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Google Voice latency to POTS

Google Voice testing latency to POTS (plain old telephone system), GSM, CDMA and a VoIP provider, because I couldn't find much information other than conjecture about actual voice latency on these systems.

I used Audacity to do the tests, it's really easy to do if you have a mic and speakers. (I'd be interested to hear what others measure. Be sure to calibrate audacity so you don't include the latency of your sound card in the measurements.)

These tests measure the time it takes, for sound to enter one device and come out the other device. In other words, the one-way time it takes for your speech to reach your calling party (and vice versa). They say that just 40 or 50ms of latency is the point at which voice delay becomes noticeable.

Here are the results!

POTS to CDMA: 149ms
POTS to GSM: 162ms
CDMA to GSM: 291ms
POTS to Google Voice to CDMA: 279ms
POTS to VOIP: 326ms
CDMA to VOIP: 450ms
VOIP to GV to CDMA: 750ms

From these, I estimate POTS has a latency around just 10ms...extremely good, and as to be expected. Once you get on a cell-to-cell call, you have almost 300ms latency. At this point conversation starts to becomes more half-duplex than full-duplex; that is, talking over one another and waiting to speak, similar to a walkie-talkie.

Google Voice seems to be like a cell phone in terms of latency, so calling Landline -> GV -> Cell is similar to a cell-to-cell call. Cell to GV to cell should be something like 430ms, quite a bit of delay.

CDMA may be slightly better than GSM, not really significantly different.

VoIP is twice as worse than a cell phone, you'd be far better off using a cell phone with a home phone adapter like Xlink. I really tried hard to get the lowest lag on VoIP too, by using 0.010 ms packet size and lowest possible jitter buffer. Ping was 50ms to SIP/RTP servers.

Google Voice does 3 things, SMS, Voicemail, and phone calls. The other features are superb. But in my opinion, the added latency for phone calls is not worth it. Calls are delayed enough with cell phones; it doesn't make sense to add more frustration when making phone calls even for the convenience of a single number.

Google Support Discussion;

Basics: Call quality - what's the truth

Why is there a huge delay on my phone calls



2 comments:

  1. Anonymous4/27/2010

    Thanks for these tests!

    These seem to confirm what I've notices qualitatively, which is that Google voice adds significant latency and in certain cases renders it nearly unusable.

    I've tried forwarding my google voice to:
    a) my cell phone
    b) my DID that then forwards to my SIPGATE Voip line (also tried with my IPKall DID)
    c) my Gizmo VOIP line

    I've found both (a) and (c) are usable, but there is definitely some latency. However, (b) adds so much latency that it is nearly impossible to have a full duplex conversation. The latency is very bad and noticed by all parties. In fact I heard comments from people asking why I was pausing so much.

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  2. Anonymous4/27/2010

    I'm not disagreeing with you, GV may very well add a delay, as noted by your own experiences.

    But you do understand that everyone is going to have different experience based on MANY different factors. The data connection someone has on their PC, the data connection on the cell, the speed of the phone or PC. If someone is using it in a house where the connection is split with 6 people.. if someone's using dial up in the boonies somewhere in the California desert, it's going to have an effect.

    There are so many factors, that a blanket "GV adds 130ms to all calls" statement is just too broad to prove. I, for one, have no issues with any delays, so I'm just saying everyone's experience will be different.

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