Telos Zephyr Xstream - Manual (Page 150)

USER’S MANUAL
Section 7: ISDN BASICS 138
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DEEP TECH NOTE!
The 56kbps limitation arises from a quirk of the older telephone infrastructure. The channel
banks that have been widely employed in the long-distance network have a native 64kbps
capability, but “rob” the low order PCM bit on every sixth frame in order to convey
supervision information (on-hook/off-hook and dial pulses). On voice calls the results is
merely a slightly increased noise floor. Therefore, data applications must not use the low
order bit, leaving a 56 kbps channel rate.
As new telephone plant is built for clear 64kbps transmission and a technology called
“Signaling System 7” is deployed to allow the various elements of the phone network to
communicate without using the robbed bits, this limitation has all but disappeared.
The European network has universal full 64kbps capability.
7.3 How to Order ISDN
See Appendix 8 (ordering ISDN:ETS‐300) and Appendix 10 (ordering ISDN for the USA & Canada)
for additional information and ISDN order forms to send to your Telco.
Dealing with the Phone Company
As is often the case when we broadcasters interface with the phone people, the lines of
communication on ISDN can get a little tangled. Face it: we are not the usual customers. The
good news is that ordering ISDN is pretty routine these days, and problems are really quite rare.
The following information is intended to help if you run into difficulties.
The first order of business is to find someone who knows what ISDN is. While your usual
account agent will be the normal entry point, you might need to talk to some other phone
company people before you find one who understands your needs. Some of the regional Bell
companies offer a single point of contact number for switched digital services. Some Telcos use
“Resellers” or “Agents”. If so, you should be sure to ask what experience the particular agent
has with ordering lines for high fidelity audio codecs. If in doubt, go direct to the Telco. And,
always order your line in writing using the ISDN order forms in the Appendix of this manual.
This section is intended to be used as an overview. It is not necessary to understand everything
in this section to get an ISDN line for a Zephyr Xstream.
The easiest (and most accurate) way to order the line is to use the appropriate Faxable ISDN
Order Form from Appendix 7 or 8 (Ordering ISDN). Appendix 8 also includes a list of contact
telephone numbers for many of the regional telephone companies in the USA & Canada.
Details, Details
In order to communicate accurately what it is you need, you might want to learn about the
nature of the ISDN service and the vocabulary used to describe it. As with anything, for best
results, it helps to know what you are talking about. We already have a good start, but there is
more to learn.