H.245 is the control protocol for multimedia communication within H.323 and H.324. It provides:
- Master Slave Determination
Helps in the mediation of potential collision situations during different phases of negotiation.
- Terminal Capability Exchange
Allows any H.323 terminal 's audio / video capabilities, audio and video codecs to communicate to the other party of communication.
- Logical Channel Signaling
Signaling logical channels. Provides the means to open logical channels, to control and to close. The main purpose of a logical channel of H.245, in the context of VoIP, the negotiation of the audio stream, i.e., the codecs to be used for what UDP port, a media stream is to be sent, and
A major disadvantage within the first version of H.323 was the need of an extensive 4-way handshake protocol to open a logical channel of a telephony meeting. Later versions introduced the H.323 Fast Connect procedure by using the fast start - element of a H.225.0 message. Another recommendation, H.460.6, Extended Fast Connect feature exists that defines a 1-way handshake.
H.245 has the ability to be tunneled within H.225 call signaling. This makes it easier to traverse firewalls.