difference between the APR_BLOCK_READ and APR_NONBLOCK_READ?

[li xu]

Hi all,
  I am now using mod_echo.c.The module works well,but i find that
after i telnet to the apache server,i could not exit the telnet
program(even the escape character '^]')..So i change the source code
of mod_echo.c(APR_BLOCK_READ to APR_NONBLOCK_READ).
But,as soon as i type something in the telnet ,the server closes my
connection.That's not what i want..

I want to know what the difference between the APR_BLOCK_READ and
APR_NONBLOCK_READ.
Could anyone help me with that?and i want to know why..

Thanks in advance.