Data Communications: History

• Data communications relates to the exchange of data between devices through a transmission medium like a wire cable.
• It involves transferring digital information between two or more points, typically in binary form.
• Data is defined as information stored in digital form.
• A network consists of devices (nodes or stations) interconnected by media links.

History of Data Communications

• 1753 represents the earliest method of electric communication, with a proposal for a 26-wire system for letters between villages.
• 1832 saw the invention of the first successful data communication system, the telegraph, by Samuel F. B. Morse, using binary-coded electrical signals.
• Morse also invented the Morse code
• In 1833, Carl Friedrich Gauss developed an unusual 5x5 matrix system for representing 25 letters (combining I and J).
• In 1840, Morse secured an American patent for the telegraph.
• 1844 marked the establishment of the first telegraph line between Baltimore and Washington, D.C., highlighted by the message "What hath God wrought!".
• 1849 witnessed the invention of the first slow-speed telegraph printer, with high-speed printers (15-bps) arriving around 1860.
• 1850 saw the formation of Western Union Telegraph Company to carry coded messages between individuals.
• 1874 - Emile Baudot invented a telegraph multiplexer, allowing up to six signals from different telegraph machines to transmit along a single wire.
• 1875: The telephone was invented by Alexander Graham Bell.
• 1899 - Guglielmo Marconi sent the first radio wireless telegraph messages
• In the late 1930s, Konrad Zuis, a German engineer, demonstrated a computing machine.
• 1940: Bell Telephone Laboratories developed the first special-purpose computer utilizing electromechanical relays for logical operations.
• February 14, 1946: Eckert and Mauchley are credited with beginning modern computing after having developed the ENIAC computer
• 1949: The U.S. National Bureau of Standards introduced the first all-electronic, diode-based computer for executing stored programs.
• 1950s: Computers utilized punch cards for input, printers for output, and magnetic tape reels for memory of information
• Batch processing was how early computers could complete one task at a time.
• The UNIVAC computer, built in 1951 by Remington Rand, stands as the first mass-produced electronic computer.
• 1969: The Internet began to evolve in
• 1970s: ARPANET was then created to connect sites in the United States, by the Advanced Research Projects Agency (ARPA).
• Intranets: Companies use private data communication networks among employees and resources for exchanging information.
• The World Wide Web (WWW): The World Wide Web (WWW) is a server-based application that allows subscribers to access the services offered by the Web.

Characteristics of Data Communications

• Delivery: Ensuring data reaches the correct destination.
• Accuracy: Maintaining the integrity of data during transmission.
• Timeliness: Delivering data in a timely manner.
• Jitter: Controlling variations in delay.
• A data communications system consists of a sender, a receiver, a message, a medium, and a protocol.

Data Representation

• Text represented as bit patterns, sequences of bits (0s or 1s).
• Numbers: also represented by bit patterns.
• Images composed of a matrix of pixels (picture elements) for a small dot.
• Audio pertains to the recording or broadcasting of sound or music.
• Video pertains to the recording or broadcasting of a picture or movie.
• Data flow can be simplex (one-way), half-duplex (either direction, but not simultaneously) or full-duplex (both directions simultaneously).

Network Topology

• Describes the layout and appearance
• Encompasses the way computers, cables, and data communication elements are interconnected physically and logically within a network
• Physical topology: how a network is physically laid out.
• Logical topology: how data flows within the network

Bus Topology

• Also known as multidrop or linear bus topology.
• Simplifies data flow control, as all stations receive every transmission.
• All remote stations are physically or logically connected via a single transmission line called a bus (main line or backbone).
• The most common, simplest, and fastest network setup.
• Advantages: Requires less wiring, is affordable, and easy to implement, especially suited for temporary networks.
• Disadvantages: Not fault tolerant with no redundancy
• Limited cable length
• Lacks the security of modern systems.

Ring topology

• The ring topology (or loop topology) features stations connected in tandem (series) to make a closed loop or circle.
• The physical connection is like a star topology, the devices are connected in a logically closed loop or ring.
• May be configured for traffic in one or both directions with bi-directional rings offering higher survivability.
• Employs bucket or token passing, has low expenses but disables if one station fails.
• Advantages: Better performance than Bus topology
• All nodes have equal access
• Disadvantages: Unidirectional and the whole network is affected by one point of failure
• Performance can decrease as the load increases
• Lacks the security of modern systems.

