H.323 is a protocol suite that is widely used in IP telephony networks to facilitate real-time audio and video communication. It is a widely accepted standard for voice and video communication over IP networks. In H.323, there are various call flows that are supported to facilitate communication between different endpoints. In this article, we will discuss the different call flows supported in H.323.
Point-to-Point Call Flow
The point-to-point call flow is the simplest call flow supported in H.323. It involves two endpoints that communicate with each other directly. When a call is initiated, the calling endpoint sends a Setup message to the called endpoint, which responds with a Call Proceeding message. The called endpoint then sends an Alerting message, indicating that the call is being set up. Once the call is established, the endpoints can begin exchanging audio or video data.
Multipoint Call Flow
The multipoint call flow is used when three or more endpoints need to communicate with each other in a single call. In this call flow, an endpoint known as the Multipoint Control Unit (MCU) is used to facilitate communication between the endpoints. When a call is initiated, the calling endpoint sends a Setup message to the MCU, which responds with a Call Proceeding message. The MCU then sends an Alerting message to the calling endpoint and begins to set up the call with the other endpoints. Once the call is established, the endpoints can begin exchanging audio or video data.
Gateway Call Flow
The gateway call flow is used when a call needs to be transferred between an IP network and a traditional public switched telephone network (PSTN). In this call flow, a gateway is used to bridge the IP network and the PSTN. When a call is initiated, the calling endpoint sends a Setup message to the gateway, which responds with a Call Proceeding message. The gateway then sends an Alerting message to the calling endpoint and begins to set up the call with the PSTN. Once the call is established, the endpoints can begin exchanging audio or video data.
Gatekeeper Routed Call Flow
The gatekeeper routed call flow is used when an H.323 gatekeeper is present in the network. In this call flow, the calling endpoint sends a Setup message to the gatekeeper, which then routes the call to the called endpoint. The gatekeeper responds to the calling endpoint with a Call Proceeding message and sends an Admission Request message to the called endpoint. Once the called endpoint responds with an Admission Confirm message, the gatekeeper sends an Alerting message to the calling endpoint and sets up the call between the endpoints.
In conclusion, H.323 is a protocol suite that supports a variety of call flows to facilitate real-time audio and video communication between endpoints. These call flows include the point-to-point call flow, multipoint call flow, gateway call flow, and gatekeeper routed call flow. Understanding the different call flows supported by H.323 is essential for ensuring effective communication in IP telephony networks.