[Ovmsdev] module GPRS connection frequency

Lee Howard lee.howard at mainpine.com
Sat Nov 8 05:33:47 HKT 2014

For what it's worth...

Even if app-to-module features existed for my vehicles (VA and XX), I 
believe that my SIM card costs would be significantly less if 
app-to-module commands (lock, preheat, etc.) were sent only by SMS text 
and not via internet - AND - the module-to-server communications were 
limited to regular/periodic times only when the status has changed.  The 
app-to-module features would be used relatively infrequently.

I recognize that diverges considerably from the operational design of 
OVMS, and I don't necessarily expect anything to be done about it.  I'm 
just saying it, though, to have it out there.



On 10/29/2014 10:06 AM, Lee Howard wrote:
> I understand.  Thank-you for the clue-stick.
> In my situation - VA and XX - there is no functionality (yet) for the 
> App to send anything useful to the car.  I can't lock/unlock the 
> doors, start pre-conditioning, or tell auto-pilot to drive the car to 
> my location.  So, for all intents and purposes OVMS serves as a 
> one-way street of information flowing from the module to the app and 
> not the other way 'round.
> Especially in the case of XX (GPS only) there is no need to update the 
> server when the car can be determined to have been stationary.
> I suppose, though, that your response is what I needed to know: this 
> is not configurable.
> Thanks,
> Lee.
> On 10/27/2014 06:59 PM, Mark Webb-Johnson wrote:
>> Lee,
>> The GPRS connection is different from the server connection.
>> Think of GPRS like a VPN. The OVMS firmware tries to keep GPRS open 
>> at all times. If a GPRS connection fails to be established, it 
>> backs-off for 15 seconds and tries again, then 30 seconds, then 45 
>> seconds, etc, etc, up to 150 seconds. Normally, cellular providers 
>> charge for data transferred within the GPRS session, and often they 
>> round it up to the nearest 1KB, 100KB or 1MB. If you establish a GPRS 
>> session, then it is lost, you get charged the minimum.
>> What pisses me off is that in 99.999% of the cases, the cause of the 
>> loss of GPRS session is the cellular provider's crappy cellular 
>> network. OVMS only purposely disconnects a GPRS session when (a) the 
>> GPRS parameters are changed, or (b) the box is turned off. All the 
>> other disconnections are because of the cellular provider's network.
>> Once a GPRS connection is established, OVMS will try to establish a 
>> TCP/IP connection over GPRS, to the server. Once that is established, 
>> OVMS will attempt to keep the server updated with the vehicle status 
>> (once every ten minutes while idle, once every minute while an App is 
>> connected). Checksums are used to only send changed data (which 
>> further reduces data charges).
>> This constant connection is necessary so that the OVMS module is 
>> always-on ready for an App to connect to it. Again, due to the 
>> cellular provider's arrangements of using private IP address spaces 
>> and NAT, the OVMS module cannot normally be contacted by the server. 
>> Instead, the module has to establish and maintain a TCP/IP connection 
>> to the server, and the server talk back to the module over that 
>> connection.
>> Regards, Mark.
>> On 28 Oct, 2014, at 5:17 am, Lee Howard <lee.howard at mainpine.com> wrote:
>>> For those of you using unlimited data plans this may not matter, but 
>>> for those of us using per-use/per-minute/per-MB plans the frequency 
>>> at which the OVMS module connects via GPRS to the OVMS server is 
>>> quite relevant for the long-term cost of using OVMS.
>>> For example, I'm using AT&T "GoPhone" per-minute plans which 
>>> basically result in a $0.01 charge every time the OVMS module 
>>> connects via GPRS to the OVMS server.  The OVMS module does this a 
>>> bit more-frequently than I had anticipated... about 3X more 
>>> frequently.  Consequently, I was a bit surprised to find what I had 
>>> hoped to be a $100-per-year account get used faster than that... 
>>> requiring me to add $100 to the account every four months or so.  So 
>>> the per-minute/per-use/per-MB plan I'm on ends up not really being 
>>> less-expensive than their $25 per-month plan.
>>> I see that the OVMS module is connecting with the OVMS server 
>>> roughly every 7 minutes... even if the car is stationary and there 
>>> have been no changes to SOC or other vehicle information.  I see 
>>> this behaviour both with module type "VA" and "XX".
>>> I would prefer to see the OVMS module connect with the server with 
>>> *greater* regularity (like, every 2 minutes) when GPS position is 
>>> changing (more than the expected 60-meter or so "jitter" that I 
>>> usually see) or when SOC is changing or some other information 
>>> changes.  However, if the vehicle is stationary and there are no SOC 
>>> changes or other information changes, then I would prefer to see the 
>>> OVMS module connect to the OVMS server very infrequently... like 
>>> only every 30-90 minutes.
>>> Is this, by chance, something configurable?  Or is this something 
>>> that I'm going to need to build-into the firmware, myself?
>>> Thanks,
>>> Lee.
>>> -- 
>>> *Lee Howard*
>>> *Mainpine, Inc. Chief Technology Officer*
>>> Tel: +1 866 363 6680 | Fax: +1 360 462 8160
>>> lee.howard at mainpine.com | www.mainpine.com
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>>> OvmsDev mailing list
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*Lee Howard*
*Mainpine, Inc. Chief Technology Officer*
Tel: +1 866 363 6680 | Fax: +1 360 462 8160
lee.howard at mainpine.com | www.mainpine.com

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