Welcome to my Blog on the IP Transport of Video! In the next several posts I'll be looking closely at the granular difference between various methods used in the transport of video over IP. I will also offer a comparison of how VideoFlow uniquely applies and combines these different features and tools to assure successful and reliable Video Transport, regardless of circumstances.
FEC (SMPTE 2022 -1 & 2)
SMPTE 2022-1/2 based Forward Error Correction, developed by the Society of Motion Picture and Television Engineers, compensates for data lost while traversing a unidirectional IP network due to network conditions, including packet loss and the variations in the transport path that a packet may take in order to reach the destination. FEC is very helpful in recreating missing information at the destination without the need for re-requesting duplicate data be delivered. The FEC works on the concept of a XOR operation between several packets and creation of a reference packet that is transmitted in parallel to the stream. The reference packet may then be used by the receiver to recover a single packet out of the original XOR operation. The receiver must continuously calculate the reference packet, calculating it at all times. The receiving side must buffer the incoming stream and wait for a certain amount of FEC reference packets in order to start the recovery process. FEC requires computationally intensive processing at the reception-end, which can increase latency, and requires additional transmission bandwidth, due to the requirement of the increased data necessary to compute and recreate what data might be missing at the distant-end. Many studies have demonstrated that the main drawback of FEC is that the added overhead can increase the total bandwidth of the stream by 25-30% (in some configurations can be even higher) yet achieves no more than 3-5% error recovery.
VideoFlow Specific:
While VideoFlow does contain FEC as a User-activated option and can accommodate FEC-enabled Transport Streams, most of the content delivered using VideoFlow DVP technology never requires implementation of Forward Error Correction. One driving consideration is the importance of keeping the total bandwidth of the overall Transport Stream as low as possible.
One implementation of FEC that can be useful includes instances where the unprotected Transport Stream being ingested into VideoFlow is suffering from missing or errored packets. FEC can be enabled within the VideoFlow instance and on the sending device, to allow VideoFlow to apply FEC calculations to rebuild the missing data on streams being ingested by VideoFlow but are not yet able to be protected by the VideoFlow DVP technology. The result is a clean ingest of the source data stream into VideoFlow, for Protected Transport and other DVP applications.