Wednesday, July 30, 2014

AT&T - The Adventure Continues

Last weekend we had two visits from two AT&T techs, and another today.  The first visit was from a premises tech who concluded that our internal wiring was sub-standard, so he and I climbed around and drilled holes to run a length of CAT5e cable from the DMARC (aka MPOE) box to a new isolated jack.  He put a line filter into the DMARC itself, which makes the install very clean.  Afterwards he found that our feed line had a couple of bridge taps which would need to be removed, so he submitted a service request ticket for that.

Observation: The premises tech was a younger guy, and in the usual banter of running wire he told me he'd been in the US Marines where he did communications and technology work.  During the clean-up phase of the wire install the tech managed to staple into the CAT5e itself.  It happens, and it's not usually a big deal since you have four pairs to work with - you just pick another pair.  I suggested that we "ohm out" the wires since we still had easy access to the ends, and that way we could avoid a debug session later.  He didn't have an ohmmeter with him, which I thought was odd.  Checking the wire pairs is fairly easy - you strip the insulation from the ends, twist one end of each pair together, and then measure resistance of each pair.  If any are obviously higher than the others, that's your problem pair and you avoid it.  Turns out he had no experience with things like this!  His military technology education had been along the lines of "If this box goes bad, remove it and install a new box."  When I went through US Coast Guard electronics school in the early 80's we were taught basic electronics, Ohm's Law, circuit-level troubleshooting, and even vacuum tube circuits before moving on to systems-level work.  Clearly a major shift in military training has occurred since then, and not for the better.

On Sunday the line tech showed up.  He removed two bridge taps from our line, and also cleared out a rodent nest from the pole-top splice boot.  He declared the line clean, although the signal level seemed a bit marginal (about 10 - 11 dBm).  As the day went on I monitored the modem's diagnostic page and noted that we were getting a LOT of forward error correction (FEC) errors.  FEC errors are considered correctable errors (unlike CRC errors which are uncorrectable) but they still cause lower performance and indicate something is wrong.  Tuesday night the network went offline - the logged FEC count in 48 hours had reached almost 100,000 and the connection speed was below 1 Mbps.  I tested using the modem's diagnostics and saw IP errors, IPv6 errors, and a lot of DNS failures.  Back on the phone with AT&T...

By now I've been on the phone with AT&T enough (almost every day) that they've given me a special Tier 2 support number and a passcode for it.  This gets me straight into their domestic tech support line, which is nice.  Another call to Tier 2, more tests from their end, another tech visit scheduled.  Today's tech agreed that the FEC errors indicated a problem, and was about to call in an order to have my DSL line card swapped at the central office.  I asked him if he had seen a lot of problems with the NVG510 modem.  (He thought I'd already had a modem swap, but I hadn't.)  I asked him if he considered the NVG589 more stable.  The NVG589 is only for VDSL installs, but he said "Hold on." and came back with a new 5168NV modem.  From what I've read, these are the "go forward" modems which AT&T will standardize on since they support everything from ADSL up through VDSL2.  The 5168NV (datasheet) also offers 802.11n 2x2 MIMO, 400 mW Wi-Fi power, and has a dual-core processor which speeds up recovery from retrains and allows faster adaptation to spectral interference.  One side benefit of the 5168NV is that the downlink receiver has much better performance than the NVG510 - I'm seeing +18 dBm on the downlink versus the previous 10 - 11 dBm.  So far the performance has been very good, Netflix picture quality is a lot better, websites are more responsive, etc.

Sunday, July 20, 2014

Thoughts on GoTenna

[Update Nov 30th 2016: The ARRL has asked Bay-Net to attempt a modification of the GoTenna for use in the amateur radio bands.  Also I should note that since I wrote this article, GoTenna has backed off on their performance claims to levels which are more in line with reality.  I'm looking forward to seeing the inside of these units and doing some real world testing.]

[Original Article posted July 20th 2014] GoTenna seems to be doing a good job of generating "buzz" for this proposed product - a cursory search of Google+ and Facebook turned up a HUGE number of posts.  Many people have forwarded this to me via email or social tagging.  The proles are calling it "Text messaging for CB radio".  facepalm

GoTenna's radio works in the MURS band - three channels at 151 MHz and two channels at 154 MHz.  Given what I know about their product, MURS rules will require them to operate on the two 154 MHz channels.  They say the product emits 2 watts, which with a 3 dB antenna would be 4 watts effective radiated power (ERP).  At that level they're going to have to undergo safety exposure testing, which is expensive - I guess this is why they're crowd-funding the project.

To be fair - GoTenna has an engineering advantage in that they're not dealing with large data streams - they send GPS coordinates, text messages (< 200 characters), and it's not real-time.  They claim 20 - 30 mile range in a "typical" urban environment - I'm struggling with the idea that something which emits 4 watts ERP can give you 20 - 30 mile urban range.

