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Tony Kamionsky
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So you want to get a connection to the internet?
Pretty simple requirement one would think…but that is before the
smarty-pants IT guy asked snotty questions like: “Would you like to have
Analogue, ISDN or ADSL access sir?”
How rude!
If you went to McDonalds and ordered a hamburger, would they
ask you what type of burger you would want?
"Errr...". In fact they would. They would ask if you wanted a cheese burger, salad burger, quarter pounder,
quarter pounder de-lux, triple-yummy burger, etc. etc.
Ignoring the fact that IT people use abbreviations that no one
understands, pretty much any product you can buy has different flavors,
features or colors. Confusing choices is not an IT invention. I suppose it is part and parcel of the society we live
in where choice is our number one freedom.
Philosophical perspective aside for the moment, it’s pretty clear that an
internet connection presents you with a few choices – the main difference between this
and a hamburger is just that
it is sometimes a lot harder to understand the choice…after all the
comparative benefits of ISDN vs. ADSL is not as easily understood as a salad
burger (yuck!) versus a quarter pounder de-lux.
Understanding the differences are essential to getting the product that
suits you best though – so in this article we are going to explain the choices
so that you can make the right decisions (about internet connections - not
hamburgers)…and don’t worry, we will keep the
discussion on a level where normal (non IT) people can follow. :-)
YAA
- Yet Another Abbreviation
First, lets deal with the abbreviations “ISDN” and “ADSL”.
ISDN stands for
Integrated Services Digital Network and ADSL for Asynchronous Digital
Subscriber Line.
There!
It’s out in the open now. Memorize it and use it at
the next braai to confuse your friends.
But let’s get back to business – the first, oldest and most often used way
of connecting to the internet: Analog modems. (We call them “analog” because
they are not “digital” – just take my word for it, you don’t want to get
into detail)
Modems
Modems are where it all started:
A modem (the name comes from modulator / demodulator - another one for the
braai) is used to connect
computer equipment over normal voice telephone lines.
The telephone
network we all use was designed to transmit the human voice over long
distances. Amplifiers or repeaters are used at regular intervals on the
phone line so that you don’t have to scream (like grandpa Koos) to be heard
on the other side.
These amplifiers are designed to make the human voice louder and to cancel
out background noises – the crackling and hiss you sometimes hear on a
bad connection.
Because the human voice and ear has a limited range (i.e.
you cannot hear a bat use it’s sonar to find prey), the electronic circuitry
is designed to amplify frequencies in the range of 20hz (sounds like a groan
when the next Big Brother TV show starts again) to a very high note at about
20 000 Hz (eg when you tell your 2 year old that he cannot have all the
chocolates in the shop).
Since computers do not communicate like people, but use electronic signals
instead, one has to convert the electronic signals into something that uses
the same frequencies as the human voice - to enable the electronics on
the telephone network to faithfully carry the signal. In order to do this,
one has to “modulate” the electronic signal before it goes into the
telephone line and “demodulate” (convert back into computer signals) on the
other side. It is this process of “modulation” that can be heard when your
modem tries to connect to the internet – the series of high and low pitch sounds until
a connection is made and the modem switches off it’s speaker.
Remember that the normal telephone network (“POTS – Plain Old Telephone
Network” - strike three for the braai) can only support a specific
frequency range, i.e. 20hz to 20Khz; which means that a finite amount of
information can be crammed into the phone line at a time. (The
capacity to carry information is called "bandwidth", and it does not
have anything to do with overweight musicians)
This is where the 33k-48Kbps
bandwidth limit for modems come from; and it effectively disproves the urban
rumor that slow modems are a Telkom ploy to drive you to drink. :-)
Some of you that are still paying attention might point out that some modems can connect at 56Kbps. This is
not completely true because the modems actually compress data before they
send it (like a .zip file) and decompress on the other side. The result is
that more data can be sent in a shorter time, but it does not alter the fact
that the normal phone line is only so “thick” (bandwidth), i.e. it can only carry x
amount of data at a time.
The distinction is important because the point is that there is a physical
limit on the amount of data a voice network can carry. No modem on earth can
exceed this bandwidth limit. Furthermore, the process of modulation and demodulation
combined with noise on the phone line forces modems to re-transmit data when
errors occur – which happens many times per second on an average phone line.
In effect the sending modem sends “I’ll be out la…” and the other (mother
modem) says: “HUH?!” And the sending modem replies "I said, I`ll..." and the
receiving modem goes: "HUH?!"...you get the point.
If you come to the conclusion that modems are
neither very fast nor very reliable – you would be correct.
When people
say “The internet is slow”, most often the cause is a bad telephone line and
their modem screaming “HUH?!” twenty times per second.
“Given these limitations, why do so many people use modems?” you may ask yourself.
In short
because they are cheap and you can use them on any phone line capable of
carrying a decent conversation; ISDN and ADSL connections on the other hand
require special lines.
ISDN - Integrated Services Digital Network
More than 30 years ago the limitations of modems and voice phone lines
became clear and a new, all digital communications protocol was invented.
ISDN entered the stage.
