Network Working Group M. Luby
Request for Comments: 5053 Digital Fountain
Category: Standards Track 
A. Shokrollahi
EPFL
M. Watson
Digital Fountain
T. Stockhammer
Nomor Research
October 2007
Raptor Forward Error Correction Scheme for Object Delivery
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document describes a Fully-Specified Forward Error Correction
(FEC) scheme, corresponding to FEC Encoding ID 1, for the Raptor
forward error correction code and its application to reliable
delivery of data objects.
Raptor is a fountain code, i.e., as many encoding symbols as needed
can be generated by the encoder on-the-fly from the source symbols of
a source block of data. The decoder is able to recover the source
block from any set of encoding symbols only slightly more in number
than the number of source symbols.
The Raptor code described here is a systematic code, meaning that all
the source symbols are among the encoding symbols that can be
generated.
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RFC 5053 Raptor FEC Scheme October 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 3
3. Formats and Codes . . . . . . . . . . . . . . . . . . . . . . 3
3.1. FEC Payload IDs . . . . . . . . . . . . . . . . . . . . . 3
3.2. FEC Object Transmission Information (OTI) . . . . . . . . 4
3.2.1. Mandatory . . . . . . . . . . . . . . . . . . . . . . 4
3.2.2. Common . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2.3. Scheme-Specific . . . . . . . . . . . . . . . . . . . 5
4. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Content Delivery Protocol Requirements . . . . . . . . . . 5
4.2. Example Parameter Derivation Algorithm . . . . . . . . . . 6
5. Raptor FEC Code Specification . . . . . . . . . . . . . . . . 8
5.1. Definitions, Symbols, and Abbreviations . . . . . . . . . 8
5.1.1. Definitions . . . . . . . . . . . . . . . . . . . . . 8
5.1.2. Symbols . . . . . . . . . . . . . . . . . . . . . . . 9
5.1.3. Abbreviations . . . . . . . . . . . . . . . . . . . . 11
5.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.3. Object Delivery . . . . . . . . . . . . . . . . . . . . . 12
5.3.1. Source Block Construction . . . . . . . . . . . . . . 12
5.3.2. Encoding Packet Construction . . . . . . . . . . . . . 14
5.4. Systematic Raptor Encoder . . . . . . . . . . . . . . . . 15
5.4.1. Encoding Overview . . . . . . . . . . . . . . . . . . 15
5.4.2. First Encoding Step: Intermediate Symbol Generation . 16
5.4.3. Second Encoding Step: LT Encoding . . . . . . . . . . 20
5.4.4. Generators . . . . . . . . . . . . . . . . . . . . . . 21
5.5. Example FEC Decoder . . . . . . . . . . . . . . . . . . . 23
5.5.1. General . . . . . . . . . . . . . . . . . . . . . . . 23
5.5.2. Decoding a Source Block . . . . . . . . . . . . . . . 23
5.6. Random Numbers . . . . . . . . . . . . . . . . . . . . . . 28
5.6.1. The Table V0 . . . . . . . . . . . . . . . . . . . . . 28
5.6.2. The Table V1 . . . . . . . . . . . . . . . . . . . . . 29
5.7. Systematic Indices J(K) . . . . . . . . . . . . . . . . . 30
6. Security Considerations . . . . . . . . . . . . . . . . . . . 43
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . . . 44
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RFC 5053 Raptor FEC Scheme October 2007
1. Introduction
This document specifies an FEC Scheme for the Raptor forward error
correction code for object delivery applications. The concept of an
FEC Scheme is defined in [RFC 5052] and this document follows the
format prescribed there and uses the terminology of that document.
Raptor Codes were introduced in [Raptor]. For an overview, see, for
example, [CCNC].
The Raptor FEC Scheme is a Fully-Specified FEC Scheme corresponding
to FEC Encoding ID 1.
Raptor is a fountain code, i.e., as many encoding symbols as needed
can be generated by the encoder on-the-fly from the source symbols of
a block. The decoder is able to recover the source block from any
set of encoding symbols only slightly more in number than the number
of source symbols.
The code described in this document is a systematic code, that is,
the original source symbols can be sent unmodified from sender to
receiver, as well as a number of repair symbols. For more background
on the use of Forward Error Correction codes in reliable multicast,
see [RFC 3453].
The code described here is identical to that described in [MBMS].
2. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC 2119].
3. Formats and Codes
3.1. FEC Payload IDs
The FEC Payload ID MUST be a 4 octet field defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Number | Encoding Symbol ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: FEC Payload ID format
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RFC 5053 Raptor FEC Scheme October 2007
Source Block Number (SBN), (16 bits): An integer identifier for
the source block that the encoding symbols within the packet
relate to.
Encoding Symbol ID (ESI), (16 bits): An integer identifier for the
encoding symbols within the packet.
The interpretation of the Source Block Number and Encoding Symbol
Identifier is defined in Section 5.
3.2. FEC Object Transmission Information (OTI)
3.2.1. Mandatory
The value of the FEC Encoding ID MUST be 1 (one), as assigned by IANA
(see Section 7).
3.2.2. Common
The Common FEC Object Transmission Information elements used by this
FEC Scheme are:
- Transfer Length (F)
- Encoding Symbol Length (T)
The Transfer Length is a non-negative integer less than 2^^45. The
Encoding Symbol Length is a non-negative integer less than 2^^16.
The encoded Common FEC Object Transmission Information format is
shown in Figure 2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transfer Length |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoding Symbol Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Encoded Common FEC OTI for Raptor FEC Scheme
NOTE 1: The limit of 2^^45 on the transfer length is a consequence
of the limitation on the symbol size to 2^^16-1, the limitation on
the number of symbols in a source block to 2^^13, and the
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RFC 5053 Raptor FEC Scheme October 2007
limitation on the number of source blocks to 2^^16. However, the
Transfer Length is encoded as a 48-bit field for simplicity.
3.2.3. Scheme-Specific
The following parameters are carried in the Scheme-Specific FEC
Object Transmission Information element for this FEC Scheme:
- The number of source blocks (Z)
- The number of sub-blocks (N)
- A symbol alignment parameter (Al)
These parameters are all non-negative integers. The encoded Scheme-
specific Object Transmission Information is a 4-octet field
consisting of the parameters Z (2 octets), N (1 octet), and Al (1
octet) as shown in Figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Z | N | Al |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Encoded Scheme-Specific FEC Object Transmission Information
The encoded FEC Object Transmission Information is a 14-octet field
consisting of the concatenation of the encoded Common FEC Object
Transmission Information and the encoded Scheme-Specific FEC Object
Transmission Information.
These three parameters define the source block partitioning as
described in Section 5.3.1.2.
4. Procedures
4.1. Content Delivery Protocol Requirements
This section describes the information exchange between the Raptor
FEC Scheme and any Content Delivery Protocol (CDP) that makes use of
the Raptor FEC Scheme for object delivery.
The Raptor encoder and decoder for object delivery require the
following information from the CDP:
- The transfer length of the object, F, in bytes
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- A symbol alignment parameter, Al
- The symbol size, T, in bytes, which MUST be a multiple of Al
- The number of source blocks, Z
- The number of sub-blocks in each source block, N
The Raptor encoder for object delivery additionally requires:
- the object to be encoded, F bytes
The Raptor encoder supplies the CDP with the following information
for each packet to be sent:
- Source Block Number (SBN)
- Encoding Symbol ID (ESI)
- Encoding symbol(s)
The CDP MUST communicate this information to the receiver.
4.2. Example Parameter Derivation Algorithm
This section provides recommendations for the derivation of the three
transport parameters, T, Z, and N. This recommendation is based on
the following input parameters:
- F the transfer length of the object, in bytes
- W a target on the sub-block size, in bytes
- P the maximum packet payload size, in bytes, which is assumed to
be a multiple of Al
- Al the symbol alignment parameter, in bytes
- Kmax the maximum number of source symbols per source block.
Note: Section 5.1.2 defines Kmax to be 8192.
- Kmin a minimum target on the number of symbols per source block
- Gmax a maximum target number of symbols per packet
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Based on the above inputs, the transport parameters T, Z, and N are
calculated as follows:
Let
G = min{ceil(P*Kmin/F), P/Al, Gmax}
T = floor(P/(Al*G))*Al
Kt = ceil(F/T)
Z = ceil(Kt/Kmax)
N = min{ceil(ceil(Kt/Z)*T/W), T/Al}
The value G represents the maximum number of symbols to be
transported in a single packet. The value Kt is the total number of
symbols required to represent the source data of the object. The
values of G and N derived above should be considered as lower bounds.
It may be advantageous to increase these values, for example, to the
nearest power of two. In particular, the above algorithm does not
guarantee that the symbol size, T, divides the maximum packet size,
P, and so it may not be possible to use the packets of size exactly
P. If, instead, G is chosen to be a value that divides P/Al, then
the symbol size, T, will be a divisor of P and packets of size P can
be used.
The algorithm above and that defined in Section 5.3.1.2 ensure that
the sub-symbol sizes are a multiple of the symbol alignment
parameter, Al. This is useful because the XOR operations used for
encoding and decoding are generally performed several bytes at a
time, for example, at least 4 bytes at a time on a 32-bit processor.
Thus, the encoding and decoding can be performed faster if the sub-
symbol sizes are a multiple of this number of bytes.
Recommended settings for the input parameters, Al, Kmin, and Gmax are
as follows: Al = 4, Kmin = 1024, Gmax = 10.
The parameter W can be used to generate encoded data that can be
decoded efficiently with limited working memory at the decoder. Note
that the actual maximum decoder memory requirement for a given value
of W depends on the implementation, but it is possible to implement
decoding using working memory only slightly larger than W.
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5. Raptor FEC Code Specification
5.1. Definitions, Symbols, and Abbreviations
5.1.1. Definitions
For the purposes of this specification, the following terms and
definitions apply.
Source block: a block of K source symbols that are considered
together for Raptor encoding purposes.
Source symbol: the smallest unit of data used during the encoding
process. All source symbols within a source block have the same
size.
Encoding symbol: a symbol that is included in a data packet. The
encoding symbols consist of the source symbols and the repair
symbols. Repair symbols generated from a source block have the
same size as the source symbols of that source block.
Systematic code: a code in which all the source symbols may be
included as part of the encoding symbols sent for a source block.
Repair symbol: the encoding symbols sent for a source block that
are not the source symbols. The repair symbols are generated
based on the source symbols.
Intermediate symbols: symbols generated from the source symbols
using an inverse encoding process . The repair symbols are then
generated directly from the intermediate symbols. The encoding
symbols do not include the intermediate symbols, i.e.,
intermediate symbols are not included in data packets.
Symbol: a unit of data. The size, in bytes, of a symbol is known
as the symbol size.
Encoding symbol group: a group of encoding symbols that are sent
together, i.e., within the same packet whose relationship to the
source symbols can be derived from a single Encoding Symbol ID.
Encoding Symbol ID: information that defines the relationship
between the symbols of an encoding symbol group and the source
symbols.
Encoding packet: data packets that contain encoding symbols
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Sub-block: a source block is sometimes broken into sub-blocks,
each of which is sufficiently small to be decoded in working
memory. For a source block consisting of K source symbols, each
sub-block consists of K sub-symbols, each symbol of the source
block being composed of one sub-symbol from each sub-block.
Sub-symbol: part of a symbol. Each source symbol is composed of
as many sub-symbols as there are sub-blocks in the source block.
Source packet: data packets that contain source symbols.
Repair packet: data packets that contain repair symbols.
5.1.2. Symbols
i, j, x, h, a, b, d, v, m represent positive integers.
ceil(x) denotes the smallest positive integer that is greater than
or equal to x.
choose(i,j) denotes the number of ways j objects can be chosen from
among i objects without repetition.
floor(x) denotes the largest positive integer that is less than or
equal to x.
i % j denotes i modulo j.
X ^ Y denotes, for equal-length bit strings X and Y, the bitwise
exclusive-or of X and Y.
Al denotes a symbol alignment parameter. Symbol and sub-symbol
sizes are restricted to be multiples of Al.
A denotes a matrix over GF(2).
Transpose[A] denotes the transposed matrix of matrix A.
A^^-1 denotes the inverse matrix of matrix A.
K denotes the number of symbols in a single source block.
Kmax denotes the maximum number of source symbols that can be in a
single source block. Set to 8192.
L denotes the number of pre-coding symbols for a single source
block.
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S denotes the number of LDPC symbols for a single source block.
H denotes the number of Half symbols for a single source block.
C denotes an array of intermediate symbols, C[0], C[1], C[2],...,
C[L-1].
C' denotes an array of source symbols, C'[0], C'[1], C'[2],...,
C'[K-1].
X a non-negative integer value
V0, V1 two arrays of 4-byte integers, V0[0], V0[1],..., V0[255] and
V1[0], V1[1],..., V1[255]
Rand[X, i, m] a pseudo-random number generator
Deg[v] a degree generator
LTEnc[K, C ,(d, a, b)] a LT encoding symbol generator
Trip[K, X] a triple generator function
G the number of symbols within an encoding symbol group
GF(n) the Galois field with n elements.
N the number of sub-blocks within a source block
T the symbol size in bytes. If the source block is partitioned
into sub-blocks, then T = T'*N.
T' the sub-symbol size, in bytes. If the source block is not
partitioned into sub-blocks, then T' is not relevant.
F the transfer length of an object, in bytes
I the sub-block size in bytes
P for object delivery, the payload size of each packet, in bytes,
that is used in the recommended derivation of the object
delivery transport parameters.
Q Q = 65521, i.e., Q is the largest prime smaller than 2^^16
Z the number of source blocks, for object delivery
J(K) the systematic index associated with K
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RFC 5053 Raptor FEC Scheme October 2007
I_S denotes the SxS identity matrix.
0_SxH denotes the SxH zero matrix.
a ^^ b a raised to the power b
5.1.3. Abbreviations
For the purposes of the present document, the following abbreviations
apply:
ESI Encoding Symbol ID
LDPC Low Density Parity Check
LT Luby Transform
SBN Source Block Number
SBL Source Block Length (in units of symbols)
5.2. Overview
The principal component of the systematic Raptor code is the basic
encoder described in Section 5.4. First, it is described how to
derive values for a set of intermediate symbols from the original
source symbols such that knowledge of the intermediate symbols is
sufficient to reconstruct the source symbols. Secondly, the encoder
produces repair symbols, which are each the exclusive OR of a number
of the intermediate symbols. The encoding symbols are the
combination of the source and repair symbols. The repair symbols are
produced in such a way that the intermediate symbols, and therefore
also the source symbols, can be recovered from any sufficiently large
set of encoding symbols.
This document specifies the systematic Raptor code encoder. A number
of possible decoding algorithms are possible. An efficient decoding
algorithm is provided in Section 5.5.
The construction of the intermediate and repair symbols is based in
part on a pseudo-random number generator described in
Section 5.4.4.1. This generator is based on a fixed set of 512
random numbers that MUST be available to both sender and receiver.
These are provided in Section 5.6.
