A Telephone VoIP Adapter (or TVA) is a device that allows traditional digital PBX (Private branch exchange) telephone handsets, e.g., Nortel Meridian, & BCM or Siemens Optiset/Optpoint, to be connected to a VoIP network, using, for example, SIP (Session initiation protocol). Comparison can be made with an ATA (Analog Telephone Adapter), which allows analog phones to be connected to VoIP networks. A TVA can also be called a Digital Telephone Adapter, as it allows digital phones to connect to a VoIP network.