Voice Over IP or IP Telephony?
<<<... In the circuit switched environment, phones are connected directly to the switch (PBX) that will take care of all signalling, call establishment and voice exchange traffic. Calls are placed via the PBX and it is permanently in the voice path throughout the length of the call. The softswitch takes part in call signalling: a station needs to ask it how to find the station it wants to communicate with, but once given the destination IP address, the two stations communicate directly, via IP, and the softswitch is no longer in the path. There is no permanent circuit between the two — the IP packets carrying voice payload are dynamically routed through the network just as any other IP traffic.
Comparative architectures The PBX and IP telephony functional architectures are more or less identical: it’s the way they are connected together that is significantly different. With a PBX, the call control, switching and user/trunk connections are consolidated, usually into one large chassis, often comprising of multiple racks of shelves. All communication between them is via a high-speed proprietary backplane. Redundancy is provided by means of multiple processors, line cards, PSUs, etc. The softswitch architecture distributes these functions throughout the network. Call control is done via the softswitch — instead of multiple CPUs, redundancy is achieved by two or more separate softswitches. Switching and user connectivity is done by the existing LAN infrastructure — this is where you have to be careful, as the main prerequisite of IP telephony is a suitable LAN,.... more >>>