Applications of Time Division multiplexing : statistical TDM
- 1. Introduction to Data communication Topic: Applications of TDM ( T & E Lines ) & Statistical TDM Lecture #3 Dr Rajiv Srivastava Director Sagar Institute of Research & Technology (SIRT) Sagar Group of Institutions, Bhopal http://www.sirtbhopal.ac.in
- 2. Unit 2 Lecture 3 Course Lecture 20 Applications of TDM ( T & E Lines ) & Statistical TDM
- 3. Digital Signal Service • Telephone companies & Internet service provides implement TDM through a hierarchy of signals, called Digital Signal (DS) service or digital hierarchy. • Figure given next shows data rates supported by each level.
- 5. T Lines • DS-0 & DS-1 are the names of the services. • Telecom companies use T lines (T-1 to T-4). • Capacity of these lines precisely matches with DS- 1 to DS-4 services. • Today T-1 & T-3 are commercially available.
- 6. T Lines for Analog transmission • T lines are digital lines • They can be used for analog service such as voice calling • For this purpose analog signal is first sampled & then time division multiplexed.
- 7. E Lines • E Lines are European version of T lines. • T lines & E lines are conceptually same
- 8. • STDM, or statistical time division multiplexing, is one method for transmitting several types of data simultaneously across a single transmission cable or line (such as a T1 or T3 line). • STDM is often used for managing data being transmitted via a local area network (LAN) or a wide area network (WAN). • In these situations, the data is often simultaneously transmitted from any number of input devices attached to the network, including computers, printers, or fax machines. Statistical Time Division Multiplexing
- 9. • In synchronous TDM, each input has a reserved slot in the output frame. This can be inefficient if some input lines have no data to send. • In statistical time-division multiplexing, slots are dynamically allocated to improve bandwidth efficiency. • Only when an input line has a slot’s worth of data to send is it given a slot in the output frame. Statistical Time Division Multiplexing
- 10. • In statistical multiplexing, the number of slots in each frame is less than the number of input lines. • The multiplexer checks each input line in round-robin fashion; it allocates a slot for an input line if the line has data to send • otherwise, it skips the line and checks the next line.
- 11. Statistical Time Division Multiplexing • Statistical TDM is a more flexible method of TDM. With static TDM the length of time allocated is not fixed for each device but time is given to devices that have data to transmit. • STDM can also be used in telephone switchboard settings to manage the simultaneous calls going to or coming from multiple, internal telephone lines
- 12. 6.12 Figure: TDM slot comparison
- 13. Frames and Addresses a. Only three computer/lines out of 5 are sending data
- 14. Frames and Addresses b. Only four lines sending data
- 15. Frames and Addresses c. All five lines sending data
- 16. Animation of STDM • http://www.mhhe.com/engcs/compsci/forouz an/dcn/graphics/animations/08_17.swf
- 17. Comparison of data multiplexer techniques Sr.N o. Parameter FDM Synchronous TDM Statistical TDM 1 Line utilization efficiency Poor Good Very good 2 Flexibility Poor Good Very good 3 Channel capacity Poor Good Excellent 4 Error control Not possible Not possible Possible 5 Multidrop capacity Very good Difficult to achieve Possible 6 Transmission delay Does not exist Low Random 7 Cost High Low Moderate
- 18. No Synchronization Bit • There is another difference between synchronous and statistical TDM, but this time it is at the frame level. • The frames in statistical TDM need not be synchronized, so we do not need synchronization bits. Bandwidth • In statistical TDM, the capacity of the link is normally less than the sum of the capacities of each channel.
- 19. Animation of TDM Switching • http://www.mhhe.com/engcs/compsci/forouz an/dcn/graphics/animations/14_10.swf • http://www.mhhe.com/engcs/compsci/forouz an/dcn/graphics/animations/14_11.swf
- 20. Thank You Dr Rajiv Srivastava Director Sagar Institute of Research & Technology (SIRT) Sagar Group of Institutions, Bhopal http://www.sirtbhopal.ac.in