Computing Zap Time
The factors that has been explained in the last section don't affect in the same way to the overall zap time. So in the table below there are an example of the zap time in IPTV DSL:
| Channel Change Latency Factor | Device/Location | Typical Latency | Cumulative Latency | |
|---|---|---|---|---|
| 1 | Send IGMP Leave for channel X | STB | < 10 ms | |
| 2 | Send IGMP Join for channel Y | STB | < 10 ms | |
| 3 | DSLAM gets Leave for channel X | DSLAM/Network | < 10 ms | |
| 4 | DSLAM gets Join for channel Y | DSLAM/Network | < 10 ms | ~ 20 - 40 ms |
| 5 | DSLAM stops channel X, and sends Channel Y | DSLAM/Network | ~ 30 – 50 ms | ~ 50 – 90 ms |
| 6 | DSL Latency (FEC/Interleave) | DSLAM/Network | ~ 10 ms | ~ 60 - 100 ms |
| 7 | Core/Agg Network Latency | Router/Network | ~ 20 – 60ms | ~ 80 – 160ms |
| 8 | De-jitter buffer | STB | ~ 300 ms | ~ 380 - 460 ms |
| 9 | Wait for PAT/PMT | STB MPEG buffer | ~ 125 ms | ~ 500 - 580 ms |
| 10 | Wait for ECM/CA | STB MPEG buffer | ~ 125 ms | ~ 620 - 700 ms |
| 11 | Wait for I-frame | STB MPEG buffer | ~ 250 ms to 2s | ~ 870 ms – 2.7s |
| 12 | MPEG buffer | STB MPEG buffer | ~ 1s to 2s | ~ 1.8s – 4.7s |
| 13 | Decode | STB | ~ 50ms | ~ 1.9s – 4.8s |
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