03 Handout 1 - 03 Transmission Modes (Midterm).pdf

IT2006 Transmission Modes Dataflow Transmission In a simplex transmission, data can only flow in one direction, which is usually from the source to the sink. In a half-d...

IT2006 Transmission Modes Dataflow Transmission In a simplex transmission, data can only flow in one direction, which is usually from the source to the sink. In a half-duplex transmission (HDX), data can flow in both directions, but never simultaneously. It first flows in one direction, and then in the other direction. In a full-duplex transmission (FDX), data can flow in both directions simultaneously. It can be viewed as a pair of simplex lines between the source and sink with one line going from the source to the sink and the other going from the sink to the source. Data Transmission Serial data transmission - when data is sent or received, the data bits are organized in a specific order since they can only be sent one after another. o Asynchronous transmission is used when data is transmitted as individual characters. In this method, each character is preceded by one start bit and one or two stop bits that are used by the receiver for synchronization purposes. o Synchronous transmission is used to transmit large blocks of data at a time. In this scheme, data is usually organized in frames and each frame is preceded by a flag that consists of a few bits and terminated by another flag. Parallel data transmission - multiple data bits are transmitted over multiple channels at the same time. Transmission Media Transmission media is a communication channel that carries the information from the sender to the receiver in which data is transmitted through the electromagnetic signals via copper wire, fiber optics, atmosphere, water, and vacuum. The function of these transmission media is to carry the information in the form of bits through the network. Guided media enables the transfer of information between two or more points that are connected by an electrical conductor. Twisted Pair - it consists of two insulated copper wires that are typically about 1mm thick and twisted together in a helical form. Coaxial Cable - to facilitate two-way communication, the cable bandwidth is split into two sets of channels: upstream channels and downstream channels. Optical Fiber - refers to the medium and the technology associated with the transmission of information as light pulses along a glass or plastic wire or fiber the optical cable. Unguided media do not require physical links between two or more devices. Wireless communication is based on radio waves communications in the frequency spectrum. o Radio waves –These are easy to generate and can penetrate through buildings. The sending and receiving antennas need not be aligned. Example: AM and FM radios and cordless phones. 03 Handout 1 *Property of STI  [email protected] Page 1 of 4  IT2006 o Microwaves – It is a line of sight (LOS) transmission i.e. the sending and receiving antennas need to be properly aligned with each other. The distance covered by the signal is directly proportional to the height of the antenna. These are majorly used for mobile phone communication and television distribution. o Infrared – Infrared waves are used for very short distance communication. They cannot penetrate through obstacles. This prevents interference between systems. It is used in TV remotes, wireless mouse, keyboard, printer, etc. Antennas It is the metal rod or dish that catches radio waves and turns them into electrical signals feeding into something like a radio or television or a telephone system. Log Periodic Antennas It is a directional antenna that is made of a series of dipoles placed along its axis at different space intervals of time followed by a logarithmic function of frequency. Wire Antennas These antennas use a length of wire for transmitting and receiving wavelengths of signals. Traveling Wave Antennas It is a directional aperiodic antenna that uses a travelling wave as its guiding structure. A traveling wave is a temporary wave that creates a disturbance and moves along the transmission line at a constant speed. Microwave Antennas This type of antenna uses microwave transmission to broadcast signals between two or more locations. Microwave is a form of electromagnetic radiation that is used mostly in point-to- point communications and radar. Frequency Spectrum It is the range of frequencies contained by a signal. The following are the frequencies that are designated by the International Telecommunications Union (ITU). EXTREMELY LOW FREQUENCY VERY HIGH FREQUENCY ELF Frequency: 3 KHz to 30 KHz VHF Frequency: 30 MHz to 300 MHz Wavelength: 100 km to 10 km Wavelength: 10 m to 1 m LOW FREQUENCY ULTRA HIGH FREQUENCY LF Frequency: 30 KHz to 300 KHz UHF Frequency: 300 MHz to 3000 MHz Wavelength: 10 km to 1 km Wavelength: 1 m to 100 mm MEDIUM FREQUENCY SUPER HIGH FREQUENCY MF Frequency: 300 KHz to 3000 