Statistical multiplexing o transmitter assigns slots

statistical multiplexing
o transmitter assigns slots to nodes
 according to priority need
o more efficient than TDM
-
frequency division multiplexing (FDM)
o unique frequency band for each communications subchennel
o cellular telephone transmission
o DSL internet access
-
Wavelength division multiplexing (WDM)
o One fiber optic connection
o Carries multiple light signals simultaneously
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Dense wavelength multiplexing (DWDM)
o Used on most modern fiber optic networks
o Extraordinary capacity

Relationships Between Nodes
Point-to-point transmission

One transmitter and one receiver
Point-to-multipoint transmission

One transmitter and multiple receivers
Broadcast transmission

One transmitter and multiple, undefined receivers

Used on wired and wireless networks

Simple and quick
Nonbroadcast

One transmitter and multiple, defined recipients
Throughput and Bandwidth
Throughput

Amount of data transmitted during given time period

Also called capacity or bandwidth

Expressed as bits transmitted per second
Bandwidth (strict definition)

Difference between highest and lowest frequencies medium can transmit

Range of frequencies

Measured in hertz (Hz)
Baseband and Broadband
Baseband transmission

Digital signals sent through direct current (DC) pulses applied to wire

Requires exclusive use of wire’s capacity

Transmit one signal (channel) at a time

Example: Ethernet
Broadband transmission

Signals modulated as radio frequency (RF) analog waves

Uses different frequency ranges

Does not encode information as digital pulses
Transmission Flaws
-
noise
o any undesirable unfluence degrading or distorting signal
-
types of noise
o EMI (electromagnetic inference)
 Radio requecny interference

o Cross talk
 Signal on one wire infringes in adjacent wire signal
 Near end cross talk (NEXT) occurs near source
-
attenuation
o loss of signals strength as it travels away from source
-
signal boosting technology
o analog signals pass through amplifier
 noise also amplified
-
regeneration
o digital signals retransmitted in original form
o repeater: device regenerating digital signals
-
amplifiers and repeaters
o OSI model physical layer
-
Latency
o Delay between signal transmission and receipt
o May cause network transmission errors
-
Latency causes
o Cable length
o Intervening connectivity device
-
Round trip time (RTT)
o Time for packet to go from sender to receiver and then back from
receiver to sender
Common media characteristics*
-
selecting transmission media
o media networking needs with media characteristics
-
physical media characteristics
o throughput
o cost
o noise immunity
o size and scalability
o connectors and media converters
throughput
-
most significant factor in choosing transmission method
-
cause of throughput limitations
o laws of physics
o noise
o signalling and multiplexing techniques
o devces connected to transmission medium
-
fiber optic cables allow faster throughput compared to wireless or copper
cost
-
precise costs difficult to pinpoint

-
media cost dependencies
o existing hardware, network size, labour costs
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