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I went to a job interview a year and a half ago where part of the interview was to give a walkthrough of my solution to short "homework" problem.

Got there and tried to connect my laptop to their wifi network. No dice. My laptop (2014-15 era) doesn't do 5ghz and they had no 2.4ghz access points. Ended up having to use a cellular wifi hotspot they had lying around to get anything to work.



Couldn't you just use your phone as a mobile hotspot? I do that all the t I'll me instead of relying on whichever local it department coming up with solutions for me.


a lot of phones have this sort of tethering disabled by carriers, who then sell "internet access dongles" as an add-on.


This sounds like 2012 to me... And even then, with a rooted phone, you could tether as you pleased. I recall using barnacle wifi tether back when my phone didn't offer it natively.

Another way of using it on Android, is to use USB tethering, while your mobile phone is connected to a Wi-Fi access point. That has worked pretty well for me, I sometimes even use that together with a computer to create a wired network from an access point. It could have worked in GP's case.


> And even then, with a rooted phone

Yes, obviously I'm talking about carrier-locked phones (typically sold with contracts). A lot of (most?) never even unlock their phone, let alone jailbreak.


How do they do it? How does carrier actually know that traffic is coming from tethered device rather than phone itself?


The carrier can inspect TTL (or hop limit in IPv6) values which decrease with every hop, so TTL at the point your packet reaches the carrier is typically lower when you are tethering.

Of course it is easy to circumvent by changing TTL on the terhered device from 64 to 65 or something like that, but I guess the solution is esoteric enough that carriers still make money doing crap like this.


Thanks for the brilliant analysis.

I didn't know this.


in iOS the whole "mobile hotspot" feature can be disabled in carrier-locked phones.


How do the carriers do it, at the technical level? Do they limit the IP TTL?


> Couldn't you just use your phone as a mobile hotspot?

At the time I had a 2010-era dumb phone which I only got rid of because Verizon said they were turning off the towers for it at the beginning of this year.


I did this until I switched phones. On my old phone the hotspot worked fine. My new phone- exact same plan, nothing changed there- prompts me to buy the hotspot plan addition. No thanks...


> Got there and tried to connect my laptop to their wifi network. No dice. My laptop (2014-15 era) doesn't do 5ghz

Wow, that’s surprising…most laptops from like 2010 onwards have done 5 GHz. Did yours have a particularly old Wi-Fi card in it?


I don't know about most, but it seems like many "not very high end" laptops from around 2015 didn't have 5 GHz.

My late 2013 mbp has it and I discovered the other day that it can actually negotiate up to around 1 Gb/s.

On the other hand, I have an HP ProBook 430 G2 lying around the office. I don't know when it was bought, but it has an i5-4210U which according to intel was launched in Q2 2014. So the laptop must be from late 2014. It has a Realtek RTL8723BE PCIe wifi card which doesn't know about 5 GHz. It works acceptably well otherwise.


I bought a new laptop a few months ago that does not do 5GHz. It's a Dell Inspiron 3195, with a Qualcomm Atheros 9565 wireless card. The laptop is still available for purchase. When I purchased it it was on sale for $200. (not sure if the link is my exact model, but all the specs are the same, and this particular model does say 2.4GHz with no mention of 5GHz)

https://www.dell.com/en-us/shop/2-in-1-laptops/inspiron-11-3...


Oh wow they're still selling 1366x768 screens in the year 2020.


What's wrong with that? I happen to prefer a "lower" resolution on a laptop (and by "lower" I mean the same pixel density as my IPS monitor, which is 1920x1200). Unless I use an operating system that has completely solved the problem of GUI scaling, I don't see the benefit of higher pixel densities, only constant issues with incompatible applications.


It's perfectly usable. (I also have an XPS13 with a 3200x1800 screen) Setting up the infinality font renderer basically negates the downsides of a low resolution screen.

TBH, in the future I'll preferentially opt for ~96 DPI when available. The 3200x1800 on my other system is completely overkill, and doesn't play particularly nice with a lot of websites or Steam.


It's a perfectly adequate screen size for most things.

The only place I run into trouble is if I try to do anything work-related on this laptop because our web design team designed our web app on large, high-density displays.

Every website I actually use at home works perfectly fine.


It was common for low cost wifi-cards to not function at 5GHz.

Actually it was only with 802.11ac (AKA WIFI5) that laptops started universally supporting 5GHz on the high and low end.

Before that you had to check the spec sheet.

In fact, it's still common for IoT devices to forgoe 5GHz, but it's becoming less common, thankfully.


> Did yours have a particularly old Wi-Fi card in it?

From lspci:

03:00.0 Network controller: Qualcomm Atheros QCA9565 / AR9565 Wireless Network Adapter (rev 01)

I don't know whether that is an old card or not. I think the laptop was in the $300-$400 range when we got it. Inspiron 15-3551, came with Ubuntu pre-installed, which has since been swapped out for Debian.

This Dell support link [1] seems to confirm that it is 2.4Ghz only.

[1] https://www.dell.com/community/Networking-Internet-Bluetooth...


Yeah, thats an ath9k card (802.11n). 5Ghz was optional in the 802.11n days, so only higher end devices tended to support it.


Not a laptop, but the Nintendo 3DS was notably first released in 2011 and does 2.4 GHz only. The iPhone 4S was also released in 2011 as a 2.4 GHz-only device, and not discontinued worldwide until 2016.


Nintendo devices seem to be generally poor at supporting networking standards. The DS did not support WPA or WPA2. The Switch does not support IPv6.


newer budget android phones also tend to forego 5GHz. i sympathise as the reduced range makes it less usefull.




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