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RFC 5053 Raptor FEC Scheme October 2007
Finally, the construction of the intermediate symbols from the source
symbols is governed by a 'systematic index', values of which are
provided in Section 5.7 for source block sizes from 4 source symbols
to Kmax = 8192 source symbols.
5.3. Object Delivery
5.3.1. Source Block Construction
5.3.1.1. General
In order to apply the Raptor encoder to a source object, the object
may be broken into Z >= 1 blocks, known as source blocks. The Raptor
encoder is applied independently to each source block. Each source
block is identified by a unique integer Source Block Number (SBN),
where the first source block has SBN zero, the second has SBN one,
etc. Each source block is divided into a number, K, of source
symbols of size T bytes each. Each source symbol is identified by a
unique integer Encoding Symbol Identifier (ESI), where the first
source symbol of a source block has ESI zero, the second has ESI one,
etc.
Each source block with K source symbols is divided into N >= 1 sub-
blocks, which are small enough to be decoded in the working memory.
Each sub-block is divided into K sub-symbols of size T'.
Note that the value of K is not necessarily the same for each source
block of an object and the value of T' may not necessarily be the
same for each sub-block of a source block. However, the symbol size
T is the same for all source blocks of an object and the number of
symbols, K, is the same for every sub-block of a source block. Exact
partitioning of the object into source blocks and sub-blocks is
described in Section 5.3.1.2 below.
5.3.1.2. Source Block and Sub-Block Partitioning
The construction of source blocks and sub-blocks is determined based
on five input parameters, F, Al, T, Z, and N, and a function
Partition[]. The five input parameters are defined as follows:
- F the transfer length of the object, in bytes
- Al a symbol alignment parameter, in bytes
- T the symbol size, in bytes, which MUST be a multiple of Al
- Z the number of source blocks
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RFC 5053 Raptor FEC Scheme October 2007
- N the number of sub-blocks in each source block
These parameters MUST be set so that ceil(ceil(F/T)/Z) <= Kmax.
Recommendations for derivation of these parameters are provided in
Section 4.2.
The function Partition[] takes a pair of integers (I, J) as input and
derives four integers (IL, IS, JL, JS) as output. Specifically, the
value of Partition[I, J] is a sequence of four integers (IL, IS, JL,
JS), where IL = ceil(I/J), IS = floor(I/J), JL = I - IS * J, and JS =
J - JL. Partition[] derives parameters for partitioning a block of
size I into J approximately equal-sized blocks. Specifically, JL
blocks of length IL and JS blocks of length IS.
The source object MUST be partitioned into source blocks and sub-
blocks as follows:
Let
Kt = ceil(F/T)
(KL, KS, ZL, ZS) = Partition[Kt, Z]
(TL, TS, NL, NS) = Partition[T/Al, N]
Then, the object MUST be partitioned into Z = ZL + ZS contiguous
source blocks, the first ZL source blocks each having length KL*T
bytes, and the remaining ZS source blocks each having KS*T bytes.
If Kt*T > F, then for encoding purposes, the last symbol MUST be
padded at the end with Kt*T - F zero bytes.
Next, each source block MUST be divided into N = NL + NS contiguous
sub-blocks, the first NL sub-blocks each consisting of K contiguous
sub-symbols of size of TL*Al and the remaining NS sub-blocks each
consisting of K contiguous sub-symbols of size of TS*Al. The symbol
alignment parameter Al ensures that sub-symbols are always a multiple
of Al bytes.
Finally, the m-th symbol of a source block consists of the
concatenation of the m-th sub-symbol from each of the N sub-blocks.
Note that this implies that when N > 1, then a symbol is NOT a
contiguous portion of the object.
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5.3.2. Encoding Packet Construction
Each encoding packet contains the following information:
- Source Block Number (SBN)
- Encoding Symbol ID (ESI)
- encoding symbol(s)
Each source block is encoded independently of the others. Source
blocks are numbered consecutively from zero.
Encoding Symbol ID values from 0 to K-1 identify the source symbols
of a source block in sequential order, where K is the number of
symbols in the source block. Encoding Symbol IDs from K onwards
identify repair symbols.
Each encoding packet either consists entirely of source symbols
(source packet) or entirely of repair symbols (repair packet). A
packet may contain any number of symbols from the same source block.
In the case that the last source symbol in a source packet includes
padding bytes added for FEC encoding purposes, then these bytes need
not be included in the packet. Otherwise, only whole symbols MUST be
included.
The Encoding Symbol ID, X, carried in each source packet is the
Encoding Symbol ID of the first source symbol carried in that packet.
The subsequent source symbols in the packet have Encoding Symbol IDs,
X+1 to X+G-1, in sequential order, where G is the number of symbols
in the packet.
Similarly, the Encoding Symbol ID, X, placed into a repair packet is
the Encoding Symbol ID of the first repair symbol in the repair
packet and the subsequent repair symbols in the packet have Encoding
Symbol IDs X+1 to X+G-1 in sequential order, where G is the number of
symbols in the packet.
Note that it is not necessary for the receiver to know the total
number of repair packets.
Associated with each symbol is a triple of integers (d, a, b).
The G repair symbol triples (d[0], a[0], b[0]),..., (d[G-1], a[G-1],
b[G-1]) for the repair symbols placed into a repair packet with ESI X
are computed using the Triple generator defined in Section 5.4.4.4 as
follows:
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For each i = 0, ..., G-1, (d[i], a[i], b[i]) = Trip[K,X+i]
The G repair symbols to be placed in repair packet with ESI X are
calculated based on the repair symbol triples, as described in
Section 5.4, using the intermediate symbols C and the LT encoder
LTEnc[K, C, (d[i], a[i], b[i])].
5.4. Systematic Raptor Encoder
5.4.1. Encoding Overview
The systematic Raptor encoder is used to generate repair symbols from
a source block that consists of K source symbols.
Symbols are the fundamental data units of the encoding and decoding
process. For each source block (sub-block), all symbols (sub-
symbols) are the same size. The atomic operation performed on
symbols (sub-symbols) for both encoding and decoding is the
exclusive-or operation.
Let C'[0],..., C'[K-1] denote the K source symbols.
Let C[0],..., C[L-1] denote L intermediate symbols.
The first step of encoding is to generate a number, L > K, of
intermediate symbols from the K source symbols. In this step, K
source symbol triples (d[0], a[0], b[0]), ..., (d[K-1], a[K-1],
b[K-1]) are generated using the Trip[] generator as described in
Section 5.4.2.2. The K source symbol triples are associated with the
K source symbols and are then used to determine the L intermediate
symbols C[0],..., C[L-1] from the source symbols using an inverse
encoding process. This process can be realized by a Raptor decoding
process.
Certain "pre-coding relationships" MUST hold within the L
intermediate symbols. Section 5.4.2.3 describes these relationships
and how the intermediate symbols are generated from the source
symbols.
Once the intermediate symbols have been generated, repair symbols are
produced and one or more repair symbols are placed as a group into a
single data packet. Each repair symbol group is associated with an
Encoding Symbol ID (ESI) and a number, G, of repair symbols. The ESI
is used to generate a triple of three integers, (d, a, b) for each
repair symbol, again using the Trip[] generator as described in
Section 5.4.4.4. Then, each (d,a,b)-triple is used to generate the
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RFC 5053 Raptor FEC Scheme October 2007
corresponding repair symbol from the intermediate symbols using the
LTEnc[K, C[0],..., C[L-1], (d,a,b)] generator described in
Section 5.4.4.3.
5.4.2. First Encoding Step: Intermediate Symbol Generation
5.4.2.1. General
The first encoding step is a pre-coding step to generate the L
intermediate symbols C[0], ..., C[L-1] from the source symbols C'[0],
..., C'[K-1]. The intermediate symbols are uniquely defined by two
sets of constraints:
1. The intermediate symbols are related to the source symbols by
a set of source symbol triples. The generation of the source
symbol triples is defined in Section 5.4.2.2 using the Trip[]
generator described in Section 5.4.4.4.
2. A set of pre-coding relationships hold within the intermediate
symbols themselves. These are defined in Section 5.4.2.3.
The generation of the L intermediate symbols is then defined in
Section 5.4.2.4
5.4.2.2. Source Symbol Triples
Each of the K source symbols is associated with a triple (d[i], a[i],
b[i]) for 0 <= i < K. The source symbol triples are determined using
the Triple generator defined in Section 5.4.4.4 as:
For each i, 0 <= i < K
(d[i], a[i], b[i]) = Trip[K, i]
5.4.2.3. Pre-Coding Relationships
The pre-coding relationships amongst the L intermediate symbols are
defined by expressing the last L-K intermediate symbols in terms of
the first K intermediate symbols.
The last L-K intermediate symbols C[K],...,C[L-1] consist of S LDPC
symbols and H Half symbols The values of S and H are determined from
K as described below. Then L = K+S+H.
Luby, et al. Standards Track PAGE 16
RFC 5053 Raptor FEC Scheme October 2007
Let
X be the smallest positive integer such that X*(X-1) >= 2*K.
S be the smallest prime integer such that S >= ceil(0.01*K) + X
H be the smallest integer such that choose(H,ceil(H/2)) >= K + S
H' = ceil(H/2)
L = K+S+H
C[0],...,C[K-1] denote the first K intermediate symbols
C[K],...,C[K+S-1] denote the S LDPC symbols, initialised to zero
C[K+S],...,C[L-1] denote the H Half symbols, initialised to zero
The S LDPC symbols are defined to be the values of C[K],...,C[K+S-1]
at the end of the following process:
For i = 0,...,K-1 do
a = 1 + (floor(i/S) % (S-1))
b = i % S
C[K + b] = C[K + b] ^ C[i]
b = (b + a) % S
C[K + b] = C[K + b] ^ C[i]
b = (b + a) % S
C[K + b] = C[K + b] ^ C[i]
The H Half symbols are defined as follows:
Let
g[i] = i ^ (floor(i/2)) for all positive integers i
Note: g[i] is the Gray sequence, in which each element differs
from the previous one in a single bit position
m[k] denote the subsequence of g[.] whose elements have exactly k
non-zero bits in their binary representation.
Luby, et al. Standards Track PAGE 17
RFC 5053 Raptor FEC Scheme October 2007
m[j,k] denote the jth element of the sequence m[k], where j=0, 1,
2, ...
Then, the Half symbols are defined as the values of C[K+S],...,C[L-1]
after the following process:
For h = 0,...,H-1 do
For j = 0,...,K+S-1 do
If bit h of m[j,H'] is equal to 1 then C[h+K+S] = C[h+K+S] ^
C[j].
5.4.2.4. Intermediate Symbols
5.4.2.4.1. Definition
Given the K source symbols C'[0], C'[1],..., C'[K-1] the L
intermediate symbols C[0], C[1],..., C[L-1] are the uniquely defined
symbol values that satisfy the following conditions:
1. The K source symbols C'[0], C'[1],..., C'[K-1] satisfy the K
constraints
C'[i] = LTEnc[K, (C[0],..., C[L-1]), (d[i], a[i], b[i])], for
all i, 0 <= i < K.
2. The L intermediate symbols C[0], C[1],..., C[L-1] satisfy the
pre-coding relationships defined in Section 5.4.2.3.
5.4.2.4.2. Example Method for Calculation of Intermediate Symbols
This subsection describes a possible method for calculation of the L
intermediate symbols C[0], C[1],..., C[L-1] satisfying the
constraints in Section 5.4.2.4.1.
The 'generator matrix' for a code that generates N output symbols
from K input symbols is an NxK matrix over GF(2), where each row
corresponds to one of the output symbols and each column to one of
the input symbols and where the ith output symbol is equal to the sum
of those input symbols whose column contains a non-zero entry in row
i.
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RFC 5053 Raptor FEC Scheme October 2007
Then, the L intermediate symbols can be calculated as follows:
Let
C denote the column vector of the L intermediate symbols, C[0],
C[1],..., C[L-1].
D denote the column vector consisting of S+H zero symbols followed
by the K source symbols C'[0], C'[1], ..., C'[K-1]
Then the above constraints define an LxL matrix over GF(2), A, such
that:
A*C = D
The matrix A can be constructed as follows:
Let:
G_LDPC be the S x K generator matrix of the LDPC symbols. So,
G_LDPC * Transpose[(C[0],...., C[K-1])] = Transpose[(C[K], ...,
C[K+S-1])]
G_Half be the H x (K+S) generator matrix of the Half symbols, So,
G_Half * Transpose[(C[0], ..., C[S+K-1])] = Transpose[(C[K+S],
..., C[K+S+H-1])]
I_S be the S x S identity matrix
I_H be the H x H identity matrix
0_SxH be the S x H zero matrix
G_LT be the KxL generator matrix of the encoding symbols generated
by the LT Encoder. So,
G_LT * Transpose[(C[0], ..., C[L-1])] =
Transpose[(C'[0],C'[1],...,C'[K-1])]
i.e., G_LT(i,j) = 1 if and only if C[j] is included in the
symbols that are XORed to produce LTEnc[K, (C[0], ..., C[L-1]),
(d[i], a[i], b[i])].
Then:
The first S rows of A are equal to G_LDPC | I_S | 0_SxH.
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RFC 5053 Raptor FEC Scheme October 2007
The next H rows of A are equal to G_Half | I_H.
The remaining K rows of A are equal to G_LT.
The matrix A is depicted in Figure 4 below:
K S H
+-----------------------+-------+-------+
| | | |
S | G_LDPC | I_S | 0_SxH |
| | | |
+-----------------------+-------+-------+
| | |
H | G_Half | I_H |
| | |
+-------------------------------+-------+
| |
| |
K | G_LT |
| |
| |
+---------------------------------------+
Figure 4: The matrix A
The intermediate symbols can then be calculated as:
C = (A^^-1)*D
The source symbol triples are generated such that for any K matrix, A
has full rank and is therefore invertible. This calculation can be
realized by applying a Raptor decoding process to the K source
symbols C'[0], C'[1],..., C'[K-1] to produce the L intermediate
symbols C[0], C[1],..., C[L-1].
To efficiently generate the intermediate symbols from the source
symbols, it is recommended that an efficient decoder implementation
such as that described in Section 5.5 be used. The source symbol
triples are designed to facilitate efficient decoding of the source
symbols using that algorithm.
5.4.3. Second Encoding Step: LT Encoding
In the second encoding step, the repair symbol with ESI X is
generated by applying the generator LTEnc[K, (C[0], C[1],...,
C[L-1]), (d, a, b)] defined in Section 5.4.4.3 to the L intermediate
symbols C[0], C[1],..., C[L-1] using the triple (d, a, b)=Trip[K,X]
generated according to Section 5.3.2
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RFC 5053 Raptor FEC Scheme October 2007
5.4.4. Generators
5.4.4.1. Random Generator
The random number generator Rand[X, i, m] is defined as follows,
where X is a non-negative integer, i is a non-negative integer, and m
is a positive integer and the value produced is an integer between 0
and m-1. Let V0 and V1 be arrays of 256 entries each, where each
entry is a 4-byte unsigned integer. These arrays are provided in
Section 5.6.
