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DATA COMMUNICATION Principles : Pulse stuffing
Pulse stuffing In practical implementations, the sum of data rates of multiplexed sources should be equal to the total line bit rate for synchronization purpose. If the aggregate data rate of the multiplexed traffic is less than the line rate then there will be gaps in the TDM frame. If nothing is transmitted in these idle time slots, the clocking information may be lost. The idle time on TDM channels are filled with pulse stuffing. Let’s suppose that C is the capacity of a line and that N traffic sources are multiplexed on this line, each allocated I/N fraction of the capacity. Let be the actual data rate of source k. Then, ideally should be equal to C/N for all values of & (1, 2. . . N). If then some of the data will be lost and if then some of the TDM slot will be unfilled. Pulse stuffing is used to the fill the partially empty TDM slots when so that can be satisfied. Pulse stuffing is performed by inserting extra bits (pulses) at known locations according to a predetermined rule. The demultiplexer of such a frame has the knowledge of pulse stuffing and can easily remove these pulses from the frame to extract and deliver the data bits that were sent by the transmitter. In practice, pulse stuffing is done for known data rates so that the number and positions of pulse stuffing are known by the transmitter and the receiver.
REFERENCES • Ahmad A. - Data Communication Principles. For Fixed and Wireless Networks • Cornelius T. Leondes - Database and Data Communication Network Systems, Three-Volume Set_. . -Academic Press