Physical Layer V What does the physical layer provide?

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1 SEMESTER 1 Chapter 8 Physical Layer V Points What does the physical layer provide? What are the four elements of delivering frames across the media? What are the three basic forms of media? What are the three concerns when the physical layer encodes bits? What does the physical layer consist of? What are the organizations that are responsible for physical layer standards? The technologies defined by these organizations include what four areas of the Physical layer standards? What are the three fundamental functions of the Physical layer? What are the two values that the physical layer encodes? How are the bits of the frame transmitted by the physical layer? provides the means to transport across the network media the bits that make up a Data Link layer frame The physical media and associated connectors A representation of bits on the media Encoding of data and control information Transmitter and receiver circuitry on the network devices Copper cable Fiber Wireless the Physical layer encodes the bits into the signals for a particular medium, it must also distinguish where one frame ends and the next frame begins hardware, developed by engineers, in the form of electronic circuitry, media, and connectors The International Organization for Standardization (ISO) The Institute of Electrical and Electronics Engineers (IEEE) The American National Standards Institute (ANSI) The International Telecommunication Union (ITU) The Electronics Industry Alliance/Telecommunications Industry Association (EIA/TIA) National telecommunications authorities such as the Federal Communication Commission (FCC) in the USA. Physical and electrical properties of the media Mechanical properties (materials, dimensions, pinouts) of the connectors Bit representation by the signals (encoding) Definition of control information signals The physical components Data encoding Signaling 1 and 0 One bit at a time

2 What is a bit time? specific amount of time each signal has to occupy the media How are the signaling and Many signaling methods use predictable receiving ends clocks transitions in the signal to provide synchronized in the LAN? synchronization between the clocks of the What characteristics can be changed to represent bits on the medium? What will happen if there is no agreement between nodes on the signaling method? What are the three characteristics of NRZ signaling? What type of transmission is NRZ suited for? What are represented by in Manchester encoding? How does the transition help maintain clock synchronization? Which medium uses Manchester encoding? What method is used to signal start and end of a frame in higher speed technologies? transmitting and the receiving devices Amplitude Frequency Phase The transmission will fail Discrete impulses Only two states Voltage jumps between levels for slow speed data links voltage transitions one voltage transition must occur in the middle of each bit time 10BaseT Ethernet Specific pattern of grouped bits What is a code group? consecutive sequence of code bits that are interpreted and mapped as data bit patterns What are the advantages of the error detection capabilities and timing transmitting symbols? synchronization between transmitting and What are the four advantages of using code groups? What are the three types of code groups? receiving devices are enhanced Reducing bit level error Limiting the effective energy transmitted into the media Helping to distinguish data bits from control bits Better media error detection Data symbols - Symbols that represent the data of the frame as it is passed down to the Physical layer. Control symbols - Special codes injected by the Physical layer used to control transmission. These include end-of-frame and idle media symbols. Invalid symbols - Symbols that have patterns not allowed on the media. The receipt of an invalid symbol indicates a frame error.

3 How does 4B/5B represent a nibble? What are the three measures for Data Transfer? What is the difference between throughput and goodput? Which measure of data transfer is most important to the end user? What are the standards for copper media defined for? What type of connector is commonly used in copper cabling? What is done to the pairs of wires to minimize signal degradation due to electronic noise? What are the other methods listed to limit the susceptibility of copper cables to noise? as five-bit values known as symbols Bandwidth Throughput Goodput Throughput is the measure of bits over a given time and goodput is the measure of usable data transferred over a given period of time Goodput Type of copper cabling used Bandwidth of the communication Type of connectors used Pinout and color codes of connections to the media Maximum distance of the media RJ-45 Shielding and twisting of the wires Selecting the cable type or category most suited to protect the data signals in 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 What is crosstalk? the interference caused by the magnetic field What is used to limit crosstalk? What changes in the twist from one pair of wires to the next pair of wires to improve the limitation of crosstalk? What are some of the elements defined by the TIA/EIA 568A standard? Why is it wasteful to install less expensive but lower rated cabling? What is UTP cable terminated with? around the adjacent pairs of wires in the cable Twisting pairs of wires The number of twists per meter changes Cable types Cable lengths Connectors Cable termination Methods of testing cable If the decision is later made to adopt a faster LAN technology, total replacement of the installed cable infrastructure may be required. RJ-45 connectors

4 What are the three types of Ethernet cables? What is a straight-through used for? What is a crossover used for? What is a rollover used for? What happens if you use the wrong type of cable when connecting devices? What are the other two type of copper cabling? What has replaced the use of coaxial cable in today s Ethernet installations? What type types of materials can be used for fiber optic cabling? What is the encoding method for fiber optic? What are the issues with implementing fiber optic cabling? What areas usually implement fiber optic cabling? What are the major advantages of using fiber optic between buildings? How many cables are needed for each fiber optic connection? Why? What are the two types of fiber optic cables? How do wireless media carry electromagnetic signals? What is the major concern for wireless signals? What are the 4 standards for wireless networks? Ethernet Straight-through Ethernet Crossover Rollover Host to network device such as a hub or switch Connecting two hosts Connecting to network intermediary devices Connecting a computers serial port to the console port of a router (with an adapter) Communication will not occur 1. Coaxial 2. Shielded Twisted-Pair (STP) UTP Glass or plastic Light pulses More expensive (usually) than copper media over the same distance (but for a higher capacity) Different skills and equipment required to terminate and splice the cable infrastructure More careful handling than copper media Backbone and between buildings optical fiber does not conduct electricity and has low signal loss 2, they can only operate in one direction Single mode and multimode radio and microwave frequencies that represent the binary digits of data communications Security IEEE IEEE IEEE Global System for Mobile Communications (GSM)