Then,
Rand[X, i, m] = (V0[(X + i) % 256] ^ V1[(floor(X/256)+ i) % 256])
% m
5.4.4.2. Degree Generator
The degree generator Deg[v] is defined as follows, where v is an
integer that is at least 0 and less than 2^^20 = 1048576.
In Table 1, find the index j such that f[j-1] <= v < f[j]
Then, Deg[v] = d[j]
+---------+---------+------+
| Index j | f[j] | d[j] |
+---------+---------+------+
| 0 | 0 | -- |
| 1 | 10241 | 1 |
| 2 | 491582 | 2 |
| 3 | 712794 | 3 |
| 4 | 831695 | 4 |
| 5 | 948446 | 10 |
| 6 | 1032189 | 11 |
| 7 | 1048576 | 40 |
+---------+---------+------+
Table 1: Defines the degree distribution for encoding symbols
5.4.4.3. LT Encoding Symbol Generator
The encoding symbol generator LTEnc[K, (C[0], C[1],..., C[L-1]), (d,
a, b)] takes the following inputs:
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RFC 5053 Raptor FEC Scheme October 2007
K is the number of source symbols (or sub-symbols) for the source
block (sub-block). Let L be derived from K as described in
Section 5.4.2.3, and let L' be the smallest prime integer greater
than or equal to L.
(C[0], C[1],..., C[L-1]) is the array of L intermediate symbols
(sub-symbols) generated as described in Section 5.4.2.4.
(d, a, b) is a source triple determined using the Triple generator
defined in Section 5.4.4.4, whereby
d is an integer denoting an encoding symbol degree
a is an integer between 1 and L'-1 inclusive
b is an integer between 0 and L'-1 inclusive
The encoding symbol generator produces a single encoding symbol as
output, according to the following algorithm:
While (b >= L) do b = (b + a) % L'
Let result = C[b].
For j = 1,...,min(d-1,L-1) do
b = (b + a) % L'
While (b >= L) do b = (b + a) % L'
result = result ^ C[b]
Return result
5.4.4.4. Triple Generator
The triple generator Trip[K,X] takes the following inputs:
K - The number of source symbols
X - An encoding symbol ID
Let
L be determined from K as described in Section 5.4.2.3
L' be the smallest prime that is greater than or equal to L
Luby, et al. Standards Track PAGE 22
RFC 5053 Raptor FEC Scheme October 2007
Q = 65521, the largest prime smaller than 2^^16.
J(K) be the systematic index associated with K, as defined in
Section 5.7.
The output of the triple generator is a triple, (d, a, b) determined
as follows:
A = (53591 + J(K)*997) % Q
B = 10267*(J(K)+1) % Q
Y = (B + X*A) % Q
v = Rand[Y, 0, 2^^20]
d = Deg[v]
a = 1 + Rand[Y, 1, L'-1]
b = Rand[Y, 2, L']
5.5. Example FEC Decoder
5.5.1. General
This section describes an efficient decoding algorithm for the Raptor
codes described in this specification. Note that each received
encoding symbol can be considered as the value of an equation amongst
the intermediate symbols. From these simultaneous equations, and the
known pre-coding relationships amongst the intermediate symbols, any
algorithm for solving simultaneous equations can successfully decode
the intermediate symbols and hence the source symbols. However, the
algorithm chosen has a major effect on the computational efficiency
of the decoding.
5.5.2. Decoding a Source Block
5.5.2.1. General
It is assumed that the decoder knows the structure of the source
block it is to decode, including the symbol size, T, and the number K
of symbols in the source block.
From the algorithms described in Section 5.4, the Raptor decoder can
calculate the total number L = K+S+H of pre-coding symbols and
determine how they were generated from the source block to be
decoded. In this description, it is assumed that the received
Luby, et al. Standards Track PAGE 23
RFC 5053 Raptor FEC Scheme October 2007
encoding symbols for the source block to be decoded are passed to the
decoder. Note that, as described in Section 5.3.2, the last source
symbol of a source packet may have included padding bytes added for
FEC encoding purposes. These padding bytes may not be actually
included in the packet sent and so must be reinserted at the received
before passing the symbol to the decoder.
For each such encoding symbol, it is assumed that the number and set
of intermediate symbols whose exclusive-or is equal to the encoding
symbol is also passed to the decoder. In the case of source symbols,
the source symbol triples described in Section 5.4.2.2 indicate the
number and set of intermediate symbols that sum to give each source
symbol.
Let N >= K be the number of received encoding symbols for a source
block and let M = S+H+N. The following M by L bit matrix A can be
derived from the information passed to the decoder for the source
block to be decoded. Let C be the column vector of the L
intermediate symbols, and let D be the column vector of M symbols
with values known to the receiver, where the first S+H of the M
symbols are zero-valued symbols that correspond to LDPC and Half
symbols (these are check symbols for the LDPC and Half symbols, and
not the LDPC and Half symbols themselves), and the remaining N of the
M symbols are the received encoding symbols for the source block.
Then, A is the bit matrix that satisfies A*C = D, where here *
denotes matrix multiplication over GF[2]. In particular, A[i,j] = 1
if the intermediate symbol corresponding to index j is exclusive-ORed
into the LDPC, Half, or encoding symbol corresponding to index i in
the encoding, or if index i corresponds to a LDPC or Half symbol and
index j corresponds to the same LDPC or Half symbol. For all other i
and j, A[i,j] = 0.
Decoding a source block is equivalent to decoding C from known A and
D. It is clear that C can be decoded if and only if the rank of A
over GF[2] is L. Once C has been decoded, missing source symbols can
be obtained by using the source symbol triples to determine the
number and set of intermediate symbols that MUST be exclusive-ORed to
obtain each missing source symbol.
The first step in decoding C is to form a decoding schedule. In this
step A is converted, using Gaussian elimination (using row operations
and row and column reorderings) and after discarding M - L rows, into
the L by L identity matrix. The decoding schedule consists of the
sequence of row operations and row and column reorderings during the
Gaussian elimination process, and only depends on A and not on D.
The decoding of C from D can take place concurrently with the
forming of the decoding schedule, or the decoding can take place
afterwards based on the decoding schedule.
Luby, et al. Standards Track PAGE 24
RFC 5053 Raptor FEC Scheme October 2007
The correspondence between the decoding schedule and the decoding of
C is as follows. Let c[0] = 0, c[1] = 1,...,c[L-1] = L-1 and d[0] =
0, d[1] = 1,...,d[M-1] = M-1 initially.
- Each time row i of A is exclusive-ORed into row i' in the decoding
schedule, then in the decoding process, symbol D[d[i]] is
exclusive-ORed into symbol D[d[i']].
- Each time row i is exchanged with row i' in the decoding schedule,
then in the decoding process, the value of d[i] is exchanged with
the value of d[i'].
- Each time column j is exchanged with column j' in the decoding
schedule, then in the decoding process, the value of c[j] is
exchanged with the value of c[j'].
From this correspondence, it is clear that the total number of
exclusive-ORs of symbols in the decoding of the source block is the
number of row operations (not exchanges) in the Gaussian elimination.
Since A is the L by L identity matrix after the Gaussian elimination
and after discarding the last M - L rows, it is clear at the end of
successful decoding that the L symbols D[d[0]], D[d[1]],...,
D[d[L-1]] are the values of the L symbols C[c[0]], C[c[1]],...,
C[c[L-1]].
The order in which Gaussian elimination is performed to form the
decoding schedule has no bearing on whether or not the decoding is
successful. However, the speed of the decoding depends heavily on
the order in which Gaussian elimination is performed. (Furthermore,
maintaining a sparse representation of A is crucial, although this is
not described here). The remainder of this section describes an
order in which Gaussian elimination could be performed that is
relatively efficient.
5.5.2.2. First Phase
The first phase of the Gaussian elimination, the matrix A, is
conceptually partitioned into submatrices. The submatrix sizes are
parameterized by non-negative integers i and u, which are initialized
to 0. The submatrices of A are:
(1) The submatrix I defined by the intersection of the first i
rows and first i columns. This is the identity matrix at the
end of each step in the phase.
(2) The submatrix defined by the intersection of the first i rows
and all but the first i columns and last u columns. All
entries of this submatrix are zero.
Luby, et al. Standards Track PAGE 25
RFC 5053 Raptor FEC Scheme October 2007
(3) The submatrix defined by the intersection of the first i
columns and all but the first i rows. All entries of this
submatrix are zero.
(4) The submatrix U defined by the intersection of all the rows
and the last u columns.
(5) The submatrix V formed by the intersection of all but the
first i columns and the last u columns and all but the first i
rows.
Figure 5 illustrates the submatrices of A. At the beginning of the
first phase, V = A. In each step, a row of A is chosen.
+-----------+-----------------+---------+
| | | |
| I | All Zeros | |
| | | |
+-----------+-----------------+ U |
| | | |
| | | |
| All Zeros | V | |
| | | |
| | | |
+-----------+-----------------+---------+
Figure 5: Submatrices of A in the first phase
The following graph defined by the structure of V is used in
determining which row of A is chosen. The columns that intersect V
are the nodes in the graph, and the rows that have exactly 2 ones in
V are the edges of the graph that connect the two columns (nodes) in
the positions of the two ones. A component in this graph is a
maximal set of nodes (columns) and edges (rows) such that there is a
path between each pair of nodes/edges in the graph. The size of a
component is the number of nodes (columns) in the component.
There are at most L steps in the first phase. The phase ends
successfully when i + u = L, i.e., when V and the all-zeroes
submatrix above V have disappeared and A consists of I, the all
zeroes submatrix below I, and U. The phase ends unsuccessfully in
decoding failure if, at some step before V disappears, there is no
non-zero row in V to choose in that step. Whenever there are non-
zero rows in V, then the next step starts by choosing a row of A as
follows:
Luby, et al. Standards Track PAGE 26
RFC 5053 Raptor FEC Scheme October 2007
o Let r be the minimum integer such that at least one row of A has
exactly r ones in V.
* If r != 2, then choose a row with exactly r ones in V with
minimum original degree among all such rows.
* If r = 2, then choose any row with exactly 2 ones in V that is
part of a maximum size component in the graph defined by V.
After the row is chosen in this step the first row of A that
intersects V is exchanged with the chosen row so that the chosen row
is the first row that intersects V. The columns of A among those
that intersect V are reordered so that one of the r ones in the
chosen row appears in the first column of V and so that the remaining
r-1 ones appear in the last columns of V. Then, the chosen row is
exclusive-ORed into all the other rows of A below the chosen row that
have a one in the first column of V. Finally, i is incremented by 1
and u is incremented by r-1, which completes the step.
5.5.2.3. Second Phase
The submatrix U is further partitioned into the first i rows,
U_upper, and the remaining M - i rows, U_lower. Gaussian elimination
is performed in the second phase on U_lower to either determine that
its rank is less than u (decoding failure) or to convert it into a
matrix where the first u rows is the identity matrix (success of the
second phase). Call this u by u identity matrix I_u. The M - L rows
of A that intersect U_lower - I_u are discarded. After this phase, A
has L rows and L columns.
5.5.2.4. Third Phase
After the second phase, the only portion of A that needs to be zeroed
out to finish converting A into the L by L identity matrix is
U_upper. The number of rows i of the submatrix U_upper is generally
much larger than the number of columns u of U_upper. To zero out
U_upper efficiently, the following precomputation matrix U' is
computed based on I_u in the third phase and then U' is used in the
fourth phase to zero out U_upper. The u rows of Iu are partitioned
into ceil(u/8) groups of 8 rows each. Then, for each group of 8
rows, all non-zero combinations of the 8 rows are computed, resulting
in 2^^8 - 1 = 255 rows (this can be done with 2^^8-8-1 = 247
exclusive-ors of rows per group, since the combinations of Hamming
weight one that appear in I_u do not need to be recomputed). Thus,
the resulting precomputation matrix U' has ceil(u/8)*255 rows and u
columns. Note that U' is not formally a part of matrix A, but will
be used in the fourth phase to zero out U_upper.
Luby, et al. Standards Track PAGE 27
RFC 5053 Raptor FEC Scheme October 2007
5.5.2.5. Fourth Phase
For each of the first i rows of A, for each group of 8 columns in the
U_upper submatrix of this row, if the set of 8 column entries in
U_upper are not all zero, then the row of the precomputation matrix
U' that matches the pattern in the 8 columns is exclusive-ORed into
the row, thus zeroing out those 8 columns in the row at the cost of
exclusive-ORing one row of U' into the row.
After this phase, A is the L by L identity matrix and a complete
decoding schedule has been successfully formed. Then, as explained
in Section 5.5.2.1, the corresponding decoding consisting of
exclusive-ORing known encoding symbols can be executed to recover the
intermediate symbols based on the decoding schedule. The triples
associated with all source symbols are computed according to
Section 5.4.2.2. The triples for received source symbols are used in
the decoding. The triples for missing source symbols are used to
determine which intermediate symbols need to be exclusive-ORed to
recover the missing source symbols.
5.6. Random Numbers
The two tables V0 and V1 described in Section 5.4.4.1 are given
below. Each entry is a 32-bit integer in decimal representation.
