Example image of eyePlorer eyePlorer map for 'Voice over Internet Protocol': Computer network Internet Internet Protocol Packet switching Speech Broadband Public switched telephone network Audio codec Digital audio Streaming media High fidelity Narrowband Speech coding Stereophonic sound Institute of Electrical and Electronics Engineers IPv4 National Science Foundation National Science Foundation Network VocalTec H.323 ITU-T Level 3 Communications Softswitch Session Initiation Protocol Asterisk (PBX) Digium Mark Spencer Open source software Private branch exchange OpenSER OpenSIPS SIP Express Router FreeSWITCH Proprietary protocol Skype Comparison of VoIP software Broadband Internet access Direct inward dialing Plain old telephone service IP Phone Ethernet Wi-Fi Computer Softphone Backhaul (telecommunications) IP Multimedia Subsystem Mobile phone Nokia Eseries Vodafone T-Mobile