Nortel Networks 553-3001-211 manual TCM loop interface circuit

Page 522 of 894 NT8D02 and NTDK16 Digital Line cards

lines carry multiplexed PCM voice, data, and signaling information as TCM loops.

The purpose of each digital line interface circuit is to de-multiplex data from the DS-30X Tx channel into eight integrated voice and data bitstreams. The circuits then transmit those bitstreams as Bi-Polar Return to Zero, Alternate Mark Inversion (BPRZ-AMI) data to the eight TCM loops. They also perform the opposite action: they receive eight BPRZ-AMI bitstreams from the TCM loops and multiplex them onto the DS-30X Rx channel. The two digital line interface circuits perform the multiplexing and de-multiplexing functions for the 16 digital telephone lines.

The digital line interface circuits also contain signaling and control circuits that establish, supervise, and take down call connections. These circuits work with the on-card microcontroller to operate the digital line interface circuits during calls. The circuits receive outgoing call signaling messages from the Call Server and return incoming call status information to the Call Server over the DS-30X network loop.

TCM loop interface circuit

Each digital telephone line terminates on the NT8D02 Digital Line card at a TCM loop interface circuit. The circuit provides transformer coupling and foreign voltage protection between the TCM loop and the digital line interface circuit. It also provides battery voltage 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 card microcontroller can remove the ±15 V dc power supply from the TCM loop interfaces. This happens when either the microcontroller gets a command from the NT8D01 controller card to shut down the channel, or the digital line card detects a loss of the 1 KHz frame synchronization signal. The ±15 V dc power supply signal is removed from all 16 TCM loop interface units at the same time.

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

553-3001-211 Standard 2.00 September 2004