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Homemade VoIP Network Over Wi-Fi Routers

Posted by timothy on Tue May 13, 2008 07:53 AM
from the warms-the-cochleas-of-the-heart dept.
Communications Hardware Hacking Networking Wireless Networking Hardware
AnInkle writes "A blogger on The Tech Report details his research and testing of wireless voice communication options for remote mountainous villages in rural undeveloped areas. The home-built project involves open-source software, low-cost wireless routers, solar power, mesh networking, unlicensed radio frequencies and VoIP technology. Although his research began several months ago, he has concluded the first stage of testing and is preparing to move near one of the sites where he hopes to eventually install the final functional network. Anyone with experience or ideas on the subject is invited to offer input and advice."
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Submission: Homemade VoIP Network Over WiFi Routers by AnInkle (882630)
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  • Urban Networks... (Score:4, Insightful)

    by PC and Sony Fanboy (1248258) on Tuesday May 13 2008, @07:59AM (#23390052) Journal
    Wouldn't this be great! You could use your networking skills to setup a private, free telephone system. And, if it was encrypted, no one could snoop in on it... and if it was in an urban environment... Hmmm....

    • Re:Urban Networks... (Score:5, Funny)

      by William Robinson (875390) on Tuesday May 13 2008, @08:19AM (#23390200)

      And, if it was encrypted, no one could snoop in on it

      Hold your horses, Osama, it's not perfect yet :)

      • Re: (Score:3, Insightful)

        by Catbeller (118204)
        Shrug. Killing the joke, but:

        Al Qaeda NEVER uses electronic communications. They communicate face to face, always. No cell phones, no computers, no GPS, no mail, no land lines, nada. This is why I scream madly at every "homeland" security citation about encryption and internet use. They don't use anything of the sort. That's why we can't find them. That's why they got away. We're building a surveillance state that has no way of watching people riding horses in mountains, but does a bang-up job in keeping us

        • Re: (Score:3, Insightful)

          by Dan541 (1032000)
          Don't tell me you Actually believe the Anti-Terrorism laws are to do with terrorists.
        • You sure seem *awfully* familiar with the internal working of Al Qaeda.

          *waves to the nice men reading all our email in Langley, Virginia* :-)

    • Re:Urban Networks... (Score:5, Interesting)

      by Opportunist (166417) on Tuesday May 13 2008, @08:30AM (#23390286)
      Zero chance. I'd even deem it unlikely that the original project survives for long. Telcos are missing out revenue when you communicate for free, the feds owe them one for the wiretapping thing, so I expect a law soon against this. Because of ... because of ... national security or whatever fits.

      • Zero chance. I'd even deem it unlikely that the original project survives for long. Telcos are missing out revenue when you communicate for free, the feds owe them one for the wiretapping thing, so I expect a law soon against this. Because of ... because of ... national security or whatever fits.

        Cell phones should be able to communicate point to point over 100 metres or so. For some reason no phone manufacturer has thought to introduce this feature.

        • Re:Urban Networks... (Score:4, Interesting)

          by jamesh (87723) on Tuesday May 13 2008, @08:40AM (#23390364)
          There are (still?) cell phones with DECT (household grade cordless phone technology) built in. I always thought this would be a much better alternative to a cell phone with wifi built in to accomplish VoIP. DECT is pretty lightweight, so do VoIP to the DECT base station, then DECT to the phone. When you are in range of the DECT base station (eg at your house) you'd make calls via that instead of the more expensive cell network.

          Not sure why this never took off... could have something to do with the less money that the cell providers would make.

          • Re: (Score:3, Insightful)

            by Spokehedz (599285)
            "Not sure why this never took off... could have something to do with the less money that the cell providers would make."

            Gee, you think?
            • It is probably more like there is no signal privacy and very limited access control with cordless phone tech that would sometimes vary from manufacturer to manufacturer and the inability for most cordless phones to carry a signal to more then one handset at a time. Things have changed but not really since wifi has taken off.

