NWD181 Notes.docx

Table of Contents {#table-of-contents.TOCHeading} ================= [Glossary: 2](#glossary) [Computer Network 3](#computer-network) [Basic Network and their components 3](#basic-network-and-their-components) [Primary Elements of a Network 3](#primary-elements-of-a-network) [Networking Advantag...

Table of Contents {#table-of-contents.TOCHeading} ================= [Glossary: 2](#glossary) [Computer Network 3](#computer-network) [Basic Network and their components 3](#basic-network-and-their-components) [Primary Elements of a Network 3](#primary-elements-of-a-network) [Networking Advantages & Disadvantages 3](#networking-advantages-disadvantages) [Network Models 4](#network-models) [Peer to Peer Network Model 4](#peer-to-peer-network-model) [Client Server Network Model 6](#client-server-network-model) [Centralised Computing Model 7](#centralised-computing-model) [Distributed Computing Model 7](#distributed-computing-model) [Planning a Network and Servers 8](#planning-a-network-and-servers) [Specialised Servers 9](#specialised-servers) [Types of Computer Network 9](#types-of-computer-network) [Local Area Network (LAN) 9](#local-area-network-lan) [Personal Area Network (PAN) 10](#personal-area-network-pan) [Metropolitan Area Network (MAN) 10](#metropolitan-area-network-man) [Wide Area Network (WAN) 11](#wide-area-network-wan) [Campus Area Network (CAN) 12](#campus-area-network-can) [Storage Area Network (SAN) 12](#storage-area-network-san) [Content Delivery Network (CDN) 12](#content-delivery-network-cdn) [Specialized Networks 13](#specialized-networks) [Extranet 13](#extranet) [Intranet 13](#intranet) [Virtual Private Network (VPN) 13](#virtual-private-network-vpn) [OSI Reference Model 14](#osi-reference-model) [Functions of each layer in the DoD Model 15](#functions-of-each-layer-in-the-dod-model) [7 Layers of the OSI Model 16](#layers-of-the-osi-model) [Transmission Medium 19](#transmission-medium) [Twisted Pair 19](#twisted-pair) [Unshielded Twisted Pair 19](#unshielded-twisted-pair) [Shielded Twisted Pair 20](#shielded-twisted-pair) [Fiber Optic Cables 20](#fiber-optic-cables) [Single-Mode Fiber 21](#single-mode-fiber) [Multi-Mode Fiber 21](#multi-mode-fiber) [Signal Attenuation in Cables 21](#signal-attenuation-in-cables) Glossary: ========= A ***Modem*** (*Modulator-Demodulator*) connects your local network to the internet by converting digital signals from your computer or network into analog signals that can travel over phone lines, cable lines, or fiber optic systems. It also converts incoming analog signals from the internet into digital data that your devices can understand. - Interfaces with the **Internet Service Provider (ISP)**. - Necessary for converting between **analog** and **digital** signals. - Types of modems include **DSL, cable, **and **fiber modems**. - A modem does not route or distribute traffic internally within a local network---it simply provides the connection to the internet. A ***router ***directs traffic between *multiple *networks, most commonly between your **local network (LAN)** and the **internet** (WAN). It decides the best path for data to travel to reach its destination and provides local devices with IP addresses. Routers may also handle Network Address Translation (NAT), which allows multiple devices to share a single public IP address. - Creates a **Local Area Network (LAN)** by distributing the internet connection from the modem to multiple devices. - Provides **security features** such as firewalls and encryption. - Manages **traffic routing** between devices within a network and to external networks. - Can be **wired** or **wireless (Wi-Fi routers)**. - Typically includes **DHCP** functionality to assign IP addresses within the LAN. - Routers often come with **multiple ports** for connecting devices directly via Ethernet cables. A ***switch ***is a device used within a *local *network to connect multiple devices (like computers, printers, and servers) together. It forwards data only to the specific device on the network that needs it, improving efficiency and reducing unnecessary data traffic. - Operates at the **Data Link Layer (Layer 2)** of the [OSI model](https://connect.belgiumcampus.ac.za/moodle/mod/page/view.php?id=29754). - Learns and stores the **MAC addresses** of devices on the network, allowing it to intelligently forward traffic to the correct device. - Used to **expand** the number of devices connected within a **LAN**. - Unlike a router, it **does not manage traffic between different networks** (e.g., between a LAN and the internet). A ***Virtual Private Network (VPN)***, is a secure network connection that extends a private network across a public network. It creates a secure, encrypted tunnel between your device and a remote server, encrypting your data to protect it from unauthorized access. It masks your IP address, preventing your online activities from being tracked and encrypts data to prevent unauthorized access.  \ Its primary usage is for privacy, security, and accessing geographically restricted content. Computer Network ================ Basic Network and their components ---------------------------------- A network links two or more nodes together to communicate and share resources. Computer network is a group of computers that share info across wireless or wired technology. The basic components of a network are: Modem router/firewall , switch, server, wifi,devices,and internet. A diagram of a computer network Description automatically generated Primary Elements of a Network ----------------------------- Networks consist of three primary components: Resources -- a resource to share. Pathway -- to transfer data (transmission medium) Protocol -- a set of rules governing how computers communicate. The benefit of a network is that data sharing is easier and email which is still used today. **Device sharing** is when more than one computer can share to one hardware device. An example of these could be printers and scanners. Networking Advantages & Disadvantages ------------------------------------- [Advantages:] Reduces costs Easy sharing