5.6.1. The Table V0
251291136, 3952231631, 3370958628, 4070167936, 123631495, 3351110283,
3218676425, 2011642291, 774603218, 2402805061, 1004366930,
1843948209, 428891132, 3746331984, 1591258008, 3067016507,
1433388735, 504005498, 2032657933, 3419319784, 2805686246,
3102436986, 3808671154, 2501582075, 3978944421, 246043949,
4016898363, 649743608, 1974987508, 2651273766, 2357956801, 689605112,
715807172, 2722736134, 191939188, 3535520147, 3277019569, 1470435941,
3763101702, 3232409631, 122701163, 3920852693, 782246947, 372121310,
2995604341, 2045698575, 2332962102, 4005368743, 218596347,
3415381967, 4207612806, 861117671, 3676575285, 2581671944,
3312220480, 681232419, 307306866, 4112503940, 1158111502, 709227802,
2724140433, 4201101115, 4215970289, 4048876515, 3031661061,
1909085522, 510985033, 1361682810, 129243379, 3142379587, 2569842483,
3033268270, 1658118006, 932109358, 1982290045, 2983082771,
3007670818, 3448104768, 683749698, 778296777, 1399125101, 1939403708,
1692176003, 3868299200, 1422476658, 593093658, 1878973865,
2526292949, 1591602827, 3986158854, 3964389521, 2695031039,
1942050155, 424618399, 1347204291, 2669179716, 2434425874,
2540801947, 1384069776, 4123580443, 1523670218, 2708475297,
1046771089, 2229796016, 1255426612, 4213663089, 1521339547,
3041843489, 420130494, 10677091, 515623176, 3457502702, 2115821274,
Luby, et al. Standards Track PAGE 28
RFC 5053 Raptor FEC Scheme October 2007
2720124766, 3242576090, 854310108, 425973987, 325832382, 1796851292,
2462744411, 1976681690, 1408671665, 1228817808, 3917210003,
263976645, 2593736473, 2471651269, 4291353919, 650792940, 1191583883,
3046561335, 2466530435, 2545983082, 969168436, 2019348792,
2268075521, 1169345068, 3250240009, 3963499681, 2560755113,
911182396, 760842409, 3569308693, 2687243553, 381854665, 2613828404,
2761078866, 1456668111, 883760091, 3294951678, 1604598575,
1985308198, 1014570543, 2724959607, 3062518035, 3115293053,
138853680, 4160398285, 3322241130, 2068983570, 2247491078,
3669524410, 1575146607, 828029864, 3732001371, 3422026452,
3370954177, 4006626915, 543812220, 1243116171, 3928372514,
2791443445, 4081325272, 2280435605, 885616073, 616452097, 3188863436,
2780382310, 2340014831, 1208439576, 258356309, 3837963200,
2075009450, 3214181212, 3303882142, 880813252, 1355575717, 207231484,
2420803184, 358923368, 1617557768, 3272161958, 1771154147,
2842106362, 1751209208, 1421030790, 658316681, 194065839, 3241510581,
38625260, 301875395, 4176141739, 297312930, 2137802113, 1502984205,
3669376622, 3728477036, 234652930, 2213589897, 2734638932,
1129721478, 3187422815, 2859178611, 3284308411, 3819792700,
3557526733, 451874476, 1740576081, 3592838701, 1709429513,
3702918379, 3533351328, 1641660745, 179350258, 2380520112,
3936163904, 3685256204, 3156252216, 1854258901, 2861641019,
3176611298, 834787554, 331353807, 517858103, 3010168884, 4012642001,
2217188075, 3756943137, 3077882590, 2054995199, 3081443129,
3895398812, 1141097543, 2376261053, 2626898255, 2554703076,
401233789, 1460049922, 678083952, 1064990737, 940909784, 1673396780,
528881783, 1712547446, 3629685652, 1358307511
5.6.2. The Table V1
807385413, 2043073223, 3336749796, 1302105833, 2278607931, 541015020,
1684564270, 372709334, 3508252125, 1768346005, 1270451292,
2603029534, 2049387273, 3891424859, 2152948345, 4114760273,
915180310, 3754787998, 700503826, 2131559305, 1308908630, 224437350,
4065424007, 3638665944, 1679385496, 3431345226, 1779595665,
3068494238, 1424062773, 1033448464, 4050396853, 3302235057,
420600373, 2868446243, 311689386, 259047959, 4057180909, 1575367248,
4151214153, 110249784, 3006865921, 4293710613, 3501256572, 998007483,
499288295, 1205710710, 2997199489, 640417429, 3044194711, 486690751,
2686640734, 2394526209, 2521660077, 49993987, 3843885867, 4201106668,
415906198, 19296841, 2402488407, 2137119134, 1744097284, 579965637,
2037662632, 852173610, 2681403713, 1047144830, 2982173936, 910285038,
4187576520, 2589870048, 989448887, 3292758024, 506322719, 176010738,
1865471968, 2619324712, 564829442, 1996870325, 339697593, 4071072948,
3618966336, 2111320126, 1093955153, 957978696, 892010560, 1854601078,
1873407527, 2498544695, 2694156259, 1927339682, 1650555729,
183933047, 3061444337, 2067387204, 228962564, 3904109414, 1595995433,
1780701372, 2463145963, 307281463, 3237929991, 3852995239,
Luby, et al. Standards Track PAGE 29
RFC 5053 Raptor FEC Scheme October 2007
2398693510, 3754138664, 522074127, 146352474, 4104915256, 3029415884,
3545667983, 332038910, 976628269, 3123492423, 3041418372, 2258059298,
2139377204, 3243642973, 3226247917, 3674004636, 2698992189,
3453843574, 1963216666, 3509855005, 2358481858, 747331248,
1957348676, 1097574450, 2435697214, 3870972145, 1888833893,
2914085525, 4161315584, 1273113343, 3269644828, 3681293816,
412536684, 1156034077, 3823026442, 1066971017, 3598330293,
1979273937, 2079029895, 1195045909, 1071986421, 2712821515,
3377754595, 2184151095, 750918864, 2585729879, 4249895712,
1832579367, 1192240192, 946734366, 31230688, 3174399083, 3549375728,
1642430184, 1904857554, 861877404, 3277825584, 4267074718,
3122860549, 666423581, 644189126, 226475395, 307789415, 1196105631,
3191691839, 782852669, 1608507813, 1847685900, 4069766876,
3931548641, 2526471011, 766865139, 2115084288, 4259411376,
3323683436, 568512177, 3736601419, 1800276898, 4012458395, 1823982,
27980198, 2023839966, 869505096, 431161506, 1024804023, 1853869307,
3393537983, 1500703614, 3019471560, 1351086955, 3096933631,
3034634988, 2544598006, 1230942551, 3362230798, 159984793, 491590373,
3993872886, 3681855622, 903593547, 3535062472, 1799803217, 772984149,
895863112, 1899036275, 4187322100, 101856048, 234650315, 3183125617,
3190039692, 525584357, 1286834489, 455810374, 1869181575, 922673938,
3877430102, 3422391938, 1414347295, 1971054608, 3061798054,
830555096, 2822905141, 167033190, 1079139428, 4210126723, 3593797804,
429192890, 372093950, 1779187770, 3312189287, 204349348, 452421568,
2800540462, 3733109044, 1235082423, 1765319556, 3174729780,
3762994475, 3171962488, 442160826, 198349622, 45942637, 1324086311,
2901868599, 678860040, 3812229107, 19936821, 1119590141, 3640121682,
3545931032, 2102949142, 2828208598, 3603378023, 4135048896
5.7. Systematic Indices J(K)
For each value of K, the systematic index J(K) is designed to have
the property that the set of source symbol triples (d[0], a[0],
b[0]), ..., (d[L-1], a[L-1], b[L-1]) are such that the L intermediate
symbols are uniquely defined, i.e., the matrix A in Section 5.4.2.4.2
has full rank and is therefore invertible.
The following is the list of the systematic indices for values of K
between 4 and 8192 inclusive.
18, 14, 61, 46, 14, 22, 20, 40, 48, 1, 29, 40, 43, 46, 18, 8, 20, 2,
61, 26, 13, 29, 36, 19, 58, 5, 58, 0, 54, 56, 24, 14, 5, 67, 39, 31,
25, 29, 24, 19, 14, 56, 49, 49, 63, 30, 4, 39, 2, 1, 20, 19, 61, 4,
54, 70, 25, 52, 9, 26, 55, 69, 27, 68, 75, 19, 64, 57, 45, 3, 37, 31,
100, 41, 25, 41, 53, 23, 9, 31, 26, 30, 30, 46, 90, 50, 13, 90, 77,
61, 31, 54, 54, 3, 21, 66, 21, 11, 23, 11, 29, 21, 7, 1, 27, 4, 34,
17, 85, 69, 17, 75, 93, 57, 0, 53, 71, 88, 119, 88, 90, 22, 0, 58,
41, 22, 96, 26, 79, 118, 19, 3, 81, 72, 50, 0, 32, 79, 28, 25, 12,
Luby, et al. Standards Track PAGE 30
RFC 5053 Raptor FEC Scheme October 2007
25, 29, 3, 37, 30, 30, 41, 84, 32, 31, 61, 32, 61, 7, 56, 54, 39, 33,
66, 29, 3, 14, 75, 75, 78, 84, 75, 84, 25, 54, 25, 25, 107, 78, 27,
73, 0, 49, 96, 53, 50, 21, 10, 73, 58, 65, 27, 3, 27, 18, 54, 45, 69,
29, 3, 65, 31, 71, 76, 56, 54, 76, 54, 13, 5, 18, 142, 17, 3, 37,
114, 41, 25, 56, 0, 23, 3, 41, 22, 22, 31, 18, 48, 31, 58, 37, 75,
88, 3, 56, 1, 95, 19, 73, 52, 52, 4, 75, 26, 1, 25, 10, 1, 70, 31,
31, 12, 10, 54, 46, 11, 74, 84, 74, 8, 58, 23, 74, 8, 36, 11, 16, 94,
76, 14, 57, 65, 8, 22, 10, 36, 36, 96, 62, 103, 6, 75, 103, 58, 10,
15, 41, 75, 125, 58, 15, 10, 34, 29, 34, 4, 16, 29, 18, 18, 28, 71,
28, 43, 77, 18, 41, 41, 41, 62, 29, 96, 15, 106, 43, 15, 3, 43, 61,
3, 18, 103, 77, 29, 103, 19, 58, 84, 58, 1, 146, 32, 3, 70, 52, 54,
29, 70, 69, 124, 62, 1, 26, 38, 26, 3, 16, 26, 5, 51, 120, 41, 16, 1,
43, 34, 34, 29, 37, 56, 29, 96, 86, 54, 25, 84, 50, 34, 34, 93, 84,
96, 29, 29, 50, 50, 6, 1, 105, 78, 15, 37, 19, 50, 71, 36, 6, 54, 8,
28, 54, 75, 75, 16, 75, 131, 5, 25, 16, 69, 17, 69, 6, 96, 53, 96,
41, 119, 6, 6, 88, 50, 88, 52, 37, 0, 124, 73, 73, 7, 14, 36, 69, 79,
6, 114, 40, 79, 17, 77, 24, 44, 37, 69, 27, 37, 29, 33, 37, 50, 31,
69, 29, 101, 7, 61, 45, 17, 73, 37, 34, 18, 94, 22, 22, 63, 3, 25,
25, 17, 3, 90, 34, 34, 41, 34, 41, 54, 41, 54, 41, 41, 41, 163, 143,
96, 18, 32, 39, 86, 104, 11, 17, 17, 11, 86, 104, 78, 70, 52, 78, 17,
73, 91, 62, 7, 128, 50, 124, 18, 101, 46, 10, 75, 104, 73, 58, 132,
34, 13, 4, 95, 88, 33, 76, 74, 54, 62, 113, 114, 103, 32, 103, 69,
54, 53, 3, 11, 72, 31, 53, 102, 37, 53, 11, 81, 41, 10, 164, 10, 41,
31, 36, 113, 82, 3, 125, 62, 16, 4, 41, 41, 4, 128, 49, 138, 128, 74,
103, 0, 6, 101, 41, 142, 171, 39, 105, 121, 81, 62, 41, 81, 37, 3,
81, 69, 62, 3, 69, 70, 21, 29, 4, 91, 87, 37, 79, 36, 21, 71, 37, 41,
75, 128, 128, 15, 25, 3, 108, 73, 91, 62, 114, 62, 62, 36, 36, 15,
58, 114, 61, 114, 58, 105, 114, 41, 61, 176, 145, 46, 37, 30, 220,
77, 138, 15, 1, 128, 53, 50, 50, 58, 8, 91, 114, 105, 63, 91, 37, 37,
13, 169, 51, 102, 6, 102, 23, 105, 23, 58, 6, 29, 29, 19, 82, 29, 13,
36, 27, 29, 61, 12, 18, 127, 127, 12, 44, 102, 18, 4, 15, 206, 53,
127, 53, 17, 69, 69, 69, 29, 29, 109, 25, 102, 25, 53, 62, 99, 62,
62, 29, 62, 62, 45, 91, 125, 29, 29, 29, 4, 117, 72, 4, 30, 71, 71,
95, 79, 179, 71, 30, 53, 32, 32, 49, 25, 91, 25, 26, 26, 103, 123,
26, 41, 162, 78, 52, 103, 25, 6, 142, 94, 45, 45, 94, 127, 94, 94,
94, 47, 209, 138, 39, 39, 19, 154, 73, 67, 91, 27, 91, 84, 4, 84, 91,
12, 14, 165, 142, 54, 69, 192, 157, 185, 8, 95, 25, 62, 103, 103, 95,
71, 97, 62, 128, 0, 29, 51, 16, 94, 16, 16, 51, 0, 29, 85, 10, 105,
16, 29, 29, 13, 29, 4, 4, 132, 23, 95, 25, 54, 41, 29, 50, 70, 58,
142, 72, 70, 15, 72, 54, 29, 22, 145, 29, 127, 29, 85, 58, 101, 34,
165, 91, 46, 46, 25, 185, 25, 77, 128, 46, 128, 46, 188, 114, 46, 25,
45, 45, 114, 145, 114, 15, 102, 142, 8, 73, 31, 139, 157, 13, 79, 13,
114, 150, 8, 90, 91, 123, 69, 82, 132, 8, 18, 10, 102, 103, 114, 103,
8, 103, 13, 115, 55, 62, 3, 8, 154, 114, 99, 19, 8, 31, 73, 19, 99,
10, 6, 121, 32, 13, 32, 119, 32, 29, 145, 30, 13, 13, 114, 145, 32,
1, 123, 39, 29, 31, 69, 31, 140, 72, 72, 25, 25, 123, 25, 123, 8, 4,
