Frequently Asked Questions About ISDN Videocommunication

What is ISDN?

ISDN (Integrated Services Digital Network) is a different way of using the ordinary telephone network, giving digital connections instead of analog connections. An ISDN line therefore compares to a normal telephone line in much the same way as a CD compares to a record.

An ISDN line is composed of two channels, each roughly equivalent to an ordinary telephone line. These channels can be used separately - for example with a telephone on one and a fax machine on the other - or they can be used together to provide a single higher capacity connection. This mode is ideal for video-telephony, which requires a lot of data to be sent reliably and without delays.

Do you need ISDN for video-telephony?

No, there is a limited amount of video-telephony equipment available that works over ordinary telephone lines (POTS or PSTN), or the Internet. However, due to the nature of these networks, the picture quality obtained from these products is of a lower standard, providing a lower frame rate and less detail.

mm series standalone videophones and mm120 videoconferencing system both operate over ISDN, allowing dramatically higher picture quality.

Can I use an ordinary telephone or fax machine over ISDN?

No, you can only use ISDN equipment on normal ISDN lines, unless you purchase a piece of equipment called a Terminal Adaptor. However, some home ISDN services allow you to use both ordinary telephone equipment and ISDN equipment on the same line without the need for a Terminal Adaptor.

How much does it cost?

ISDN calls cost the same as ordinary calls, with each ISDN channel counting as one call. Videophone calls using both ISDN channels therefore cost twice as much as an ordinary speech call. Normal discounts such as Friends and Family and Off-peak calling apply.

How do I set up my SCOTTY product for US ISDN?

ISDN, particulary in the US, is complex. Because there are several different ISDN providers, each doing things slightly differently, it's often difficult to give straightforward instructions -- witness all the mays and probablys in the following! This information is based on our own experience and that of our US customers, but unfortunately we can't guarantee that it's the whole story. Please mail us if you can add anything that may be helpful to others.

There are a few things you must check when you install your videophone or videoconferencing system, and three configuration settings that must be set correctly before you will be able to make and receive calls:

• The first thing to check is the ISDN socket on the wall:

mm series products require an S-interface, while in the US it is normal for ISDN providers to supply a U-interface to consumers. However, if you are connecting to a local exchange such as a corporate PBX, you may well have an S-interface. (Unfortunately, S- and U-interface sockets are the same size and shape, so that it is quite possible to plug your mm series ISDN cable into the U-interface. However you won't be able to make any calls!)

To convert your U-interface to an S-interface you will need a piece of equipment known as an NT-1 (Network Termination type 1), which plugs into the U-interface socket and gives you an S-interface socket to plug your ISDN cable into.

Your ISDN provider (or, for a corporate exchange, your IT/Telecoms department) will be able to tell you whether you have an S- or a U-interface, and will supply you with an NT-1 if you need one. Your videophone supplier may also be able to supply an NT-1, or advise you where to buy one.

• The next thing to check is your ISDN variant:
  
  There are several commonly used ISDN variants in the US:
  • The most common one is National ISDN (NI) with sub variants 1 and 2.  mm series products support NI2 which is backward compatible with NI1.
  • We also support DMS100 and AT&T Custom. Again, your ISDN provider will be able to tell you which variant you have.

You must ensure that your videophone is configured with the correct ISDN variant. If not, you may not be able to make or receive calls. (You may find that you can make and receive video calls but not speech calls.) See Configuring the ISDN variant, SPIDs and Directory Numbers below for instructions.

• Finally, if you have National ISDN (NI1 or NI2), you will probably need to supply Service Profile IDentifiers (SPIDs) and Directory Numbers before you can make and receive calls:

A SPID is like a password for the network and allows you to use certain ISDN features. If your ISDN line requires a SPID but you do not have it correctly configured, you will not be able to make outgoing calls.

The Directory Number is the telephone number that the exchange broadcasts to the S-interface. A piece of equipment will only respond to incoming calls if its Directory Number exactly matches the one broadcast by the exchange. Therefore if your Directory Number is not correctly configured you will not receive incoming calls. Note, however, that SPIDs and Directory Numbers are not always required. Some ISDN providers call their service "point to point", and these rarely require SPIDs or Directory Numbers.

• Your ISDN provider will be able to tell you whether you need to configure SPIDs and Directory Numbers, and if so, what they should be. They may give you a single SPID and a single Directory Number, or two SPIDs and two Directory Numbers, one for each B-channel.)

Configuring the ISDN variant, SPIDs and Directory Numbers:

• ISDN Variant:
  • Press the Configuration / CONFIG button to bring up the main Configuration screen.
  • Use the Up and Down arrows to select the Installation item at the top and press OK.
  • Use the Up and Down arrows to select the ISDN item, then use the Left or Right arrow to select either NI2, AT&TCust or DMS100. (Choose NI2 if you have either NI2 or NI1.)
  • Press OK to save the new value and return to the main Configuration screen.
• SPIDs and Directory Numbers:
  • Press the Configuration / CONFIG button to bring up the main Configuration screen.
  • Use the Up and Down arrows to select the ISDN Profile item at the top and press OK.
  • If your line requires SPIDs and Directory numbers, you must fill in all the boxes. (If not, you must leave all the boxes empty.)
    (Use the Down arrow to move from one box to the next):
  • Enter the first (or only) SPID in SPID 1, and the second (or only) SPID in SPID 2.
  • Enter the first (or only) Directory number in Local Number 1, and the second (or only) Directory number in Local Number 2.
  • Press OK to save the new values and return to the main Configuration screen.

Troubleshooting:

In order to minimise the unknowns, we recommend that you find out the ISDN variant and the SPID/Directory number information from your ISDN provider if at all possible. Otherwise, you are reduced to trial and error.

If you are sure that the SPID and Directory Number are right but are having problems then change the ISDN variant to another setting. Similarly, if you are sure the variant is correct then make sure the SPID and Directory Number are correct.

If you have to guess the SPID and Directory number, try the following scheme, which is used by several ISDN providers. If the number of your line is:

<area code> <local number>
(123) 456 7890 - <area code>=123; <local number>=4567890:

• set Local number 1 and Local number 2 to <local number> (e.g. 4567890)
• set SPID 1 and SPID 2 to <area code><local number>0101 (e.g. 12345678900101)
• If this doesn't work, try setting the SPIDs to <area code><local number> (e.g. 1234567890)

You should enter only digits in your SPIDs and Local numbers. There should be no spaces, hyphens, etc.

For more information on this subject, consult your User Manual, particularly:

• Installation and ISDN Profile sections.
• Preliminary checks and Call connection sections.