Differences between Connection-oriented and Connection-less Services.

As an analogy, we can think of connection-oriented services as telephone systems, where a connection needs to be established between a sender and a receiver before they can exchange data. In contrast, connection-less services are like traditional postal systems where data exchange can take place between a sender and a receiver without establishing a connection.

Go through this article to find out the major differences between connection-oriented and connection-less services.

What is Connection-oriented Service?

A connection-oriented service is a data transfer mechanism used at the session layer. In contrast to its opposite, connectionless service, connection-oriented service necessitates establishing a session connection between the sender and recipient, similar to a phone call.

Although not all connection-oriented protocols are reliable, this strategy is generally more reliable than a connectionless service. It starts with a connection establishment and ends with connection termination. This service uses handshake method to establish a connection between sender and receiver.

In a packet-switched network, a connection-oriented service can be a circuit-switched link or a virtual circuit connection. A connection identifier, which is typically a small integer of 10 to 24 bits, is used to identify traffic flows in the latter case. This is used instead of specifying the destination and source addresses.

Before data can be transferred between linked terminals, a connection-oriented service requires that a connection be established between peers. This handles real-time traffic better than connectionless protocols because it arrives in the same order as it was delivered. Protocols that are based on connections are also less prone to errors.

For real-time and isochronous traffic streams, asynchronous transfer mode is a connection-oriented service that Ethernet has not supplanted. Increasing the bandwidth isn't always the answer to service issues. In many cases, a competent connection-oriented service can give higher quality than greater bandwidth. Despite this, certain connection-oriented services have been developed to handle both connectionless and connection-oriented data.

During a communication session, all the data is sent over the same path in a connection-oriented, packet-switched data link layer or network layer protocol. The protocol needs to supply a channel/data stream number, also known as a virtual circuit identifier, to each packet instead of routing information (full source and destination addresses) (VCI). During the connection establishment phase, routing information may be sent to network nodes, where the VCI is defined in tables in each node. As a result, rapid hardware can handle packet switching and data transport rather than slow, software-based routing.

What is Connection-less Service?

Connection-less Service is like a postal system. It doesn't have to establish a connection to transfer data. Data packets can follow any route to reach their destination.

Connectionless service is a data communications concept used to transfer data at the transport layer of the OSI model (layer 4). It refers to data being delivered from one node to another without first ensuring that the destination is available and ready to accept the data. The sender does not need to establish a session connection with the recipient; instead, the sender begins transferring data. Because the message or datagram is sent without prior arrangement, it is less reliable but faster than a connection-oriented service.

Connectionless service refers to the ability of a terminal or node to transfer data packets to a destination without first establishing a connection. This is possible because of error-handling protocols that allow for error corrections such as retransmission requests. LANs are connectionless systems, with each computer can transmit data packets as soon as it has network access.

The Internet is a massive connectionless packet network where Internet providers handle all packet delivery. When necessary, TCP provides connection-oriented services to IP. TCP can provide all of the required top-level connection functions to ensure that data is delivered correctly.

Difference between Connection-oriented and Connection-less Services

The following table highlights the major differences between Connection-oriented Services and Connection-less Services.

Key Connection-oriented Services Connection-less Services
Usage Connection-oriented Services are used in case of long and steady communication. Connection-less services are used in bursty communication.
Connection In Connection-oriented Services, connection is necessary. In Connection-less services, connection is not necessary.
Congestion No congestion occurs in connection-oriented services. Congestion can occur in connection-less services.
Guarantee of Reliability Connection-oriented Services give guarantee of reliability. Connection-less services don't give guarantee of reliability.
Data Packets In Connection-oriented Services, data packets follow the same route. In Connection-less services, data packets may follow any route.


In general, connection-oriented services are more dependable than connection-less services. Connection-oriented services are the preferred mode of communication where data integrity is of utmost importance. Connection-less services are not resource intensive but there is always a danger of losing a few data packets in transition.

Updated on: 11-Aug-2022

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