MGCP and H.248/MEGACO were designed to provide an architecture where call control and services could be centrally added to a VoIP network. In that sense, an architecture using these protocols closely resembles the existing PSTN architecture and services.

MGCP and H.248/MEGACO define most aspects of signaling using a model called packages. These packages define commonly used functionality, such as PSTN signaling, line-side device connectivity, and features such as transfer and hold. In addition, session definition protocol (SDP) is used to convey capabilities exchange.

Figure 2. MGCP/H.248/MEGACO Networks
(Click on image for full-size version.)

In a centralized architecture, MGCP and H.248/MEGACO allow companies to build large-scale networks that are scalable, resilient, and redundant. It provides mechanisms for interconnecting with other VoIP networks and for adding intelligence and features to the call agent.