As we have seen, there is no sure way to distinguish between UDP packet-loss and loss in the underlying
TS packets. One way to deal with the situation is to have a probe doing zero readings close to the signal
source before the network can introduce UDP packet loss.
B.4 Multicast Thresholds
It is useful to configure individual threshold settings for IAT for each stream unless they are fixed at the
same bit-rate. Streams that are being monitored by several probes should have equal Ethernet thresholds
configured on each probe to make it easy to compare measurements for a stream across several probes.
As a rule of thumb the IAT warning threshold could be set to 50% above the max IAT value observed
over a considerable period of time, the last 24h or so. The IAT error threshold could be set a little
below the maximum jitter the system can tolerate – usually limited by the STB jitter tolerance. STB
manufacturers should be able to provide information about how much jitter they can handle. Setting the
Ethernet warning-threshold too high results in a graph where almost all plots are close to the x-axis and
it becomes less useful to visually compare MediaWindow graphs.
For streams with TS/UDP mapping the default MLR threshold is set so that errors are reported if the
number of CC errors exceeds the number of TS packets in one UDP frame (assumed to be 7).
B.5 Dedicated interface for OTT
As a rule of thumb, you should never have OTT traffic on the same network as multicasts. This means
that you should either use one Probe for multicast and one for OTT, or you should use different and
dedicated interfaces for each.
The interface used for OTT traffic is controlled using the Setup — Routing view.
B.6 OTT descrambling with Verimatrix
If you are using a Verimatrix VCAS 3.7 server to encrypt your OTT stream, you can get the Probe to
descramble the chunks. It will uses the same API to descramble the chunks, as the encoder or segmenter
uses to encrypt the chunks. To achieve this, the Probe need to be able to reach the VCAS server’s
private encoder interface.
Since the Probe only uses a single interface for OTT, your network needs to be configured such as the
Probe can reach both the VCAS server and your origin server on the same interface.
258 VB2xx GigE User’s Manual version 5.4
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