Forward Error Correction schemes used in Scilla's products

A Forward Error Correcting (FEC) scheme provides methods for correcting packet loss. The advantage with FEC is that it does not require feedback or a return channel and can immediately recover lost packets without having to wait for feedback from the source. This is convenient for broadcast networks with long latency links or any communications connections without an upstream channel, such as satellite links and mobile TV distribution networks.

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FEC schemes help client applications to recover data that is lost in the transmission chain.

FEC Schemes Used in Scilla's Products

Scilla uses the following FEC algorithms in its stream processor, carousels server and base station products.

Generic FEC

Generic FEC (RFC 2733) is engineered for FEC algorithms based on the exclusive-or (parity) operation. The payload format allows end systems to transmit using arbitrary block lengths and parity schemes. It also allows for the recovery of both the payload and critical RTP header fields.

Low Density Parity Check (LDPC)

LDPC is an application layer FEC that uses large block FEC codes as an alternative to small block FEC codes like in Reed-Solomon. The main advantage of such large block codes is the possibility to operate efficiently on source blocks with a size of several tens of thousands of source symbols.

LDCP FEC is offered in Scilla's C2300 Push-VOD Server and FLUTE server; C2400 Filecasting Server.

ProMPEG CoP #3

The Pro-MPEG Code of Practice #3 Release 2 FEC scheme uses the RTP transport protocol as a building block for providing packet recovery in order to ensure reliable real-time media transport on IP networks

Pro-MPEG CoP #3 FEC is standard feature in Scilla products offering TS over RTP as input or as output.

Reed-Solomon

Reed-Solomon error correction is an error-correcting code that works by oversampling a polynomial constructed from the actual data. The polynomial is evaluated at several data points, and these values are sent together with the actual data. Sampling the polynomial more often than is necessary makes the polynomial over-determined. As long as it receives most of the data points correctly, the receiver can recover the original polynomial even in the presence of a few bad data points.

Multi-Protocol Encapsulation uses Reed-Solomon as R-S(255,191,64) to include FEC section into the MPE streams.

The MPEG-2 Transport Stream packet size is 188 bytes. DVB-ASI may add 16 bytes of Reed-Solomon FEC data.

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