Q. What is ISDN? - Back to top
ISDN is a type of telephone service. It stands for Integrated Services Digital Network. It’s really just a method of sending digital transmissions over normal copper phone lines.

Q. What does ISDN do? - Back to top
ISDN allows you to send and receive data over normal phone wires at a much higher rate of speed than a line using standard analog transmission methods.

Q. How is ISDN different than a regular phone line? - Back to top
The way it all works has to do with the type of waveform an analog modem sends versus a digital modem waveform.

An analog waveform might look something like this:

But that can only happen in a perfect world. In the real world, an analog phone line will by nature, pick up a lot of static, or Electromagnetic Interference, the proper term. Once that line gets noise, the waveform looks a lot more like this:

You can see that with the waveform distorted like that, it becomes much more difficult for the modems to determine what is really being transmitted. If a modem incorrectly receives part of that waveform, then it must be resent, slowing it down even further. If the noise gets too bad, then the modems might not be able to determine what’s being sent at all, and terminate the connection completely.

ISDN gets around this problem by sending a different type of waveform. An ISDN signal may look more like this:

That’s a digital signal. There is no degree of variation; the signal is either up or down. When static gets introduced, here’s what can happen.

Even now, with all that static, it’s much easier for the modem to determine how the waveform looks. It’s still easy to determine what’s up and what’s down. These drawings are pretty crude, but you should get the basic idea of it.

The problem with the digital signal is that it cannot travel as far a distance over copper lines as an analog signal can. That’s why an ISDN line has to be conditioned to work properly, and special equipment has to be installed that can strengthen and “repeat” the signal as it travels down the line.

Q. Why is ISDN faster? - Back to top
The above question and answer explain part of the reason ISDN is faster, but there are other factors as well. Since the waveform is very easy to determine, even if there is a lot of static, the signal can be sent much faster, without worrying about errors. ISDN can also use two phone lines simultaneously. An ISDN line is broken down into 3 parts. There are two B (Bearer) channels. The Bearer channels are what actually carry voice, data, and other services. Each B channel is capable of 64 Kilobits Per Second (Kbps). The D (Delta) channel carries control and signaling information about the two B channels back to the phone company.

The two Bearer channels will each receive their own phone number.  Each of these lines can be used for voice or data, interchangeably or simultaneously.  These two 64k Bearer channels can be merged together (called bonding).  When merged, these channels can achieve 128kbps.  To break it down even further, 64 kiloBITS per second translates to roughly 8 kiloBYTES per second (8 bits equals 1 byte).  So, we can determine that when using a single 64k channel to access the internet, you can download around 8K per second, and around 16K per second when using two 64k channels (128k total).

Q. So how much faster is ISDN than a regular connection? - Back to top
A 56k modem can achieve around 5.5K per second on an IDEAL connection.  Realistically , a 56k modem will see transfer rates around 4.5K per second, and a 33.6k modem will see around 3.5K per second.  So, ISDN is about 3 to 5 times faster than regular modems.

Q. What do I need to do to get ISDN? - Back to top
The first step is to find out if ISDN is available in your area.  Call your phone company and ask if they offer ISDN.  If they do, give them your address and see if it's available to you, and try to get a quote on the price.  If everything is available to you, schedule a time for the phone company to come to your location and set up the line.  It will usually take about 2 weeks for them to get to you.  Once you've gotten a date for installation, give ICOM a call so we'll know that you need your account converted.  Now you need to get your equipment...

Q. What equipment do I need? - Back to top
The phone company will install everything necessary on their end, but you'll have to have different equipment connected to your computer for ISDN to work.  You can use either a ISDN modem or an ISDN router.  If you want to connect multiple computers to a network to share the connection, you'll also need to get network cards and cable installed.

What's the difference between a modem and a router, and how much do they cost? -Back to top
A modem connects directly to one computer, and will allow only that one computer to connect to the internet.  That computer can share its connection to the internet with other computers, but it will need special software called a Proxy Sever to do so.  An ISDN modem will function almost just like a regular modem, only a lot faster.  ISDN modems cost about the same as higher end regular modems, in the $80 to $150 range.

A router can be considered an ISDN modem with the built in ability to share the internet connection.  A router makes it much easier to connect multiple computers on a network to the internet.  Most routers also have many other built in functions like time management, remote access, PPP tunneling, and user authentication, making them ideal for small office / home network use.  The Toshiba TR650 which ICOM recommends for small office or home use sells for around $150.  Routers for larger business use with more features sell for $250 or more.

