Nova drops connection after a while


#1

Hello,

I am using a Nova modem on a Raspberry Pi A+ with an AT&T Sim card (note: not a Hologram sim). I am able to connect to the internet using sudo hologram modem connect which creates a ppp0 interface. I then am going about uploading files via a python script.

However, it seems that after some amount of time or bandwidth, the modem drops the connection. My python requests all begin to fail with Failed to establish a new connection: [Errno -2] Name or service not known, and I am unable to ping anything from the command line (even ip addresses). The ppp0 interface still exists but seems like I have no internet access.

Is there anything you can tell me about this situation or a way to properly debug? I often times need to keep a connection open for 30-60 minutes uploading files, so having it die after a few minutes is detrimental.

Thanks!


#2

Hi @misterf - As you’re using an AT&T SIM card it will be harder to trace the issue as it may be on the network side.
To confirm, you made updates to the SDK to change the APN to AT&T’s to setup the initial ppp interface via the CLI sudo hologram modem connect command?
Also, can you explain more about your Python script for how it’s handling the file uploads? Is it handling any connectivity or presuming that the internet access is available.

-Ryan


#3

hey @ryanHologram thanks for the response.

that’s correct. I modified the chat script to instead of sending OK AT+CGDCONT=1,"IP","hologram" it sends OK AT+CGDCONT=1,"IP","broadband". It is generally able to connect, but holding the connection becomes problematic.

I have a cron bash script that runs sudo hologram modem connect. then, once that succeeds, it runs a python script to handle file uploads using the request library. that essentially looks like the code below (some helper functions omitted):

def sendImages(*imgs):
    files = {}

    try:
        printnow('Uploading ' + str(imgs))

        i = 0
        for img in imgs:
            files['imageData-' + str(i)] = open(IMAGE_DIR + '/' + img, 'rb')
            i += 1

        r = requests.put(UPLOAD_URL, headers=headers, files=files, timeout = 60)
        printnow(str(r.status_code) + ": " + str(imgs))

imagesToSend = [...]

printnow('Sending these images: ' + str(imagesToSend))
imageChunks = list(chunks(imagesToSend, NUM_IMAGES_TO_SEND_PER_REQUEST)) # splits list into sublists of size 2
for imageChunk in imageChunks:
    sendImages(*imageChunk)
    
printnow('Finished uploading')

I’ve actually switched back to the hologram sim to see if it was perhaps a problem with my network/sim config (hologram tries to use t-mobile), but on that side, i’m seeing a lot of this immediately after connection (it doesn’t hold it for long at all)

Oct 20 15:46:39 raspberrypi pppd[1102]: LCP terminated by peer
Oct 20 15:46:39 raspberrypi pppd[1102]: Connect time 0.4 minutes.
Oct 20 15:46:39 raspberrypi pppd[1102]: Sent 1961 bytes, received 4223 bytes.
Oct 20 15:46:42 raspberrypi pppd[1102]: Connection terminated.
Oct 20 15:46:43 raspberrypi pppd[1102]: Modem hangup

but that seems like it may potentially be another issue altogether.

one thing that seems suspicious to me is that the nova light is double blinking blue, which indicates 2g. as far as i know, AT&T does not support a 2g network, so not sure how it even connects. and i am in downtown atlanta, so i am skeptical that there is no 3g at&t or t-mobile available.

i know there’s a lot to digest here, but let me know if I can answer anything else for you!


#4

Hi, which antenna are you using?


#5

The larger, black one. Hologram is out of its case.


#6

hello, any update here? My device thinks I have a connection so it never retries the ppp connect, and so it just hangs in limbo for forever until I manually disconnect and reconnect it.

Ideally if there is a bad connection, it would just drop it and reconnect, but I’m not seeing that behavior on the AT&T network. Please advise.


#7

T mobile indicated that they would keep their 2g network up for a few more years, while ATT shut theirs down a couple of years ago. T mobile was using att’s 2g for a lot of coverage, but that’s gone so just their limited coverage (2g) is available.
As for the session closing, there is a network ( ATT or T mobile) timeout for inactivity. Hologram should be able to tell you what it is. It can be up to 24 hrs or as short a minutes. There is also a timer in the radio that will close the socket if no data is sent.