Data Communication Systems

Data Communications Systems

• Data transmission occurs over communication lines like telephone lines or cables.
• Data transmission systems evolved from centralized data processing to distributed processing and networked personal computers.

Centralized vs. Distributed Data Processing

• Centralized Data Processing means all hardware, software, and processing are in one location.
• The need for physical transport of data makes this inconvenient.
• Distributed Data Processing means computers are located remotely with access to a central system.
• Efficiency is improved because some processing occurs locally.
• Used in businesses with multiple locations.

Networks and Network Components

• Networks connect computers and resources via communication equipment.
• A Local Area Network (LAN) shares data within an office or building.
• Basic Network Components include sending/receiving devices, communication links, and modems.
• Sending device: The source of data transmission.
• Communication link: The medium through which data is transmitted.
• Receiving device: The endpoint that receives the transmitted data.
• Modem: Converts digital data into transmittable signals and vice versa.

Digital vs. Analog Transmission

• Digital Signals: Data represented as discrete electrical pulses (0s and 1s).
• Analog Signals: Continuous signals used in traditional telephone lines that require conversion for digital devices.
• Modulation: Conversion of digital signals to analog for transmission over telephone lines.
• Demodulation: Conversion of analog signals back to digital for computer processing.
• Carrier wave properties: Amplitude Modulation (AM) varies the height of the wave while Frequency Modulation (FM) varies the frequency of the wave to encode data.

Modems & Data Transmission Speeds

• External Modem: Separate from the computer, connected via cables.
• Internal Modem: Built directly into the computer.
• PC Card Modem: Small, portable modem for laptops.
• Data Speeds are measured in bits per second (bps).
• Early modems: 300 bps.
• Modern modems: Up to 56,000 bps (FCC limits receiving speeds to 53,000 bps).

Communication Devices & Transmission Technologies

• ISDN (Integrated Services Digital Network): Uses a special telephone circuit for data transmission at 128,000 bps and supports multiple simultaneous connections.
• DSL (Digital Subscriber Line): Uses telephone lines for high-speed internet. Always on but requires proximity to a switching office.
• Cable Modems: Uses coaxial cables for high-speed data transfer, bandwidth is shared among users, affecting performance.
• Cellular Modems: Utilize mobile networks for internet access but are typically slower than wired connections.

Data Synchronization & Transmission Modes

• Asynchronous transmission sends data one character at a time, each with start and stop signals.
• Synchronous transmission transmits large blocks of data together, increasing efficiency.
• Simplex: One-directional communication (e.g., TV broadcast).
• Half-Duplex: Data flows both ways, but only one direction at a time (e.g., walkie-talkies).
• Full-Duplex: Simultaneous two-way communication (e.g., phone calls).

Communication Media & Bandwidth

• Wire Pairs: Traditional telephone wiring.
• Coaxial Cables: Used for cable TV and internet.
• Fiber Optics: Uses light signals for high-speed data transmission.
• Microwave Transmission: Wireless, line-of-sight communication.
• Satellite Transmission: Used for global communication.
• Wireless Transmission: Includes Wi-Fi and cellular data.
• Bandwidth measures the data-carrying capacity of a communication link.

Network Protocols & Standards

• A Protocol is a set of rules that govern how data is exchanged between devices.
• Transmission Control Protocol/Internet Protocol (TCP/IP): The fundamental protocol suite that enables internet communication.
• Network Topologies include star, ring, and bus:
• Star: All devices connect to a central hub.
• Ring: Devices are connected in a circular format.
• Bus: All devices share a single communication line.

Wide Area Networks (WANs) & Components

• WAN: A network spanning large geographic areas such as cities or countries.
• Metropolitan Area Network (MAN): A network covering a single city.
• WAN Components include: Communications services (switched and dedicated), WAN hardware (mainframe computers, front-end processors, and multiplexers), and WAN Software (handles data transfer between PCs and mainframes).

Local Area Networks (LANs)

• LAN: A network connecting computers within a confined space, such as an office or home.
• LAN components include network cables, Network Interface Cards (NICs), routers, and gateways.
• Network Cables: Physical medium for data transmission.
• Network Interface Cards (NICs): Enable network connectivity in computers.
• Routers: Direct traffic between networks.
• Gateways: Convert protocols for communication between different networks.
• A Wireless Access Point enables wireless connections in a LAN.

