Nortel Networks 553-3001-211 manual Signaling

Overview Page 39 of 894

Figure 5

Digital line interface unit block diagram

DS-30X loop
Tx PCM			Tip
Rx PCM	Digital	4-wire	TCM loop
	line	to	interface
	interface	2-wire	and
	circuit	conversion	protection
1 kHz frame			Ring
sync
±15 V dc power supply
			553-6154

voltage protection between the TCM loop and the digital line interface circuit. It also provides power for the digital telephone.

To prevent undesirable side effects from occurring when the TCM loop interface cannot provide the proper signals on the digital phone line, the system controller can remove the ±15 V dc power supply from the TCM loop interface. This happens when either the card gets a command from the NT8D01 Controller card to shut down the channel, or when the digital line card detects a loss of the 1 KHz frame synchronization signal.

Each TCM loop interface circuit can service loops up to 3500 ft. in length when using 24 gauge wire. The circuit allows for a maximum ac signal loss of 15.5 dB at 256 KHz and a maximum DC loop resistance of 210 ohms.

Signaling

The digital line interface units also contain signaling and control circuits that establish, monitor, and take down call connections. These circuits work with

Circuit Card Description and Installation