ADSL is transmitted on the same copper twin wires as analogue or ISDN telephony. To separate the frequency ranges for telephony and ADSL a crossover, so-called splitters, are used. With the introduction of Voice over IP telephony more and more DSL connections are installed that do not require a splitter. These are often referred to as Annex-J connectors and they transfer calls directly into the IP data stream. The use of cloud PBX requires no separate frequency range for analogue or ISDN telephony. The available upload and download bandwidth is important. They limit, among other factors, the maximum number of parallel calls.