Cisco / Linksys series – PAP2T, SPA2102, PAP112, SPA122 are propably most widely used around the world for VoIP communication. Most common issues related to VoIP Gateways are unreachable phone in incoming calls, DTMF not passing through or not working properly with alarm/elevator systems. Problem 1: VoIP gateway not reachable on incoming call. Mostly this