Improved reliability [Disadvantages:] Not all programs are network compatible Security threats -- need for security measures to protect the network from unauthorized access. A network requires attention by special personnel such as network Administrators and other data centre professionals. **Packet switching** transmits data across digital networks by breaking it down into blocks or packets for more efficient transfer using various network devices. **Server** is a computer program or device that provides services to other computer programs **Client** is one that accesses shared resources. Network Models ============== Peer to Peer Network Model -------------------------- **Peer** is a computer that acts as a server and provides resources to other machines. An example would be two desktops' PCs in a network. However, P2P networks are the most basic network and is created by connecting each device together through a hub or switch. In a P2P each node can both request and provide services. [Features:] There is no dedicated server. Each computer is responsible for sharing its own resources. Typical environment of a few computers of 10 of few computers with a maximum of 20. Security is not important and limited growth. [Peer-to-Peer Networks Key Features] Decentralization: No central server or authority controls the network, allowing equal capabilities and responsibilities among peers. This eliminates single points of failure.\ Self-organizing system: Networks dynamically adjust and reorganize as peers join and leave, demonstrating robustness and flexibility.\ Resource sharing: Peers contribute their own resources to the network, maximizing utilization and reducing the burden on individual peers or central servers.\ Direct communication: Peers interact directly, facilitating efficient and real-time communication. This is particularly useful in applications like instant messaging, voice and video calling, and distributed collaboration.\ Scalability: The network can handle higher loads and accommodate more users without relying on a centralized infrastructure.\ Fault tolerance and redundancy: The network is more resilient to failures as there is no central point of control.\ Privacy and security: Direct communication between peers allows for encrypted data transfer, protecting the confidentiality of information exchanged.\ [Advantages and Disadvantages of P2P Networks\ Advantages:\ ] Decentralization and resilience: Networks can continue to operate even if individual peers go offline or leave the network.\ Easy scalability: Networks can easily scale horizontally by adding more peers.\ Efficient resource utilization: Networks promote efficient resource utilization by distributing the load across multiple peers.\ Cost savings: P2P networks can reduce infrastructure and operational costs compared to client-server architectures.\ Direct communication and faster content delivery: Direct communication between peers facilitates faster content delivery, real-time interactions, and efficient distribution of data or media files.\ Enhanced privacy and security: Direct communication between peers can be encrypted, ensuring the confidentiality of data transferred within the network.\ Legal and copyright concerns: P2P networks have been associated with copyright infringement and illegal sharing of copyrighted material. [Disadvantages:\ ] Lack of centralized control: Difficulty in managing and coordinating network activities due to lack of centralized control.\ Network management complexity: Network management tasks like addressing, security, and performance optimization are distributed among participants, requiring additional coordination.\ Dependency on peer availability: The availability of resources and services in a P2P network depends on the active participation of peers.\ Performance and efficiency variability: The performance of a P2P network can be influenced by factors such as the number and quality of participating peers, their available resources, and the network topology.\ Security risks: P2P networks can introduce security risks if proper precautions are not taken.\ Legal and copyright concerns: P2P networks have been associated with copyright infringement and illegal sharing of copyrighted material.\ \ [Key Applications of Peer-to-Peer Networks\ ] File Sharing: P2P networks, like BitTorrent, allow users to download and upload files directly, reducing the need for a central server.\ Instant Messaging: P2P technology is used in applications like Skype and WhatsApp for direct communication and file exchange.\ Cryptocurrency: P2P networks facilitate transactions between users without a central bank or financial institution, allowing direct fund transfers and participation in the consensus mechanism.\ Content Delivery: P2P technology is used in Content Delivery Networks (CDNs) to distribute content efficiently, reducing server load and improving delivery speed.\ Collaborative Computing: P2P networks enable collaborative computing, allowing multiple peers to solve complex tasks.\ Virtual Private Networks (VPNs): P2P connections establish secure and private communication between users, providing enhanced privacy and bypassing restrictions. Client Server Network Model --------------------------- **Client server** network is a network model designed for the end users to access the resources and services from a central computer. A server is responsible for managing all the resources example would be a printer. Dedicated servers are faster at sharing resources. In a client server network, the client nodes request services and the server node provide them. The client-server model is a distributed application framework that divides tasks between servers and clients, either within the same system or communicating through a computer network or the Internet. Clients send requests to servers to access services, while servers run programs that distribute resources among clients. Communication follows a request-response pattern and follows a common communications protocol, typically the TCP/IP protocol suite. TCP protocol manages data distribution, transfers, and