Telos TWOx12 - Page 27

TELOS TWOX12 USER’S MANUAL
INSTALLATION
CHAPTER 2 15
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CURIOSITY NOTE!
While the D channel is always present for signaling, 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. D channel packet service is
not widely available, and is not used by the TWOx12 or other Telos equipment.
Data and Voice
ISDN lines may be used for voice signals encoded in standard fashion to allow inter-
working with analog telephones, or may be used to transmit digital data streams. The latter
mode is used for such applications as high-speed Internet access. It is also the mode used
with MPEG codecs, in which case the ISDN line may be carrying voice signals, but is
doing so in a format that is not compatible with the analog part of the telephone network.
The distinction is made in the automatically conveyed “Setup” message that begins each
call.
t
DEEP TECH NOTE!
The voice mode may well be able to transmit digital data–and some Telephone
Companies charge more money for data capability. That is why some ISDN
“modems” have a special data- over- voice option that fools the central office into
billing as if it were a voice connection.
Normally, the Telos TWOx12 uses only the voice mode, so data capability is not necessary.
Of course, you may use a line with both capabilities with the system at any time. Just be
sure the BRI circuit supports the Circuit Switched Voice (CSV) capability as well as data.
h
HOT TIP!
If this line may be “borrowed” at times for use with an audio codec, such as the Telos
Zephyr or ZephyrExpress, then you need to be sure that the Circuit Switched Data
(CSD) capability is enabled.
Hunt Groups
The most common configuration for on-air phone system is to have the different phone
numbers linked in a “Hunt Group,” also called “Rollover Lines,” or “Incoming Service
Grouping (ISG).” A hunt group allows you to give out a single number to the audience and