              Without a lot of the security and stuff that WIFI offers, it could generally be possible to just walk down the street and connect to someone else's land line through their cordless phone
          • BT tried something not a million miles from this in the UK. Went by the name of BT Fusion and the principle was that the compatible handsets used Bluetooth to communicate with a base station (which was also a DSL Router) and thus your mobile/cell phone used that to route calls when in range. AFAIK the base station used normal PSTN lines to route the calls out, but that's just a technicality - it could have been doing whatever at that point, it would be transparent to the end user
          • T-Mobile I believe has that already in place. When you're near a wifi hotspot, it'll give you VoIP service. When you're not, they use the cell towers. It does appear that you also have to have t-mobile broadband though. Service is part of T-Mobile HotSpot I think.
          • It sounds like what I have at home right now through T-Mobile. see: http://talkforever.t-mobile.com/ [t-mobile.com] My Linksys router has slots for SIM cards too.
          • Unfortunately in many countries the cellphone networks have set up thier price plans such that (unless you ave a very light user who is better off on a pay as you go plan) you pay them for a new cellphone every year or so whether you actually take said phone or not,

            While pay as you go users don't get "free" phones from the network there is often still some subsidy of the phone price and of course a lot of pay as you go users are using phones handed down by contract users who have since received a new "free"
        • Actually, iDEN (Nextel) allows one to use the PTT service without a tower.

        • Cell phones should be able to communicate point to point over 100 metres or so. For some reason no phone manufacturer has thought to introduce this feature.

          GSM at least is encrypted. The SIM that goes in your phone is registered with the HLR for that company and it includes the key used for encryption. You wouldn't want people to be able to easily eavesdrop on your conversations, would you?

        • Why would they want people to be able to make free calls?

          Why would they want to screw their customers?

  • Why not cellular? (Score:4, Insightful)

    by ostiguy (63618) on Tuesday May 13 2008, @08:03AM (#23390094)
    Read this yesterday, still don't get it. Can omni directional wifi ever compete with a cell tower's coverage range? Cellular has the advantage of insanely cheap commoditized phones.

    Seems a bit like trying to use bluetooth to connect two buildings in a campus together - nominally cheap hardware, but probably cannot be coerced into doing what you seek.

    • Re: (Score:3, Insightful)

      by Anonymous Coward
      Insanely cheap commoditized phones subsidized by an insanely marked up cell phone plan. The point of this exercise is to provide the infrastructure where private business currently doesn't feel there would be return on investment. Think OLPC for VoIP.
      • Perhaps I missed the point too, but, isn't keeping the power low what maintains this frequencies free? If someone attempts to exceed the power in those frequencies, the first thing a government will do, is regulate those frequencies to avoid people abusing from transmitting power.

        IMHO, that's what will happen if someone decides to transmit at high power in unregulated frequency bands.

    • Re: (Score:3, Insightful)

      by MichaelSmith (789609)

      Read this yesterday, still don't get it. Can omni directional wifi ever compete with a cell tower's coverage range? Cellular has the advantage of insanely cheap commoditized phones.
      But cellular base stations have to transmit at high power. Doing that attracts attention from authorities. Wireless mesh networks can be low power everywhere.
    • Wifi has the advantage of insanely cheap communication.

    • That's not the point of this research project.

      The point is that many developing countries do not have the economical manpower to deploy cellular antennas everywhere, thus eliminating the possibility of many areas receiving cell phone service. This person is attempting to solve that problem by using consumer-grade hardware and open-source software.

      Though it will surely not deliver the kind of quality one would receive from using VoIP or even cellular, it would probably be a highly desirable alternative t

    • one problem with cell phones is that if the company who builds them doesn't think there are enough people in the area then that area doesn't get a tower.

      there are still huge sections of the USA who can't get cable TV as they are to spread out for a cable company to find value in it.