retransmission, while IP is a connectionless protocol. Client requests are organized and prioritized in a scheduling system, allowing servers to handle multiple requests from different clients. This approach allows general-purpose computers to expand their capabilities by utilizing shared resources from other hosts. Popular applications include email, the World Wide Web, and network printing. [Advantages:] This network contains the centralized system and therefore we can back up the data easily. The network has a dedicated server → improves the overall performance of the whole system. Security is better in this network as a single server administers the shared resources. [Disadvantages:] It is expensive as it requires the server with large memory. A server has a Network Operating System (NOS) to provide the resources to the clients, but the cost of NOS is very high. It requires a dedicated network administrator to manage all the resources.  Centralised Computing Model --------------------------- **Centralized computing systems** are where all computing is controlled through a central terminal server (S), which centrally provides the processing and storage. It connects single or multiple computers (PCs) of users (clients). **Thin client** is a computer that's uses resources housed inside a central server. Connects to a server-based environment that hosts most memory, that users need. They are used for input and display purposes. They have minimal hardware components and store no data locally. **Workstation** connects to the server where all tasks are performed. These are more expensive than thin clients and they need more powerful equipment and results in more energy, which needs more cooling. [Centralized Systems Characteristics and Use Cases] Single Point of Control:\ Central entity makes all decisions and manages resources.\ Centralized data management ensures all data processing, storage, and retrieval occur within the system.\ \ Hierarchical Structure:\ Centralized systems often have a hierarchical structure, with lower-level nodes reporting to and receiving instructions from the central authority.\ \ Communication Flow:\ Communication within a centralized system typically flows from peripheral nodes to the central node.\ \ Simplicity in Management:\ Centralized systems are simpler to manage and administer, leading to efficient coordination and streamlined operations. [Use Cases:] Small Office Network: One main computer stores files, helps access the network, and checks worker identities.\ Traditional Client-Server Architecture: Older programs work one way, with computers connecting to the main server for services.\ Standalone Applications: Apps run on one machine perform and store tasks locally, resulting in a centralized system. Distributed Computing Model --------------------------- **Distributed computing system** is a system where processing and data storage is distributed across multiple devices or systems. Every user has their own PC for processing program and storage. Each PC can receive input and process info without another computer. Multiple computers process independently. **Distributed parallel computing** uses multiple computing devices to process those tasks. **Parallel computing** on a single computer uses multiple processors to process tasks in parallel. [Characteristics of Distributed Systems] Decentralized Control: Each node in a system has autonomy and can make decisions independently.\ Distributed Data Management: Data and resources are distributed across multiple nodes, allowing each node to store a subset of data or perform specific tasks.\ Peer-to-Peer Communication: Direct communication between nodes without a central intermediary allows for information exchange, coordination, and collaboration.\ Fault Tolerance: Distributed systems are designed to be resilient to failures, allowing the system to continue operating even if individual nodes experience issues or failures.\ Scalability: Distributed systems can be highly scalable, allowing for the addition of new nodes to accommodate increased workload or user demand. [Use Cases of Distributed Systems] Cloud Computing Platforms: Cloud services share resources over data centres, offering computing on demand.\ Peer-to-Peer Networks: These networks allow direct communication between computers without a central server.\ Distributed Databases: These systems store information across several computers or nodes, making them highly available, fault-tolerant, and scalable. Planning a Network and Servers ============================== A plan includes a method for ensuring business and technical requirements are met before implementation, a roadmap for network implementation, and a historical reference of the network design for future use.  Specialised Servers ------------------- Application Server makes the server side of client/server applications as well as the data available to clients. File and Print Server Provide basic networked file storage and retrieval services. Mail Server Handles e-mail messages on behalf of network users, this involves acting as a clearing house for a local exchange of messages. Database Server A program that provides database services to other programs or computers as per client/server model. Web Server Is a computer that stores web server software and a website\'s component files (e.g. HTML documents, images, CSS stylesheets, and JavaScript files). Name Server A network service for resolving queries for host names to Internet Protocol (IP) addresses. Types of Computer Network ========================= Local Area Network (LAN) ------------------------ A local area network (LAN) connects several computers located geographically close to each other. [Types of LANs:\ ] Token Ring LAN: Uses a token-passing protocol for fair access.\ Token Bus LAN: Employs a bus topology for data transmission.\ Wireless LAN (WLAN): Uses wireless technology for device connectivity.\ Wired LAN: Utilizes physical cables for reliable and high-speed data transfer.\ Cloud Managed LAN: Leverages cloud-based management for central administration and monitoring.