What Is TCP/IP?

TCP/IP is the foundational protocol suite that runs the internet by addressing, routing, and reliably delivering data between networked devices. TCP/IP combines the Transmission Control Protocol (TCP), which delivers data reliably and in order, with the Internet Protocol (IP), which addresses and routes packets between networks. The Internet Engineering Task Force (IETF) defines the suite in a series of Request for Comments (RFC) documents, and it organizes communication into four layers.

This article defines TCP/IP, describes its four layers, explains how TCP and IP work together, compares TCP with UDP, sets out the role of the suite in the internet, and relates it to the OSI model. A comparison table summarizes the four layers.

Each section states one part of the topic and connects it to the addressing and reliable delivery at the center of the suite. The result is a complete account of what TCP/IP is, how its layers divide the work, and why it forms the basis of the modern internet.

What Is TCP/IP?

TCP/IP is the foundational internet protocol suite that combines the Transmission Control Protocol for reliable delivery with the Internet Protocol for addressing and routing. TCP/IP organizes network communication into four layers, each handling one function, so data moves from an application on one device to an application on another across many networks. The defining traits of TCP/IP are listed below:

• A protocol suite groups TCP, IP, UDP, and related protocols into one cooperating set.
• A four-layer model divides communication into link, internet, transport, and application layers.
• Reliable delivery comes from TCP, which acknowledges and reorders data.
• Addressing and routing come from IP, which carries source and destination addresses on every packet.

TCP/IP is the suite of network protocols that the internet runs on, named for its two core members. The addresses IP assigns to each device are defined in the overview of an IP address.

What Are the Four Layers of TCP/IP?

The TCP/IP model has four layers: the link layer, the internet layer, the transport layer, and the application layer, each serving the layer above and using the layer below. A layer handles one part of communication and passes data to the next, dividing a complex task into manageable stages. The four layers of TCP/IP are listed below:

• The link layer moves frames across the physical medium using hardware addresses on the local network.
• The internet layer addresses and routes packets between networks using the Internet Protocol.
• The transport layer delivers data between applications using TCP for reliability or UDP for speed.
• The application layer carries application data through protocols such as HTTP, DNS, and FTP.

The hardware address the link layer uses on the local network is the MAC address, while the internet layer uses logical IP addresses to cross networks. Dividing the address space into networks and hosts depends on the subnet mask.

How Do TCP and IP Work Together?

TCP and IP work together by dividing the task: IP addresses and routes each packet between networks, while TCP ensures the packets arrive complete and in order at the destination. IP carries data across networks without guaranteeing delivery, and TCP adds the reliability that IP alone does not provide. The division of work is described below:

• Internet Protocol places source and destination addresses on each packet and routes it toward the target network.
• Transmission Control Protocol breaks data into segments, numbers them, and confirms each segment’s arrival.
• IP delivers packets independently, so they can take different routes and arrive out of order.
• TCP reorders and retransmits, reassembling the segments and requesting any that fail to arrive.

Internet Protocol handles addressing and routing while Transmission Control Protocol handles reliability, so the two together move data accurately across the global internet. The route packets follow between networks is traced in the explanation of how data travels on the internet.

How Does TCP Differ From UDP?

Transmission Control Protocol (TCP) delivers data reliably and in order through acknowledged connections, while User Datagram Protocol (UDP) delivers data faster without acknowledgments. Both run at the transport layer of TCP/IP, but TCP confirms delivery and UDP does not. The differences are listed below:

• TCP is connection-oriented, establishing a session and confirming each segment before continuing.
• UDP is connectionless, sending datagrams without a session or delivery confirmation.
• TCP retransmits lost data and orders segments, suiting web pages, email, and file transfer.
• UDP skips retransmission for lower delay, suiting live voice, video, and online gaming.

TCP and UDP both sit above IP at the transport layer, and an application chooses between them based on whether reliability or low delay matters more, according to the IETF specifications RFC 793 and RFC 768. The Internet Protocol underneath carries either one to the destination.

What Is the Role of TCP/IP in the Internet?

