Computer Networks: LANs, WANs and Network Types

• A Computer Network is a group of computers connected to each other via some interface, allowing them to exchange information.

Local Area Network (LAN)

• A LAN covers a small geographic area such as a home, office, school, or group of buildings
• It connects computers, peripherals, terminals, and other devices

Wide Area Network (WAN)

• A WAN covers a large geographic area, such as metropolitan, regional, or national boundaries
• It connects user networks over great distances, enabling communication for businesses

Network Categories

• Server-Based: Relies on a central server to manage network resources
• Peer-to-Peer: All computers have equal capabilities and responsibilities
• Network software supports each computer, providing server or client functionality
• The 'Media' refers to the hardware such as copper cables, fibre optic cables, or wireless transmissions used to transmit data across the network

Peer-to-Peer Networks

• Networked computers act as equal partners or peers
• Each computer can function as both a client and a server
• Individual users control their own resources and can share files with others, often requiring passwords for access
• There is no central point of control or administration
• Users must back up their own systems to prevent data loss
• Performance may be reduced when a computer acts as a server
• Relatively easy to install and operate because no additional equipment is needed beyond a suitable OS
• No dedicated administrators are required
• Coordination becomes difficult as the network grows because it works best with 10 or fewer computers
• Efficiency decreases rapidly as the number of computers on the network increases
• Security can be difficult to maintain since individual users control access to resources

Client/Server Networks

• Can be used to overcome peer-to-peer network limitations
• Network services are located on a dedicated computer called a Server, which responds to client requests
• The server is a central computer continuously available to respond to requests from clients for various services
• Most network operating systems adopt this model
• Desktop computers typically act as clients while one or more computers with additional resources function as Servers
• Servers are designed to handle requests from multiple clients simultaneously
• Clients must be identified and authorized before accessing server resources
• Each client is assigned an account name and password verified by an authentication service that guards access to the network
• Centralization of user accounts, security, and access control simplifies administration for large networks

Networking Components

• Computer Networks consist of computers, Network Interface Cards/Adapters, Networking Media, Networking Devices, Peripheral Devices, and a Network Operating System
• Networking devices allow a greater number of nodes to connect to the network
• Networking devices increase the distance over which a network can extend
• Networking devices localize traffic on the network
• Networking devices isolate network problems for easier diagnosis

Network Interface Card/Adapter (NIC)

• A NIC plugs into a computer's interface slot (system bus)
• It acts as an interface between the network and the computer
• The NIC communicates with the network through a serial connection and with the computer through the parallel interface
• Some computers use an external network interface connected through the USB port
• Newer computers have the network interface built-in with the motherboard
• Factors for consideration when selecting a Network Interface are type of Network (Ethernet, Token Ring, or FDDI), type of Media (Twisted Pair, Coaxial Cable, or Fiber-Optic Cable), and type of Computer Interface (PCI, ISA or USB)

Hubs

• Hubs are commonly used to connect segments of a LAN
• They connect network segments at the Physical Layer (Layer 1) of the OSI model
• A Hub contains multiple ports
• When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets

Bridge

• A Bridge connects multiple network segments at the Data Link Layer (Layer 2) of the OSI model
• It allows computers on either segment to access resources on the other and can divide large networks into smaller segments

Switches

• A Switch filters and forwards packets between LAN segments using MAC Addresses
• Switches operate at the Data Link Layer (Layer 2) and sometimes the Network Layer (Layer 3) of the OSI Reference Model

Routers

• A Router forwards data packets along networks using their logical address
• Routers work at the Network Layer (Layer 3) of the OSI reference model

Repeater

• A Repeater connects two segments of a network cable
• It strengthens weakened signals, cleans them up, amplifies them, and sends them on, thereby increasing the distance a network can operate
• Repeaters work at the Physical Layer (Layer 1) of the OSI Network model

Networking Media

• Networking Media is responsible for carrying data (binary bits) from the source host to the destination host
• Network Media can be classified into Copper Media, Optical Media, and Wireless Media
• Different types of media used at the physical layer to interconnect the network are Twisted Pair Cable, Coaxial Cable, Fiber Optic Cable and Air (wireless)
• The standard cabling for computer networks is the 100Base-T Category 5 Ethernet Cable, which is twisted copper cabling terminated on each end by an RJ-45 connector and maximum segment length is 100 meters

Hardware Address (MAC Address)

• Every node on a network must have a unique identifier so the file server knows the source and destination for the information
• This unique identifier is hardwired into the NIC
• When a workstation requests data, it sends its network address with the request so that the server knows which node to reply to
• Known as Media Access Control (MAC) Address, Ethernet Address, Physical Address, and Network Interface Card (NIC) Address
• It is a 12-character hexadecimal address unique to all network cards ever manufactured
• There are potentially 2^48 possible MAC addresses.
• The first six hexadecimal characters represent the manufacturer and are assigned by IEEE as the Organizational Unique Identifier (OUI)
• The last six hexadecimal characters form a unique serial number that the card manufacturer has assigned to it, known as the Burned-In Addresses' (BIA) or the 'Universally Administered Addresses' (UAA)

Network Topology

• Network topology describes the method used to do the physical wiring of the network
• In other words, it defines the structure of the network

Aspects to topology definition

• Physical Topology refers to the actual layout of the wire/media
• Logical Topology defines how data flows through the network

Common Physical Topologies

• Bus: Uses a single backbone segment where all hosts connect directly
• Ring: Connects each host to the next, forming a physical ring of cable
• Star: Connects all cables to a central point, usually a Hub or Switch
• Extended Star: Links individual stars together by linking the Hubs/Switches, extending the network's length and size
• Hierarchical: Similar to an Extended Star but links Hubs/Switches to a computer that controls traffic
• Mesh: Connects each host to all other hosts, providing multiple paths to any one location

Network Performance

• Digital Bandwidth measures how much digital information can flow from one place to another within a specific time frame, measured in bits per second
• Digital Bandwidth is not infinite and has limitations due to the laws of physics and technological constraints
• Throughput refers to actual, measured bandwidth at a specific time of day using specific Internet routes, while downloading a specific file
• Throughput is often far less than the maximum possible Digital Bandwidth of the medium being used

Factors Determining Throughput and Bandwidth

• Networking Devices
• Type of Data being transferred
• Network Topology
• Number of Users
• User's Computer