networking - Webify embedded linux-based controller through cellular network -

need basic direction in following project.

there linux based controller doing industrial control stuff. box equipped cellular modem , capable online through cellular carrier. cellular communication used because controller installed no cables or short range radio available. places sun don't shine :)

the task allow internet clients connect directly box basic control/monitoring stuff. problem connectivity - how clients discover box? - i'd have box act server (if possible). assuming cellular carrier allows box online doesn't mean box public ip able connected. understanding cellular network acts gateway working inside of it, , reaching in network outside isn't possible. wrong? looking generic solution, not solution around particular cellular provider. controller installed in different countries, need find standard way "webify" it.

the software (and hardware) in box ours, can anything, looking right way in order avoid surprises different providers later. btw, solution doesn't have technical, may it's possible buy permanent ip's per box, or setup vpns.. way should dig to? questions ask?

your ideas welcome!

your summary of problem correct. i've implemented several systems this, , odds of success good.

the way tackle depend on number of remote units expect single user interact with. if each user handle 1 or 2 devices, it's plausible implement web server on remote device. if each user handles many devices, consider centralising administration possible. i've implemented using zenoss data logging, , custom control server.

if web server sits on remote device, can either buy sim static ip, or use proxy server. recommend setting proxy server unless number of devices small.

there 3 options sims:

• static ip address on public internet expensive, , negotiating deal each provider in each country irksome. no proxy server required.
• private apn sims give option of static address, in private address range. negotiation mobile network still required, , require proxy server sit between public internet , private address range,
• standard data sims connect internet through nat. can use these host service opening vpn connection (we used openvpn) server. can reach devices directly connecting same vpn, or through proxy server.

if use openvpn, here more tips:

• give each unit public serial number, , private key. store these in firmware of unit, , in central database. put public serial number on outside of unit. can use openvpn login script ensure particular unit appears @ correct ip address, keeps proxy configuration static.
• you can control openvpn's bandwidth usage adjusting keepalive behaviour, , how renegotiates. measure , tune before large deployment.
• the nat timeouts in mobile networks between 5 , 15 minutes. device must send packet server enough keep nat alive.
• cheap sim deals may web limited ports.

other tips:

• gprs modem firmware can (rarely) crash internally. if hardware supports it, provide software ability power cycle modem.
• test box in areas poor coverage in own country before send out international shipments.