Telnet session starts with 21 bytes of crap

Question

within a small embedded application I'm providing a Telnet server for sending simple commands to it. For testing I connect to it using putty. Now I found there are 21 bytes of some data are sent to the server on connection. So...what could this be? Is it a initialisation sequence?

From my understanding telnet is a plain connection which should not have such data...

Thanks!

Answer 1

OK, I got it: when selecting "Active auto negotiation mode" in Putty it sends these data with additional information of whatever...so one has tod rop all characters with an ASCII code larger than 127 to ignore these data.