OSI Physical Layer
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| 4B/5B | An encoding scheme (called 4B/5B coding). 4B/5B uses 5-bit symbols or codes to represent 4 bits of data. It is used in 100BASE-TX Ethernet.
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| Attenuation | The loss of communication signal on the media. This loss is due to degradation of the energy wave over time.
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| Bit Time | The time required to send a single bit over some transmission medium. The time can be calculated as 1/speed, where speed is the number of bits per second sent over the medium.
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| coax | Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor.
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| coaxial cable | Has 3 different layers of material surrounding the inner conducting material: the outer conductor, the insulator, and the protective outer jacket.
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| Code Group | A grouping of code that meets a certain, already specified, condition for entering in that certain group.
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| crossover cable | A UTP cable used in Ethernet in which some pairs of twisted-pair wires are crossed when comparing the RJ-45 connectors on either end of the cable.
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| Encode | To change the energy levels transmitted over some networking medium to transmit bits over that medium.
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| fiber-optic cable | Physical medium that uses glass or plastic threads to transmit data. A fiber-optic cable consists of a bundle of these threads, each of which is capable of transmitting data into light waves.
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| Goodput | Application-level throughput. It is the number of useful bits per unit of time from a certain source address to a certain destination, excluding overhead and excluding retransmitted data packets.
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| hybrid fiber-coax (HFC) | A network that incorporates both optical fiber along with coaxial cable to create a broadband network. Commonly used by cable TV companies.
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| Kilobits per second (kbps) | A unit of measurement of the number of times 1000 bits can be transmitted in 1 second. 1kbps
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| Manchester encoding | Line code in which each bit of data is signified by at least one voltage level transition.
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| Megabits per second (Mbps) | A unit of measurement of the number of times 1,000,000 bits can be transmitted in 1 second. 1Mbps
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| Noise | In networking, a general term referring to any energy signal in a transmission medium that is not part of the signal used to transmit data over that medium.
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| Nonreturn to Zero (NRZ) | Line code in which 1s are represented by one significant codition and 0s are represented by another.
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| Optical Time Domain Reflectometer (OTDR) | A popular certification method for fiber systems.
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| Physical Media | The cabling and connectors used to interconnect the network devices.
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| Pinout | Defines which wires in a cable should connect to each pin on the connectors on both ends of a cable.
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| RJ-45 | A rectangular cabling connector with eight pins, often used with Ethernet cables.
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| rollover cable | A UTP cable pinout that specifies that the wire at pin 1 of an RJ-45 connector on one end of the cable connects to pin 8 on ther other end;pin 2 to pin 7; pin3 to pin 6; pin 4 to pin 5.
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| shielded twisted pair (STP) cable | A type of network cabling that includes twisted-pair wires, with shielding around each pair of wires, as well as another shield around all the wires in the cable.
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| Signal | The optical or electrical impulse on a physical medium for purposes of communication.
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| straight-through cable | A UTP cable pinout that specifies that the wire at pin 1 of RJ-45 to pin 1 on the other side and so on. Used to connect a computer to a switch/hub.
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| Throughput | The actual data transfer data rate between two computers at some point in time.
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| Unshielded Twisted Pair (UTP) cable | A general type of cable, with the cable holding twisted-pairs of copper wires and the cable itself having little shielding.
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| Copper cable and fiber-optic cable are examples of ________, which is used to carry the communication signal. | Physical Media
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| What is the purpose of encoding? | Encoding represents the data bits by using different voltages, light patterns, or electromagnetic waves as they are placed onto the physical media.
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| What two signaling methods use voltage to encode bits? | NRZ (non-return to zero) and Manchester.
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| What best describes the purpose of the physical layer? | The chief purpose of the physical layer is to define the functional specifications for links betwen end systems and the electrical, optical, and radio signals that carry data.
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| What is the most common UTP connector type? | RJ-45
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| Through what process does UTP cable help to avoid crosstalk? | Crosstalk is reduced by the twisting of cables in the UTP cable. UTP has no cladding, shielding, or grounding points.
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| What is the required order of wires in a connector called? | Pinout
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| What are the advantages of using fiber-optic cable over copper cable? Name 3 | Immunity to electromagnetic interference, Longer maximum cable length, and Greater bandwidth potential.
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| The physical media most suseptable to security breaches is __________? | Wireless because it is open to interception.
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| What is the purpose of cladding in fiber-optic cables? | Cladding helps to prevent light loss.
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| A ___________ cable is also known as a Cisco cable because it is generally used as a connection to Cisco equipment. | Rollover/Console
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| The measure of the actual transfer rate over a medium is called what? | Throughput
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| What is synchronization? | The timing mechanism devices use when transmitting data.Synchronization between devices allows them to know when frames begin and end.
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| Explain "bit time" | It is the time it takes for a NIC to move a bit from the data link layer to the Layer 1 media. Bit time changes depending on the speed of the NIC.
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| Explain "slot time" | The time it takes a bit to traverse the network is called slot time. It counts bits, not bytes.
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