Network Models & Uses

• Client/Server Model: A centralized system where the server manages resources and clients request services.
• Peer-to-Peer Model: All computers have equal status and share resources. Common in small offices, though performance may be slower.
• LAN Protocols: Ethernet, the most widely used LAN technology, and Token Ring, where data is passed sequentially around the network.

Networking Fundamentals Reviewer

What is a Network?

• A network refers to two or more connected computers that can share resources such as data, a printer, an Internet connection, applications, or a combination of these resources.

Types of Networks

• Local Area Network (LAN): Covers a small geographical area like a home, school, or office.
• Metropolitan Area Network (MAN): Spans a city or large campus.
• Wide Area Network (WAN): Covers large geographical areas, often using leased telecommunication lines.

WAN Technologies

• Circuit-Switched: Uses asynchronous and synchronous serial connections like ISDN and leased lines.
• Leased Line: A dedicated communication line reserved for continuous use between locations.
• Broadband Access: Includes cable, DSL, and wireless WAN.
• Frame Relay: Uses synchronous serial connections.

Network Topologies

• Bus Topology: All devices share a single communication line.
• Star Topology: All devices connect to a central hub.
• Extended Star Topology: Multiple star networks connected together.

OSI Model and Its Layers

• The OSI (Open Systems Interconnection) model is a conceptual framework that divides network communication into seven layers to standardize and simplify networking.
• Layer 1 - Physical Layer: Defines electrical, mechanical, and procedural aspects of data transmission and specifies transmission media (twisted-pair cables, fiber optics, wireless) and Converts data into electrical, optical, or radio signals.
• Layer 2 - Data Link Layer: Provides physical addressing using MAC addresses and handles error detection and correction.
• MAC (Media Access Control): Controls access to the network medium.
• LLC (Logical Link Control): Manages frame synchronization and error checking. Devices: Switches, Bridges.
• Layer 3 - Network Layer: Responsible for logical addressing and path selection and uses IP addressing to identify devices and handles packet routing across different networks. Devices: Routers, Layer 3 Switches.
• Layer 4 - Transport Layer: Ensures end-to-end communication reliability and uses TCP (Transmission Control Protocol) for reliable, connection-oriented communication and uses UDP (User Datagram Protocol) for faster, connectionless communication and handles flow control and error recovery.
• Layer 5 - Session Layer: Establishes, manages, and terminates communication sessions and controls dialogue between devices.
• Layer 6 - Presentation Layer: Translates data formats for compatibility between systems and handles encryption, compression, and encoding and ensures readable data transmission for applications.
• Layer 7 - Application Layer: interfaces with end-user applications and provides network services such as HTTP (web browsing), FTP (file transfer), SMTP (email), and DNS (domain name resolution) and enables applications to send and receive data over the network.

Physical Media Types

• Twisted-Pair: Uses RJ-45 connectors.
• Coaxial: Uses BNC connector.
• Fiber Optics: High-speed, long-distance transmission.
• Wireless: Uses radio signals for transmission.

Network Devices

• Hub (Repeater): A device that broadcasts data to all ports, a central connection point for several network devices.
• Switch: Forwards data to the correct destination using MAC addresses.
• Router: Routes data packets between networks.
• Layer 3 Switch: Combines switching and routing functions.
• Gateway: Connects dissimilar networks by translating protocols.
• Firewall: Manages network security and access control.

Data Link Layer

• Handles MAC addressing.
• Devices operating at this layer included bridges and switches.

Network Layer

• Uses IP addressing for logical identification.
• Devices: Routers and Layer 3 Switches.

Transport Layer

• Uses TCP for reliable transmission and UDP for faster, connectionless communication.

Firewalls

• Protects networks by managing traffic between internal and external environments.

Gateway

• Combination of hardware and software that connects dissimilar network environments.

Exploring the Network - Comprehensive Reviewer

Networks in Our Daily Lives

• The "human network" allows for global connectivity.
• Advancements in networking technologies create a world without boundaries.
• The Internet has impacted education, work, and entertainment.

The Role of Networks in Learning, Working, and Playing

• Online learning eliminates the need for physical classrooms.
• Methods of communication include: Texting, Social Media, Collaboration Tools, Blogs, Wikis, Podcasting.
• Online gaming and entertainment are heavily supported by networks.

