I think it mostly comes down to the fact that they can only really guarantee 2 or 4 wires to a premise for residential telco, probably more modern deployments a full 8 wires (ala CatX), though their traditional copper distribution isn't built for it unless commercial (their big PED on the roads your neighborhood comes back to.  Probably something in the telcordia standards back to ma bell days that says that is just how it is.  Since the plants are non-shielded, non-twisted pair cabling too, it can only modulate so high, particularly when poorly run/done, which is why you're stuck at 12mbps.

If they had to change your home copper, they'd just run fiber, neither will happen likely.

The DSL bonding is already a hack to get more bandwidth when DSL itself is stuck in time now at raw theoretical limits.  Combining more physical channels as these were would be trivial, if copper were available, and telcos wanted to support it.  Someone would need to make the modem too.  Technically cable modems do this, literally taking "channels" or slices or spectrum on the wire, and load-balancing them internally, up to 24 or 32 channels for multi-gig capabilities.  Same with ethernet, taking 8 into a port-channel and balancing across them, whether 100 megabit or 400 gigabit ethernet. 

AT&T is the most ghetto provider out there still, and always has been imho.  Moving to San Jose in '99, there was AT&T Cable TV installed by the owners, which consisted of 2x of your standard coax ala modern cable from the outside, and required a physical a/b switch box to switch between 13 channels on one, and 13 channels on another.  First I looked at it, and was confused enough I had to call them and ask wtf the cable "channels" worked to realize just how bad it was, and I then worked for the original @home cable isp company then supporting AT&T cable modems!  The images were even snowy, the service was so bad even a tech couldn't (read: wouldn't) improve.  When I asked about a cable modem, they laughed at me, so I had to get DSL (phat 1.5mbps then), disconnected the useless cable tv (yay usenet alt.binaries.video even then), and threw up a finger to AT&T.

I can only imagine how bad AT&T's DSL is if they couldn't figure out even coax.  My experience supporting their customers for Cable Modem data in '99, relatively new tech then, wasn't much better, as if the cable plant to your house was broke, it tended to just stay broke despite our rolling their techs to fix it.  Then they'd get angry at us for doing so and tell us to stop rolling so many trucks to fix things.

Sigh.

Having grown up in Phoenix where Dimension, and later Cox actually had their shit (relatively) together, this was an inconceivable atrocity but exactly what I'd expect of AT&T.  Thanks to them (and Comcast, all the media cartels now really) owning the FCC now with your tax dollars, it'll never, ever, get better either.  Good thing Net Neutrality and consumer rights weren't really needed after all!

-mb


On Sat, Aug 15, 2020 at 12:42 PM Jim via PLUG-discuss <plug-discuss@lists.phxlinux.org> wrote:

150 Mbps, you're lucky.  Here AT&T has to bond  2 pairs so I can get 25 Mbps.    At least it's not comcast.  I wonder how many pairs they could bond.  Is there a technical limit or is it just a matter of how many they want to bond?  As more people abandon landlines, that leaves more capacity for AT&T to bond multiple pairs for internet customers.

On 8/10/20 11:21 AM, Michael Butash via PLUG-discuss wrote:
So I went through this moving from Cox to CenturyLink, and pretty much as described, fairly painless.

<tldr>

I had scheduled a CL tech to install me for new service a few years ago, and we first hit the outside where CL ran their cabling in.  It was an ancient telephony distribution from the 90's, and I've never had a land-line in my house since owning it in 2002.  My house built in 95 at least used cat5 or like, so I have 4 pairs to every room, so 2 pairs I need was just fine for bonded DSL  He ripped out the old block, removing the house cabling but the one, and isolated the particular line we needed to my office where the modem lives, added an approved jack, done.  Bonded dsl is 2x 2-wire channels, and they essentially load-balance 75+75mbps channels.  I have tested this to n-by gigabit upstreams.

Phone only guarantees 2 wires are available, so telcos built on this 100 years ago are a bit assed-out on passable high-frequency modulation schemas in use for data and other things to move beyond where they're at.  DSL makes up for this, particularly when double up on wires it gets better, but still unshielded and prone to breakdown.  Problem is mostly it isn't shielded, thus capable of very high frequency modulation ala Cable/DOCSIS, so it will never go much further than it has today whereas Cable scales to gigabits with channelization and QAM modulation at 32bit rates.

VDSL tech is capable of roughly 75mbps per channel, and 2x of these get you to around CL's bonded DSL limits.  This also includes your distance limitations to your local DSLAM, or regional router that terminates your data that degrades this eventually further you are from it, so it's a bit tricky.  It's been stuck here for years, and pretty much at life end.  This is why my cousin living half a mile from me can only get 75mbps from CL and I can with bonded @150mbps here.  Old crap network there.

Fiber, particularly Single Mode, gives you whatever to ~100GbE, but depends on how your provider does low-rate Passive Optical Networking (PON) today for residential fiber.  Not quite the same as a business data network, but any fiber is better than copper networks.

Why Centurylink's only hope for the future is fiber vs. copper in new builds.  I like my 25yr old house still, so no fiber for me ever.  Unless I street cut my block for fiber myself, which I've considered, just need to get my neighbors to buy into me as their new gigabit isp.  ;)

-mb


On Sat, Aug 8, 2020 at 1:27 PM Jim via PLUG-discuss <plug-discuss@lists.phxlinux.org> wrote:

Ok.  I won't complain if I have to go out and buy a 4 conductor phone cord.

On 8/7/20 9:05 AM, Stephen Partington wrote:
My understanding of this is that they will activate the second pair that is commonly used in the RJ-43 port in your wall. This will allow 2 lines active to the device.

Changes inside might need to happen if your residence does not have 4 wire (2 line) compatibility. (IE 2 pairs to the jack vs 1 pair)

On Thu, Aug 6, 2020 at 9:10 PM Jim via PLUG-discuss <plug-discuss@lists.phxlinux.org> wrote:
Where I live, I get AT&T for my DSL service.  I've signed up for an
upgrade from 10 Mbps to 25.  I finally got someone there who would tell
me why a technician visit is required for the upgrade. They're bonding 2
pairs to supply the faster speed here.  I've read up online about DSL
bonding.  I understand that one pair will carry some of the data, and
the other pair will carry some.  But one thing I didn't find out was
whether or not anything will change between the wall jack and the
modem.  Is everything done outside or do they have to come inside?  I
currently have a 2 conductor cord connecting my modem to the wall jack. 
Will that have to be replaced with a 4 conductor cord?  Do they install
an extra box outside or inside?  I guess all will be answered on the
18th when the guy is scheduled to be here.   I'm really curious how this
works.
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