Physical Layer Flashcards
What are the components of a wireless router access point?
a) The wireless antennas
b) Several ethernet switch ports
c) An internet Port
How to connect to a wireless router through a wired connection?
Network Interface Cards: Network interface cards (NICs) connect a device to the network. Ethernet NICs are used for a wired connection
Talk about the physical layer
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.
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 are the three functional areas that the physical layer addresses?
1) Physical Components
2) Encoding
3) Signaling
Define the Physical Components
the electronic hardware devices, media, and other connectors that transmit the signals that represent the bits. Hardware components such as NICs, interfaces, and connectors… are all specified in standards associated with the physical layer.
Define Encoding
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.
Define 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
Define 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.
(Number of bits per second not speed that bits travel)
What are the factors that determine the practical bandwidth of a network?
1) The properties of the physical media
2) The technologies chosen for signaling and detecting network signals
What are the terms used to measure the quality of bandwidth?
1) Latency
2) Throughput
3)Goodput
Define Latency
The amount of time, including delays, for data to travel from one given point to another.
Define Throughput
Throughput is the measure of the transfer of bits across the media over a given period.
Throughput does not match the specified bandwidth in physical layer implementations
What are the factors that influence throughput?
a) The amount of traffic
b) The type of traffic
c) The latency created by the number of network devices encountered between the source and destination
Define Goodput
The measure of usable data transferred over a given period. Goodput is throughput minus traffic overhead for establishing sessions, acknowledgments, encapsulation, and re-transmitted bits. Goodput is always lower than throughput, which is generally lower than bandwidth.
Advantages of copper cabling
1) Inexpensive
2) Easy to install
3) Has low resistance to electrical current
Disadvantage of copper cabling
Limited by distance and signal interference.
Define attenuation
The farther the signal travels, the more it deteriorates
What are the sources that interfere with the electrical pulses?
- Electromagnetic interference (EMI) or radio frequency interference (RFI)
- Crosstalk
Talk about EMI and 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.
Talk about 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
How data transmission can be affected by interference?
1) A pure digital signal is transmitted
2) On the medium, there is an interference signal
3) The digital signal is corrupted by the interference signal
4) The receiving computer receives a changed signal.
How to counter the negative effects of EMI and RFI?
Some types of copper cables are wrapped in metallic shielding and require proper grounding connections.
How to counter the negative effects of cross talk?
Some types of copper cables have opposing circuit wire pairs twisted together, which effectively cancels the cross-talk.
How to limit the susceptibility of copper cables to electronic noise?
1) Selecting the cable type or category most suited to a given networking environment
2) Designing a cable infrastructure to avoid known and potential sources of interference in the building structure
3) Using cabling techniques that include the proper handling and termination of the cables
What are they types of copper cabling?
1) Un-shielded Twisted Pair
2) Shielded Twisted Pair
3) Coaxial cable
Talk about Un-shielded Twisted Pair
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.
What are the characteristics of
unshielded twisted pairs?
1) The outer jacket protects the copper wires from physical damage
2) Twisted pairs protect the signal from interference
3) Color-coded plastic insulation electrically isolates wires from each other and identifies each pair.
Talk about Shielded Twisted Pair (STP)
provides better noise protection than UTP cabling. However, compared to UTP cable, STP cable is significantly more expensive and difficult to install. 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. If the cable is improperly grounded, the shield may act as an antenna and pick up unwanted signals.
What are the key features of shield twisted pair cable
1) Outer jacket
2) Braided or foil shield
3) Foil shields
4) Twisted pairs
Talk about coaxial cable
Gets its name from the fact that two conductors share the same axis
What does a coaxial cable consist of?
- A copper conductor is used to transmit electronic signals.
- A layer of flexible plastic insulation surrounds a copper conductor.
- The insulating material is surrounded by a woven copper braid, or metallic foil, that acts as the second wire in the circuit and as a shield for the inner conductor. This second layer, or shield, also reduces the amount of outside electromagnetic interference.
- The entire cable is covered with a cable jacket to prevent minor physical damage.
What are the types of connectors used with coax cables?
1) The Bayonet Neill–Concelman (BNC)
2) N-type
3) F-type
When is the coaxial cable used?
1) Wireless installations - Coaxial cables attach antennas to wireless devices. The coaxial cable carries radio frequency (RF) energy between the antennas and the radio equipment.
2) 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 coaxed cable
What are the key features of copper cabling?
a) Outer Jacket
b) Braided copper shielding
c) Plastic insulation
d) Copper conductor
What are the other ways that can limit the negative effects of cross talk?
- 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.
What are the standards established by the TIA/EIA-568 for UTP cabling?
- Cable types
- Cable lengths
- Connectors
- Cable termination
- Methods of testing cable
What are the UTP categories?
- Category 3 was originally used for voice communication over voice lines but was later used for data transmission.
- Categories 5 and 5e are 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. It supports up to 10 Gbps.
- Category 7 also supports 10 Gbps.
- Category 8 supports 40 Gbps.
What are the main cable types that are obtained by using specific wiring conventions?
- Ethernet Straight-through - Commonly used to interconnect a host to a switch and a switch to a router. Both ends either T568A or T568B
- Ethernet Crossover - A cable used to interconnect similar devices.
Connects two network hosts
Connects two network intermediary devices (switch to switch or router to router)
Uses one end T568A and another end T568B
(Using them incorrectly can impact connectivity)
Talk about the T568A and T568B standards
T568A: White Green/Green/White Orange/Blue/White Blue/Orange/White Brown/Brown
T568B: White orange/Orange/White Green/Blue/White Blue/Green/White Brown/Brown
Talk about Rollover cable type
Connects a workstation serial port to a router console port, using an adapter
What are the properties of fiber optic cabling?
