PHP developer Rob Holmes recently asked us on Twitter:
— Rob Holmes (@robholmes) February 19, 2015
When using VoIP calling functionality with Sinch, it’s app to app calling where you can have HD quality calling and app to phone calling where you have to fallback to codecs that are supported in the phone network. The VoIP bandwidth numbers below are per channel, and typically in a phone conversation you will have two channels; one you listen on and one you transmit on.
There are many articles online about VoIP bandwidth and data consumption, but this one is specifically related to Sinch.
ISAC is an adaptable codec that changes its bit rate based on the available VoIP bandwidth. This ensures the best quality and user experience. The bit rates are varying between 10–52kbps. Adding a 10% additional margin that we have seen been used in real-life, the final data usage will be:
Minimum (without a good network speed): 10+0.1=10.1kbps = 1.27KB/sec
Maximum data need (with a good network speed): 52+5.2=57.2kbps = 7.15KB/sec
Opus is a relatively new codec that is free and open, and can be both adaptive and variable in its data transmission. Here at Sinch, we are using variable configuration right now but we are releasing an adaptive SDK during Q2 for data calling. Compared to the other codecs, it gets a little bit trickier to assume the exact data usage because it depends on how much you talk.
The standard specifies OPUS as sending audio in 6 kb/s to 510 kb/s. And in real work traffic we add 10% that gives us a data usage between 6.6–561kps per second
(0.8KB/S – 70.12 KB/S)
UPDATE 2015-08-14: @chintan39 one of our partners correctly spotted that the header data is missing in this calculation. So with headers of 2KB per second, the correct usage is
Read more about opus here.
Understanding app to phone calling is a bit easier. The codec that is used between the client and your SIP server is G.711. It has a bitrate of 64kbps, so the expected KB/s size (adding the 10%) is (64+6.4)/8 = 8.8KB/sec.
As always, if you have any questions, feel free to contact us here.
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