Tracking AT&T's rise to dominance in 4G network responsiveness

We recently published our latest report on the State of Mobile Networks in the U.S., where the network speed and 4G availability awards were dominated by a couple of operators. But AT&T won one notable accolade in OpenSignal's metrics – the best 4G latency.

Our latency metric tends not to get as much attention as speed or availability, but it is becoming an important measure of the overall mobile network experience. Everytime you click a link, press play on a video, or feint left in multiplayer mobile game, your device generates a data request, which must traverse the network, querying a server for content. The time it takes for that request to reach its destination and a response to be returned is the latency of the network. The lower the latency score, the better. And response rates are coming to the fore as mobile user habits shift.

Online gaming is one of the big beneficiaries from low latency. Multiplayer gaming apps such as Fortnite and PUBG are hugely popular right now, and rely on fast response times for a smooth and consistent player experience.

Mobile web browsing also benefits, particularly when streaming music or video. Lower latency cuts the delay between the browser on the phone requesting the file, and the server responding and starting the stream. The faster the latency, the sooner the server responds. A quicker "time to start playing" in video streaming is especially important as users watch a lot of short videos in quick succession, e.g. on YouTube or Facebook. Better network response times are also indicative of improved performance in other growing mobile application areas such as VoLTE and video communications services. And as U.S. mobile consumers begin to move away from Wifi and rely more on cellular networks, lower latency is more vital than ever.

But AT&T hasn't always been the top dog in our U.S. 4G latency metric. In fact, the operator was in fourth place just 16 months ago: in April 2017 it had the slowest 4G latency of any of the national operators, at 64 milliseconds in our measurements. However by August Ma Bell had overtaken its rivals, and has been in the lead ever since, as our latest historical analysis of U.S. 4G latency data shows.

During the latter half of 2017, AT&T recorded major improvements in its latency experience that saw it jump from last to first place in our 4G latency metric, which could indicate improvements in its network architecture. And our results show AT&T is extending this lead, as its 4G latency has improved by nearly 10ms over the past year to reach 54ms in our March-May 2018 test period – over 1.5ms better than its closest rival T-Mobile, 8ms ahead of Verizon and a whole 10ms clear of Sprint in our results.

The third quarter of 2017 saw a notable spike in lag time for both Sprint and Verizon. But the reason for these peaks is likely to be different for each operator. Verizon reintroduced unlimited data plans in early 2017 to counter the aggressive offers from T-Mobile. This is likely to have led to increased data consumption and congestion, affecting both 4G speeds and latency. AT&T also introduced unlimited plans at around the same time, but we did not see the same spike in its latency. This is most likely due to a number of 4G and backhaul network upgrades it performed during 2017, and it could also point to upgrades to its LTE core.

The rise we observed in Sprint's latency score in mid-2017 is likely to be related to tweaks the operator performed on its TD-LTE network to improve download speeds. But since TD-LTE uses a single frequency band for both upload and download, the reallocation of bandwidth to download is likely to have a detrimental impact on upload speeds. This is something we observed in our recent blog on 4G upload speeds in the U.S. Slower upload speeds often correlate with higher latency in our data, as we found with our latency scores in the U.S.

From September 2017, 4G latency for all the U.S. operators began to show considerable improvement as their attention began to turn from growing LTE reach to improving network capacity. Some benefited from fresh spectrum in the 600 MHz band in early 2017, most notably T-Mobile which invested nearly $8 billion in the auction. As smartphone penetration in the U.S. grows and users demand a more responsive experience on their devices, we expect to see more focus on latency as a key measure of the mobile network experience.

What's your experience of network responsiveness in the U.S? Is AT&T the best for VoIP and video calling, or are you getting a better live gaming experience with one of its rivals? Let us know in the comments below. And don't miss our latest State of Mobile Networks report for the U.S.