Module 4
Which of these is a measure of the transfer of bits across the media? throughput goodput bandwidth
thoughput
Which of the following is the most common network media?
Answer: UTP
Which media uses patterns of microwaves to represent bits? copper wireless fiber-optic
wireless
What is the purpose of the OSI physical layer?
Answer: transmitting bits across the local media
Wireless installations
Coaxial cables attach antennas to wireless devices. The coaxial cable carries radio frequency (RF) energy between the antennas and the radio equipment.
A wireless LAN is being deployed inside the new one room office that is occupied by the park ranger. The office is located at the highest part of the national park. After network testing is complete, the technicians report that the wireless LAN signal is occasionally affected by some type of interference. What is a possible cause of the signal distortion?
Answer: the microwave oven
A network administrator is designing a new network infrastructure that includes both wired and wireless connectivity. Under which situation would a wireless connection be recommended? -the end-user device needs mobility when connecting to the network - the end-user device requires a dedicated connection because of performance requirements - the end-user device only has an Ethernet NIC - the end-user device area has a high concentration of RFI
Answer:
Why are two strands of fiber used for a single fiber optic connection? -The two strands allow the data to travel for longer distances without degrading -they allow for full-duplex connectivity -they increase the speed at which the data can travel -they prevent crosstalk from causing interfaces on the connection
Answer: -they allow for full-duplex connectivity
Which standards organization oversees development of wireless LAN standards? IEEE IANA TIA ISO
Answer: IEEE
Which of the following counters EMI and RFI by using shielding techniques and special connectors?
Answer: STP
What is a characteristic of UTP cabling? woven copper braid or metallic foil immunity to electrical hazards cancellation cladding
Answer: cancellation
Which of the following attaches antennas to wireless devices? It can also be bundled with fiber-optic cabling for two-way data transmission. UTP STP coaxial
Answer: coaxial
Which of the following terminates with BNC, N type and F type connectors?
Answer: coaxial
The physical layer of the receiving device passes bits up to which higher-level layer? application data link network presentation
Answer: data link
What PDU is received by the physical layer for encoding and transmission? frame segment packet
Answer: frame
Which statement correctly describes frame encoding?
Answer: it converts bits into a predefined code in order to provide a predictable pattern to help distinguish data bits form control bits
Which of the following fiber-optic cable types can help data travel approximately 500 meters? multimode single-mode
Answer: multimode
Which of the following fiber-optic cable types is used within a campus network? multimode single-mode
Answer: multimode
Which of the following fiber-optic cable types use light-emitting diodes (LEDs) as a data light source transmitter? multimode single-mode
Answer: multimode
A network administrator is troubleshooting connectivity issues on a server. Using a tester, the administrator notices that the signals generated by the server NIC are distorted and not usable. In which layer of the OSI model is the error categorized? data link layer network layer presentation layer physical layer
Answer: physical layer
What type of cable is used to connect a workstation serial port to a Cisco router console port? straight-through crossover rollover coaxial
Answer: rollover
Which of the following fiber-optic cable types can travel approximately 100 km? multimode single-mode
Answer: single-mode
Which of the following fiber-optic cable types is used to connect long-distance telephony and cable TV applications? multimode single-mode
Answer: single-mode
Which of the following fiber-optic cable types use lasers in a single stream as a data light source transmitter? multimode single-mode
Answer: single-mode
Which type of UTP cable is used to connect a PC to a switch port? console rollover crossover straight-through
Answer: straight-over
What is the definition of bandwidth?
Answer: the amount of data that can flow from one place to another in a given amount of time
Which characteristic describes crosstalk?
Answer: the distortion of the transmitted messages from signals carried in adjacent wires
What is indicated by the term throughput?
Answer: the measure of the bits transferred across the media over a given period of time
Which procedure is used to reduce the effect of crosstalk in copper cables? -requiring proper grounding connections -wrapping the bundle of wires with metallic shielding -avoiding opposing circuit wire pairs together -designing a cable infrastructure to avoid crosstalk interference -twisting opposing circuit wire pairs together
Answer: twisting opposing circuit wire pairs together
Optical fiber is a flexible, but extremely thin, transparent strand of very pure glass, not much bigger than a human hair. Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a waveguide, or "light pipe," to transmit light between the two ends with minimal loss of signal.
As an analogy, consider an empty paper towel roll with the inside coated like a mirror. It is a thousand meters in length, and a small laser pointer is used to send Morse code signals at the speed of light. Essentially that is how a fiber-optic cable operates, except that it is smaller in diameter and uses sophisticated light technologies.
