Connection-less Service

A Connectionless Service is technique that is used in data communications to send or transfer data or message at Layer 4 i.e., Transport Layer of Open System Interconnection model. This service does not require session connection among sender or source and receiver or destination. Sender starts transferring or sending data or messages to destination.

In other words, we can say that connectionless service simply means that node can transfer or send data packets or messages to its receiver even without session connection to receiver. Message is sent or transferred without prior arrangement. This usually works due to error handling protocols that allow and give permission for correction of errors just like requesting retransmission.

In this service, network sends each packet of data to sender one at a time, independently of other packets. But network does not have any state information to determine or identify whether packet is part of stream of other packets. Even the network doesn’t have any knowledge and information about amount of traffic that will be transferred by user. In this, each of data packets has source or destination address and is routed independently from source to destination.

Therefore, data packets or messages might follow different paths to reach destination. Data packets are also called datagrams. It is also similar to that of postal services, as it also carries full address of destination where message is to send. Data is also sent in one direction from source to destination without checking that destination is still present there or not or if receiver or destination is prepared to accept message.

Connectionless Protocols :
These protocols simply allow data to be transferred without any link among processes. Some Of data packets may also be lost during transmission. Some of protocols for connectionless services are given below:

• Internet Protocol (IP) –
  This protocol is connectionless. In this protocol, all packets in IP network are routed independently. They might not go through same route.
• User Datagram Protocol (UDP) –
  This protocol does not establish any connection before transferring data. It just sends data that’s why UDP is known as connectionless.
• Internet Control Message Protocol (ICMP) –
  ICMP is called connectionless simply because it does not need any hosts to handshake before establishing any connection.
• Internetwork Packet Exchange (IPX) –
  IPX is called connectionless as it doesn’t need any consistent connection that is required to be maintained while data packets or messages are being transferred from one system to another.

Types of Connectionless Services :

Service	Example
Unreliable Datagram	Electronic Junk Mail, etc.
Acknowledged Datagram	Registered mail, text messages along with delivery report, etc.
Request Reply	Queries from remote databases, etc.

Advantages :

• It is very fast and also allows for multicast and broadcast operations in which similar data are transferred to various recipients in a single transmission.
• The effect of any error occurred can be reduced by implementing error-correcting within an application protocol.
• This service is very easy and simple and is also low overhead.
• At the network layer, host software is very much simpler.
• No authentication is required in this service.
• Some of the application doesn’t even require sequential delivery of packets or data. Examples include packet voice, etc.

Disadvantages :

• This service is less reliable as compared to connection-oriented service.
• It does not guarantee that there will be no loss, or error occurrence, misdelivery, duplication, or out-of-sequence delivery of the packet.
• They are more prone towards network congestions.