Although the lower-layer switching is connectionless, or it may be a data link layer or network layer switching mode, where all data packets belonging to the same traffic stream are delivered over the same path, and traffic flows are identified by some connection identifier reducing the overhead of routing decisions on a packet-by-packet basis for the network.
Asynchronous Transfer Mode (ATM), Frame Relay and Multiprotocol Label Switching (MPLS) are examples of connection-oriented unreliable protocols.
A connection-oriented transport layer protocol, such as TCP, may be based on a connectionless network-layer protocol such as IP, but still achieves in-order delivery of a byte-stream by means of segment sequence numbering on the sender side, packet buffering, and data packet reordering on the receiver side.
Rather than using complete routing information for each packet (source and destination addresses) as in connectionless datagram switching such as conventional IP routers, a connection-oriented protocol identifies traffic flows only by a channel or data stream number, often denoted virtual circuit identifier (VCI).
Thus, the actual packet switching and data transfer can be taken care of by fast hardware, as opposed to slower software-based routing.