The CRC value in the FCS field of the received frame is
compared to the computed CRC value of that frame, in order
to verify the integrity of the frame. If the two values do not
match, then the frame is discarded.
to verify the logical address in the frame
to verify the integrity of the received frame
to verify the physical address in the frame
to compute the checksum header for the data field in the frame
Bandwidth is the capacity of a medium to carry data in a given
amount of time. It is typically measured in kilobits per second
(kb/s) or megabits per second (Mb/s).
Logical Link Control (LLC) is the data link sublayer that defines
the software processes that provide services to the network
layer protocols. LLC places information in the frame and that
information identifies the network layer protocol that is
encapsulated in the frame.
Single-mode fiber uses a laser as the light source. Its small
core produces a single straight path for light and it is
commonly used with campus backbones. Multimode fiber uses
LEDs as the light source. Its larger core allows for multiple
paths for the light. It is commonly used with LANs.
LED as light source
only one ray of light into the fiber
laser as light source
generally used with LANs
generally used for campus backbone
several paths of light into the fiber
A hybrid topology is a variation or combination of a point-to-
point, hub and spoke, or mesh topology. This may include a
partial mesh or extended star topology.
A hybrid topology is one that is a variation or a
combination of other topologies. Both partial mesh and the
extended star are examples of hybrid topologies.
hub and spoke
An encoding technique converts a stream of data bits in a
predefined code that can be recognized by both the transmitter
and the receiver. Using predefined patterns helps to
differentiate data bits from control bits and provide better
media error detection.
to distinguish data bits from control bits
to provide better media error correction
to identify where the frame starts and ends
to reduce the number of collisions on the media
to increase the media throughput
Throughput is the measure of the transfer of bits across the
media over a given period of time. Throughput is affected by a
number of factors such as, EMI and latency, so it rarely
matches the specified bandwidth for a network medium. The
throughput measurement includes user data bits and other
data bits, such as overhead, acknowledging, and
encapsulation. The measure of the usable data transferred
across the media is called goodput.
the capacity of a particular medium to carry data
the guaranteed data transfer rate offered by an ISP
the measure of the usable data transferred across the media
the measure of the bits transferred across the media over a given period of time
the time it takes for a message to get from sender to receiver
EMI and RFI signals can distort and corrupt data signals that
are carried by copper media. These distortions usually come
from radio waves and electromagnetic devices such as motors
and florescent lights. Crosstalk is a disturbance that is caused
by adjacent wires bundled too close together with the magnetic
field of one wire affecting another. Signal attenuation is caused
when an electrical signal begins to deteriorate over the length
of a copper cable.
extended length of cabling
EMI and RFI can distort network signals because of
interference from fluorescent lights or electric motors.
Attenuation results in deterioration of the network signal as it
travels along copper cabling. Wireless devices can experience
loss of signals because of excessive distances from a access
point, but this is not crosstalk. Crosstalk is the disturbance
caused by the electric or magnetic fields of the signal carried
on an adjacent wire within the same cable.
the loss of wireless signal over excessive distance from the access point
the distortion of the network signal from fluorescent lighting
the weakening of the network signal over long cable lengths
the distortion of the transmitted messages from signals carried in adjacent wires
To help prevent the effects of crosstalk, UTP cable wires are
twisted together into pairs. Twisting the wires together causes
the magnetic fields of each wire to cancel each other out.
wrapping a foil shield around the wire pairs
encasing the cables within a flexible plastic sheath
twisting the wires together into pairs
terminating the cable with special grounded connectors
A straight-through cable is commonly used to interconnect a
host to a switch and a switch to a router. A crossover cable is
used to interconnect similar devices together like switch to a
switch, a host to a host, or a router to a router. If a switch has
the MDIX capability, a crossover could be used to connect the
switch to the router; however, that option is not available. A
rollover cable is used to connect to a router or switch console
1 – crossover, 2 – straight-through, 3 – rollover
1 – rollover, 2 – straight-through, 3 – crossover
1 – crossover, 2 – rollover, 3 – straight-through
1 – rollover, 2 – crossover, 3 – straight-through
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