- Audio over Ethernet
In
audio engineering (and now inbroadcast engineering ), audio over Ethernet (sometimes AoE) is theconcept of using anEthernet -based network to transmitdigital audio . It is designed to replace bulkysnake cable s, and to use the existingwiring infrastructure in a facility, providing a reliable backbone for any audio application, such as for multiplestudio s or stages.While on the surface it bears a resemblance to
voice over IP (VoIP), it differs in several very important ways. First, AoE is high-bandwidth, intended forhigh-fidelity and therefore high-bitrate professional audio, rather thanvoice . In addition, it is also forisochronous and multi-channel use, rather than independent streams. Second, it is designed to have very highreliability , including very low latency (under sixmillisecond s) and almost nopacket loss . Because of this, audio over Ethernet is also uncompressed, which prevents both delay and unwantedcompression artifact s. Likewise, AoE by definition runs on a dedicatedlocal-area network (LAN), or at minimum on avirtual LAN (VLAN), so thatquality of service (QoS) is guaranteed to provide uninterrupted and uncorrupted audio. AoE also does not use TCP or UDP forlayer 4 andInternet Protocol forlayer 3 (seeOSI model ), but rather its own protocol that creates data packets and data frames that are transmitted directly onto the Ethernet (layer 2 ) forefficiency and lack of overhead. Theword clock may be provided bybroadcast packet s.Protocols
There are several different and incompatible protocols for audio over Ethernet:
Using
category 5 cable and100BASE-TX signaling at 100 MB/second, each protocol can generally transmit between 32 and 64 channels at a 48kHzsampling 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 inchannel capacity . On some this is accomplished throughchannel bonding , while others use individually-scalable channels.AoE is not necessarily intended for
wireless network s, thus the use of various802.11 devices may or may not work with various (or any) AoE protocols.Protocols can be broadly categorized into Layer 1 and Layer 2+ systems.
Layer 1 protocols
Layer 1 protocols use Ethernet wiring and signaling components but do not use the Ethernet frame structure. Layer 1 protocols often use their own use their own
media access control lers (MAC) rather than the one native to Ethernet, which generally createsComputer compatibility issues.*
A-Net byAviom [http://www.aviom.com/Products/Aviom-About-A-Net.cfm]
*AES50
**SuperMAC , Implementation ofAES50 bySonyOxford [http://www.sonyoxford.co.uk/supermac]
*EtherSound byDigigram [http://www.ethersound.com]
**NetCIRA byFostex [http://www.netcira.com]
*M11 by AudioRail [http://www.audiorail.com/]
*MaGIC by Gibson [http://www.gibson.com/Products/Audio/MaGIC%20(2)]
*REAC by Roland [http://www.roland.com/products/en/RSSbyRoland/]Layer 2 and 3 protocols
Layer 2 and 3 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.
*
AES51 , A method of passing ATM services over Ethernet that allowsAES3 audio to be carried in a similar way toAES47
*AoIP by Wheatstone Corp (used with PC driver as sound card substitute inbroadcasting ) [http://www.wheatstone.com/aoIP.html]
*AVB (Audio Video Bridging) is currently under development by theIEEE AVB task group [http://www.ieee802.org/1/pages/avbridges.html] , [http://www.pldesignline.com/showArticle.jhtml?articleID=204201017&] , [http://www.pldesignline.com/howto/204300408]
*CobraNet byPeak Audio (now owned byCirrus Logic ) [http://www.cobranet.info]
**RAVE byQSC Audio [http://www.qscaudio.com/products/network/rave/rave.htm]
*DANTE by Audinate [http://www.audinate.com]
*Hydra by Calrec [http://www.calrec.com/product/hydra.htm]
*Livewire by Axia/Telos (mainly used inbroadcasting ) [http://www.axiaaudio.com/livewire/]imilar concepts
The
Audio Engineering Society 'sMADI orAES10 , although similar in function, uses 75-ohm coaxial cable withBNC connector s instead. It is most similar in design toAES3 , which can carry only two channels (stereo).The
Audio Engineering Society 'sAES47 , provides linear audio networking by passingAES3 audio transport over an ATM network using structured network cabling (both copper and fibre). This is used extensively by contractors supplying theBBC 's wide area real-time audio connectivity around the UK.In broadcasting and to some extent in studio and even live production, many
manufacturer s equip their ownaudio engine s to be tied together with Ethernet. This may also be done withgigabit Ethernet andoptical fibre rather thanwire . 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 theInternet , but may not be as instantaneous, and are only as reliable as thenetwork route — such as the path from aremote broadcast back to the main studio, or thestudio/transmitter link (STL), the most critical part of theairchain . 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 avirtual circuit , usually on aleased line such as T1/E1, or at minimumISDN orDSL .ee also
* Ethernet Powerlink
*Audio Contribution over IP
Wikimedia Foundation. 2010.