Physical LAYER Flashcards
What type of network is common in many corporate offices, where employees have desktop or laptop computers physically connected, via cables, to a shared switch?
This type of setup is a wired network. Data is transmitted through a physical cable.
What other connectivity options do many businesses provide, besides wired connections, enabling usage of laptops, tablets, and smartphones via wireless networks ?
With wireless devices, data is transmitted using radio waves.
Devices on a wireless network must be connected to a wireless access point (AP) or wireless
router like the one shown in the figure.
How do network interface cards (NICs) facilitate device connectivity to a network?
Network interface cards (NICs) connect a device to the network.
Ethernet NICs are used for a wired connection.
An end-user device may include one or both types of NICs.
Other devices, such as tablets and smartphones, might only contain a WLAN NIC and must use a
wireless connection.
Describe the process by which this layer encodes frames into signals for transmission over local media?
- The OSI physical layer provides the means to transport the bits that make up a data link layer
frame across the network media. - This layer accepts a complete frame from the data link layer and encodes it as a series of signals
that are transmitted to the local media. - The encoded bits that comprise a frame are received by either an end device or an intermediate
device. - The physical layer encodes the frames and creates the electrical, optical, or radio wave signals
that represent the bits in each frame. - These signals are then sent over the media, one at a time.
How does the destination node’s physical layer process signals received from the media?
The destination node physical layer retrieves these individual signals from the media, restores
them to their bit representations, and passes the bits up to the data link layer as a complete
frame.
What entities are responsible for designing the software used to implement the protocols and operations of the upper layers of the OSI model? Additionally, who defines the services and protocols within the TCP/IP suite, and what organization oversees this standardization process?
The protocols and operations of the upper OSI layers are performed using software designed by
software engineers and computer scientists. The services and protocols in the TCP/IP suite are
defined by the Internet Engineering Task Force (IETF).
What are the key standards organizations responsible for defining and governing aspects such as physical layer hardware, media, encoding, and signaling standards?
For instance, the physical layer hardware, media, encoding, and signaling standards are defined
and governed by these standards organizations:
* International Organization for Standardization (ISO)
* Telecommunications Industry Association/Electronic Industries Association (TIA/EIA)
* International Telecommunication Union (ITU)
* American National Standards Institute (ANSI)
* Institute of Electrical and Electronics Engineers (IEEE)
* National telecommunications regulatory authorities including the Federal Communication
Commission (FCC) in the USA and the European Telecommunications Standards
Institute (ETSI)
What are the three main functional areas addressed by the physical layer standards?
The physical layer standards address three functional areas:
* Physical Components
* Encoding
* Signaling
What is Physical Components?
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.
What is the purpose of encoding, and how does it relate to line encoding?
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.
What term is used to describe how bits are represented, and what aspect of signaling do physical layer standards specify?
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.
For example, a long pulse might represent a 1 whereas a short pulse might represent a 0.
What does the term “bandwidth” ?
Bandwidth is the capacity at which a medium can carry data.
How is digital bandwidth defined?
Digital bandwidth measures the amount of data that can flow from one place to another in a given
amount of time.
What factors contribute to determining the practical bandwidth of a network?
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
What are some terms used to assess the quality of bandwidth?
Terms used to measure the quality of bandwidth include:
* Latency
* Throughput
* Goodput
Could you explain the meaning of Latency?
Latency refers to the amount of time, including delays, for data to travel from one given point to
another.
Could you explain the meaning of Throughput ?
Throughput is the measure of the transfer of bits across the media over a given period of time.
. Throughput is usually lower than the bandwidth. There are many
factors that influence throughput:
* The amount of traffic
* The type of traffic
* The latency created by the number of network devices encountered between source and
destination
Could you explain the meaning of Goodput ?
Goodput is the measure of usable data transferred over a given period of time.
Why are copper media commonly used in networks?
Networks use copper media because it is inexpensive, easy to install, and has low resistance to
electrical current.
What are some limitations of copper media in networking, and how do these limitations affect its performance? Additionally, could you describe the method by which data is transmitted on copper cables?
However, copper media is limited by distance and signal interference.
Data is transmitted on copper cables as electrical pulses.
What are the two main sources of interference that affect the timing and voltage values of electrical pulses transmitted on copper media? Could you provide examples of each source and explain how they can distort or corrupt data signals? Additionally, what is crosstalk, and how does it occur in copper media?
The timing and voltage values of the electrical pulses are also susceptible to interference from
two sources:
* Electromagnetic interference (EMI) or radio frequency interference (RFI) - EMI and
RFI signals can distort and corrupt the data signals being carried by copper media.
Potential sources of EMI and RFI include radio waves and electromagnetic devices, such
as fluorescent lights or electric motors.
* Crosstalk - Crosstalk is a disturbance caused by the electric or magnetic fields of a
signal on one wire to the signal in an adjacent wire. In telephone circuits, crosstalk can
result in hearing part of another voice conversation from an adjacent circuit. Specifically,
when an electrical current flows through a wire, it creates a small, circular magnetic field
around the wire, which can be picked up by an adjacent wire.
How do certain types of copper cables mitigate the adverse effects of electromagnetic interference (EMI) and radio frequency interference (RFI)? Could you explain the role of metallic shielding and proper grounding connections in reducing these effects? Additionally, how do specific configurations of copper cables address crosstalk, and what technique is employed to minimize its impact on data transmission?
To counter the negative effects of EMI and RFI, some types of copper cables are wrapped in
metallic shielding and require proper grounding connections.
To counter the negative effects of crosstalk, some types of copper cables have opposing circuit
wire pairs twisted together, which effectively cancels the crosstalk.
What is the most common networking media, and what types of devices are typically interconnected using this media?
The most common networking media is Unshielded Twisted-Pair (UTP) cabling. It is used for interconnecting network hosts with intermediary networking devices such as switches and routers.
How is UTP cable structured, and what protective features does it possess?
UTP cable consists of four pairs of color-coded wires twisted together and encased in a flexible plastic sheath. The twisting of wires helps protect against signal interference from other wires.
