Sorry for having naive questions and using improper terminologies. I heard that

  • 2G networks are said to transmit voice only, while 3G both voice and data, and 4G data only.

  • When the 3G coverage isn't good enough to make calls, a mobile carrier will use 2G instead.

My questions are:

  1. In 3G networks, what technology(s) is (are) used to transmit voice?

    • is voice transmitted over data, like VoIP? If yes, don't both 3G and 4G transmit data only?
    • or is voice transmitted in a similar way in 3G networks as in 2G networks?
    • or can voice be transmitted in either of the above two ways?
  2. If a 3G network contains a data part and a voice part, do data and voice always have the same coverage?

  3. What does "when 3G coverage isn't good, change to use 2G networks for voice service" mean?

    • when data coverage in a 3G network isn't good, change from using the data part of the 3G network to using the voice part of the 3G network to transmit voice,

    • or when the 3G network coverage isn't good (for both data and voice), change to use 2G for voice service?



In 3G voice is transmitted digitally (i.e. as is data), however, the voice data is treated differently than other data. In 4G there is only data, but a client application can utilize that data for a telephone call or other voice application using any protocol supported by both that client and some server with connectivity to the network. Common VoIP standards include SIP and SCCP (skinny), but I'm sure there are more.

"when 3G coverage isn't good, change to use 2G networks for voice service" just means that you may well reach a 2G base station even when you can't reach a 3G one. That could be for any number of reasons - range (if they aren't collocated), frequency band that each uses, and number of users using the service at that instant, for examples.


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