85, 8, 25, 39, 25, 39, 85, 138, 25, 138, 25, 33, 102, 70, 25, 25, 31,
25, 25, 192, 69, 69, 114, 145, 120, 120, 8, 33, 98, 15, 212, 155, 8,
Luby, et al. Standards Track PAGE 31
RFC 5053 Raptor FEC Scheme October 2007
101, 8, 8, 98, 68, 155, 102, 132, 120, 30, 25, 123, 123, 101, 25,
123, 32, 24, 94, 145, 32, 24, 94, 118, 145, 101, 53, 53, 25, 128,
173, 142, 81, 81, 69, 33, 33, 125, 4, 1, 17, 27, 4, 17, 102, 27, 13,
25, 128, 71, 13, 39, 53, 13, 53, 47, 39, 23, 128, 53, 39, 47, 39,
135, 158, 136, 36, 36, 27, 157, 47, 76, 213, 47, 156, 25, 25, 53, 25,
53, 25, 86, 27, 159, 25, 62, 79, 39, 79, 25, 145, 49, 25, 143, 13,
114, 150, 130, 94, 102, 39, 4, 39, 61, 77, 228, 22, 25, 47, 119, 205,
122, 119, 205, 119, 22, 119, 258, 143, 22, 81, 179, 22, 22, 143, 25,
65, 53, 168, 36, 79, 175, 37, 79, 70, 79, 103, 70, 25, 175, 4, 96,
96, 49, 128, 138, 96, 22, 62, 47, 95, 105, 95, 62, 95, 62, 142, 103,
69, 103, 30, 103, 34, 173, 127, 70, 127, 132, 18, 85, 22, 71, 18,
206, 206, 18, 128, 145, 70, 193, 188, 8, 125, 114, 70, 128, 114, 145,
102, 25, 12, 108, 102, 94, 10, 102, 1, 102, 124, 22, 22, 118, 132,
22, 116, 75, 41, 63, 41, 189, 208, 55, 85, 69, 8, 71, 53, 71, 69,
102, 165, 41, 99, 69, 33, 33, 29, 156, 102, 13, 251, 102, 25, 13,
109, 102, 164, 102, 164, 102, 25, 29, 228, 29, 259, 179, 222, 95, 94,
30, 30, 30, 142, 55, 142, 72, 55, 102, 128, 17, 69, 164, 165, 3, 164,
36, 165, 27, 27, 45, 21, 21, 237, 113, 83, 231, 106, 13, 154, 13,
154, 128, 154, 148, 258, 25, 154, 128, 3, 27, 10, 145, 145, 21, 146,
25, 1, 185, 121, 0, 1, 95, 55, 95, 95, 30, 0, 27, 95, 0, 95, 8, 222,
27, 121, 30, 95, 121, 0, 98, 94, 131, 55, 95, 95, 30, 98, 30, 0, 91,
145, 66, 179, 66, 58, 175, 29, 0, 31, 173, 146, 160, 39, 53, 28, 123,
199, 123, 175, 146, 156, 54, 54, 149, 25, 70, 178, 128, 25, 70, 70,
94, 224, 54, 4, 54, 54, 25, 228, 160, 206, 165, 143, 206, 108, 220,
234, 160, 13, 169, 103, 103, 103, 91, 213, 222, 91, 103, 91, 103, 31,
30, 123, 13, 62, 103, 50, 106, 42, 13, 145, 114, 220, 65, 8, 8, 175,
11, 104, 94, 118, 132, 27, 118, 193, 27, 128, 127, 127, 183, 33, 30,
29, 103, 128, 61, 234, 165, 41, 29, 193, 33, 207, 41, 165, 165, 55,
81, 157, 157, 8, 81, 11, 27, 8, 8, 98, 96, 142, 145, 41, 179, 112,
62, 180, 206, 206, 165, 39, 241, 45, 151, 26, 197, 102, 192, 125,
128, 67, 128, 69, 128, 197, 33, 125, 102, 13, 103, 25, 30, 12, 30,
12, 30, 25, 77, 12, 25, 180, 27, 10, 69, 235, 228, 343, 118, 69, 41,
8, 69, 175, 25, 69, 25, 125, 41, 25, 41, 8, 155, 146, 155, 146, 155,
206, 168, 128, 157, 27, 273, 211, 211, 168, 11, 173, 154, 77, 173,
77, 102, 102, 102, 8, 85, 95, 102, 157, 28, 122, 234, 122, 157, 235,
222, 241, 10, 91, 179, 25, 13, 25, 41, 25, 206, 41, 6, 41, 158, 206,
206, 33, 296, 296, 33, 228, 69, 8, 114, 148, 33, 29, 66, 27, 27, 30,
233, 54, 173, 108, 106, 108, 108, 53, 103, 33, 33, 33, 176, 27, 27,
205, 164, 105, 237, 41, 27, 72, 165, 29, 29, 259, 132, 132, 132, 364,
71, 71, 27, 94, 160, 127, 51, 234, 55, 27, 95, 94, 165, 55, 55, 41,
0, 41, 128, 4, 123, 173, 6, 164, 157, 121, 121, 154, 86, 164, 164,
25, 93, 164, 25, 164, 210, 284, 62, 93, 30, 25, 25, 30, 30, 260, 130,
25, 125, 57, 53, 166, 166, 166, 185, 166, 158, 94, 113, 215, 159, 62,
99, 21, 172, 99, 184, 62, 259, 4, 21, 21, 77, 62, 173, 41, 146, 6,
41, 128, 121, 41, 11, 121, 103, 159, 164, 175, 206, 91, 103, 164, 72,
25, 129, 72, 206, 129, 33, 103, 102, 102, 29, 13, 11, 251, 234, 135,
31, 8, 123, 65, 91, 121, 129, 65, 243, 10, 91, 8, 65, 70, 228, 220,
243, 91, 10, 10, 30, 178, 91, 178, 33, 21, 25, 235, 165, 11, 161,
Luby, et al. Standards Track PAGE 32
RFC 5053 Raptor FEC Scheme October 2007
158, 27, 27, 30, 128, 75, 36, 30, 36, 36, 173, 25, 33, 178, 112, 162,
112, 112, 112, 162, 33, 33, 178, 123, 123, 39, 106, 91, 106, 106,
158, 106, 106, 284, 39, 230, 21, 228, 11, 21, 228, 159, 241, 62, 10,
62, 10, 68, 234, 39, 39, 138, 62, 22, 27, 183, 22, 215, 10, 175, 175,
353, 228, 42, 193, 175, 175, 27, 98, 27, 193, 150, 27, 173, 17, 233,
233, 25, 102, 123, 152, 242, 108, 4, 94, 176, 13, 41, 219, 17, 151,
22, 103, 103, 53, 128, 233, 284, 25, 265, 128, 39, 39, 138, 42, 39,
21, 86, 95, 127, 29, 91, 46, 103, 103, 215, 25, 123, 123, 230, 25,
193, 180, 30, 60, 30, 242, 136, 180, 193, 30, 206, 180, 60, 165, 206,
193, 165, 123, 164, 103, 68, 25, 70, 91, 25, 82, 53, 82, 186, 53, 82,
53, 25, 30, 282, 91, 13, 234, 160, 160, 126, 149, 36, 36, 160, 149,
178, 160, 39, 294, 149, 149, 160, 39, 95, 221, 186, 106, 178, 316,
267, 53, 53, 164, 159, 164, 165, 94, 228, 53, 52, 178, 183, 53, 294,
128, 55, 140, 294, 25, 95, 366, 15, 304, 13, 183, 77, 230, 6, 136,
235, 121, 311, 273, 36, 158, 235, 230, 98, 201, 165, 165, 165, 91,
175, 248, 39, 185, 128, 39, 39, 128, 313, 91, 36, 219, 130, 25, 130,
234, 234, 130, 234, 121, 205, 304, 94, 77, 64, 259, 60, 60, 60, 77,
242, 60, 145, 95, 270, 18, 91, 199, 159, 91, 235, 58, 249, 26, 123,
114, 29, 15, 191, 15, 30, 55, 55, 347, 4, 29, 15, 4, 341, 93, 7, 30,
23, 7, 121, 266, 178, 261, 70, 169, 25, 25, 158, 169, 25, 169, 270,
270, 13, 128, 327, 103, 55, 128, 103, 136, 159, 103, 327, 41, 32,
111, 111, 114, 173, 215, 173, 25, 173, 180, 114, 173, 173, 98, 93,
25, 160, 157, 159, 160, 159, 159, 160, 320, 35, 193, 221, 33, 36,
136, 248, 91, 215, 125, 215, 156, 68, 125, 125, 1, 287, 123, 94, 30,
184, 13, 30, 94, 123, 206, 12, 206, 289, 128, 122, 184, 128, 289,
178, 29, 26, 206, 178, 65, 206, 128, 192, 102, 197, 36, 94, 94, 155,
10, 36, 121, 280, 121, 368, 192, 121, 121, 179, 121, 36, 54, 192,
121, 192, 197, 118, 123, 224, 118, 10, 192, 10, 91, 269, 91, 49, 206,
184, 185, 62, 8, 49, 289, 30, 5, 55, 30, 42, 39, 220, 298, 42, 347,
42, 234, 42, 70, 42, 55, 321, 129, 172, 173, 172, 13, 98, 129, 325,
235, 284, 362, 129, 233, 345, 175, 261, 175, 60, 261, 58, 289, 99,
99, 99, 206, 99, 36, 175, 29, 25, 432, 125, 264, 168, 173, 69, 158,
273, 179, 164, 69, 158, 69, 8, 95, 192, 30, 164, 101, 44, 53, 273,
335, 273, 53, 45, 128, 45, 234, 123, 105, 103, 103, 224, 36, 90, 211,
282, 264, 91, 228, 91, 166, 264, 228, 398, 50, 101, 91, 264, 73, 36,
25, 73, 50, 50, 242, 36, 36, 58, 165, 204, 353, 165, 125, 320, 128,
298, 298, 180, 128, 60, 102, 30, 30, 53, 179, 234, 325, 234, 175, 21,
250, 215, 103, 21, 21, 250, 91, 211, 91, 313, 301, 323, 215, 228,
160, 29, 29, 81, 53, 180, 146, 248, 66, 159, 39, 98, 323, 98, 36, 95,
218, 234, 39, 82, 82, 230, 62, 13, 62, 230, 13, 30, 98, 0, 8, 98, 8,
98, 91, 267, 121, 197, 30, 78, 27, 78, 102, 27, 298, 160, 103, 264,
264, 264, 175, 17, 273, 273, 165, 31, 160, 17, 99, 17, 99, 234, 31,
17, 99, 36, 26, 128, 29, 214, 353, 264, 102, 36, 102, 264, 264, 273,
273, 4, 16, 138, 138, 264, 128, 313, 25, 420, 60, 10, 280, 264, 60,
60, 103, 178, 125, 178, 29, 327, 29, 36, 30, 36, 4, 52, 183, 183,
173, 52, 31, 173, 31, 158, 31, 158, 31, 9, 31, 31, 353, 31, 353, 173,
415, 9, 17, 222, 31, 103, 31, 165, 27, 31, 31, 165, 27, 27, 206, 31,
31, 4, 4, 30, 4, 4, 264, 185, 159, 310, 273, 310, 173, 40, 4, 173, 4,
Luby, et al. Standards Track PAGE 33
RFC 5053 Raptor FEC Scheme October 2007
173, 4, 250, 250, 62, 188, 119, 250, 233, 62, 121, 105, 105, 54, 103,
111, 291, 236, 236, 103, 297, 36, 26, 316, 69, 183, 158, 206, 129,
160, 129, 184, 55, 179, 279, 11, 179, 347, 160, 184, 129, 179, 351,
179, 353, 179, 129, 129, 351, 11, 111, 93, 93, 235, 103, 173, 53, 93,
50, 111, 86, 123, 94, 36, 183, 60, 55, 55, 178, 219, 253, 321, 178,
235, 235, 183, 183, 204, 321, 219, 160, 193, 335, 121, 70, 69, 295,
159, 297, 231, 121, 231, 136, 353, 136, 121, 279, 215, 366, 215, 353,
159, 353, 353, 103, 31, 31, 298, 298, 30, 30, 165, 273, 25, 219, 35,
165, 259, 54, 36, 54, 54, 165, 71, 250, 327, 13, 289, 165, 196, 165,
165, 94, 233, 165, 94, 60, 165, 96, 220, 166, 271, 158, 397, 122, 53,
53, 137, 280, 272, 62, 30, 30, 30, 105, 102, 67, 140, 8, 67, 21, 270,
298, 69, 173, 298, 91, 179, 327, 86, 179, 88, 179, 179, 55, 123, 220,
233, 94, 94, 175, 13, 53, 13, 154, 191, 74, 83, 83, 325, 207, 83, 74,
83, 325, 74, 316, 388, 55, 55, 364, 55, 183, 434, 273, 273, 273, 164,
213, 11, 213, 327, 321, 21, 352, 185, 103, 13, 13, 55, 30, 323, 123,
178, 435, 178, 30, 175, 175, 30, 481, 527, 175, 125, 232, 306, 232,
206, 306, 364, 206, 270, 206, 232, 10, 30, 130, 160, 130, 347, 240,
30, 136, 130, 347, 136, 279, 298, 206, 30, 103, 273, 241, 70, 206,
306, 434, 206, 94, 94, 156, 161, 321, 321, 64, 161, 13, 183, 183, 83,
161, 13, 169, 13, 159, 36, 173, 159, 36, 36, 230, 235, 235, 159, 159,
335, 312, 42, 342, 264, 39, 39, 39, 34, 298, 36, 36, 252, 164, 29,
493, 29, 387, 387, 435, 493, 132, 273, 105, 132, 74, 73, 206, 234,
273, 206, 95, 15, 280, 280, 280, 280, 397, 273, 273, 242, 397, 280,
397, 397, 397, 273, 397, 280, 230, 137, 353, 67, 81, 137, 137, 353,
259, 312, 114, 164, 164, 25, 77, 21, 77, 165, 30, 30, 231, 234, 121,
234, 312, 121, 364, 136, 123, 123, 136, 123, 136, 150, 264, 285, 30,
166, 93, 30, 39, 224, 136, 39, 355, 355, 397, 67, 67, 25, 67, 25,
298, 11, 67, 264, 374, 99, 150, 321, 67, 70, 67, 295, 150, 29, 321,
150, 70, 29, 142, 355, 311, 173, 13, 253, 103, 114, 114, 70, 192, 22,
128, 128, 183, 184, 70, 77, 215, 102, 292, 30, 123, 279, 292, 142,
33, 215, 102, 468, 123, 468, 473, 30, 292, 215, 30, 213, 443, 473,
215, 234, 279, 279, 279, 279, 265, 443, 206, 66, 313, 34, 30, 206,
30, 51, 15, 206, 41, 434, 41, 398, 67, 30, 301, 67, 36, 3, 285, 437,
136, 136, 22, 136, 145, 365, 323, 323, 145, 136, 22, 453, 99, 323,
353, 9, 258, 323, 231, 128, 231, 382, 150, 420, 39, 94, 29, 29, 353,
22, 22, 347, 353, 39, 29, 22, 183, 8, 284, 355, 388, 284, 60, 64, 99,
60, 64, 150, 95, 150, 364, 150, 95, 150, 6, 236, 383, 544, 81, 206,
388, 206, 58, 159, 99, 231, 228, 363, 363, 121, 99, 121, 121, 99,
422, 544, 273, 173, 121, 427, 102, 121, 235, 284, 179, 25, 197, 25,
179, 511, 70, 368, 70, 25, 388, 123, 368, 159, 213, 410, 159, 236,
127, 159, 21, 373, 184, 424, 327, 250, 176, 176, 175, 284, 316, 176,
284, 327, 111, 250, 284, 175, 175, 264, 111, 176, 219, 111, 427, 427,
176, 284, 427, 353, 428, 55, 184, 493, 158, 136, 99, 287, 264, 334,
264, 213, 213, 292, 481, 93, 264, 292, 295, 295, 6, 367, 279, 173,
308, 285, 158, 308, 335, 299, 137, 137, 572, 41, 137, 137, 41, 94,
335, 220, 36, 224, 420, 36, 265, 265, 91, 91, 71, 123, 264, 91, 91,
123, 107, 30, 22, 292, 35, 241, 356, 298, 14, 298, 441, 35, 121, 71,
63, 130, 63, 488, 363, 71, 63, 307, 194, 71, 71, 220, 121, 125, 71,
Luby, et al. Standards Track PAGE 34
RFC 5053 Raptor FEC Scheme October 2007
220, 71, 71, 71, 71, 235, 265, 353, 128, 155, 128, 420, 400, 130,
173, 183, 183, 184, 130, 173, 183, 13, 183, 130, 130, 183, 183, 353,
