Telos Zephyr Xstream User Manual page 151

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 using standard voice phone service and allows ISDN to interwork (i.e. to call) with
analog 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" or "Alternate voice/data" means both capabilities are supported.
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.
Zephyr Xstream allows the option of a voice call on either of the channels as well as the coded
hi‐fi audio. This capability exists on both channels. Thus, you can make calls to any normal
telephone number on one channel while a program is being transmitted on the other. The
Xstream even allows you to place two of these voice calls, but then, of course, you would not be
able to transmit hi‐fidelity codec data, since both channels would be in use.
Calls from a Zephyr Xport that is connected to an analog "POTS" line also use CSV.
Therefore, you will want to order CSV as well as CSD on one or both B channels. Typically, 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.
NT1s
The ISDN standard specifies two reference points, the 'U' and the 'S' interfaces.
The U is the single‐pair bare copper from the Telco CO. This is sometimes referred to as the "2‐
wire" interface. A device called a 'Network Termination, Type 1' (NT1 or NT‐1) converts this to
the two‐pair S interface. The S interface sometimes is called the "4‐wire interface. The NT1 can
also be generically be referred to as NCTE (Network Channel Termination Equipment).
Outside the USA & Canada, the NT1 (and NCTE for other types of lines) is nearly always provided
by the telephone company, and therefore the S interface must be on user equipment. In some
countries, it is referred to as a NTBA (Network Termination Basic Access). In the USA and
Canada, the NT1 is usually provided by the user. Therefore, the Zephyr Xstream includes both
interfaces. The U interface on the Zephyr Xstream is on a 2‐pin 6‐position miniature modular
plug (RJ‐11 style). The S interface is on an 8‐pin 8‐position miniature modular plug (RJ‐45 style).
Refer to manual Section 3 (Guided Tour of the Hardware) for additional information on Zephyr
Xstream's built‐in NT1.
USER'S MANUAL
Section 7: ISDN BASICS 139