H.323 is a protocol developed by the International
Telecommunication and Union and Telecommunication Standardization Sector
(ITU-T) to enable simultaneous voice, video, and data transmission over ISDN
connections. The protocol has been adapted to function in LAN
environments.
The Session Initiation Protocol (SIP) is the successor to H.323 and
was developed by the Internet Engineering Task Force (IETF). SIP is a
lightweight and scalable protocol; however, it currently lacks support for
advanced features in VOIP networks.
The Media Gateway Control Protocol (MGCP) is a client/server VOIP
signaling protocol. Most of the gateway configuration is performed in MGCP,
which uses a call agent.
The Skinny Client Control Protocol (SCCP) is a Cisco proprietary
VOIP protocol designed for signaling and control between Cisco Unified
Communication Manager and Cisco IP phones. SCCP is not widely supported, and
only a limited number of Cisco gateways use it. SCCP devices report all
actions to the communication manager server, which response with the actions
the device should take, similar to MGCP.
| Protocol | Description | Advantages | Disadvantages |
| H.323 | Enables simultaneous voice, video, and data transmission over ISDN connections | Good for long distance connections, supports multiple media types | Complex to implement, requires high bandwidth, poor NAT/firewall traversal |
| MGCP | Client/server VOIP signaling protocol; majority of gateway configuration is done in MGCP on what is called as call agent | Simple and efficient, centralized control, easy to troubleshoot | Lack of vendor support, limited flexibility for customization |
| SIP | Successor to H.323; lightweight and scalable protocol | Good for real-time communication, supports multiple media types, easy to implement | Lacks support for advanced features in VOIP networks, poor NAT/firewall traversal |
| SCCP | Cisco proprietary VOIP protocol designed for signaling and control between Cisco Unified Communication Manager and Cisco IP phones | Highly secure, provides detailed call control, easy to manage | Limited vendor support, not widely used, lacks flexibility |