\ \ [Characteristics of LANs:\ ] Limited geographical area: Covers a small physical area.\ High data transfer rates: Enables quick communication and resource sharing.\ Localized administration: Allows control over network resources.\ Shared infrastructure: Connects devices using shared network infrastructure.\ \ [Purposes of LANs:\ ] Facilitating communication: Improves collaboration.\ Resource sharing: Reduces costs and improves efficiency.\ Centralized data storage and backup: Provides a centralized location for important data.\ Access to shared applications and databases: Enables streamlined workflow and access to critical information. Personal Area Network (PAN) --------------------------- A Personal Area Network (PAN) connects devices within an individual\'s vicinity, enabling communication and data sharing between personal devices like smartphones, tablets, laptops, smartwatches, and other wearables. [Types of PANs:\ ] Wired PAN: Connects devices using cables or wires, enabling reliable and high-speed data transfer.\ Wireless PAN: Uses wireless technologies to establish connections between devices without physical cables. Bluetooth is the most common wireless technology used for PANs.\ \ [Uses of PANs:\ ] File Sharing: Allows seamless file transfer between devices.\ Peripheral Device Connectivity: Enables devices to connect wirelessly to peripherals.\ Personal Device Synchronization: Facilitates data synchronization between personal devices.\ Audio Streaming: Enables wireless audio streaming to headphones, speakers, or car audio systems.\ Wearable Device Integration: Connects wearable devices like smartwatches to smartphones or tablets.\ \ [Examples of PANs:\ ] Bluetooth headsets to smartphones.\ Smartwatch syncing with smartphones.\ File transfer between laptops and smartphones.\ Wireless printing from tablets to Bluetooth-enabled printers. Metropolitan Area Network (MAN) ------------------------------- A Metropolitan Area Network (MAN) is a computer network that connects multiple local area networks (LANs) within a city, efficiently transmitting data, voice, and video between different locations. [Examples and Types of MAN\ ]\ Cable TV Network: Provides television signals and internet services to subscribers.\ Educational Institutions: Interconnects departments, libraries, and research facilities.\ Government Networks: Connects different government buildings for efficient communication and data sharing.\ Large Corporations: Connects offices and facilities of multinational companies with multiple branches.\ Types of MAN: Fiber Distributed Data Interface (FDDI), Asynchronous Transfer Mode (ATM), Ethernet MAN (E-Man), Wireless MAN (WMAN).\ Classification and availability of specific MAN types may vary with network technologies\' evolution. Wide Area Network (WAN) ----------------------- A Wide Area Network (WAN) is a computer network that connects multiple LANs, enabling data, voice, and video transmission over long distances, facilitating communication and resource sharing among organizations.\ \ [Examples of WAN:\ ] Virtual Private Network (VPN): Secure tunnels over public networks like the internet for secure communication and resource sharing.\ Internet-based WAN: Leverages technologies like IPsec, MPLS, or SD-WAN to connect remote sites.\ Leased Lines: Provides dedicated point-to-point connections between locations for reliable data transmission.\ Satellite Networks: Establishes WANs in remote areas with limited terrestrial infrastructure.\ \ [Characteristics of WAN:\ ] Large Geographic Coverage: Covers significant geographic areas.\ Diverse Connectivity Technologies: Uses technologies like leased lines, fiber optics, satellite links, microwave connections, and internet-based networks.\ Reliance on Public or Private Infrastructure: Utilizes public networks or private leased lines for data transmission.\ Network Protocols and Routing: Employs routing protocols like BGP to efficiently direct data packets across interconnected networks.\ Quality of Service (QoS): Prioritizes certain types of traffic to ensure optimal performance and minimize latency.\ \ [Types of WAN:\ ] Packet Switching: Circuit-switched and packet-switched networks.\ TCP/IP Protocol Suite: TCP provides reliable, connection-oriented communication between devices.\ Packet over SONET/SDH (PoS): Allows for transmitting packet-switched data over synchronous optical networks or synchronous digital hierarchy networks.\ Multiprotocol Label Switching (MPLS): Combines benefits of circuit-switching and packet-switching to route IP packets efficiently. Campus Area Network (CAN) ------------------------- A Campus Area Network (CAN) is a computer network that connects multiple buildings within a specific geographic area, facilitating high-speed communication and data sharing between departments and resources. [CAN Examples and Characteristics\ ]\ Educational Institutions: CANs interconnect academic buildings, research centers, libraries, and administrative offices for efficient communication.\ Corporate Campuses: CANs facilitate internal communication, resource sharing, and centralized IT management.\ Government or Military Facilities: CANs connect various facilities, command centers, and administrative offices.\ Healthcare Campuses: CANs connect different departments, clinics, and healthcare facilities for secure patient data sharing.\ Geographic Scope: CANs cover a limited geographic area.\ High-Speed Connectivity: CANs offer high-speed data transmission capabilities.\ Wired and Wireless Infrastructure: CANs incorporate technologies for network access.\ Scalability and Flexibility: CANs allow easy expansion and adaptation to campus needs. Storage Area Network (SAN) -------------------------- A Storage Area Network (SAN) is a specialized network infrastructure that offers high-speed, block-level access to consolidated storage resources, ensuring efficient, scalable, and secure data storage and retrieval. [SAN Components and Architecture]\ Storage Devices: Includes disk arrays, tape libraries, or SSDs, managed centrally.