Physical layer Flashcards
Simplex
A data connection that works in one direction only.
Half Duplex
A data connection that will work in 2 directions,
but only a single direction at a time
Full duplex
A data connection that will work in 2 directions,
both working simultaneously.
Bit Encoding
Bits must be converted to physical signals for transmission across
a medium
Bits can be encoded to voltage levels for transmission over
copper cables
* binary zero = 0 volts
* binary one = +5 volts
Bits can be encoded to optical light levels for transmission over
fiber optic cables
* binary zero = dim light
* binary one = bright light
bandwidth
maximum rate bits can be moved
throughput/goodput
measurement of actual bits through media
Media types
copper
fiber optic
radio frequency
Copper wire
twisted pair cables
unshielded
- most common
-inexpensive compared to the rest
-more suspectable to noise than stp
shielded
-each twisted pair is surrounded by foil
- foil reduces EMI/RFI noise interference
- more expensive then utp and usually used in noisy environments
optic fiber
- Optical Fiber (or Fibre) conducts light
- A thin tube of very clear glass about the diameter of a
human hair - Capable of very high bitrates over very long distances
- 1 Tbps (1000 Gbps) over 100 Km (single mode)
- Light is not affected by electrical noise
twisted pairs
multiple pairs of wires that are twisted and each pair is twisted separately
-Usually have 4 pairs of wires
- Signals are transmitted or received on a single wire pair.
- The twisting reduces both the emition of ‘noise’ from the pair and the reception of ‘noise’ by the pair. (Created by induction on the wires.)
- Each pair in the cable has a different rate of twists per foot so signals emitted by one pair will not be received by another pair. (called Crosstalk)
RJ-45 connector
rj = registered jack
TIA/EIA 568 standard
8 pins
most common type in UTP
RJ-11 connector
smaller than the 45
4 pins
phone connections
most rj45 females will accept a rj 11 jack
RJ 45 patch collectors
An RJ-45 jack (male connector) on both ends
* The T568 Specification has two pinout patterns
* T568A and T568B
Straight through cables
can be either T568A OR T568B on each side of the cable
- connect to unlike devices
- exPC to switch
Cross over cable
One end has T568 A and the other side has T568B
-connects to like devices
-PC to PC, PC to router
single mode
- Long distance – 100 km+,
between cities, etc. - Use a single light stream
(1310 or 1550 nm), usually
generated by a laser or laser
diode. - Outer jacket will have a yellow
colour, per standards.
multi mode
- Short distance – 0.5-0.6 km,
between floors, maybe
buildings. - Uses multiple light streams
(850-1300 nm), usually
generated by an LED. - Outer jacket will be coloured
orange, aqua, or lime green
based on Optical Mode rating.
