WebSocket vs TCP

WebSocket and TCP are not competing choices: WebSocket runs on top of TCP. TCP is the transport-layer protocol that delivers a reliable, ordered stream of bytes between two hosts. WebSocket adds a handshake, message framing, and a persistent full-duplex channel that browsers and servers can use directly.

So the practical question is rarely "TCP or WebSocket" but "how close to the wire do I need to be". Browser code cannot open a raw TCP socket at all, which settles the choice for most web applications. Backend services that talk only to each other can go straight to TCP, or reach for server-sent events or webhooks when the traffic is one-directional.

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How TCP works

TCP is one of the core protocols of the Internet Protocol (IP) suite and operates at the transport layer. It provides a reliable, ordered, and error-checked delivery of a stream of bytes between applications running on hosts communicating over an IP network. TCP is responsible for establishing a connection between the client and server, ensuring that data packets are delivered in the correct order, and handling retransmissions in case of lost or corrupted packets. TCP is fundamental to many other higher-level protocols, such as HTTP, FTP, and SMTP, and is used wherever reliable data transfer matters: file transfers, email, and web browsing.

How WebSocket works

WebSocket is a protocol that operates over TCP but is specifically designed to facilitate real-time, bidirectional communication between a client (typically a web browser) and a server. WebSocket starts with an HTTP handshake to establish a connection, which is then upgraded to a persistent WebSocket connection. This connection allows for continuous, full-duplex communication, enabling both the client and the server to send and receive data simultaneously. WebSocket is widely used in web applications that require low-latency, real-time communication, such as chat applications, live sports updates, online gaming, and collaborative tools.

How WebSocket and TCP differ

	TCP	WebSocket
Layer	Transport	Application, carried over TCP
Unit of data	Byte stream with no boundaries	Discrete messages, framed
Connection setup	Three-way handshake	HTTP request, then 101 Switching Protocols
Browser access	None	new WebSocket(url)
Usual ports	Any	80 for ws://, 443 for wss://
Comes with	Ordering, retransmission, flow control	Framing, ping/pong keepalive, close codes, subprotocols

Layer of operation

The key difference between WebSocket and TCP lies in their layer of operation. TCP is a transport layer protocol, providing the foundation for reliable communication. It is a low-level protocol that ensures the delivery of data across the network, handling the segmentation of data into packets, retransmissions, and reordering of out-of-sequence packets. TCP does not dictate how data is structured or interpreted, leaving those responsibilities to higher-level protocols.

WebSocket, on the other hand, operates at a higher level, on top of TCP. It is a messaging protocol that uses TCP to transport data but adds its own framing and control messages to facilitate full-duplex communication in web applications. WebSocket handles the continuous exchange of messages between a client and server, making it easier to implement real-time features in web applications.

Use cases

TCP is a general-purpose protocol used wherever reliable, ordered delivery of data is essential. It is the backbone of most internet communications, supporting web traffic (HTTP), email (SMTP), file transfers (FTP), and many other protocols. TCP's reliability and widespread adoption make it suitable for any application where the integrity and order of data transmission matter.

WebSocket is specifically designed for scenarios where real-time, bidirectional communication is needed within web applications. It is ideal for applications that require low-latency interactions, such as live chat systems, real-time notifications, online multiplayer games, and live streaming. WebSocket simplifies the process of maintaining an open connection between the client and server, allowing for instant data exchange without the overhead of repeatedly establishing new connections. If only the server needs to push, SSE is a lighter option.

Complexity and implementation

Implementing TCP directly in an application requires handling various low-level details, such as packet assembly, connection management, error detection, and retransmission. While this provides maximum control and flexibility, it also increases the complexity of the application, especially when developing custom communication protocols.

WebSocket abstracts much of this complexity by providing a higher-level interface for real-time communication. It handles the intricacies of maintaining a persistent connection, message framing, and managing the HTTP upgrade process, allowing developers to focus on the application’s real-time features rather than the underlying communication mechanics.

Performance

TCP is highly efficient and reliable for the general transport of data, with extensive optimizations developed over decades of use. However, in applications requiring frequent and real-time data exchange, using raw TCP may involve significant overhead, as developers need to manually manage the continuous flow of data.

WebSocket, built on top of TCP, is optimized for scenarios where low latency and minimal overhead are essential. By maintaining a single persistent connection, WebSocket reduces the overhead associated with establishing multiple connections, making it more suitable for real-time applications that require frequent and small data exchanges.

Choosing between TCP and WebSocket

TCP and WebSocket serve different purposes within network communications. TCP, as a fundamental transport protocol, is essential for ensuring reliable data transmission across a network, and it underpins many higher-level protocols, including WebSocket. WebSocket, operating on top of TCP, provides a higher-level abstraction specifically tailored for real-time, bidirectional communication in web applications. Reach for raw TCP when you control both ends and want to define your own protocol; reach for WebSocket when a browser is involved or you would otherwise be rebuilding framing and connection management yourself. And if the client only needs to be told when something happened, neither one is the answer: compare webhooks and WebSockets before you keep a socket open for every user.