{ Transmission Media

 Information can be transmitted through a medium by varying some physical property.  The physics of the universe places some limits on what can be sent over a channel.  Purpose of the physical layer -- to transport a raw bit stream from one machine to another  Guided and Unguided media Theoretical

The protocol determines the following: Type of error checking to be used if any Type of error checking to be used if any Data compression method. Data compression method. Method for sending device to indicate that it has finished sending a message. Method for sending device to indicate that it has finished sending a message. Method for receiving device to indicate that it has received a message Method for receiving device to indicate that it has received a message Whether transmission is to be synchronous or asynchronous Whether transmission is to be synchronous or asynchronous Protocols

 Coaxial Cable consists of 2 conductors. The inner conductor is held inside an insulator with the other conductor woven around it providing a shield.  An insulating protective coating called a jacket covers the outer conductor.  The outer shield protects the inner conductor from outside electrical signals.  The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. Coaxial Cable

Advantages: Not susceptible to interference Transmits faster With FDM it can carry 10,000 voice channels Disadvantages: Heavy & bulky Needs booster over distance. Like repeaters or amplifiers are needed every few Km.

 Optical Fiber consists of thin glass fibers that can carry information at frequencies in the visible light spectrum and beyond.  The typical optical fiber consists of a very narrow strand of glass called the Core.  Around the Core is a concentric layer of glass called the Cladding.  A typical Core diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns. Optical Fiber

Advantages: Security: cannot tap into cable. Large Capacity due to BW (bandwidth) No corrosion Longer distances than copper wire Smaller and lighter than copper wire Faster transmission rate Disadvantages : Physical vibration will show up as signal noise. Limited physical arc of cable. Bend it too much & it will break. Difficult to split.

 Twisted pair cable consists of a pair of insulated wires twisted together. It is a cable type used in telecommunication for very long time. Cable twisting helps to reduce noise pickup from outside sources and crosstalk on multi-pair cables.  Twisted pair cable is good for transferring balanced differential signals. The practice of transmitting signals differentially dates back to the early days of telegraph and radio. Twisted pair cable

Advantage: Improved signal-to-noise ratio, crosstalk, and ground bounce that balanced signal transmission bring are particularly valuable in wide bandwidth and high fidelity systems Disadvantage: The application originally designed for some other type of cabling need usually special adapters which cost money

What is Bluetooth? Bluetooth is a short-range wireless technology used for connecting and transferring information between devices such as mobile phones, laptops, PCs, PDAs, printers, digital cameras, mice and keyboards. Bluetooth makes it easy to connect two devices wirelessly when it would be otherwise impossible to connect them with cables. Bluetooth Logo A master Bluetooth device can communicate with a maximum of seven devices in a network. (the picture right is the diagrammatic sketch of the Bluetooth network)

{{ Bluetooth vs Wi-Fi BluetoothWi-Fi Range:10 meters100 meters Bandwidth:Low ( 800Kbps )High (11Mbps ) Cost:LowHigh Power Consumption: LowHigh Bluetooth vs Infar-Red BluetoothInfar-red Range:10 meters1 meters Versatility:Every devices could work together Need specific devices. Orientation:Does not require a direct line of sight Requires a direct line of sight Connectivity:Many To ManyOne to one Comparison with other wireless technologies

3G has dominated the modern world in just a few years. 3G has dominated the modern world in just a few years. ///////////// WHAT IS 3G G is the third generation of wireless technologies. It comes with enhancements over previous wireless technologies, like high- speed transmission, advanced multimedia access and global roaming. 3G is mostly used with mobile phones and handsets as a means to connect the phone to the Internet or other IP networks in order to make voice and video calls, to download and upload data and to surf the net. 1G---transmitted analog data only 2G---transmitted digital data at speeds of kbps 3G---transmitted digital data at speeds from 144kbps to 2.4 Mbps