    • Re:Why not cellular? (Score:5, Interesting)

      by Timberwolf0122 (872207) on Tuesday May 13 2008, @08:12AM (#23390154) Journal
      I think the main drive according to the article is the 802.11x frequencies tend to be de-regulated and free to use, cell networks have ongoing fees to use that portion of the spectrum. Also wireless routers have very low power requirements and can be run via hippy fuel (aka solar) instead of some poor bugger having to run the mother of all extension cords up a mountain.

    • Re:Why not cellular? (Score:5, Informative)

      by William Robinson (875390) on Tuesday May 13 2008, @08:14AM (#23390172)
      FTFA,

      Technology alone is not sufficient. For any project like this to work for more than a couple of years, it must have a sustainable business model. (In the long run, at least as much money needs to come in as is going out.) Village Phone, which builds on traditional cell phone technology, has been very successful in bringing communications to rural Africa. Their model, in summary, involves an entrepreneur from the village purchasing a cell phone, roof antenna, and charger with the help of a microloan. They are then able to sell minutes to villagers for a profit. The cell phone antenna must be within about 35 km of a cell phone tower and have line of sight, thus making the technological aspect of this model unworkable in many rural or mountainous regions.The business model, however, could potentially be used just as successfully with other technologies, including WiFi paired with VoIP.

      • 35km line of sight for the cellular bridge station isn't bad - any wifi based technology is going to need line of sight for those same distances. Cellular means cheap GSM phones that work everywhere, as opposed to wifi phones that have limited coverage in the village, and perhaps none elsewhere (the route to the nearest urban center, and perhaps within the city itself, as it is likely already blanketed with GSM)
        • 35km line of sight for the cellular bridge station isn't bad - any wifi based technology is going to need line of sight for those same distances

          In a mountainous region you are sometimes lucky to get 10km line of sight. If you can't get enough users to cover the cost of installation, then the tower won't be put in place.

    • Re: (Score:3, Informative)

      by Steauengeglase (512315)
      Why not? Easy, you could give your kids an old PDA or hacked Skype phone or something for use around the neighborhood without having to pay an extra phone bill.

  • In a somewhat similar vein (Score:5, Informative)

    by fuzzyfuzzyfungus (1223518) on Tuesday May 13 2008, @08:08AM (#23390126) Journal
    David Rowe [rowetel.com] has been quite busy working on cool, low-cost telcomm stuff. His site also has links and comments and so forth from others interested in the subject, including people doing actual, in the field, deployments in fairly poor and hostile(to the tech) environments.
  • the two do not mix well, mountains will severely block radio waves from any part of the spectrum...
    • ...when strategically placed can deal with that.

    • Re: (Score:2, Informative)

      by klapaucjusz (1167407)

      mountains will severely block radio waves from any part of the spectrum...

      The way I read the article, he's using carefully positioned directional antennas to get line-of-sight links.

    • Any part of the spectrum? So how do I pick up all those shortwave and longwave stations and talk to my buddies back home on 20M while at base camp?

  • Tried something similar... didn't work well (Score:5, Interesting)

    by cciRRus (889392) on Tuesday May 13 2008, @08:32AM (#23390296) Homepage
    I experimented with 5 units of WRT54G wireless routers running Freifunk firmware [freifunk.net] and I tried saturating the link with several G.729 VoIP calls. The system doesn't scale well. Over 3 hops, the number of calls greatly reduces as there is just too much random delay. In order for voice communication to be worthwhile, the latency cannot be more than 200ms although there are good forward error correction schemes and huge buffers.

    Latency is a real problem especially when you are doing it over several hops. The "lag" isn't consistent. It will hit you at random interval, and that can be extremely irritating. This may be due to the use of CSMA/CA and RTS/CTS (depending on configuration). I haven't found a way to improve it though...
    • Sounds like a job for ATM [wikipedia.org]
    • i have one of those WRT54G routers and they are as light as a feather, the wifi radio part of it is probably no more powerful than one of those FRS radios you see for sale for 20 dollars (cheap and low power) i bet the transmitter does not kick out more than 1 watt...

