Okay, first off, I am so surprised that this is a problem for so many
here and that the answers haven't been that /correct/. That is sad,
this is relatively simple (or it can be).
Why people are using Telstra for Internet, well that is very sad too as
they are usually the most expensive option or amongst the most expensive
on the rare occasion that they are not the most expensive. There are
times when there is not much choice and if the line is in bad condition,
it is easier to get it fixed if you use a Telstra only "solution", if
the line is good and there are competitive options at your exchange,
then Telstra is almost always the worst choice you could make; although
there are other reasons why you might choose Telstra, but for most
people, it would be a bad choice indeed.
In simple terms, your modem can operate in a number of modes; the
simplest is as a modem/router connecting to the exchange via PPP (either
PPPoE or PPPoA, more on that later). The modem makes a physical link to
the exchange's DSLAM port using ATM networking; this is not an Ethernet
connection, it is an ATM connection. Then the mode determines how
communication travels over and beyond the ATM connection.
Your modem tries, like old dial-up, to make that ATM connection as
quickly as it can depending on the quality of the phone line. If the
line (overall) is good and you are close to the exchange, then it will
generally sync up close to 24 Mb/s down and around 1 Mb/s up. These are
rough figures, not many people get the full speed for all sorts of
reasons; mostly due to the line length and/or quality and also due to an
almost complete lack of maintenance by Hel$tra (yes Telstra should
really have this name). The line first needs to sync with the DLSAM, if
it doesn't then nothing else is possible.
Let's assume that the connection is made between the modem and the DSLAM
port at the exchange, usually a PPP or Internet light will be lit on the
modem; this light might be flashing due to authentication failure or
network activity; it may be off if the ATM link isn't possible, ie when
there is no line sync. So, if you don't have line sync, then you need
to fix that first. If you do have line sync, then the modem needs to
login to the ISP service.
The modem then tries to login to the Internet service, but it won't even
try this if the line isn't synced with the DSLAM. The line itself is
tagged with an ISP specific code and all login information is passed
from the modem to the ISP due to this code. If the ISP is not Telstra
(or Big Pong ... err I mean Big Pond), then Telstra's involvement is
mostly providing the physical phone line (which they own, but should
NOT, that was a government policy blunder). If Telstra is the ISP or
the ISP uses a wholesale port from Telstra, then the DSLAM is owned by
Telstra. If the ISP is using an alternate DSLAM provider, then you are
using Telstra with the lowest level of involvement by them. So, you are
either connected to a Telstra DSLAM or a competitor DSLAM that Telstra
has begrudgingly allowed a competitor to install at /their/ exchange.
The physical connection between the modem and the DSLAM is established;
the code on the "line" will cause communication to go down a specific
track to the ISP's own authentication server -- if the username is
wrong, the ISP will see that wrong username regardless of the form. It
is also possible to make this connection without any username or
password, but that is not the common way. So, traveling from your modem
to the DSLAM and then via specific routing for the ISP, the
authentication of the PPP service will be handled by the ISP PPP server
(you might lookup up RADIUS to get an idea about this).
If your ISP has pre-configured the modem, it is usual that you just plug
it in appropriately and everything will work. Generally, for simple
Internet usage, you will have your network port (wired or wireless) set
to get it's configuration details via DHCP. With DHCP, your computer
will get it's details from the modem/router in order to have an IP
address, DNS and routing settings (via the modem/router). If you set
these up yourself, then you need to consider how well that fits in with
the details that would have been provided automatically from the DHCP
service in the modem/router.
There is a bit more about how the data gets from the local telephone
exchange to the ISP, sometimes this is via the ISP's own links, other
times it pays a ransom to Hel$tra to transport that data to the ISP's
own POP (point of presence). This is often why most of which you pay to
an ISP can end up in Hel$tra'a coffers and there is little left for the ISP.
Okay, so your line is in sync and is able to communicate with the ISP's
PPP server. Now you just need the right AUTH details and the ISP's
server will work like a DHCP server and give the modem/router the
details it needs to connect to the Internet, including a public IP
address (for the modem), DNS and routing settings.
The router part of the modem/router acts as a bridge from your local
network to the Internet via the modem parts.
Once everything is working, then you can consider adjustments to the
setup, but you need to understand what you are doing.
Oh and before you even connect the phone line to the telephone socket,
you want to make sure that WiFi is properly configured in the
modem/router if it provided wireless directly; you also want to make
sure that your login to the modem itself is not using the default
username and password (separate to the ISP's PPP login details). You
secure the local device as much as possible before connecting it to the
I have gone in to a reasonable amount of detail here, there is more
complexity if you want it; but for most people, they just make
everything more complex by not understanding the basics first.
Using your modem in bridged mode requires much more understanding and
doing so has it's advantages, but it isn't for everyone. If you do run
in bridged mode, then you are likely to have a Linux or similar router
that has a firewall configured. Typically modem/routers have their own
firewall, but it is used in /normal/ modes and not when the modem is in
bridged mode. Firewalls are a whole new subject for discussion.
So, keep things simple if you are a DSL newbie and don't try to
complicate things with "I'm running Linux" ... your computer is just
another device that the modem/router sees, it can be anything with an
Ethernet port or anything with a suitable wireless NIC. A computer, a
phone, a printer, they are all just devices that operate under TCP/IP --
although a printer might only have USB, but that is not recommended.
Any device capable of getting details via DHCP should be handled easily
by you modem/router in simple setup modes, such as PPPoE or PPPoA.
Okay, I said earlier I would describe PPPoE and PPPoA. These are the
most common transport protocols used by the PPP (RADIUS) server. PPPoE
is PPP over Ethernet, you MTU setting is going to be 1492 typically (but
your devices will usually sort that out themselves). PPPoA is PPP over
ATM .. so "more pure", but the modem/router will bridge the ATM network
with the local Ethernet network; the MTU will likely be 1500 as it is
with most Ethernet devices by default.
I have used undefined terms, if you don't know what they are, perhaps a
query later, you will have the answer.