Data Communication Fundamentals

• Telecommunication happens when communication occurs at a distance.
• Data is information presented in a format agreed upon for creation and use.
• Data communications involves exchanging data between two devices using a transmission medium like wire cables or wireless.
• To achieve accurate data communication, the following are necessary:
• Delivery happens at the correct destination.
• Accuracy of data.
• Timeliness of real-time transmission.
• Minimal jitter, to ensure even delay.

Data Communication Components

• A data communication system involves the following components:
• A message, which is the information to be communicated.
• A sender, which transmits the data.
• A receiver, which receives the data.
• A transmission medium, which is the channel through which data is sent.
• A protocol, which are the rules governing data communication.

Data Representation

• Data can be represented in various forms:
• Text
• Numbers
• Images
• Audio
• Video

Data Flow

• Simplex mode allows one-way communication.
• Half-duplex mode allows two-way communication, but only one device can send at a time.
• Full-duplex mode allows both devices to send and receive simultaneously.

Networks

• A network comprises devices called nodes connected by communication links.
• A node can be any device capable of sending or receiving data.

Network Criteria

• Networks are evaluated based on:
• Performance
• Reliability
• Security

Types of Connections

• Point-to-point involves a dedicated link between two devices.
• Multipoint involves multiple devices sharing a single link

Physical Topologies

• Mesh topology: Every device has a dedicated point-to-point link to every other device.
  • A fully connected mesh network with n devices requires n(n-1)/2 physical channels
  • Each device needs n-1 input/output ports.
  • Dedicated links carry traffic only between connected devices.
  • Advantages of mesh topology are:
  • Less traffic congestion
  • Robustness
  • Enhanced security
  • Ease of maintenance.
  • Disadvantages of mesh topology are:
  • High resource requirements (cable and ports)
  • Expense.
• Star topology: Each device connects to a central hub via a dedicated point-to-point link.
  • No direct link exists between devices.
    • Advantages of star topology are:
    • Lower cost
    • Easy installation and reconfiguration
    • Robustness.
    • The primary disadvantage is the single point of failure.
• Bus topology: All devices connect to a backbone cable via drop lines and taps.
  • Drop lines are connections between the device and the main cable
  • Taps either splice into the main cable or puncture its sheathing to make contact.
    • Advantage: Ease of installation
  • Disadvantages:
  • Difficult reconnection and fault isolation
  • A break in the bus cable can halt all transmission.
• Ring topology: Each device connects to exactly two other devices, forming a ring.
  • Each device incorporates a repeater for signal regeneration.
  • The advantages of a ring topology are:
  • Relatively easy to install and reconfigure.
  • Simplified fault isolation
  • Disadvantage: Unidirectional traffic.
• Tree topology: Integrates multiple topologies, such as connecting multiple star topologies to a bus.
  • It supports point-to-point wiring for individual segments
  • It has compatibility with hardware and software vendors.
  • The disadvantages are:
  • Limited overall length of each segment.
  • If the backbone line breaks, the entire segment fails.
  • More difficult to configure and wire.
• Hybrid Topology: A combination of different topologies, like a star backbone with bus networks.

Categories of Networks

• Local Area Network (LAN)

• Wireless Local Area Network (WLAN)

• Metropolitan Area Network (MAN)

• Wide Area Network (WAN)

• WAN types:

• Switched WANs connect through a network of switches

• Point-to-point WANs establish a direct link between two points via modems, etc.

• The Internet is a heterogeneous network made of interconnected networks.

Internet

• The Internet is a system that has transformed daily life, business practices, and leisure activities.
• Key milestones in its development include:
  • 1967: ACM
  • 1969: UCLA, UCSB, SRI, UoU
  • 1972: TCP
• Today, Internet Service Providers (ISPs) provide access to the Internet.

Internet Organization

• The Internet is hierarchically organized, with national, regional, and local ISPs.
• National ISPs interconnect through Network Access Points (NAPs).

