# ASD Tutorial Lesson 3: tcpEcho

This lesson builds on top of lesson 2. Here we go a step further by opening a TCP listening socket and wait for incoming byte streams. Once data is received, they are written to the sender verbatim.

One can telnet to port 7 of the raven to test the echo server.

Note that the windows telnet program sends a character as soon as a key is pressed (without waiting for a carriage return). Consequently, if you use the windows telnet program to test this code, you will see something like the following:

HHEELLOOWWOORRLLDD

Where the repeated character is the echoed character from the Raven

server.c - initializes the wireless interface and opens a TCP socket for listening

echo.c - maintains a TCP socket that listens on port 7 and writes the received byte stream back to the sender