Redundant operation supported when using CobraNet
A new feature in MediaMatrix 3.0, along with CobraNet support, is the ability to build fully redundant MediaMatrix systems for mission critical applications. This page discusses some of the redundant capabilities built into MediaMatrix 3.0, CobraNet, and the new CAB's:
CAB Redundancy using the built in "Buddy Link" feature
CABs can be paired to provide audio input and output redundancy. Given a pair of Input CABs (CAB-8i) or Output Cab's (CAB-8o), one is declared the primary, with the other being the secondary, or backup.
This is accomplished by connecting the Link Out of the primary CAB to the Link In of the secondary CAB. Both units are configured to use the same Network Channels. As long as the primary unit is powered on, and it sees a good CobraNet connection (Ethernet link status good), and it has not experienced a fault, it generates a signal which inhibits the secondary from taking over. In the case of an Input CAB, the secondary is inhibited from transmitting onto CobraNet. In the case of an Output CAB, the secondary's audio output relays are turned off.
If a Buddy Link wire fails (or is interrupted by a manually operated A/B switch), and both units are operational, the following takes place. In the case of Input Cab's, the secondary will take over transmission because its CobraNet Transmit Request Priority has (automatically) been made higher than that of the primary. In the case of Output Cab's, both units will generate analog output, so there will probably be some gain and spectral distortion in the resulting signal.
Through software remote control, the Buddy Link inhibit action on the secondary can be disabled (having the same result as severing the link wire), and which unit is on-line can then be controlled remotely. Also, in the case of Input Cab's, once inhibit is disabled, the Network Channel of an off-line unit can be changed to an unoccupied slot so that its audio input can be monitored at a control room location.
MediaMatrix Redundancy
To eliminate a possible single point of failure, two MediaMatrix systems running identical view files are used. The system given preference when there is no problem is considered the primary and the other the secondary. Only one of the systems is allowed to be on-line and the other system is off-line.
Both units are configured to use the same CobraNet Network Channels, so both receive the same audio input. The off-line unit is made to suppress its transmission of CobraNet audio output (as controlled through view file devices representing the CobraNet daughter cards). This is considered important since it keeps a mixture of Network Channels from the two systems from ever being output - something that could happen if only some of the network connections of the primary system failed.
A serial MediaMatrix Buddy Link can be used to connect the primary system to the secondary to provide automatic switchover in case of a primary failure. A constant character stream is sent from primary to secondary, acting to keep the secondary system off-line as long as the primary is powered up, healthy and on-line.
If the Buddy Link cable fails, both the on-line and off-line systems will try to output CobraNet data to the same Network Channels. This causes no real problem - if both systems are configured with the same CobraNet Transmitter Request Priorities, the currently on-line system will continue to dominate, otherwise the highest priority unit will take over.
A mechanical switch which interrupts the Buddy Link can act as a manual A/B selector - when the stream is interrupted, the secondary (B) system will attempt to transmit. If the secondary system has been configured with a higher CobraNet Transmitter Request Priority, the secondary will take over.
The audio output from an off-line unit can be monitored at a control room location if an Output CAB separate from the redundant pairs is provided, and if the network output to that CAB is excluded from the audio output inhibit list.
The MediaMatrix Serial Buddy LinkT
CobraNet Hub Redundancy
To eliminate another possible single point of failure, the Ethernet hubs used for CobraNet can be arranged in redundant pairs as long as redundant CAB pairs are also used. The use of paired, connected, hubs provides two things:
If a hub, or the connection between the MediaMatrix and the hub, fails, then the alternate MediaMatrix and CAB's set can be switched to
Redundant System Example
A diagram of a system employing redundant MediaMatrix systems, redundant network hubs and redundant audio inputs and outputs follows this section.
The slanted lines between MediaMatrix systems and between CAB's units represent the Buddy Links, which provide automatic switchover. Here are some failure scenarios:
A catastrophic failure of the primary MediaMatrix will automatically bring the secondary system on-line, and should only result in a momentary audio discontinuity on the audio outputs. After that, both primary and secondary hubs are in use, and the primary CAB's are in use (if no CAB's have failed).
As long as either MediaMatrix system is on-line, and as long as both primary and secondary hubs are functioning, one CAB out of each pair can fail with no loss in audio input and output. If a primary CAB fails, the secondary will be automatically switched to (dependent upon the exact failure mode). The switchover results in a momentary loss of audio for the channels involved.
If a hub within a redundant hub pair fails, only the alternate set of CAB's on that CobraNet network are then accessible, and only one of the MediaMatrix systems can access that particular CobraNet network. At that point, for each hub attached to the off-line MediaMatrix system that fails, only CAB redundancy for that network is lost, but no audio input or output is lost. If however, a hub attached to the on-line system fails, then that CobraNet network is lost.
