H.245 is a control channel
protocol used with
ne.g.
H.323 and
H.324 communication sessions, and involves the line transmission of non-
telephone
A telephone, colloquially referred to as a phone, is a telecommunications device that enables 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 ...
signals. It also offers the possibility to be tunneled within
H.225.0 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 spre ...
traversing.
H.245 is capable of conveying information needed for multimedia communication, such as
encryption
In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...
,
flow control,
jitter
In electronics and telecommunications, jitter is the deviation from true periodicity of a presumably periodic signal, often in relation to a reference clock signal. In clock recovery applications it is called timing jitter. Jitter is a signifi ...
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 hands, and in most cases, it is accompanied by a brief up-and-down movement of the grasped hands. Customs surrounding hands ...
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