Networking Media (Tutorial-5)

Transmission Media

        A medium is a carrier of something.

Coaxial Cable

Coaxial Cable

• 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)‏

Unshielded Twisted Pair (UTP)‏

• Does not contain additional shielding 
• Advantage over STP is that it is less expensive 
• Absence of shielding, however, makes it more prone to noise

Straight Through Cable

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

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.