VBrick Systems VB6000, VB4000, VB5000 manual Optimizing System Performance, Mixed Model Appliances

Figure 5. On Demand Playback

It is important to note that on demand playback uses FTP and progressive download for playback, and the viewing experience is sub-optimal compared with content from a dedicated VOD server. See Progressive Download on page 54 explains how to create and view these files.

Optimizing System Performance

VBrick appliances are designed to accommodate a variety of configurations. VBrick configuration choices enable the widest range of features and capabilities and are designed to provide the user with a high degree of flexibility. In some extreme cases, users can create configurations that exceed the normal processing capacity of the unit causing it to not perform optimally. VBrick units provide statistical counters and status variables indicating current device utilization and can even be configured to report SNMP trap alarm conditions when these situations occur. Corrective action usually involves reducing a video rate or disabling a channel. In general, video quality improves when video rate is increased toward the maximum of 4 Mbps. In short, video quality is subjective and relates to other components such as the response of the human eye, the quality of the original content and signal, and the quality of the decoder and monitor. As a general rule, use the lowest video rate that best suits the application.

When configuring VBrick units, pay close attention to the total bit rate of all streams exiting the unit. The sum of all streaming traffic should be closely monitored and kept to a minimum whenever possible. Once you have selected and applied a configuration to the unit, you can check the status of the processor and device load via the IWS or CLI. The CPU utilization and overloaded status variables are an excellent indication on the unit's overall health. If the CPU utilization is high or an overloaded condition is occurring, you can simply reduce bit rates, reduce the number of clients, and re-run the test. As a part of regular maintenance, you should periodically check the CPU utilization and the overloaded and "buffer full" count status variables to ensure the unit remains within normal operating limits.

Mixed Model Appliances

In addition to dual devices (for example two encoders, or an MPEG-2 encoder and MPEG-2 decoder), VBrick supports mixed model appliances (for example a WM encoder and an MPEG-4 encoder). VBrick appliance v4.1 software supports almost any combination of VBrick devices in Slots 1 and 2 so you can mix and match as necessary. For example, you can have a WM encoder in Slot1 and an MPEG-4 encoder in Slot2, or you can have an MPEG-2 encoder in Slot1 and MPEG-4 decoder in Slot2. The only exception is that you cannot have a

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