5 What are the two network devices necessary to implement a wireless network? What are the WLAN Ethernet standards? What are some of the CAT5 termination that may performed onsite? What are the differences in the termination of the two cables pictured? What could happen if wires are not terminated correctly? What are the three main splicing errors when using fiber optic cabling? Wireless Access Point (AP) - Concentrates the wireless signals from users and connects, usually through a copper cable, to the existing copper-based network infrastructure such as Ethernet. Wireless NIC adapters - Provides wireless communication capability to each network host. IEEE a, IEEE b, IEEE g, IEEE n crimped connections to terminate Cat5 media with RJ-45 plugs to make patch cables, and the use of punched down connections on 110 patch panels and RJ-45 jacks Insulation cut back to far and wires untwisted too much damaging voltage levels may be applied between interconnected devices Misalignment - the fiber-optic media are not precisely aligned to one another when joined. End gap - the media do not completely touch at the splice or connection. End finish - the media ends are not well polished or dirt is present at the termination. * The 3 fundamental functions of the Physical layer are The physical components the electronic hardware devices, media and connectors that transmit and carry the signals to represent the bits. Data encoding Encoding is a method of converting a stream of data bits into a predefined code. Signaling The Physical layer must generate the electrical, optical, or wireless signals that represent the "1" and "0" on the media. * What is Optical Time Domain Reflectometer (OTDR)? What is TDR? An optical time-domain reflectometer (OTDR) is an optoelectronic instrument used to characterize an optical fiber. o An OTDR may be used for estimating the fiber's length and overall attenuation, including splice and mated-connector losses. It may also be used to locate faults, such as breaks, and to measure optical return loss. TDR is an electronic instrument used to characterize and locate faults in metallic cables * Fiber media vs. metallic cable: Fibers are more expensive (usually) than copper media over the same distance (but for a higher capacity) Optical fiber cables consist of a PVC jacket and a series of strengthening materials that surround the optical fiber and its cladding.

6 fiber can transmit optical pulses for long distances The fibers media is immune to electromagnetic interference and will not conduct unwanted electrical currents. Optical fibers are thin and have relatively low signal loss, they can be operated at much greater lengths than copper media. In most enterprise environments, optical fiber is primarily used as backbone cabling for high-traffic connections and for the interconnection of buildings in multi-building campuses. * The following are main cable types: Ethernet Straight-through Ethernet Crossover Rollover * Wireless is not restricted to conductors or pathways, as are copper and fiber media. Wireless media carry electromagnetic signals at radio and microwave frequencies that represent the binary digits of data communications. * Know the usage of the following types of connectors: - RJ-45: the RJ-45 connector is used widely in LANs - RJ11: often used for terminating telephone wires - BNC: used for coaxial cable - Type F: used for cable modem * Fiber optic cables can be broadly classified into two types: Single-mode optical fiber Carries a single ray of light, usually emitted from a laser. This type of fiber can transmit optical pulses for long distances. Multimode fiber Typically uses LED emitters that do not create a single light wave. LED light source used with it, are cheaper than single-mode fiber and its laser-based emitter technology. * Data transfer can be measured in three ways: Bandwidth Throughput Goodput * This cancellation effect also helps avoid interference from internal sources called crosstalk. Crosstalk is the interference caused by the magnetic field around the adjacent pairs of wires in the cable.

7 * It is essential that all copper media terminations be of high quality to ensure optimum performance with current and future network technologies. Each time copper cabling is terminated, there is the possibility of signal loss and the introduction of noise to the communication circuit. * Signle mode vs. multi-mode. Full Duplex or Half Duplex Unlike an RJ-45 port, a single fiber port is actually divided into two separate unidirectional ports. One port sends data and the other port receives data. Some fiber add-on modules are capable of sending and receiving data at the same time. This is known as full duplex (FDX) operation. Other add-on modules are only capable of either sending or receiving data and cannot do both at the same time. This is known as half duplex (HDX). Obviously, Fast Duplex or FDX is the faster of the two. * The benefits of wireless data communications technologies The savings on costly premises wiring The convenience of host mobility. * Unshielded twisted-pair (UTP) cabling, as it is used in Ethernet LANs, consists of 4 pairs of color-coded wires that have been twisted together and then encased in a flexible plastic sheath. The twisting has the effect of canceling unwanted signals. Cable types with shielding or twisting of the pairs of wires are designed to minimize signal degradation due to electronic noise. The susceptibility of copper cables to electronic noise can also be limited by: