Digital cross connect system

A digital cross connect system, comprising:

• first interface means including a plurality of first interface circuits for converting an input line signal into a VT signal having a reserved path overhead part having at least one predetermined bit, and the VT signal having a VT frame format in conformance with synchronous optical network standards;
• switching means for cross connecting the VT signal received from said first interface means forming a cross connected VT signal;
• and
• second interface means including a plurality of second interface circuits for converting the cross connected VT signal received from said switching means into a line signal,
• each of the plurality of first interface circuits of said first interface means including signal inserting means for inserting a frame synchronizing signal within the reserved path overhead part of the VT signal, said signal inserting means including producing means for producing the frame synchronizing signal by inverting the at least one predetermined bit of the reserved path overhead part of the VT signal, and
• each of the plurality of second interface circuits of said second interface means including synchronization means for achieving frame synchronization of the VT signal in response to the frame synchronizing signal.