Optical fiber cable transmits data over longer distances and at higher bandwidths than any other networking media. Unlike copper wires, the fiber-optic cable can transmit signals with less attenuation and is completely immune to EMI and RFI. Optical fiber is commonly used to interconnect network devices.
Optical fiber is a flexible, but extremely thin, transparent strand of very pure glass, not much bigger than human hair. Bits are encoded on the fiber as light impulses. The fiber-optic cable acts as a wave-guide, or “light pipe,” to transmit light between the two ends with minimal loss of signal.
What are the types of fiber optic cabling?
- Single-mode fiber (SMF)
- Multi-mode fiber (MMF)
Define SMF
consists of a very small core and uses expensive laser technology to send a single ray of light, it’s popular in long-distance situations
Define MMF
MMF consists of a larger core and uses LED emitters to send light pulses. Specifically, light from a LED enters the multimode fiber at different angles. They are popular in LANs because they can be powered by low-cost LEDs
What is one of the highlighted differences between MMF and SMF?
Dispersion (the spreading out of a light pulse over time).
Increased dispersion means the increased loss of signal strength. MMF has a greater dispersion than SMF.
What are the usages of Fiber optic cabling?
1) Enterprise Networks - Used for backbone cabling applications and interconnecting infrastructure devices
2) Fiber-to-the-Home (FTTH) - Used to provide always-on broadband services to homes and small businesses
3) Long-Haul Networks - Used by service providers to connect countries and cities
4) Submarine Cable Networks - Used to provide reliable high-speed, high-capacity solutions capable of surviving in harsh undersea environments at up to transoceanic distances.
What is a fiber optical connector and what are its types?
An optical fiber connector terminates the end of an optical fiber.
The main difference among the types are dimensions and methods of coupling
1) Straight Tip (ST) connectors
2) Subscriber Connector (SC) connectors
3) Lucent Connector (LC) Simplex connectors
4) Duplex Multi-mode LC connectors
Talk about Straight Tip (ST) connectors
ST connectors were one of the first connector types used. The connector locks securely with a ‘twist-on/twist-off bayonet-style mechanism.
Talk about Subscriber connector (SC)
Sometimes referred to as ‘square connectors’ or ‘standard connectors’. They are a widely-adopted LAN and WAN connector that uses a push-pull mechanism to ensure positive insertion. This connector type is used with multimode and single-mode fiber.
Talk about Lucent Connector (LC) simple connector
A smaller version of the SC connector. These are sometimes called little or local connectors and are quickly growing in popularity due to their smaller size.
Talk about Duplex Multi-mode LC connector:
Similar to an LC simplex connector but uses a duplex connector.
Talk about Fiber Patch Cords
Fiber patch cords are required for interconnecting infrastructure devices. The use of color distinguishes between single-mode and multimode patch cords. A yellow jacket is for single-mode fiber cables and an orange (or aqua) is for multimode fiber cables.
1) SC-SC Multi-Mode Patch Cord
2) LC-LC Single-Mode Patch Cord
3) ST-LC Multi-Mode Patch Cord
4) SC-ST Single-Mode Patch Cord
What are the properties of wireless media?
1) Carry electromagnetic signals that represent the binary digits of data communications using radio or microwave frequencies.
2) It provides the greatest mobility options of all media, and the number of wireless-enabled devices continues to increase.
3) Wireless is now the primary way users connect to home and enterprise networks.
What are some limitations of the wireless?
- Coverage area - Wireless data communication technologies work well in open environments. However, certain construction materials used in buildings, structures, and the local terrain will limit effective coverage.
- Interference - Wireless is susceptible to interference and can be disrupted by common devices such as household cordless phones, fluorescent lights, and other wireless communications.
- Security - Wireless communication coverage requires no access to a physical strand of media. Therefore, devices and users, not authorized access to the network, can gain access to the transmission. Network security is a major component of wireless network administration.
- Shared medium - WLANs operate in a 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.
What should areas have in order for the physical layer specifications to be applied?
- Data to radio signal encoding
- Frequency and power of transmission
- Signal reception and decoding requirements
- Antenna design and construction
What are the wireless standards?
- Wi-Fi (IEEE 802.11)
*Bluetooth (IEEE 802.15)
*WiMAX (IEEE 802:16)
*Zigbee (IEEE 802.15.4)
Talk about Wi-Fi
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.
Talk about 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.
Talk about 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.
Talk about Zigbee (IEEE 802.15.4)
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 has typically been used for industrial and Internet of Things (IoT) environments such as wireless light switches and medical device data collection.
What are the devices that a WLAN requires?
*Wireless Access Point (AP)
*Wireless NIC adapters
Talk about Wireless Access Points (AP)
These concentrate the wireless signals from users and connect to the existing copper-based network infrastructure, such as Ethernet
Talk about wireless (NIC) adapters
These provide wireless communication capability to network hosts.
What are the organizations involved in establishing and maintaining physical layer standards?
1) International Organization for Standardization (ISO)
2) Telecommunications Industry Association/Electronic Industries Association (TIA/EIA)
3) International Telecommunication Union (ITU)
4) American National Standards Institute (ANSI)
5) Institute of Electrical and Electronics Engineers (IEEE)
6) Federal Communication Commission (FCC) in the USA
7) European Telecommunications Standards Institute (ETSI)
Where are the TCP/IP standards implemented?
in software in all layers except the physical
its governed by IETF
Where are the physical layer standards implemented?
in hardware in the physical layer
governed by many organizations including
ISO
IEEE
ANSI
