7.2 Physical Signaling and Encoding

	There are several signaling methods used to differentiate between the zero and the one, which are the two digits that form all digital communication.
	There are several signaling methods used to differentiate between the zero and the one, which are the two digits that form all digital communication.
	There are several signaling methods used to encode the data in the context of physical layer such as Non-Return to Zero (NRZ), Return to Zero (RZ), Manchester encoding, and 4B/5B encoding methods.
	In NRZ method (Figure 1-3), the signal has only two levels with one of them (in positive logic it will be the most positive value) represents logic 1, while the other level represents logic 0.

Figure 1-3: Encoding of sequence 010100110 using NRZ encoding meth

7.2 Physical Signaling and Encoding

In RZ method (Figure 1-4), the signal must return to zero during each bit duration and in most cases it returns to zero at the middle of the bit duration, with one level represents logic 1 (the most positive value when we use positive logic) and the other level represents logic 0.

Figure 1-4: Return to Zero encoding for the bit sequence 10010

7.2 Physical Signaling and Encoding

In Manchester encoding (Figure 1-5), the data is encoded using the signal transition; with a transition from 1 to 0 represents certain logic value while the transition from 0 to 1 represents the other logic value.

Figure 1-5: Encoding of sequence 110100 using Manchester encoding method

	In 4B/5B encoding methods, each consecutive 4 bits are encoded into 5 bits. There are several reasons behind this encoding method such as reducing bit-level error, distinguishing data bits from control bit, providing error detection, and identifying the beginning or ending of the frame.
	There are several metrics that are commonly used to evaluate the transmission of data in the physical layer, the most common of them are:

7.2 Physical Signaling and Encoding

		Bandwidth: Represents the amount of data that could flow across a network segment in a given length of time. In other words, it represents the capacity of the medium.
		Throughput: Represents the actual rate of transfer of bits at a given time.
		Goodput: Represents the usable data transfer rate.