What is connectionless?

In telecommunications, connectionless describes communication between two network endpoints in which a message can be sent from one endpoint to another without prior arrangement. The device at one end of the communication transmits data to the other without first ensuring that the recipient is available and ready to receive the data. The device sending a message simply sends it addressed to the intended recipient. If there are problems with the transmission, the sender might need to resend the data several times.

Internet Protocol (IP) and User Datagram Protocol (UDP) are connectionless protocols that enable connectionless operations. But that leads to the following question: What is a connectionless service in a computer network?

The term connectionless describes a type of communication service that enables data to be transferred between network endpoints. The sending endpoint does not try to establish a dedicated, end-to-end connection with the receiving endpoint or even try to ensure that the receiver is available to accept the data.

The sender transmits the data in a packet -- sometimes referred to as datagrams. Although the packets are addressed to the recipient, they're sent independently of each other and treated independently by the network. The packets might be routed along different paths or received in an order different from how they were sent. It's up to that endpoint to reassemble the packets in the correct order.

Connectionless network communications are carried out by connectionless protocols, such as the following:

  • IP. Network layer protocol that addresses and routes data packets between network endpoints.
  • UDP. Transport layer protocol used primarily to establish low-latency and loss-tolerating connections between applications on the internet.
  • Internet Control Message Protocol. Network layer protocol used by network devices, such as routers, to communicate data transmission issues to the source IP address.
  • Hypertext Transfer Protocol. Application layer protocol for transferring files such as Hypertext Markup Language documents over the web.

Connectionless protocols are usually described as stateless because the endpoints have no protocol-defined way to remember where they are in a "conversation" of message exchanges. The alternative to the connectionless approach uses connection-oriented protocols, which are sometimes described as stateful because they can keep track of a conversation.

What are connection-oriented and connectionless?

Connection-oriented and connectionless are two common approaches used in network communications.

Unlike connectionless services, the connection-oriented approach establishes a connection with a network endpoint before transmitting data. After communications are complete, the sender releases the connection. Transmission Control Protocol is one example of a connection-oriented protocol.

Connectionless and connection-oriented services support network communications in different ways. The following table describes the main differences between the two approaches.

Connectionless vs. connection-oriented network communications

Why is the internet connectionless?

Much of the traffic on the internet is connectionless because this approach makes it easier to handle certain types of traffic without incurring the overhead of data transmission services, such as connection-oriented protocols.

For example, UDP is often used to support domain name system or Network Time Protocol services. UDP can also be a good choice for streaming media or supporting multiplayer video games. But UDP is not the only protocol commonly used by the internet. IP also plays a pivotal role by providing the addressing and routing services that make the internet possible.

UDP vs. TCP protocols

A connectionless approach offers many advantages in supporting internet connectivity:

  • It results in lower overhead because no extra packets need to be exchanged to transmit data to an endpoint.
  • A network node can broadcast or multicast messages to multiple recipients.
  • Connectionless services are simpler in general than many alternatives; the sender can start sending messages without establishing a session or authenticating the connection.
  • If a router fails when transmitting data, the data can travel an alternative path.
  • Data transmission can be faster because there's no need to set up a connection or wait for acknowledgment.

Connectionless services are essential to keeping the internet running and to support applications that can tolerate packet loss and unreliable services. Some application protocols include error correction capabilities that can help address some of this unreliability.

This was last updated in August 2021

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