Help with Wifi-router for FXO/FXS wireless POTS plus Modem

Discussion in 'Cisco/Linksys Wireless Routers' started by d9dd, Oct 31, 2007.

  1. d9dd

    d9dd LI Guru Member

    Note: I drew up a sketch to post here, of the system as I currently envision it....but no "attachment" field is showing below...even tho the page says "you MAY do attachments".

    Problem: Our neighbors, an elderly couple living in an off-grid mountain cabin, have just lost their phone line. The wire was installed about 40 years ago, crossing a 500 foot wide canyon between the road and the cabin. The trees that the cable was hung on grew differentially, and finally the tension snapped the cable recently.

    Project: Extend the analog POTS line across this 500-foot canyon WIRELESSLY; and support both analog-phone use and 56k modem use at the cabin. At the same time, provide shared Internet access via WiFi to multiple laptops at the cabin.

    Situation and Constraints: Regular phone line runs along the road that is across the canyon from the cabin. Only regular analog POTS line available; no DSL or Cable available. No AC power available at either end; so everything must run from batteries and solar-PV, which is expensive as hell per installed-watt (so hardware should be as low in power-consumption as possible).

    Proposed Solution; using hardware which I know exists and is cheap:

    Put an FXO box at the roadside and hook it to phone-company POTS line. Mount a Wireless-Bridge box there also, and plug the FXO into the Bridge via 10baseT. Across the canyon at the cabin, mount the 2nd Wireless-Bridge box, and an FXS box, and hook those together via 10baseT. This should accomplish the basic extension of the POTS line.

    Plug the regular analog phone, and a 56K modem, into the POTS on the FXS. Connect the Modem's RS-232 port to a WiFi Access Point that has a serial port on it; which box is HOPEFULLY smart enough to control the modem and share the data over the WiFi link to the laptops.

    As an alternate, use a laptop with built-in 56K modem and WiFi card to act as the AP. This is MUCH less desirable, because it will use TEN TIMES the power as a dinky little WRT box (50w vs. 5w).

    Here's a far more OPTIMUM Solution; using hardware (and firmware) which I HOPE exists:

    Find a SINGLE box that includes an FXS-port, WiFi AP, AND a 56K modem, all built in; with firmware that can control the modem and share it over the WiFi for multiple laptop Internet Access. For the other side of the canyon, use a typical WiFi 'router' with an FXO port on it to connect to the phone-co POTS line.

    (note; if I understand correctly, the FXS port on these common 'router' boxes can also be used as an FXO; i.e. connected to a phone-co POTS line)

    This scenario would be by far the best solution; because it minimizes power-consumption...just a single modern low-power box at each end. Also, it would save the old folks quite a few bucks; by using the built-in WiFi hardware to jump the canyon as well as serving the laptops, it eliminates a pair of expensive 900mhz bridges.


    1) Most important question: With an FXO and FXS box on each end of the bridge link, CAN they talk to each other? In other words, directly to each other...without any 'server' and without any 'account' at a VOIP provider?

    I am not up to speed on SIP protocol, or VOIP in general; but I've seen screen-shots of some "Wifi Router plus VOIP" boxes which scare me....they all seem full of config fields like "Account", "username", "password", etc..

    Again, I need these two boxes (the FXO and FXS on each end of the wireless-bridge) to talk to EACH OTHER.....NOT to some kind of VOIP "server" or "service".

    ALL I am trying to do is use them to physically EXTEND an existing analog POTS phone line.

    I really really need confirmation that the common FXO and FXS ATA boxes CAN talk directly to each other. Otherwise, this whole idea is out the window, and these folks are looking at a huge bill to either replace the wire or use some sort of much more expensive wireless system.

    2) Another thing I've seen that scares me are hints that the FXS traffic can ONLY be routed over the RJ45 port...NOT over the built-in WiFi (now talking about boxes like WRT54GP2 that combine an FXS port with a Wifi router; i.e. the preferred solution).

    I'd be VERY grateful if someone would post firm confirmation that the FXS call CAN be routed over the Wifi...AND received over the WiFi on the similar box across the canyon.

