This page was originally located on the 68kMLA, but I moved it here because it is very much more of a personal research project.
Long Reach Networking
This page, and my research so far, is almost exclusively about wired technologies that bridge moderately distant (one to sixteen kilometers, in different situations) Ethernet networks, often using variants of DSL. Even longer distances are possible with fiber, and of course Ethernet on its own using Cat5, 5e, 6, 7 is good for approximately 100 meters.
Early research is specifically about G.SHDSL.bis and VDSL2 standards, which are relatively well-documented online and have products focused on long-reach ethernet and ethernet in the first mile available. I have also included some information about ADSL2+ devices and equipment, but that's getting away from "long reach LAN" and into the "small, local ISP" territory and I'm not anywhere near ready to talk to issues such as setting up a PPPoE/A server.
There are several companies making these things, but among the most notable are ZyXEL and Planet.
SHDSL is an old synchronous standard. Officially, it is good for up to about 5.6 megabits on a single pair under optimal conditions. This won't exactly light the world on fire, but there are situations where it may be appropriate. The main reason to use SHDSL today is that it has very favorable distance properties. While ZyXEL suggests that VDSL2 devices can communicate at up to about 1.5KM, it doesn't even list a maximum distance for SHDSL. Another site suggests that using high quality copper, you can run SHDSL up to about 16 kilometers. At 16 kilometers, you'll be getting about 192 kilobits per second, the slowest speed at which SHDSL can officially sync. How acceptable this is is going to depend on the application and the budget. At up to $300 a pop, new, devices such as the P793H mentioned below aren't cheap. A three-point LAN will cost you $900, before cables. However, this may well be less expensive than deploying fiber. (As of 2014-02-18, this is simply not something I've researched.)
SHDSL has a few interesting devices as well, in particular the ZyXEL P793H. The P793H is not inexpensive, for what essentially amounts to a slightly more interesting version of an old four-port Ethernet router. However, the P793H is a bonded SHDSL modem, with some interesting operation modes. For starters, you can achieve 11.4 megabits from one point to another, because it does pair bonding. Or, if you buy three of them, you can set your "CO" device to host each of your two "CPE" devices independently. If you're linking a second and third floor in a building, or your two closest neighbors want to be on a LAN with you, then it could be slightly less expensive (and also easier to set up) to buy into fiber (for long distances) or to buy four single-port devices (for runs up to 1.5KM.)
In addition, if you are running a small dark-net, the P793H has routing capabilities built in, and the "CO" device can be the DHCP server for a LAN. (This would be useful if you're connecting older machines and/or do not have other networking expertise.
The P793H expliticly states compatibility with other SHDSL.bis devices. It's worth noting that plain SHDSL seems to have a maximum data rate of about 2.3 megabits and SHDSL will go up to about 5.3 or 5.6, on a single wire.
VDSL2 is a much newer standard, and is notable for...
Not needing to be symmetric, although it is possible to configure devices to try for the most symmetric possible connection.
Having a much more modern and more diverse set of equipment available.
Industrial equipment is probably compatible with consumer-focused equipment, lowering cost. Some of this consumer equipment can be bought at retail.
Providing both very high speeds on short hauls, and relatively long distances. (1.5km is actually quite a ways away.)
Having a fair range of configuration flexibility. Many "legit" VDSL2 DSLAMs will fall-back to VDSL or ADSL/2/2+ allowing a miniature network operator flexibility in CPE choices. In addition, even standalone "CO" devices often let you set a maximum or target sync rate.
VDSL2 has several profiles. Many of the industrial VDSL2 bridges will use profiles 17A or 30A, but the others are common on consumer deployment. CenturyLink in particular serves most of its customers on 8A profiles, though higher profiels may be used for customers further away from the DSLAM, such as 8B which offers a higher transmit power, or who are closer to the DSLAM and would like a higher speed (17A/30A) which have lower transmit power.
