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my attempt at VoIPoCDMA2000

 
 
Kyler Laird
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      11-04-2004
I would love to have some (wide area) mobile VoIP phones.
I've been searching for a solution for awhile and finally
decided to just see how bad it would be to use a current
mobile phone network to achieve this functionality.

I've been a SprintPCS user for years so after getting
reports of sub-400ms ping times, I decided to give their
data card a try. The nearest stores (in Indy) only had
the Novatel Wireless Merlin C201 so that's what I got.

As has been reported, after initializing this card (under
MS Windows) it is readily usable by Linux. Once up (as a
PPP device), it yielded ping times mostly in the 300 to
400ms range. It seemed fairly robust. I didn't get the
many-second-long silences that I expect from GPRS.
--- yahoo.com ping statistics ---
50 packets transmitted, 50 received, 0% packet loss, time 49431ms
rtt min/avg/max/mdev = 307.951/453.274/1437.838/214.054 ms, pipe 2

I discovered that port 80 is run through a transparent
HTTP proxy. (Some of my photos were recompressed.) Most
communications seemed unfettered though. Unfortunately,
when I tried using a SIP phone over this connection it
failed to even register. I suspect timing was the issue
but I don't have an eye for spotting SIP problems. (The
packets seemed to be passing o.k.)

Recently I found iaxComm, an IAX softphone. I decided to
give it a whirl and it registered without any problems.
Making calls seemed o.k. and the audio was decent. When
I tried to send audio, however, it fell apart. It
*really* chokes on ulaw (of course) but even GSM is
unusable.
50 packets transmitted, 50 received, 0% packet loss, time 49007ms
rtt min/avg/max/mdev = 366.003/1182.807/2815.567/536.911 ms, pipe 3

I like having this card but the latency is too high for
me to justify keeping it at $80/month. I'm hoping for
UMTS to arrive someday soon...

--kyler
 
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carcarx
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      11-04-2004
Thanks for letting us know about your experiment.

I tethered my Sanyo 6400 to my XP Pro laptop and tested Skype.

It sounded fine, but had occasional packet delay.
(The audio fidelity of Skype is awesome!)

 
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Central
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      11-04-2004
On Thu, 04 Nov 2004 02:08:05 +0000, Kyler Laird wrote:
<snip>
>
> Recently I found iaxComm, an IAX softphone. I decided to
> give it a whirl and it registered without any problems.
> Making calls seemed o.k. and the audio was decent. When
> I tried to send audio, however, it fell apart. It
> *really* chokes on ulaw (of course) but even GSM is
> unusable.
> 50 packets transmitted, 50 received, 0% packet loss, time 49007ms
> rtt min/avg/max/mdev = 366.003/1182.807/2815.567/536.911 ms, pipe 3
>
> I like having this card but the latency is too high for
> me to justify keeping it at $80/month. I'm hoping for
> UMTS to arrive someday soon...
>
> --kyler


The main problem with sprintpcs data network is that it is an a-sync
burst-able medium. ULAW, if I recall is 64kbit/s audio or around 8KB/s
both ways while GSM is 13kbit/s or around 1.6KB/s both ways. Main issue
you were running into was mostly likely packet loss due to the connection
being utilized both up/downstream at those rates. You might want to look
into some of the commercial codecs like G.729 which would be around
9kbit/s or around 1.1KB/s both ways. For the most part gsm should have
enough bandwidth it is just that since the sprintpcs data network is
burst-able and focuses on high downstream rates you sometimes run into an
issue where you have good incoming line but outgoing falls apart. Of
course this also varies by location, how many people are active on the
pipe providing the tower, etc. As far as latency is concerned I doubt you
will find anything in the 200-300ms range cheap. After all in most cases
the signal still has to travel at least half a mile to the tower and then
spider through sprintpc's internal network first. Most of the time I avg
600ms with spikes up to 1300ms when using the connection. As always your
mileage will vary.
 
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Kyler Laird
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      11-04-2004
"carcarx" <(E-Mail Removed)> writes:

>(The audio fidelity of Skype is awesome!)


Yeah, I've heard iLBC is worth using but I haven't gotten it
configured in Asterisk and iaxComm yet. Think that'll make a
significant difference?

--kyler
 
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yum
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      11-07-2004
I believe that SprintPCS PTT(Push To Talk) feature is VoIP on CDMA2000. It
uses the same concept of VoIP in the wireless mobile phone. It should work.
UMTS will not be better that CDMA2000 EVDO.


"Kyler Laird" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>I would love to have some (wide area) mobile VoIP phones.
> I've been searching for a solution for awhile and finally
> decided to just see how bad it would be to use a current
> mobile phone network to achieve this functionality.
>
> I've been a SprintPCS user for years so after getting
> reports of sub-400ms ping times, I decided to give their
> data card a try. The nearest stores (in Indy) only had
> the Novatel Wireless Merlin C201 so that's what I got.
>
> As has been reported, after initializing this card (under
> MS Windows) it is readily usable by Linux. Once up (as a
> PPP device), it yielded ping times mostly in the 300 to
> 400ms range. It seemed fairly robust. I didn't get the
> many-second-long silences that I expect from GPRS.
> --- yahoo.com ping statistics ---
> 50 packets transmitted, 50 received, 0% packet loss, time 49431ms
> rtt min/avg/max/mdev = 307.951/453.274/1437.838/214.054 ms, pipe 2
>
> I discovered that port 80 is run through a transparent
> HTTP proxy. (Some of my photos were recompressed.) Most
> communications seemed unfettered though. Unfortunately,
> when I tried using a SIP phone over this connection it
> failed to even register. I suspect timing was the issue
> but I don't have an eye for spotting SIP problems. (The
> packets seemed to be passing o.k.)
>
> Recently I found iaxComm, an IAX softphone. I decided to
> give it a whirl and it registered without any problems.
> Making calls seemed o.k. and the audio was decent. When
> I tried to send audio, however, it fell apart. It
> *really* chokes on ulaw (of course) but even GSM is
> unusable.
> 50 packets transmitted, 50 received, 0% packet loss, time 49007ms
> rtt min/avg/max/mdev = 366.003/1182.807/2815.567/536.911 ms, pipe 3
>
> I like having this card but the latency is too high for
> me to justify keeping it at $80/month. I'm hoping for
> UMTS to arrive someday soon...
>
> --kyler
>



 
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Kyler Laird
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Posts: n/a
 
      11-08-2004
"yum" <(E-Mail Removed)> writes:

>I believe that SprintPCS PTT(Push To Talk) feature is VoIP on CDMA2000. It
>uses the same concept of VoIP in the wireless mobile phone. It should work.


Latency is hardly an issue for PTT.

--kyler
 
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Central
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Posts: n/a
 
      11-09-2004
On Mon, 08 Nov 2004 03:08:05 +0000, Kyler Laird wrote:

> "yum" <(E-Mail Removed)> writes:
>
>>I believe that SprintPCS PTT(Push To Talk) feature is VoIP on CDMA2000. It
>>uses the same concept of VoIP in the wireless mobile phone. It should work.

>
> Latency is hardly an issue for PTT.
>
> --kyler


Latency isn't any issue because there is less overhead with PTT. Not to
mention sprintpcs has their network setup to let PTT through with more
priority then say your vision web access. I would imagine if PTT had to go
the same distance/cost as a voip connection from a tethered laptop you
would have just as much of a latency issue.
 
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