ILCS.NET Support

Modem Help

ISDN Information

ISDN is a system that provides all digital phone lines. The normal type of ISDN connection is called Basic Rate ISDN, or BRI. This is the equivalent of two phone lines, called B channels. Each B channel can handle either a normal phone call, or a digital data connection.

Because ISDN is all digital, each B channel can run at its full speed of 64KBPS. Normal analog modems have to convert the digital data stream to analog so it can be carried to the curbside or phone exchange where it is converted to digital. Then, at the other end of your connection, it is converted back to analog at the remote exchange or curbside, and converted from analog back to digital inside your modem. All those transfers between analog and digital degrade the maximum performance of your modem. By the sampling theorem, in a best case scenario, it is possible to approach 1/2 of the speed of the digital line, or not quite 32KBPS. Typically, about 28.8 is possible under ideal conditions, hence the maximum speed of 28.8 for most analog modems. In reality, conditions are much less than ideal, and 24KBPS is typical for very good to excellent phone lines, and 21.6KBPS for good phone lines.

Newer 56k modems use an ISDN connection at the ISP (ILCS) end, eliminating one of the analog phases of the connection. This makes speeds of around 48kbps possible, competitive with the 64KBPS of an ISDN B channel.

ISDN, however, can reach speeds of 128KBPS by BONDING the two B channels together. This is rather like having two modems connecting you at one time, dividing the data flow between them. Bonding can be a bit difficult to get working; there remain some compatibility problems between ISDN devices.

Why would I want ISDN?

ISDN is typically 2-2.5 times as fast as an 56k modem. By virtue of being all digital, it is impervious to line noise, preventing carrier drops and degraded performance.

Why would I NOT want ISDN?

ISDN is much harder to get working than a standard modem, and an ISDN connection is much more expensive than a standard modem connection. Since the advent of 56k modems, ISDN is much less desirable, and is probably worth the much higher cost and complexity to only a handful of users.

It is possible to use two 56k modems and two phone lines to connect to ILCS at speeds of about 90KBPS using the MultilinkPPP support in Windows98 or 2000, although this feature is somewhat unstable.

ISDN vs.ADSL service.

Pricing for ADSL is similar to ISDN, and it is also quite complex to setup, but performance can be greatly improved over ISDN. Unlike ISDN, ADSL is an analog service, and performance depends a great deal on line quality, the peak speed for most types of ADSL is 1500KBPS, but typical speeds are in the 300-500KBPS range for most users. At this time ADSL does not have the reliability of ISDN. Also ADSL is not as widely available everywhere as is ISDN making ISDN the choice for many.

How much does it cost?

Residential ISDN service is about $50/month, and business ISDN service is about $90/month. Installation fees vary widely; if you are in an area that is already served by ISDN, the fee is minimal or waived.

ILCS charges $200.00/month for a dedicated ISDN service, but only $29.95/month for non-dedicated which includes the first 200 hours of usage each month, additional usage is $1/hour. You can connect using up to 2 B channels, for 128kbps speed. Bellsouth is now charging fees for ISDN usage above 320 hours/month.

What do I need to do to get started?

Call Bellsouth and order your ISDN line. Be sure to get the phone numbers and SPID's (more on this later) for the TWO B channels you get in your Basic Rate line. Purchase your Terminal Adapter and configure it with your phone numbers and SPID's. Unlike a modem, until you program it with your SPID's and phone numbers, it WILL NOT WORK. We have configuration information for the Motorola Bitsurfer Pro.

Send e-mail to support@ilcs.net and request an ISDN dedicated account if need be. Note: ILCS ISDN service is only available in Miami-Dade county.

What can go wrong?

The most common problem is incorrectly entered SPID's. Make sure this information is entered correctly into the Terminal Adapter. Oddly, you often have to add a 01 to the end of the SPID to make it work even if your SPID already ends in a 01. I don't know why. Always try it at 56k or 64k first.