Host Devices (CO mode, DSLAMs)
One of the easiest devices to use in this fashion is the ZyXEL P871M. The P871M costs just shy of $220, is attractive (You could put it on a desk and nobody would look or think twice) and has a hardware switch to flip between "CO" and "CPE" modes. When you connect two of them together, or one of them to a client, they will automatically negotiate the best possible speed profile and VDSL2 mode. If you have a desire to set the speed profile manually, they can be managed via a serial console port. The P871M is a pure bridge device, and probably one of the nicest "CO" devices, but it is one of the more expensive ones.
For the low cost of $180, Planet Technologies has a kit that includes a single-port VDSL2 bridge and a VDSL2 gateway with four port ethernet switch. Both devices are configurable to work in CO or CPE mode, with interleaved or fastpath channels, at Profile 17A or 30A or with different SnR requirements using DIP switches. This kit is probably one of the cheapest ways to get started if you just need a single link. The likely scenario is that you're going to install the one-port bridge on the "CO" side of your arrangement and the four-port router on the "customer" side of your aggangement. The CPE device has the DIP switches for configuration, but also features a console port and, if you're using a true DSLAM or need a VDSL2 modem for your home Internet provider, supports more profiles than the bridge does. A kit with just two bridges is $170 and a kit with two of the CPE/modem devices is $185. The extenders are also sold in 10 and 20 packs, where they go down to $85 each. Theoretically, there is also a small shelf that the small extenders can sit in, but if you need more than about three links, it makes a lot of sense to consider moving on up to a real DSLAM.
The cheapest DSLAM money can buy is also one of the easiest to configure. VersaTek is selling the Planet VC820M DSLAM, which accepts a single gigabit LAN input and up to eight POTS/PSTN lines and then dumps out eight VDSL2 connections. The VC820M can be managed by a web interface or by console. It allows each port to have its own configuration, including speed limits and using different VDSL2 profiles per port. This is useful if you're selling access to a network to subscribers woh might be paying different amounts of money, or may be in physically disparate locations. (Within the 1.5KM limitation for VDSL2, of course.) At $800, it's a bit more expensive than buying ten standalone converters, but it fits in a rack and is a lot more convenient to use, without going all the way to needing punchdown 66-blocks for wiring purposes. It may of course be most convenient to simply let the DSLAM configure itself, especially if you're going to install more than one of them, and/or you're not selling tiered services through it.
If you are a true DSL slumlord, say, retrofitting a large-ish building or a small, otherwise un-wired neighborhood for DSL access then you might to move to an even bigger DSLAM. For the low cost of $63/port, plus additional wiring complication, VersaTek sells a more traditional DSLAM that features Telco50 connectors. The VX-M2024S is similar to the VC820M in that it's actually quite flexible if you'd like to do any configuration on it. Larger DSLAMs, ranging from 12-port ADSL2+ models all the way out to devices supporting 48 and more ports are available.
If you're truly starting a slum-lord ISP, a 48-port DSLAM such as the Versatek VX-1000HDZ ADSL2+ DSLAM may be a good place to look. ADSL2+ equipment is much slower than VDSL2, but modems and gateways and modems are typically very inexpensive (at the expense of often not having features that are nearly as cool as VDSL2), as low as $80 for a wireless N gateway with a four-port switch. Even less if you only have one computer at the endpoint and/or do not want wireless. The main disadvantage is that there's a significant down/up disparity. ADSL2+ can sync at up to about 24M/3.3M, compare with up to 100/100 for VDSL2. ADSL2+ an VDSL2 have similar reach properties and are probably going to be about the same speed at their furthest distances. (That guy who lives in the mobile home at the back of your slums will only be syncing at 800 kilobits/second with either VDSL2 or ADSL2+.) some sources suggest that ADSL2+ may be faster at even longer distance, potentially up to about 5KM, but if you're going to accept sub-megabit speeds and need long distance, SHDSL may also be worth looking at, especially for point to point scenarios or for a very low number of overall points.
