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-60 supports up to 100Mbps 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-60
supports up to 45Mbps SMPTE-2022 when a 7 DVB Packet payload exists for each RTP
packet.
TCP ( Transmission Control Protocol ) support, a connection based protocol, has recently
been added at an attempt to overcome some of the fundamental limitations of UDP and RTP.
UDP and RTP are ‘one way street’ types of protocols where the transmitter sends data and
never knows if the data makes it to the destination. TCP streams generally have higher
latency ( takes longer to transmit data and verify data has been transmitted ), but are more
reliable because each packet is accounted for by the receiver. If a packet is lost, the
transmitter will be informed to re-transmit the packet. The transmitter and receiver
continue to communicate about the quality of the reception and attempt to adjust packet
delivery accordingly. The TCP mechanism when combined with large IP receive buffers can
be more forgiving with packet loss, jitter, and out of order packets. The RD-60 supports up
to 15 Mb/s when a 7 DVB Packet payload exists for each TCP packet. Multicast is
not
supported with TCP streams.
The RD-60 supports both unicast ( point to point ) and multicast ( broadcast ) streams. The
RD-60 operates in UDP/RTP mode by default. To setup an IP Rx session, first configure the
IP Rx operation mode. A unit reboot is required (WebUI asks for confirmation when
changing) when changing between UDP/RTP Rx and TCP Rx modes.
