Troubleshooting connection speeds - AT&T, Quectel EC25

Installing and Using OpenWrt
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Hi all,

I'm trying to hook a powerful PTZ camera up to the Internet to contribute to a wildlife conservation project, and while I've managed to stumble into getting anything working at all, it really doesn't perform well enough for my project's needs, and I'm too inexperienced to really troubleshoot effectively.

I've purchased the solar-powered 4G router with wifi and PoE access from outdoorrouter.com (TODO: identify the SKU and figure out the board they use), and installed a SIM card harvested from a working AT&T smartphone dedicated to the project. My project has also had a dedicated SIM card issued, but I've had trouble getting that to work at all, so I'm scrabbling for any kind of progress. I've googled enough to get the connection settings right, or at least right enough to send data from the wired network to the world and back.

The problem is that it's slow. When I hook my laptop up and use an FTP client to test connection speeds with an AWS-hosted FTP server (so no throttling), I see 10-15 KB/s down and 50 KB/s up initially, dwindling down to ~10 KB/s up after a few seconds. My personal phone sitting adjacent has standard mobile broadband speeds - Youtube and email with large attachments work fine - and an EE buddy tells me that the signal strength numbers reported through the LuCi interface look healthy, so it's not the RF environment. 50 KB/s up is too fast for the modem to have gone mad and negotiated down to 3G for some reason. I can get high-res video from the camera to my laptop over the wired network, so it's not router or switch performance; further evidence: logging into the router console and doing wget to a file of known size online yields the same 10 KB/s down. Sending standard web traffic through sees about the same numbers, so it's not AT&T only throttling certain protocols.

Theories I'm entertaining:

  • flaky antenna - but then why would the numbers be healthy? RSSI was ~-98 dBm on my last experiment, if my memory serves.
  • ISP throttling - I don't know whether or not tethering is supported on the phone I stole the working SIM from; if AT&T sees non-phone-like traffic coming from what's supposed to be a phone they may well just try to annoy me into abandoning that connection.
  • modem misconfiguration - if the modem can talk to the 4G network at the full rate, but only hand off traffic to the router over a slow link, that'd certainly be slow. Doesn't explain why uploads start at 50KB/s and then slow down, though, surely both sides would try to saturate the link between?

What could be going on here? What other information can I gather? Thanks in advance for any help.

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Worth to read: What is happening? SIM card that gives me 100 Mbps on my iPhone but when I plug it in my 4G router it only gives me 20 Mbps????

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Thanks for the reply!

Fast googling gives https://www.quectel.com/infocenter/news/283.htm , which claims that it's certified as class 4 on AT&T, so 150 Mb down and 50 up best case, which is much more than enough for my needs - I'd be happy with even 1/10 that if I got it reliably. 80 Kb down and 120Kb up? 1/1600? Less so.

I don't understand the math here. Is the idea that his phone sees 100 Mb down when the chip supports 300, so his phone modem only uses 1 channel of the 3 needed to get the rated 300, so his router modem can only use one channel, so it's reasonable that the router modem will only get 1/3 its rated max of 50 Mb?

I'm hoping really hard that it's not AT&T playing games, but I'll work that angle, thanks for sanity-checking it.

How do I get the device ID, so I can look it up in the hardware lists? How badly am I hurting if it's some no-name that doesn't appear?

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You should compare apples with apples. The phone used as a reference should use

  • single band (no Carrier Aggregation)
  • same band as the modem

All that has nothing to do with OpenWrt.

1 Like
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Using the EC25 on different devices with different carriers, I usually get up to 15 MBits/s downstream, on 3g (PPP).

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The dedicated SIM card I was using was mis-provisioned as voice-only, and after a few days to let the phone SIM's usage history cool off I saw 300-Kbps downlink speeds. I conclude that ATT was indeed throttling it upstream, and that the router hardware and OpenWRT are working entirely as intended.

Thanks everyone for your insights.

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