Patent ID: 6870877

Claim:
A transmission unit which transmits and receives digital signals over a first and second network systems, comprising: (a) a first signal interface means for receiving a first network signal and converting the received first network signal into a first internal signal with a fixed bit rate, and for sending an outgoing first network signal which is converted from a given second remapped internal signal with the same fixed bit rate; (b) a second signal interface means for receiving a second network signal and converting the received second network signal into a second internal signal with the fixed bit rate, and for sending out an outgoing second network signal which is converted from a given first remapped internal signal with the same fixed bit rate; (c) a two-way signal conversion means for making conversions between the first and second network signal, comprising: a downward conversion means receiving the first and second internal signals and producing lower-level signals by converting the first and second internal signals down to a lower hierarchical level at which the first and second network systems are compatible with each other in terms of logical signal structures, an upward conversion means for producing a first or second remapped internal signal by convening a given lower-level signal up to a higher hierarchical level which complies with the first or second network system, and a looping back means for looping back, at the lower hierarchical level, the lower-level signals from said downward conversion means to said upward conversion means to cause the lower-level signals deriving from the received first and second network signals to be converted to the first and second remapped internal signals, respectively; (d) a switching means for providing and controlling circuit paths to route the first internal signal, the second internal signal, the first remapped internal signal, and the second remapped internal signal; and wherein said two-way signal conversion means makes the conversions between the first and second network signals which include at least one of: two-way conversions between Synchronous Digital Hierarchy(SDH) signals and Synchronous Optical Network(SONET) signals; two-way conversions between Plesiochronous Digital Hierarchy(PDH) signals; and two-way conversions between Asynchronous Transfer Mode(ATM) signals.