title: How to upload file to ftp server by sim900 in AT commands(ftp session close)?
body: <p>My AT Commands:</p>
  
  <pre><code>AT+CREG?
  AT+SAPBR=3,1,"Contype","GPRS"
  AT+SAPBR=3,1,"APN","mtnirancell"
  AT+SAPBR=3,1,"USER","xxxx"
  AT+SAPBR=3,1,"PWD","xxxxx"
  AT+SAPBR=1,1
  AT+FTPCID=1
  AT+FTPSERV="yzd.ir"
  AT+FTPPORT=21
  AT+FTPUN="xxxx"
  AT+FTPPW="xxxx"
  AT+FTPPUTNAME="ehsan.txt"
  AT+FTPPUTPATH="/"
  AT+FTPPUT=1
  AT+FTPPUT=2,10
  </code></pre>
  
  <p>server log:</p>
  
  <pre><code>Jul 21 13:42:36 yzd proftpd[2019] yzd (::ffff:5.116.194.141[::ffff:5.116.194.141]): FTP session opened.
  Jul 21 13:42:36 yzd proftpd[2019] yzd (::ffff:5.116.194.141[::ffff:5.116.194.141]): USER xxxx: Login successful.
  Jul 21 13:42:38 yzd proftpd[2019] yzd (::ffff:5.116.194.141[::ffff:5.116.194.141]): FTP session closed.
  </code></pre>