Types and Sizes of Networks

• Small Home Networks: Connects a few devices to the Internet.
• Small Office/Home Office (SOHO): Connects a home or remote office to a corporate network.
• Medium to Large Networks: Hundreds or thousands of interconnected computers.
• World Wide Networks: Millions of computers connected globally (e.g., the Internet).

Clients, Servers, and Peer-to-Peer Networks

• Clients request services, servers provide them (e.g., web, email servers).
• Peer-to-Peer Networks: no dedicated server, each device acts as both client and server.
• Easy set up, low cost, less secure & not scalable.

Network Overview

• A network can be as simple as a single cable connecting two computers or as complex as a collection of networks that span the globe.
• Network infrastructure contains three broad categories of network components: Devices, Media, Services.

Network Components

• End Devices: The origin and receiver of any message. Examples include computers, smartphones, printers, and tablets.
• Intermediary Devices: Interconnects the end devices in the network; examples include switches, wireless access points, routers, and firewalls. They regenerate and retransmit data signals, maintain information about pathways through the network, and notify other devices of errors and communication failures.
• Network Media: Communication across a network occurs through a medium. There are three types of network media: Metallic Wires (Copper): Includes twisted-pair and coaxial cables. Fiber Optics (Glass): High-speed data transmission over long distances. Wireless Transmission: Uses radio waves, microwave or infrared for communication.

Network Representations and Topologies

• Network Representations: Network diagrams, often called topology diagrams, use symbols to represent devices within the network.
• Network Interface Card (NIC): Hardware component enabling network connectivity.
• Physical Port: Connection point on a device for network communication.
• Interface: A point of interaction between different components or networks.
• Physical Topology: Actual layout of devices.
• Logical Topology: Flow of data within a network.
• Common Topologies: Bus, Star, Ring, Mesh.

Types of Networks

• Local Area Network (LAN): Small geographic area, high speed.
• Wide Area Network (WAN): Large area, slower speed, managed by multiple providers.
• Other Networks: Metropolitan Area Network (MAN), Wireless LAN (WLAN), Storage Area Network (SAN).

Internet, Intranets, and Extranets

• Internet: Global interconnection of LANs and WANs.
• Intranet: Private network for an organization.
• Extranet: Controlled access for external users.

Internet Access Technologies

• Home/Small Office:
• Cable: High bandwidth, always-on Internet provided by cable TV companies.
• Digital Subscriber Line (DSL): High-speed Internet over telephone lines.
• Cellular: Uses mobile networks (3G, 4G, 5G) for wireless Internet access.
• Satellite: Provides Internet access in remote or rural areas where other connections are unavailable.
• Dial-up: Low-speed, inexpensive option using traditional telephone lines.
• Business Class:
• Leased Lines: Dedicated circuits within the service provider's network for private voice and data.
• Ethernet WAN: Extends LAN technology over wide areas using service providers.
• Business DSL: Variants like SDSL (Symmetric DSL) provide balanced upload/download speeds.
• Metro Ethernet: High-speed connections designed for businesses within metropolitan areas.

Traditional vs. Converged Networks

• Traditional: Separate networks for voice, data, and video.
• Converged: Single infrastructure for multiple services.

Network Architectures

• Fault Tolerance: Redundancy in case of failures.
• Scalability: Can expand without performance issues.

Other architecture qualities

• Quality of Service (QoS): Ensures priority for critical applications and ensures reliable delivery of content for all users.
• Security: Protection from unauthorized access.

Network Security

• Infrastructure Security: Protection of network devices.
• Information Security: Ensuring confidentiality, integrity, and availability.
• Security Threats: Viruses, hacker attacks, denial-of-service (DoS), data theft.
• Security Solutions: Firewalls, Intrusion Prevention Systems (IPS), VPNs.

Emerging Trends in Networking

• Bring Your Own Device (BYOD): Employees use personal devices for work.
• Online Collaboration: Cisco WebEx, video conferencing.
• Cloud Computing: Access to storage and applications over the Internet; Includes public, private, hybrid and custom clouds.
• Smart Home Technology: Internet-connected appliances.

