Newtec M6100 - Maximum Traffic Jitter and Buffer Delay

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Data Interfaces M6100 Broadcast Satellite Modulator
11.6.8 Maximum Traffic Jitter and Buffer Delay
M6100>TS over IP >> Max Buffer Delay
A typical IP network is introducing jitter on the arrival time of the IP packets which contain the
encapsulated Transport Stream (TS). While, depending upon the network, jitter can be as low as 10
ms, the M6100 can compensate, for CBR streams, network jitter up to 500 ms.
Compensation is done by using a buffer. We refer to figure at the end of this section.
The buffer stores input data up to a certain level. This level is called the buffer delay. The buffer
outputs Transport Stream data at a constant rate.
During start up the queue is filled until the configured buffer delay is reached. From this moment
onwards, the traffic leaves the de-jitter buffer (First In First Out).
The rate is set by the Input TS Bit Rate (M6100 >> TS over IP >> Input TS Bit Rate) parameter. Any
high frequency jitter is removed this way.
In case of VBR mode, the buffer is bypassed and there is no jitter removal at all.
For the correct functioning of the system, it is very important that the Input TS Bit Rate
is configured correctly! Use the Transport Stream Analyser on-board the M6100
modulator.
Its measured PCR rate (M6100 >> TS Analyser >> Estimated TS Rate) is the most
accurate indication for the TS input rate.
The buffer not only de-jitters the high-frequency jitter of the incoming data, it also takes care of any
difference in rate between the reference clocks of the incoming TS and the modulator by the use of
a (slow) control loop which targets to keep the buffer fill level constant at the same buffer delay .
The slow control loop guarantees an output clock variation lower than 10 ppm/hour in
accordance with DVB standard requirements. For a 3 ppm difference in clock rate
between the reference clocks of the TS and the modulator, a 20 ms buffer delay is
sufficient. Coping with a difference of up to 30 ppm between the reference clocks of
the TS and the modulator requires a 200 ms buffer delay. 30 ppm is the maximum
allowed by DVB standard requirements. Buffer delay values are valid up to a 150
Mbps TS input rate.
Control parameters:
The user has two parameters for the configuration of the buffer.
Max Traffic Jitter: between 0 and 300 ms