The Crocus Quad E1 Interface allows for the simultaneous transport of up to 4 G.703/E1 connections by using the Crocus fibre modems or Crocus E3 multiplexer.

It is used as an interface in the Crocus FO 10M, Crocus FO45M, or Crocus E3 Mux.

The interface board fits in both the desktop and the card-versions of the Crocus equipment, allowing for a cost-effective solution for both end-user and central-office equipment. Thanks to integrated bit-stuffing algorithms, the four available G.703 interfaces on the board allow for the connection of totally independent applications, which do not have to be frequency locked.