37 replies to this topic

[shadragon]

Dead on Racer184...!

Warning: The theoretical maximum bandwidth supported by a cell phone modem varies depending on the communication standards your phone service supports. Below are example modem speed ratings for common cell phone data communication protocols. Compare these to dial-up Internet modems that handle a theoretical maximum bandwidth of 56 Kbps:

* GSM - 9.6 Kbps
* CDMA - 9.6 Kbps to 14.4 Kbps
* CDPD - 19.2 Kbps
* GPRS - 9.6 Kbps to 115 Kbps
* EDGE - 384 Kbps
* EV-DO - 1.5 Mbps - 2.4 Mbps

These are theoretical maximum rates so real world would be 60-70% of that at best. Only EV-DO has a prayer of crude VoIP and even that would be challenged. Most DSL / Cable companies advertise download speeds as they are usually higher, but the upload speed is all important for you top talk to someone else. Minimum of 1MB upload is needed for home VoIP and don't download large files while trying to use the phone...

[Fordan]

Unless I misread it, I don't think people were talking about doing VoIP over a mobile Internet connection, but putting the SD phone number on the cell phone and using the Internet connection for web/email/etc as appropriate.

You don't really need 1Mbps up to do voice, unless you're trying to give yourself lots of overhead for doing other stuff simultaneously. A standard voice channel in the telephony world is 64kbps (a DS0, which uses G.711). When you add in the overhead of sticking it in IP, you're looking at like 80-90kbps. G.711 is uncompressed audio, there are a number of codecs more common for use on the Internet which compress the audio and take significantly less bandwidth.

The real killer in cellular use of VoIP is latency and jitter. Latency is how long it takes your packets to get from your computer to your destination, and when it goes up, you start getting either echo issues or lots of verbal "collisions" where you and the other person start talking at the same time, since you don't hear each other talking until like half a second or a second after you both start. Jitter is how much latency changes, and can cause either excessive buffering (adding latency as part of that) or audio dropouts when the packet that should have been played at a given time hadn't arrived by that time.

3G networks are decent for latency & jitter, but when I used edge, gprs, and cdpd I often saw large latencies, on the order of half a second each way.

[drbill]

Telephone? Isn't that what we used to use to connect our modems to in a long by-gone era?

Seriously, I have found this discussion interesting since I am considering Skype so I can communicate with several friends (you guessed it, lovely lady divers) in other countries. Thanks to those who have contributed and to WW for asking the question in the first place.

Edited by drbill, 09 April 2009 - 08:36 AM.

[WreckWench]

Telephone? Isn't that what we used to use to connect our modems to in a long by-gone era?

Seriously, I have found this discussion interesting since I am considering Skype so I can communicate with several friends (you guessed it, lovely lay divers) in other countries. Thanks to those who have contributed and to WW for asking the question in the first place.

Ya know...I've ALWAYS had questions...now they are just more URGENT!

[WreckWench]

Clarification:

1. I think ideally if its possible I'd like to use/access the exisiting internet access where I'll be working. I MAY be able to tap into it and just add my add'l service needs such as VoIP etc on top of it. That is ideal but has some technological hurdles so may not work.

2. If that does not work then I'll set up a separate internet account which is where the discussion of dsl/cable or cellular/air card has come into the equation.

3. I want to keep the SD.com primary number 214-350-7003 regardless. So far it seems I can port it to VoIP (Vonage or packet8) or possibly keep it via the phone company and just forward all calls from it to a celfone or landline.

4. In the course of this entire change I will need a new celfone and celfone plan. This has opened up the discussion on using Blackberry/cellular modem access for travel purposes etc.

So hopefully this helps to clarify what we need and want. Primary objective is to keep our number and good service levels and the second focus is to save money or ensure that I get more value for what I pay for if at all possible.


Thank you all! I am so thankful for the outpouring of help, suggestions and information. It has blown me away!

[damselfish]

I use Skype all the time to talk to and see my daughter on an internet call for free. The sound and picture is ok. I love technology. (except that I have to brush my hair before I call because all her dorm friends talk to me too lol. )
Good luck. ~ D

[Divegirl412]

I use skype routinely to call my folks in Africa and the UK, and it has been very reliable. But that is not business use, so I would say listen to those who have business experience. My main comment pertains to Fordan's comments re ATT and T-mobile which use GSM vs CDMA/ TDMA (Verizon/ Sprint). I have found it invaluable and eons cheaper to use my ATT GSM palm treo phone and get a SIM card in whichever country I am traveling. It gives me a local number while I am in the country and is much cheaper than using the ATT international roaming service. And as I found out when in Mexico, not using my phone at all, but just having it on, so I could tell when someone called... you are charged even if you don't answer any calls and they go to voicemail. They call it something ridiculous like a voicemail notification fee. It is in the very fine print. So turn your phones off when traveling if you want to avoid that. As long as I have an internet connection, I can use Skype to call back to my home and cell phone voicemails and collect messages AND return them that way. Again avoiding expensive international roaming fees.

Just a few thoughts....

[Wakemaker]

For my office, the faxes work fine over VoIP, but my credit card machines did NOT like it at all! I ran into nothing but dead-ends with my Merchant Services provider and their equipment options, so I ended up installing a stand-alone traditional phone line just for my credit card machine!!!

Impressive. Why do divers always brag about their equipment? Okay, fine. I'll save my money and get a Iridium 9555 Satellite Phone! Did someone say satellite phone? So, there. (I want to watch You & Kamala consider envy)