Integrated Service Digital Network Frame Synchronizer
Original Publication Date: 1989-Jan-01
Included in the Prior Art Database: 2005-Jan-27
CCITT I.430 defines the characteristics of line signals for Integrated Service Digital Network (ISDN). A logic zero is represented by a 0.75- volt pulse of either plus or minus polarity. A logic one is represented by zero volts. In order to have no net DC voltage on the line, each data zero has a polarity that is opposite from the most recent previous data zero. Clocking is obtained using a phase-locked oscillator running at the bit rate of 192 Kbps. An example of a data stream is shown in Fig. 1. The zeros shown are positive, negative and positive. Framing Bits are grouped together to make a frame 48 bits long. In order to mark the boundaries of frames, a combination of data bits and polarity rule violations is used.