9160 tcp comminication question

[William.wei]

hi support team,

     i have one question about 9160 TCP communication,  is data re-transmission fulfillment by the modem? how does it work when in psm mode?

     for example, when in PSM mode, i send one packet to server, and use %XRAI to release connection, will the data be re-transmitted by the modem?

     Thanks in advance!

[Sigurd]

Hi,

William.wei said:

i have one question about 9160 TCP communication,  is data re-transmission fulfillment by the modem?

Yes. The modem have internal buffers for handling TCP re-transmissions. Re-transmissions are done when the counterpart does not send an acknowledge.

William.wei said:

how does it work when in psm mode?

If the application needs to transmit data while the modem is in eDRX or PSM mode, it'll wake up and send the specific data, then go back to eDRX or PSM. PSM and eDRX is for receive "polling" only, you can send data at any time.

William.wei said:

for example, when in PSM mode, i send one packet to server, and use %XRAI to release connection, will the data be re-transmitted by the modem?

Assuming, AT%XRAI=3, and if you are e.g. both downloading an uploading data. As you then only expect a single response before you might get released from the network, this might cause some problems. If the DL data arrives when you expect an ACK, you might get released before the ACK is received. As the modem will believe that the server did not ACK the transmission, it might re-connect in order to re-transmit the data.

In general, to use XRAI properly, the application will need a very good understanding of the communication between the modem and the server.

[William.wei]

Thank you Sigurd. so maybe because of the bad signal, the 91 may not go to sleep mode because modem need to re-trans the data, right?

[Sigurd]

I will check with team about this, and get back to you.