We made some preliminary tests using vodafone's USB dongle and VoIP was
perfect.
USB dongle was connected to a router which accepts USB card which was to
a Thompson Speedtouch 716 acting as an ATA.
The far end voip device was a grandstream GXP2000 connected to a BT DSL
line, codec was G729 - VoIP was peer to peer meaning we did not bring
RTP stream onto our network.
As I mention these were very preliminary, we only tested VoIP to VoIP
calls (and to be honest I was very surprised at quality) we will be
doing some more rigorous testing to see if we can consistent results.
VoIP phones have built in echo cancellation (as do mobile phones) and
calls to PSTN are likely to be very echo sensitive unless VoIP/PSTN
gateways use aggressive hardware echo cancellation (which costs). You
tend to get echo problems (to analogue phones) when ping times go over
50ms, in the TDM world national calls don't need echo cancellation as
the round trip time would be sub 20ms, international destinations
normally have echo cancellation as a longer round trip time is expected.
It's different in the IP world where switches introduce delay and local
call latency is dependent your hops to the ITSP you are using. My point
here is that if the VoIP network is prepared for high latency then echo
should not really be an issue, and the only symptom of the large round
trip time is some delay in speech.
Packet loss and jitter are another thing, for the moment you will
probably find hot-spots which can support VoIP well, but coverage will
be limited. It's early days for VoIP over mobile broadband and I would
expect we will see big improvements as demand heightens and networks
improve with HSUPA, HSOPA etc..
Anyway, I think it's a milestone when you can currently make a VoIP call
over vodafone and quality is crystal clear with a package that only
costs 25/month -even if it's limited in coverage. I think everyone
(except the mobile operators) would welcome days when you could have
free calls on your mobile with no roaming costs (yes, you can pick up a
SIM in each country and keep the phone number) and keep your home phone
number.
/KB
Michael Watterson wrote:
> Alan Ryan wrote:
>> 2009/3/5 Alan Ryan <alan at codecrunchers.ie>
>>>>>>> Hi Joerg,
>>>>>>>>> The e270 is up and running, pretty reliable. Used a softphone
>>> today, but
>>> the quality was pretty bad alright. I could hear them fine, but the
>>> other
>>> side said that there was a delay and terrible echo. Is it the e270
>>> or the
>>> o2 connection that you think the problem might lie with?
>>>>>> Alan
>>>> The problem is Mobile Internet, not specifically O2 or the Modem.
>> It has 100ms to 2000ms latency, typically 150ms
> High Jitter
> speed varies from 0.050Mbps to 5Mbps +
> Packet loss can be high or OK.
>> It's inherently unsuitable for VOIP. If more than about 10 people are
> using your sector it's likely to be poor.
> It's possible to get more consistent VOIP on 40Kbps dialup!
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