QSC Audio S series user manual Introduction How It Works

Introduction: How It Works

Ethernet networks are used most often for data communica- tions, such as with file or print sharing on an office LAN (Lo- cal Area Network). A typical application might include a num- ber of PCs or workstations, servers and shared printers all connected to common Ethernet hardware. Messages (Ether- net frames) are communicated between devices on the LAN in a random and non-deterministic manor. Network response to print messages or file access is usually noncritical so long as the intended outcome occurs in a reasonable amount of time. For example, when multiple users are attempting to share a common printer at the same time, some users will likely experience delays in output. Collisions or failed attempts to access the network may also be acceptable so long as the intended messages are retransmitted. Most often, a limited amount of collisions are expected and are usually transpar- ent to the user.

Audio networks are different because late arrival or failed attempts to transmit audio messages are immediately per- ceived by the listener. Therefore, audio network transmission must be error free with low latency and delivery must be pre- cisely defined. To do this, RAVE incorporates the CobraNet protocol. CobraNet is the industry’s most reliable audio deliv- ery mechanism. CobraNet provides low latency, determinis- tic delivery of audio over Ethernet on either network repeat- ers or switches. Collisions are prevented on shared media links, such as repeater hubs, by CobraNet’s proprietary “order persistent” media access scheme. On dedicated media links, such as with network switches, collisions are prevented due to separate transmit and receive paths in a full-duplex con-

nection and/or an abundance of bandwidth dedicated to a single device on each switch port. On network switches, RAVE establishes a half-duplex link to a dedicated port. The 100 Mbps of bandwidth available at a switched port is more than enough to support all of the typical communications require- ments of RAVE while providing for an ample amount of con- trol and monitoring through the MI via SNMP messages.

A network of CobraNet devices can be thought of as a syn- chronized orchestra. The unit acting in the “conductor” role provides the system clock and grants network permissions to the “performer” units. Each RAVE has a local internal clock so that any RAVE may arbitrate for the role of network “conduc- tor”. RAVE devices may also be synchronized to an external clock source, which is attached to a rear-panel BNC connec- tor. External synchronization requires configuration setup through the front-panel interface or via SNMP. The permis- sions list is a message sent with the system clock that allow individual units access to the network and reserve bundle as- signments.

RAVE routes audio in bundles that are populated with a de- fault value of 8 channels per bundle. The actual number of channels per bundle may be altered, from 0 to 8, from the management interface using SNMP. Reducing channel count reduces system bandwidth requirements. On the models sup- porting CobraNet transmission (81/88/161/188) audio is brought into the RAVE using the rear panel connectors.

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