Is G729 codec 32kbps or 8 kbps?

Question

I'm building a VOIP app for iphone and android. I'm currently using the GSM codec ( I chose it arbitrarily) on both versions of my app and on my asterisk server.

Now that I'm fine tuning my app, I'd like to try different audio codecs. I'm considering G729. I did a research and wasn't sure why some sites say the G729 codec uses about 32kbps as in this site here

http://voip.about.com/od/voipbandwidth/f/How-Much-Of-My-Mobile-Data-Plan-Does-Voip-Consume.htm

while others say it is 8kpbs like this site here

http://www.javvin.com/protocolG7xx.html

I did some tests and it seems that 1 minute of conversation with the G729 codec uses up 0.5 mb of data. So it seems like the first link is correct. But i've seen other sites list similar stats of 8kbps...why the discrepancy?

According to Wikipedia (en.wikipedia.org/wiki/G.729), G.729 is an 8 kilobit/sec (kbps) codec. 60 sec * 8,000 bits/sec = 480,000 bits, which is like 0.5 megabits (Mb). — mtrw
Just clarification, on the last point...1 minute of conversation used up 0.5 megabytes of data. Based on your calculatoin i see it takes 480,000 bits, which is equivalent to 60,000 bytes (because there are 8 bits to a byte). So one minute conversation should be 60kbytes, or 0.06 megabytes, which is not the case in my actual tests. — John
Can you recheck your measurement? Even at 32 kbps, 60 sec * 32,000 bits/sec = 1,920,000 bits = 240 kB. So not sure how you're seeing over double that. — mtrw
Your last comment is correct, it should be DOUBLE, because 240kB for download plus 240kB for the upload (because it's a two way call). So I see you used 32kbps...but why do other sites like 8kbps when it's actually 32kbps? — John
All the docs say 8 kbps, maybe you're not actually using the codec that you think you are? How many channels are you encoding? Two directions, and also two channels per direction? — mtrw

Mick Mick · Accepted Answer · 2013-09-03T22:44:23

If you look towards the bottom of the first link you show, it hints at the reason - the 8kbps is how much is used to encode the speech itself. You then need to send that encoded speech out over the network to the other end of the VoIP call, and hence need to pack it into an IP 'packet', typically using the RTP protocol.

The actual number of bits transmitted will depend on the number of samples taken per second, the number of samples packed into each IP packet, the protocol headers etc. Much of this is influenced by the codec chosen - the following link gives a good overview (see the table in the section titled 'VOIP - Per Call Bandwidth'):

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094ae2.shtml

Is G729 codec 32kbps or 8 kbps?

1 Answers