Notes On Communication Systems

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Term | Definition- Communication systems | Communication system | * Systems that enable users to send and receive data and information * Source, transmitter, transmission medium, receiver, destination | Synchronizing | * Asynchronous * Sending each character/packet separately using special stop and start bits * Inexpensive * Slow transmission speed * Synchronous * Requires all data to be sent at the same time. * Faster and more efficient | Protocol | * A set of rules that governs the transfer of data between computers. * It defines how the information be transmitted and how the errors are detected * Two computers must use the same protocol to communicate | Handshaking | * A series of signals made between computers to indicate the type of protocol to use. | Hardware flow control | * Uses a wire to connect devices in a network | Software flow control | * Uses a special code sent with the data. * Used for long distances. | Parity checking | * An error detection method of checking for errors by using an additional bit called a parity bit. * Only 50% accurate * When an odd parity bit is chosen, the number of 1’s in the message must be odd | Checksum | * Checking for errors by dividing the data packets and summing up the number of bits * If the count matches at destination, then they assume a successful arrival * However, the order of arrival may be incorrect | Cyclic redundancy check | * The data is divided by a fixed divisor and the remainder is put in the trailer. * If the same remainder is calculated at the destination, then successful * 99.99% accurate | Error correction | * Retransmit data * Character substituting. | Application level | HTTP: * Hypertext transfer protocol * Protocol in web browsers to communicate and receive web pages SMTP: * Simple mail transfer protocol * Used to allow sending and receiving of email addresses using internet SSL: * Secured socket layer * Provides security when transferring data over the internet * Encrypts data into a code. | Communication control and addressing level | TCP * Transmission control protocol * Transmits data across the internet * Checks for errors using checksum * Ensures that every byte is sent and received. * Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. IP * Controls the address part of each data packet (datagram) so it gets to the right destination. * IP doesn’t guarantee that they will successfully reach the destination. * Helps data packets to move from sender to receiver. | Transmission level | * Ethernet and Token ring * Ways of transmitting messages between nodes in different networks * Ethernet- star and bus networks * Operates in the physical level and it must have the required hardware requirements to send and receive data. * The first LAN access method. * Allows data to be transmitted to all nodes simultaneously based on the network in both directions * A node transmits data when there is no signal on the bus. * All nodes can sense signals on the network through CSMA/CD * Token Ring- ring networks * A LAN access method * Sending the message via a ‘token’ and the destination node acknowledges it and sends back to the original node. | Bus topology | * Nodes are attached to a direct line called a bus * All nodes only recognize data intended for it. * Data collisions can occur if many data packets are sent simultaneously. | Star topology | * Has a central computer with all other nodes connected to it * All messages are sent through the central node * Most common for LAN networks * Network is dependent on the reliability and efficiency of central node. | Ring topology | * All nodes are arranged so the
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