Skype over 3g is unfortunately, irrelevant

April 2, 2009

If Skype was allowed to transmit voice calls over a cell data network, for several reasons, it would be unusable. There’s overhead in buffering and accommodating the effects of cellular data service in order to provide reasonable voice quality. Whereas IP packets and browsers don’t care if there is a slight delay, voice has stricter latency requirements and that’s one reason cell phone networks didn’t start out as data networks to begin with! Triangulation, echo cancellation, and multiplexing are systems that IP isn’t built for and even if it was, it would be like powering a computer with a solar panel that’s fed by a light bulb, plugged into the power grid.

If you’d like an example, get a 3g laptop card and open Skype on your laptop, then try and hold a phone call as a passenger traveling in a vehicle at 55mph; you’ll soon be disconnected or be unable to understand the call. Skype and the Internet it runs over has no idea you’re switching from Cell Tower 5 to Cell Tower 14 and to expect parts of the call in a different order from the different towers; even if it did, the towers aren’t aware of skype and the bandwidth overhead for the towers to communicate between Skype’s system and your cell phone would be excessive and negatively impact the network as a whole. ATT isn’t handicapping anybody, it’s just not that simple.

I can understand consumer advocacy but some things just don’t work. If it was really practical to run VoIPoCell then none of us would have Cell phones. Skype’s best effort would be to find a carrier to work with them at a higher level than just the iPhone; if Skype wants you to seamlessly transfer your call between the most efficient network, they’ll need much more than Apple’s cooperation.

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7 Responses to “Skype over 3g is unfortunately, irrelevant”

  1. steve Says:

    unless using a cs RT call

  2. steve Says:

    Circuit swithced real time call. Used for streaming so that the ATM packet all arrive in the right order.


  3. @steve

    I agree, but that still wouldn’t happen over the IP link. ATM over IP over would add even more overhead. Skype would stutter as soon as the cell phone leaves range of a tower.

    Also, my reference to “oCell” is referring to cellular, not necessarily ATM. Even if it is ATM, the IP network which Skype’s iPhone app would have access to isn’t privy to the ATM network it resides.

    • steve Says:

      I think you are being unfair to 3g. Expecting data on a changing RF environment is challenging, and then you expect it to be real time…..Is there an alternative, WiFi, WiMax…? I don’t think so. WiMax there are no uk networks with any coverage and wifi is not mobile….so give 3g a break and use it for what it’s intended. Not may people stream RT data (2-3%) and most use bundled voice minutes. For high speed data dounload it works just fine…

  4. Bob Says:

    Totally wrong. This is untrue.

    Cellular data can carry VOIP calls and in such a way that quality doesn’t affect the outcome significantly enough to disrupt call. In the end you pay for what you get. You aren’t going to get the sustained level of quality via the cellular voice or landline networks.

    I use the cellular data network all the time to make voIP calls.

    Are you basing this on some biased absolutism?

    Never say never – celluar data networks have come a long way.

    Latency, speed and capacity are no longer the issues they were in cutting edge networks.


    • all,

      Even the best cellular networks are multiplexed for voice, not data, and any congestion will result in significantly lowered priority for data. When you combine this, link-layer complexities (whether ATM or not), and that your VoIP Provider is “somewhere on the Internet” and not on the other side of a switched network, the statements in my post apply.

      Folks can go back and forth over what’s possible but the fact remains, and I stated very specifically, VoIP over Cellular results in significant overhead and would negatively impact the network (whether it’s just your connection or the tower). Thus, mass adoption is impractical because no matter how hard you try, it’s putting a square peg in a round hole.

      Overall, calling out ATT over this is an auspicious act to make something free which while profitable (mobile voice), isn’t free to provide. I’m not saying ATT isn’t a coward, however the suggestion that Voice over Cellular is practical is an implausible dispute for ATT’s network. The real issues are that ILECs are state-regulated monopolies, ATT’s cellular network is really crappy, and POTS is still the status quo for calls. Even if you fix the first and last issue, and even with the permission ATT has recently given app developers to allow VoIP over Cellular, their data network still sucks and so will your VoIP calls.

      As far as absolutism – no – and um, who said Never?

      As far as I’m concerned, practical includes reliable between two phones when traveling. Good luck with that with VoIP over Cellular.


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