353, 183, 242, 183, 183, 306, 324, 324, 321, 306, 321, 6, 6, 128,
306, 242, 242, 306, 183, 183, 6, 183, 321, 486, 183, 164, 30, 78,
138, 158, 138, 34, 206, 362, 55, 70, 67, 21, 375, 136, 298, 81, 298,
298, 298, 230, 121, 30, 230, 311, 240, 311, 311, 158, 204, 136, 136,
184, 136, 264, 311, 311, 312, 312, 72, 311, 175, 264, 91, 175, 264,
121, 461, 312, 312, 238, 475, 350, 512, 350, 312, 313, 350, 312, 366,
294, 30, 253, 253, 253, 388, 158, 388, 22, 388, 22, 388, 103, 321,
321, 253, 7, 437, 103, 114, 242, 114, 114, 242, 114, 114, 242, 242,
242, 306, 242, 114, 7, 353, 335, 27, 241, 299, 312, 364, 506, 409,
94, 462, 230, 462, 243, 230, 175, 175, 462, 461, 230, 428, 426, 175,
175, 165, 175, 175, 372, 183, 572, 102, 85, 102, 538, 206, 376, 85,
85, 284, 85, 85, 284, 398, 83, 160, 265, 308, 398, 310, 583, 289,
279, 273, 285, 490, 490, 211, 292, 292, 158, 398, 30, 220, 169, 368,
368, 368, 169, 159, 368, 93, 368, 368, 93, 169, 368, 368, 443, 368,
298, 443, 368, 298, 538, 345, 345, 311, 178, 54, 311, 215, 178, 175,
222, 264, 475, 264, 264, 475, 478, 289, 63, 236, 63, 299, 231, 296,
397, 299, 158, 36, 164, 164, 21, 492, 21, 164, 21, 164, 403, 26, 26,
588, 179, 234, 169, 465, 295, 67, 41, 353, 295, 538, 161, 185, 306,
323, 68, 420, 323, 82, 241, 241, 36, 53, 493, 301, 292, 241, 250, 63,
63, 103, 442, 353, 185, 353, 321, 353, 185, 353, 353, 185, 409, 353,
589, 34, 271, 271, 34, 86, 34, 34, 353, 353, 39, 414, 4, 95, 95, 4,
225, 95, 4, 121, 30, 552, 136, 159, 159, 514, 159, 159, 54, 514, 206,
136, 206, 159, 74, 235, 235, 312, 54, 312, 42, 156, 422, 629, 54,
465, 265, 165, 250, 35, 165, 175, 659, 175, 175, 8, 8, 8, 8, 206,
206, 206, 50, 435, 206, 432, 230, 230, 234, 230, 94, 299, 299, 285,
184, 41, 93, 299, 299, 285, 41, 285, 158, 285, 206, 299, 41, 36, 396,
364, 364, 120, 396, 514, 91, 382, 538, 807, 717, 22, 93, 412, 54,
215, 54, 298, 308, 148, 298, 148, 298, 308, 102, 656, 6, 148, 745,
128, 298, 64, 407, 273, 41, 172, 64, 234, 250, 398, 181, 445, 95,
236, 441, 477, 504, 102, 196, 137, 364, 60, 453, 137, 364, 367, 334,
364, 299, 196, 397, 630, 589, 589, 196, 646, 337, 235, 128, 128, 343,
289, 235, 324, 427, 324, 58, 215, 215, 461, 425, 461, 387, 440, 285,
440, 440, 285, 387, 632, 325, 325, 440, 461, 425, 425, 387, 627, 191,
285, 440, 308, 55, 219, 280, 308, 265, 538, 183, 121, 30, 236, 206,
30, 455, 236, 30, 30, 705, 83, 228, 280, 468, 132, 8, 132, 132, 128,
409, 173, 353, 132, 409, 35, 128, 450, 137, 398, 67, 432, 423, 235,
235, 388, 306, 93, 93, 452, 300, 190, 13, 452, 388, 30, 452, 13, 30,
13, 30, 306, 362, 234, 721, 635, 809, 784, 67, 498, 498, 67, 353,
635, 67, 183, 159, 445, 285, 183, 53, 183, 445, 265, 432, 57, 420,
432, 420, 477, 327, 55, 60, 105, 183, 218, 104, 104, 475, 239, 582,
151, 239, 104, 732, 41, 26, 784, 86, 300, 215, 36, 64, 86, 86, 675,
294, 64, 86, 528, 550, 493, 565, 298, 230, 312, 295, 538, 298, 295,
230, 54, 374, 516, 441, 54, 54, 323, 401, 401, 382, 159, 837, 159,
54, 401, 592, 159, 401, 417, 610, 264, 150, 323, 452, 185, 323, 323,
185, 403, 185, 423, 165, 425, 219, 407, 270, 231, 99, 93, 231, 631,
756, 71, 364, 434, 213, 86, 102, 434, 102, 86, 23, 71, 335, 164, 323,
Luby, et al. Standards Track PAGE 35
RFC 5053 Raptor FEC Scheme October 2007
409, 381, 4, 124, 41, 424, 206, 41, 124, 41, 41, 703, 635, 124, 493,
41, 41, 487, 492, 124, 175, 124, 261, 600, 488, 261, 488, 261, 206,
677, 261, 308, 723, 908, 704, 691, 723, 488, 488, 441, 136, 476, 312,
136, 550, 572, 728, 550, 22, 312, 312, 22, 55, 413, 183, 280, 593,
191, 36, 36, 427, 36, 695, 592, 19, 544, 13, 468, 13, 544, 72, 437,
321, 266, 461, 266, 441, 230, 409, 93, 521, 521, 345, 235, 22, 142,
150, 102, 569, 235, 264, 91, 521, 264, 7, 102, 7, 498, 521, 235, 537,
235, 6, 241, 420, 420, 631, 41, 527, 103, 67, 337, 62, 264, 527, 131,
67, 174, 263, 264, 36, 36, 263, 581, 253, 465, 160, 286, 91, 160, 55,
4, 4, 631, 631, 608, 365, 465, 294, 427, 427, 335, 669, 669, 129, 93,
93, 93, 93, 74, 66, 758, 504, 347, 130, 505, 504, 143, 505, 550, 222,
13, 352, 529, 291, 538, 50, 68, 269, 130, 295, 130, 511, 295, 295,
130, 486, 132, 61, 206, 185, 368, 669, 22, 175, 492, 207, 373, 452,
432, 327, 89, 550, 496, 611, 527, 89, 527, 496, 550, 516, 516, 91,
136, 538, 264, 264, 124, 264, 264, 264, 264, 264, 535, 264, 150, 285,
398, 285, 582, 398, 475, 81, 694, 694, 64, 81, 694, 234, 607, 723,
513, 234, 64, 581, 64, 124, 64, 607, 234, 723, 717, 367, 64, 513,
607, 488, 183, 488, 450, 183, 550, 286, 183, 363, 286, 414, 67, 449,
449, 366, 215, 235, 95, 295, 295, 41, 335, 21, 445, 225, 21, 295,
372, 749, 461, 53, 481, 397, 427, 427, 427, 714, 481, 714, 427, 717,
165, 245, 486, 415, 245, 415, 486, 274, 415, 441, 456, 300, 548, 300,
422, 422, 757, 11, 74, 430, 430, 136, 409, 430, 749, 191, 819, 592,
136, 364, 465, 231, 231, 918, 160, 589, 160, 160, 465, 465, 231, 157,
538, 538, 259, 538, 326, 22, 22, 22, 179, 22, 22, 550, 179, 287, 287,
417, 327, 498, 498, 287, 488, 327, 538, 488, 583, 488, 287, 335, 287,
335, 287, 41, 287, 335, 287, 327, 441, 335, 287, 488, 538, 327, 498,
8, 8, 374, 8, 64, 427, 8, 374, 417, 760, 409, 373, 160, 423, 206,
160, 106, 499, 160, 271, 235, 160, 590, 353, 695, 478, 619, 590, 353,
13, 63, 189, 420, 605, 427, 643, 121, 280, 415, 121, 415, 595, 417,
121, 398, 55, 330, 463, 463, 123, 353, 330, 582, 309, 582, 582, 405,
330, 550, 405, 582, 353, 309, 308, 60, 353, 7, 60, 71, 353, 189, 183,
183, 183, 582, 755, 189, 437, 287, 189, 183, 668, 481, 384, 384, 481,
481, 481, 477, 582, 582, 499, 650, 481, 121, 461, 231, 36, 235, 36,
413, 235, 209, 36, 689, 114, 353, 353, 235, 592, 36, 353, 413, 209,
70, 308, 70, 699, 308, 70, 213, 292, 86, 689, 465, 55, 508, 128, 452,
29, 41, 681, 573, 352, 21, 21, 648, 648, 69, 509, 409, 21, 264, 21,
509, 514, 514, 409, 21, 264, 443, 443, 427, 160, 433, 663, 433, 231,
646, 185, 482, 646, 433, 13, 398, 172, 234, 42, 491, 172, 234, 234,
832, 775, 172, 196, 335, 822, 461, 298, 461, 364, 1120, 537, 169,
169, 364, 694, 219, 612, 231, 740, 42, 235, 321, 279, 960, 279, 353,
492, 159, 572, 321, 159, 287, 353, 287, 287, 206, 206, 321, 287, 159,
321, 492, 159, 55, 572, 600, 270, 492, 784, 173, 91, 91, 443, 443,
582, 261, 497, 572, 91, 555, 352, 206, 261, 555, 285, 91, 555, 497,
83, 91, 619, 353, 488, 112, 4, 592, 295, 295, 488, 235, 231, 769,
568, 581, 671, 451, 451, 483, 299, 1011, 432, 422, 207, 106, 701,
508, 555, 508, 555, 125, 870, 555, 589, 508, 125, 749, 482, 125, 125,
130, 544, 643, 643, 544, 488, 22, 643, 130, 335, 544, 22, 130, 544,
544, 488, 426, 426, 4, 180, 4, 695, 35, 54, 433, 500, 592, 433, 262,
Luby, et al. Standards Track PAGE 36
RFC 5053 Raptor FEC Scheme October 2007
94, 401, 401, 106, 216, 216, 106, 521, 102, 462, 518, 271, 475, 365,
193, 648, 206, 424, 206, 193, 206, 206, 424, 299, 590, 590, 364, 621,
67, 538, 488, 567, 51, 51, 513, 194, 81, 488, 486, 289, 567, 563,
749, 563, 338, 338, 502, 563, 822, 338, 563, 338, 502, 201, 230, 201,
533, 445, 175, 201, 175, 13, 85, 960, 103, 85, 175, 30, 445, 445,
175, 573, 196, 877, 287, 356, 678, 235, 489, 312, 572, 264, 717, 138,
295, 6, 295, 523, 55, 165, 165, 295, 138, 663, 6, 295, 6, 353, 138,
6, 138, 169, 129, 784, 12, 129, 194, 605, 784, 445, 234, 627, 563,
689, 627, 647, 570, 627, 570, 647, 206, 234, 215, 234, 816, 627, 816,
234, 627, 215, 234, 627, 264, 427, 427, 30, 424, 161, 161, 916, 740,
180, 616, 481, 514, 383, 265, 481, 164, 650, 121, 582, 689, 420, 669,
589, 420, 788, 549, 165, 734, 280, 224, 146, 681, 788, 184, 398, 784,
4, 398, 417, 417, 398, 636, 784, 417, 81, 398, 417, 81, 185, 827,
420, 241, 420, 41, 185, 185, 718, 241, 101, 185, 185, 241, 241, 241,
241, 241, 185, 324, 420, 420, 1011, 420, 827, 241, 184, 563, 241,
183, 285, 529, 285, 808, 822, 891, 822, 488, 285, 486, 619, 55, 869,
39, 567, 39, 289, 203, 158, 289, 710, 818, 158, 818, 355, 29, 409,
203, 308, 648, 792, 308, 308, 91, 308, 6, 592, 792, 106, 106, 308,
41, 178, 91, 751, 91, 259, 734, 166, 36, 327, 166, 230, 205, 205,
172, 128, 230, 432, 623, 838, 623, 432, 278, 432, 42, 916, 432, 694,
623, 352, 452, 93, 314, 93, 93, 641, 88, 970, 914, 230, 61, 159, 270,
159, 493, 159, 755, 159, 409, 30, 30, 836, 128, 241, 99, 102, 984,
538, 102, 102, 273, 639, 838, 102, 102, 136, 637, 508, 627, 285, 465,
327, 327, 21, 749, 327, 749, 21, 845, 21, 21, 409, 749, 1367, 806,
616, 714, 253, 616, 714, 714, 112, 375, 21, 112, 375, 375, 51, 51,
51, 51, 393, 206, 870, 713, 193, 802, 21, 1061, 42, 382, 42, 543,
876, 42, 876, 382, 696, 543, 635, 490, 353, 353, 417, 64, 1257, 271,
64, 377, 127, 127, 537, 417, 905, 353, 538, 465, 605, 876, 427, 324,
514, 852, 427, 53, 427, 557, 173, 173, 7, 1274, 563, 31, 31, 31, 745,
392, 289, 230, 230, 230, 91, 218, 327, 420, 420, 128, 901, 552, 420,
230, 608, 552, 476, 347, 476, 231, 159, 137, 716, 648, 716, 627, 740,
718, 679, 679, 6, 718, 740, 6, 189, 679, 125, 159, 757, 1191, 409,
175, 250, 409, 67, 324, 681, 605, 550, 398, 550, 931, 478, 174, 21,
316, 91, 316, 654, 409, 425, 425, 699, 61, 699, 321, 698, 321, 698,
61, 425, 699, 321, 409, 699, 299, 335, 321, 335, 61, 698, 699, 654,
698, 299, 425, 231, 14, 121, 515, 121, 14, 165, 81, 409, 189, 81,
373, 465, 463, 1055, 507, 81, 81, 189, 1246, 321, 409, 886, 104, 842,
689, 300, 740, 380, 656, 656, 832, 656, 380, 300, 300, 206, 187, 175,
142, 465, 206, 271, 468, 215, 560, 83, 215, 83, 215, 215, 83, 175,
215, 83, 83, 111, 206, 756, 559, 756, 1367, 206, 559, 1015, 559, 559,
946, 1015, 548, 559, 756, 1043, 756, 698, 159, 414, 308, 458, 997,
663, 663, 347, 39, 755, 838, 323, 755, 323, 159, 159, 717, 159, 21,
41, 128, 516, 159, 717, 71, 870, 755, 159, 740, 717, 374, 516, 740,
51, 148, 335, 148, 335, 791, 120, 364, 335, 335, 51, 120, 251, 538,
251, 971, 1395, 538, 78, 178, 538, 538, 918, 129, 918, 129, 538, 538,
656, 129, 538, 538, 129, 538, 1051, 538, 128, 838, 931, 998, 823,
1095, 334, 870, 334, 367, 550, 1061, 498, 745, 832, 498, 745, 716,
498, 498, 128, 997, 832, 716, 832, 130, 642, 616, 497, 432, 432, 432,
Luby, et al. Standards Track PAGE 37
RFC 5053 Raptor FEC Scheme October 2007
432, 642, 159, 432, 46, 230, 788, 160, 230, 478, 46, 693, 103, 920,
230, 589, 643, 160, 616, 432, 165, 165, 583, 592, 838, 784, 583, 710,
6, 583, 583, 6, 35, 230, 838, 592, 710, 6, 589, 230, 838, 30, 592,
583, 6, 583, 6, 6, 583, 30, 30, 6, 375, 375, 99, 36, 1158, 425, 662,
417, 681, 364, 375, 1025, 538, 822, 669, 893, 538, 538, 450, 409,
632, 527, 632, 563, 632, 527, 550, 71, 698, 550, 39, 550, 514, 537,
514, 537, 111, 41, 173, 592, 173, 648, 173, 173, 173, 1011, 514, 173,