Bandwidth
Bits per second = bps = 1 bps = fundamental unit of bandwidth Kilobits per second = kbps = 1kbps = 1 Kbps = 1,000 bps = 103 bps Megabits per second = Mbps = 1 Mbps = 1,000,000 bps = 106 bps Gigabits per second = Gbps = 1 Gbps = 1,000,000,000 bps = 109 bps Terabits per second = Tbps = 1 Tbps = 1,000,000,000,000 bps = 1012 bps
Which of the following wireless standards is used for Personal Area Networks (PANs) and allows devices to communicate over distances of 1 to 100 meters? Zigbee WiMax Wi-Fi Bluetooth
Bluetooth
Ethernet Straight-through
Both ends T568A or both ends T568B Connects a network host to a network device such as a switch or hub
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.
specifically, TIA/EIA-568 stipulates the commercial cabling standards for LAN installations and is the standard most commonly used in LAN cabling environments
Cable types Cable lengths Connectors Cable termination Methods of testing cable
Rollover
Cisco proprietary Connects a workstation serial port to a router console port, using an adapter
WiMAX (IEEE 802:16)
Commonly known as Worldwide Interoperability for Microware Access (WiMAX), this wireless standard uses a point-to-multipoint topology to provide wireless broadband access.
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.
Fiber-optic
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.
True or false? The physical layer is only concerned with wired network connections.
False
True or false? When a frame is encoded by the physical layer, all bits are sent over the media at the same time.
False
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. This is similar to how Morse code encodes a message using a series of dots and dashes.
For example, Manchester encoding represents a 0 bit by a high to low voltage transition, and a 1 bit is represented as a low to high voltage transition.
Goodput
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. Goodput is always lower than throughput, which is generally lower than the bandwidth.
Unshielded twisted-pair (UTP) cabling is the most common networking media. UTP cabling, terminated with RJ-45 connectors, is used for interconnecting network hosts with intermediary networking devices, such as switches and routers.
In LANs, UTP cable consists of four pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath that protects from minor physical damage. The twisting of wires helps protect against signal interference from other wires.
Latency
Latency refers to the amount of time, including delays, for data to travel from one given point to another.
Ethernet Crossover
One end T568A, other end T568B Connects two network hosts Connects two network intermediary devices (switch to switch or router to router)
The physical layer standards address three functional areas
Physical Components Encoding Signaling
Single-Mode Fiber
SMF consists of a very small core and uses expensive laser technology to send a single ray of light, as shown in the figure. SMF is popular in long-distance situations spanning hundreds of kilometers, such as those required in long-haul telephony and cable TV applications.
Signaling
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. For example, a long pulse might represent a 1 whereas a short pulse might represent a 0.
Fiber-optic cable
The signals are patterns of light.
Wireless
The signals are patterns of microwave transmissions.
Wireless Access Point (AP)
These concentrate the wireless signals from users and connect to the existing copper-based network infrastructure, such as Ethernet. Home and small business wireless routers integrate the functions of a router, switch, and access point into one device, as shown in the figure.
Wireless NIC adapters
These provide wireless communication capability to network hosts.
Bluetooth (IEEE 802.15)
This is a wireless personal area network (WPAN) standard, commonly known as "Bluetooth." It uses a device pairing process to communicate over distances from 1 to 100 meters.
Throughput
Throughput is the measure of the transfer of bits across the media over a given period of time.
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. Notice in the figure that the orange/orange white pair is twisted less than the blue/blue white pair. Each colored pair is twisted a different number of times.
Shared medium
WLANs operate in half-duplex, which means only one device can send or receive at a time. The wireless medium is shared amongst all wireless users. Many users accessing the WLAN simultaneously results in reduced bandwidth for each user.
Wi-Fi (IEEE 802.11)
Wireless LAN (WLAN) technology, commonly referred to as Wi-Fi. WLAN uses a contention-based protocol known as carrier sense multiple access/collision avoidance (CSMA/CA). The wireless NIC must first listen before transmitting to determine if the radio channel is clear. If another wireless device is transmitting, then the NIC must wait until the channel is clear. Wi-Fi is a trademark of the Wi-Fi Alliance. Wi-Fi is used with certified WLAN devices based on the IEEE 802.11 standards.
Security
Wireless communication coverage requires no access to a physical strand of media. Therefore, devices and users, not authorized for access to the network, can gain access to the transmission. Network security is a major component of wireless network administration.
Coverage area
Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings and structures, and the local terrain, will limit the effective coverage.
Interference
Wireless is susceptible to interference and can be disrupted by such common devices as household cordless
Which of the following wireless standards is best suited for industrial and IoT environments? Zigbee WiMax Wi-Fi Bluetooth
Zigbee
Zigbee (IEEE 802.15.4)
Zigbee is a specification used for low-data rate, low-power communications. It is intended for applications that require short-range, low data-rates and long battery life. Zigbee is typically used for industrial and Internet of Things (IoT) environments such as wireless light switches and medical device data collection.
Which of these is the name for the capacity of a medium to carry data? throughput goodput bandwidth
bandwidth
Which media uses electrical pulses to represent bits? copper wireless fiber-optic
copper
True or false. Wireless LANs operate in full-duplex allowing all devices to send or receive data at the same time so the number of users does not impact performance.
false
True or false. Wireless is not well suited for enterprise networks.
false
Which media uses patterns of light to represent bits? copper wireless fiber-optic
fiber-optic
Copper cable
he signals are patterns of electrical pulses.