In H323 protocol, TCS (Terminal Capability Set) and OLC (Open Logical Channel) are important elements that allow communication between endpoints.
TCS is a message exchange between H323 endpoints that is used to exchange the terminal capabilities of each endpoint, such as the supported codecs, video resolution, frame rate, and other communication capabilities. When two endpoints are establishing a call, they exchange TCS messages to determine the communication capabilities of each endpoint. This information is used to negotiate a set of capabilities that can be used for the call. The TCS message is sent as part of the H225 Setup message and is used to convey the terminal capabilities of the originating endpoint to the called endpoint.
OLC, on the other hand, is used to establish logical channels between two H323 endpoints. Logical channels are used to transport media streams, control messages, and other types of data between endpoints. When a logical channel is opened, the two endpoints negotiate the type of channel to be used, the format of the data to be exchanged, and other parameters related to the communication. Once the logical channel is established, media streams and control messages can be sent between the endpoints. The OLC message is sent as part of the H245 message and is used to establish and control logical channels.
In summary, TCS and OLC are both important elements of the H323 protocol that are used to establish and control communication between endpoints. TCS is used to exchange the terminal capabilities of each endpoint and negotiate a set of capabilities for the call. OLC is used to establish logical channels between endpoints and negotiate the type of channel to be used, the format of the data to be exchanged, and other parameters related to the communication. Together, these elements ensure that H323 endpoints can communicate effectively and efficiently.