Chapter 2 - Communication

2.1 Networks including the Internet

Networks

A network consists of two or more computers or electronic devices connected to exchange data, e.g., share files, message, share a printer. It uses cables, wireless signals, telephone lines, modems, fibre-optics, satellites as connection media.

Local Area Network (LAN)

• One building/site and one organisation/business
• Uses cables for connections
• Geographically small area and dedicated company-owned architecture
• Doesn’t use the internet to connect
• Faster connection, higher bandwidth, more stable (less issues with wires and distance), and more secure

Wireless Local Area Network (WLAN)

• Uses radio signals instead of cables
• At the centre is a WAP (Wireless Access Point) connected to a switch. Laptops with a wireless network interface card use wireless technology to transmit
• Freedom of movement between different rooms
• No need for a physical connection/cable
• Easy to expand and add devices; less cabling and less expertise for a less costly initial setup

Wide Area Network (WAN)

Large geographical area, such as the internet. Joining several LANs. Uses optical fibres, satellites, and microwaves.

Network Topologies

Name	Description	Pros	Cons
Point-To-Point	2 computers connected with a network link. The simplest topology
Bus	All devices attached to a shared link	Easier to set-up and extend Less cables	Performance degrades if the main cable breaks Difficult to troubleshoot an individual station Less efficient with more devices Collisions may occur - unsuitable with heavy traffic Less secure - all computers receive a signal
Mesh	Each computer has a point-to-point connection or direct link with each other computer
Star	Each computer has a point-to-point connection with only a central device	More secure - signals only go to destination Easy to connect and remove and troubleshoot Centralized management Failure of one node doesn’t affect others Performance doesn’t degrade under load Fewer collisions	If the central device fails, the whole network goes down Performance depends on the central device
Hybrid	Uses two or more different topologies. A mix of bus, mesh, ring, and star topologies

CSMA/CD →

Carrier Sense Multiple Access/Collision Detection

• Workstation/node monitors if the network is idle and only sends data if it is idle
• As computers use the same transmission medium, a collision can occur.
• Halts transmission when a collision occurs and waits a random amount of time before retrying

Transmission Media →

Bandwidth = amount of data sent per second

• Twisted Pair: copper cable of four twisted pairs. Can be shielded or unshielded to reduce interference. Least expensive and easy to install as flexible. More expertise, Worst interference, lower bandwidth, most need for repeaters and middle attenuation at higher frequencies
• Coaxial: copper cable that is a straight wire. Signal degrades over longer distances. Middle cost, most attenuation at higher frequencies, middle interference, most need for repeaters
• Fibre-optic Cables: use a bundle of glass/plastic threads and light to send data
  • Pros:
    • Larger bandwidth and faster transmission
    • Less interference
    • Less signal boosting as the signal doesn’t degrade
    • More secure and harder to hack
    • Needs fewer repeaters and less attenuation at high frequencies
  • Cons:
    • Higher costs
    • Specialists and trained personnel needed
    • Difficult to terminate as electronics are more complex at each end
    • Fibres break when bent

Wireless →

• Radio: also called WiFi. Uses electromagnetic waves
• Satellite: communication system in earth’s orbit that receives and transmits data
• Cell Phone Network: internet access provided by mobile phone companies that act as ISPs. Communicates with standard cell tower to access wireless telephone network, providing a connection to the internet

Pros	Cons
Devices are more mobile and don’t connect to a cable Easier to set up without cables Easier to add devices Can connect many different types of devices	Easier to hack More interference Signal degrades quickly Weather-dependent in some instances More costly

LAN Hardware

• Hub: A device connecting computers in a LAN and broadcasting data packets to all computers
• Switch: Connects computers to make a LAN. Learns which devices are connected to which ports and stores the address of each computer, then receives packets with the address of the recipient. Determines the recipient and transmits the packet directly to the recipient
• Bridge: Connects different parts of a LAN into one. Connects two LANs with the same protocol
• Network Interface Card (NIC): Needed to allow a device to connect to a network
• Network Cables (Ethernet Cables): Faster data transfer and more secure
• Repeater: Device connecting two cables to give the second cable a full-strength signal
• WiFi: Technology in WLANs. Smartphones and laptops with a WNIC can connect to the internet via WiFi at any WAP connected to a switch
• Wireless Network Interface Card (WNIC): Allows devices to connect to a wireless network and acts as an interface to the wireless network. Receives radio signals and transmits radio signals via an antenna. Can encrypt and decrypt data and convert from analogue to digital
• Wireless Access Point (WAP): Hardware component providing radio communication from a central device to nodes on a wireless network