TCP/IP is the protocol suite that makes the internet work by giving every connected device a common addressing and delivery standard across independent networks. The internet is a network of networks, and TCP/IP provides the shared rules that let those separate networks exchange data. The role of TCP/IP in the internet is described below:

• A universal standard lets devices on different networks and operating systems communicate.
• Global addressing through IP gives every device a reachable address across the internet.
• End-to-end delivery through TCP moves data accurately between distant applications.
• Routing between networks lets packets cross many networks to reach any destination.

TCP/IP gives the internet one common standard so independently operated networks interconnect, which is why the suite is called the foundation of the internet. The two versions of Internet Protocol addressing in use are compared in the IPv4 versus IPv6 comparison.

How Does TCP/IP Relate to the OSI Model?

The four-layer TCP/IP model maps onto the seven-layer OSI model, with the TCP/IP layers combining several OSI layers into broader functions. The OSI model is a reference framework, while TCP/IP is the suite actually used, so the two describe the same communication at different levels of detail. The mapping is described below:

• The TCP/IP application layer covers the OSI application, presentation, and session layers.
• The TCP/IP transport layer matches the OSI transport layer, where TCP and UDP operate.
• The TCP/IP internet layer matches the OSI network layer, where IP routes packets.
• The TCP/IP link layer covers the OSI data link and physical layers.

The OSI model provides a seven-layer reference that describes communication in finer detail than TCP/IP’s four layers, explained in the overview of the OSI model. The ISO defines the OSI model, while the IETF defines TCP/IP, so the two frameworks come from different standards bodies.

TCP/IP Four-Layer Comparison Table

What Is the TCP Three-Way Handshake?

The TCP three-way handshake is the three-step exchange that establishes a connection before data transfer, synchronizing both devices through SYN, SYN-ACK, and ACK messages. A TCP connection opens with this handshake so both ends agree on sequence numbers before sending data. The three steps of the handshake are listed below:

1. SYN is the first message, in which the client sends a synchronize request with its initial sequence number.
2. SYN-ACK is the second message, in which the server acknowledges and sends its own sequence number.
3. ACK is the third message, in which the client acknowledges the server’s sequence number to open the connection.

The three-way handshake makes Transmission Control Protocol connection-oriented, since both devices confirm readiness before transfer, according to the IETF specification RFC 793. User Datagram Protocol skips this handshake, which lowers its delay but removes its delivery guarantee. A TCP connection closes with a separate exchange of FIN and ACK messages, releasing the session once both devices finish sending data.

What Supporting Protocols Run Within TCP/IP?

Supporting protocols within TCP/IP include ICMP, ARP, DNS, and DHCP, each handling a task that TCP and IP do not perform alone. A supporting protocol fills a specific role, from reporting errors to resolving names, so the suite functions end to end. The main supporting protocols are listed below:

• Internet Control Message Protocol (ICMP) reports errors and runs diagnostics such as the ping command.
• Address Resolution Protocol (ARP) maps an IP address to a hardware address on the local network.
• Domain Name System (DNS) translates domain names into the IP addresses that IP routes to.
• Dynamic Host Configuration Protocol (DHCP) assigns IP addresses to devices automatically as they join a network.

Address Resolution Protocol links the internet layer to the hardware address defined in the description of a MAC address, while the Domain Name System resolves names to the addresses in the overview of an IP address. These protocols run alongside TCP and IP to complete the suite.

Key Takeaways

• TCP/IP is the foundational internet protocol suite combining TCP and IP.
• The four layers are link, internet, transport, and application.
• IP addresses and routes packets, while TCP delivers them reliably and in order.
• TCP delivers reliably, while UDP delivers faster without acknowledgments.
• TCP/IP is the standard that lets independent networks form the internet.
• The four TCP/IP layers map onto the seven layers of the OSI reference model.

Last Thoughts on TCP/IP

TCP/IP is the protocol suite that runs the internet by addressing, routing, and reliably delivering data between devices. The four layers, link, internet, transport, and application, divide the work, with IP addressing and routing packets and TCP ensuring they arrive complete and in order. TCP delivers reliably while UDP delivers faster without acknowledgments, and the suite gives independent networks the common standard that forms the internet.

The four TCP/IP layers map onto the seven layers of the OSI reference model. Readers can continue with the overview of the OSI model, the explanation of network protocols, the IPv4 versus IPv6 comparison, or the guide to how networks work.