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Wireless Networking Communications Hardware IT

Signal Handoff Could Mean Roaming VoIP over WiFi 91

wassup writes "According to this article in MIT tech review (and here), researchers at University of California San Diego have developed a technology called SyncScan that will reduce handoff delay in WiFi networks to a few milliseconds. VoIP roaming will be here soon!"
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Signal Handoff Could Mean Roaming VoIP over WiFi

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  • voip-a-doip (Score:2, Funny)

    by Anonymous Coward
    Can you hear me now? Good, I'm wartalking
  • just wait... (Score:5, Insightful)

    by jleq ( 766550 ) * < minus pi> on Saturday April 16, 2005 @01:26PM (#12256216)
    ... until the wireless providers find out. We will finally break the speed of light when all of their lawyers run crying to the FCC and FTC. "OmG, unfair competition!" This, combined with municipal wi-fi, could lead to a much less expensive wireless future for us all. Yay!

    • And cell phone operators will lobby congress to label WiFi as a "telecommunications service", thus increasing regulation of WiFi. Will Joe User with an open WiFi access point have to pay taxes as a telecommunications service provider?
  • I know I'm ignorant. But I'm curious, which is why I'm asking the question. Will this be better than cell phones?
    • Re:Cell phone? (Score:1, Interesting)

      by djkoolaide ( 729441 )
      In short, yes. It very well could be. I know that Skype is MUCH higher quality than even my landline phone. VoIP has a lot of potential.
    • Re:Cell phone? (Score:1, Interesting)

      by Anonymous Coward
      Compare the cost of Voip to your cellular carrier charges and it will very quickly make sense.
    • Think about how much more bandwidth is on a WiFi network than on a cellular network. More bandwidth == More redundancy, better audio codecs, clearer calls (CD quality anyone?).

      I for one am sick of the low quality audio used in cellphone networks and I would like to see them put the additional bandwidth to good use.
      • Re:Cell phone? (Score:1, Informative)

        by Anonymous Coward
        UMTS (3G GSM) which allows flexible amounts of bandwidth for a voice call has wideband (higher fidelity) codecs defined. I have heard voice encoded with these codecs and it is excellent. Note that this is possible with today's cellular radio technology without additional BW.

        In addition to the slow roll out of UMTS, the issue is the cost to change all the user terminals, the sound quality the handset can provide, and that most of the other telecommunication network entities (your house phone and all the ot
    • I think so, but since there is very few Hot-Spots (at least here in Toronto) I can't see this being very practicle. Even if large cities adopt Wifi, when you leave the city your "cell phone" won't work anymore.

      So maybe in the not so distant future...

      • It's called hand-off dumbass. Automatically using the cell phone network and wifi with minimal interuption. And if you were to drive around toronto with netstumbler I bet you'd find a ton of wireless access points in neighborhoods... Not that you'd be able to use them when driving around...
    • In a way it will be similar. This technology is certainly more like cell phone networks in regard to handign off anyway. The bandwidth is much greater, however!
      • The bandwidth is much greater because the range sucks. Don't worry, cellular networks are here to stay. Perhaps it'll be integrated so your phone uses the cheapest transport it can find - your wi-fi at home and the office and cellular in the car - but it won't go much further. All these people thinking the world will be flooded with wi-fi that will be acessible to them are living in cloud-cuckoo land.
  • 1. attach phone to toolbelt.

    2. duct tape a voip converter box to toolbelt.

    3. add a power supply (solar panels or car battery

    4. Save money on your mobile voip setup.

    5. Profit!

  • by hgilde ( 153412 ) on Saturday April 16, 2005 @01:29PM (#12256232)
    Last I checked, VOIP uses TCP sockets. When you move between WiFi base stations, you first must discover your new DHCP server, then get a new local IP address, then reconnect to the VOIP server.

    This will definitely be an annoying delay.
    • True... unless, of course, the access points are all on the same network (and therefore use the same DHCP server)
    • Last I checked, VOIP uses TCP sockets.

      VoIP generally runs over UDP. TCP is just used for session establishment, if at all. (Can SIP run over UDP? If it's stateless and can recover from lost packets/responses, it certainly can.)

    • by Anonymous Coward
      Last I checked, VOIP uses TCP sockets

      Ummm no, try again. They don't call it VOTCP for a reason. VOIP is a generic term for ANY technology or implementation of voice communication over IP. So it could be TCP, UDP, or even some other protocol (though this is unlikely as it would cause compatibility issues, and UDP serves the need just fine).

      Furthermore, the actual voice traffic is generally transported over UDP in almost all cases.