Protocols and Standards

• A protocol is a set of rules
• Standards are agreed-upon rules.
• Protocols define the syntax, semantics, and timing of data communication:
• Syntax: the format of the data.
• Semantics: the meaning of each data section.
• Timing: when and how fast data should be sent.

Standards

• "De facto" standards are established by common usage or practice, but not formally approved.
• "De jure" standards are established by law.

Standard Organizations

• International Organization for Standardization (ISO)
• International Telecommunication Union - Telecommunication Standards (ITU-T)
• American National Standards Institute (ANSI)
• Institute of Electrical and Electronics Engineers (IEEE)
• Electronic Industries Association (EIA)

Network Models

• A network model is a layered architecture where tasks are divided into subtasks.
• Subtasks are implemented separately in layers within a stack.
• Functions are required in both systems.
• Peer layers communicate.
• Protocol:
• This represents a set of rules that govern data communication
• It is an agreement between communicating devices.

Tasks Involved in Sending a Letter

• The processes of sender, receiver, and carrier form a hierarchy of services.

OSI Model

• The International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model to standardize network communications. It was introduced in the late 1970s.
• ISO is the organization, and OSI is the model.

Layered Architecture

• Seven Layers:
• Layer 7: Application, interacts with the user applications using the network.
• Layer 6. Presentation, responsible for data representation, encryption, and decryption.
• Layer 5. Session, manages communication sessions between systems.
• Layer 4. Transport, handles reliable transmission.
• Layer 3. Network, handles routing of data packets.
• Layer 2. Data Link, handles the addressing and access to the medium.
• Layer 1. Physical, transmits the raw bit stream over the physical medium.
• A layered model has each layer performing a subset of required communication functions.
• Each layer relies on the next lower layer for more primitive functions
• Each layer provides services to the next higher layer
• Changes in one layer should not require changes in other layers
• The processes on each machine at a given layer are called peer-to-peer processes.

Peer-To-Peer Process

• Devices move downwards through the layers on the sending device during communication
• Signals move over the communication channel, and upward move to the receiving device.
• In a sending device, each layer adds its own information to messages received from the layer above.
• Data passes the whole message down an adjacent later.
• In the receiving device, messages are unwrapped layer-by-layer.
• Each process receiving and removing data meant only for it.
• Passing data, and network information down through the layers is possible by an interface, between each pair of adjacent layers
• The interface defines information and services that a layer must provide for the layer above it.

OSI Model Layers

• Physical Layer:
  • Responsible for the actual movements of individual bits from hop to hop.
  • Functions
  • Includes physical characteristics, interfaces and media
  • Representation of bits
  • Data rate specification
  • Bit synchronisation
  • Line configuration
  • Point-to-Point or MultiPoint
  • Physical topology, the actual layout of the network
  • Mesh, Star, Ring or Bus
  • Transmission mode
  • Simplex, Half-Duplex or Duplex
• Data Link Layer:
  • Responsible for moving any frames from one hop to the next.
  • Function
  • Framing, process of dividing bits of the physical layer into controllable frames
  • Physical Addressing, adds header to define sender/receiver of data unit
  • Flow Control, prevent fast sender overwhelming slow receiver
  • Error Control, mechanisms to detect/retransmit damaged/lost frames.
  • Access Control, determines which device has control over the link, at any given time
• Network Layer:
  • Delivery of individual packets, from the source host to destination host
  • It includes source-to-destination delivery
  • Original source must send packets to their final destination
  • Functions
  • Include logical Addressing: Assign sender and receiver with a logical address
  • Routing: when independent networks or links are connected to create internetworks
• Transport Layer:
  • Delivery of a message from one process to another
  • Process-to-Process Delivery
  • Functions
  • Port Addressing, uses port numbers to deliver packets to correct processes
  • Segmentation and reassembly, divides messages into transmittable segments
  • Connection Control, either connection-oriented or connection-less
  • Connection-Oriented: A virtual connection established between transport layers
  • Connection-less: The messages are treated independently; each packet travels the network using the best available route
  • Flow control, applied end-to-end, rather than across a single link
  • Error Control, applied end-to-end, to ensure the integrity of the information
• Session Layer:
  • Responsibilities include dialog control, synchronization.
  • It maintains and synchronizes interaction between communicating systems
  • Function
  • Dialog Control: Allows two systems to have dialog in half-duplex/full-duplex mode
  • Synchronization: Adds checkpoints to stream of data so, after a failure, transmission can continue from the checkpoint, not the beginning.
• Presentation Layer:
  • Responsibilities translation compression and encryptions
  • Translation: systems exchange information is different encoding formats
  • Encryption: sender transforms original information to another form, sends the new message
  • Compression: reduces number of bits contained in information
• Application Layer:
  • Provides services to the user.
  • Function
  • Network Virtual Terminal, a software version of a physical terminal, create this for remote log-in
  • File Transfer, allows user to access to manipulate files
  • Mail Services, allows users to redirect e-mails, collect email address, manage database email addresses
  • Directory Services, distributed databases for providing access to global information about various objects