    3) Does the WiFi function in one of these "wifi router with voip" boxes act as an AP? In other words, multiple laptops can access the internet over the wifi?

    4) Can I use the WiFi function in one of these "wifi router with voip" boxes to both serve the laptops AND bridge to another similar box ??

    5) Am I correct that an FXS port CAN be used as an FXO port? (i.e., connected to a phone-co POTS line, receive ring-voltage and calls from the phone-co, go off-hook and dial and make calls on the phone-co line). If not, can anyone recommend a WiFi box that has an FXO port in it, instead of the usual FXS ?

    note: I'd prefer to do both ends with 2-port devices if possible. Since these folks don't have DSL available to them, another possibility to improve their internet is to bond a pair of dialup-lines. ps: they can only achieve around 28.8kb on these lines; due to distance from switch.

    6) I'd be real grateful for hardware recommendations. Especially for boxes running Linux variants; and most especially those with some sort of 'following' give some chance of non-mfg future support. However, if you know of boxes that aren't open linux, but do exactly what I need, that's fine too. As long as they work as required, and do the job reliably (i.e. without going down every two days...LOL).

    The two units I'm looking at so far are:

    1) For the more complex solution; where I use seperate wireless-bridge boxes:
    Linksys SPA-2002 2 Port FXS Analog VoIP Adapter $68.95

    2) For the optimum solution; where a single box on each end does the whole job: (although none of these has a modem)

    Linksys WRT54GP2 Wireless-G Broadband Router with 2 Phone Ports

    DVG-G1402S > Wireless Broadband VoIP Router



    (or something there a similar Linksys/linux product?)

    7) Does anyone know of ANY access-point or 'router' Wifi boxes with a built-in modem; or at least an RS-232 port and the firmware to control and share a modem?

    (I am capable of adding a DB-9 to any box that has the serial-port on-board but not wired out to a connector)

    Similarly, does anyone know of WRT-type firmware which DOES support the control and sharing of a 56k modem?

    8) What's the best firm to order this kind of product from?? I.e., with at least reasonably good discount prices, but also with fast response and good clear-english communications. I.e., good all around firm to do biz with. ??

    Thanks VERY much for any help you guys can give on this project. The old folks up the road will appreciate it a lot too....they don't have a lot of money, and they do need their phone.
  2. pablito

    pablito Network Guru Member

    I don't think I can answer all of your questions, I can't even read them all. :) So this isn't comprehensive but just ideas.
    If you want to get POTS and internet at the cabin I don't think you'll want to run a modem at the cabin. Modems like faxes are audio modulated and don't easily work over SIP/VoIP. However you can easily extend your POTS line to the cabin with an FXO/FXS combo. The FXS at the cabin can connect to the FXO at the road and out the POTS. No need for a VOiP provider which wouldn't work anyway at modem speeds. Over the same wireless link that gets you FXS you can do internet at the cabin. The cabin would run normal ethernet speeds, route over the wireless link, and out a router connected to the modem at the FXO side.

    First task is to find a router that does serial to a modem for the WAN port. This router should behave well and only dial when required for internet. You need the modem offline in order to use the telephone (only one phone line?). On the LAN side of the router is your FXO that Ts off the POTS. Add a wireless AP and you're ready to link the cabin. If you can find all the pieces in one device great but that won't be easy.

    At the cabin you need a wireless router that can do a client/bridge/WDS to the other side. Client or bridge mode is easiest but might require 3rd party firmware depending on what you buy. On the LAN side of the cabin router is your FXS, telephone, and computer(s). The FXS is configured to connect to your FXO.

    The trick is keeping the modem offline until required for internet. So many devices and software these days want to chat over the internet for updates, current time, DNS, etc. So careful configuration is required but I think it is possible. Of course you want the lowest power requirements and a solar/wind/battery combo that can keep everything running well.

    I just thought of another option. To keep power needs down you could run a laptop with wireless at the cabin and use a softphone that talks to the FXO. No need for an FXS or router at the cabin. But I'd still like a whole network at the cabin for flexibility if possible.
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