Sencore VB330, User Manual

Page: 193 / 203

For VBR streams a similar packet-loss will not necessarily affect the IAT graph even if the time between
two neighboring packets doubles. The pink line represents the IAT and MLR value measured for the
missing packet.
B.3.2 Identifying UDP Packet Loss
This discussion does not apply to streams with TS/RTP mapping since in that case identifying UDP
packet loss is straight forward.
There is no fail-safe way to distinguish packet loss caused by dropping UDP packets from packet loss
caused by dropping packets inside the TS layer. IP based networks will generally not introduce new
errors in the TS layer. As soon as the TS layer is wrapped inside UDP packets all further processing
operates on the UDP packets.
The pink line indicates a packet loss of 1-4 with no jitter component.
As a rule of thumb, the co-existence of small MLR readings (1-4) and no IAT readings can be assumed to
have been caused by packet loss in the original TS data.
The pink line indicates a packet loss of 6 or 7 and a doubling of the jitter component.
A UDP packet-drop will usually show up in the MLR value as a multiple of the mapping value; for a
mapping value of 7 TS packets into each UDP packet, the MLR component will be equal to 7, 14, 21 etc.
Slightly lower values such as 6, 13, and 20 can be expected if a missing UDP packet did contain one TS
packet without continuity counter (i.e. a PCR packet with no payload).
VB3xx 10G Probe User’s Manual version 5.3 193