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1. •Data Encoding is a method to convert the data into
signal form because we cannot transmit data until it is
converted into signal.
•Whenever we transmit a data it is always in the form of
a signal. It can be in digital or analog form.

2. Encoding
Method
Digital to
Digital
Digital to Analog to
Analog Analog
Analog to
Digital

4. •It is logical to represent digital data with a digital
signal
•Signal changes value as the data changes value
from 0 to 1 and 1 to 0
•It involves various methods: Unipolar Encoding,
Bipolar Encoding and Polar Encoding.

5. •It uses single voltage level (only one polarity) to
represent data.
•The polarity of the pulse shows whether it is positive or
negative logic.
•Positive logic refers to binary 1.
•Negative logic refers to binary 0.
• To represent binary 1(high voltage is transmitted)
• To represent binary 0(no voltage is transmitted)

7. •It uses two voltage level a positive
and one negative.
•It includes :
1. NRZ: Non-Return to Zero
2. RZ: Return to Zero
3. Biphase

9. NRZ: Non-
Return to Zero
NRZ: Non-
Return to Zero
L-Type
NRZ: Non-
Return to Zero
Inversion

10. NRZ-L: Non-Return to Zero L-Type
•It is a Low or –ve logic encoding technique of
NZR.
•+ve voltage level is represented by 0 and –ive
voltage is represented by 1.

11. NRZ-I: Non-Return to Zero
Inversion
•In it bits are represented between +ive and –ive voltages.
•If bit is zero there is no change
•But if next bit is one the change take place.

12. Difference in NRZ-L and NRZ-I Signal

13. RZ: Return to Zero
•It uses three values +ive,-ive and zero.
•In RZ, Signal change not between bits but during each bits.
•In RZ, the signal is return to zero in midway of each duration.
•Bit 1 is represented by +ive to zero and 0 by –ive to zero.

14. Biphase Encoding
•In it signal does not return to zero instead it continues
to opposite polarity and the middle transition of each
bit is used for synchronization.
•It is of two types:
1.Manchester
2.Differential Manchester

15. Manchester:
•Transition in middle of each bit period
•Transition serves as clock and data
•Low to high represents one
•High to low represents zero
•Used by IEEE 802.3

17. Differential Manchester:
•Mid bit transition is clocking only
•Transition at start of a bit period represents zero
•No transition at start of a bit period represents one
•Note: this is a differential encoding scheme
•Used by IEEE 802.5

19. •It also uses three voltage level +ive,-ive and zero.
•Bit 0 is represented by voltage level zero.
•Bit 1 is represented by both +ive and –ive voltage level.
•If a bit is 1 and represents by +ive then the second bit 1
is represents by –ive voltage level

20. Block Coding
Famous block coding are 4B/5B encoding and 8B/6T encoding. The number of bits are processed in
different manners in both these processes.
4B/5B Encoding
In Manchester encoding, for sending data, the clocks with double speed is required. As the name
implies, 4 bits of code is mapped with 5 bits with a minimum number of 1 bits in the group.
By assigning a word of 5 bits in the place of each block of 4 consecutive bits, the clock
synchronization problem is avoided in NRZ-I encoding. These 5-bit words are found in dictionary.
Basic idea behind selecting a 5-bit code is that it should have one leading 0 and it must have no more
than two trailing 0s. Hence, these words are chosen such that two transactions take place per block of
bits.
8B/6T Encoding
To send a single bit over a single signal we have used two voltage levels. If we use more than 3
voltage levels, we can send even more bits per signal.
Techniques above are used for converting digital data into digital signals by coding or compressing
for reliable transmission of data.