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Q-Lite Satellite Modem Installation and Operating Handbook
6-69
6.2.4.14 PCR Restamping
PCR restamping is an On/Off control that controls whether MPEG2 Program Clock
Reference (PCR) timestamps in received MPEG2 transport stream packets (via the ASI
or IP interfaces) are adjusted for any delay introduced by the modem. By adjusting the
timestamps as required, potential jitter in the play out of the packets at the
receiver/decoder can be eliminated.
6.2.4.15 MPEG Over IP Type
UDP/TS This indicates that the MPEG2 transport stream packets are
encapsulated into into IP packets using the UDP protocol
.
UDP/RTP/TS This indicates that the MPEG2 transport stream packets are
encapsulated into into IP packets using the UDP and RTP
protocols
.
Table 6-60 MPEG Over IP Type
When sending MPEG2 packets encapsulated inside IP packets, the modem can reduce
the satellite transmission overhead by removing the IP headers and sending only the
MPEG2 packets. On the receive side, the MPEG2 packets are encapsulated back into IP
packets, using IP address and port number information entered by the user. When
decapsulating and encapsulating MPEG2 packets, the modem needs to know whether
the IP packets contain just UDP headers, or UDP and RTP headers.
6.2.4.16 TS Data Rate and Nominal De-jitter Buffer Delay
These settings control a de-jitter buffer that can be used to remove IP network jitter that
may be present in MPEG-over-IP transport streams. De-jittering of multiple concurrent
transport streams is supported, regardless of whether the streams have been generated
using independent clocks or not (i.e. whether or not the various stream PCR reference
clocks are asynchronous with respect to each other).
The
TS data rate is the MPEG-over-IP transport stream bit rate being input to the modem.
A value must be entered in order to use the de-jitter buffer. Note that the normal Tx data
rate defines the transmit data rate after any transport stream rate adaption by the
modem.
Setting the de-jitter buffer delay to 0 sets the buffer depth to give maximum resilience to
IP network jitter.
Setting the de-jitter buffer larger than necessary will increase packet latency (the buffer
can accommodate a maximum of over 1000 MPEG packets). Consequently, if the peak-
to-peak IP network jitter is known, latency can be minimised by setting the de-jitter buffer
depth to a little over half of the peak-to-peak jitter value. For example, if the TS data rate
is 6Mbps (which is 750k bytes per second), the de-jitter buffer latency for a half-full
quiescent level will be K * 750e3 = 136.533ms (where K is the de-jitter buffer size, which