Data Communications PDF

Data Communications History 1753 - Proposal submitted to a Scottish magazine to run a communication line between villages comprising 26 parallel wires representing each letter of the alphabet. (1833) Carl Freidrich Gauss -​ German mathematician and physicist; Regarded as one of the greatest ma...

Data Communications History 1753 - Proposal submitted to a Scottish magazine to run a communication line between villages comprising 26 parallel wires representing each letter of the alphabet. (1833) Carl Freidrich Gauss -​ German mathematician and physicist; Regarded as one of the greatest mathematicians of all time. -​ Developed a system based on a 5x5 matrix representing 25 letters so messages could be sent in a single wire. (1834) Samuel Finley Breese Morse -​ American painter and inventor; Contributed to the invention of single-wire telegraph. -​ Invented the telegraph, the first successful data communication system that used binary coded electrical signals to transmit information. -​ Also developed Morse Code which uses dots and dashes. 1840 - Morse secured American patent for the telegraph. 1844 - The first telegraph line was established. First message conveyed - “What hath God wrought!” (1875) Alexander Graham Bell -​ Was a Scottish-born American inventor, scientist, and engineer -​ Credited with inventing the telephone. -​ Founded the American Telephone and Telegraph Company in 1885. (1899) Guglielmo Macorni -​ Italian inventor and radio pioneer -​ succeeded in sending radio (wireless) telegraph messages. 1957 Launch of Sputnik-1 - Earth’s first satellite -​ Launched into elliptical low orbit by the Soviet Union on October 4, 1957. 1963 Launch of Syncom-1 (February) -​ Intended to be the first geosynchronous satellite but was lost on the way due to electronics failure. 1963 Launch of Syncom-2 (July) -​ World’s first geosynchronous communications satellite -​ Experimental communications satellite placed over the Atlantic Ocean and Brazil. 1964 Launch of Syncom-3 (August) -​ Was the first geostationary satellite. -​ Provided live television coverage of the 1964 Olympic games in Tokyo. Diwata-1 - A.K.A PHIL Microsat-1 -​ First Philippine Satellite and Microsatellite launched. -​ Philippine Microsatellite launched to the ISS on MArch 23, 2016. Maya-1 - First Filipino Nanosatellite (June 2018 - November 2020). Maya-3 and Maya-4 (Oct 2021 - Aug 2022) -​ Filipino-made cube satellites; Returned to earth after 10-month mission. NETWORK Computer Network - two or more computers interconnected with one another for the purpose of sharing resources. Elements of Computer Network: ​ Protocols - rules and agreements on how the different parts of the network will operate. Protocol Stack - list or set of protocols used by the system ​ Data and Messages - information used or transmitted/received by the network. ​ Communications medium - interconnects the different devices in the network. ​ Devices - includes computers, routers, switches, bridges, hubs, etc. Classification of Computer Networks (according to geographic scope) ​ Personal Area Network (PAN) ​ Local Area Network -​ Computers confined to one building or cluster of buildings. -​ Usually privately owned. ​ Metropolitan Area Network -​ Computers located within a city or cluster of cities. -​ Usually use facilities of telecom or network service providers. ​ Wide Area Network -​ Computers located outside a building or cluster of buildings.  -​Computers may be located between two or more cities, or between two or more countries. ​ Global Area Network -​ Computers located in different countries around the world. (Internet) Network Model Server - computer or system that provides resources, data, services or programs to other computers over a network Client - makes the request to the server Two Basic Network Model Peer to peer - All computers share their resources with all the other computers in the network. Dedicated client/server - one or more computers are assigned as a server and the rest of the computers are client (Comp Shop) Network Topology - refers to the appearance or the way the network is laid out. Physical Topology - Refers to the physical layout of the computers in a network. Logical Topology - Describes how data actually flows through the network. Most Basic Topologies ​ Point to point (P2P) - Two stations are connected. ​ Multipoint - Connects three or more stations. NETWORK TOPOLOGY Point to Point - Only two stations are connected by transmission medium. Pros: Very simple. Cons: Less stations can communicate with each other directly. Physical Mesh Topology - every station has a direct two point communication to every other station. Also known as fully connected. Pros: -​ Computer can communicate easily. -​ Robust (Data can have alternate routes). -​ Has more privacy and security. -​ Easier fault isolation.  Cons: -​ More expensive and bulkier cabling lines -​ More communication ports are needed. -​ More cumbersome installation and reconnection. -​ Could have higher total cost of ownership. Physical Star Topology - Stations are connected directly to a centrally located device which acts like a multipoint connector. Central node is sometimes called the central control/switch. Pros: -​ If one computer fails, others can still communicate. -​ Requires less cable and communication ports than mesh. -​ Less expensive than mesh. -​ Easier to install than mesh. Cons: -​ If the central hub breaks down, all communications are down. -​ Less robust compared to mesh topology. -​ Often requires more cable than bus. Physical Bus Topology - All stations are connected to a single transmission medium. Also called multidrop, linear bus, horizontal bus. Pros: -​ Requires no special routing/circuit switching. -​ Not necessary to store and forward messages. -​ Requires less cable than other topologies. -​ Requires less communication ports than ring and mesh. Cons: -​ Computer could not communicate anytime (due to collision). -​ If cable breaks down, the entire network could be disrupted. -​ More difficult fault isolation. -​ Not suitable when stations are transmitting most of the time. Physical Ring Topology - All stations are connected in tandem to form a closed loop or circle Pros: -​ Requires less cable than mesh. -​ Requires less communication ports than mesh. -​ Relatively easy to install -​ Could be less expensive than mesh Cons: -​ Delay is longer at non-adjacent stations. -​ If one cable breaks down, the entire network could be disrupted. -​ Requires more communication port than bus or star. Physical Tree Topology - A central root node (top level of hierarchy) is connected to one or more other nodes that are one level lower. Pros: -​ Leaf nodes can add one or more nodes in the hierarchical chain. Provides high scalability -​ The other nodes in the network are not affected if one of their nodes are damaged. -​ Provides easy maintenance and easy fault identification. -​ Can hold more nodes Cons: -​ Very difficult to configure compared to other topologies. -​ Presence of large number of nodes makes the network of topology a bit slower, -​ If the first level is erroneous, the next level will also have a problem. -​ Requires a large number of cables compared to star and ring. Hybrid - combines two or more complex traditional topologies to form a large, more complex topology. Pros: -​ Combines the benefits of traditional topologies used. Cons: -​ Combines the disadvantages of different topologies used.