Case Study: Solution for DVB-S DVB-T Master Headends

Above a typical headend architecture in a DVB-T deployment.
A selection of typically 25 to 30 transponders are received and descrambled in the IRDs and then delivered for further elaboration.  A bank of two 1RU chassis equipped with two satellite input VB270 modules each to monitor all satellite transponders of interest. This enables round-robin coverage of up to 24 transponders with a round-robin cycle time of ~5 minutes. All transponders are checked for faults according to the TS 101 290 specification. Typical faults at the ingress monitoring stage include:
• Signal loss or degradation due to weather or things flying into the downlink path;
• Unscheduled changes to the signal structure done by the satellite operators;
• Undetected faults in the satellite provider headend propagated.
After ingress monitoring the services are monitored at the IP level before multiplexing. A single 1RUchassis populated with one VB220 IP-PROBE and two VB280 Content Extractor modules is deployed for this.  All streams are checked for decodeability and an alarm is generated if this is not the case. Alarms are also generated for freeze-frame and audio silence at this stage. A thumbnail mosaic is built-up ideal for visual inspection in the NOC. Typical faults detected by the content monitoring stage include:
• Smart card failures in the IRDs resulting in black or green being fed to encoders
• Loss of access rights in the IRDs
• ENCODER and IRD hardware failures .
After encoding the TV multicasts are fed to the MPEG multiplexing stage for MPTS buildup, CA insertion, EPG insertion.. The output of the multiplexer is either IP or ASI-based. In the drawing above an ASI version is shown. In a single frequency network the final stage before network adaption and transmission is SFN adaption. SFN adaptation is either a function inside the multiplexer or is handled by an external unit.
Egress monitoring is performed at this stage by deploying a 1RU chassis populated with one VB120 IP-PROBE and one VB250 COFDM input module. The VB250 module is further responsible for SFN drift alarming. Typical faults detected by the egress monitoring stage include:
• Conditional Access failures (EMM failures, stuck control words, loss of scrambling..)
• Multiplexer failures
• EIT failures
• SFN failure and drop of synchronization