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My spouse and I were driving onI84/81 in Annville, PA. Her iPhone 6S was in LTE mode. My iPhone SE was in Edge. We both have T-Mobile as a carrier.

  • Do the two iphones have the same radios on the same frequencies?
  • If so, why would I have Edge on one and she had LTE?
  • Is there something wrong with my iPhone 6S?
  • Is this something that can be tested in the T-Mobile store?

In a nutshell - what process can I use to get answers to these ideas I have as to why one phone isn't working as well as another?

  • We generally close questions that aren't a single question, but I've made an edit since there seems to be one question worth answering - is there a way to measure performance. – bmike Aug 20 '16 at 18:43
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You can do some work to narrow down performance, but you'll need carrier help if you find that there's an issue with one device.

  1. Use Safari to do a speed test http://fast.com on both devices - even if you are using different devices, different cell towers (just because two phones are in the same place - they can negotiate different frequencies, different towers or get different levels of service from the same tower at the same frequency).

By focusing on measuring the flow of data - you can over time know if one device has hardware limitations or hardware issues.

Next, put each device in field test mode: Dial *3001#12345#* - if you can see in the menu bar a number like -76 then record those for each device and then call your cellular company to help determine if you have coverage issues or need to update your phone's settings or software.

_Note: not all carriers have a useful field test mode. See this and this and that for more details. Basically, each cell tower is a time share. It juggles all the devices in range - tells some to be on LTE, others to be on 3G, others to be on EDGE. Unless your phones don't work at all - the cause of differential service is almost always a device that's stuck and needing reboot or a congestion issue on the carrier end. Apple can also run diagnostics if you believe the hardware is faulty - but that's usually a low chance of being the cause.

  • Is field test mode an international structure, or US only? It goes busy then just errors, "Error performing request/Unknown error" with only a Dismiss option on my UK 6S. The number isn't stored in dialling history either. – Tetsujin Aug 20 '16 at 19:03
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    @Tetsujin It's an internal function that does different things based on the carrier profile on the device. Initially, it was awesome and gave great actionable data. Over time, it's been gutted by Apple or the carriers here in the US. If you get good data, it's great - I almost didn't answer since on TMobile in the US it's mostly worthless today. – bmike Aug 20 '16 at 19:59
  • This is useful. However, the speeds will clearly be different, because one iPhone was in LTE mode and the other was in Edge mode. I verified that—my mail client wasn't very responsive on the phone in Edge mode. The real question is why did one phone see LTE and the other see Edge. – vy32 Aug 21 '16 at 18:55
  • @vy32 the cell tower directs the phone to connect over edge. the phone always asks to connect to the fastest frequency available - but when too many devices ask for LTE, the tower chooses which ones to downgrade. That's why you need to get the carrier involved. They control who connects how and when. – bmike Aug 21 '16 at 19:02
  • @bmike, it's very hard to get the carrier involved when one is sitting in the passenger seat of a car moving at 50MPH. I don't live in that area, we were just passing through. I'm really trying to find out if the iPhone 6S has the same wireless electronics as the iPhone SE, or if the 6S has a better RF section. – vy32 Aug 22 '16 at 22:17

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