A session border controller is like a fiewall for VoIP. Since it works similar to firewall, it protects your internal/enterprise network from outside attacks and let’s you capture stats and usage details.
SBC enable you to do policy-based access control, call accounting / recording, QoS, transcoding, topology concealment etc.
Session is basically a “call” in VoIP context.
SBC enables and controlls the VoIP calls. The name SBC owes to early focus on the borders between two service provider networks. SBC often works like SIP Back-To-Back User Agent.
IP PBX was born as a result of vendor’s attempt to re-invent traditional TDM PBX equipments for IP communications. IP PBX is endowed with legacy of hardware based telephony solutions and as more and more software based solutions (SBCs) ae gaining ground;
IP PBX is declining in use.