Physical LAYER

Question 1

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?

Answer 1

This type of setup is a wired network. Data is transmitted through a physical cable.

Question 2

What other connectivity options do many businesses provide, besides wired connections, enabling usage of laptops, tablets, and smartphones via wireless networks ?

Answer 2

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.

Question 3

How do network interface cards (NICs) facilitate device connectivity to a network?

Answer 3

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.

Question 4

Describe the process by which this layer encodes frames into signals for transmission over local media?

Answer 4

• 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.

Question 5

How does the destination node’s physical layer process signals received from the media?

Answer 5

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.

Question 6

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?

Answer 6

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).

Question 7

What are the key standards organizations responsible for defining and governing aspects such as physical layer hardware, media, encoding, and signaling standards?

Answer 7

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)

Question 8

What are the three main functional areas addressed by the physical layer standards?

Answer 8

The physical layer standards address three functional areas:
* Physical Components
* Encoding
* Signaling

Question 9

What is Physical Components?

Answer 9

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 10

What is the purpose of encoding, and how does it relate to line encoding?

Answer 10

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 11

What term is used to describe how bits are represented, and what aspect of signaling do physical layer standards specify?

Answer 11

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.

Question 12

What does the term “bandwidth” ?

Answer 12

Bandwidth is the capacity at which a medium can carry data.

Question 13

How is digital bandwidth defined?

Answer 13

Digital bandwidth measures the amount of data that can flow from one place to another in a given
amount of time.

Question 14

What factors contribute to determining the practical bandwidth of a network?

Answer 14

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

Question 15

What are some terms used to assess the quality of bandwidth?

Answer 15

Terms used to measure the quality of bandwidth include:
* Latency
* Throughput
* Goodput

Question 16

Could you explain the meaning of Latency?

Answer 16

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

Question 17

Could you explain the meaning of Throughput ?

Answer 17

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

Question 18

Could you explain the meaning of Goodput ?

Answer 18

Goodput is the measure of usable data transferred over a given period of time.

Question 19

Why are copper media commonly used in networks?

Answer 19

Networks use copper media because it is inexpensive, easy to install, and has low resistance to
electrical current.

Question 20

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?

Answer 20

However, copper media is limited by distance and signal interference.
Data is transmitted on copper cables as electrical pulses.

Question 21

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?

Answer 21

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.

Question 22

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?

Answer 22

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.

Question 23

What is the most common networking media, and what types of devices are typically interconnected using this media?

Answer 23

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.

Question 24

How is UTP cable structured, and what protective features does it possess?

Answer 24

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.

Question 25

How does Shielded Twisted-Pair (STP) cable differ from UTP cable in terms of noise protection and installation complexity?

Answer 25

STP provides better noise protection than UTP but is significantly more expensive and difficult to install.

Question 26

What techniques does STP cable employ to counter EMI, RFI, and crosstalk?

Answer 26

Like UTP cable, STP uses an RJ-45 connector.
STP cables combine the techniques of shielding to counter EMI and RFI, and wire twisting to
counter crosstalk.
To gain the full benefit of the shielding, STP cables are terminated with special shielded STP
data connectors.

Question 27

What potential issue may arise if the shield of an STP cable is improperly grounded?

Answer 27

If the cable is improperly grounded, the shield may act as an antenna and pick up unwanted
signals.
The STP cable shown uses four pairs of wires, each wrapped in a foil shield, which are then
wrapped in an overall metallic braid or foil.

Question 28

Describe the construction of coaxial cable and its key components.

Answer 28

Coaxial cable consists of a copper conductor for transmitting electronic signals, surrounded by flexible plastic insulation, a woven copper braid or metallic foil acting as a shield, and a cable jacket for protection.

Question 29

What are the main types of connectors used with coaxial cable?

Answer 29

The main types of connectors used with coaxial cable are the Bayonet Neill–Concelman (BNC), N type, and F type connectors.

Question 30

In what situations is coaxial cable still commonly used despite UTP cable’s prevalence in Ethernet installations?

Answer 30

Wireless installations - Coaxial cables attach antennas to wireless devices. The coaxial
cable carries radio frequency (RF) energy between the antennas and the radio
equipment.
* Cable internet installations - Cable service providers provide internet connectivity to
their customers by replacing portions of the coaxial cable and supporting amplification
elements with fiber-optic cable. However, the wiring inside the customer’s premises is still
coax cable.

Question 31

How UTP can limit the negative effect of
crosstalk?

Answer 31

• Cancellation - Designers now pair wires in a circuit. When two wires in an electrical
  circuit are placed close together, their magnetic fields are the exact opposite of each
  other. Therefore, the two magnetic fields cancel each other and also cancel out any
  outside EMI and RFI signals.
• Varying the number of twists per wire pair - To further enhance the cancellation effect
  of paired circuit wires, designers vary the number of twists of each wire pair in a cable.
  UTP cable must follow precise specifications governing how many twists or braids are
  permitted per meter (3.28 feet) of cable.

Question 32

What standards govern UTP cabling, and what are some of the elements defined in these standards?

Answer 32

UTP cabling conforms to the standards established jointly by the TIA/EIA.
Specifically, TIA/EIA-568 stipulates the commercial cabling standards for LAN installations and is
the standard most commonly used in LAN cabling environments.
Some of the elements defined are as follows:
* Cable types
* Cable lengths
* Connectors
* Cable termination
* Methods of testing cable

Question 33

How are the electrical characteristics of copper cabling rated, and what categories are used for classification?

