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PLS62-W FTPS Delays | Telit Cinterion IoT Developer Community

July 14, 2020 - 4:46am, 1744 views

We are using the built-in FTP client in the PLS62-W modem, and have recently switched to FTPS from FTP.

To improve throughput, we are using multiple concurrent sessions. The example below shows two concurrent sessions, each sending 5 files from the modem's flash file system.

Both sessions seem to start up OK, but we receive no response from the modem after 2 minutes, at which point we try to close the connection. The serial port then becomes unresponsive for 7 minutes, after which the modem reports the sessions have failed.

Is this expected behaviour? We are in good coverage, so taking 9 minutes to eventually fail is not optimal behaviour. We also lost the ability to use the serial port for file writes and network monitoring during this time.

Would it help to reduce the TCP retry limit? Or is there something else we should do when giving up on an FTP connection?

00:04 AT^SISS=1,"srvType","Ftp"
00:04 AT^SISS=1,"conId","1"
00:04 AT^SISS=1,"address","ftps://*****"
00:05 AT^SISS=1,"cmd","fput"
00:05 AT^SISS=1,"files","68-10.log,68-11.log,68-12.log,68-13.log,68-14.log"
00:05 AT^SISS=1,"user","*****"
00:05 AT^SISS=1,"passwd","*****"
00:05 AT^SISO=1

00:05 ^SIS: 1,0,2100,"Ftp open(*****:990)"

00:06 AT^SISS=2,"srvType","Ftp"
00:06 AT^SISS=2,"conId","1"
00:07 AT^SISS=2,"address","ftps://*****"
00:08 AT^SISS=2,"cmd","fput"
00:08 AT^SISS=2,"files","68-15.log,68-16.log,68-17.log,68-18.log,68-19.log"
00:08 AT^SISS=2,"user","*****"
00:08 AT^SISS=2,"passwd","*****"
00:08 AT^SISO=2

00:08 ^SIS: 2,0,2100,"Ftp open(*****:990)"

00:08 ^SIS: 1,0,2100,"SSL-Info: TLS, 3.3, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA"
00:08 ^SIS: 1,0,2100,"SSL-Cert: C=XX;O=*****;CN=*****"
00:08 ^SIS: 1,0,2100,"220 (vsFTPd 3.0.2)"
00:11 ^SIS: 1,0,2100,"FTP Login OK"
00:11 ^SIS: 1,0,2100,"fput 68-10.log,68-11.log,68-12.log,68-13.log,68-14.log"

00:11 ^SIS: 2,0,2100,"SSL-Info: TLS, 3.3, TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA"
00:11 ^SIS: 2,0,2100,"SSL-Cert: C=XX;O=*****;CN=*****"
00:12 ^SIS: 2,0,2100,"220 (vsFTPd 3.0.2)"
00:13 ^SIS: 2,0,2100,"FTP Login OK"
00:15 ^SIS: 2,0,2100,"fput 68-15.log,68-16.log,68-17.log,68-18.log,68-19.log"

02:05 AT^SISC=1

09:26 OK
09:26 ^SIS: 1,0,100,"isRunning --> FALSE"
09:26 ^SIS: 1,0,2100,"226 Transfer complete."
09:28 ^SIS: 2,0,2100,"FPUT : 68-15.log 102662 bytes"
09:28 ^SIS: 2,0,100,"IOError -149, Unknown during socket:: write \0a"