User Datagram Protocol (UDP) is one of the core IP protocols. UDP with its connectionless model, no handshaking dialogues makes it a suitable transport for systems with constrained bandwidth like Bluetooth low energy. Unreliable data transmission may be seen as a drawback but application layer protocols like CoAP specify mechanisms of reliable delivery of data if need be.
UDP is supported both on Nordic's IPv6 stack and lwIP stack, and examples are provided using both the implementations of UDP. The examples that demonstrate UDP as transport for IoT applications using the two IPv6 stacks are identical in philosophy. Both define a server that responds to a certain ping message from the client, but vary in implementation details like data format, and so on.