Extended range enhanced skew controller

Abstract

An apparatus and method for extending the range of a digital data network by enhancing skew control. The apparatus is a circuit for use in a network interface unit. The apparatus measures the distance of the network interface unit from the head-end retransmission unit of the network by transmitting a series of signal packets on the network and counting the time it takes for the packets to be received back at the interface unit. All transmissions on the network take place with reference to a timing mark transmitted by the head-end unit at a regular interval. The apparatus sends the first in the series of signal packets at a pre-determined pre-skew interval before the timing mark. The apparatus counts the number of clock cycles after the timing mark before the signal packet is received back at the network interface unit. If the signal packet is not received back at the network unit within a pre-determined number of clock cycles, the apparatus sends a new signal packet at a new, larger pre-skew interval before the timing mark and again counts the clock cycles after the timing mark. This process is repeated until a signal packet is successfully received back at the network interface unit. Once a signal packet is successfully received back at the network interface unit, the pre-skew value at which the packet was sent and the value of the number of clock cycles after the timing mark at which the packet was received back is stored in the interface unit and all subsequent transmissions by that unit on the network are done at an interval before the timing mark defined by the stored skew value.