      Anyway, it would be my guess that what these guys are designing is made to
    • by c_g_hills ( 110430 ) <{chaz} {at} {}> on Saturday April 16, 2005 @01:55PM (#12256394) Homepage Journal
      This is why IPv6 is a much better network (layer 3) protocol for VoIP as it supports mobility [] natively, allowing TCP and UDP sessions to be maintained when roamning from one network to the next.

      In fact, the Internet Society point out that IPv6 is necessary for mobile and wireless internet. []
    • by LordoftheFrings ( 570171 ) <[ac.tsefgarf] [ta] [llun]> on Saturday April 16, 2005 @02:05PM (#12256452) Homepage
      VOIP does use TCP sockets for the initial data setup but UDP for actual voice streaming. This problem could be solved with some overlap of the wireless access point ranges and two network interfaces. One could get a DHCP lease on the upcoming network while the other still streams, and then once the first network is out of range instantly switch over to the other interface. Just a thought.
      • The trouble with this is you'd need two TCP stacks running concurrently, more if you plan on overlapping 3 or 4 networks. Network interfaces in my experience aren't too happy with being told they need to use multiple stacks for the same protocol.
    • sip can go over tcp or udp, it's most often used over udp though. The actual rtp audio stream goes exclusively over udp to minimize delay/complexity (it doesn't matter if some packets get dropped).
    • VoIP works on UDP, not TCP. WIFI association and the address disovery can be done while the call is still in progress (ever heard of having two addresses on the same interface?). Then there is almost no impact on the media path. See for example [].
    • "Last I checked, VOIP uses TCP sockets."

      The last time I checked, my VoIP infrastructure used UDP.

      I suspect that there are enough implementations out there now to make 'VoIP' a useless term for determining the underlying technology.

      • It always was, really. All it ever meant was, - well, I don't need to say it do I?

        VOIP is a general term whereas specific protocol identifiers exist, such as SIP and IAX which define exactly how the 'voice' travels.

        Also, VOIP is unfortunately sometimes used where the voice doesn't travel over IP, or be encapsulated in it at all. Sooner or later, when such things are so commonplace, they'll just be called 'voice calls'; there won't be any clear difference between the softphone on my PC and the cellphone

    • by Anonymous Coward
      You are correct about the TCP/IP issues, but the design for multi-AP networks
      is to have them all on the same subnet. Then the act of roaming between APs
      is scoped to L2.

      That leaves a couple different sources for delay/glitch:

      One is if the wireless client were to set the WiFi interface "down" upon
      dissassociating with the initial AP, then setting the interface back "up"
      once it associates with the next AP. This may have the affect of triggering
      the IP stack to release it's address information, and then resta
    • Last I checked, VOIP uses TCP sockets.

      It seems that most people have corrected you on this point already.

      When you move between WiFi base stations, you first must discover your new DHCP server, then get a new local IP address, then reconnect to the VOIP server.

      This think that this aspect of mobility is a good concern. GSM networks go to great lengths to co-ordinate handovers such that the delay is minimised as much as possible. I'm not sure that wifi has been designed with the same concerns, and

    • Not applicable. Base station handoff happens below even the network level (IP), not even just below the transport layer (TCP/UDP). Reducing handoff times may only make sense in a single network, where you can keep your IP address indefinitely. 802.11 networks are easy to transparently interconnect with ethernet equipment. As it is, you can walk around with a laptop at our site with an SSH connection working at all times, even when you are connected/typing continously. You *might* notice some smaller,
    • And this is why roaming on WiFi is best done at the L2 instead of L3+ level. Imagine a romaing scenario where an entire office is covered by L2 bridges, all routed to a switch, to a router/dhcp server. No need to change IPs since the bridges can handle your roam pretty easily with some help from IAPP.

      Furthermore, if you're using WPA2, you can use pre-authentication to use a cached authentication key if your APs support it.
  • When the V starts standign for Video rather than VoiceOverIP, then I'll start drooling.
  • I just hope (Score:4, Funny)

    by Pinefresh ( 866806 ) <`moc.liamg' `ta' `nospmis.mailliw'> on Saturday April 16, 2005 @01:30PM (#12256239)
    this research wasn't randomly generated
  • by Anonymous Coward
    The sync up is interesting.
    If you're on one of 11 channels and you spend 10ms every 100ms checking for a beacon on each of the other 10 channels it takes you one second to check 1/10 of the channel-beacon slots. So, after 10 seconds, you've got all slots nailed down to 10ms windows. Once you have all the slots you can update the signal strengths on the active channels once per second and discover any new beacon within 10 seconds.
    Yep, pretty cool....
    • It might be pretty cool in terms of Wifi.. but compared to 3G it's pretty lame.