\ SAN Fabric: Comprises switches, hubs, and routers, interconnecting storage devices and servers.\ Host Bus Adapters (HBAs): Specialized network interface cards (NICs) for server connection to SAN fabric and shared storage resources.\ Storage Management Software: Provides centralized control and monitoring of SAN infrastructure for tasks like provisioning, volume management, data replication, and backup. Content Delivery Network (CDN) ------------------------------ A Content Delivery Network (CDN) is a network of servers that delivers web content faster, secure, and reliably, playing a crucial role in modern Internet infrastructure. [Purpose of CDNs\ ] Optimize web content and applications delivery.\ Enhance user experience by reducing latency.\ Ensure content availability during traffic spikes or server failures.\ Protect websites and applications from threats like DDoS attacks.\ Manage bandwidth usage effectively to reduce costs and improve performance.\ \ [Types of CDNs\ ] Web CDNs: Optimize web content like images, CSS, and JavaScript files.\ Video Streaming CDNs: Optimize video content delivery.\ Application CDNs: Tailored for dynamic, database-driven applications.\ DNS CDNs: Optimize domain name resolution for faster website access.\ IoT CDNs: Distribute data from IoT devices efficiently.\ Mobile CDNs: Optimize content for mobile devices.\ \ [Advantages of CDNs\ ] Improved performance: Reduces latency, speeds up content delivery.\ Enhanced reliability: Increases content availability and reduces server failure risk.\ Scalability: Handles traffic spikes and growing user loads effectively.\ Bandwidth savings: Reduces data transfer costs.\ Security: Offers DDoS protection and security features.\ Global Reach: Enables global access to content.\ \ [Disadvantages of CDNs\ ] Cost: High-traffic websites can incur significant costs.\ Complex setup: Implementing a CDN can be complex.\ Cache Invalidation: Timely updating cached content.\ Potential Data Privacy Concerns: CDNs may store user data.\ Limited Control: Need for more control over network and caching policies. Specialized Networks ==================== Extranet -------- An extranet is a communication network based on internet protocol, allowing information sharing among authorized users with valid login credentials. It operates as a lower level of internetworking and requires at least one external network connection. Intranet -------- Intranets are private networks for employees within an organization, facilitating information and resource sharing, enhancing productivity, and streamlining workflows through group work and teleconferencing features. Virtual Private Network (VPN) ----------------------------- VPN Purposes and Protocols\ Secure Remote Access: Allows secure connection to a private network.\ Privacy and Anonymity: Conceales user\'s IP address and online activities from surveillance.\ Bypassing Geo-restrictions: Enables access to geographically restricted content or services.\ \ VPN Protocols and Technologies\ IPsec: Provides strong encryption and authentication for IP communication.\ SSL/TLS: Widely used for securing web communication.\ OpenVPN: Open-source VPN protocol with SSL/TLS encryption and secure remote access.\ L2TP/IPsec: Combines features of PPTP and Cisco's L2F.\ PPTP: Basic encryption and authentication, considered less secure than other options. OSI Reference Model =================== An Open System Interconnection (OSI) is a reference model for network communication, providing a visual design of each communication layer from physical cabling to the application. It divides a communication system into smaller layers, grouped into logical layers. This model is used for product development and network understanding, allowing each task or activity to be handled separately and its issues solved independently. A white paper with red text Description automatically generated Functions of each layer in the DoD Model ---------------------------------------- The DoD model consists of four layers: Process Layer, Host-to-Host Layer, Internet Layer, and Network Access Layer. The Process Layer implements user-level applications like mail delivery and file transfer. The Host-to-Host Layer controls flow and re-transmission of lost packets using TCP and UDP protocols. The Internet Layer routes data across networks, including IP, and the Network Access Layer delivers data segments over specific hardware media using protocols like CSMA/CD. [The four layers of DoD model from top to bottom are:] Process Layer: Responsible for implementation of user-level applications such as mail delivery, file transfer, and remote login. Host-to-Host Layer: Responsible for flow control, and re-transmission of lost packets. TCP, and UDP protocols work at this layer. Internet Layer: Responsible for routing data across a network of networks. Routed protocols such as IP work at this layer and are therefore also associated with this layer. Network Access Layer: Responsible for the delivery of data segments over a given hardware media. Different protocols such as CSMA/CD work at this layer. 7 Layers of the OSI Model ------------------------- Layer 7 is the application layer, allowing users to interact with applications or networks, such as web browsers and internet-connected apps like Outlook and Skype. Application Layer Functions\ Network Virtual Terminal (NVT): Enables user login to remote hosts.\ File Transfer Access and Management (FTAM): Allows access, retrieval, and management of remote files.\ Mail Services: Provides email services.\ Directory Services: Provides distributed database sources and global information access. Layer 6. This layer translates or formats data for the application layer based on the semantics or syntax the application accepts. This layer also handles the encryption and decryption that the application layer requires. Presentation Layer Functions\ Translation: ASCII to EBCDIC.\ Encryption/Decryption: Translates data into ciphertext and plain text.\ Compression: Reduces network bit transmission.