VoIP Protocols
Protocols are a set of rules that allow communication devices to 'talk' to each other. For VoIP the two main protocols are SIP and H.323.
Fast becoming the standard for VoIP, Session Initiation Protocol (SIP) defines standards for a number of different services including caller ID, conference calls, call forwarding, and user mobility. And, as well as being able to handle voice, SIP can transmit multimedia information.
SIP works by assigning users unique addresses, independent of physical location, allowing them to make and receive calls anywhere in the world.
When a SIP call is initiated, the caller sends an "invite" request to the intended recipient. Once they are found, response codes are sent back. There are separate codes for searching, ringing, and success; as well as codes to indicate server failures or that the other party is unavailable.
Once the call has finished, a "bye" command is issued to terminate the connection.
Like SIP, H.323 can be used for transmitting multimedia and works well with traditional telephone networks. But, even though it was developed first, H.323 has been losing ground since 3GPP, the organisation responsible for setting standards for 3rd generation mobile communication devices, adopted SIP.
