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GUIDE TO TELEPHONE TERMINOLOGY | 113
perfection!
U Interface- e interface between the ISDN “BRI” line and the
“NT1”. ANSII standards for the US call for 2B1Q line coding,
which is also used in some other places (though not necessar-
ily). is can be considered the ISDN “phone jack” in the USA &
Canada, and is frequently in the form of a RJ-11 or RJ-45 style
telephone jack. e center 2 pins are used on these jacks.
V.35- A serial data interface/connector pin out for synchronous
data. V.35 uses balanced signal and data lines. e Zephyr/Zephyr
Xstream models 9X01, 9X00, support V.35 using part #9812 cable.
Variant- e particular protocol (i.e. National ISDN-1 or ETS
300) running on a specific switch. Not all variants are valid for a
specific switch. e switch brand and model plus the variant defines
the ISND protocol. Applies to configuring the 2101. See ISDN
Protocol.
Virtual ISDN- An alternative to repeaters which uses a local Telco
Switch to act as a repeater and which then sends the signal onto
another switch which supports ISDN. See also Repeater.
Work Order- See Trouble Ticket
X.21- A serial data interface for synchronous data popular in
Europe. X.21 uses balanced data and unbalanced signal lines. e
Zephyr models 9X01, and 9X00 support X.21 using part #9822
cable.
Yellow Alarm- An alarm on a T-carrier circuit that is returned by
the local equipment if it is in a Red Alarm state. A Red Alarm indi-
cates a loss of inbound signal; a Yellow alarm indicates (indirectly) a
loss of outbound signal. See Red Alarm, Blue Alarm and LOS.
Tie Line- See Tie Trunk.
Tie trunk- A Trunk between two PBXs. Note, a tie line is a dedi-
cated circuit, not a switched circuit. See Trunk.
TR-008 - See SLC-96
Trouble Ticket-A Telco “work order” used to track Customer Re-
pairs within the Telco. If you call someone “inside” the Telco’s repair
department, they will need this number to proceed. It will also be
needed whenever you call to check on the status of a repair. Always
ask for this number when initiating a repair request.
Trunk- A communications path between two switching systems.
Note that many trunks may be on a single circuit (if that circuit has
multiple channels). e trunks most users will deal with are between
the Telco switch and a PBX. However, a Tie Trunk can connect two
PBXs. See also Tie Trunk and Trunk Group
Trunk Group- A number of telephone channels which are func-
tionally related. Most common is the Hunt Group. Other com-
mon types include Incoming Trunk Groups and Outgoing Trunk
Groups. See also Combination Trunks and Two-way DID Trunks.
Trunk Side- 1) e side of a central office that faces the network.
Historically many CO switches could not make trunk to trunk
connections (as opposed to tandem and long distance switches, that
are always used to connect trunk together). Hence the need to dis-
tinguish between the “line side” and the “trunk side” of the switch.
See also Line Side.
2) e side of a PBX that connects to the Telco. Historically many
PBXs could not make trunk to trunk connections. Hence the need
to distinguish between the “line side” and the “trunk side” of the
switch. Since a trunk is a switch-to-switch circuit, these circuits can
be called trunks. Beware, even though you have a PBX, the Telco
may still call these ‘lines’ (even though your PBX considers them
trunks). See also Trunk and Line Side.
Two-way DID trunk- An ISDN PRI equipped for direct inward
dialing. Most PBX trunks are related to a given phone number,
either alone or as part of a hunt group. In the case of a “normal” (i.e.
analog) DID Trunk, a group of phone numbers are associated with
that DID trunk (or group of trunks) and incoming calls include the
DID number, so the PBX can route that call to the correct DID ex-
tension. ese are one-way (i.e. inward only) trunks. is is exactly
how ISDN PRI functions, with the DID information coming in
over the D channel. ere is a big difference between a normal DID
Trunk and a Two-way DID trunk over ISDN PRI. For one thing,
ISDN PRI is digital. Another distinction is that you cannot dial out
over a true DID trunk, while you can dial out over a PRI (hence the
conflicting designation “Two Way Direct Inward Dialing Trunk”).
Two Wire – A circuit path where only a single pair of wires is used.
A hybrid is used to convert from two wire to four wire circuits. No
hybrid is perfect, and those used by the phone company can be poor.
However, the hybrids in Telos TWO/2101 family are approaching