1.2 Physical Layer Characteristics

Answer 1

The physical layer standards address three functional areas:

1. Physical Components
2. Encoding
3. Signaling

Question 2

1. Physical Components

Answer 2

The physical components are the electronic hardware devices, media, and other connectors that transmit the signals that represent the bits. Hardware components such as NICs, interfaces and connectors, cable materials, and cable designs are all specified in standards associated with the physical layer.

Question 3

2. Encoding

Answer 3

Encoding or line encoding is a method of converting a stream of data bits into a predefined “code”. Codes are groupings of bits used to provide a predictable pattern that can be recognized by both the sender and the receiver. In other words, encoding is the method or pattern used to represent digital information.

Question 4

3. Signaling

Answer 4

The physical layer must generate the electrical, optical, or wireless signals that represent the “1” and “0” on the media. The way that bits are represented is called the signaling method. The physical layer standards must define what type of signal represents a “1” and what type of signal represents a “0”. This can be as simple as a change in the level of an electrical signal or optical pulse.

Question 5

BANDWIDTH

Answer 5

Bandwidth is the capacity of a network medium to carry data.

Is he amount of data that can be transmitted and received during a specific period of time, measured in bits per seconds.

Answer 6

Different physical media support the transfer of bits at different rates. Data transfer is usually discussed in terms of bandwidth. Bandwidth is the capacity at which a medium can carry data. Digital bandwidth measures the amount of data that can flow from one place to another in a given amount of time. Bandwidth is typically measured in kilobits per second (kbps), megabits per second (Mbps), or gigabits per second (Gbps). Bandwidth is sometimes thought of as the speed that bits travel, however this is not accurate.

A combination of factors determines the practical bandwidth of a network:

The properties of the physical media
The technologies chosen for signaling and detecting network signals
Physical media properties, current technologies, and the laws of physics all play a role in determining the available bandwidth.

Question 7

LATENCY

Answer 7

Latency refers to the amount of time, including delays, for data to travel from one given point to another.

Question 8

THROUGHPUT

Answer 8

Throughput is the measure of the transfer of bits across the media over a given period of time.

Question 9

GOODPUT

Answer 9

Goodput is the measure of usable data transferred over a given period of time. Goodput is throughput minus traffic overhead for establishing sessions, acknowledgments, encapsulation, and retransmitted bits.