Last Revised: Tuesday, October 27, 1998
| ISDN is becoming available in more markets every
day. Ordering and installing a new service should not be too painful, unless you have the
misfortune of being the first one in your town. ISDN is supposed to be the replacement for
Plain Old Telephone Service. As such, it is often marketed and installed as if it were a
standard phone line. Your Telephone business office is the first place to go shopping, it
they don't handle the service directly they should be able to tell you where to go.
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| You will need to provide certain information to
the phone company when you order service. What is asked for tends to vary slightly from
location to location. It may be possible to describe all your concerns with one Terminal
Code, however these are not universally supported.
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| ISDN can be used for transmitting many types of
data. Specifying a service type determines what class of calls the switch will send to
your ISDN. It doesn't make much sense to send a Group III Fax to your terminal if there is
no equipment there to decode it. Wide-band audio does not have a specifically defined Type
of Service. Audio and Voice sound promising but are in fact not. Specify DATA
as the Type of Service for any Wideband Audio codec.
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| The same major long distance carriers than
handle voice traffic also provide ISDN service. Your choice determines your default
carrier for calls placed from your terminal. This doesn't effect the carrier for incoming
calls nor does it prevent you from using any other carrier on a per-call basis by
preceding the call with the appropriate 10xxx code. Some long distance carriers are more difficult than others to obtain service, and experimentation using other 10xxx codes will become one of your troubleshooting tricks when you have problems placing long distance calls.
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| The phone company wants to know what type of
terminal equipment you plan to use, that is the Terminal Adapter used to place calls. They
don't care what happens after that and probably don't even know of, or care about, the
differences between a CCS-Micro56+ and a Telos Zephyr. Speaking of the Telos Zephyr, it
has a built-in terminal adapter. If they question what this thing is, tell them it is
equivalent to an Adtran ISU-128. We have interchanged these units on the same line with no
apparent problems.
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| It is becoming possible to specify the
configuration of the BRI by using one of several ISDN Ordering Codes. The IOCs are
supported to varying degrees by the various Local Exchange Companies. The most common codes are...
Generics B & C are appropriate for a 1B+D circuit while Generics I, J & M are appropriate for a 2B+D. Note that what the Phone Company calls "voice" is really an ISDN telephone, using the G.711 protocol. Typical broadcast users would choose Generic B or Generic I .
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| Once they have grilled you about your
intentions, its your turn to get information from them that will be needed to configure
the terminal adapter.
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| Most protocols specify one Service
Program IDentifier for each "B" Channel. The
SPID usually contains the 7 digit phone number for the line plus some additional digits.
Though there do appear to be some basic rules regarding the assignment of SPIDs, there are
enough exceptions to make these rules meaningless.
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| Local Directory Numbers are the seven digit
number associated with each "B" channel. In most cases you will have two LDNs
for an ISDN service. Don't be surprised if the numbers are not sequential.
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| This is the manufacturer and model of telephone
switch in the central office. Most switches in North America will be either AT&T 5ESS
or Northern Telecom DMS-100. This information is related to, but not identical, to the
protocol.
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| There is a national standard protocol known as
"National ISDN-1" which is available from all manufacturers of central office
switches. Unfortunately this is a new standard and may not yet be implemented on the
switch you are serviced by. Each manufacturer formerly had a proprietary standard which
are, of course, not compatible. Fortunately most terminal adapters will support most of
these protocols and local phone companies are quickly adopting National ISDN-1. Fallback
on the switch type if they haven't used the words "National ISDN 1" somewhere in
the conversation. It is probably prudent to check with your local carrier and equipment
provider to ensure that your equipment will work on your service.
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There are two data rates in common use for ISDN:
56 and 64Kbits. You may also hear of 112, 128 and 384K rates but these are, in fact,
multiples of either 56 or 64K. This is a useful piece of information to know since it
gives you a place to start from when placing your call. The actual rate available for a
particular call will be the slowest of the following:
If you know your service is 64K then try each call at 64, if it doesn't work you can reconfigure for 56K. An alternate approach would be to place all calls at 56, but this gives up the significant improvement in audio quality (especially with G7.22) and compatibility with international sites.
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| Most of what's listed above does not apply
outside of North America. The rest of the world uses EuroISDN, a protocol with several
minor variations. Service should be ordered as Point to Multipoint and be
terminated on ANSI RJ-45 connectors. EuroISDN does not use SPIDs but some
variations use LDNs which are renamed MSNs. Check with the local PTT for more information.
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| Following these steps increases your chances of
being able to plug and play but does not guarantee them. There are still a number of
vagaries and differences of interpretation of "standards", The watch words are:
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