    • Re: (Score:3, Informative)

      by klapaucjusz (1167407)

      Over 3 hops, the number of calls greatly reduces as there is just too much random delay.

      Yes, there are a number of issues with building multihop mesh networks over wifi.

      If you're using omni-directional antennas, the most serious issue is that the multiple hops interfere with each other. Ideally, you'd have multi-radio nodes [wikipedia.org] that use different frequencies, and a routing protocol that attempts to maximise path diversity, but the multiple radios increase total cost, and building a routing protocol that ta

      • babel ( http://www.pps.jussieu.fr/~jch/software/babel/ ) will handle this as required
        • How does babel fix this? It seems like babel is just a routing mechanism, does it modify the MAC as well? This problem arises because of channel reservation messages & collisions, so not modifying the MAC is going to give limited improvement.

          • (Sorry for the delay, I was busy rotating all of my ssh keys.)

            Babel [jussieu.fr] will handle this as required

            How does babel fix this? It seems like babel is just a routing mechanism, does it modify the MAC as well? This problem arises because of channel reservation messages & collisions, so not modifying the MAC is going to give limited improvement.

            In case you didn't get the joke -- please mod sxpert as +1, Sarcastic.

            Babel could potentially alleviate the problem, since its one of the few routing protocols

            • If you rotate your keys, I will still be able to guess them. You should use gentoo, the developers are far too busy refreshing the packages and compiling their own systems to do something useless like memory debugging.

              I think OFDM and FFT chips are becoming cheap enough that multi-radio isn't much of an issue. Having multiple channels doesn't fix what cciRRus is complaining about, the delay of multiple hops... now you have lots of slow, non-conflicting channels... so the per-hop delay of a successful tran

      • If you're using omni-directional antennas, the most serious issue is that the multiple hops interfere with each other. deally, you'd have multi-radio nodes that use different frequencies, and a routing protocol that attempts to maximise path diversity, but the multiple radios increase total cost, and building a routing protocol that takes diversity into account is not completely trivial.

        Exactly. Unfortunately the simple WRT54G setup is unable work with multiple directional antennas.

        Interestingly, I was advised to disable one of the two omni-directional antennas (and disable diversity) to improve the overall connectivity of the mesh. I didn't try it with two antennas to investigate any the diffences though. Would this really help?

        • Interestingly, I was advised to disable one of the two omni-directional antennas (and disable diversity) to improve the overall connectivity of the mesh. I didn't try it with two antennas to investigate any the diffences though. Would this really help?

          No, it probably wouldn't. First, it's only spacial diversity, which isn't particularly interesting with omnidirectional antennas. Second, the diversity algorithm is very primitive â" every packet is sent using the antenna that had the best reception of the previous packet. There's no way to control it from the higher layers (i.e. the routing protocol).

      • Sorry to follow up on myself, but there's third issue as well, specific to the Linksys routers.

        The binary wl driver for the Broadcom chip has an annoying tendency to drop for a few seconds while it is performing a scan. If you were seeing massive jitter on fairly unloaded mesh networks, that's probably the cause.

        I have no idea whether the new b43 driver has the same issue.

  • i know someone (Score:4, Funny)

    by extirpater (132500) on Tuesday May 13 2008, @08:49AM (#23390442)

    Anyone with experience or ideas on the subject is invited to offer input and advice.
    http://img368.imageshack.us/img368/5753/macgyver2rs.png
  • ALOHA!

    And now for some filler to get the filter to let me post.

  • overhead (Score:3, Interesting)

    by sgt scrub (869860) <saintium@nosPAM.yahoo.com> on Tuesday May 13 2008, @05:09PM (#23396696) Homepage
    This brings me to a thought I have every time someone wants to know if they have enough bandwidth for voip. How much of h323, voip, etc.. is consumed to keep the whole accounting; pay per call, distance of call, who is calling, etc.. type stuff together? It seems to me a constant open stream where audio could traverse in any direction and any distance would not be that bandwidth intensive. Maybe I just don't understand everything involved.

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