Adtec RD-71 User Manual page 84

UDP / RTP / FEC / TCP IP Rx
The RD-71 supports a number of IP based protocols for the reception of transport streams
via private and public networks. The RD-71 will automatically determine if an IP stream is
UDP, RTP, or a SMPTE-2022 FEC stream. TCP reception is a less common implementation
for transmission of broadcast transport streams, but has recently been added to the RD-71.
UDP ( User Datagram Protocol ) multicast/unicast streams are commonly used for broadcast
transport streams in local or private networks that contain little to no packet loss. UDP
offers no protection against dropped packets or packets received out of order (usually due
to packets taking a different amount of time to traverse network devices). Due to the low
reliability of UDP, it is NOT recommended to be used over the public internet or in
environments where the potential of packet loss, increased jitter, or out of order packets is
high. If packets are lost or received out of order, service anomalies will occur. The RD-71
supports up to 100Mb/s when a 7 DVB Packet payload exists for each UDP packet.
RTP ( Real-time Transport Protocol ) is another type of multicast/unicast stream that is
better to use than UDP in some environments. RTP is built upon the building blocks of UDP,
but adds packet sequence identification. Packet sequencing gives a receiver the information
needed to detect and correct packets that were received 'out of order'. RTP is highly
recommended when timely delivery of each consecutive packet may not be guaranteed.
The RD-71 supports up to 100Mb/s when a 7 DVB Packet payload exists for each RTP
packet.
RTP + FEC or SMPTE-2022 is an additional method used in dealing with lost packets, where
RTP alone can only tolerate packets received out of order. FEC ( Forward Error Correction )
streams add overhead to the overall data rate, but add protection in case of a lost packet.
FEC ( detection and correction of lost packets ) adds latency and data overhead as opposed
to UDP where no protection mechanisms exist. The amount of packet redundancy and
overhead can be configured at the RTP/FEC transmitter. Each multicast/unicast FEC stream
is transmitted on base port N and two FEC streams are sent on N+2 and N+4 respectively.
When receiving FEC streams behind firewalls, please bear in mind that two additional ports (
N+2 and N+4 ) must be allowed through for proper error recovery to occur. The RD-71
supports up to 45Mb/s SMPTE-2022 when a 7 DVB Packet payload exists for each RTP
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