Guided Transmission Media- Twisted Pair

     A twisted-pair cable consists of one or more twisted-pair. Each twisted-pair wire usually is color coded for identification. Its wires are twisted together and separately insulated to each other. They are usually in the form of bundles called cables. They are installed in building during construction.

Transmission Characteristic:

1. Limited distance.

2. Limited Bandwidth of 1 MHz.

3.  Limited data rate of of 100 MHz.

4. Use both analog (amplifier every 5 km) and digital signals (repeater every 2 km).

5.  Susceptible to interference and noise.

Types of Twisted Pair Cables:

a) Unshielded Twisted Pair (UTP): It acts as ordinary telephone wire. It characteristics are: cheapest, easy to install, and suffer from external interference.

b) Shielded Twisted Pair (STP): It is made up of metal braid that reduces interference. More expensive, and harder to handle.

                                               Table: UTP Category

UTP Category	Data Rate	Max. Length	Cable Type	Applications
CAT1	1 Mbps	-	Twisted Pair	Old Telephone Cable
CAT2	4 Mbps	-	Twisted Pair	Token Ring Networks
CAT3	10 Mbps	100 m	Twisted Pair	Token Ring
CAT4	16 Mbps	100 m	Twisted Pair	Token Ring
CAT5	100 Mbps	100 m	Twisted Pair	Token Ring, Ethernet
CAT5e	1 Gbps	100 m	Twisted Pair	Ethernet, Fast Ethernet
CAT6	10 Gbps	100 m	Twisted Pair	Gigabit Ethernet
CAT6a	10 Gbps	100 m	Twisted Pair	Gigabit Ethernet
CAT7	10 Gbps	100 m	Twisted Pair	Gigabit Ethernet

Application of Twisted Pairs:

1. They are used in telephone networks between house and local exchange called Subscriber Loop.

2. Within buildings.

3. For private branch exchange.

4. Local area networks.

Pros and Cons:

1. Easy to work with

2.  Short range

3. Low data rate

4. Cheap

Figure: A twisted-pair cable consists of one or more twisted-pair. Each

twisted-pair wire usually is color coded for identification.

Transmission Media

   Transmission Media is a pathway that carries the data information from transmitter to receiver. There are different types of waves or cables to transmit data. Information is transmitted normally through electrical (Current) or electromagnetic signals (at different frequencies). These signals can be transmitted through different Medias like copper wires, atmosphere, water, and optical fibre. Different media have different properties like bandwidth, ease of installation, cost and delay. Characteristic and quality are determined by signal and medium. For guided transmission, medium is important. For unguided transmission, bandwidth is important. Key concerns in transmission are data rate and distance.

Types of Transmission Media

   Transmission media is divided into two groups:

1.     Guided or Wired or Bounded Transmission Media

2.     Unguided or Wireless or Unbounded Transmission Media

                                     Figure: Transmission medium and physical layer

There are various design factors:
1. Bandwidth: Higher bandwidth gives higher data rate
2. Interference
3. Transmission Impairments
4. Number of Receivers: More receivers introduce more attenuation, need more amplifiers and repeaters.

  Guided or Wired Media are the cables that have physical existence and are limited by environmental geography. Mostly used wired media are co-axial cable, twisted pair cable, and optical cable. Each  media has its own properties like speed of transmission, effect of noise, cost etc.

  Unguided or Wireless Media are the way of transmitting information without using any physical media or cables. It is also known as wireless communication. Example, wireless LAN are used in office and college campuses. This transmission uses radio wave, microwave, infrared waves. 

                           Table: Transmission Characteristics of Guided Media

	Frequency Range	Typical Attenuation	Typical Delay	Repeater Spacing
Twisted Pair	0 to 3.5 KHz	0.2 dB/km	50 µs/km	2 km
Coaxial Cable	0 to 500 MHz	7 dB/km	4 µs/km	1 to 9 km
Optical fiber	186 to 370 Thz	0.2 to 0.5 dB/km	5 µs/km	40 km

Guided Transmission Media

      Twisted Pair

      Coaxial Cable

      Optical Fiber

Wireless Transmission

     Antennas

     Terrestrial Microwave

      Satellite Microwave

      Broadcast Radio

      Infrared

Wireless Propagation

     Ground Wave Propagation

     Sky Wave Propagation

     Line-of-Sight Propagation

Line-of-Sight Transmission

     Free Space Loss

     Atmospheric Absorption

     Multi path

     Refraction

Label: Comparison of Gudied Media