Applications of Time Division multiplexing : statistical TDM

These slides cover a topic on Applications of Time Division multiplexing and statistical TDM in Data Communication. All the slides are explained in a very simple manner. It is useful for engineering students & also for the candidates who want to master data communication & computer networking.

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.

4. 6.4
Figure: Digital hierarchy

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
1Line utilization
efficiency
Poor Good Very good
2Flexibility Poor Good Very good
3Channel capacity Poor Good Excellent
4Error control Not
possible
Not possible Possible
5Multidrop capacityVery good Difficult to
achieve
Possible
6Transmission
delay
Does not
exist
Low Random
7Cost 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