For companies with multiple locations connecting their phone systems (PBX) is a game changer. Internal phone calls between the connected phone systems become possible, when the bandwidth provided by the internet is sufficient. Required is a bandwidth of at least 100KBit per voice channel. Especially SDSL internet connections are advantageous, because they offer the same bandwidth for uploads and downloads which is required for VoIP.
Another advantage of connecting PBXs via the internet is that you don’t need additional phone lines. Additionally, you can transfer calls between locations without the caller recognizing the difference.
Connected IP phone systems can also share the same ISDN lines. If for example one location has a PRI (also called E1 or T1; ISDN with 30 channels), all other locations can use these ISDN lines by connecting to this PBX via the internet. This is usually much cheaper than providing ISDN at all locations, because only one set of ISDN hardware and only contract with a phone company is required.
IP PBXs at multiple locations can be connected via VPN (Virtual Private Network). Voice is encrypted before being transmitted. IAX is a widely used protocol to connect PBXs via IP networks.
In the first scenario there are three interconnected PBXs. Each PBX has their own internal extensions and every extension is capable of calling extensions of the interconnected PBX directly, without dialing a prefix.
Here you can see an example where two PBXs are configured in two different networks. Every PBX has their own extensions. By dialing a prefix, one can reach the connected PBX and even dial out through a provider, physically connected to the interconnected PBX. This is also called remote breakout.
This case shows three connected networks. Each with the same, internal extensions. Using the internal extensions of the own PBX, one can call extensions directly. Using prefixes makes it possible to call extensions in the other networks.
AskoziaPBX telephone systems fully support the interconnection of multiple PBXs in different locations.