Q. What will the ISDN line cost from the phone company? - Back to top
It depends on where you live, and what phone company you're with.  Right now an ISDN line in Kinston through Sprint is around $40 per month.  $40 per month is pretty reasonable, considering you're getting two separate phone lines, and the ability to have high speed internet access.  Bellsouth in Goldsboro charges a ridiculous $250 per month for the exact same service.  We recommend customers in the Bellsouth territory call and request that ISDN be sold at a reasonable rate, comparable to what Sprint charges, only one city away.  As to why Bellsouth charges so much, it is our understanding that the switching equipment in place in the Goldsboro Bellsouth office is too outdated to handle  ISDN (which by the way was developed in the late 1970's) and that ISDN service is actually pulled from as far as Raleigh, where their equipment is not outdated.  Currently, if you subscribe to ISDN in Goldsboro, you will receive a Raleigh phone number.  Kinston has no problems at all receiving local ISDN from Sprint.

Q. Can I send faxes over ISDN? - Back to top
Yes.  However, you will still need a fax machine or fax modem to plug into your ISDN equipment.  Plug the fax machine or fax modem into a POTS jack on the ISDN equipment.  Click here for more info about POTS.

Q. Can I make regular phone calls over ISDN? - Back to top
Yes.  Plug your phone into a POTS jack on the ISDN equipment, and it will work like a normal phone.  Click here for more information on POTS jacks.  Click here for more info about POTS.

Q. Will you describe what exactly POTS is? - Back to top
POTS stands for Plain Old Telephone Service.  A POTS jack is what you plug your phone into in the wall.  Most ISDN modems or routers have two POTS jacks on the back, that you can plug regular phone line equipment into.  Since ISDN has two phone numbers, you can use them both for different things.

Q. With ISDN, can you be on the internet and on the phone at the same time? - Back to top
This can get fairly complicated to explain.  To make it easier to understand, here's a diagram:

You can see that there are three things connecting to the ISDN equipment.  Since the ISDN has B channels, you can use two of them at the same time.  For instance, you can be talking on the phone or sending a fax with one 64k line, and surfing the internet with the other. 

Also, you could be sending a fax with one B channel, and talking on the phone with the other.  However, since this would tie up both the available 64k B channels, you would not be able to surf the internet until one of those calls disconnected.

ISDN also has the ability to drop a data line if it receives an incoming analog call.  If both your channels are on the internet, and you have an incoming call, your ISDN equipment can drop one channel, and let the new call thru.  When the analog call is disconnected, the data call can resume like nothing ever happened.

Q. How much does ICOM charge for ISDN based internet service? - Back to top
The price depends on what speed you want to use.  For a single 64k channel, the cost is $25 per month.  For 128k access the cost is $40 per month.  You will have to call ICOM and let us know that you want to use ISDN and which service you would like.  We have to set you account to work at the higher speed.

Q. What about Email accounts? - Back to top
Other than the fact that ISDN is faster, we configure the accounts the same.  As with any account, you get 1 email address, and 10meg of storage for a personal web page.

Q. If I get a router, how many computers can connect over it at the same time? - Back to top
Most routers won't have a physical limit on how many different computers can access the internet at the same time.  There are, however, practical limits on how many people you would want downloading at once.  If you have a total of 16K per second bandwidth available, it will decrease every time someone else taps into that bandwidth.  Realistically you wouldn't want more than 4 or 5 people downloading large files at once.  Surfing web pages and Email is much less demanding on bandwidth however, and 6 to 8 people could surf happily all at once.

Q. Does ICOM charge more if multiple computers are accessing thru a single ISDN line? - Back to top
No.  Since the modem or router is the only thing that truly connects directly to the internet, there is no charge for additional computers.

Q. What operating systems does ISDN support on my computer or network? - Back to top
The ISDN line itself is not computer or operating system specific, but the internet connection is. You can use any operating system that supports TCP/IP.  This includes Windows95/98/NT/2000, MacOS, UNIX based operating systems, Linux based operating systems, and some versions of Windows 3.1, OS/2, and Novell.
 
 

When the router receives a packet from one of the workstations, it remembers which machine the packet came from, translates the local IP address to the WAN IP address, and sends it out.

When a packet arrives back, the router checks it, looks to see which machine requested it, and sends it back to that machine.

Q. What's the best way to assign IP address on my local network? - Back to top
A great thing about most routers is that they support DHCP (Dynamic Host Configuration Protocol).  DHCP can automatically assign computers an IP address when they boot up.  When you set up DHCP on the router, you'll specify a range of IP address to use for the client pool, and only those address will be automatically assigned.

You can also manually specify IP addresses in your OS.  ICOM suggests using one of the three following IP address ranges:

10.0.0.0 - 10.255.255.255.255
172.16.0.0 - 172.31.255.255
192.168.0.0 - 192.168.255.255

These numbers have been reserved by the IANA (Internet Assigned Numbers Authority) specifically for private networks.