In audio engineering and broadcast engineering, Audio over Ethernet (sometimes AoE - not to be confused with ATA over Ethernet) is the use of an Ethernet-based network to distribute real-time digital audio.
It is designed to replace bulky snake cables and fixed wiring, and instead use a standard network structured cabling in a facility, providing 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 on the surface AoE bears a resemblance to Voice over IP (VoIP), AoE is intended for high-fidelity, low-latency professional audio. Because of the fidelity and latency constraints, audio over Ethernet systems generally do not utilize audio data compression. AoE systems use a much higher bit rate (typically 1 Mbit per channel) and much lower latency (typically less than 10 milliseconds) than VoIP.
Audio over Ethernet requires a high performance network. Performance requirements may be met through use of a dedicated local-area network (LAN) or virtual LAN (VLAN), Overprovisioning and/or Quality of service features.
Most AoE systems use proprietary protocol(s) (at the higher OSI layers) which create data packets and data frames that are transmitted directly onto the Ethernet (layer 2) for efficiency and reduced overhead. The word clock may be provided by broadcast packets.
Contents |
There are several different and incompatible protocols for audio over Ethernet. For example, using category 5 cable and 100BASE-TX signaling at 100 Mbits/second, each link can generally transmit between 32 and 64 channels at a 48kHz sampling rate. Some can handle other rates, such as 44.1kHz (CD-quality), 88.2 and 96kHz (2× oversampling), even 192kHz (4×), as well as up to 32-bit samples, with a corresponding reduction in channel capacity. On some, this is accomplished through channel bonding, while others use individually-scalable channels.
AoE is not necessarily intended for wireless networks, thus the use of various 802.11 devices may or may not work with various (or any) AoE protocols.
Protocols can be broadly categorized into Layer 1, Layer 2 and Layer 3 systems based on the lowest 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 Computer compatibility issues.
Layer 2 protocols encapsulate audio data in standard Ethernet packets. Most can 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 standard IP packets (usually UDP/IP or RTP/UDP/IP). Use of the IP protocol improves interoperability with standard computing platforms and in some cases, improves scalability of the audio distribution system. The layer 3 audio over Ethernet protocols are not designed to traverse the Internet (see Audio over IP for this capability).
The Audio Engineering Society's MADI or AES10, although similar in function, uses 75-ohm coaxial cable with BNC connectors instead. It is most similar in design to AES3, which can carry only two channels (stereo).
The Audio Engineering Society's AES47, provides linear audio networking by passing AES3 audio transport over an ATM network using structured network cabling (both copper and fibre). This is used extensively by contractors supplying the BBC's wide area real-time audio connectivity around the UK.
In broadcasting and to some extent in studio and even live production, many manufacturers equip their own audio engines to be tied together with Ethernet. This may also be done with gigabit Ethernet and optical fibre rather than wire. This allows each studio to have its own engine, or for auxiliary studios to share an engine. By connecting them together, different sources can be shared among them. Logitek Audio is one such company using this approach.
An audio over IP setup differs in that it works at a higher layer, encapsulated within Internet Protocol. These systems are usable on the Internet, but may not be as instantaneous, and are only as reliable as the network route — such as the path from a remote broadcast back to the main studio, or the studio/transmitter link (STL), the most critical part of the airchain. This is similar to VoIP, however AoIP is comparable to AoE for a small number of channels, which are usually also data-compressed. Reliability for permanent STL uses comes from the use of a virtual circuit, usually on a leased line such as T1/E1, or at minimum ISDN or DSL.
|
|||||||||||||||||||||||