1. M. Luby, Digital Fountain
ALC track
M. Luby, Digital Fountain

2. ALC track overall status
ALC PI – RFC 3450 pub as Experimental
LCT BB – RFC 3451 pub as Experimental
FEC BB – RFC pub as Experimental
FEC INFO – RFC 3452 pub as Informational
WEBRC BB – past WG last call – to IESG??
Compact FEC BB
Scoped by the FEC BB
Draft 00
Should go to WG last call soon  Experimental RFC

3. Compact FEC BB A supplement to RFC 3452 (FEC building block)
Introduces two new FEC Encoding IDs
FEC Encoding ID 0 (Fully-specified)
No coding
Useful for interoperability testing
Requested by several entities
FEC Encoding ID 130 (Under-specified)
Similar to FEC Encoding ID 128
More compact payload header
Relaxes requirements from FEC Encoding IDs 128 and 129
Object length not required as part of FEC OTI

4. FEC Payload ID FEC Payload ID for existing 128
| Src. Blk. No | Enc. Sym. ID |
32 bits bits
FEC Payload ID for new 0 and 130
| SrcBlkNo | EncSymID |
16 bits bits

5. FEC Object Transmission Info.
FEC Encoding ID (0 or 130)
FEC Instance ID (only for 130 since it is Under-Specified)
Encoding Symbol Length
Source Block Length
Not the object length (different than RFC 3452)
Allows for delivery of objects of unknown length
May not be able to obtain object length before transmission starts
On-line compression or encryption is used
Transmitted object length != Delivered object length
Object is a stream
Object has no a priori length
Recommend for others when RFC 3452  Proposed Standard

6. FEC Encoding ID 0 Definitions Sender Receiver
L = Encoding Symbol Length (in bytes)
X = Source Block Length (in bytes)
N = X/L rounded up (recommended to be integral)
Source Block consists of N pieces each of length L
Sender
Sender chooses Y randomly in range [0,…,N-1]
Sends carousels pieces Y, Y+1, Y+2, … (mod N)
Receiver
For a Source Block with Source Block Number I, do the following:
Allocate and initializes a boolean array RECEIVED[0,…,N-1] to all false
Allocate a byte array SRCBLK[0,…,N*L-1]
When piece Y arrives:
RECEIVED[Y] is set to true
The piece is placed into bytes SRCBLK[L*Y,…,L*(Y+1)-1]
Source Block I is recovered when RECEIVED[0,…,N-1] are all true

7. Available FEC codes Fully-Specified Under-Specified
No Coding (FEC Encoding ID 0)
Under-Specified
Luigi Rizzo’s implementation of Reed-Solomon codes
Embedded Fountain Core Technology
Digital Fountain’s most powerful encoder/decoder
Development and Product License programs