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IP audio: The new audio format
That was until February 2008 when the European Broadcast Union (EBU) finalized a standard for IP audio. The solution was simple: Just add another protocol on top of the UDP protocol. Remember that all things in the data communications world utilize a layered architecture. The Open System Interconnect (OSI) model is based on seven layers, although IP transmission only needs four. There has been much written on the subject, but the simple explanation is that encoded data flows through several different layers, each with a specific job. These layers take care of the creation, packaging, management and control of data. It handles everything including getting the signal through the cable. The process is reversed on the receiving end.
The EBU used a protocol called RTP (Real-time Transport Protocol), a protocol standard created in the late 1990s specifically for the purpose of sending audio, video and telephony over the Internet. It provides a complete set of tools for the transmission of a wide variety of multimedia formats and provides management functions that minimize some problems found with transmissions over UDP alone. The details of RTP are an article in itself, but basically the data from a codec is packaged in the RTP packet layer then sent to the UDP layer for transmission.
Other protocols used for IP audio include:
- SIP (Session Initiation Protocol), which can control the setup, termination and flow of the session, similar to how a telephone network controls a call.
- SDP (Session Description Protocol) provides information about the specific audio format to the destination. This permits the codec on the receiving end to match that of the transmitted format.
- SNMP (Simple Network Management Protocol) provides control and monitoring of the equipment. While SNMP has been a time-tested protocol for this purpose, the EBU is currently working on an IP audio specific standard.
The EBU specifies four primary audio encoding formats: MPEG Layer 2, ITU G.711, ITU G.722, and PCM. However, RTP can also support a number of other current and future formats.
As manufacturers all move toward the IP audio environment and you only need to deal with power and data, I wonder if anyone will miss the days of punching down all those cables?
McNamara is president of Applied Wireless, Cape Coral, FL.
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