DATA COMMUNICATION Lecture-30
Recap of Lecture 29 Transmission Impairments Performance of Transmission Medium Wavelength Shannon Capacity Media Comparison
Overview of Lecture 30 Time Division Multiplexing Asynchronous TDM Inverse Multiplexing The Telephone System
Bit Stuffing The time slot length is fixed When the speeds are not integer multiples of each other, bit stuffing is used In bit stuffing, the multiplexer adds extra bits to a device’s source stream
Asynchronous TDM Also called statistical TDM or concentrator Total speed of input lines can be greater than the capacity of the path For n input lines, the frame contains no more than m slots, with m less than n
Asynchronous TDM Support more devices than synchronous TDM Each slot is available to any of the attached input lines that has data to send
Asynchronous TDM Frames Multiplexer scans the input lines and accepts data until a frame is filled Frame may be transmitted only partially filled
Asynchronous TDM Frames
Aspects of Asynchronous TDM Addressing and overhead Variable-length time slots
Inverse Multiplexing Breaks one high-speed line into several lower-speed lines High-rate data (video, for example) can be inversely multiplexed over multiple lines
Inverse Multiplexing
Telephone System North American telephone system includes many common carriers Local companies and long-distance providers
Telephone System
Summary Time Division Multiplexing Asynchronous TDM Inverse Multiplexing The Telephone System
Suggested Reading Section 8.4,8.5 “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan