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NETW202 Ch 8

OSI Physical Layer

QuestionAnswer
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.
Attenuation The loss of communication signal on the media. This loss is due to degradation of the energy wave over time.
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.
coax Cable consisting of a hollow outer cylindrical conductor that surrounds a single inner wire conductor.
coaxial cable Has 3 different layers of material surrounding the inner conducting material: the outer conductor, the insulator, and the protective outer jacket.
Code Group A grouping of code that meets a certain, already specified, condition for entering in that certain group.
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.
Encode To change the energy levels transmitted over some networking medium to transmit bits over that medium.
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.
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.
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.
Kilobits per second (kbps) A unit of measurement of the number of times 1000 bits can be transmitted in 1 second. 1kbps
Manchester encoding Line code in which each bit of data is signified by at least one voltage level transition.
Megabits per second (Mbps) A unit of measurement of the number of times 1,000,000 bits can be transmitted in 1 second. 1Mbps
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.
Nonreturn to Zero (NRZ) Line code in which 1s are represented by one significant codition and 0s are represented by another.
Optical Time Domain Reflectometer (OTDR) A popular certification method for fiber systems.
Physical Media The cabling and connectors used to interconnect the network devices.
Pinout Defines which wires in a cable should connect to each pin on the connectors on both ends of a cable.
RJ-45 A rectangular cabling connector with eight pins, often used with Ethernet cables.
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.
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.
Signal The optical or electrical impulse on a physical medium for purposes of communication.
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.
Throughput The actual data transfer data rate between two computers at some point in time.
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.
Copper cable and fiber-optic cable are examples of ________, which is used to carry the communication signal. Physical Media
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.
What two signaling methods use voltage to encode bits? NRZ (non-return to zero) and Manchester.
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.
What is the most common UTP connector type? RJ-45
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.
What is the required order of wires in a connector called? Pinout
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.
The physical media most suseptable to security breaches is __________? Wireless because it is open to interception.
What is the purpose of cladding in fiber-optic cables? Cladding helps to prevent light loss.
A ___________ cable is also known as a Cisco cable because it is generally used as a connection to Cisco equipment. Rollover/Console
The measure of the actual transfer rate over a medium is called what? Throughput
What is synchronization? The timing mechanism devices use when transmitting data.Synchronization between devices allows them to know when frames begin and end.
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.
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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