Transmission Control Protocol (TCP) is one of the core IP Protocols. It is a connection oriented protocol and provides reliable transport. This reliability comes at the cost of control packets overhead of the protocol itself, making it unsuitable for bandwidth constrained applications.

To demonstrate TCP protocol support on nRF5x, lwIP stack is used. Nordic's stack does not currently support TCP.

As TCP is used as transport for the application, the actual physical transport used to communicate between TCP server and client does not matter as long as they are reachable at IPv6 level. Figure 1 below emphasizes on this fact by showing that the complementary role for nRF5x TCP server or client could be PC applications.

Figure 1: Setup of lwIP based IPv6 TCP examples.

The TCP client acts as an echo client sending requests to which the TCP server responds as demostrated in the MSC below.

Figure 2: TCP data exchange.

Note: The client does not wait for the response before sending the next request. Requests are sent periodically every 200 ms. An initial delay of 2 s before sending the requests periodically is used to ensure neighbor discovery procedures are complete and the system has a global address that can be used to reach out to devices outside the link-local scope. The server itself does not ever initiate a request to the client.

Client

Server