KHz SHF Frequency: 3 GHz to 30 GHz Wavelength: 100 km to 10 km Wavelength: 100 mm to 10 mm HIGH FREQUENCY EXTREMELY HIGH FREQUENCY HF Frequency: 3 MHz to 30 MHz EHF Frequency: 30 GHz to 300 GHz Wavelength: 100 m to 10 m Wavelength: 10 mm to 1 mm 03 Handout 1 *Property of STI  [email protected] Page 2 of 4  IT2006 Wave Propagation These waves are basically defined as superimposed oscillations of an electric and a magnetic field in space with their direction of propagation perpendicular to both. These are the following propagation that is currently used today: Ground Wave This is used for a low-frequency range transmission, mostly less than 1 MHz. This type of propagation employs the use of large antennas order of which is equivalent to the wavelength of the waves and uses the ground or Troposphere for its propagation. Sky Wave This is used for the propagation of EM waves with a frequency range of 3-30 Mhz. These waves makes the use of ionosphere in which it is the ionized part of the earth’s upper atmosphere. Space Wave This is used for a line of Sight communication (LoS). Space satellite communication and very high- frequency waves use this propagation Source: https://images.app.goo.gl/DbyHBKhadNxNvThy8 method. Multiplexing Multiplexing (MUX) is a way of sending multiple signals or streams of information over a communications link at the same time in the form of a single, complex signal. The receiver recovers the separate signals, a process called demultiplexing. Networks use multiplexing for two reasons: To make it possible for any network device to talk to any other network device without having to dedicate a connection for each pair. To make a scarce or expensive resource stretch further. In layman’s term, multiplexing is having multiple inputs and outputs in a single line medium. Media Sharing Technique The utilization of such media can be increased by allowing multiple users to transmit their data simultaneously, or close to simultaneously. Frequency-division multiplexing (FDM) where the frequency spectrum of the medium is partitioned into multiple frequency blocks called channels that are assigned to users who can use these channels simultaneously without interference from each other. Time-division multiplexing (TDM) where transmission time is divided into non-overlapping time slots that are assigned to users. Transmissions are staggered using a round-robin method to schedule the transmissions. Spread spectrum (SS) where the output signal, which appears like noise, occupies more bandwidth than the original signal. 03 Handout 1 *Property of STI  [email protected] Page 3 of 4  IT2006 Source: https://images.app.goo.gl/cL28QBmeCy7WzUu36 Media Access Methods Carrier Sense Multiple Access with Collision Detection (CSMA/CD) o Carrier Sense means that each station on the LAN continually listens to (tests) the cable for the presence of a signal before transmitting. o Multiple Access means that many computers are attempting to transmit and compete for the opportunity to send data (i.e., they are in contention). o Collision Detection means that when a collision is detected, the stations will stop transmitting and wait a random length of time before retransmitting the data. Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) o Instead of detecting and reacting to collisions, CSMA/CA tries to avoid them by having each computer signal its intention to transmit before transmitting. Token passing o It is a media access method by which collisions are prevented. Collisions are eliminated under token passing because only a computer that possesses a free token (a small data frame) can transmit. This method also allows different priorities to be assigned to different stations on the ring. Demand priority o In demand priority, an active hub is an essential requirement that can control access to the network. The terminals on a network are required to obtain permission from the hub before they start transmitting the bytes over a network. References: Ibe, O. (2018). Fundamentals of Data Communication Networks [1st ed.]. US: Wiley. Kurose, F., et. al. (2017). Computer Networking – A Top-Down Approach [7th ed.]. NY: Pearson. Media Access Methods. (n.d.). In Mysolutionguru.com. [Web Article]. [Web Content]. Retrieved on April 23, 2020 https://www.mysolutionguru.com/ps/media-access-methods/112 Propagation of Electromagnetic Waves. (n.d.). In toppr.com. Retrieved on April 23, 2020 from https://www.toppr.com/guides/physics/communication-systems/propagation-of-electromagnetic-waves/ Sklar, B. (2017). Digital Communications – Fundamentals and Applications [2nd ed.]. NJ: Prentice Hall. Speidel, J. (2019). Introduction to Digital Communications. Switzerland: Springer Nature. Woodford, C. (April 21, 2019). Antennas and transmitters. [Web Article]. Retrieved on April 23, 2020 from https://www.explainthatstuff.com/antennas.html 03 Handout 1 *Property of STI  [email protected] Page 4 of 4