Network Topologies & LAN/WAN

A Computer Network is a set of devices (often referred to as nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.

Networks are designed to facilitate communication, share resources (like printers and storage), and allow collaborative computing.

1. Types of Networks (By Geographical Scope)

Networks are generally categorized by their size and the geographical area they cover.

1. LAN (Local Area Network): Usually privately owned and links the devices in a single office, building, or campus. Today, LANs operate at speeds of 100 Mbps to 10 Gbps. Ethernet is the most common LAN technology.
2. WAN (Wide Area Network): Provides long-distance transmission of data, image, audio, and video information over large geographic areas that may comprise a country, a continent, or even the whole world. The Internet is the largest WAN in the world.
3. MAN (Metropolitan Area Network): A network with a size between a LAN and a WAN. It normally covers the area inside a town or a city (e.g., the cable television network in a city).
4. PAN (Personal Area Network): A very small network used for communicating among devices close to one person (e.g., connecting Bluetooth headphones to a smartphone).

2. Physical Topologies

The term topology refers to the way in which a network is laid out physically. The topology of a network is the geometric representation of the relationship of all the links and linking devices to one another.

Mesh Topology

In a mesh topology, every device has a dedicated point-to-point link to every other device. The term dedicated means that the link carries traffic only between the two devices it connects.

• Pros: Robust (if one link fails, the others survive), highly secure, no traffic congestion.
• Cons: Extremely expensive due to the massive amount of cabling and I/O ports required ($n(n-1)/2$ links for $n$ nodes).

Star Topology

In a star topology, each device has a dedicated point-to-point link only to a central controller, usually called a hub or switch. The devices are not directly linked to one another.

• Pros: Less expensive than mesh, easy to install and reconfigure, robust (if one link fails, only that link is affected).
• Cons: Single point of failure. If the central switch/hub goes down, the entire network dies.

Bus Topology

A bus topology is multipoint. One long cable acts as a backbone to link all the devices in a network. Nodes are connected to the bus cable by drop lines and taps.

• Pros: Easy to install, uses less cable than mesh or star.
• Cons: Fault isolation is difficult. If the backbone cable breaks, the entire network goes down. Signal reflection at the ends requires terminators.

Ring Topology

In a ring topology, each device has a dedicated point-to-point connection with only the two devices on either side of it. A signal is passed along the ring in one direction, from device to device, until it reaches its destination.

• Pros: Easy to install; to add or delete a device requires changing only two connections.
• Cons: Unidirectional traffic. A break in the ring (such as a disabled station) can disable the entire network. Token passing overhead is high.