T-VIPS CP560 - F.3 How to set ETT

188 Estimated Transmission Time
CP560 DVB-T2 Gateway User’s Manual Rev. 2.2 (3686) ID: um_t2gateway
• Absolute timestamp: The modulator will not transmit since the transmission time is in
the past.
• Relative timestamp: The modulator will not notice that the transmission time is in the
past since the Relative timestamp wraps every second. The modulator will transmit
if still within buffer requirements, and destroy the SFN if any of the other modulator
received the signal prior to transmission time.
F.3 How to set ETT
1. Estimate the total network delay from the CP560 to each modulator in an SFN region.
Remember to account for possible jitter in your network, especially if using IP trans-
mission.
2. Find the required processing delay for each modulator. Should be stated somewhere
by the modulator manufacturers.
3. Calculate required transmission delay for each network and modulator.
4. Set ETT to the highest transmission delay found under point 3, and add some extra
delay for safety.
Alternatively a more practical approach may be applied:
1. Start with a high ETT, and reduce this number until the first modulator breaks down.
This will be the largest transmission delay for your SFN region.
2. Set ETT to the highest transmission delay found under point 1, and add some extra
delay for safety.