Connectionless Service and Protocols

A connectionless service does not require the sender and receiver to establish a session before sending packets to the destination. Networks can implement this service in the Network layer or the Transport layer of the OSI model.

The following are characteristics of connectionless service:

• Packets can arrive at the destination out of sequence, but the receiving station must reassemble them in sequence.

• No time is required to establish a session ”indeed, there is no session setup because a session is not used ”and data can be sent immediately.

• It does not use acknowledgments to check for packet delivery.

Note

Another connectionless protocol that you should already be aware of is the Internet Protocol (IP). IP is used by the Transmission Control Protocol (TCP) to establish sessions that must be set up before the data exchange can begin, and torn down in an orderly manner when the session ends.

The Internet is the largest connectionless network in the world, and it uses the Internet Protocol (IP) to deliver the packets to their destinations. IPX is the connectionless-oriented protocol that Novell systems use to deliver packets, and it operates at the OSI Network layer. A connectionless protocol is similar to a radio broadcast or letter delivery. The sender receives no acknowledgment for receipt of the letter delivery or radio broadcast.

This connectionless protocol is best used for disseminating information that is time sensitive and does not need retransmission, such as real-time video and audio. If a packet is not received, it's pointless to retransmit the packet after the remaining packets in that sequence have been sent to the video/audio processing software.

Connectionless protocols at the Transport layer take advantage of the port structure already in place. For example, say you have two hosts, one transmitting real-time audio, and the other connecting to the first host to receive the transmission. The second host receives the transmission on a UDP (User Datagram Protocol) port identified by the software that is receiving the real-time audio transmission. No error correction or packet acknowledgment is coordinated between the two hosts , but both use the same port for the transmission and receipt of the data. In effect, connectionless protocols, such as IP, IPX, and UDP, are similar to sending a letter or a radio broadcast because the sender is not concerned whether the recipient actually received the packet.