A round on the data usage calculators on the Internet shows that most, if not all of them, do not include VoIP data usage in their consideration of what consumes data in a data plan. VoIP data usage is the amount of kilobytes and megabytes you use up in your data plan for voice communication. Many people do not use their mobile data plan for voice communication, and they lose a lot. Making voice calls on your mobile phone over your data plan allows you to save a lot of money on communications, see for that the reasons why people use VoIP. Besides, using your data minutes to make voice calls is a lot more worthy than streaming video or downloading MP3’s, for example. So, if VoIP is an item on your mobile data usage, here is how you estimate the bandwidth you need for voice calls for a month. You can then add that value to what your data usage calculator shows.
How Many Minutes?
Have an estimate of the amount of calling minutes you will need. Include both outgoing and incoming calls. This is no easy task. One way of getting through it is to take a sample month for noting down the calls you made and received and their durations. If you have a smartphone, you are saved from using pen and paper. Moreover, you can have apps that do the work for you in the background. Search the Android Market, Apple App Store, BlackBerry App World or Nokia Ovi Store for those apps.
You will want to differentiate between the types of calls you make. There are calls which need to go through GSM. You will choose VoIP for calls such as international calls, contacts that are using the same VoIP service as you (these calls are free) or calls that are free locally through a particular VoIP service (e.g. see Gmail calling).
Number of Bytes Consumed
To know exactly how many bytes a voice conversation consumes, you need to know which codec your VoIP service is using. A codec is a compression engine that transforms your (analog) voice into digital data, removing the silent moments (which make up to half of all conversations), and do other things to render the data load as light as possible. Read more on codecs there.
Here are approximate values for data consumption of the most common codecs used for VoIP:
G.711 - 87Kbps
G.729 - 32 Kbps
G.723.1 - 22 Kbps
G.723.1 - 21 Kbps
G.726 – 55 Kbps
G.726 – 47 Kbps
G.728 - 32 Kbps
These values will give you matter for calculation. For example, for one minute of talk with the G.729 codec, we will do the following calculation:
G.729 takes 32 kilobits per second,
which is 1920 kilobits (60 x 32) in one minute,
which in turn is 240 kilobytes (KB) per minute (1 byte is 8 bits)
Now that’s only for the data going out. Inbound data (which also counts) takes the same load, so we double the figure to 480 KB.
Finally, we can round the value to 0.5 MB per minute of conversation.
The G.729 codec is one of the best performing voice codecs and most good VoIP services use it.
You should note that there are many parameters, that are rather technical in nature, affecting the values above. Among them are the size (payload) of the voice packets, the intervals at which they are sent and the number of packets sent in one second (frequency). For most of us, what we want is an approximation for an estimate. So, we can easily do away with the accuracy. Also, we might not know which codec is being used. Personally, I take the average value of 50 kbps for any codec. This gives (after calculations and approximations) 0.75 MB per minute of conversation.
So, if you plan an hour of conversation, it will be roughly 45 MB.