[Ovmsdev] module GPRS connection frequency

Tom Saxton tom at idleloop.com
Tue Nov 11 12:20:32 HKT 2014

H20 Wireless is cheaper than AT&T GoPhone, just over $40/year for OVMS. I
wrote up my experience and instructions here:


Other folks are reporting even lower costs with GeoSIM later in that same


-----Original Message-----
From: Lee Howard <lee.howard at mainpine.com>
Reply-To: OVMS Developers <ovmsdev at lists.teslaclub.hk>
Date: Monday, November 10, 2014 at 8:10 PM
To: OVMS Developers <ovmsdev at lists.teslaclub.hk>
Subject: Re: [Ovmsdev] module GPRS connection frequency

>Thanks for your reply, Mark.
>As for the SMS messages... couldn't the app simply tie-into the phone's
>own SMS features?  So the SMS is sent from the phone and not from the
>server.  Granted... not all compatible devices are phones, but at least,
>then, the cost and ability to use the feature is put into the hands of
>the user and does not burden the server operators.
>For the SIM cards, I'm using the AT&T "GoPhone" plans which, basically
>are $100 per-year if the usage is low-enough.  That's $8/mo.  However,
>the usage isn't low-enough because of the frequent GPRS
>disconnects/reconnects.  I appear to be running at about double the
>expected cost.
>For users in the US, I would be happy to know of a better (lower-cost
>and reliable) alternative.
>On 11/10/2014 05:50 PM, Mark Webb-Johnson wrote:
>> Lee,
>> We can (technically) actually do this from the server. The issue is the
>>lack of business model to support it.
>> With users buying their own SIM cards and paying for their own SMS and
>>data plans, things are simple. If we start having to pay for a large
>>number of SMS messages server->car, that isn't going to work out.
>> Some interesting numbers on the SMS provisioning system that we run. We
>>do this free-of-charge, but ask for sponsorship. Currently, it runs
>>approximately break-even (I had to sponsor quite a few top-ups at the
>>start, but haven't had to pay anything extra in the past year, as
>>sponsorships cover it - just). For every 1 sponsor, there are
>>approximately 5 users not paying at all. At break-even, that means 1 in
>>6 are paying 6 times more than they personally use, and 5 in 6 are
>>paying zero. I guess that is human nature, and so long as I don't end up
>>personally paying I guess I don't mind too much, but that model
>>definitely wouldn't work if using SMS from the server for wake-up. The
>>other issue is that both ends pay, and that can end up pricey.
>> Technically, I hate wake-up. It is messy and slow. It is also the thing
>>most users of the vehicle's own telemetry system complain about (and
>>perhaps complain about most). The modems can go into a low-power state
>>and in that state GPRS won't work but they can still receive USSD and
>>SMS messages. The wake up involves establishing a GPRS session, then
>>bringing up a TCP/IP connection over that, and can take a while.
>> A very good alternative is pure USSD. That is free, very reliable, but
>>(a) kludgy and liable to pissing off the cellular providers as it is not
>>intended to be used for what we need it for, and (b) kind of pricey at
>>the moment (perhaps US$8 a month, which is more than most OVMS users are
>>paying). But, it is low-powered, fast, flat-rate, globally roaming, and
>>doesn't require GPRS at all.
>> Regards, Mark.
>> On 8 Nov, 2014, at 5:33 am, Lee Howard <lee.howard at mainpine.com> wrote:
>>> 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.
>>> Thanks,
>>> Lee.
>>> 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
>>>>> Regards, Mark.
>>>>> On 28 Oct, 2014, at 5:17 am, Lee Howard <lee.howard at mainpine.com>
>>>>>> 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
>>>>>> _______________________________________________
>>>>>> OvmsDev mailing list
>>>>>> OvmsDev at lists.teslaclub.hk
>>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>>>> _______________________________________________
>>>>> OvmsDev mailing list
>>>>> OvmsDev at lists.teslaclub.hk
>>>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>>> -- 
>>> *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
>>> _______________________________________________
>>> OvmsDev mailing list
>>> OvmsDev at lists.teslaclub.hk
>>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>> _______________________________________________
>> OvmsDev mailing list
>> OvmsDev at lists.teslaclub.hk
>> http://lists.teslaclub.hk/mailman/listinfo/ovmsdev
>*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
>OvmsDev mailing list
>OvmsDev at lists.teslaclub.hk

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