Chris Gagné

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Tag: sf bay area

T-Mobile Connectivity and Latency on CalTrain

I commute most days of the week from San Francisco to San Jose on CalTrain. I’ve been very frustrated by the poor signal quality for most of the route. T-Mobile kept insisting that I needed to provide a speed test from a single, fixed location. Given that a CalTrain “Baby Bullet” express train travels nearly a mile in the ~40 seconds it takes to run a speed test (their top speed is 79 MPH), this basically isn’t feasible.

I decided to do the next best thing. On 12/2/2016 I pinged, one of Google’s free DNS servers, every second from the train departing San Jose Diridon Station until it passed by the 22nd St Station (my usual stop).

I was northbound on the express train #365. The train arrived at the San Francisco terminus station only a couple of minutes late, so it would be very easy to extrapolate the times on the graphs to the train’s position. (The train usually arrives at the station a couple of minutes early so people can board/onboard and departs at the time listed on the schedule.)


What you can see is that there are periods of <100ms latency and few dropped packets, so we can rule out the device or any “faraday cage” effects from the train. You can also see where there are long stretches of very high latencies and high numbers of dropped packets.


I also explored the use of the LocateMe command-line tool to plot the approximate location of the train, but found that the location response was too heavily cached to be useful.

Here’s the shell script I used:

Unfortunately the response from T-Mobile was lack-luster at best:

Thank you for sharing your experience as well as staying in touch with us here. I have personally reviewed the recent ticket that was filed and according to our engineering team the info we provided wasn’t quite specific enough. We would love to work with you to nail down what the issue is, but the info provided thus far doesn’t give us enough to get you some real answers. I can tell you I personally depend on my phone for everything including work and school, so I totally understand why being without coverage for any length of time just wouldn’t be acceptable for you! We do need a bit more info here:

Time and date, location, and data speeds. I understand you haven’t had the opportunity to run a speed test just yet, but that’s quite alright! If we can get time, date, and location where you’re experiencing slower speeds we can most definitely get you some answers. Thanks in advance! *AlishaC”

Folks on Reddit advised that they were having better luck with Verizon, so it might be time to switch…

Housewarming Party Photos

Thanks to my friends and loved ones who came out to my housewarming party!

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