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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
I think his problem is more on the radio link level than on the codec
level.
Using G.711 would be 80kbps worth of data and very timing sensitive
usually.
Most modern IP phones use G.729. Now if the other side recodes the voice in
something like G.728 then you have a serious quality issue due to double
compression.
On 09.02.2007, at 21:48, Chet Seligman wrote:
Hopefully your folks
use the G.711 codec. If so you can do a capture and save forward and reverse
streams as a .au file. This will play with Windows Media and you will hear
what they are hearing. Else the following still
applies:
- WS will make delay and jitter
graphics
- Filter the capture for RTP and
save the filtered version.
- Export to CSV and read with
Excel
- Determine the standard
deviation of the delta time between packets column
- Make a frequency table of the
delta t
- 4 x stdev = 99.97% of a normal
distribution. If 4x stdev is less than 20ms then you are loosing very few
packets and have micro-jitter. Else, the reverse.
- If you meet the standard
deviation test then the network is doing a good job and the ip-phones are
not. Often phone firmware or lousy wires are responsible. More than 50% of
ip-phone problems are speed/duplex mismatches at the network
jack.
Help. I do not know much
about anything.... I am trying to see if a wireless connection between 2
buildings is adequate. I have played wire Wireshark and see that if I
use my IP address as the interface, and a computer's IP address somewhere else
locally, I can see packets sent and received, with no dropped packets. I
plan to go to a friends site to do this exercise between 2 buildings.
This in itself is not a big deal, but I want to get an idea of the available
bandwidth between the buildings. Their problem is that their IP phones
have very poor quality. The people who installed their antennas say it
is the IP phone system. The antenna people report 8 megabit
thru-put. The IP phone vendors say it is the wireless connection.
I want to get to the bottom of this. Any suggestions? How can I
measure bandwidth? If there are no dropped packets between the buildings
should I assume the problem lies with the IP
phones??
Office: (770) 218-0008 xt
222
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