Hub
A hub is the central part of a circular object, such as a wheel or propeller, to which spokes, blades, or other components are attached, enabling rotation around an axle while supporting the structure's weight and facilitating smooth movement.[1] More broadly, the term denotes a focal point or center of activity, radiation, or connection, often used to describe key locations like transportation nodes, commercial districts, or organizational cores where multiple elements converge.[2] In computing, a hub specifically refers to a basic networking device that connects multiple computers or peripherals in a local area network (LAN), operating at the physical layer to broadcast data to all connected devices without intelligent filtering.[3]Mechanical and Structural Uses
In mechanical engineering, wheel hubs are critical components in vehicles and machinery, housing bearings that reduce friction and allow the wheel to rotate efficiently while transmitting torque from the axle.[4] Modern automotive wheel hubs often integrate sealed bearings, ABS sensors, and mounting points for brake rotors, forming pre-assembled units that enhance durability and ease of replacement in passenger cars, trucks, and bicycles.[5] These assemblies must withstand high loads, vibrations, and environmental exposure, with materials like steel or aluminum chosen for strength and weight reduction.[6]Metaphorical and Systemic Applications
Beyond physical structures, "hub" metaphorically describes centralized systems in various fields; for instance, a transportation hub like an airport or port serves as a primary interchange point for routes, passengers, and cargo, optimizing connectivity and efficiency in global logistics.[1] In business and urban planning, innovation or financial hubs refer to geographic or institutional clusters that concentrate resources, talent, and infrastructure to drive economic activity, such as Silicon Valley as a technology hub.[2]Networking and Technology Context
Network hubs, introduced in the 1980s for Ethernet LANs, function as multi-port repeaters that extend cable lengths and consolidate connections but are largely obsolete today due to their inefficiency in handling traffic collisions compared to switches.[7] USB hubs extend this concept to peripherals, allowing multiple devices like keyboards, mice, and drives to connect to a single port on a computer, with powered variants providing additional electricity to support high-demand gadgets.[8] Despite their simplicity, hubs remain relevant in low-cost, small-scale setups or legacy systems, though modern networks favor intelligent devices for better performance and security.[9]General concepts
Mechanical and engineering
In mechanical engineering, a hub refers to the central part of a wheel that connects the axle or spindle to the rim, typically featuring flanges or spokes for secure attachment and load distribution. This component serves as the mounting point for the wheel assembly, enabling rotation while supporting radial and axial loads from the vehicle's weight and motion.[10][5] The term "hub" originated in the 1640s as a wheelwright's term for the solid center of a wheel, derived from the Middle English "hubbe," meaning a lump, round protuberance, or boss, possibly related to "hob" denoting a projection. By the 17th century, it described essential components in carriages and early vehicles, evolving from basic wooden projections to more complex metal structures as transportation advanced.[11] Modern wheel hubs are engineered for durability, weight reduction, and performance, commonly using materials such as steel for high-strength applications, aluminum alloys for lightweight efficiency (reducing weight by 20-30% compared to steel in compact cars), and composites in specialized high-performance or industrial contexts to enhance corrosion resistance and fatigue life. Types include fixed hubs, which rigidly connect to the axle for direct drive; freehubs in bicycles, featuring a ratcheting mechanism with pawls that allow coasting while engaging under pedaling torque; and hub motors in electric vehicles, where the motor is integrated into the hub to deliver propulsion directly to the wheel. In hub motors, torque is calculated as \tau = F \times r, where \tau is torque, F is the tangential force from the motor, and r is the wheel radius, enabling efficient power delivery up to several hundred Nm depending on vehicle design.[12][13][14][15][16] Wheel hubs find applications in automotive wheels, where they integrate with bearing units to handle speeds up to 200 km/h and loads exceeding 1,000 kg per wheel; in bicycles, employing sealed bearing systems for low-friction rotation and quick-release or thru-axle interfaces; and in industrial machinery such as conveyor systems, where robust hubs support continuous operation under heavy, repetitive loads in environments like manufacturing plants.[10][17][18][19] A cross-section of a typical wheel hub reveals the central axle interface, often secured by nuts or swaging for spindle integration; surrounding double-row angular contact or tapered roller bearings that provide preload and sealing against contaminants; and outer flanges or mounting points for attaching the rim, brake components, or wheel sensors, ensuring precise alignment and smooth rotation.[20][21]Computing and networking
