Data Communication And Networking

TRANSMISSION MEDIA

We have to learn following topics : What is transmission Media ? Types of Transmission Media 1) Guided Media :

What is guided Media & It’s types A) Twisted Pair CableB) Coaxial CableC) Fiber optics Cable

2) Unguided (Wireless) Media : What is unguided Media , Reasons for Unguided Media ? Types of Unguided Media

A) BluetoothB) Wi-Fi

C) Mobile ComputingD) InfraredE) Microwave

TRANSMISSION MEDIA: Enables computer to Send &Receive messages

but do not guarantee that the message will be understood or not.

Guided ( Wired ) The medium itself is more important in determining the limitations of transmission. The transmission capacity, in terms of either data rate or bandwidth, depends critically on the distance and on whether the medium is point-to-point or multipoint.

Now we see one by one of them as follows:-

1) Twisted Pair Cable

A basic twisted pair cable consist of two strands of copper wire twisted together, this twisting reduces sensitivity of cable.

The twisted pair cable are most significant because of it’s low cost . It is inexpensive to install and offers the lowest cost per foot of any cable.

The figure shows the twisted pair cable with insulating jackets and conductors.

There are two types of twisted pair cable as follows :--

1) Shielded 2) Unshielded

Shielded twisted cable

Shielded twisted pair cable consist of one or more twisted pairs of cables enclosed in a foil wrap & woven copper shielding. The shield is connected to the ground portion of the electronic device to which the cable is connected.

STP(Shielded twisted cable) is less costly ,than coaxial cable or optical fiber cable.

STP cable has theoretical capacity of 500Mbps , although exceeds 155Mbps But, Most common data rate for STP is 16Mbps.

The shield in STP results in Good EMI characteristics.

Advantages & Disadvantages of STP

1) Requires amplifiers every 5 to 6Kms for analog signals.

2) Limited in terms of data rate and distance.3) Requires repeaters for every 2 to 3Kms for digital

signals.4) Autonuation is strong function of frequency.5) Twisting reduces low frequency interference.6) susceptible to interference and noise.

Unshielded twisted cable doesn’t incorporate a braided shield into it’s structure.

Several twisted pairs can be bundled together in a single cable. These pairs are typically differentiated by colour .

UTP cable is less costly as compare to any other although category 5 type to be more costly.

UTP cable is easy to install & have attenuation characteristic that limit the length of cable runs to a 100 Mtrs limit .

Unshielded twisted cable

2) Coaxial Cable

It consist of center conductor usually consist of sold copper wire. an outer conductor forms a tube surrounding the center conductor

this consist of Braided wires , metallic foils or both . And insulation layer keeps the outer conductor spaced from the

inner conductor. A plastic encasement (jacket) protects the cable from damage. There are two types of coaxial cable as:1) Thinnet2) Thicknet

Advantages & Disadvantages of Coaxial cable

1) Requires amplifiers every 5th kms. For long distance.2) Useable spectrum for analog signalling upto 500Mhz.3) Requires repeaters for every 5th kms for digital

signalling.4) Most commonly used in T.V.5) Can carrying more than 10,000 voice channel .6) Short range connection between devices.

1) Optical fiber Cable

Bundle of Optical fiber

The centre conductor of fiber cable is the ideal cable for data transmission. The centre conductor is consist of highly refined glass or plastic designed.

A glass core supports a longer cabling distance, but a plastic core is typically easier to work with.

A fiber is coated with a cladding that reflects signals back into the fiber to reduce the signal loss .

A plastic sheath protects the fiber.

characteristics The cost of the fiber cable and connectors has significantly

fallen in recent years . But fiber-optic cable is also the most expensive cable type. Greater skill is required to install fiber –optic cable than to

install most copper cables. Fiber-optic cable can support high data rates (as high as

200,000Mbps) even with long cable runs. Normally fiber –optic cable can transmit 100Mbps signals

for several kms . Attenuation is much lower in fiber than copper cables. Fiber optic cable doesn’t use electric signals for data

transmission hence ,they are totally immune to EMI.

Unguided (Wireless) Media The extraordinary convenience of wireless

communication has placed an increased emphasis on wireless networks in recent years.

Wireless networks are especially useful for Spaces where cabling would be impossible or inconvenient Eg:open lobbies. and people who move around a lot within their work environment

Temporary installation & people who travel outside of the work environment uses wireless networks.

These are classified into following types as :

1) Bluetooth2) Wi-Fi3) Satellite Microwave4) Infrared

Bluetooth: Bluetooth is a low-cost, low power, short range wireless

communication technology used in. networking, mobile phones and other portable device.

Bluetooth wireless technology also enables devices to communicate with each other as soon as-they come within range. no need to connect, plug into, install, enable or configure anything.”

Wi-Fi : Wi-Fi or Wireless Fidelity refers to the technology

surrounding the radio transmission of internet protocol data from an internet connection wirelessly to a host computer.

Most often the internet connection is a higher speed one such as satellite, DSL or cable rather than slower dial-up connections.

A Wi-Fi Network Works Basic concept is same as Walkie- talkies. A Wi-Fi hotspot is created by installing an access point to an internet connection. An access point acts as a base station. When Wi-Fi enabled device encounters a hotspot the device can then connect to that network wirelessly. A single access point can support up to 30 users and can function within a range of 100 – 150 feet indoors and up to 300 feet outdoors.

Satellite Microwave: Satellite Microwave: Satellite is relay station Receives on one

frequency, amplifies or repeats signal and transmits on another frequency Eg. Uplink 5.925-6.425 ghz & downlink 3.7-4.2 ghz

Typically requires geo-stationary orbit Height of 35,784km Spaced at least 3-4° apart

Typical uses Television Long distance telephone Private business networks Global positioning

Infrared: Infrared technology allows computing devices to

communicate via short-range wireless signals. With infrared, computers can transfer files and other digital

data bidirectionally. The infrared transmission technology used in computers is

similar to that used in consumer product remote control units.

Modulate noncoherent infrared light End line of sight (or reflection) Are blocked by walls No licenses required Typical uses TV remote control IRD port