Strengths of H.323, SIP, and MGCP

H.323

H.323, which was the only viable option in VoIP signaling and call control solutions for a long period of time, is mature and attracts supporters. Consequently, H.323 products are widely available and deployed extensively.

When properly designed, H.323 is both scalable (accommodates the implementation of large distributed networks) and adaptable (allows for the introduction of new features). The H.323 call control model works well for large enterprises because gatekeeper-centralized call control provides some capability for Operation, Administration, and Maintenance (OA&M).

SIP

SIP is a multimedia protocol that uses the architecture and messages found in popular Internet applications. By using a distributed architecture, with URLs for naming, and text-based messaging, SIP takes advantage of the Internet model for building VoIP networks and applications.

SIP is used in a distributed architecture and allows companies to build large-scale networks that are scalable, resilient, and redundant. SIP provides mechanisms for interconnecting with other VoIP networks and for adding intelligence and new features on the endpoints, SIP proxy, or redirect servers.

Although the IETF is progressive in defining extensions that allow SIP to work with legacy voice networks, the primary motivation behind SIP is to create an environment supporting next-generation communication models that utilize the Internet and Internet applications. In addition, the lack of centralized management support makes SIP more suitable for growing, dynamic organizations and Internet telephony service providers.

MGCP

MGCP describes an architecture in which call control and services such as OA&M are centrally added to a VoIP network. As a result, MGCP architecture closely resembles the existing PSTN architecture and services.

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

MGCP works well for organizations that are comfortable with centralized management and control. For example, service providers are well suited for MGCP.