TCP/IP is the pair of protocols that form the foundation of how data travels across the internet. TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. Together, they define how computers address each other, break data into packets, send those packets across networks, and reassemble them at the destination. Every time you load a webpage, send an email, or stream a video, TCP/IP is handling the delivery underneath.
IP handles addressing and routing. Every device on the internet gets an IP address, a unique number that identifies it on the network. When you send data, IP wraps it in packets, each stamped with the source and destination addresses. Routers along the way read the destination address and forward the packet one hop closer to where it needs to go. IP does not guarantee delivery or order. Packets can arrive out of sequence, get duplicated, or be lost entirely. IP just makes a best effort to get them there.
TCP adds reliability on top of IP. Before sending any data, TCP establishes a connection using a three-way handshake: the client sends a SYN packet, the server replies with SYN-ACK, and the client confirms with ACK. Once connected, TCP numbers every packet so the receiver can put them back in order. If a packet goes missing, the receiver notices the gap and asks the sender to retransmit it. TCP also manages flow control, slowing down the sender if the receiver cannot keep up, and congestion control, backing off when the network is overloaded.
The TCP/IP model has four layers. The link layer handles the physical connection (Ethernet, Wi-Fi). The internet layer handles addressing and routing (IP). The transport layer handles reliable delivery (TCP) or fast, connectionless delivery (UDP). The application layer handles protocols like HTTP for web pages, SMTP for email, and FTP for file transfers. This layered design means each part can evolve independently. You can swap Wi-Fi for cellular at the link layer without changing anything above it. TCP/IP has been running the internet since the 1980s and remains the backbone of all networked communication.