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122 | Appendix 3
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. (In contrast to PSD, Packet
Switched Data, which is possible, but irrelevant to our needs.)
CSD is not required for Telos Nx12 connections. Even though you are sending a
stream of data, the phone network knows to translate this back to analog at the far
end due to the call setup message sent on the D channel when the call is made. If
this ISDN BRI circuit will also be used with an audio codec such as the Zephyr or
Zephyr Xstream then CSD should be ordered as it is required for audio codec calls.
CSV is for interworking with voice phone service and allows ISDN to interwork
with analog phone lines and phones.
You will be ordering one or more ISDN BRI 2B+D circuits with CSV (required)
and CSD (optional) on each B channel. Euro ISDN normally provides both CSV
and CSD which is acceptable.
NT1s
e ISDN standard specifies two reference points, the “U” and the “S” interfaces.
e U is the single-pair bare copper from the Telco CO. A device called a “Net-
work Termination, Type 1” converts this to the two-pair S interface.
In Europe, Asia, South America, and most of the world the NT1 is always pro-
vided by the phone company, and only the S interface may be on user equipment.
If you plan on taking your TWOx12 to Canada or North America you will need
to rent or purchase an external NT1 for use while in those countries. One rental
source is Silver Lake. See their website at www.silverlakeaudio.com .
Hunt Groups
Just as with analog lines, ISDN BRI lines can be placed in a “hunt group” where
a single number can be given to callers and the calls will “roll over” from busy
channels to idle channels. is is sometimes referred to as ISG (incoming service
grouping) or rollover lines. is would usually be a requirement for an on-air phone
system. You may choose to exclude 1 or 2 channels from the hunt group (ie the
Hot line and the Warm line). Be sure to specify to your Telco how you expect this
to work.
Line Deactivation
e Euro ISDN standard allows ISDN BRI lines to be deactivated by the Telecom
when not in use. It is impossible to distinguish a deactivated line from a line
which is defective and out of service. If your application is critical you may wish to
request that the Telecom disable line deactivation.
FAXABLE ISDN ORDER FORM (for Euro ETS 300)
e following form may be used to place orders for ISDN lines in countries using
the ETS 300 protocol. ese should give the Telecom all of the information they
need.