Networking Media (Tutorial-5)

Transmission Media

A medium is a carrier of something.

Consists of a central copper core surrounded by an insulator, a braided metal shielding, called braiding, and an outer cover, called the sheath or jacket
High bandwidth – Up to 400 MHz
Max. used data rates – 100 Mbps
High quality of data transmission
Signal loss at high frequencies

Thicknet Coaxial Cable

Is a rigid coaxial cable approximately 1-cm thick used for the original Ethernet networks
Also called ‘thick Ethernet’, ‘yellow Ethernet’
IEEE designates Thicknet as ‘10Base5’ Ethernet, interpreted as follows –
‘10’ for transmission rate of 10 Mbps
‘Base’ for baseband transmission
‘5’ for the max. segment length of a Thicknet cable, which is 500 m

Thicknet Coaxial Cable

Thinnet Coaxial Cable

Popular medium used in Ethernet LANs in the 1980s
IEEE designates Thinnet as ‘10Base2’ Ethernet, interpreted as follows –
’10’ for transmission rate of 10 Mbps
‘Base’ for baseband transmission ‘2’ for the max. segment length which is around 200 m

Thinnet Coaxial Cable

Twisted Pair Cable

Consists of colour-coded pairs of twisted & insulated copper wires
Used extensively in telephone cables
Number of twists per unit length is known as ‘twist ratio’. More the twist ratio, lesser the noise and therefore better the quality
Is inexpensive, flexible, and easy to install
One drawback to twisted-pair is that, because of its flexibility, it is more prone to physical damage than coaxial cable
All twisted pair cables fall into two categories –

Shielded Twisted Pair (STP)‏
Unshielded Twisted Pair (UTP)‏

Shielded Twisted Pair (STP)‏

The insulated inner twisted pairs are surrounded by an additional shielding usually made of metallic foil or braid.
The shielding acts as a barrier to external signals, thus reducing noise .
The shielding may be grounded to enhance its protective effect.

Shielded Twisted Pair (STP)‏

Straight Through Cable

It is a type of UTP cable
The color coding of the internal wires inside both ends of the cable are similar
Straight through cables could be used to connect dissimilar devices like
Connecting a router to a hub or switch
Connecting a server to a hub or switch

Table Straight Through Cable

Crossover Cable

It is a type of UTP cable
The colour coding of the internal wires inside both ends of the cable are dissimilar
Straight through cables could be used to connect similar devices like
Connecting hubs to switches
Connecting 2 hubs

Table Crossover Cable

UTP Types

Fiber Optic Cable

Cables contain fiber lines in their cores instead of the usual copper wires
Technique uses light pulses to transmit information through these optic fibers
Very high bandwidths of up to several Gbps
Could be used for long distances covering hundreds of kilometers
Provide very high bandwidth – up to 20, 000 MHz
Low interference provides highly efficient transmission High costs are currently the only drawback

Fiber Optic Cable

Radio

Radio - 10 Khz to 1 Ghz. It is broken into many bands including AM, FM, and VHF bands. The Federal communications Commission (FCC) regulates the assignment of these frequencies. Frequencies for unregulated use are:902-928Mhz - Cordless phones, remote controls.
2.4 Ghz
5.72-5.85 Ghz

Microwave

Terrestrial - Used to link networks over long distances but the two microwave towers must have a line of sight between them. The frequency is usually 4-6GHz or 21-23GHz. Speed is often 1-10Mbps. The signal is normally encrypted for privacy. Two nodes may exist.
Satellite - A satellite orbits at 22,300 miles above the earth which is an altitude that will cause it to stay in a fixed position relative to the rotation of the earth. This is called a geosynchronous orbit. A station on the ground will send and receive signals from the satellite. The signal can have propagation delays between 0.5 to 5 seconds due to the distances involved. The transmission frequency is normally 11-14GHz with a transmission speed in the range of 1-10Mbps.

Infrared

Infared is just below the visible range of light between 100Ghz and 1000Thz. A light emitting diode (LED) or laser is used to transmit the signal. The signal cannot travel through objects. Light may interfere with the signal. The types of infared are
Point to point - Transmission frequencies are 100GHz-1,000THz . Transmission is between two points and is limited to line of sight range. It is difficult to eavesdrop on the transmission. The speed is 100Kbps to 16MbpsBroadcast - The signal is dispersed so several units may receive the signal. The unit used to disperse the signal may be reflective material or a transmitter that amplifies and retransmits the signal. The transmission frequency is normally 100GHz-1,000THz with transmission distance in 10's of meters. Installation is easy and cost is relatively inexpensive for wireless.
Broadcast - The signal is dispersed so several units may receive the signal. The unit used to disperse the signal may be reflective material or a transmitter that amplifies and retransmits the signal. The transmission frequency is normally 100GHz-1,000THz with transmission distance in 10's of meters. Installation is easy and cost is relatively inexpensive for wireless.

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