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Andreas:
Thanks for your detailed response.
I don't question the value of G.729, which has the largest
installed base with the best trade-off in terms of voice quality and
bandwidth. But your previous statement said that most modern IP phones use
G.729. They may support it, but I don't think it's
used.
To the best of my knowledge, PacketCable installations (of
which there are over 2M in the U.S.) generally use G.711, as do most enterprise
installations. SpectraLink (being purchased by Polycom) does use APIC in
their SRP.
G.729 will never have a higher MOS than G.711 in
good links (http://www.ciscopress.com/articles/article.asp?p=606583&seqNum=4&rl=1),
though if the link has a limited amount of bandwidth and/or is easily congested,
G.729 will generally perform better because of its lower bandwidth needs.
G.711 would suffer excessive latency and/or packet loss, reducing
MOS.
There are some wireless Skype phones that don't require a
host PC, namely the:
- Edge-Core WM4201
- Netgear SPH101
- Belkin F1PP000GN-SK
- Accton SkyFone VM1185-T
- SMC Networks SMCWSKP100
- Logitec LAN-WSPH01WH
- Airwise Technology SkyAir DT 190204
- Linksys WIP320
- Buffalo WSKP-G
- RTX DUALphone 3088
Not all of these have gone to market, but they were
announced in for or another.
Kind regards,
Frank Bulk
On 10.02.2007, at 17:44, Frank Bulk wrote:
Andreas:
On what basis do you say that most modern IP phones use
G.729? Is there a certain class of IP phones (PacketCable, Vonage, 8x8,
enterprise (Cisco, Avaya, etc), VoFi) that you had in
mind?
Frank
G.729 is one of the best codecs when it comes to efficiency and providing
excellent quality. For software implementations its a bit problematic because of
patent issues. The hardware versions don't have this because you simply buy
chips which do G.729 and youre done because the chips vendor has a license for
G.729 and they usually do much bigger volumes than a small software company
developing a soft phone.
If you compare the different codecs out there:
G.726 ADPCM is also good but doesnt compress so much so uses quite a bit of
bandwith. Perfect choice for "a little bit of compression but not too
much".
G.711 dont compress and waste a lot of bandwith (80kbps)
GSM codec is popular on soft phones and open source because its free to use
(even there are patents about it).
G.728 is not so good in quality and not so efficient than G.729 but less
CPU intensive.
G.723 is the one which compresses most (as low as 5.3kbps without IP
headers) but its clearly audible and quality is not considered very good. But
useful for applications where minimizing the bandwidth is more
important than quality.
From the experience with IP phones,
especially WiFi IP phones, we learned that those people who care about quality
and provide phones which actually work (there's unfortunately a lot of crap out
there too), they usually implement G.726, G.729, GSM and of course G.711 a-law
and G.711 µ-law for the guys with tons of bandwidth available.
The Cisco IP phones (Desk phones) as far as I know do G.711 and G.726. UTS
Starcom does G.711, G726 and G.729. The Hitachi WiFi Phones WIP3000 and
WIP5000A do G.711, G.729 and GSM. Asterisk, the open source PABX does
G.711, G.729 (not for free), GSM and I think also G.726 and a few other
codecs. The Grandstream phone adapters also do G.729
I wont mention any "fake" wireless IP phones like the wireless Skype
phones. Those are nothing else than a microphone and a loudspeaker connected to
the computer and all the processing is done on the computer. So you get whatever
codec the soft phone has and the phone is just dumb. I prefer real WiFi phones
like the Hitachi Cable WIP 5000A which you can use on any accesspoint and just
work. And I prefer G.729 because its excellent quality.
Just my personal opinion...
Andreas
Fink
Global Networks Schweiz
AG
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