Summary of Layers

• There is translation,encryption, and compression of data at the presentation layer
• The application layer allows for access to the network resources
• The network layer has packets from source, which move to their destination, also provides inter-networking
• Data Link Layer organizes bits into frames, and provides hop-to-hop delivery
• Transmits bits over a medium, provides physical/electrical specfications

TCP/IP Protocol Suite

• TCP/IP has five layers: physical, data link, network, transport, and application
• It relies on IP at the internet layer:

Internet Layer Protocols

• Address Resolution Protocol (ARP)
• Reverse Address Resolution Protocol (RARP)
• Internet Control Message Protocol (ICMP)
• Internet Group Message Protocol (IGMP)

Transport Layer Protocols Include

• User Datagram Protocol (UDP)
• Transmission Control Protocol(TCP)
• Stream Control Transmission Protocol (SCTP)

Addressing

• Four address levels are used to provide physical, logical, port, and specific addressing.

TCP/IP Addressing

• Includes four types of addresses, physical, logical, port and specific
• The physical layer has physical addresses
• The data link layer has underlying physical networks
• The network layer has IP and other the protocols
• The transport layer has transmission control protocol ( TCP), stream control transmission protocol (SCTP), user datagram protocol (UDP).
• The application layer is responsible for processes and has specific addresses.

Physical Addresses

• Physical addresses are imprinted on the Network Interface Card (NIC).
• Ethernet networks use a 48-bit (6-byte) physical address, also known as the MAC address
• This is shown as 12 hexadecimal digits separated every two digits by a colon
• Example Address: 07:01:02:01:2C:4B
• The MAC address is the address of a node, defined by the LAN or WAN.
• Included in the data link layers frame, and may change from hop to hop.

Logical Addresses

• Necessary for independent of physical, universal communications networks.
• Internet addresses are 32-bit, that uniquely define which is used
• The physical address will change from hop to hop, but logicals remain the same.

Port Addresses

• Processes are allocated a port address that is unique
• All port numbers are 16bit, with a range of 0 to 65535
• When data has "Destination port number it is needed for delivery.
• When data has "source port number" it is needed for receiving a reply as an acknowledgments.
• Example Port address: 753
• Physical addresses can change from hop to hop, but port and logcial addresses will remain the same

Specific Addresses

• Example email address: [email protected]
• Web URL Example: www.daystar.ac.ke
• The Domain Name System (DNS) translates URLs into IP addresses for resolution.
• www.example.com being translated into 208.77.188.166

Explore the basics of data communication, including its components, necessary conditions for accurate transmission, and various forms of data representation. Learn about messages, senders, receivers, transmission mediums, and protocols involved in data exchange between devices.