On Sat, 24 Dec 2005 02:09:24 -0000, "Martin²" <never@give.one> wrote:
>deadmail:
>>In any case VOIP doesn't use the GSM CODECs within the phone, does it?
>>What have I misunderstood here?
>
>Yes, you have. VoIP calls are transmitted over the internet using various
>codecs (compression algorithms).
>You can select which one to use, provided it is also available at the
>receiving end.
>One of them is GSM, same as used for mobile phones, this is particularly
>'lossy', and uses least bandwidth.
>However, as the packets on the internet are nearly always subject to some
>delay, the sound you hear isn't quite continuous, the loss of some of the
>sound gets more noticeable and your brain can't quite guess what is being
>said. Often the conversation becomes impossible.
>Other, less 'lossy' codecs, are much better allowing normal conversation,
>but of course use more bandwidth.
>
>Mobile phone networks are designed to carry GSM voice traffic with minimum
>delay, allowing your brain to subconsciously make up for the loss. But you
>would be aware it's not as good as std. telephone line.
>Regards,
>Martin
Sorry Martin, but I have to agree with the other poster in that is utter
cobblers.
VOIP does use various compression algorithms like G.711 and G.729 but it
most definitely does not use
GSM (Global System for Mobile communications).
Some of these algorithms use very high compression which produce calls of
GSM-like quality, but usually this is only where bandwidth is limited.
True VOIP is currently only available on
3G devices running some sort of
client (like Skype) which can provide an always on broadband-like
connection.
As to your assertion that mobile networks are also designed with deliberate
"gaps" that your brain has to fill in...well I don't think I've ever heard
such nonsense. In telephony terms, the human audio range is considered to
be from about 3-3000Hz. When VOIP compression is used, this range is
considerably shortened to something like 250-2000Hz, meaning that any loss
in quality is not from the crucial mid-ranges, but the top an bottom, the
result is the "flat" tones that you get on VOIP and funnily enough ..
GSM
VOIP is also particularly sensitive to packet loss and jitter, as well as
round-trip delay and if any of these criteria are exceeded, the VOIP link
normally drops.
Whilst I *know* what you have posted is erroneous, you have stated that you
have a source for you (mis)information.
Please be so kind to share those sources with the group.
--
Regards
John [Essex, UK]
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