# Before You Configure an Interface

Before you configure a channelized T3 interface, verify the following:

- You have installed the line module and the I/O module correctly.
- Each configured line module is able to transmit data to and receive data from your switch connections.

For more information about installing line modules and I/O modules, see the ERX Hardware Guide.

You should also have the following information available:

- Framing type, clock source, cable length, and the loopback method for each T3 controller
- Framing type and clock source for each T1 channel
- Timeslot mapping and line speed for each fractional T1 channel
- HDLC channel information, such as data inversion information, cyclic redundancy check (CRC) type, idle character, maximum transmission unit (MTU), and maximum receive unit (MRU)