Socket

A socket is basically an endpoint for sending or receiving data across a network. It’s an abstraction that allows programs to communicate over TCP/IP (or other protocols) without worrying about the low-level details of packets, IP addresses, or hardware.

Definition

A socket is a software structure (usually provided by the operating system) that allows an application to:

• Connect to another machine on the network.
• Send and receive data.

It’s like a door on your computer: you send data out, receive data in, and the socket manages how it flows over the network.

Structure

Socket = IP address + Port number

A socket is identified by:

• IP address – which device to talk to.
• Port number – which application/service on that device.
• Protocol – usually TCP (reliable) or UDP (fast, connectionless).

Example: 192.168.1.10:80 is a socket endpoint for HTTP on a device.

Types of sockets

Type	Description
Stream socket (TCP)	Connection-oriented, reliable, guarantees order and delivery.
Datagram socket (UDP)	Connectionless, faster, no guarantee of delivery or order.
Raw socket	Gives direct access to lower layers (used for ICMP/ping, custom protocols).

• SOCK_STREAM → TCP
• SOCK_DGRAM → UDP

Things work without sockets

• Most application-level network communication uses sockets.
• Not all network communication involves sockets—hardware, protocols, and OS-level packet forwarding can happen entirely below the socket layer.

Scenario	How it works
Routing protocols (OSPF, BGP)	Routers exchange packets directly at Layer 3/4, often without using OS-level socket APIs.
Network devices (switches, NICs)	Use MAC addresses and hardware logic (Layer 2), not sockets.
Low-level network tools	Tools like ping send ICMP packets, which can bypass standard TCP/UDP sockets via raw sockets.
Kernel-level communication	OS kernel or drivers may move packets between layers without involving sockets at all.
Embedded devices / IoT	Sometimes send/receive packets via microcontroller registers, not high-level socket APIs.

Application Ports

In networking, different ports are used for various purposes. Generally, these port ranges can be divided into three categories. Below, you can find these port ranges:

• Well-Known Ports ( 1 to 1024 )
• Registered Ports ( 1025 to 49151 )
• Private Ports ( 49152 to 65535 )