Transmission media

Network Transmission
Media

Transmission Basics
• In data networking, transmit means to issue
signals to the network medium
• Transmission refers to either the process of
transmitting or the progress of signals after
they have been transmitted

Analog and Digital Signals
• Information transmitted via analog or digital signals
– Signal strength proportional to voltage
• In analog signals, voltage varies continuously and
appears as a wavy line when graphed over time.
• Analog transmission susceptible to transmission
flaws such as noise

Analog and Digital Signals (continued)
• Digital signals composed of pulses of precise,
positive voltages and zero voltages
– Positive voltage represents 1
– Zero voltage represents 0
– Typically represents one piece of information
• Overhead: describes non-data information that must
accompany data for a signal to be properly routed
and interpreted

Transmission Direction:
Simplex, Half-Duplex, and Duplex
• Simplex transmission: signals may travel in only one
direction
• Half-duplex transmission: signals may travel in both
directions over a medium
– Only one direction at a time
• Full-duplex or duplex: signals free to travel in both
directions over a medium simultaneously
– Used on data networks
– Channel: distinct communication path between
nodes
• May be separated logically or physically

Transmission Direction: Multiplexing
• Multiplexing: transmission form allowing multiple
signals to travel simultaneously over one medium
– Channel logically separated into subchannels

• Multiplexer (mux): combines multiple signals
– Sending end of channel

• Demultiplexer (demux): separates combined signals
and regenerates them in original form
– Receiving end of channel

Relationships Between Nodes

Figure 2-10: Point-to-point versus broadcast transmission

Wireless Transmission
• Networks that transmit signals through the
atmosphere via infrared or RF waves are known as
wireless networks or wireless LANs (WLANs)

Wireless LAN Architecture (continued)

Antennas
• Radiation pattern describes relative strength over
three-dimensional area of all electromagnetic energy
the antenna sends or receives
• Directional antenna issues wireless signals along a
single direction
• Omni directional antenna issues and receives
wireless signals with equal strength and clarity in all
directions
• Range: geographical area an antenna or wireless
system can reach

Infrared Transmission
• Transmitted by frequencies in the 200-GHz to
200,000-GHz range
• Most often used for communications between
devices in same room
– Relies on the devices being close to each other
– May require line-of-sight path
– Throughput rivals fiber-optics

Microwave
• High frequency EM wave that is used for point to
point communication
• Microwave Categories:
– Terrestrial – Relay towers are used to transmit
radio signals between earth stations
– Satellite – Radio signals are transmitted between
different base stations using satellites

Transmission media

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Transmission media