Protocol stacks are the underlining signaling technology that allows communication between different IP telephony applications. In simple language, signaling protocol stacks establish and manage a call between two or more entities. H.323 protocol stacks are stacks that adhere to the ITU-T H.323 suite of international signaling standards and thus insure complete interoperability with other vendor's IP telephony products.

Agora Labs has two distinct H.323 protocol stacks, the EX3230S and the PX3230S protocol stacks. The PX3230S stack was specifically designed for host-based applications on platforms like Microsoft Windows or Linux. The EX3230S was specifically designed for embedded environments but is also used extensively in host-based applications due to its simple architecture. Each of these H.323 protocol stacks were originally developed by Lucent elemedia™.