Developments in Audio Networking Protocols By: Mel Lambert
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TECHNICAL FOCUS: SOUND Copyright Lighting&Sound America November 2014 http://www.lightingandsoundamerica.com/LSA.html Developments in Audio Networking Protocols By: Mel Lambert It’s an enviable dream: the ability to prominent of these current offerings, ular protocol and the basis for connect any piece of audio equip- with an emphasis on their applicability Internet-based systems: IP, the ment to other system components within live sound environments. Internet protocol, handles the and seamlessly transfer digital materi- exchange of data between routers al in real time from one device to OSI layer-based model for using unique IP addresses that can another using the long-predicted con- AV networks hence select paths for network traffic; vergence between AV and IT. And To understand how AV networks while TCP ensures that the data is with recent developments in open work, it is worth briefly reviewing the transmitted reliably and without industry standards and plug-and-play OSI layer-based model, which divides errors. Popular Ethernet-based proto- operability available from several well- protocols into a number of smaller cols are covered by a series of IEEE advanced proprietary systems, that elements that accomplish a specific 802.3 standards running at a variety dream is fast becoming a reality. sub-task, and interact with one of data-transfer speeds and media, Beyond relaying digital-format signals another in specific, carefully defined including familiar CAT-5/6 copper and via conventional AES/EBU two-chan- ways. Layering allows the parts of a fiber-optic cables. nel and MADI-format multichannel protocol to be designed and tested All AV networking involves two pri- connections—which requires dedicat- more easily, simplifying each design mary roles: control, including configur- ed, wired links—system operators are stage. For example, TCP/IP is a pop- ing, monitoring, and device command looking for the ability to direct digital material from one location to another by labeling the outgoing stream in such a way that it will be routed only to the targeted input port. In this way, we will be able to re- configure complex systems with a few keystrokes rather than having to dis- connect and reconnect multiple XLR, DB-25, and assorted physical connec- tors. Once the physical I/O ports have been selected and assigned a unique network virtual address, a browser- based interconnect scheme can vector outputs from a front-of-house console directly to the corresponding loud- speaker inputs, or a bank of micro- phone signals to the corresponding console inputs. A number of existing open-standard and proprietary networking schemes provide reliable connections for live sound systems with I/O counts in the hundreds, and hence are suitable for multi-function performance spaces, music theatre, touring rigs, sports are- nas, houses of worship, and the like. This article will consider the more Extreme Networks Summit Series AVB-compliant multiport switches. 126 • November 2014 • Lighting&Sound America using a communication protocol via the application layer; and transport, which handles data transfer. Usefully, the OSI model defines seven layers used to frame and transfer data: 1. Physical layer, which describes the network’s electrical charac- AVnu-certified BSS Audio Soundweb London BLU-805 for AVB networks. teristics. 2. Data link layer, or the logic con- nection, which defines the type to be sent across a network. approach to IP-based audio sys- of network and how packets are 7. Application layer, which supports tems by using only Ethernet’s encoded and decoded. application and end-user physical layer and customized 3. Network layer, which provides processes by identifying commu- routers for point-to-point data switching and routing technolo- nication partners, quality of serv- transfer; audio samples are gies, utilizing addressing, inter- ice/QoS, user authentication, pri- streamed continuously, using networking, and error handling. vacy, etc. Ethernet frames to achieve a far 4. Transport layer, which provides Layer 1, networking schemes more efficient use of the available data transfer and is responsible based on physical CAT-5/6 wiring and bandwidth. for end-to-end error recovery and interconnections, include: • Aviom A-Net. flow control. • AES50-2005 (also known as • Calrec Hydra2 for broadcast 5. Session layer, which establishes, SuperMAC and HyperMAC), pro- applications. manages, and terminates con- moted by Behringer through its • Riedel RockNet and MediorNet, nections between applications. Midas and Klark Teknik brands, based on a proprietary redundant- 6. Presentation layer (or syntax), but also supported by other ven- ring topology. which formats and encrypts