The SPA3000 is a single port FXO, single port FXS device, and the predecessor to the SPA3102. The major difference between this unit and the SPA3102 is that the SPA3000 has no in-built router. As such, it is compulsory that you have a spare RJ-45 port on your network in order to use this device, it cannot be connected between a network port and a PC (unlike the SPA3102).