Coding gain from a forward error correction engine could help, but I can't imagine an effective coding gain of more than 10 dB.  (The device is battery-powered, and claims a 30 hours continuous on time - processors which could give them > 10 dB coding gain are going to wipe out a battery fairly fast.)  Let's be generous and say their coding gain 10 dB - this gives effectively 40 watts.  I suppose depending on your definition of "urban" this might be enough to cover 20 - 30 miles.  A more reasonable coding gain will be in the 6 dB range, which means effectively 16 watts - and I don't see 16 watts covering urban areas very well.

Here's a post on from Raphael Abrams, the GoTenna RF designer:

GoTenna claims that the device can be used in-flight on commercial airliners.  This is a Bad Idea™, and I don't see the FAA signing off on this any time soon.

Lots of speculation on GoTenna right now in the radio community, but not many answers to the head-scratcher questions.

Saturday, July 19, 2014


Recently I switched our DSL from Earthlink to AT&T U-Verse, and bundled the plan with a U-Verse Voice line.  I was somewhat reluctant to do so, given how for years I've believed that in a major emergency a copper POTS line with 48 VDC sourced from the central office is a better idea than a VOIP line with a four-hour battery backup.  However the cost savings were too good to pass up, E-911 is finally deploying, and 75% of the family have their amateur radio licenses.  If the poo-poo hits the rotating blade, I think we'll be OK - So bye-bye POTS line.

I have been pleasantly surprised by the service I've received.  The install went very well, and when the tech realized I used to work in telecom he even offered to double-bond my pairs so I now have a nice low-resistance line.  45 Mbps possible to a local fiber loop, I'm seeing about 30 Mbps effective with higher rates during the night.  Every customer service agent I've spoken to has been polite and knowledgable, and they seemed genuinely interested in making sure I'm happy with U-Verse.

Of course, I don't believe for a second that the Death Star has been magically transformed into a chirpy little startup full of love, compassion, and (with apologies to +Sandra Meow and +Paul Lannuier) cute cat GIFs.  The tiger can't change its stripes.  They're just hiding their megacorporate stupidity under a veneer of "We Wuv U" until I'm past my 30 day no-risk trial.  Which is why I'm not very surprised by today's incident.

Our U-Verse service was installed on 7-July.  Our old POTS service billing date was the 13th of each month.  I should have received a pro-rated refund on the extra five days, but I wasn't going to sweat that.  Then the 13th rolls around and I get a bill for my old POTS line.  I call the 800 number, wait on hold for 15 minutes, they quack at me for 10 minutes, and then tell me I need to speak with the other people in the POTS line department.  Call is transferred, gets lost in transit, call drops.  I call back, get through to someone, but their system starts sending DTMF tone sequences over and over again, so I have to hang up.  Call back again.  This time I get a human, and I explain the situation.  The following conversation occurs after I ask why I'm being billed for a month of my old POTS line:
  • Agent: "That's just the way AT&T billing works."  
  • Me: "I'm sorry, but I'm confused.  I switched to U-Verse on July 7th.  This bill is for services from July 13th through August 12th.  I'm already paying for U-Verse as of July 7th.  Why would I also pay for my old line?"
  • Agent: "Let me see what I can do..."  [Much typing in background ensues]
  • Agent: "Since you're a valued customer, I can offer you a credit of 50% on your bill."
  • Me: "Well, I appreciate your offer, but you haven't really answered my question.  I'm paying for U-Verse now.  And I'm happy with it, by the way.  Why are you asking me to pay for my old service too?"
  • Agent: "That's just the way AT&T works."
  • Me: "You seem like a nice guy.  Let me ask you this...  Just between you and me.  Does this bill make sense?  I understand that you're just following company guidelines given to you by your boss.  If our roles were reversed, would this make sense to you?  Let's set aside the idea that this is quote-unquote "the way AT&T works."  Would you think this bill is fair?"
  • Agent: [Pause] "Since I see that you switched to U-Verse, I can credit you for the entire bill."
I realize this is a naive notion, but wouldn't it be better if I didn't have to spend 30 minutes on the phone arguing for fairness in billing?  Clearly it's within their power to NOT try to double bill me.  This wasn't a mistake; the agent said clearly it's "the way AT&T works".  Had he said "Sorry, this is a mistake, I'll credit you in full right now." I would have accepted it as a mistake.  Did they think I wouldn't notice?  Why try to double bill me in the first place?  Why risk making me angry?  Why offer me 50% credit, then cave to 100% credit when it's clear I'm not going to back down?  I've been happy with U-Verse so far, even telling friends that I'm pleased so far with the equipment performance and the customer service.  That's gone out the window now.  I'm not sure if the agent realized I was still within my 30 day no-risk trial, or if maybe I got through to him on a personal level.  (The negotiator in me would like to believe it was the latter, of course.)  Regardless of what happened with the agent, the fact remains - this was a deliberate attempt by AT&T to take my money under false pretenses, and I'm unlikely to trust them again.