1. DATA COMMUNICATION
Lecture-30

2. Recap of Lecture 29 Transmission Impairments
Performance of Transmission Medium
Wavelength
Shannon Capacity
Media Comparison

3. Overview of Lecture 30 Time Division Multiplexing Asynchronous TDM
Inverse Multiplexing
The Telephone System

4. 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

5. 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

6. Asynchronous TDM Support more devices than synchronous TDM
Each slot is available to any of the attached input lines that has data to send

7. Asynchronous TDM Frames
Multiplexer scans the input lines and accepts data until a frame is filled
Frame may be transmitted only partially filled

8. Asynchronous TDM Frames

10. Aspects of Asynchronous TDM
Addressing and overhead
Variable-length time slots

11. 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

12. Inverse Multiplexing

13. Telephone System
North American telephone system includes many common carriers
Local companies and long-distance providers

14. Telephone System

15. Summary Time Division Multiplexing Asynchronous TDM
Inverse Multiplexing
The Telephone System

16. Suggested Reading
Section 8.4,8.5 “Data Communications and Networking” 2nd Edition by Behrouz A. Forouzan