\ Device or Protocol Use: JPEG, MPEG, GIF. Layer 5 manages communication between applications, ensuring authentication and reconnection after interruptions. It determines system wait time using protocols like X.225 and ZIP. Session Layer Functions\ Establishes, maintains, and terminates connections between two processes.\ Identifies errors and ensures data re-synchronization.\ Facilitates communication in half-duplex or full-duplex.\ The \"Application Layer\" integrates all three layers, also known as Upper Layers or Software Layers.\ Implemented by the network application.\ Uses protocols like NetBIOS and PPTP. Layer 4 the transport layer manages data transfer across networks, ensuring error-checking and data flow controls. It selects TCP port numbers to categorize and organize data transmissions, exemplified by TCP within the TCP/IP suite. Transport Layer Functions and Services\ Segmentation and Reassembly: Accepts messages from the session layer and breaks them into smaller units. Each segment has a header.\ Service Point Addressing: Provides a service point address or port address to ensure message delivery to the correct process.\ \ Services Provided by Transport Layer\ Connection-Oriented Service: Three-phase process including connection establishment, data transfer, and termination/disconnection.\ Connectionless Service: One-phase process with data transfer, allowing faster communication between devices.\ \ Note: Data in the Transport Layer is called Segments.\ Operated by the Operating System and communicates with the Application Layer through system calls.\ Used by Devices or Protocols: TCP, UDP NetBIOS, PPTP. Layer 3 of the network layer facilitates data movement through networks by packaging data with correct address information, selecting appropriate routes, and forwarding it to the transport layer. Network Layer Functions\ Routing: Defines suitable route from source to destination.\ Logical Addressing: Identifies each device uniquely through an addressing scheme.\ Packet: Refers to the segment in the network layer.\ Implemented by networking devices like routers and switches. Layer 2 the data-link layer, also known as the protocol layer, manages data transfer between physical network links, preventing bit transmission errors and ensuring data flow doesn\'t overwhelm devices, allowing for network routing. Data Link Layer Functions\ \ Framing: Enables sender to transmit meaningful bits to receiver by attaching special bit patterns.\ Physical Addressing: Adds physical addresses (MAC addresses) of sender and/or receiver in the header of each frame.\ Error Control: Detects and retransmits damaged or lost frames.\ Flow Control: Coordinates the amount of data sent before receiving an acknowledgment.\ Access Control: Determines which device has control over a shared communication channel.\ Note: Frame is the packet in the Data Link layer.\ Handled by Network Interface Card and device drivers of host machines. Layer 1 The physical layer transports data through electrical, mechanical, or procedural interfaces, establishing physical connections and converting bits into predictable signals through electrical, optical, or radio waves. Physical Layer Functions\ Bit Synchronization: Provides a clock for bit level synchronization, controlling both sender and receiver.\ Bit Rate Control: Defines transmission rate, i.e., number of bits sent per second.\ Physical Topologies: Specifies arrangement of devices/nodes in network, such as bus, star, or mesh topology.\ Transmission Mode: Defines data flow between connected devices, including Simplex, half-duplex, and full-duplex.\ Note: Hub, Repeater, Modem, and Cables are Physical Layer devices. Transmission Medium ===================  [Cable Characteristics Overview]\ Bandwidth Rating: Measures the number of bits or bytes of information that can be carried over a unit of time.\ Maximum Segment Length: Defines the distance a cable can transmit data before signal weakening.\ Maximum Number of Devices Per Segment: Defines the maximum number of devices per segment.\ Interference Susceptibility: Considers environmental factors like Electro-Magnetic Interference (EMI) and Radio Frequency Interference (RFI).\ Bend Radius: Different cabling types have different bending resistance.\ Material Costs: Each cable type has associated costs per unit of length.\ Connection Hardware: Each cable type has connectors influencing its connection to specific hardware. Twisted Pair ------------ ### Unshielded Twisted Pair [ ] Common in computer networking, particularly for Ethernet and telecommunications.\ Consists of pairs of insulated copper wires twisted together within a common sheath.\ Lacks external shielding to protect against electromagnetic interference (EMI).\ Lighter, cheaper, and easier to install than shielded cables like STP.\ \ Purpose of Twisting\ Minimizes Crosstalk: The twist rate is designed for each pair to minimize interference from one pair.\ Reduces Electromagnetic Interference (EMI): The twisting protects the signal from external EMI.\ Maintains Signal Integrity: The twists prevent signal degradation and reduce interference errors, crucial for high-speed data transmission. ### Shielded Twisted Pair Types of Shielding\ Foil shielding (FTP): A thin layer of aluminium or polyester foil wrapped around each pair of wires or the entire cable.\ Braid shielding (S/UTP): A woven mesh of copper or aluminium wires surrounding the entire cable of wire pairs.\ Drain Wires: A bare copper wire running parallel to the shield, providing a simple and effective path to ground for the cable\'s shield.\ \ Overall Construction\ The construction of a STP cable includes various elements.\ \ Practical Considerations\ Proper grounding (or earthing): The shielding in STP must be properly grounded to prevent ground loops and provide effective EMI protection.\ Shield continuity: The shielding in STP must be continuous throughout the cable run to provide effective protection against interference.\ Increased Cable Diameter: The shielding in STP cables adds extra material and bulk compared to UTP, making the cables thicker and less flexible.\ Terminations: Proper termination of STP cables is critical as poor termination can expose the cable to interference, negating the benefits of shielding.