data dors. AES50 takes a very different Layer 2, AoE (Audio over Ethernet) www.lightingandsoundamerica.com • November 2014 • 127 TECHNICAL FOCUS: SOUND and monitoring data. • Roland REAC. Layer 3, AoIP (Audio over IP) schemes that use standard IP packets over a distance, include: • AES67-2013 (formerly code- named AES-X-192), which offers high-performance streaming audio-over-IP, plus planned inter- operability with Audinate Dante; ALC NetworX Ravenna (favored by a number of European firms), AVnu-certified Crown DCi Series amplifiers for AVB networks. LiveWire Wheatnet/IP, Q-LAN, and AVB (via a future Layer 3 mode). • Audinate Dante. schemes that utilize standard Ethernet • Calrec Hydra for broadcast appli- • QSC Audio Q-LAN. packets, include: cations. • Telos/Axia Audio Livewire for • AES51-2006, which carries AES3- • Cirrus Logic CobraNet, one of the broadcast applications. format audio using ATM earliest audio-specific protocols. • Wheatstone/IP, used in a range of (Asynchronous Transfer Mode) • EtherSound, licensed for use in a broadcast consoles. over Ethernet. variety of products to provide bi- Most Layer 1 schemes enable • AVB/Audio Video Bridging is TSN directional and low-latency trans- simple point-to-point configurations (Time-Sensitive Networking) using fer of up to sixty-four 24-bit chan- with no individual addressing of IEEE 802.1 standards (and pro- nels at a 48kHz sample rate, components located on an Ethernet- moted by AVnu Alliance). together with embedded control compliant network, and hence must use a dedicated infrastructure. Adding Layer 2 and Layer 3 function- ality offers enhanced flexibility in terms of user-programmable routing and other interrogation/monitoring capabilities. And control of systems components—maybe mut- ing/unmuting of console outputs, or initialing additional DSP functionali- ty—can be implemented via open- standard or proprietary command Studio Technologies Dante-compatible Model 214, 215, and 216 announcer’s consoles. protocols using TCP/IP and/or UDP/IP communication; usually, this control data coexists on the same network as audio data. Some Layer ufacturers, including Yamaha and dom offered to competitive brands. 2 systems—for example, CobraNet DiGiCo; Optocore’s SANE— The reasons are obvious. Aside from and AVB—have a limited ability to Synchronous Audio Networking plus recovering developmental costs, get- coexist with other network applica- Ethernet—protocol is said to enable ting Ethernet-based systems to reliably tions on an Ethernet network, while synchronous digital audio transfer carry multiple channels of digitized Layer 3 systems offer maximum con- over standard CAT5/6 cables.) audio, video, and control data is a far- vergence by supporting IP network- from-trivial exercise—which explains ing. (While not a true networking pro- Proprietary versus open- why some first-generation protocols tocol, Optocore carries AES/MADI- standard protocols simply dedicated a network to carrying compliant signals over fiber-optic Most current networking schemes are digitized data; by optimizing that single links and is favored by several man- proprietary to their developers and sel- function, low latency and accurate www.lightingandsoundamerica.com • November 2014 • 129 TECHNICAL FOCUS: SOUND system synchronization could be guar- AES67-2013 IP-based Ethernet switches. The managed net- anteed. As faster switches and cabling networking work can transmit several hundred became available, companies could “There are three key elements to con- stereo channels via a 1Gbit connec- offer enhanced bandwidths, but the sider when designing any open-stan- tion, and provides low latency primary goals of on-time data delivery dard for data networks,” says Tim between AES67-compliant devices, meant that highly customized, often Shuttleworth, a networking expert with IEEE 1588 being responsible for proprietary protocols were the norm. who helped shepherd AES67-2013 accurate synchronization; audio clocks Cirrus Logic’s CobraNet and through its gestation and ratification, sync to a master clock within five sec- Audinate’s Dante are both licensed, and currently serves as engineering onds of connecting to the network. whereas AVB and AES67-2013 are manager at Renkus-Heinz. “Firstly, IEEE 1588-compliant networks nomi- open standards available to any firm how are we going to synchronize the nate a single clock or “grandmaster” that elects to use them; AVnu certifica- network?—in other words: What is —normally the most stable and accu- tion necessitates AVnu Alliance mem- our master clock? Secondly, how do rate one; many systems use a GPS- bership dues and certification fees. you take audio data and turn it into a referenced clock—as a master timing Moving beyond the interoperability of payload? And thirdly, how do we reference that is transmitted