1 Networking Fundamentals
Learn how networks exchange data, how protocol layers and data units support delivery, and how clients, servers, TCP/IP, and OSI fit into the picture.
Networks and protocols
A is a group of connected devices that exchange data according to agreed rules called protocols. Networks may connect devices in one room or link networks across the world. The Internet is a network of interconnected networks.
How data moves through layers
Communication starts when an application has data to send. Networking functions add information needed to deliver that data; this process is called . At the destination, decapsulation interprets and removes the added information so the receiving application can use the data.
For example, when a browser requests a webpage, it prepares an application message. Transport and Internet protocols add information that helps identify the communicating applications and the source and destination hosts. A local network carries the data toward its next destination. If the destination is on another network, routers forward the IP between networks. The receiving device passes the data up through its networking functions to the web service or browser. Each layer follows its own rules, and the layers work together to complete the exchange.
Packets and data units
Network data is divided and labeled so that devices and protocols can handle it. The name of a data unit depends on its and layer: application data may be carried in a TCP segment or UDP datagram, placed inside an IP , and transmitted over a local link in a frame. These units include headers, which contain control information such as addresses or identifiers, and usually include the data being delivered. Terminology can vary, but data is wrapped in layers of information as it travels.
Packets are forwarded individually and may pass through multiple networks and routers before reaching the destination. The route taken by one is not necessarily a permanent connection between devices. At the destination, information helps deliver each unit to the appropriate next layer and application.
Clients and servers
A is a device or program that requests a service, while a is a device or program that provides one. These terms describe roles in a communication, not necessarily different kinds of hardware: one computer can act as a in one exchange and a in another.
For example, a browser acts as a when it requests a page, and the web is the program that responds with page data. A typically makes a service available for clients to contact. Protocols and addressing information help deliver requests to the correct service. Communication is often two-way: the sends a request, and the sends a response.
The
Network models organize communication functions into layers. Each layer has a defined role and uses services from the layer below it. Layering makes complex communication easier to describe and allows different technologies to work together when they follow compatible protocols.
A common four-layer describes the suite used for Internet communication:
Application: Supports services used by network applications, including web, email, and name-resolution protocols.
Transport: Provides communication between applications on hosts. TCP or UDP can distinguish applications at the endpoints.
Internet: Addresses and forwards packets between networks, using IP and routing.
Link: Moves data across a directly connected network using local network technologies and frames.
Some explanations split the Link layer into separate data-link and physical layers, yielding five layers. The number of layers is a teaching convention; the essential functions remain similar. Internet standards describe link, Internet, transport, and application functions, while tutorials commonly group or label them in different ways.
The and how models relate
The is a seven-layer reference model. From highest to lowest, its layers are Application, Presentation, Session, Transport, Network, Data Link, and Physical. It provides a structured vocabulary for discussing network functions and troubleshooting. It is conceptual, not a requirement that every real-world map neatly to exactly one layer.
The TCP/IP and OSI models are related ways to organize networking concepts, but their layers do not match one-to-one in every description. For example, the TCP/IP Link layer may cover functions associated with both the OSI Data Link and Physical layers. Use a model as a guide to where a function fits, rather than as a rigid description of every implementation.