Data Communications

Network: Collection of computers that communicate over transmission line.

Three basic types of networks: Local area network (LAN), Wide area network (WAN), and Internet.

LAN: Connected computers that reside in a single geographic location, within a small distance of each other, connects two-several hundred computers, and organisation controls the installation of the communications media.


Components of LAN: Switch/router (special purpose computer receives/transmits messages), LAN device (switch, wireless communication device, & devices for connecting to WAN and via WAN to internet), Network interface card (NIC) (hardware that connects each device’s circuitry to cable), UTP (unshielded twisted pair) cable (four pairs of twisted wires to reduce interference), and Optical fibre cables (light rays to transmit data).

LAN protocols: Ethernet or IEEE 802.3 protocol (supports 10/100/1000 Mbps Ethernet). Hardware characteristics and how messages are packaged and processed for transmission.

Wireless LAN protocols: IEEE 802.11 protocol used in the home and within small offices to connect to LANs. Bluetooth used over very short distances to replace wires, e.g. connecting a keyboard. Connect to an access point (modem/router). Processes messages and communicates with the LAN switch.

WAN: Connects computers at different geographic locations across metropolitan, state, regional, national areas, and uses communication networks from vendors that are licensed by government. Use routers and public communications links between sites.

Alternative to WAN, Internet service provider (ISP): A company that provides paying customers with access/gateway to the internet (legitimate internet address). Connected by DSL line, cable TV line, or Wireless, requiring digital data to be converted to analogue (or wavy) signal using modem (abbreviation for modulator/demodulator).


Internet: Any network of networks, connecting LANs, WANs and Internets. Many public/private Internets, usually refers to: used to access a website; Variety of communication methods and conventions; Seamless flow of data provided by standardised layered protocol (rules that two devices must follow in order to communicate).

Wireless network interface card (WNIC): Replaces an NIC to enable wireless connection.

Digital Subscriber Line (DSL) Modems: Operates over standard telephone lines, data signals do not interfere with voice telephone service.

Asymmetric digital subscriber lines (ASDL): Different upload/download speeds, used in most homes and small businesses.

Symmetrical digital subscriber lines (SDSL): Same upload/download speeds which are often very fast, used by larger businesses.

Cable modems: Provide high-speed data transmission. High-capacity optical fibre cable run to a distribution center in local area. Television cables connect at distribution center and run to subscriber’s house or business. Does not interfere with television transmission. Up to 500 user sites connected at each center. Performance can vary based on number connected. Download speed up to 50 Mbps, upload up to 512 kbps

You ↔ Your LAN ↔ Internet (WAN 1↔WAN 2↔WAN 3↔WAN 4) ↔ Uni’s LAN ↔ University

TCP (Transmission Control Protocol): Important protocol in transport layer

IP (Internet Protocol): Primary protocol of internet layer

Packet: Piece of message handled by programs that implement IP

Router: Special-purpose computer, moves packet traffic according to IP rules

TCP / IP Protocol Architecture:


Application Layer Protocols: Hypertext Transport Protocol (HTTP) (between browsers & web servers); SMTP (Simple Mail Transfer Protocol) (email transmissions & other protocols); FTP (File Transfer Protocol) (move files over internet).

IP address: # that identifies particular device

Public IP addresses: Identifies particular device on public internet

Private IP addresses: Identifies particular device on private network, usually on LAN

Domain name: Name affiliated with public IP address

URL (Uniform Resource Locator): Internet address

Three Tier Arch.png

Web page: Document code in markup language (often HTML), transmitted using HTTP.

Web server: Program runs on server tier computer and manages HTTP traffic, sending/receiving web pages.

Browser: Computer program on client computer to process web pages.

Commerce server: Application program run on server tier. Interacts with web server to: retrieve product data from database.

Web farm: Multiple web server computers e.g. minimise customer delays.

Virtual private network (VPN): Uses internet or private internet to create appearance of private, secure (encrypted communications), point-to-point connections. VPN client to VPN server point-to-point connection is called a tunnel, client software encrypts data and receiving VPN server decrypts it. Users and their keys must be registered with VPN server. Users are authenticated and can use network as if physically onsite.

Remote Using VPN: Actual vs Apparent Connections:

Actual vs Apparent.png

WAN using VPN:

WAN using VPN.png

Featured image supplied free from Unsplash.