title: Communication with arduino + GSM Module + android app wirelessly
body: <p>I have been trying to get some information on how a GSM/GPRS module can communicate bidirectionally with a PC that is connected to the Internet via a static IP address. I have reviewed the available posts on this forum as well as a few others and have read a few tutorials on this topic. Following is what I managed to gather so far and would like to get the expert opinion of fellow members on this topic.</p>
  
  <p>1 - The PC cannot directly initiate a connection with the GSM/GPRS module. A data session ALWAYS has to be initiated by the GPRS module first before the PC can talk to it.</p>
  
  <p>2 - The PC is able to talk to the GPRS module only via the dynamic IP address that is assigned by the GGSN on the network. The PC is able to access this IP address ONLY AFTER the GPRS module initiates a data session. This IP address can change if the GPRS connection is terminated for whatever reason (i.e. bythe user or the network or due to an unexpected link failure). In case of such terminations, the GPRS module has to re-initiate a new PDP session for the PC to talk to the module again. Otherwise, the PC will not be able to send data to the GPRS module because it does not know the renewed IP address  assigned to the module after a reconnection to the GSM network.</p>
  
  <p>3 - As discussed in M2M.com's various posts, the only way for the PC to initiate a data session with the GPRS module is to send an SMS with a content equivalent to "call home" that prompts the GPRS module to start a data session to receive the pending data from the PC.</p>
  
  <p>4 - There is no method to predefine a table of fixed IP addresses on a GPRS module to use during data sessions. The IP address assignments are ALWAYS done by the GSM network that the GPRS module is registered to and they cannot be known or fixed in advance. No assumptions can be made on the pool of IP addresses that can be assigned to the GPRS module.</p>
  
  <p>Thank you for all your input and interest in this discussion.</p>