Client Devices (CPE)
There are a lot of different VDSL2 client devices available. Most industrial or other point to point devices can be configured to operate in both CO mode and as a client, but looking at some other client options may be worthwhile if you want to form a whole LAN on the other end of the link. Unfortunately, a directly computer-connected VDSL2 modem, such as a PCI/e card or a bus-powered USB modem simply doesn't exist, but there is a lot of choice in the market, and things like multiple ethernet ports, wireless access points, gigabit switches, and bridges to other LAN/Ethernet technologies (such as MoCA/HPNA), and VoIP analog telephony adapters are all available from various vendors.
The ActionTec (CenturyLink) C1000A supports VDSL2 line modes: 8a, 8b, 12b, 17A (U0) and 30A, and should therefore be widely compatible with both traditional DSLAMs (where you might use profile 8b for a long run, and profile 12b for a shorter but faster run) as well as industrial equipment, which tends to host only on 17a or 30a. The C1000a has a four-port gigabit switch, 802.11N wireless networking, and buildt in POTS/PSTN pass-through, if you're building a network where that's important. You can also configure it for bridge mode or to be an IP client on a larger network, just depending on how you want to separate the clients. Management is done completely by web interface. If I had to recommend a strategy for using multiple C1000As on a larger network, it would be to manually assign them IPs outside of the DHCP range, and then label them with the IP you are using. ZyXEL also sells a version of this gateway called the C1000Z. Because CenturyLink set the spec on these devices and both ActionTec and ZyXEL built them, it should have identical specifications. Older versions called the Q1000 and Q1000z exist, and there's also the Q100, which ZyXEL built and has only one ethernet port.
As a CPE device, the ZyXEL P871m can be managed via serial, but it is otherwise a simple bridge with few, if any configuration options.
ZyXEL has several far more conventional pieces of CPE which, like the Actiontec C1000a feature ethernet switches and web based management consoles. Good examples are the P870H and the P873HNUP (which also supports bonding, and has a configurable WAN/LAN fifth ethernet port, bonding, and fallback to ADSL2+.) If you are linking multiple homes together, the P873HNUP may be a good idea because it can be connected to a local gigabit switch at the "client" premises, as well as to a local co-axial network using the HPNA 3.1 standard ZyXEL doesn't talk about what it does, but the P873HUP also has a USB port. NAS appliance? I won't talk about it too terribly much, but ZyXEL sells the HLA3105, an HPNA 3.1 client which might be used to create a medium-sized LAN in an existing house that was wired for TV but not computers.
Actually, ZyXEL sells a whole lot of VDSL2 gateways, and if you're starting an ISP and buying a gateway in bulk, it would be worth investigating what they've got to see how it does or doesn't fit your particular needs. For example, while bonding might not be worth your time, VoIP may be a very good idea, or even necessary.
Because I gave a mention to ADSL2+ CO equipment above, it's worth noting that there's a lot of ADSL2+ CPE, and it's typically available very cheap. Most stores will sell inexpensive Netgear routers, along with ActionTec and ZyXEL devices. Netgear offers the cheap, single port DM111PSP, the sensible DGN D3700, and the insane DGN D6200, (I don't even know of any shipping VDSL2 gear with 802.11AC as of this writing.) As I said above, it all depends on what you're doing. If you are deploying ADSL2+, there are single, dual, and quad-port ADSL PCI card modems, which present themselves to a host computer as a regular Ethernet device. Granted, if you need quad-bonded ADSL2+ at each endpoint, you should really just pick another technology. On an ADSL2+ DSLAM, the only devices to avoid are probably AT&T's IPDSL devices (U-Verse RGs), but that might be worth more research. 2Wire devices are also extremely popular, but I can't recommend them purely based on the fact that they are all ancient at this point in time. Pace, on the other hand, may be worth investigating, if you can buy them locally.
Fiber is sort of the next frontier. If you have a lot more money for your long-run LAN project and absolutely demand more than about 200 megabits of performance, or you need to go a long distance, it has to be fiber. The most convenient device I can find for this off hand is from StarTech, and uses single mode LC fiber. There are direct to fiber gateways, but most ISP fiber installs use an optical network terminal, which is similar to the StarTech device. Point to multipoint fiber, as if you were wiring a large campus up for gigabit ethernet, is another ballgame entirely.