\ Cost: STP cabling is more expensive than UTP due to the added shielding and the need for special connectors and grounding.\ \ When to Use STP Cabling\ High-interference environments: In areas with significant EMI sources, such as industrial facilities, data centers, or near electrical equipment.\ Long cable runs: For extended distances where signal attenuation and interference are more likely to occur.\ Sensitive applications: In applications that require high data integrity and reliability, such as real-time control systems or high-speed data transmission. Fiber Optic Cables ------------------ Fiber Optic Cables Overview\ Trades electrical pulses for optical equivalents.\ Highly secure due to immunity to interference.\ Eliminates electronic eavesdropping.\ Ideal for high bandwidth, speed, and long distance data transmission.\ Thicknet cable transceiver uses Vampire tap.\ Types of Fiber Optic Connectors: Straight Tip (ST), Straight Connection (SC), Medium interface connector (MIC), Subminiature Type A (SMA). Fiber optic cables are crucial in computer networking for high-speed data transmission over long distances. They transmit data as light pulses, offering faster speeds and greater bandwidth than copper cables like UTP. There are two main types: Single-mode fiber (SMF) and Multi-mode fiber (MMF), with SMF having a smaller diameter of 10 microns and MMF having a larger diameter of 50 microns, affecting light transmission. ### Single-Mode Fiber Single-Mode Fiber (SMF) Overview\ \ Ideal for long-distance, high-bandwidth applications like telecommunications and data center backbones.\ Core diameter: 8-10 microns.\ Light Source: Typically uses a laser.\ Transmission Distance: Capable of transmitting data over tens of kilometers.\ Bandwidth: Higher than multi-mode fiber due to single light path.\ Applications: Primarily used in long-distance communication links.\ Advantages: Suitable for long-distance data transmission.\ Disadvantages: More expensive due to laser light source precision and installation. ### Multi-Mode Fiber Suitable for short-distance, cost-effective solutions in LANs and data centers.\ Utilizes LEDs or VCSELs as light source.\ Best suited for shorter distances (up to 300-400 meters for 10 Gbps Ethernet).\ Lower bandwidth due to multiple light paths causing modal dispersion.\ Commonly used in LANs, data centers, server connections, and other short-distance networking environments.\ Advantages: Less expensive, easier to install and terminate.\ Disadvantages: Not suitable for long distances due to signal degradation from modal dispersion. Signal Attenuation in Cables ---------------------------- Signal attenuation in a cable refers to the loss of signal strength as it travels along the cable.\ Factors contributing to this loss include cable length, type, frequency, and environmental factors.\ Signal attenuation is typically measured in decibels (dB), with higher dB values indicating greater attenuation.\ Two common methods for measuring attenuation are Insertion Loss Measurement and Return Loss Measurement.\ Tools used for measuring attenuation include cable analyzers, Time Domain Reflectometers (TDRs), and oscilloscopes. Connectivity Devices -------------------- ### Hub A hub is a common connection point for devices in a network. Commonly used for a LAN. #### Passive Hub They do not contain any electronic components and do not process the data signal in any way. #### Active Hub electronic components that can amplify and clean up the electronic signals that flow between the networks. #### Intelligent Hub (Switch) enhanced active hub with two special functionalities. - Hub Management enables the hub to send packets to a central network console. - Switching, routes signals between ports on the hub. Does this by learning MAC address of devices connected. ### Repeaters A repeater is a network device that repeats a signal from one port onto other ports to which it is connected. Work from the physical layer of the OSI. The advantages of this method include easy network expansion, minimal impact on speed, and connection between media, but the disadvantages also lack addressing information, cannot connect different network architectures, do not alleviate congestion issues, and have limited repeater numbers. ### Bridge A bridge is more selective and passes only those signals targeted for a computer. Operates at the MAC and sublayer of OSI Model. Broadcasting extends network distance, filters traffic, and connects networks with different media, but is slower, more expensive, and requires bridges for broadcast packets. ### Routers Routes connect to the internet and remote network locations. Routing is the process of forwarding a packet to its destination using an IP address, typically achieved through an interconnectivity device called a router. Advantages of routers is that bridges connect networks of different physical media and architectures, choose optimal packet paths, and reduce network traffic by not forwarding broadcasts or corrupt packets. However the disadvantages, they are more expensive, complex, and work with routable protocols, causing traffic and slowing down network performance. Types of routing: - Static -- the administrator must update the routing table manually. Each route must be added. - Dynamic -- uses discovery process to find out about available routers ( routers update each other about routes). Topology -------- Topology is the way the end points of PC are attached to the network. ### Bus Topology A bus topology is a LAN topology where nodes are connected to a single cable, called a backbone, which fails if the backbone is broken. Advantages:\ Simple, reliable, and easy to use in small networks.\ Requires minimal cable.\ Easy to extend with BNC connector.\ Repeaters can boost signal.\ \ Disadvantages:\ Each BNC barrel connector weakens electrical signals.\ Troubleshooting individual device issues can be challenging.\ Bus topology isn\'t ideal for large networks.\ Additional devices can slow down the network.  ### Star Topology A star topology is a LAN topology where nodes are connected to a central hub or switch, implementing a spoke-hub distribution paradigm in computer networks. [Advantages:\ ] Easy modification.\ Detects and isolates issues.\ Can use multiple cable types.\ [Disadvantages:]\ Central hub failure can cause network failure.\ Requires a central device for signal regeneration.\ Requires more cable than BUS or ring topology. ### Ring Topology A ring topology is a network configuration where devices form a circular data path, connected like points on a circle. Advantages:\ No monopoly by one computer.\ Fair sharing allows graceful network degradation.\ Ring topology performs better under heavy traffic. Disadvantages\ One computer failure can affect entire network.\ Difficulty in troubleshooting.\ Disruption from adding or removing devices.  TCP Protocols -------------  [Common ICMP Messages:]\ \ Echo Request: Troubleshooting message for IP connectivity.\ Echo Reply: Response to an ICMP Echo request.\ Redirect: Router informs sending host of better route to destination IP address.\ Source Quench: Router informs sending host of dropped IP datagrams due to router congestion.\ Destination unreachable: Sending host informs sending host that datagram cannot be reached. IP Addressing ------------- An IP address is 32 bits, divided into four 8-bit octets, each converted to a decimal number and separated by a dot, using dotted decimal notation. [DHCP Process:] 1. DCHP Discover 2. DHCP Offer 3. DHCP Request 4. DHCP Ack  Name Resolution --------------- Name Resolution in computer networking involves obtaining assigned IP addresses for communication with known devices, while IP addresses work with 32-bit hosts, but users excel in name recognition. ### Host Name Guidelines - Must be a text string consisting of only letters, digits from 0-9, and signs (-) or (.). - Cannot have spaces - First character cannot be a sign - Length is up to 24 characters ### DNS Space Structure  Root Domain: the root of the namespace indicated with a null Top level domain: directly below root, indicates type of organisation on internet. (e.g. com, ac.za) Second level domain: identifies a specific organisation. ICANN responsible for maintaining second level domain. Subdomains: responsible for the creation and maintenance of subdomains Example: Ftpsrv.wcoast.reskit.com. Root of the DNS is the (.) Top level of DNS is the com, indicates a commercial organisation Second level of DNS reskit, indicates the organisation Subdomain of DNS is wcoast, indicates the division in the organisation Ftpsrv of the DNS is name of the FTP Server ### Name Resolution Queries Clients can make three types of queries.\ DNS information stored in database, reverse lookup, cache, and boot files. Recursive query: Queried name server responds with requested data.\ Iterative query: Queried name server provides best current answer.\ Inverse query: Request to resolve host name associated with known IP address. Computer Security ----------------- Computer security protects computer systems and networks from theft, damage, and disruption of services, ensuring the safety and integrity of hardware, software, and electronic data. ### Share-Level Security: A network consists of multiple computers connected to a Windows network, where users can access shared folders by selecting the folder in network places.  ### User-Level Security: A server domain controller authenticates users, assigning access permissions to workstation resources, and the administrator determines access to resources in a domain. ### User Password Practices Regularly change passwords, avoid easily guessed passwords, enforce password history, ensure minimum length, complexity, well-chosen passwords, and follow a password audit policy. You need to change your password every90 days because, you may share it with friends and family, your many write them down allowing you to be exposed. May be guessed by humans or software. May be tricked into revealing your password (phishing). Eliminates risk if you lose your backups. ### Fault Tolerance Disaster planning involves having a disaster plan in place before a disaster.\ A disaster is any event significantly impacting a company\'s operations.\ An example of a worst-case scenario is identifying critical systems, users, and resources.\ Physical data security is crucial, including live redundant copies, regular backups, and testing backups.\ Critical systems are also protected, with physical data, locked doors, and UPS installed on critical servers and workstations. Information system availability is crucial for business success, as downtime can lead to customer frustration and revenue loss. Implement fault tolerance mechanisms to ensure system availability. ### Types of Backups Full Back up, this will back up all the data on the server and remove archive attribute. (The archive attribute will switch on when a file is changed) Incremental Backup will back up any data changed since the last backup and remove the archive attribute. Differential Backup will back up any data that has changed since the last full backup. This type does not mark the file as being backed up. Daily copy will back up any file that has changed on the day it was selected and will also not be marked as backed up Copy -- will backup selected files, and won't change the archive bit ### RAID Redundant Array of Independent Disks RAID technology, a modern network tool, combines multiple disks to create a large structure for storing redundant data copies. Striping is a method of segmenting sequential data, storing consecutive segments on different physical storage devices. [RAID Levels Overview]\ \ RAID Level 0: Disk Striping without parity: Data is distributed block by block across drives, requiring at least two disks. RAID Level 1: Mirror Sets: Data is mirrored across two drives, improving performance. RAID Level 2: Bit-Level Striping with dedicated Hamming-Code Parity: Synchronized disk spindle rotation and striped data on different drives. RAID Level 4: Block-Level Striping with dedicated Parity: Equivalent to RAID 5, but all parity data is stored on a single drive.