Raptor code over User Datagram Protocol

RC-UDP implements Raptor Coding over UDP transport protocol with tunable overhead.

The package provides two utilities - a RC-UDP Reader (Client) and a RC-UDP Writer (Server). Message encoding/decoding is based on the Raptor fountain code (also called the R10 code) from RFC 5053.

Naming convention

In this package a message means the complete data blob to be transmitted on the wire.
Packet is the UDP packet which includes a single block of the message.
Blocks are the segments which a message is encoded to.

Writer

rcudp.Writer(...) function is a UDP client that uses gofountain Raptor Code encoder to split a message into source blocks. An encoded block together with metadata is marshalled into a UDP packet with following structure:

    MessageID           8 bytes
	NumSourceSymbols    2 bytes
	PaddingSize         2 bytes
	TransferLength      4 bytes
	BlockID             4 bytes
	BlockData        1452 bytes

Note that overall size of a packet is up to 1472 (=1500-8-20) bytes. (default MTU size minus UDP Header size minus IPv4 header size)

The size of a complete wire message is TransferLength - PaddingSize. A limitation is that the code supports a maximum of 8192 source blocks. With current BlockData size of 1452, the maximum length of a message that can be transmitted is 1452*8192 (~11.89 MB)

NumSourceSymbols - K. Must be in the range [4, 8192] (inclusive). This is how many source symbols the input message will be divided into.

Tuning

backoffTimeout (config.go) - defines delay before each UDP socket write. This is intended to reduce the load on both sender and recv udp buffers.

writeBufferSize (config.go) - UDP Sender buffer size can be up to net.core.wmem_max (Linux)

redundancyFactor input param - defines the count of additional encoded blocks to be generated and sent

Reader

UDPReader is a UDP server that collects Raptor fountain code blocks from the wire and makes attempts to decode (recover) the complete and original message. It correlates blocks by MessageID. When a message is decoded, its processing is delegated to the MessageCollector (a callback).

Tuning

staleTimeout - The size of the time-window within which a message should be completely received and decoded. Out of this time-window, the message is marked as stale and deleted.

readBufferSize - UDP Recv buffer size can be up to net.core.rmem_max (Linux)