What Are Computer Networks?

Computer networks are collections of computing devices connected by communication links that allow the exchange of data and the sharing of resources. A network is defined by the hardware that forms its nodes (computers, routers, switches, and access points), the physical or wireless media that carry signals between them, and the protocols that govern how data is formatted, addressed, transmitted, and received. The field draws on electrical engineering, information theory, and distributed systems research to design networks that are fast, reliable, and secure.

Networking research and practice are organized around layered protocol models, most commonly the seven-layer OSI reference model or the four-layer TCP/IP model. Each layer provides services to the layer above it and depends on the layer below, allowing different components of a network system to be designed and replaced independently.

Ethernet and Local Area Networks

A local area network (LAN) connects devices within a limited geographic area, such as a building or campus, at high data rates with low latency. Ethernet, standardized by the IEEE 802.3 working group, is the dominant LAN technology. It has evolved from the 10 Mbps coaxial-cable networks of the early 1980s through 100 Mbps Fast Ethernet and 1 Gbps Gigabit Ethernet to 400 Gbps variants used in modern data centers. The IEEE 802.3 standard family defines the physical and data-link layer specifications for Ethernet, including frame format, collision avoidance, and auto-negotiation. Switched Ethernet, which replaced shared-medium hubs in the 1990s, gives each device a dedicated collision domain and allows simultaneous full-duplex communication across multiple ports.

Wide Area Networks

A wide area network (WAN) spans large geographic distances, interconnecting LANs across cities, countries, or continents. WANs use a mix of physical media, including fiber optic cables (for backbone links), copper lines (for last-mile access), and satellite links (for remote locations). The public internet is the largest WAN, built from thousands of independently operated autonomous systems that exchange routing information using the Border Gateway Protocol (BGP). Enterprise WANs connect branch offices to central data centers using leased lines, MPLS (Multiprotocol Label Switching) circuits, or software-defined WAN (SD-WAN) overlays that route traffic dynamically across multiple physical links based on cost and performance policies.

Network Topology and Management

Network topology describes the physical or logical arrangement of nodes and links in a network. Common topologies include bus, ring, star, mesh, and tree configurations, each with different trade-offs in resilience, cost, and scalability. In practice, large networks use hierarchical designs that combine access, distribution, and core layers, with redundant paths at each level to prevent single points of failure. Network management encompasses the processes and tools used to monitor performance, detect faults, configure devices, and enforce policies. The Simple Network Management Protocol (SNMP) and newer frameworks such as NETCONF and RESTCONF allow operators to query and configure network devices programmatically. NIST Special Publication 800-189 addresses resilient interdomain traffic exchange and routing security in complex network topologies.

Peer-to-Peer and Ad Hoc Networks

Peer-to-peer (P2P) networks distribute computation and storage across participating nodes rather than concentrating it in dedicated servers. Each node acts simultaneously as a client and a server, contributing resources to the network while consuming them. P2P architectures underpin distributed file-sharing systems, blockchain networks, and distributed communication platforms. Ad hoc networks are a related class of infrastructure-free networks in which mobile nodes communicate directly with one another, forming and reconfiguring their topology dynamically as nodes move or disconnect. Mobile ad hoc networks (MANETs) are used in military field communications and disaster response scenarios where fixed infrastructure is unavailable. Content distribution networks (CDNs) address a different scale challenge, caching web content at edge servers distributed geographically to reduce latency for end users. IEEE Communications Surveys and Tutorials provides peer-reviewed survey articles covering P2P, ad hoc, and CDN architectures across their protocol design and performance dimensions.

Applications

Computer networks have applications in a wide range of disciplines, including:

• Internet access and web services, through the global TCP/IP infrastructure connecting billions of devices
• Industrial automation and process control, via industrial Ethernet and fieldbus networks
• Telecommunications, including voice over IP (VoIP) and video conferencing systems
• Healthcare, through hospital information networks that connect imaging, records, and monitoring systems
• Scientific research, using high-bandwidth research networks such as ESnet to transfer large experimental datasets