Difference between Connection-oriented and Connection-less Services

Connection-oriented and Connection-less Services are used to establish connections between two or more devices.

Connection-oriented Services

A connection-oriented service is one that establishes a dedicated connection between the communicating entities before data communication commences. It is modeled after the telephone system. To use a connection-oriented service, the user first establishes a connection, uses it and then releases it. In connection-oriented services, the data streams/packets are delivered to the receiver in the same order in which they have been sent by the sender.

Connection-oriented services may be done in either of the following ways −

• Circuit-switched connection: In circuit switching, a dedicated physical path or a circuit is established between the communicating nodes and then data stream is transferred.

• Virtual circuit-switched connection: Here, the data stream is transferred over a packet switched network, in such a way that it seems to the user that there is a dedicated path from the sender to the receiver. A virtual path is established here. However, other connections may also be using this path.

Connection-oriented services may be of the following types −

• Reliable Message Stream: e.g. sequence of pages

• Reliable Byte Stream: e.g. song download

• Unreliable Connection: e.g. VoIP (Voice over Internet Protocol)

Advantages of Connection-Oriented Services

• This is mostly a reliable connection.

• Congestions are less frequent.

• Sequencing of data packets is guaranteed.

• Problems related to duplicate data packets are alleviated.

• Suitable for long connection.

Disadvantages of Connection-Oriented Services

• Resource allocation is needed before communication. This often leads to under-utilized network resources.

• The lesser speed of connection due to the time is taken for establishing and relinquishing the connection.

• In the case of router failures or network congestions, there are no alternative ways to continue communication.

Connection-less Services

A Connectionless service is a data communication between two nodes where the sender sends data without ensuring whether the receiver is available to receive the data. Here, each data packet has the destination address and is routed independently irrespective of the other packets. Thus the data packets may follow different paths to reach the destination. There’s no need to setup connection before sending a message and relinquish it after the message has been sent. The data packets in a connectionless service are usually called datagrams.

Protocols for connectionless services are −

• Internet Protocol (IP)

• User Datagram Protocol (UDP)

• Internet Control Message Protocol (ICMP)

Connectionless services may be of the following types −

• A datagram with Acknowledgement: e.g. text messages with delivery report

• Request-Reply: e.g. queries from remote databases

Advantages of Connectionless Services

• It has low overhead.

• It enables to broadcast and multicast messages, where the sender sends messages to multiple recipients.

• It is simpler and has low overhead.

• It does not require any time for circuit setup.

• In case of router failures or network congestions, the data packets are routed through alternate paths. Hence, communication is not disrupted.

Disadvantages of Connectionless Services

• It is not a reliable connection. It does not guarantee that there will not be a loss of packets, wrong delivery, out – of – sequence delivery or duplication of packets.

• Each data packet requires longer data fields since it should hold all the destination address and the routing information.

• They are prone to network congestions.

Differences

Following are the important differences between Connection-oriented and Connection-less Services.

Sr.No.	Key	Connection-oriented Services	Connection-less Services
1	Analogy	Connection-oriented Services are similar to Telephone System.	Connection-less Services are similar to Postal System.
2	Usage	Connection-oriented Services are used in long and steady communication networks.	Connection-less Services are used in volatile networks.
3	Congestion	No Congestion in Connection-oriented Service.	Congestion is quiet possible in Connection-less Services.
4	Reliablility	Connection-oriented Service are highly reliable.	In Connection-less Services, no guarantee of reliablity.
5	Packet Routing	In Connection-oriented Service, packets follows same route.	In Connection-less Services, packets can follow any route.