CIS 26A Physical Layer
fiber-optic cable
A cable that transmits data at close to the speed of light along very pure glass strand. immune to EMI and RFI
Wired Network
A network in which computers and other devices are connected to the network via physical cables.
How does the IEEE rate UTP cabling?
By performance Cat 5 Cat 6
There are of regional cabling standards such as:
CSA (Canadian Standards Association), CENELEC (European Committee for Electrotechnical Standardization), and JSA/JIS (Japanese Standards Association), which develop local specifications.
Elements defined by TIA/EIA 568
Cable types Cable lengths Connectors Cable termination Methods of testing cable
Ways UTP limits the negative effect of crosstalk?
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. 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.
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.
The physical layer standards address three functional areas:
Physical Components Encoding Signaling
What are UTP cables usually terminated with?
RJ-45 connector
Dispersion
Refers to the spreading out of light over time leading to signal loss MMF is worse than SMF
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. Manchester encoding is used in older Ethernet standards such as 10BASE-T. Ethernet 100BASE-TX uses 4B/5B encoding and 1000BASE-T uses 8B/10B encoding. used for 10Mbps ethernet
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.
Types of fiber media
Single-mode fiber (SMF) Multimode fiber (MMF)
Types of coax connectors
The Bayonet Neill-Concelman (BNC), N type, and F type.
Digital bandwidth measures
The amount of data that can flow from one place to another in a given amount of time.
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. The various ports and interfaces on a Cisco 1941 router are also examples of physical components with specific connectors and pinouts resulting from standards.
How does the physical layer provide the means to transport the bits that make up a data link layer frame across the network media?
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.
Wireless Network
a network that uses wireless instead of wired technology Devices on a wireless network must be connected to a wireless access point (AP) or wireless router like the one shown in the figure.
Categories of UTP cabling
-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.
the physical layer hardware, media, encoding, and signaling standards are defined and govern
-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)
The susceptibility of copper cables to electronic noise can also be limited using these recommendations:
-Selecting the cable type or category most suited to a given networking environment -Designing a cable infrastructure to avoid known and potential sources of interference in the building structure -Using cabling techniques that include the proper handling and termination of the cables
Factors affecting throughput:
-The amount of traffic -The type of traffic -The latency created by the number of network devices encountered between source and destination Throughput is usually lower than the bandwidth.
factor that determine the practical bandwidth of a network.
-The properties of the physical media -The technologies chosen for signaling and detecting network signals
coaxial cable
-gets its name from the fact that there are two conductors that share the same axis. Consists of: -A copper conductor is used to transmit the electronic signals. -A layer of flexible plastic insulation surrounds a copper conductor. -The insulating material is surrounded in 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 different colors used to distinguish fiber patch cords?
A yellow jacket is for single-mode fiber cables and orange (or aqua) for multimode fiber cables.
Limitations of Wireless Media
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 phones, some types of fluorescent lights, microwave ovens, and other wireless communications. 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. 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.
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.
Physical layer standards include the following:
Data to radio signal encoding Frequency and power of transmission Signal reception and decoding requirements Antenna design and construction
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.
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) Crosstalk
types of industry using fiber-optic cabling
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.
How do devices connect to a network?
Ethernet NIC are used for wired connections WLAN NIC are used for wireless NIC- Network interface card
UTP main cable types
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. Another type of cable is a rollover cable, which is Cisco proprietary. It is used to connect a workstation to a router or switch console port.
signaling method
How 1's and 0's are represent bits on media - varies depending on encoding scheme This is similar to the signaling method used in Morse code, which may use a series of on-off tones, lights, or clicks to send text over telephone wires or between ships at sea.
The electrical characteristics of copper cabling are defined by?
Institute of Electrical and Electronics Engineers (IEEE)
The physical layer is what part of the OSI and TCP/IP models?
It is the bottom of the stack for the OSI model It is part of the Network Access Layer of the TCP/IP model
Terms used to measure the quality of bandwidth include:
Latency Throughput Goodput
Latency
Latency refers to the amount of time, including delays, for data to travel from one given point to another.
Multimode Fiber
MMF consists of a larger core and uses LED emitters to send light pulses. Specifically, light from an LED enters the multimode fiber at different angles, as shown in the figure. MMFs are popular in LANs because they can be powered by low-cost LEDs. It provides bandwidth up to 10 Gbps over link lengths of up to 550 meters.
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.
Most common networking media?
UTP
Media used for interconnecting network hosts with intermediary networking devices, such as switches and routers?
UTP cabling terminated with RJ-45 connectors.
Three main types of copper media in networking
Unshielded Twisted-Pair (UTP) Cable Shielded Twisted-Pair (STP) Cable Coaxial Cable
How do fiber cables send data back and forth on the same cable?
Using different wavelengths of light.
The Wire less standards
Wi-Fi (IEEE 802.11) Bluetooth (IEEE 802.15 WiMAX (IEEE 802:16) Zigbee (IEEE 802.15.4)
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.
Situations coax cable design is used:
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.
How does wireless media work?
Wireless media carry electromagnetic signals that represent the binary digits of data communications using radio or microwave frequencies.
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.
What should be the first troubleshooting action if connectivity is not achieved?
check the correct cable is being used.
The IEEE and telecommunications industry standards for wireless data communications cover both the?
data link and physical layers.
What does UTP consist of when used as a network medium?
four pairs of color-coded copper wires that have been twisted together and then encased in a flexible plastic sheath.
Why do networks use copper media?
inexpensive, easy to install, low resistance to electrical current negative is it is limited by distance and signal interference.
Measurement of bandwidth
kilobits per second (kbps), megabits per second (Mbps), or gigabits per second (Gbps)
Encoding or line encoding
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. This is similar to how Morse code encodes a message using a series of dots and dashes.
What does the twisting of the wires in a UTP cable help solve?
protects against signal interference from other wires.
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. improper grounding of the shield may have it act as an antenna.
counter the negative effects of EMI and RFI
some types of copper cables are wrapped in metallic shielding and require proper grounding connections.
counter the negative effects of crosstalk
some types of copper cables have opposing circuit wire pairs twisted together, which effectively cancels the crosstalk.
TIA/EIA-568
stipulates the commercial cabling standards for LAN installations and is the standard most commonly used in LAN cabling environments.
Goodput
the amount of usable data that crosses a given point in a network over a certain period of time throughput minus traffic overhead for establishing sessions, acknowledgments, encapsulation, and retransmitted bits.
Bandwidth
the capacity at which a medium can carry data.
signal attenuation
the longer the signal travels, the more it deteriorates