Answer 33

The electrical characteristics of copper cabling are rated by the IEEE, which categorizes cables based on their performance. Categories include Category 5, Enhanced Category 5, Category 6, and Category 6a, with each category indicating the cable’s ability to carry higher bandwidth rates.

Question 34

What are the three categories of UTP ?

Answer 34

Category 3 was originally used for voice communication over voice lines, but later used
for data transmission.
* Category 5 and 5e is used for data transmission. Category 5 supports 100Mbps and
Category 5e supports 1000 Mbps
* Category 6 has an added separator between each wire pair to support higher speeds.
Category 6 supports up to 10 Gbps.
* Category 7 also supports 10 Gbps.
* Category 8 supports 40 Gbps.

Question 35

How are UTP cables terminated, and what standard governs the wire color codes and pin assignments for Ethernet cables?

Answer 35

UTP cables are usually terminated with an RJ-45 connector, and the wire color codes and pin assignments (pinouts) for Ethernet cables are described by the TIA/EIA-568 standard.

Question 36

Why might different wiring conventions be required for UTP cables, and what are the main cable types obtained by using specific wiring conventions?

Answer 36

• Ethernet Straight-through - The most common type of networking cable. It is commonly
  used to interconnect a host to a switch and a switch to a router.
• Ethernet Crossover - A cable used to interconnect similar devices. For example, to
  connect a switch to a switch, a host to a host, or a router to a router. However, crossover
  cables are now considered legacy as NICs use medium-dependent interface crossover
  (auto-MDIX) to automatically detect the cable type and make the internal connection.

Question 37

Cable Types and Standards

Answer 37

Ethernet Straight-through
Both ends T568A or both ends
T568B
Connects a network host to a network device such as a switch or hub
Ethernet Crossover
One end T568A, other end T568B
Connects two network hosts Connects two network intermediary
devices (switch to switch or router to router)
Rollover
Cisco proprietary
Connects a workstation serial port to a router console port, using an
adapter

Question 38

What distinguishes fiber-optic cabling from copper cabling in terms of transmission capabilities and susceptibility to interference?

Answer 38

Fiber-optic cabling transmits data over longer distances and at higher bandwidths compared to copper cabling. It experiences less attenuation and is completely immune to EMI and RFI.

Question 39

What are the two main types of fiber-optic cables, and what are their primary characteristics?

Answer 39

The two main types of fiber-optic cables are Single-Mode Fiber (SMF) and Multimode Fiber (MMF). SMF has a small core and uses laser technology for long-distance applications, while MMF has a larger core and utilizes LED emitters for shorter-distance LANs.

Question 40

what industries is fiber-optic cabling being increasingly utilized, and what are some specific applications within these industries?

Answer 40

Fiber-optic cabling is now being used in four types of industry:
* Enterprise Networks - Used for backbone cabling applications and interconnecting
infrastructure devices
* Fiber-to-the-Home (FTTH) - Used to provide always-on broadband services to homes
and small businesses
* Long-Haul Networks - Used by service providers to connect countries and cities
* Submarine Cable Networks - Used to provide reliable high-speed, high-capacity
solutions capable of surviving in harsh undersea environments at up to transoceanic
distances. Search the internet for “submarine cables telegeography map” to view various
maps online.

Question 41

What are some common types of optical-fiber connectors, and what are their distinguishing features?

Answer 41

Common types of optical-fiber connectors include ST connectors, SC connectors, and LC connectors. They differ in dimensions and coupling methods, such as bayonet-style, push-pull, and simplex/duplex configurations.

Question 42

How do wireless media transmit data communications, and what frequencies are commonly used?

Answer 42

Wireless media transmit data communications using electromagnetic signals at radio or microwave frequencies.

Question 43

What are some limitations of wireless communication, and how do they impact its effectiveness?

Answer 43

Some limitations of wireless communication include coverage area restrictions, susceptibility to interference from various devices, security vulnerabilities, and shared medium issues that can reduce bandwidth for multiple users.

Question 44

What aspects of wireless data communications do IEEE and telecommunications industry standards cover?

Answer 44

IEEE and telecommunications industry standards cover both the data link and physical layers of wireless data communications, including specifications for data to radio signal encoding, transmission frequency and power, signal reception and decoding, and antenna design.

Question 45

What are the main wireless standards, and what are their respective applications?

Answer 45

The main wireless standards include Wi-Fi (IEEE 802.11) for wireless LAN (WLAN) technology, Bluetooth (IEEE 802.15) for wireless personal area networks (WPANs), WiMAX (IEEE 802.16) for wireless broadband access, and Zigbee (IEEE 802.15.4) for low-data rate, low-power communications in IoT environments.

Question 46

What is the contention-based protocol used in Wi-Fi, and what does it involve?

Answer 46

Wi-Fi uses a contention-based protocol known as Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA). Before transmitting, the wireless NIC must listen for other transmissions on the channel and wait for it to be clear to avoid collisions.

Question 47

What network devices are typically required for a wireless LAN (WLAN) implementation?

Answer 47

A WLAN typically requires Wireless Access Points (APs) to concentrate wireless signals and connect to the existing network infrastructure, as well as Wireless NIC adapters to provide wireless communication capability to network hosts.