Lecture 3: Wire Circuits and Synchronization PDF

ECEN100 Communications 4: Data Communications LECTURE 3: WIRE CIRCUITS AND SYNCHRONIZATION Introduction to Wire Circuits Types of Wire Circuits Two-wire Circuits. It uses a single pair of wires to carry signals, one wire for signals,...

ECEN100 Communications 4: Data Communications LECTURE 3: WIRE CIRCUITS AND SYNCHRONIZATION Introduction to Wire Circuits Types of Wire Circuits Two-wire Circuits. It uses a single pair of wires to carry signals, one wire for signals, signals and one wire for ground. ground In this type of circuit, data transmission occurs in one direction at a time, which is known as half-duplex half-duplex communication. The same pair of wires is used for both sending sending and receiving receiving signals, but not simultaneously. Ground is explicitly included to provide common reference and complete the circuit for signal. Four-wire Circuits It uses two pairs of wires—one pair for transmitting transmitting and another pair for receiving receiving signals. An additional ground wire is optional but often included. The separation of sending and receiving paths helps reduce interference interference and allows for higher data higher data transfer rates. In 4-wire circuits, ground ground may not be explicitly required because the differential differential pairs already handle signal integrity and noise rejection. The following wires are: a. Transmit DataPositive Transmit Data Positive (TD+). Carries positive side of the differential signal for transmitting. b. Transmit DataNegative Transmit Data Negative (TD-). Carries the negative side of the differential signal for transmitting. ReceiveData c. Receive Data Positive Positive (RD+). Carries the positive side of the differential signal for receiving. d. Receive ReceiveData Negative (RD-). Data Negative Carries the negative side of the differential signal for receiving. Methods of Switching Circuit Switching. It establishes a dedicated dedicated communication path between two devices for the duration of the communication session. Data is transmitted along the established path with a consistent bandwidth bandwidth and latency. latency Traditional telephone networks are a prime Traditional telephone example of circuit-switched systems. Packet Switching. Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Packet switching divides divides data into small packets packets , which are sent independently through the network and reassembled at the destination. If a path fails, packets can be rerouted rerouted through alternate paths, providing greater reliability. Modern Modern data data networks networks, including the Internet, predominantly use packet switching. Data Encoding Techniques Techniques used for different types of transmission a. Analog to Analog signal – Amplitude Modulation, Frequency Modulation, Phase Modulation b. Analog to Digital signal – Pulse Code Modulation, Delta Modulation c. Digital to Analog signal – Amplitude Shift Keying, Frequency Shift Keying, Phase Shift Keying d. Digital to Digital signal – Non Return to Zero, Return to Zero, Manchester, Differential Manchester, Bipolar Encoding Encoding Encoding is the process of using various patterns of voltage or current levels to represent 1s and 0s of the digital signals on the transmission link. The common types of line encoding are Unipolar, Unipolar Polar, Polar Bipolar, Bipolar and Manchester. Manchester The data encoding technique is divided into the following types, depending upon the type of data conversion. Unipolar Scheme All signals are either above above or below below the axis. a. NRZNRZ (Non Return to Zero) - positive voltage (Non Return to Zero) defines bit 1 and the zero voltage defines bit 0. Signal does not return to zero at the middle of the bit thus it is called NRZ. Polar Scheme both sides of the axis. Voltages are on both a. NRZ-L (NRZ-Level) - the level of the voltage determines the value of the bit, typically binary 1 logic-level high map to logic-level high, and binary 0 maps to logic-level low. Some systems use the opposite logic-level low convention depending on the assumption assumption of level. b. NRZ-I (NRZ-Invert) - two-level signal has a transition at a boundary if the next bit that we are going to transmit is a logical logical 11, and does not have a transition if the next bit that we are going to logical 00 transmit is a logical c. RZ (Return to Zero) - uses three three values positive, negative, and zero and in this scheme signal goes to 0 in the middle middle of each bit, for bit 1 half of the signal is represented by +V +V and half by zero and for bit 0 half of the signal is represented by -V -V and half by zero voltage. d. Manchester Manchester - for bit 1 there is transition form - VVto +V volts in the middle of the bit and for bit to +V Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications 0 there is transition from +V +V to -V volts in the middle of the bit. to -V Differential Manchester e. Differential Manchester - there is always a transition at the middle middle of the bit but the bit values are determined at the beginning of the bit. If the next bit is 0,0 there is a transition, transition if 1 there is no the next bit is 1, transition no transition Bipolar Schemes In this scheme there are three three voltage levels positive, negative, and zero. The voltage level for one data element is at zero, while the voltage level for the other element alternates between positive and negative. Alternative Mark a. Alternative Mark Inversion (AMI) (AMI) - neutral Inversion zero voltage represents binary 0. Binary 1’s are alternating represented by alternating positive and negative voltages Pseudoternary - bit 1 is encoded as a zero b. Pseudoternary zero voltage and the bit 0 is encoded as alternating alternating positive and negative voltages Synchronization Methods Synchronous Transmission Asynchronous Transmission Data is sent in form of blocks or frames Data is sent in form of bytes or characters Transmission is fast Transmission is slow Transmission is costly Transmission is economical Time interval of transmission is constant Time interval of transmission is not constant, it is random Users have to wait till the transmission is Users do not have to wait for the completion of complete before getting a response back from transmission in order to get a response from the the server server No gap present between data Gap present between data Efficient use of transmission lines is done Transmission line remains empty during a gap in character transmission Start and stop bits are not used in transmitting Start and stop bits are used in transmitting data data that imposes extra overhead Needs precisely synchronized clocks for the Does not need synchronized clocks as parity bit information of new bytes is used in this transmission for information of new bytes Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering  ECEN100 Communications 4: Data Communications Errors are detected and corrected in real time Errors are detected and corrected when the data is received Low latency due to real-time communication High latency due to processing time and waiting for data to become available Examples: Telephonic conversations, Video Examples: Email, File transfer,Online forms conferencing, Online gaming Prepared by: Engr. Rhodonelle S. Duatin, ECE, ECT, RAOC Department of Computer, Electronics and Electrical Engineering