 The magazine of the Melbourne PC User Group Internet Newsletter No 12 George Skarbek gskarbek@melbpc.org.au |
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Status Report
All of our services have been performing very well and we have no real
problems of any type. Another 30 digital modems have arrived but we are still waiting for Telstra to install
the phone lines. Some of these lines will be used to replace the old 33.6 kbit/s analogue Intranet lines that
were recently phased out. The new phone number is 8626 5001.
How Does Melb PC Internet Work?
Many Internet users have very little idea of how the Internet actually works. Probably even less how the
Melb PC Internet service is configured and what computers make it up. This newsletter will provide a
relatively simple explanation aimed at the new user.
What Is the Internet?
The Internet is a collection of many thousands (perhaps millions) of linked computers. They are connected via
the public and no doubt some private telecommunications networks. The World Wide Web (WWW) can be considered
as all the computer resources and the computer users whose browsing software utilises HTTP (Hypertext
Transport Protocol). A protocol can be considered a language that both computers must speak in order to
communicate successfully.
Other protocols are also used. Mail is sent via SMTP (Simple Mail Transfer Protocol). Mail is received via
POP (Post Office Protocol) and files are often transferred (copied) via FTP (File Transfer Protocol). The
transport mechanism for each of the above is small packets of data that rely upon TCP/IP (Transmission
Control Protocol/Internet Protocol). It is still THE protocol of the Internet and it enables computers
running different operating systems to transfer information with a high degree of reliability.
There is no governing body, just a global Web of computers providing many services. These computers are
mainly running UNIX (an operating system that competes with Windows NT), but they are able to be accessed via
PCs running Windows. The Internet demonstrates the degree of cooperation that can be achieved at a technical
level, almost entirely without government intervention or regulation.
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Figure 1 shows the main hardware used at Melb PC while the
photos show some of the computers and other equipment mentioned in the schematic diagram. Note, the majority
of computers have no monitor connected. They can all be administered via another computer whether from this
room via the LAN or remotely via the Internet. The banks of digital modems are in five comparatively small
boxes without any lights on the front and they contain a total of 330 modems. Some of the other items are
computers, Hubs, UPSs (Uninterruptible Power Supplies) tape drives and of course the essential Cisco router
which is just another nondescript, small box.
A router is a very fast, intelligent, electronic switch that maintains a table of the available routes and
determines the best route for a given packet of information so that it reaches its destination. Cisco is a
company that dominates the router market to a far greater degree than Microsoft dominates the software
market.
When a Melb PC member wants to use the Internet, he or she dials into one of our banks of modems. Upon making
a connection, the user name and password are verified using a program called RADIUS (Remote Authorisation
Dial In User Service). Once your identity has been established you can read your mail and news or surf the
net. (Surfing refers to browsing the many Web sites on the Internet.) Both the mail and news reside on
our computers. There can be over 6 GB of news arriving each day (more than six complete Encyclopaedia
Britannica) so this means that news cannot remain on the disk for too long.
However, mail, unlike news is kept until the user deletes it. Mail readers should be set up so that when you
have successfully downloaded your mail onto your own hard disk, it is deleted from the server.
In order that we can successfully surf the Net, the DNS (Domain Name Server) is the most important computer.
It keeps most IP (Internet Protocol) addresses and the corresponding names we humans use. It is much easier
for us to remember a URL (Uniform Resource Locater), which is usually the address of a Web site on the
Internet (eg. www.microsoft.com), than it is for us to remember its IP number 207.46.130.17. The Internet
protocol works only with IP numbers, not the URLs.
When you've typed or clicked on an address, your request goes via the router to the proxy server that checks
to see if your requested data has been recently accessed, either by yourself or another user. If it has, then
the data is transferred from a local computer (in Melbourne) rather than from the distant site. This action
has several benefits. Firstly, you get your data sooner, secondly it cuts down on the international traffic
and finally is saves the group a lot of money. Our proxy server has 88 GB of disk space for caching and it
runs on a dual Pentium computer with two ultra wide SCSI controllers connected to drives that can
theoretically transfer data at 80 MB/Sec. The hit rates are above 30% That is, more than 30% of requests for
data can be fulfilled from the local cache.
Between the internal computers and the Internet is a hardware/software combination known as a Firewall. The
Firewall is designed to keep intruders out and improve our security. A Firewall moves all traffic through a
single point examining every packet and filtering out any packets that may be potentially harm. A packet is
the unit of data that is routed between an origin and a destination on the Internet. When a file or e-mail
message is sent from one place to another on the Internet it is split into very small chunks. Each of these
packets includes the Internet address of the destination. The individual packets for a given file may even
travel different routes through the Internet due to local congestion but when they have all arrived they are
reassembled into the original file. Although Firewalls improve our security and filter out potentially
harmful packets they cannot recognise viruses, and it is the responsibility of individual subscribers to
provide their own anti-viral measures.
Melb PC Internet Statistics
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. Last
financial year the bill for our traffic charges was nearly $200,000 while the phone bill was over $160,000
for our phone lines - and we never make any outgoing calls.
In a typical day about 3200 different users connect to Melb PC. Many log in more than once a day. The average
connect time is 63 minutes (per day) and this figure varies by only a few minutes from month to month. About
5300 different users log in during a month. This load is the reason why we have many powerful computers with
lots of memory and disk capacity. They must continually process large amounts of data for activities such as
validating users, checking connection times, receiving, sending and deleting mail and news, downloading
files, monitoring the modems, screening out intruders, writing logs, backing up data, updating a myriad of
statistics - all while sending and receiving data to/from every user who clicks on a link in a browser or
reads another news message.
As mail is probably the most important Internet application for the large majority of members, we have
recently upgraded the hardware for the mail servers. They are dual Pentium Dell servers running Solaris. Both
the system disk and data disks are mirrored so that if one fails, the computer keeps functioning. Also at
approximately 10 minutes past every hour all mail is backed up from one computer to the other and daily onto
tapes.
The speed of response depends upon many factors. The main bottleneck is the 1 MB link which can be regarded
as the main pipe to the outside world. This link is being shared by all Melb PC users who are connected via
all those modems. The bandwidth of this link is our major cost and Melb PC will be upgrading this in the near
future. Another reason for poor response can be clogged conditions further upstream but this is outside our
control. However, the speed of your computer is not one of them.
All the planning, updating and running of our Internet service is done by a few volunteers. We are always
trying to improve the service by adding benefits such as the free bonus time. In a typical month the total
bonus minutes exceed 130,000. This is the main reason why our costs are much lower than most other services
providers, and we've always felt that the level of service the Group provided was better than many commercial
ISPs. This has been prove by a recent independent survey that rated our service as the best in Victoria Our
ISP renewals are many times higher than the industry average and WE feel that this reflects the level of
service that we strive to give to our members.
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Reprinted from the October 2000 issue of PC Update, the magazine of Melbourne PC User Group, Australia
