AT&T 7500 series, 7100 series, 2500 series, 7200 series, 7400 series Signaling Protocols, Trunk Type

1-40TRUNKING

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signals on-hook on all calls by opening the path between the tip and the ring.

∙LS (loop start) supervision — A supervisory signaling scheme used between a telephone and a PBX in which the telephone completes the loop current path. Some PBXs provide loop start trunk arrangements, but due to the difficulties with glare resolution, AT&T PBXs do not provide these trunks as standard offerings.

∙RB (reverse battery) supervision — A supervisory technique on 1-way trunks that uses open and closure signals from the originating end and reversals of battery and ground from the terminating end (normally used on DID trunks).

Signaling Protocols

Signaling protocols are conventions for alerting the far end of an incoming call. Signaling protocol is an administrative option for trunks on System 75, System 85, G1, and G2. On System 85 and G2, you specify the signaling protocol when you specify the signaling type with PROC 100. On System 75 and G1, you enter the signaling protocol as the trunk type at the Trunk Group screen.

Network trunks operate as automatic, immediate start, dial tone, wink start, delay-dial, or dial-repeating according to the type of start-dial signal the switch sends out or expects to receive. The different signaling protocols are:

∙Automatic — The originating switch sends no digits or start-dial signal, expecting the terminating switch to complete the call. The call is usually completed by the attendant or other service such as Centralized Attendant Service (CAS). (Use with E & M, GS, or RB.)

∙Immediate start — The originating switch sends digits immediately after seizure (off-hook) without waiting for a start-dial signal from the terminating switch. (Use with E & M and RB.)

∙Dial tone — The terminating switch sends precise dial tone to the originating switch, indicating that the terminating switch is ready to receive digits. (Use with E & M or GS.)

∙Wink start — The terminating switch sends a wink start (momentary off-hook) signal to the originating switch, indicating that the terminating switch is ready to receive digits. (Use with E & M.)

∙Delay-dial — The terminating switch sends a delay-dial signal (an off-hook signal followed by an on- hook signal) to the originating switch, indicating that the terminating switch is ready to receive digits. (Use with E & M.)

∙Dial-repeating — The originating switch sends digits after waiting for a dial tone from the terminating switch. The connection is said to be "cut through" because the connection with the destination switch is established before the destination extension is dialed. This type of alerting is used in tandem tie trunk networks. (Use with E & M.)

Trunk Type

Trunk type is an administration option on System 85 and G2 switches. You set the trunk type through PROC 100 Word 1.

On System 85/G2 switches, there are over 100 administrable trunk types (see appendix C). Each type is a numeric code that represents a designated combination of trunking application, and signaling types. Each combination is represented by a different code.

Listed on the tables that follow are some trunk types that may warrant further explanation. They are as follows: