The New iPad, LTE, Backhaul and User QoS

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 I’ve been playing around with The New iPad since Friday now, and the thing that’s most annoying at the moment is not the device at all. It’s Verizon. I’ve been of course testing LTE speeds and comparing to my Verizon 3G speeds and I must say, the latest iPad has a good receiver performance for a user device. I can burst at peak rates on Verizon’s network when I’m in good SNR conditions. I get lots of peaks with available high order modulations over the air, ready to travel but unfortunately the buffers are mostly empty when returning from the network. There is also some pauses in transmission but not due to link faults or retransmissions. Expectedly, the performance has been worst in public places like airports and close to business districts but the air performance is really not bad at all, it’s really really good according to my tools. Simplistically, this chart sums up what I (we all) expect from our LTE connection:

It’s not that different on ATT, only slightly more annoying.

This all points to one of two culprits.

  1. The Scheduler
  2. The Backhaul

I highly doubt it’s the scheduler because I’ve surely been on both vendor’s eNBs by now, and like I said, ATT and VZW have similar over the air performance. There is one smoking gun though. The latency. The packet latency is really pretty high on both networks! In SNRs of 30, I regularly get 50-65ms one way trips. Working backwards, I suspect that these guys are taking the packets on an odyssey from site, transport with various aggregators and ultimately to a distant EPC. I complained about the fact the iPad didn’t allow FaceTime on the LTE network… Perhaps that’s because of the fact that (A) the latency is crazy high and (B) the backhaul seems to be inadequate already.

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