      With WCDMA 3G, the network tells the UE (user equipment == phone, laptop, PDA, whatever) which are the surrounding cells it must look for. Not only that, but when the UE starts getting a good signal from another cell, the network will add a new radio link from that cell so that the UE can have links to more than one cell at a time. The handover is completely seamless. It's called soft handover.

      By the way, strictly speaking ro

  • Shouldn't let VoIP go roaming now should you? That'll teach you when it just leaves you for good...
  • by Anonymous Coward
    It's just one big LAN and easy pickings for 1337 kiddies with packet sniffers.

    And why would you want to join an untrusted network anyway ? So the admin of that network can keep nice juicy logs of everything you are doing ?


  • Got to say, UCSD is getting a very strong group in networking. Savage and Voelker and Snoeren [], plus the folks at SDSC [], plus CalIT2 [] (Larry Smarr's latest deal). Watch that space...

  • by wingsofchai ( 817999 ) on Saturday April 16, 2005 @01:50PM (#12256360)
    I'm sure the FCC will step in and protect us from this innovative and helpful new technology with plenty of arbitrary regulations that make little or no sense...
    • Re:Don't worry... (Score:4, Insightful)

      by Saeger ( 456549 ) <> on Saturday April 16, 2005 @04:10PM (#12257196) Homepage
      It's just greedy human nature. Machiavelli put it best 500 years ago:
      "Innovation makes enemies of all those who prospered under the old regime, and only lukewarm support is forthcoming from those who would prosper under the new."
      I've had that quote up on my wall for a number of years, since it helps to remind me how consistantly people -- and especially the cashcow status quo -- resist any disruptive change that shifts net benefit/power to a greater number of people.
  • NO thanks (Score:5, Funny)

    by Timesprout ( 579035 ) on Saturday April 16, 2005 @01:53PM (#12256385)
    I will stick with my current approach of having a team of engineers follow me around 24/7 laying cat5 cable for my skype connection.
  • Obvious really (Score:2, Interesting)

    by smoker2 ( 750216 )
    This idea is obvious in retrospect, as all really useful ideas are. Its basically a modification of the normal behaviour to take into account recent changes in WiFi usage. Instead of intensively hunting for a new AP when the signal has nearly died, the system checks more regularly, but much less intensively, so that it is ready to switch at a moments notice.
    I hope they get paid for this.
    Of course, this will only work for APs that you have legitimate access to, so if you come within reach of a restricted AP
  • Is about an hour around here, because there's hardly a WiFi hotspot to be found.

    But in a closed environment like a school, this technology might be useful for VoIP.

  • VoIPoWiFi (Score:2, Interesting)

    by t_allardyce ( 48447 )
    I don't know about the name. Phone companies have always worked on the basis that they had something we needed - a network of transmitters maintained 24/7 and connected to the general phone system. Local calls in cities don't need to touch the phone system, or even the internet, just switch on some cheap routers and let them create a city wide network at practically no cost - it would be like one big cordless phone, sure it would probably be patchy, but people would live with it for most calls - which in th
    • This isn't going to replace the phone company.

      Phone companies work on the assumption -- and it's a good one -- that you want service 24/7/365. Even wireless companies (and I'm no huge fan, trust me) put some thought into taking transmitters on and offline so as not to blackout huge service areas.

      I'm not sure I'd want to replace that with a patchwork of small transmitters, each running for their own reasons and on their own schedules, with my phone service basically as an afterthought.
      This is why I think

      • Yes a properly maintained phone network is more reliable and part of the price you pay, in theory, is for being able to depend on the network working everywhere all the time. In practice though it must be only the special premium customers that get this service because my network certainly isn't dependable. Wifi will definitely be an add-on and it will definitely be utilised allot, not only for voip but for games, and file sharing. I reckon some people will just not bother using real phone networks and they
  • by cpeterso ( 19082 ) on Saturday April 16, 2005 @02:32PM (#12256627) Homepage

    Cell operators like Verizon spend BILLIONS on proprietary "3G" networks. Their networks require lots of towers, yet have poor coverage and lots of "signal shadows". WiMax access points have ranges from 30-50 MILES and don't have the same signal shadow problems. WiMax phone networks will steamroll cell operators with cheap networks yet better coverage and service.
    • I agree, but who do you think will be deploying WiMax? Probably cell phone operators like Verizon.
    • Cell operators like Verizon spend BILLIONS on proprietary "3G" networks.
      Actually, they aren't proprietary. They are according to 3GPP Standards (

      And anyway, who do you think will be deploying these Wimax networks? My guess is large telecoms corporations.. the very same ones you claim will be destroyed by this.

