I work for an Avaya and Cisco business
partner certifying networks for IP-Tel.
These companies recommend G.711 for LAN
and G.729 for WAN.
The testing that I do shows that in a “perfect
network” i.e. virtually no losses, G.711 renders a MOS (Mean Opinion
Score) of 4.4 and G.729 renders 4.1. I don’t think the human ear can
really tell the difference.
When Voicemail is involved, Avaya best
practices says to use G.711 because the repeated application of the algebraic
compression algorithm causes loss of voice quality. Avaya says to use G.711 for
voicemail, even over a WAN. I don’t have Cisco’s position on that.
From:
wireshark-users-bounces@xxxxxxxxxxxxx
[mailto:wireshark-users-bounces@xxxxxxxxxxxxx] On Behalf Of Andreas Fink
Sent: Saturday, February 10, 2007
12:17 PM
To: frnkblk@xxxxxxxxx; Community support list for Wireshark
Subject: [Norton AntiSpam] Re:
[Wireshark-users] Help. I do not know much about anything.... Iamtrying to see
if a wireless connection between 2
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...
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