The Internet was originally built as an overlay upon the telephone network, while today (through the advent of VoIP), the telephone network is increasingly turning into an overlay network built on top of the Internet.
因特网自身最初也是作为一个电话网络之上的覆盖网络构建，而当今（藉由VoIP的引入），电话网络正越来越变成一个建立在因特网之上的覆盖网络。