173, 514, 166, 648, 355, 161, 166, 648, 497, 327, 327, 550, 650, 21,
425, 605, 555, 103, 425, 605, 842, 836, 1011, 636, 138, 756, 836,
756, 756, 353, 1011, 636, 636, 1158, 741, 741, 842, 756, 741, 1011,
677, 1011, 770, 366, 306, 488, 920, 920, 665, 775, 502, 500, 775,
775, 648, 364, 833, 207, 13, 93, 500, 364, 500, 665, 500, 93, 295,
183, 1293, 313, 272, 313, 279, 303, 93, 516, 93, 1013, 381, 6, 93,
93, 303, 259, 643, 168, 673, 230, 1261, 230, 230, 673, 1060, 1079,
1079, 550, 741, 741, 590, 527, 741, 741, 442, 741, 442, 848, 741,
590, 925, 219, 527, 925, 335, 442, 590, 239, 590, 590, 590, 239, 527,
239, 1033, 230, 734, 241, 741, 230, 549, 548, 1015, 1015, 32, 36,
433, 465, 724, 465, 73, 73, 73, 465, 808, 73, 592, 1430, 250, 154,
154, 250, 538, 353, 353, 353, 353, 353, 175, 194, 206, 538, 632,
1163, 960, 175, 175, 538, 452, 632, 1163, 175, 538, 960, 194, 175,
194, 632, 960, 632, 94, 632, 461, 960, 1163, 1163, 461, 632, 960,
755, 707, 105, 382, 625, 382, 382, 784, 707, 871, 559, 387, 387, 871,
784, 559, 784, 88, 36, 570, 314, 1028, 975, 335, 335, 398, 573, 573,
573, 21, 215, 562, 738, 612, 424, 21, 103, 788, 870, 912, 23, 186,
757, 73, 818, 23, 73, 563, 952, 262, 563, 137, 262, 1022, 952, 137,
1273, 442, 952, 604, 137, 308, 384, 913, 235, 325, 695, 398, 95, 668,
776, 713, 309, 691, 22, 10, 364, 682, 682, 578, 481, 1252, 1072,
1252, 825, 578, 825, 1072, 1149, 592, 273, 387, 273, 427, 155, 1204,
50, 452, 50, 1142, 50, 367, 452, 1142, 611, 367, 50, 50, 367, 50,
1675, 99, 367, 50, 1501, 1099, 830, 681, 689, 917, 1089, 453, 425,
235, 918, 538, 550, 335, 161, 387, 859, 324, 21, 838, 859, 1123, 21,
723, 21, 335, 335, 206, 21, 364, 1426, 21, 838, 838, 335, 364, 21,
21, 859, 920, 838, 838, 397, 81, 639, 397, 397, 588, 933, 933, 784,
222, 830, 36, 36, 222, 1251, 266, 36, 146, 266, 366, 581, 605, 366,
22, 966, 681, 681, 433, 730, 1013, 550, 21, 21, 938, 488, 516, 21,
21, 656, 420, 323, 323, 323, 327, 323, 918, 581, 581, 830, 361, 830,
364, 259, 364, 496, 496, 364, 691, 705, 691, 475, 427, 1145, 600,
179, 427, 527, 749, 869, 689, 335, 347, 220, 298, 689, 1426, 183,
554, 55, 832, 550, 550, 165, 770, 957, 67, 1386, 219, 683, 683, 355,
683, 355, 355, 738, 355, 842, 931, 266, 325, 349, 256, 1113, 256,
423, 960, 554, 554, 325, 554, 508, 22, 142, 22, 508, 916, 767, 55,
1529, 767, 55, 1286, 93, 972, 550, 931, 1286, 1286, 972, 93, 1286,
1392, 890, 93, 1286, 93, 1286, 972, 374, 931, 890, 808, 779, 975,
975, 175, 173, 4, 681, 383, 1367, 173, 383, 1367, 383, 173, 175, 69,
238, 146, 238, 36, 148, 888, 238, 173, 238, 148, 238, 888, 185, 925,
925, 797, 925, 815, 925, 469, 784, 289, 784, 925, 797, 925, 925,
1093, 925, 925, 925, 1163, 797, 797, 815, 925, 1093, 784, 636, 663,
925, 187, 922, 316, 1380, 709, 916, 916, 187, 355, 948, 916, 187,
Luby, et al. Standards Track PAGE 38
RFC 5053 Raptor FEC Scheme October 2007
916, 916, 948, 948, 916, 355, 316, 316, 334, 300, 1461, 36, 583,
1179, 699, 235, 858, 583, 699, 858, 699, 1189, 1256, 1189, 699, 797,
699, 699, 699, 699, 427, 488, 427, 488, 175, 815, 656, 656, 150, 322,
465, 322, 870, 465, 1099, 582, 665, 767, 749, 635, 749, 600, 1448,
36, 502, 235, 502, 355, 502, 355, 355, 355, 172, 355, 355, 95, 866,
425, 393, 1165, 42, 42, 42, 393, 939, 909, 909, 836, 552, 424, 1333,
852, 897, 1426, 1333, 1446, 1426, 997, 1011, 852, 1198, 55, 32, 239,
588, 681, 681, 239, 1401, 32, 588, 239, 462, 286, 1260, 984, 1160,
960, 960, 486, 828, 462, 960, 1199, 581, 850, 663, 581, 751, 581,
581, 1571, 252, 252, 1283, 264, 430, 264, 430, 430, 842, 252, 745,
21, 307, 681, 1592, 488, 857, 857, 1161, 857, 857, 857, 138, 374,
374, 1196, 374, 1903, 1782, 1626, 414, 112, 1477, 1040, 356, 775,
414, 414, 112, 356, 775, 435, 338, 1066, 689, 689, 1501, 689, 1249,
205, 689, 765, 220, 308, 917, 308, 308, 220, 327, 387, 838, 917, 917,
917, 220, 662, 308, 220, 387, 387, 220, 220, 308, 308, 308, 387,
1009, 1745, 822, 279, 554, 1129, 543, 383, 870, 1425, 241, 870, 241,
383, 716, 592, 21, 21, 592, 425, 550, 550, 550, 427, 230, 57, 483,
784, 860, 57, 308, 57, 486, 870, 447, 486, 433, 433, 870, 433, 997,
486, 443, 433, 433, 997, 486, 1292, 47, 708, 81, 895, 394, 81, 935,
81, 81, 81, 374, 986, 916, 1103, 1095, 465, 495, 916, 667, 1745, 518,
220, 1338, 220, 734, 1294, 741, 166, 828, 741, 741, 1165, 1371, 1371,
471, 1371, 647, 1142, 1878, 1878, 1371, 1371, 822, 66, 327, 158, 427,
427, 465, 465, 676, 676, 30, 30, 676, 676, 893, 1592, 93, 455, 308,
582, 695, 582, 629, 582, 85, 1179, 85, 85, 1592, 1179, 280, 1027,
681, 398, 1027, 398, 295, 784, 740, 509, 425, 968, 509, 46, 833, 842,
401, 184, 401, 464, 6, 1501, 1501, 550, 538, 883, 538, 883, 883, 883,
1129, 550, 550, 333, 689, 948, 21, 21, 241, 2557, 2094, 273, 308, 58,
863, 893, 1086, 409, 136, 1086, 592, 592, 830, 830, 883, 830, 277,
68, 689, 902, 277, 453, 507, 129, 689, 630, 664, 550, 128, 1626,
1626, 128, 902, 312, 589, 755, 755, 589, 755, 407, 1782, 589, 784,
1516, 1118, 407, 407, 1447, 589, 235, 755, 1191, 235, 235, 407, 128,
589, 1118, 21, 383, 1331, 691, 481, 383, 1129, 1129, 1261, 1104,
1378, 1129, 784, 1129, 1261, 1129, 947, 1129, 784, 784, 1129, 1129,
35, 1104, 35, 866, 1129, 1129, 64, 481, 730, 1260, 481, 970, 481,
481, 481, 481, 863, 481, 681, 699, 863, 486, 681, 481, 481, 55, 55,
235, 1364, 944, 632, 822, 401, 822, 952, 822, 822, 99, 550, 2240,
550, 70, 891, 860, 860, 550, 550, 916, 1176, 1530, 425, 1530, 916,
628, 1583, 916, 628, 916, 916, 628, 628, 425, 916, 1062, 1265, 916,
916, 916, 280, 461, 916, 916, 1583, 628, 1062, 916, 916, 677, 1297,
924, 1260, 83, 1260, 482, 433, 234, 462, 323, 1656, 997, 323, 323,
931, 838, 931, 1933, 1391, 367, 323, 931, 1391, 1391, 103, 1116,
1116, 1116, 769, 1195, 1218, 312, 791, 312, 741, 791, 997, 312, 334,
334, 312, 287, 287, 633, 1397, 1426, 605, 1431, 327, 592, 705, 1194,
592, 1097, 1118, 1503, 1267, 1267, 1267, 618, 1229, 734, 1089, 785,
1089, 1129, 1148, 1148, 1089, 915, 1148, 1129, 1148, 1011, 1011,
1229, 871, 1560, 1560, 1560, 563, 1537, 1009, 1560, 632, 985, 592,
1308, 592, 882, 145, 145, 397, 837, 383, 592, 592, 832, 36, 2714,
2107, 1588, 1347, 36, 36, 1443, 1453, 334, 2230, 1588, 1169, 650,
Luby, et al. Standards Track PAGE 39
RFC 5053 Raptor FEC Scheme October 2007
1169, 2107, 425, 425, 891, 891, 425, 2532, 679, 274, 274, 274, 325,
274, 1297, 194, 1297, 627, 314, 917, 314, 314, 1501, 414, 1490, 1036,
592, 1036, 1025, 901, 1218, 1025, 901, 280, 592, 592, 901, 1461, 159,
159, 159, 2076, 1066, 1176, 1176, 516, 327, 516, 1179, 1176, 899,
1176, 1176, 323, 1187, 1229, 663, 1229, 504, 1229, 916, 1229, 916,
1661, 41, 36, 278, 1027, 648, 648, 648, 1626, 648, 646, 1179, 1580,
1061, 1514, 1008, 1741, 2076, 1514, 1008, 952, 1089, 427, 952, 427,
1083, 425, 427, 1089, 1083, 425, 427, 425, 230, 920, 1678, 920, 1678,
189, 189, 953, 189, 133, 189, 1075, 189, 189, 133, 1264, 725, 189,
1629, 189, 808, 230, 230, 2179, 770, 230, 770, 230, 21, 21, 784,
1118, 230, 230, 230, 770, 1118, 986, 808, 916, 30, 327, 918, 679,
414, 916, 1165, 1355, 916, 755, 733, 433, 1490, 433, 433, 433, 605,
433, 433, 433, 1446, 679, 206, 433, 21, 2452, 206, 206, 433, 1894,
206, 822, 206, 2073, 206, 206, 21, 822, 21, 206, 206, 21, 383, 1513,
375, 1347, 432, 1589, 172, 954, 242, 1256, 1256, 1248, 1256, 1256,
1248, 1248, 1256, 842, 13, 592, 13, 842, 1291, 592, 21, 175, 13, 592,
13, 13, 1426, 13, 1541, 445, 808, 808, 863, 647, 219, 1592, 1029,
1225, 917, 1963, 1129, 555, 1313, 550, 660, 550, 220, 660, 552, 663,
220, 533, 220, 383, 550, 1278, 1495, 636, 842, 1036, 425, 842, 425,
1537, 1278, 842, 554, 1508, 636, 554, 301, 842, 792, 1392, 1021, 284,
1172, 997, 1021, 103, 1316, 308, 1210, 848, 848, 1089, 1089, 848,
848, 67, 1029, 827, 1029, 2078, 827, 1312, 1029, 827, 590, 872, 1312,
427, 67, 67, 67, 67, 872, 827, 872, 2126, 1436, 26, 2126, 67, 1072,
2126, 1610, 872, 1620, 883, 883, 1397, 1189, 555, 555, 563, 1189,
555, 640, 555, 640, 1089, 1089, 610, 610, 1585, 610, 1355, 610, 1015,
616, 925, 1015, 482, 230, 707, 231, 888, 1355, 589, 1379, 151, 931,
1486, 1486, 393, 235, 960, 590, 235, 960, 422, 142, 285, 285, 327,
327, 442, 2009, 822, 445, 822, 567, 888, 2611, 1537, 323, 55, 1537,
323, 888, 2611, 323, 1537, 323, 58, 445, 593, 2045, 593, 58, 47, 770,
842, 47, 47, 842, 842, 648, 2557, 173, 689, 2291, 1446, 2085, 2557,
2557, 2291, 1780, 1535, 2291, 2391, 808, 691, 1295, 1165, 983, 948,
2000, 948, 983, 983, 2225, 2000, 983, 983, 705, 948, 2000, 1795,
1592, 478, 592, 1795, 1795, 663, 478, 1790, 478, 592, 1592, 173, 901,
312, 4, 1606, 173, 838, 754, 754, 128, 550, 1166, 551, 1480, 550,
550, 1875, 1957, 1166, 902, 1875, 550, 550, 551, 2632, 551, 1875,
1875, 551, 2891, 2159, 2632, 3231, 551, 815, 150, 1654, 1059, 1059,
734, 770, 555, 1592, 555, 2059, 770, 770, 1803, 627, 627, 627, 2059,
931, 1272, 427, 1606, 1272, 1606, 1187, 1204, 397, 822, 21, 1645,
263, 263, 822, 263, 1645, 280, 263, 605, 1645, 2014, 21, 21, 1029,
263, 1916, 2291, 397, 397, 496, 270, 270, 1319, 264, 1638, 264, 986,
1278, 1397, 1278, 1191, 409, 1191, 740, 1191, 754, 754, 387, 63, 948,
666, 666, 1198, 548, 63, 1248, 285, 1248, 169, 1248, 1248, 285, 918,
224, 285, 1426, 1671, 514, 514, 717, 514, 51, 1521, 1745, 51, 605,
1191, 51, 128, 1191, 51, 51, 1521, 267, 513, 952, 966, 1671, 897, 51,
71, 592, 986, 986, 1121, 592, 280, 2000, 2000, 1165, 1165, 1165,
1818, 222, 1818, 1165, 1252, 506, 327, 443, 432, 1291, 1291, 2755,
1413, 520, 1318, 227, 1047, 828, 520, 347, 1364, 136, 136, 452, 457,
457, 132, 457, 488, 1087, 1013, 2225, 32, 1571, 2009, 483, 67, 483,
Luby, et al. Standards Track PAGE 40
RFC 5053 Raptor FEC Scheme October 2007
740, 740, 1013, 2854, 866, 32, 2861, 866, 887, 32, 2444, 740, 32, 32,
866, 2225, 866, 32, 1571, 2627, 32, 850, 1675, 569, 1158, 32, 1158,
1797, 2641, 1565, 1158, 569, 1797, 1158, 1797, 55, 1703, 42, 55,
2562, 675, 1703, 42, 55, 749, 488, 488, 347, 1206, 1286, 1286, 488,
488, 1206, 1286, 1206, 1286, 550, 550, 1790, 860, 550, 2452, 550,
550, 2765, 1089, 1633, 797, 2244, 1313, 194, 2129, 194, 194, 194,
818, 32, 194, 450, 1313, 2387, 194, 1227, 2387, 308, 2232, 526, 476,
278, 830, 830, 194, 830, 194, 278, 194, 714, 476, 830, 714, 830, 278,
830, 2532, 1218, 1759, 1446, 960, 1747, 187, 1446, 1759, 960, 105,
1446, 1446, 1271, 1446, 960, 960, 1218, 1446, 1446, 105, 1446, 960,
488, 1446, 427, 534, 842, 1969, 2460, 1969, 842, 842, 1969, 427, 941,
2160, 427, 230, 938, 2075, 1675, 1675, 895, 1675, 34, 129, 1811, 239,
749, 1957, 2271, 749, 1908, 129, 239, 239, 129, 129, 2271, 2426,
1355, 1756, 194, 1583, 194, 194, 1583, 194, 1355, 194, 1628, 2221,
