A bit (binary digit) is the smallest unit of information • N = 2n where N is the number of representations and n is the number of bits (ex. ASCII, Unicode, PCM code etc.) • Data communications transfer information using codes that are transmitted as signals (either analog or digital) • In general, analog lines provide a slow service that contains high error rates. However, digital lines cannot transmit analog data unless it is converted to a binary format first • Encoder is used to convert the information transmitted by the sender and decoder converts the information back to its original form for the receiver. | Transmission Methods Dr. Ming Huang Topics Bits, Signals, Frames, and Codes Transmission Modes Multiplexing Bits, Signals, and Codes A bit (binary digit) is the smallest unit of information N = 2n where N is the number of representations and n is the number of bits (ex. ASCII, Unicode, PCM code etc.) Data communications transfer information using codes that are transmitted as signals (either analog or digital) In general, analog lines provide a slow service that contains high error rates. However, digital lines cannot transmit analog data unless it is converted to a binary format first Encoder is used to convert the information transmitted by the sender and decoder converts the information back to its original form for the receiver Basic Concepts of Signals All data can be represented by electromagnetic signals. Depending on the transmission medium and the communications environment, either analog or digital signals can be used to convey information Any electromagnetic signal, analog | Transmission Methods Dr. Ming Huang Topics Bits, Signals, Frames, and Codes Transmission Modes Multiplexing Bits, Signals, and Codes A bit (binary digit) is the smallest unit of information N = 2n where N is the number of representations and n is the number of bits (ex. ASCII, Unicode, PCM code etc.) Data communications transfer information using codes that are transmitted as signals (either analog or digital) In general, analog lines provide a slow service that contains high error rates. However, digital lines cannot transmit analog data unless it is converted to a binary format first Encoder is used to convert the information transmitted by the sender and decoder converts the information back to its original form for the receiver Basic Concepts of Signals All data can be represented by electromagnetic signals. Depending on the transmission medium and the communications environment, either analog or digital signals can be used to convey information Any electromagnetic signal, analog or digital, is made up of a number of constituent frequencies. A key parameter is bandwidth. In general, the greater bandwidth of the signal, the greater its information-carrying capacity A frame contains data and control information. To distinguish between the two, data transparency is desired The designer of a communications facility must deal with four factors: bandwidth of the signal, data rate, transmission impairments, and the level of error rate that is acceptable Analog vs. Digital Analog vs. Digital (cont.) Transmission at high bit rates can only be sustained for a relatively short distance due to transmission impairments Analog Signals An analog signal is continuous and it can have an infinite number of values in a range. The primary shortcomings of analog signals is the difficulty to separate noise from the original waveform An example is a sine wave which can be specified by three characteristics: q(t) = A sin (2 p f t + f) A: amplitude f : frequency f : phase Sine Wave .