    • There is a lot of hype around WiMax! The WiMax modulation (OFDM) may be efficient, but it is not dramatically better than the new modulation proposals used for 3rd generation cell phones. At the end of the day, coverage depends on noise, energy, and frequency bands -- all of which are pretty much equivalent for WiMax and 3G. So, if you want to provide high bandwidth to many users, you will need about as many towers with WiMax as with 3G.

      By the way, that is precisely why roaming between Wi-Fi access points

    • Not to piss on your wet dream, but:

      WiMax supports huge distances, sure. But in order to avoid needing a line of sight with the tower, you need to use low frequencies - that multiple-tens-of-GHz mumbo-jumbo is useless for penetrating things like trees, buildings, and cars.

      Thankfully, old analog TV spectrum (such as the lower 700MHz band []) is suitable and available for use in this way.

      But realize that there's only so much information bandwidth that can be squeezed out of a slice of spectrum, and that the f
  • wifi hotspots can cover remote areas like deserts, mountains, etc. given that WiFi has such a short range and it's basically impractical to build wifi networks in anywhere besides highly dense areas, it looks like there is a still a use for cell phones.

    however, given that certain cities are deploy WiFi hardward throughout the city giving everyone free wireless internet, VOIP WiFi is an excellent idea to start testing there. i personally make 90% of my calls within the city. sometimes i make calls from the
    • Actually (Score:5, Insightful)

      by bluGill ( 862 ) on Saturday April 16, 2005 @03:41PM (#12257014)

      Actually VOIP over WiFi is more likely to be useful in deserts and other remote areas because those who care can setup their own network. It might not be worthwhile for a cell phone company to put up a cell tower, but a farmer can put a WiFi station on his silo and get pretty good coverage of his ranch. Sure it won't have a large coverage areas, but it covers his needs.

      • Actually VOIP over WiFi is more likely to be useful in deserts and other remote areas because those who care can setup their own network. It might not be worthwhile for a cell phone company to put up a cell tower, but a farmer can put a WiFi station on his silo and get pretty good coverage of his ranch. Sure it won't have a large coverage areas, but it covers his needs.

        Yeah... Isn't that what cordless phones are all about?

        I'm all for solving problems in a more complicated matter than something that has e
        • Depends, can your cordless phone roam all over your ranch? The US has limits on range, which means they can't cover the ranch. WiFi roaming means you can put up several base stations (solar powered or something) around the ranch to get service where you want it.

          When your bring your cordless phone to the neighbors or town does it still have your phone number? WiFi, when in range, makes this easy. The phone always has your number, just like a cell phone. Perhaps you have noticed the access points are

  • Airespace (, recently acquired by Cisco, has had this functionality in it's wireless products for some time now. They claim roaming between their access points does not adversely interfere with VoIP call clarity. Obviously, this is designed to work within a single network that has twenty or thirty APs connected to the same network that cover an entire building, not your neighborhood which has a few APs connected to diverse ISPs which are scattered around the block. ;-)
  • Will we be able to connect to several networks at once?

    The really badass cisco servers have been able to do this for like 40 years.

    But it never filtered down, it would have been awsome to have 2 Modems and phone lines or Use Both my and My neighbors Cable while he used both his and mine.

    I guess they are making good use of the wifi channels but this could still be better :(
  • I just watched a presentation last week where some grad students were looking to replace Mobility IP with their protocol IPMN. It only has a delay of 100 -> 200 ms. when switching networks, and no data packets are dropped. To test it they made VOIP calls to texas and VA.
  • "VoIP roaming will be here soon!"

    Already here. It's called a cell phone.
  • NetMotion Wireless [] has products that have been doing this for years.

  • VoIPoWiFi ? Kinda catchy.
  • From what little the article said, it looks like just another 3rd tier professor claiming to solve a major problem, but not really understanding all the issues involved.

    As others have pointed out, this doesn't solve the issue of AP's being on different networks. But that's not an issue on many campus's. (Educational & Industrial)

    It also doesn't address the increased power needs that such an algorithm would create, nor the performance problems that might be created as well.

    On the whole, either
    • also, the second article notes something of importance, that the first seems to have (intentionally ??) missed, quote :

      Professor Stefan Savage, of the Jacobs School of Engineering, and graduate student Ishwar Ramani have a patent pending on the basic invention behind a technology known as SyncScan.

      Now, if this thing is patented, it will either never serve anyone, or it has already been bought by verizon & friends

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