Grazed from CloudCow. Author: Hoofer.
The cloud isn’t just a medium for hosted computer applications – it’s also a medium for complex telephony applications. In fact, many companies are now integrating their old-style PBX systems with front-end software that allows older VoIP PBX gear to leverage the Internet for outside unified communications activity, such as phone calls, video calls, multiparty conferences, IM, media streaming, etc. The software that makes all of this possible is referred to as SIP (Session Initiation Protocol) software.
A PBX with SIP is able to connect to the public telephone network (a.k.a. PSTN), via a SIP trunk provider who effectively acts as a gateway from the Internet to the PSTN. Hence, VoIP traffic, which is Internet-based, is seemlessly translated, or "trunked" onto the PSTN via the SIP-trunking provider, and vice-versa; yet, all other communication activity is handled by the native Internet…