Powerline Networking and Wireless Broadband

• Powerline Networking: Uses electrical wiring for network connections.
• Wireless Broadband: Uses mobile networks or wireless ISPs for connectivity.

Network Protocols and Configuration - Comprehensive Reviewer

Importance of Protocols in Network Communication

• Protocols define rules for network communication.
• Enable interoperability between different devices and software.
• Ensure reliability, security, and efficiency in data transfer.

Standards Organizations in Networking

• Internet Society (ISOC): Oversees Internet development.
• Internet Architecture Board (IAB): Develops Internet standards.
• Internet Engineering Task Force (IETF): Maintains TCP/IP technologies.
• Internet Corporation for Assigned Names and Numbers (ICANN): Manages IP address allocation and domain names.
• Institute of Electrical and Electronics Engineers (IEEE): Develops networking standards.
• Telecommunications Industry Association (TIA): Sets radio, VoIP, and satellite communication standards.
• International Telecommunications Union (ITU-T): Creates standards for broadband, IPTV, and video compression.

Communication Rules and Message Formatting

• Encapsulation: Data is formatted into a frame before transmission.
• Message Size: Large messages are broken into smaller frames.
• Message Timing:
• Access Method: Determines when devices can send data.
• Flow Control: Prevents overwhelming the receiver.
• Response Timeout: Defines wait time for acknowledgments.
• Message Delivery Options: Unicast (one-to-one), Multicast (one-to-many), and Broadcast (one-to-all).

Network Protocols

• Define the format and rules for message exchange.
• Examples: HTTP, TCP, IP, Ethernet.
• Protocol Interaction
• HTTP → Application Layer (Web communication)
• TCP → Transport Layer (Manages conversations)
• IP → Network Layer (Encapsulates and routes packets)
• Ethernet → Data Link Layer (Physical transmission of data)

Protocol Suites

• Definition: A set of protocols working together for network communication.
• TCP/IP Protocol developed by ARPANET (precursor to the Internet).
• Encapsulation Process: HTML page → HTTP → Transport Layer (TCP Segments) → IP Packet → Ethernet Frame
• De-encapsulation: Reverse process at the receiving end.

OSI and TCP/IP Models

• OSI Model Layers:
• Application: User interface protocols (HTTP, FTP, SMTP).
• Presentation: Data format translation and encryption.
• Session: Manages data exchanges.
• Transport: Ensures data delivery (TCP/UDP).
• Network: Routing and addressing (IP).
• Data Link: Frame transmission (Ethernet, MAC addresses).
• Physical: Electrical and mechanical aspects of transmission.
• TCP/IP Model Layers:
• Application, Transport
• Internet, Network Access Fewer layers than OSI but similar functionality.

Data Encapsulation and Transfer

• Message Segmentation: Large data streams split for efficient transfer.
• Protocol Data Units (PDU):
• Data (Application Layer)
• Segment (Transport Layer)
• Packet (Network Layer)
• Frame (Data Link Layer)
• Bits (Physical Layer)
• Encapsulation Process: Data moves from Application Layer downward, adding headers at each layer.
• De-encapsulation Process: Reverse operation at the receiving device.

Network Addresses

• IP Addressing
  • Source IP Address: Identifies sending device.
  • Destination IP Address: Identifies receiving device.
• MAC Addressing
  • Source MAC Address: Address of sending device.
  • Destination MAC Address: Address of receiving device.
• Data Link Addresses: Used for frame delivery on a local network.
• Routing Between Networks: Data frames are updated at each router hop.

Cisco IOS and Network Configuration

• Accessing Cisco IOS
  • Console Port: Physical access for device management.
  • Secure Shell: Secure remote access.
  • Telnet: Remote access (less secure).
• IOS Modes:
  • User EXEC Mode: Basic monitoring.
  • Privileged EXEC Mode: Configuration and management.
  • Global Configuration Mode: Allows system-wide changes.
  • Sub-Configuration Modes: Interface, line, and routing modes.

IOS Commands and Syntax

• Command Syntax
  • Keywords: Predefined commands.
  • Arguments: User-defined values.
• Command Examples:
  • hostname Router1 → Assigns a device name.
  • enable secret password123 → Sets privileged mode password.
  • show running-config → Displays active configuration.

