# Before You Configure an Interface

Before you configure a cOCx/STMx interface, verify the following:

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

For more information about installing modules, see ERX Hardware Guide, Chapter 4, Installing Modules.

Make sure you also have the following information available:

- Framing type, clock source, and the cable length for each controller
- Framing type, line code, and clock source for each channel
- Timeslot mapping and line speed for each fractional channel
- HDLC channel information, such as data inversion information, CRC type, idle character, MTU, and MRU