AT&T Please fix tower 15932433

We spend a lot of time testing codec performance on real-life 4G networks. We've found several spots in cities that function well as worst-case scenarios, including the vicinity of the White House and Times Square. We've also found a good testing ground closer to home--the Boston Common. It's a wide open spot in the center of the city where you can count on changing cell towers pretty regularly as you walk around.

We had some interesting results yesterday while testing our LiveShot video codec there. We had three modems attached. (for you audio codec users, this capability is coming soon in firmware 4.0) Verizon and Sprint modems were champs, but depending on location our AT&T modem would behave miserably--to the point where it's presence was actually more of a hindrance to the overall stream than a help.

That was actually good news, since we were trying to tweak our algorithms to minimize or quarantine the data from a bad network. But we took it a bit further and started reading the stats on the modem as it entered and exited the "zone of doom". Sure enough, it was a discrete tower switch at the exact moment the channel fell apart.

The above graph illustrates the percentage of packet loss over time in one second intervals. When viewed on the product, this graph moves in real-time from right (most recent) to left (60 seconds ago). It's pretty obvious when you're on the bad tower.

Why is this particular cell so bad?  Is it located in a place where multipath is a problem on the Common? Is there a local transmitter with a spur in the 700MHz region blanking the cell tower receiver? I'm sure bribing an AT&T tech would be the only answer, and none were around.

In case you think this problem is specific to AT&T, we were at this exact location about 10 months ago, and AT&T was flawless throughout the area. But at that time, an identical situation occurred on Verizon, at the opposite end of the test area. Go figure.

Is POTS dead?

No profound insights or innovative solutions to talk about today. Just a bit of navel-gazing.

We're getting more and more war stories of broadcasters unable to find a "real" POTS line at a venue from which they need to broadcast. The phone jacks they used to rely on get terminated in a VoIP switch. POTS codecs rely on a very intricate modem balance on a phone line. And VoIP systems treat modems like a weed on a putting green-- A nuisance to be destroyed.

Of course the answer is "Go IP", but that's a pretty cold response to someone who doesn't have the budget for shiny new hardware. And IP codecs are still hot commodities hard to find on Ebay. POTS codecs are relatively easy and cheap to find there (possibly a testament to their demise?)

It's really hard to gauge how rough things really are-- we don't hear about the successes as often as the failures. But at a minimum it seems those who show up assuming that RJ-11 is connected to the CO by a pair of copper wires will be disappointed in short order.