H.245 is a control channel

protocol Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technolog ...

used with ne.g. H.323 and H.324 communication sessions, and involves the line transmission of non-

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

signals. It also offers the possibility to be tunneled within

H.225.0 H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, m ...

call signaling messages. This eases

firewall Firewall may refer to: * Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts * Firewall (construction), a barrier inside a building, designed to limit the spr ...

traversing. H.245 is capable of conveying information needed for multimedia communication, such as

encryption In cryptography, encryption is the process of encoding information. This process converts the original representation of the information, known as plaintext, into an alternative form known as ciphertext. Ideally, only authorized parties can de ...

, flow control, jitter management, preference requests, as well as the opening and closing of logical channels used to carry media streams. It also defines separate ''send'' and ''receive'' capabilities and the means to send these details to other devices that support H.323.

Handshake issues

One major drawback within the initial version of H.323 was the lengthy, four-way H.245 protocol

handshake A handshake is a globally widespread, brief greeting or parting tradition in which two people grasp one of each other's like hands, in most cases accompanied by a brief up-and-down movement of the grasped hands. Customs surrounding handshakes a ...

required during the opening up of the logical channels of a telephony session. Later versions of H.323 introduced the ''Fast Connect'' procedure, using the fastStart element of an H.225.0 message. Fast Connect brought the negotiation down to a two-way handshake. Another recommendation, H.460.6, Extended Fast Connect Feature, exists that defines a one-way handshake.

External links

ITU-T H.245 Recommendation
ITU-T recommendations Videotelephony