 The communication channel or simply channel refers either to a physical transmission medium such as a wire, or two logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used to convey an information signal, for example a digital bit stream, from one or several senders or transmitters to one or several receivers. A channel has a certain capacity for transmitting information, often measured by its bandwidth in hertz or its data rate in bits per second. Communicating data from one location to another requires some form of pathway or medium. These pathways, called communication channels, used to types of media, cable twisted pair wire, cable, and fiber optic cable and broadcast microwave, satellite, radio, and infrared. Cable or wire line media use physical wires of cables to transmit data and information. Twisted pair wire and coaxial cables are made of copper, and fiber optic cable is made of glass. In information theory, a channel refers to a theoretical channel modeled with sir and error characteristics. In this more general view, a storage device is also a kind of channel, which can be sent to written and received from reading. A channel can be modeled physically by trying to calculate the physical processes which modify the transmitted signal. For example, in wireless communications the channel can be modeled by calculating the reflection of every object in the environment. A sequence of random numbers might also be added in to simulate external interference and slash or electronic noise in the receiver. Statistically a communication channel is usually modeled as a triple consisting of an input alphabet, an output alphabet, and for each pair I, so of input and output elements a transition probability P I O. Semantically, the transition probability is the probability that the symbol O is received given that I was transmitted over the channel.