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How to Determine if Phone Line is ISDN

Q. ADSL requires an analog line. How can I tell if my phone line is analog or ISDN?

A. If your line is digital (ISDN), you'll have an ISDN T/A (modem) on the line between the telephone and the wall.

Follow the Wire

The easiest way to find out is to look for an ISDN T/A (modem). If you have a telephone plugged in and it works, follow the wire from the phone to the wall. If there is NO device between the phone and the wall then you have an analog line.

Look for a device between the phone and the wall:

graphic of ISDN device on phone line

If There is a Device

Then you might have ISDN. Skip the next section and read about the differnt types of devices to see which one you have.

If There is No Device

If there is no device and the phone works, then the line is analog and no conversion is needed. If there is no device and the line doesn't work, then it probaby means no service is connected. In this case, no conversion is needed. All you need to do is request analog service.

Not All Such Devices are ISDN!

DSL modems, which work on analog lines, are similar in general appearance to ISDN modems so you have to check the markings on the device. If that device is marked with "ISDN," "INS-64," "V-30," or "T/A" then it is ISDN (a digital ISDN phone line).

If it says "ADSL," "DSL," "eAccess" or "Yahoo! BB" then the phone line is analog.

"Lite" or Regular

Another two ways that NTT phone lines can be differentiated is whether they are "owned" or "rented." Actually, it's a Subscription Right to use the line that is owned (not the wires, etc.). If the user of a line owns a Subscription Right, then the line is "Regular." If the user doesn't own a Right, then the line is "Lite" and the user pays a ¥263/month surcharge for the use of the line.

The Regular/Lite types apply to both analog and IDSN phone lines. The difference is important for Yahoo! BB connections because while conversion of Regular ISDN to analog may be requested when applying for Yahoo! BB ADSL service, conversion of Lite ISDN lines cannot. If your line is ISDN Lite, then you must make arrangements at NTT to have it converted to analog before filing an application for Yahoo! BB service.

Confirming Type with NTT

If you have no idea whether the line is regular or Lite, the best thing to do is call NTT and ask them.

The Foreign Language Customer Support number is 0120-565-950 (9 AM - 5 PM, Monday-Friday from mobile phones and NTT landlines only). That number is usually very busy so I recommend calling them at exactly 09:00 AM when they open. In Japanese, call them at 116 (7 days, 9:00 AM-9:00 PM from NTT landlines only).

First ask if your line is analog or ISDN. If they say ISDN, then ask if it's Lite or regular.

Types of NTT phone lines:

Here is a recap of the four types of NTT phone lines and their status with regards to applying for Yahoo! BB ADSL service:

    • Analog Regular--OK for Yahoo! BB ADSL install
    • Analog Lite--OK for Yahoo! BB ADSL install
    • ISDN Regular--Can be converted during Yahoo! BB ADSL install--indicate on application
    • ISDN Lite--must be converted to analog before filing ADSL application

Converting ISDN Lite Lines

If your line is ISDN "regular," then Yahoo! BB can arrange conversion for you. If it's Lite, however, you must arrange the conversion to analog yourself. You can do that be calling the above mentioned phone numbers.

Converting won't make any sense, however, if ADSL service isn't available so, before you convert, it is recommended that you file an Availability Request.

Hope this helps!


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