1. Multiplexing

2. Outline Of the Lecture Why Multiplexing Basic Concepts of Multiplexing
Frequency Division Multiplexing
Wavelength Division Multiplexing
Time Division Multiplexing
Synchronous
Asynchronous
Inverse TDM

3. Why Multiplexing?
Most individual data-communicating devices typically require modest data rate.
Communication media usually have much higher bandwidth.
Two communicating stations do not utilize the full capacity of data link
At the time of sending voice data rate requires less than provided bandwidth
When we have to send data and also receive the data from same sender and the receiver at that time we have to divide the given bandwidth in two half using FDM User A-B and User B-A
Ex 2400Hz given Bandwidth then 1200 for User A-B and 1200 Hz for User b-A

4. Many to one/one to many
Types of multiplexing
Telephone system

5. Basic Concepts
A device known as Multiplexer(MUX) combines n channels for transmission through a single medium or link.
At the other end a demultiplexer (DEMUX) is used to separate out the n channels

6. Multiplexing vs. No Multiplexing

7. Key Points
MUX: Combines different signal to single transmission signal.
DEMUX: separates the stream back into different signal.
PATH: Physical Link.
CHANNEL: Portion of a path.

9. Frequency Division Multiplexing(FDM)
It is an analog technique.
Applied when bandwidth of link is greater than the combined bandwidth of the signal to be transmitted.
Carrier frequency are separated by Guard Band.
Actual Bandwidth is lowered by suppressing half the band.

11. FDM, Time Domain

12. Multiplexing, Frequency Domain

13. Demultiplexing, Time Domain

14. Demultiplexing, Frequency Domain

15. Time Division Multiplexing (TDM)
It is digital technique
Capacity of transmission medium is greater than the data rate required by the sending and receiving devices.

16. Synchronous TDM
Synchronous: multiplexer allocate the same time to each devices at all the time.

17. Frames: Time slots are grouped into frame.
n input lines each frame contains n slots
Interleaving: It is compared with fast rotating switch.
It moves constantly on fixed packets.
Wastage of frames

18. TDM, Multiplexing

19. TDM, Demultiplexing

20. Framing Bits

21. Asynchronous TDM

22. Inverse Multiplexing

23. Multiplexing Application Telephone System

26. Analog Switched Service
It is familiar dial-up services.
It uses two wire(one pair).

27. Analog Leased Service
It is a dedicated line i.e. Permantly connected to another user.
Conditioned Line: To improve the signal quality

28. Analog Hierarchy
Group
Super-group
Master-group
Jumbo-group

31. Switched/56 Service Digital Version of analog switched line.
It allows data rate up to 56kbps.
Both parties must subscribe.

32. Digital Data Services(DDS)
Digital version of Leased Line.
Max Data rate up to 64 kbps.
It require DSU.
No need of Keypad

33. Digital Hierarchy of Digital Services
DS-0 Similar to DDS
DS Mbps (24*64Kbps +8 overhead)
DS Mbps
DS Mbps
DS Mbps
T Lines are used to implement .
It is Designed for Digital System.
T Frames are used 24 slots * = 193.
T-1 Carry 8000 frames per seconds .

35. T1 Frame

36. Analog Transmission using T1 Line

37. Digital Subscriber Unit (DSU)
It has been developed to facilitate high speed digital communication over existing local loop.
Different types of DSU
ADSL, SDSL, HDSL, VHDSL

38. Asymmetric DSL(ADSL)
It provides higher data rate in the downstream direction than the upstream direction.
Bandwidth is divided into three bands
0-25 KHz
KHz
KHz

39. Error Detection and Correction
Types of Errors
Detection
Correction

41. Single-bit error

42. Multiple-bit error

43. Burst error

45. Vertical Redundancy Check (VRC)

46. Longitudinal Redundancy Check (LRC)

47. Cyclic Redundancy Check (CRC)

48. Binary Division

49. Polynomial

50. Checksum

52. Checksum detects all error involving an odd numbers of bits
It also detect most error involving even no of bits

54. Error Correction Two Basic Approach Backward Error Correction
If error occurred at that time user request to send same packet which is error prone, is called as Automatic Repeat Request (ARQ) technique.
Forward Error Correction
Use more redundancy in transmitted data to not only detect but also correct the error in received data.

55. Error Correction

56. Hamming Code

57. Hamming Code

58. Example of Hamming Code