1269, 2425, 1756, 1355, 1355, 1583, 1033, 427, 582, 30, 582, 582,
935, 1444, 1962, 915, 733, 915, 938, 1962, 767, 353, 1630, 1962,
1962, 563, 733, 563, 733, 353, 822, 1630, 740, 2076, 2076, 2076, 589,
589, 2636, 866, 589, 947, 1528, 125, 273, 1058, 1058, 1161, 1635,
1355, 1161, 1161, 1355, 1355, 650, 1206, 1206, 784, 784, 784, 784,
784, 412, 461, 412, 2240, 412, 679, 891, 461, 679, 679, 189, 189,
1933, 1651, 2515, 189, 1386, 538, 1386, 1386, 1187, 1386, 2423, 2601,
2285, 175, 175, 2331, 194, 3079, 384, 538, 2365, 2294, 538, 2166,
1841, 3326, 1256, 3923, 976, 85, 550, 550, 1295, 863, 863, 550, 1249,
550, 1759, 146, 1069, 920, 2633, 885, 885, 1514, 1489, 166, 1514,
2041, 885, 2456, 885, 2041, 1081, 1948, 362, 550, 94, 324, 2308, 94,
2386, 94, 550, 874, 1329, 1759, 2280, 1487, 493, 493, 2099, 2599,
1431, 1086, 1514, 1086, 2099, 1858, 368, 1330, 2599, 1858, 2846,
2846, 2907, 2846, 713, 713, 1854, 1123, 713, 713, 3010, 1123, 3010,
538, 713, 1123, 447, 822, 555, 2011, 493, 508, 2292, 555, 1736, 2135,
2704, 555, 2814, 555, 2000, 555, 555, 822, 914, 327, 679, 327, 648,
537, 2263, 931, 1496, 537, 1296, 1745, 1592, 1658, 1795, 650, 1592,
1745, 1745, 1658, 1592, 1745, 1592, 1745, 1658, 1338, 2124, 1592,
1745, 1745, 1745, 837, 1726, 2897, 1118, 1118, 230, 1118, 1118, 1118,
1388, 1748, 514, 128, 1165, 931, 514, 2974, 2041, 2387, 2041, 979,
185, 36, 1269, 550, 173, 812, 36, 1165, 2676, 2562, 1473, 2885, 1982,
1578, 1578, 383, 383, 2360, 383, 1578, 2360, 1584, 1982, 1578, 1578,
1578, 2019, 1036, 355, 724, 2023, 205, 303, 355, 1036, 1966, 355,
1036, 401, 401, 401, 830, 401, 849, 578, 401, 849, 849, 578, 1776,
1123, 552, 2632, 808, 1446, 1120, 373, 1529, 1483, 1057, 893, 1284,
1430, 1529, 1529, 2632, 1352, 2063, 1606, 1352, 1606, 2291, 3079,
2291, 1529, 506, 838, 1606, 1606, 1352, 1529, 1529, 1483, 1529, 1606,
1529, 259, 902, 259, 902, 612, 612, 284, 398, 2991, 1534, 1118, 1118,
1118, 1118, 1118, 734, 284, 2224, 398, 734, 284, 734, 398, 3031, 398,
734, 1707, 2643, 1344, 1477, 475, 1818, 194, 1894, 691, 1528, 1184,
1207, 1501, 6, 2069, 871, 2069, 3548, 1443, 2069, 2685, 3265, 1350,
3265, 2069, 2069, 128, 1313, 128, 663, 414, 1313, 414, 2000, 128,
2000, 663, 1313, 699, 1797, 550, 327, 550, 1526, 699, 327, 1797,
1526, 550, 550, 327, 550, 1426, 1426, 1426, 2285, 1123, 890, 728,
Luby, et al. Standards Track PAGE 41
RFC 5053 Raptor FEC Scheme October 2007
1707, 728, 728, 327, 253, 1187, 1281, 1364, 1571, 2170, 755, 3232,
925, 1496, 2170, 2170, 1125, 443, 902, 902, 925, 755, 2078, 2457,
902, 2059, 2170, 1643, 1129, 902, 902, 1643, 1129, 606, 36, 103, 338,
338, 1089, 338, 338, 338, 1089, 338, 36, 340, 1206, 1176, 2041, 833,
1854, 1916, 1916, 1501, 2132, 1736, 3065, 367, 1934, 833, 833, 833,
2041, 3017, 2147, 818, 1397, 828, 2147, 398, 828, 818, 1158, 818,
689, 327, 36, 1745, 2132, 582, 1475, 189, 582, 2132, 1191, 582, 2132,
1176, 1176, 516, 2610, 2230, 2230, 64, 1501, 537, 1501, 173, 2230,
2988, 1501, 2694, 2694, 537, 537, 173, 173, 1501, 537, 64, 173, 173,
64, 2230, 537, 2230, 537, 2230, 2230, 2069, 3142, 1645, 689, 1165,
1165, 1963, 514, 488, 1963, 1145, 235, 1145, 1078, 1145, 231, 2405,
552, 21, 57, 57, 57, 1297, 1455, 1988, 2310, 1885, 2854, 2014, 734,
1705, 734, 2854, 734, 677, 1988, 1660, 734, 677, 734, 677, 677, 734,
2854, 1355, 677, 1397, 2947, 2386, 1698, 128, 1698, 3028, 2386, 2437,
2947, 2386, 2643, 2386, 2804, 1188, 335, 746, 1187, 1187, 861, 2519,
1917, 2842, 1917, 675, 1308, 234, 1917, 314, 314, 2339, 2339, 2592,
2576, 902, 916, 2339, 916, 2339, 916, 2339, 916, 1089, 1089, 2644,
1221, 1221, 2446, 308, 308, 2225, 2225, 3192, 2225, 555, 1592, 1592,
555, 893, 555, 550, 770, 3622, 2291, 2291, 3419, 465, 250, 2842,
2291, 2291, 2291, 935, 160, 1271, 308, 325, 935, 1799, 1799, 1891,
2227, 1799, 1598, 112, 1415, 1840, 2014, 1822, 2014, 677, 1822, 1415,
1415, 1822, 2014, 2386, 2159, 1822, 1415, 1822, 179, 1976, 1033, 179,
1840, 2014, 1415, 1970, 1970, 1501, 563, 563, 563, 462, 563, 1970,
1158, 563, 563, 1541, 1238, 383, 235, 1158, 383, 1278, 383, 1898,
2938, 21, 2938, 1313, 2201, 2059, 423, 2059, 1313, 872, 1313, 2044,
89, 173, 3327, 1660, 2044, 1623, 173, 1114, 1114, 1592, 1868, 1651,
1811, 383, 3469, 1811, 1651, 869, 383, 383, 1651, 1651, 3223, 2166,
3469, 767, 383, 1811, 767, 2323, 3355, 1457, 3341, 2640, 2976, 2323,
3341, 2323, 2640, 103, 103, 1161, 1080, 2429, 370, 2018, 2854, 2429,
2166, 2429, 2094, 2207, 871, 1963, 1963, 2023, 2023, 2336, 663, 2893,
1580, 691, 663, 705, 2046, 2599, 409, 2295, 1118, 2494, 1118, 1950,
549, 2494, 2453, 2046, 2494, 2453, 2046, 2453, 2046, 409, 1118, 4952,
2291, 2225, 1894, 1423, 2498, 567, 4129, 1475, 1501, 795, 463, 2084,
828, 828, 232, 828, 232, 232, 1818, 1818, 666, 463, 232, 220, 220,
2162, 2162, 833, 4336, 913, 35, 913, 21, 2927, 886, 3037, 383, 886,
876, 1747, 383, 916, 916, 916, 2927, 916, 1747, 837, 1894, 717, 423,
481, 1894, 1059, 2262, 3206, 4700, 1059, 3304, 2262, 871, 1831, 871,
3304, 1059, 1158, 1934, 1158, 756, 1511, 41, 978, 1934, 2603, 720,
41, 756, 41, 325, 2611, 1158, 173, 1123, 1934, 1934, 1511, 2045,
2045, 2045, 1423, 3206, 3691, 2512, 3206, 2512, 2000, 1811, 2504,
2504, 2611, 2437, 2437, 2437, 1455, 893, 150, 2665, 1966, 605, 398,
2331, 1177, 516, 1962, 4241, 94, 1252, 760, 1292, 1962, 1373, 2000,
1990, 3684, 42, 1868, 3779, 1811, 1811, 2041, 3010, 5436, 1780, 2041,
1868, 1811, 1780, 1811, 1868, 1811, 2041, 1868, 1811, 5627, 4274,
1811, 1868, 4602, 1811, 1811, 1474, 2665, 235, 1474, 2665
Luby, et al. Standards Track PAGE 42
RFC 5053 Raptor FEC Scheme October 2007
6. Security Considerations
Data delivery can be subject to denial-of-service attacks by
attackers that send corrupted packets that are accepted as legitimate
by receivers. This is particularly a concern for multicast delivery
because a corrupted packet may be injected into the session close to
the root of the multicast tree, in which case, the corrupted packet
will arrive at many receivers. This is particularly a concern when
the code described in this document is used because the use of even
one corrupted packet containing encoding data may result in the
decoding of an object that is completely corrupted and unusable. It
is thus RECOMMENDED that source authentication and integrity checking
are applied to decoded objects before delivering objects to an
application. For example, a SHA-1 hash [SHA1] of an object may be
appended before transmission, and the SHA-1 hash is computed and
checked after the object is decoded but before it is delivered to an
application. Source authentication SHOULD be provided, for example,
by including a digital signature verifiable by the receiver computed
on top of the hash value. It is also RECOMMENDED that a packet
authentication protocol, such as TESLA [RFC 4082], be used to detect
and discard corrupted packets upon arrival. This method may also be
used to provide source authentication. Furthermore, it is
RECOMMENDED that Reverse Path Forwarding checks be enabled in all
network routers and switches along the path from the sender to
receivers to limit the possibility of a bad agent successfully
injecting a corrupted packet into the multicast tree data path.
Another security concern is that some FEC information may be obtained
by receivers out-of-band in a session description, and if the session
description is forged or corrupted, then the receivers will not use
the correct protocol for decoding content from received packets. To
avoid these problems, it is RECOMMENDED that measures be taken to
prevent receivers from accepting incorrect session descriptions,
e.g., by using source authentication to ensure that receivers only
accept legitimate session descriptions from authorized senders.
7. IANA Considerations
Values of FEC Encoding IDs and FEC Instance IDs are subject to IANA
registration. For general guidelines on IANA considerations as they
apply to this document, see [RFC 5052]. This document assigns the
Fully-Specified FEC Encoding ID 1 under the ietf:rmt:fec:encoding
name-space to "Raptor Code".
Luby, et al. Standards Track PAGE 43
RFC 5053 Raptor FEC Scheme October 2007
8. Acknowledgements
Numerous editorial improvements and clarifications were made to this
specification during the review process within 3GPP. Thanks are due
to the members of 3GPP Technical Specification Group SA, Working
Group 4, for these.
9. References
9.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4082] Perrig, A., Song, D., Canetti, R., Tygar, J., and B.
Briscoe, "Timed Efficient Stream Loss-Tolerant
Authentication (TESLA): Multicast Source Authentication
Transform Introduction", RFC 4082, June 2005.
[RFC 5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, August 2007.
9.2. Informative References
[CCNC] Luby, M., Watson, M., Gasiba, T., Stockhammer, T., and W.
Xu, "Raptor Codes for Reliable Download Delivery in
Wireless Broadcast Systems", CCNC 2006, Las Vegas, NV ,
Jan 2006.
[MBMS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS);
Protocols and codecs", 3GPP TS 26.346 6.1.0, June 2005.
[RFC 3453] Luby, M., Vicisano, L., Gemmell, J., Rizzo, L., Handley,
M., and J. Crowcroft, "The Use of Forward Error Correction
(FEC) in Reliable Multicast", RFC 3453, December 2002.
[Raptor] Shokrollahi, A., "Raptor Codes", IEEE Transactions on
Information Theory no. 6, June 2006.
[SHA1] "Secure Hash Standard", Federal Information Processing
Standards Publication (FIPS PUB) 180-1, April 2005.
Luby, et al. Standards Track PAGE 44
RFC 5053 Raptor FEC Scheme October 2007
Authors' Addresses
Michael Luby
Digital Fountain
39141 Civic Center Drive
Suite 300
Fremont, CA 94538
U.S.A.
EMail: luby@digitalfountain.com
Amin Shokrollahi
EPFL
Laboratory of Algorithmic Mathematics
IC-IIF-ALGO
PSE-A
Lausanne 1015
Switzerland
EMail: amin.shokrollahi@epfl.ch
Mark Watson
Digital Fountain
39141 Civic Center Drive
Suite 300
Fremont, CA 94538
U.S.A.
EMail: mark@digitalfountain.com
Thomas Stockhammer
Nomor Research
Brecherspitzstrasse 8
Munich 81541
Germany
EMail: stockhammer@nomor.de
Luby, et al. Standards Track PAGE 45
RFC 5053 Raptor FEC Scheme October 2007
Full Copyright Statement
Copyright © The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Luby, et al. Standards Track PAGE 46
Raptor Forward Error Correction Scheme for Object Delivery
RFC TOTAL SIZE: 113743 bytes
PUBLICATION DATE: Tuesday, October 23rd, 2007
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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