking at (browsing) Internet Web sites.
The files that make up a Web site can be on any number of machines anywhere in the world. In contrast, mail
(sent to our subscribers) and news (the postings from groups we receive) are stored on our computers.
Mail sent to our subscribers is kept on our mail server until the subscriber deletes it. Most mail readers
are set up to delete messages from the server, once the message has been downloaded successfully. Check
yours, because if it is not set up this way, you may suddenly stop receiving mail, when your "inbox" becomes
full. If you receive a lot of mail, this is liable to happen sooner rather than later.
It's a different story for news. There can be up to 6 GB of news messages every day. With a total storage
capacity for news of 24 GB, that means that we can't hold news messages forever. Although different group
hierarchies are set to have different ageing parameters, within any group, the newest messages are displacing
the oldest.
For surfing purposes, the Domain Name Server (DNS) is the most important computer. It keeps track of most IP
(Internet Protocol) addresses and the corresponding names humans use. It is much easier for humans to
remember a Uniform Resource Locator (URL) such as www.microsoft.com than to remember Microsoft's IP number
207.46.130.17. However, all the computers that make up the Internet use these numbers, not names, in their
protocols to identify themselves and others.
When you enter a URL or click on a hyperlink on a Web page, your request goes via our router to a proxy
server. The proxy server checks to see if the page you requested has been accessed recently, by you or
someone else. If it has, the data is transferred from whichever local computer (in Melbourne) has it, rather
than going to the distant (originating) site. Using the proxy server in this way has several
benefits:
- You get your data more quickly from the local computer
- It cuts down on international traffic
- It saves Melb PC a lot of money.
A firewall moves all traffic through a single point, examines every packet and filters out any that may be potentially harmful. The firewall doesn't examine the content of messages. A firewall looks at a packet's structure, source and destination, to identify unauthorised access attempts or attempts to run unauthorised processes.
A packet is the unit of data that is routed between an origin and a destination on the Internet. When any file (program, image, Web page or e-mail message) is sent from one place to another on the Internet, it is split into very small chunks (called packets). Each of these packets includes an identifying code and the Internet address of the packet's destination. The individual packets for a single file may travel different routes to arrive at the same destination, and the identifying code is used to re-assemble the file into its original format.
Melb PC Internet statistics
By far our biggest single expense is the traffic charge. This is the fee that we pay to the organisations that supply the cables, satellite links, computers and routers to connect Melb PC computers to the Internet. For example, the phone bill for over 200 lines, and a charge for the volume of data transmitted over those lines.
Last financial year the bill for our traffic charges was about $180,000 while the phone bill was nearly $100,000.
In a typical day more than 2000 users connect to Melb PC in more than 4000 sessions. Now you know why we have many powerful computers with lots of memory and disk capacity to run the system. Melb PC's computers are processing a lot of data continually--everything from validating a user's identity to checking connection times, receiving, sending and deleting mail and news messages, downloading files, monitoring the modems, screening out intruders, writing logs, backing up data, and updating a myriad of statistics. At the same time they are sending and receiving data for every user who clicks on a link in a browser or reads a news message.
The speed of response depends of many factors. One bottleneck can be the 512 KB link, which you can regard as the main supply pipe to the outside world. How many users are logged on at any one time, and what each of them is doing, effects response speed, because the link is being shared with the other Melb PC users logged on at the time.
The bandwidth of this link is our major cost, and we will be upgrading this in the near future.
Another reason for poor response times can be clogged conditions further upstream, anywhere between us and the machine you are trying to reach, and these factors are outside our control.
One thing that probably does not have an effect on the response speed is the speed of your computer. If your modem is slow or there is a lot of line noise on the local line, it can influence the maximum speed at which your modem transfers information, and thus limit response time. But this is not generally the limiting factor.
Just a very few volunteers perform all the administration of our Internet service. This is the main reason why the costs are much lower than most other service providers.
Recently substantial changes have occurred in the way we obtain our bulk data, that is our connection to the rest of the world. A new $16,000 Cisco router was purchased to give us an alternate supply and redundancy. In the near future we will be investing more money to purchase additional phone lines, new V90 modems and, as I wrote earlier, more bandwidth.
All this is designed to improve our system and response. To this end, I do daily performance monitoring to establish a baseline for our response so that we can see if something has changed over a longer term.
I'm pleased to report that although our response is slightly worse than OzEmail or Telstra (both of which charge far more than we do) it is very much better than the only large ISP that is cheaper than us.
For example, if you were using OzEmail for just one hour per day it would cost $1850 for one year. We give you up to two hours per day for $140 per year.
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Reprinted from the October 1998 issue of PC Update, the magazine of Melbourne PC User Group, Australia