Star Topology

• It features cable segments connecting remote stations directly to a central location like a computer or central connectivity via a hub or switch multi port connector.
• Remote stations cannot communicate without relaying information through the hub.
• Economical for light traffic but becomes inefficient as traffic grows, thus survivability can be poor.
• Used commonly to connect many terminals and PCs to a larger mainframe or minicomputer.
• Advantages: Easy to design and implement due to a centralized administration.
• Disadvantages: Prone to bottlenecks and single point of failure
• Increases cost because of a switch/hub

Mesh Topology

• It is a fully connected one where station every possesses a direct point-to-point communications link toward any or all other stations in a network.
• Excellent survivability
• Considered to be the very most consistent and reliable of the network topologies.
• If full mesh connectivity is trully followed, it is expensive.
• Advantages: Fault tolerant , Reliable
• Disadvantages: Issues with broadcasting messages
• It is expensive and impractical for large networks

Number of Links Needed Formula for Mesh Topology

• L = n(n - 1) / 2
• L = number of links
• n = number of terminals

Formula for Number of I/O Ports Needed by Each Terminal for Mesh

• P = n - 1
• Where: P = number of input/output ports
• n = number of terminals

Two Primary Categories of Networks

• Local Area Network (LAN): Usually privately owned for linking devices within a single office, building, or campus.
• Wide Area Network (WAN): Provides long-distance transmission of information over large geographic areas that may comprise a country, a continent or the whole world.

Open Systems Interconnection (OSI)

• The name for a specific set of standards for communications among computers for the aim of serving as the structural set of guidelines for exchanging information between computers, networks and terminals
• OSI is endorsed by the ISO and ITU-T
• This model consists of 7 layer communications architecture reference model with the specific protocols of communicating built in those layers.
• The OSI models exists to specify communication protocols in which makes it less difficult to achieve and easier to accomplish compatibility amongst the system components

Application Layer

• It is the seventh as well as highest layer from the hierarchy.
• The most intelligent of all layers.
• Responsibilities include:
• Serving as the user/network interface
• Providing distributed information services
• Controlling the application action order
• Allowing network resources access

Presentation Layer

• The 6th layer following the session layer.
• Responsible to ensure any code or syntax is converted for presenting data in a standard communications format, and determining display.
• Providing independence to the programs of application as a service through the code and syntax conversion that is vital to the process
• Tasks includes:
  • dialogue procedures
  • algorithms for compressing data
  • synchronizing, disrupting, and terminating tasks
  • code and character set translation

Session Layer

• The 5th layer following the transport layer.
• Includes maintaining and managing communication sessions, as well as terminating these.
• The network availability helps and offers logical links to application through protocol transfers and sending emails
• User authentication using network logon and log off procedures
• Responsibilities:
  • Determining the dialogical available (full or half duplex or simplex)

Transport Layer

• The 4th layer following the session layer.
• Acts as the communication and interface in between both the network and session layer which acts as the very peak with regards towards highest layer for communications.
• Including to ensure through controlling and integrity the end-to-end for information with devices over the network and reliable transparent transport as protocols used.
• Responsibilities:
  • Error recovery
  • Segmentizing and segmenting
  • End to ensure end end integration/integrity

Network Layer

• The 3rd layer following the data link layer.
• Responsibilities:
  • Providing the details to enable efficient data routing
  • Logical Addressing and the process moving data with packets point-to-point for protocols.
• It takes a look at IP Addresses and the packets information units also consists of a great many the routing protocols to perform RIP & RIP

Data Link Layer

• The 2nd layer succeeding the physical layer.
• Responsibilities include:
  • Providing error-free communications
  • Maintaining Data integrity from node-to-node
  • Organizes bits into frames
  • It looks for medium access control address which looks for physical numbers with protocol like ARP,RARP, and ICMP

Physical Layer

• It is the first and lowest layer of the hierarchy.
• Responsibilities:
  • Providing that access towards a data communications Network
  • The actual propagation for unstructured data bits because, the a transmission occurs with the medium for both the bit rate, and determining the bit synchronization the media used.
• Looks at data by physical port numbers and has a unit of information as bits.

Character Types

• Data Link Control Characters: Facilitate the orderly flow of data from source to the destination
• Graphic Control Characters: Syntax or presentation of information that can take place on the received terminals.
• Alphanumeric Characters - To represent the various symbols that are utilized in a language such as the English language.

Error correction

• Symbol Substitution: To detect and error symbols are substituted for any character by errors.
• Retransmission: an error detection scheme and the receiving terminal automatically ask any retransmission for any information in any errors discovered.
• Forward Error: The only error correction at the end without calling retransmission.

Hamming Code

• A prominent error correction code developed by Richard Hamming.
• Used to correct errors in data channels. It implements the use to correct also to identify and to rectify data
• Limitations:
  • It can not correct multiple errors or burst errors.
  • Cannot Identify the errors that occur in its bits themselves Formula:2n > m + n + 1 Where n = number of correct Hamming-bits m = number of bits in the data character