1 Network Fundamentals
Learn how networks connect devices, how their scope and arrangements differ, and how data moves between devices with different performance and delivery characteristics.
What networks connect
A is a group of connected devices that exchange information and share resources. It may link computers, phones, printers, servers, and other devices. Connections can use wired or wireless media, while provide shared rules for communication.
Network scope and connections
Networks are often classified by the geographic area they serve. A personal area network (PAN) connects devices around one person, such as a phone and wireless earbuds. A serves a limited area, such as a home, office, school, or campus; a LAN can combine wired Ethernet and wireless connections. A connects users or networks across larger distances, such as an organization's offices. The Internet is a large network of interconnected networks.
These boundaries are practical rather than exact: network size alone does not determine its type. The key distinction is the area and purpose served. A is a LAN that uses radio communication for some or all device connections, and Ethernet is a widely used LAN technology.
A LAN and a WAN can be parts of the same organization's network. For example, computers in a branch office communicate over its LAN, and a router can forward traffic toward a WAN connection to reach another office or an Internet service. A router connects and forwards traffic between networks, while a switch typically connects devices within a LAN.
Communication essentials
Communication involves a sender, a receiver, a message, a medium, and shared . The medium may be copper cable, fiber-optic cable, or radio waves. specify matters such as how data is formatted, addressed, and transmitted, as well as how errors are handled.
Packets and transport services
Most modern networks use : a message is divided into smaller units called packets, which travel through the network toward a destination and are reassembled by the receiving system. Each packet carries addressing and control information, and its route may pass through multiple links and routers.
provides addressing and delivery between networks. By itself, however, does not guarantee that packets arrive, arrive in order, or arrive only once. For applications that need reliable, ordered delivery, provides transport-layer services such as retransmission and sequencing. provides a simpler, connectionless transport service without 's delivery guarantees. Applications choose transport services suited to their needs.
Understanding network performance
Network performance is commonly described using several distinct measures:
is a link's maximum data-carrying capacity, usually measured in bits per second.
is the rate of data successfully delivered in practice.
is the time data takes to travel from source to destination.
refers to data packets that fail to reach their destination.
A video call may benefit from low and low , while a large file transfer may depend more on sustained . High does not necessarily mean low .
Ways devices share services
In a arrangement, client devices request services from servers; for example, a laptop may request a webpage from a web server. In a arrangement, devices can share resources directly without relying on a central server for every exchange. A network can combine both arrangements.