by passing AES3 audio transport over an ATM network using structured network cabling (both copper and fibre). This was used extensively by contractors supplying the BBC's wide area real-time audio connectivity around the UK. Audio over IP differs in that it works at a higher layer, encapsulated within Internet Protocol. Some of 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. In broadcasting, and to some extent in studio and even live production, many manufacturers equip their own audio engines to be tied together. 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. 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. See also Comparison of audio network protocols Ethernet Powerlink HDBaseT References Audio engineering Broadcast engineering Ethernet Audio network protocols