Telos ZephyrExpress - Manual (Page 123)

7-8 ISDN
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 experi-
ence 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 or-
der forms in the Appendix of this manual.
This section is intended to be used as a reference. It is probably not necessary to under-
stand everything in order to get an ISDN line for ZephyrExpress.
The easiest way to order the line is to use the Faxable form in the Appendix, ISDN BRI,
ZephyrExpress, & You. There is also a list of contact telephone numbers for most of the
regional telephone companies.
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’re talking about. We already have a good start,
but there is more to learn.
CSD and CSV
Recall that each ISDN BRI has two possible B channels. It is possible to order a line with
one or both of the B channels enabled – and each may be enabled for voice and/or data
use. Phone terminology for the class of service is CSV for Circuit Switched Voice and
CSD for Circuit Switched Data.
CSV is for calls to standard voice phone service and allows ISDN to interwork with ana-
log phone lines and phones. CSD is required for Zephyr connections. Even though you
may be sending voice, the codec bitstream output looks like computer data to the phone
network. Alternate CSD/CSV means both are supported.
t
DEEP TECH NOTE
Both CSD and CSV are different from PSD Ñ Packet Switched Data (which is irrele-
vant to ZephyrExpress).
ZephyrExpress allows voice calls on either of the channels as well as the coded hi-fi
audio. Thus you can make calls to any normal telephone number on one channel while a
program is being transmitted on the other.
Therefore, you may want to order CSV as well as CSD on one or both B channels. To get a
line with one B channel to be used with either hi-fi or speech, you would request an
ISDN BRI 1B+D line with alternate CSV/CSD capability; for both B channels, you would
order an ISDN BRI 2B+D line with alternate CSV/CSD on both channels; if you don’t
need voice possibility on the channels, you want 2B+D with only CSD enabled.
h
HOT TIP!
While the D channel is always present for signaling purposes, it can, in theory, be
used for packet data connections. ISDN lines where the D channel is used for signaling
only are
sometimes referred to as 2B+0D rather than 2B+D service. D channel packet
service is not widely available.