Securing Network Devices

• Physical Security: Place devices in locked racks.
• Password Protection
  • Console Access: password Cisco + login.
  • Remote Access (VTY Lines): line vty 0 15 + password Cisco.
  • Encryption: service password-encryption.
• Banner Messages: Display legal notices on login.

Configuration Management

• Saving Configurations
• copy running-config startup-config → Saves active settings.
• erase startup-config → Resets device.
• reload → Reboots with saved settings.
• Backup Configurations: Save to text file for future restoration.

IP Addressing and VLANS

• IP Address Components:
• IP Address: Identifies the device.
• Subnet Mask: Defines the network range.
• Default Gateway: Routes traffic outside the network.
• Switch Virtual Interface : Enables remote switch management.
• Manual vs. DHCP IP Configuration:
• Manual: User assigns IP settings. -DHCP: Automatically assigns IP settings.

Network Addressing for Different Devices

• Same Network Communication: Uses MAC addresses.
• Remote Network Communication: Data sent via routers using IP addresses.
• Default Gateway: The router interface responsible for forwarding packets beyond the local network.

Ethernet and Network Cable - Comprehensive Reviewer

Physical Layer Connection and Its Types

• The Physical Layer is responsible for transmitting raw data bits over a communication channel.
• Types of Physical Layer Connection: Wired Connections: Ethernet cables, fiber optics. Wireless Connections: WiFi, Bluetooth, radio waves.

Network Interface Cards and WLAN

• Network Interface Card (NIC): A hardware component that connects devices to a network. Wireless LAN (WLAN): Each NIC has a unique MAC address for identification. Provides network access without physical cables. Uses radio signals and follows Wi-Fi standards .

Purpose of the Physical Layer

• Defines the mechanical, electrical, functional, and procedural characteristics of network transmission.
• Converts data into signals for transmission.
• Ensures data is transmitted over the physical medium without corruption.

Physical Layer Protocols

• Bandwidth: Measures data capacity over a medium.
• Digital bandwidth defines bits transferred per second.
• Throughput: Actual bit transfer rate, lower than theoretical bandwidth. Affected by network traffic, latency, and hardware limitations.
• Goodput is throughput minus protocol overhead.

Three Basic Forms of Network Media

• Copper Wires: Uses electrical signals; prone to interference and signal degradation.
• Fiber Optic Cables: Uses light pulses; faster and more reliable than copper, immune to EMI..
• Wireless Transmission: Uses radio frequencies, convenient but more secure.

Physical Layer Standards and Characteristics

• Defined by organizations like IEEE, ITU, and TIA/EIA. Govern transmission speeds, cable types, and electrical properties.
• Ensures interoperability between networking devices.

Ethernet Sublayers

• Data Link Layer (Layer 2) Sublayers include:
• Logical Link Control. Handles communication between upper and lower layers. Identifiers network protocols . Media Access Control access to physical media. Uses MAC addresses for device identification. Governs collision detection and frame transmission.

Copper Cabling

• Uses electrical signals for data transmission; It’s is subject to attenuation, and EMI/RFI can disrupt signals and crosstalk issues.
• Types: UTP: Most common, uses RJ45 connectors; twisted wire pairs reduce crosstalk. STP: More protection from interference; expensive and harder to install. Coaxial Cable: Used in cable internet and wireless antennas, inner copper conductor with shielding.

UTP Cabling Standards:

• Standards and defines and categories of cat3 and cat5 and cat6 cables
• UTP Connectors: RJ-45 (male) plugs into network devices and female ones sockets in walls, switches, patch panels.
• Testing UTP Cables: Checks wire mapping, length, attenuation, and crosstalk.

Fiber Optic Cabling

• Advantages: High-speed data over long distances, immune to EMI/RFI, lower attenuation than copper cables.
• Components: Core, Cladding, Buffer, Strengthening Material, Jacket.
• Types: Single-mode fiber (SMF): Long-distance, laser-based and Multi-mode fiber (MMF): Short-distance, LED-based.
• Connectors: Straight-Tip (Locking mechanism), Subscriber Connector (Push-pull insertion), Lucent Connector (Compact design for high-density usage) Duplex Multimode LC (Similar to LC but using a duplex connector).

Physical vs. Logical Topologies

• Physical Topology: Defines device connections
• Logical Topology: Describes data flow and addressing in a network.