# Real World Topology Usage ## Home Networks Home networks almost universally use star topology. A router or combination modem-router device sits at the center of the network and all devices connect to it either through Ethernet cables or WiFi. The router connects to the internet through the internet service provider's modem. All internet traffic from devices in the home passes through the central router. Home networks are simple star networks because they typically have only one central device and a small number of connected devices. ## Small Business Networks Small businesses typically use a star topology with one or a few switches and a router. Devices such as computers, printers, and phones connect to switches in each area of the office. The switches connect to the router that provides internet access. A simple server may be added to provide file sharing and backup services. The network may include wireless access points to provide WiFi coverage throughout the office. ## Enterprise Campus Networks Large enterprise networks use a hierarchical tree topology with three distinct layers. The access layer consists of switches in each room or area that connect end user devices. The distribution layer consists of switches that connect access layer switches together and route traffic between different areas. The core layer consists of high-speed switches that connect the distribution layer switches and provide fast paths between all parts of the network. Redundant connections are added between distribution and core layer switches to provide fault tolerance. Multiple routers connect the campus network to the internet. ## Data Center Networks Data centers use specialized network topologies designed for high speed and low latency between servers. A common architecture is the spine and leaf design, where leaf switches connect servers and spine switches connect all the leaf switches together. Every leaf switch connects to every spine switch, creating a partial mesh at the top level. This ensures that any server can reach any other server with at most two hops. Data centers require extremely high bandwidth and very low latency because many servers communicate intensively with each other. ## Internet Service Provider Networks Internet service provider networks use complex hybrid topologies. Within a city, providers use ring or mesh topology for resilience. Core backbone networks connecting cities and countries use partial mesh topology with multiple redundant high-speed fiber links between major locations. Routing protocols like BGP manage traffic across these complex topologies automatically, finding the best paths and rerouting around failures. ## Wireless Sensor Networks and IoT Internet of Things applications often use mesh topology for wireless sensor networks. In a wireless mesh network, each sensor device can relay data from other devices, so data can reach the central collection point even if some devices are out of direct radio range. This is useful in applications like smart city monitoring, agricultural sensors spread over large fields, and building automation systems.