# Connecting to a T1 network

Caution: | You must complete all required performance tests, and a type approval certificate must be granted by the appropriate regulatory authority in the target country before you can connect the CG 6565E board configured as T1 to the public network.

The CG 6565E daughterboard has up to eight T1 trunk interfaces. For typical T1 communications, each trunk interface connects to a channel service unit (CSU) that is connected to a T1 trunk line. The CSU provides a DSX-1 interface to the T1 line and also contains circuitry that allows the central office (CO) to perform diagnostic tests remotely.

The following illustration shows a CG 6565E trunk interface with a CSU:

Trunks synchronize when the OAM API boots the board.

You can purchase or lease the CSU from the telephone company or other vendor. The CSU must be compatible with DSX-1 specifications.

Warning: | Important safety note for telephony connections The cables attached to this product must be isolated by a channel service unit (CSU) before the cables leave the building.

You can also connect the board directly to the T1 line, without a CSU. This setup is most common in applications where the T1 line is proprietary and is not connected directly to the public network.

The following illustration shows a CG 6565E trunk interface without a CSU:

To avoid causing T1 service provider alarms, make sure that the board always sends a valid signal, either by looping back at the CSU, or by connecting the CSU to a functioning CG 6565E board. The best way to loop back the signal is to unplug the cable from the CSU. The modular connection on most CSUs loops back the transmit signal to the receive signal when nothing is plugged in.