Audio networking

In audio and broadcast engineering, Audio networking is the use of a network to distribute real-time digital audio. Audio Networking replaces bulky snake cables or audio-specific installed low-voltage wiring with standard network structured cabling in a facility. Audio Networking provides a reliable backbone for any audio application, such as for large-scale sound reinforcement in stadiums, airports and convention centers, multiple studios or stages.

While Audio Networking bears a resemblance to voice over IP (VoIP) and audio contribution over IP (ACIP), Audio Networking is intended for high-fidelity, low-latency professional audio. Because of the fidelity and latency constraints, Audio Networking systems generally do not utilize audio data compression. Audio Networking systems use a much higher bit rate (typically 1 Mbit/s per channel) and much lower latency (typically less than 10 milliseconds) than VoIP. Audio Networking requires a high-performance network. Performance requirements may be met through use of a dedicated local area network (LAN) or virtual LAN (VLAN), overprovisioning or quality of service features.

Some Audio Networking systems use proprietary protocols (at the lower OSI layers) which create Ethernet frames that are transmitted directly onto the Ethernet (layer 2) for efficiency and reduced overhead. The word clock may be provided by broadcast packets.

There are several different and incompatible protocols for Audio Networking. Protocols can be broadly categorized into layer-1, layer-2 and layer-3 systems based on the layer in the OSI model where the protocol exists.

Layer-1 protocols use Ethernet wiring and signaling components but do not use the Ethernet frame structure. Layer-1 protocols often use their own media access control (MAC) rather than the one native to Ethernet, which generally creates compatibility issues and thus requires a dedicated network for the protocol.

Layer-2 protocols encapsulate audio data in standard Ethernet frames. This is called Audio over Ethernet. Most protocols make use of standard Ethernet hubs and switches, though some require that the network (or at least a VLAN) be dedicated to the audio distribution application.

Layer-3 protocols encapsulate audio data in OSI model layer 3 (network layer) packets. By definition it does not limit the choice of protocol to be the most popular layer-3 protocol, the Internet Protocol (IP). In some implementations, the layer-3 audio data packets are further packaged inside OSI model layer-4 (transport layer) packets, most commonly User Datagram Protocol (UDP) or Real-time Transport Protocol (RTP). Use of UDP or RTP to carry audio data enables them to be distributed through standard computer routers, thus a large distribution audio network can be built economically using commercial off-the-shelf equipment.

Although IP packets can traverse the Internet, most layer-3 protocols cannot provide reliable transmission over the Internet due to the limited bandwidth, significant End-to-end delay and packet loss that can be encountered by data flow over the Internet. For similar reasons, transmission of layer-3 audio over wireless LAN are also not supported by most implementations.