Asus Cripples Surplus Routers

In the past couple months a router has become a favorite on Amazon and deal aggregator sites as a low-cost workhorse router. The router in question is the Asus T-Mobile Personal CellSpot Wi-Fi Cellspot Router (TM-AC1900). As of the time of this writing, these are selling for $60, sometimes lower.

What were these routers for? #

I like T-Mobile quite a bit. Unfortunately their network wasn’t always so decent. One of T-Mo’s former drawbacks was that their network lacked low-band spectrum until 2016. The effect of lacking low-band spectrum is that their network had difficulty penetrating the walls in people’s houses: Especially if they were located in a rural setting with towers further apart. They had to fix the gap of making calls work at home, while indoors.

Building new towers closer is a bitch due to zoning, getting fiber and power run, and overcoming old people’s complaints of having an eyesore or ‘radiation’. So until the rollout was complete, T-Mobile had a few options to help customer retention. The first was to use amplifiers or boosters to catch the signal outside and rebroadcast it indoors. But this sucked because it either required lots of cables to be run up to a roof or attic, or it required a wireless link usually on 5GHZ that screwed up wifi performance in the house.

The second option was to make the calls go through Wi-Fi instead of a cell tower. T-Mobile had previously messed around with this on old BlackBerry phones using a technology called UMA (unlicensed mobile access), but with LTE, there was already upgrades done to the network to put calls over data. This required phone support, but Apple, BlackBerry, and a handful of Android phones sold and branded by T-Mobile would carry the new style of Wi-Fi calling.

The thing is, Wi-Fi calling usually worked well until people started downloading other stuff or doing heavy streaming on the network. In order for calls to not sound choppy or delayed, the router needs to support and be configured to prioritize the voice traffic through a mechanism called QoS. The T-Mobile router was something you could call support and ask for, and they’d ship one to you for free or for a refundable deposit,. It had all the QoS parameters set up inside and was essentially just a software modified version of Asus’s retail RT-AC68U. T-Mobile gave these out starting in September 2014 and probably stopped sometime early 2017, I’m not really sure when.

The network got good enough that it wasn’t required anymore. In the situations it still didn’t cut it, they now offer to ship a full femtocell that acts as a true tower for the network.

The Problem With The Router #

Asus made the router. T-Mobile certified the firmware. This took time and meant the retail RT-AC68U got swift security updates, while the TM-AC1900 languished. Once T-Mobile discontinued shipping them, you could keep your model but it would no longer receive updates. If you recall back not just a month or so ago the FBI was warning users to reboot their routers due to Russian malware attacking unpatched routers1. It’s a bad situation to put users in.

In the past few months I guess T-Mobile shipped all their customer returns and surplus to refurbishers that have flooded markets with these routers. There’s normally nothing wrong with that. If Asus let the refurbishers convert the TM-AC1900 into a retail RT-AC68U I wouldn’t have written this blog post as that’s still supported and has a robust alternative firmware community backing it.

New Asus routers sell for around $200 with this feature set. The T-Mobile refurbs sell for around $50 and carry the same hardware specs. It’s pretty obvious what most shoppers will go for.

Asus has shipped a series of checks with their later firmwares that prevent the flashing of third party software. The most recent even detects converted models and downgrades them to stock (flashing over the bootloader). There’s a step-by-step guide[2][#f2] that will let a user revert. I recommend the Asuswrt-Merlin firmware, but the creator of the firmware claims using a converted model is explicitly illegal. This is because the stock RT-AC68U contains a few features that the T-Mobile variant is missing, and hence hasn’t been licensed to use. I don’t use those features so I’m not very concerned about legality.

Anyways, I wrote this while fighting a failing update on my Merlin converted unit. There was a new step needed, wiping the MD5 partition that the guide I linked in the footnotes covers.

1 FBI Notice About Botnet
2 Conversion Guide


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