In essence, ISDN is a technology standard used by telephone service
providers to cut out or bypass the existing voice network, so that one can
send digital signals directly over the line without the process of
modulation/demodulation. Instead of amplifiers desgned to amplify the human voice, digital repeaters are used to boost computer
signals.
The advantage of the ISDN network is that existing networks can be
upgraded to ISDN equipment at relatively little cost. ISDN is
also compatible with the voice network. This means that one can seamlessly make
calls from an ISDN line to a voice line and vice-versa.
Since ISDN is digital from point to point, it is possible to send (and
simultaneously receive) 64Kbps of data at a time. To compare apples with
apples, a modem connection is at best 48Kbps while an ISDN connection
reaches 128Kbps – with one very important distinction: there are very few
transmission errors on an ISDN connection, which means that you send and
receive data at a perceived 500% improvement in speed!
Another huge plus is that an ISDN connection to the internet can be made in
about 1.5 seconds – instead of the 15 to 30 seconds it takes for a modem to
connect.
To use ISDN in South Africa, you have to get Telkom to install an ISDN line
(with a little box at your home) and you have to get an ISDN adapter for
your PC (+- R 450.00). Telkom installation costs are in the region of R
300.00 and the monthly rental is about R 200.00.
Call charges are the same as a normal phone call.
An important benefit of installing an ISDN line is that the one line gives you up to 4 “channels”. In other words, you can be speaking on the
phone, receive a fax and browse the internet all at the same time – on the
same line. In fact, you can get 4 different telephone numbers assigned to
your ISDN line.
This ability to run multiple calls on the same line is extremely useful for
small businesses where more than one line is needed - AND it can be a huge
benefit to families where a fight over who gets to use the phone line can
result in blood being spilt.
And that brings us to the latest fixed line technology Telkom has to offer:
ADSL. (In some countries they refer to “DSL” – which is more or less the
same thing)
ADSL works on the same basic principles as ISDN (in fact it is considered to
be ISDN’s big brother) with two very important distinctions: a) an ADSL line
is always connected so there are no telephone charges for connecting to the
internet and b) ADSL connections can reach communication speeds of up to
512Kbps.
Because you are always connected to the internet when you have an ADSL line,
you never have to wait to send or receive email and web browsing is a
different ballgame altogether. (Instead of roller skates, think blood
red, turbo charged Porsche, with fuel injection, and.....but I digress.)
A drawback of ADSL is that the line must be shorter than 5Km
(between you and the local Telkom exchange) to prevent an unacceptably high error rate.
Of course the local exchange must be
equipped to handle ADSL.
For these reasons ADSL is not available everywhere in South Africa - in
fact, it is only available in the major cities if you are lucky enough to
live within a 5Km radius from a Telkom exchange.
512Kps is just a number until you see it in action. It is f-a-s-t. So fast
in that it places a strain on the bandwidth resources of South African
ISPs.
The problem is that an ADSL connection can be had for less than R 1000 per
month, while an ISP will pay in the region of R 30 000 per month for the
same bandwidth on a fixed line.
This results in a disparity between the amount of bandwidth available to
users (you) and the amount of bandwidth available to ISPs at reasonable
cost. The final consequence is that ADSL users do not get the real benefit of
ADSL
technology because it is not financially viable for ISPs to supply the full
bandwidth demand, i.e. South African servers are a lot slower (to ADSL
users) than they need be – thanks to the fact that Telkom overcharges ISPs
for bandwidth at a HUGE rate compared to the rest of the developed world.
Telkom introduced a 3 Gb “cap” (limit) on ADSL users to fit into its
business model of milking South Africans for every cent while they still
can. As Telkom owns most of the local internet infrastructure, it can
support local internet traffic at virtually no cost to themselves – or, to
put it another way, at a HUGE profit margin. International traffic however
is an entirely different issue.
(Just to give you a tangible idea on how big 3Gb is: it would take about 150 hours per modem to send/receive)
To get internet traffic to and from the rest of the world, Telkom has to
make use of undersea cables and satellite connections. Once landed in
Washington or London, international carriers charge Telkom for the amount of
data it sends and receives.
Since Telkom has to PAY for international connectivity (gasp!) WE have to
pay – hence their rule that if you send or receive more than 3 Gb of data
per month, your international ADSL connection will be artificially slowed
down to the same speed as a normal modem.
You gotta love ‘em. :(
As long as Telkom has a monopoly in South Africa (and perhaps long
thereafter) good quality internet connectivity in South Africa will continue
to be very expensive and out of financial reach for most people.
All of the above not withstanding, ADSL is still an excellent technology and
extremely useful. If your internet phone bill is in the region of R 800 per
month or if your business depends on internet connectivity, ADSL is a much
better proposition than ISDN or a voice line.
Remember that regardless of which connection option you choose (modem, ISDN
or ADSL), you should budget for the Telkom costs AND the access costs
provided by your ISP. Telkom charges a fixed monthly fee for the line
(and call charges in for modem and ISDN connections), and your ISP has to
levy a charge to provide you with internet access once you are connected to
the network on top of this.
And that, gentle reader, sums up the differences between modems, ISDN and
ADSL.
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