Albalá Ingenieros IPA3000C01, Руководство пользователя

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Albalá Ingenieros | Manual IPA3000C01
4.4. Description of the TS over IP encapsulators/de-encapsulators
Several different protocols exist for encapsulation of DVB transport streams over IP.
• Protocol UDP: This is the simpler protocol that can be used, but it is the least robust.
UDP consists of grouping up to seven TS packets and transmitting them within one
UDP packet. This protocol does not detect dropped packets nor packets arriving out of
sequence.
• Protocol RTP: This protocol is similar to UDP with respect to the way in which packets
are grouped for transmission but adds a header that includes a continuity flag for
detection of dropped packets and packets received out of sequence along with a
timestamp to facilitate elimination of jitter introduced by the network. When using the
RTP protocol a single frame (FEC Type A) or two frames (FEC Type B) of auxiliary data
can be sent in order to correct errors or dropped packets. When using the RTP protocol
the IPA3000C01 can be configured to substitute dropped and non-recoverable packets
of the TS with null packets.
4.5. System latencies
When transporting DVB frames over ASI interfaces the latency introduced due to
serialization and de-serialization is minimal in comparison to other delays that may exist
in the system. During encapsulation of the DVB over IP frames mechanisms are
employed to correct errors and absorb any jitter generated by the IP networks. These
mechanisms introduce delays in the transport of the frames that may on occasion need
to be accounted for. This section describes the latencies introduced for each of the
modules within the IPA3000C01:
• IP Transmitters:
The latency introduced by the IP transmitter is negligible in comparison with the other
latencies and can be assumed to be equal to the number TS packets transmitted in each
IP packet. If error correction is employed during transmission then the delay for each FEC
packet is configurable as per the SMPTE 2022-1-2007 standard.
• IP Receivers:
The latency of the IP receiver depends upon the transmission protocol used and
dynamically adapts based upon the protocol detected at the input.
- UDP: The latency equals 12 IP packets.
- RTP without FEC: The latency equals 12 IP packets (in order to permit reordering of up
to ten packets as per the standard).
- RTP with FEC: The latency depends upon the size of the correction matrix used and is
calculated as follows: Latency = (2 x L x D) + 10. This latency stems from the column
FEC packets which can be transmitted with a delay of up to 2 x L x D IP packets (as per
the standard) and ten reordering margin packets.
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