I’m trying to make virtual serial connection between two measurement devices using GPRS with two Telit GM862-QUAD-PY modems. I need to send and receive text between the two devices. The other end has temperature measurement device which responses when it is asked for. The other end has the master device which has display and is asking the results.
The problem is I can not make them connect between each other. I do get IP-addreses for both of the devices and I can connect to www.google.com from both of the modems. I did open firewall from the other device and I’m listening 1024 port, but if I try to make “socket dial” (#SKTD) it just won’t connect to the other device. Am I doing something wrong or is it possible even to do what I’m trying to?
I tried Datacall earlier between the two devices and that worked perfectly.
Unless you’re paying extra to get a public IP address for at least the master device, this probably won’t work. Normally the carrier will put GPRS devices behind a NAT or NATP router, preventing incoming connections.
So I’d also recommend putting a server between the 2 devices.
(Note that is based on my experience with TMobile and AT&T in the US)
Sometimes even if you’re behind a NAT, the IP addresses assigned to the two GPRS-connected devices allow them to reach each other. That is the case for Vodafone Romania, I can connect from a device behind a Vodafone modem to another device behind another modem by simply using its private IP. However, the same setup does not work for Orange Romania (they do not route between the two). You would have to experiment but if you want something that will always work, use a server.