In computing and networking, a hub is a hardware device that connects multiple Ethernet or USB devices, broadcasting incoming data packets from one port to all other connected ports, thereby enabling communication within a local area network (LAN).[22] Unlike more advanced devices such as switches, which intelligently direct traffic to specific destinations based on MAC addresses, hubs operate without examining packet contents, leading to potential inefficiencies in larger networks.[22] Hubs function at Layer 1 (the physical layer) of the Open Systems Interconnection (OSI) model, where they simply regenerate and distribute electrical signals without processing or filtering data.[22] In Ethernet hubs, all connected devices share a single collision domain, meaning simultaneous transmissions from multiple devices can result in data collisions, requiring retransmissions and reducing effective throughput.[22] Bandwidth is shared across all ports connected to a common backplane; for example, in a 10 Mbps Ethernet hub with multiple active devices transmitting, the effective per-device speed approximates the total bandwidth divided by the number of active transmitters.[23] Common types of hubs include passive hubs, which provide basic connectivity without signal processing or amplification; active hubs (also known as repeaters), which amplify signals to extend network reach; and intelligent hubs, which incorporate management features like SNMP for monitoring and configuration.[22] For USB hubs, defined under Base Class 09h in the USB specification, types include full-speed hubs, hi-speed hubs with single or multiple transaction translators to handle compatibility between USB speeds.[24] Ethernet hubs emerged in the late 1980s alongside the adoption of twisted-pair cabling for 10BASE-T networks, facilitating the shift from coaxial Ethernet setups and enabling multi-device LANs in offices and homes.[25] Their popularity waned in the 1990s and early 2000s as affordable switches provided better performance by segmenting collision domains and offering dedicated bandwidth per port.[22] USB hubs, introduced with the USB standard in 1996, evolved significantly; modern USB 3.2 hubs support power delivery up to 100 W via USB Power Delivery (PD) 3.0 specifications, while USB4 hubs support up to 240 W via PD 3.1.[26] Hubs find applications in home networking for connecting devices like computers and printers to a shared Ethernet or USB backbone, in office setups to extend LAN ports cost-effectively for small teams, and as USB docking stations that consolidate peripherals such as monitors, keyboards, and external drives for portable laptops.[22] Despite their decline in Ethernet contexts, USB hubs remain essential for peripheral expansion in contemporary computing environments.[26]Business and logistics
In business and logistics, a hub denotes a central node or facility in economic and supply chain networks where goods, information, or services converge for processing, consolidation, and redistribution, enabling efficient coordination across dispersed operations. This structure optimizes resource allocation by centralizing activities that would otherwise require direct point-to-point connections, reducing redundancy and enhancing scalability in global trade and organizational models. Drawing from the mechanical metaphor of a wheel hub as a connecting pivot, the concept adapts this centrality to abstract economic strategies. The hub-and-spoke model exemplifies this approach, particularly in logistics, where shipments are routed to a primary hub before distribution to secondary "spoke" destinations, minimizing overall transit distances and operational complexity. Originating in the airline industry following the 1978 U.S. Airline Deregulation Act, which removed entry barriers and spurred network consolidation, the model allowed carriers to achieve higher load factors and lower fares through focused operations at key airports. By the 2000s, it expanded to e-commerce fulfillment, with companies leveraging centralized warehouses to handle surging online orders, as seen in the growth of regional distribution networks that supported rapid scaling during the digital retail boom. Efficiency in hub-and-spoke systems is quantified through optimization models that minimize total costs, expressed asTC = C_h + C_t + C_i
where TC is the total cost, C_h represents fixed and variable handling costs at the hub (such as storage and processing), C_t denotes transportation costs between spokes and the hub, and C_i accounts for inter-hub linkages if multiple hubs are involved; centralization reduces C_t by consolidating flows, though it elevates C_h if volumes overwhelm capacity. Notable examples include Singapore's port, the world's busiest transshipment hub, which processed 40.9 million twenty-foot equivalent units (TEUs) in 2024 by serving as a nexus for Asia-Pacific trade routes with advanced connectivity to over 600 global ports.[27] Similarly, urban innovation hubs like Silicon Valley foster startup ecosystems by integrating incubators, venture funding access, and collaborative networks, driving economic growth through concentrated knowledge exchange and resource sharing. While hubs offer advantages such as inventory centralization for better demand forecasting and cost offsets via economies of scale—enabling faster delivery times and reduced empty-mileage in transport—their reliance on single points of convergence introduces vulnerabilities to disruptions. For instance, the 2021 global supply chain crises, exacerbated by COVID-19 surges, port congestions, and the Suez Canal blockage, amplified delays at major hubs, underscoring the risks of over-centralization and the need for resilient backups like diversified routing.