TCP/IP Network

TCP/IP network TCP/IP

Glossary

A TCP/IP network is based on two interacting core protocols: the Transmission Control Protocol (TCP) and the Internet Protocol (IP). Together they form the internet’s fundamental communication protocol and the basis for practically every data transfer between connected devices, from websites via email to file transfer and real-time communication.

The division of labour: TCP and IP

  • Internet Protocol (IP): connectionless, responsible for addressing and routing. Every device is assigned a unique IP address by which data packets are routed through the network, with no guarantee that a packet actually arrives.
  • Transmission Control Protocol (TCP): connection-oriented, responsible for reliable transmission. TCP ensures packets arrive complete, undamaged and in the correct order, and automatically requests lost packets again.

The three-way handshake

Before data is transferred over TCP, client and server establish a connection via a fixed sequence:

  1. SYN: the client sends a request to establish a connection.
  2. SYN-ACK: the server confirms and signals readiness.
  3. ACK: the client confirms in turn – the connection stands.

This mechanism is also security-relevant: in a SYN flood, a classic form of DDoS attack, massive numbers of SYN requests without a concluding ACK are deliberately sent to exhaust server resources.

TCP vs. UDP

Not every application needs TCP’s reliability guarantees:

TCPUDP
ConnectionConnection-oriented (handshake)Connectionless
ReliabilityGuaranteed, with retransmission of lost packetsNo guarantee
SpeedSlower due to overheadFaster, lower latency
Typical applicationsWebsites, email, file transferVideo streaming, online gaming, VoIP

Ports: how applications within a device are addressed

While the IP address identifies a device, the port number determines which application on that device is responsible for incoming data. Well-known examples: port 80 (HTTP), 443 (HTTPS), 21 (classic FTP) or 389/636 (LDAP/LDAPS). Only the combination of IP address and port uniquely identifies a concrete communication endpoint.

Protocols building on TCP/IP

TCP/IP forms the foundation on which a whole family of further protocols runs – HTTP/HTTPS for websites, FTP for file transfer, WebSocket for bidirectional real-time communication or SSL/TLS for encrypted connections. That’s why the “TCP/IP protocol family” is more frequently spoken of than just two individual protocols.

Conclusion

Even after decades, TCP/IP remains the invisible foundation on which practically every internet application builds, from the simple website to complex, distributed software architecture. We’re happy to support you with designing and securing your network infrastructure as part of our cyber security services or in an informal chat, with no strings attached.

Häufige Fragen

What's the difference between TCP and IP?
IP handles the addressing and routing of data packets – it makes sure a packet finds its destination at all but doesn’t guarantee it arrives. TCP builds on top and handles reliable transmission: missing packets are resent, the correct order is ensured. Only the interplay of both protocols makes reliable data transfer on the internet possible.
What's the difference between TCP and UDP?
TCP is connection-oriented and guarantees reliable, complete transmission in correct order, with corresponding overhead. UDP (User Datagram Protocol) forgoes these guarantees in favour of speed and lower latency. For websites, email or file transfer, TCP is used practically always; for video streaming, online gaming or VoIP, often UDP, where an occasionally lost packet disturbs less than delay would.
What is the three-way handshake?
The three-way handshake is TCP’s connection establishment: the client sends a SYN packet, the server answers with SYN-ACK, the client confirms with ACK. Only then does the connection count as established and data can be transferred. This mechanism is also exploited in so-called SYN flood attacks, a classic form of DDoS attack.
What do port numbers mean in TCP/IP?
A port number identifies, within a device, which service or application is responsible for incoming data – the IP address identifies the device, the port the concrete application on it. Well-known examples are port 80 for HTTP, 443 for HTTPS or 21 for FTP.
Why is it called a TCP/IP network when more than two protocols are actually involved?
TCP and IP are the two eponymous core protocols on which practically all remaining internet communication builds. In practice, a whole family of further protocols runs over or alongside them – HTTP, FTP, WebSocket, DNS and many more – which is why people often speak of the “TCP/IP protocol family” rather than just two individual protocols.
Does the internet work entirely without TCP/IP?
No, TCP/IP remains to this day the fundamental standard on which practically all internet communication is based, regardless of whether IPv4 or IPv6 is used as the addressing scheme. Alternative network protocols exist but play practically no role on the public internet.
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