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Versions: (draft-yang-nwcrg-bats-code) 00 01 02 03

Internet Engineering Task Force                                  S. Yang
Internet-Draft                                                  CUHK(SZ)
Intended status: Informational                                  X. Huang
Expires: November 26, 2020                                    R.W. Yeung
                                                                    CUHK
                                                                J.K. Zao
                                                                    NCTU
                                                            May 25, 2020


            BATS Coding Scheme for Multi-hop Data Transport
                        draft-yang-nwcrg-bats-03

Abstract

   This document describes a BATS coding scheme for communication
   through multi-hop networks.  BATS code is a class of efficient linear
   network coding scheme with a matrix generalization of fountain codes
   as the outer code, and batch-based linear network coding as the inner
   code.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 26, 2020.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Procedures  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Data Delivery Procedures  . . . . . . . . . . . . . . . .   4
       2.2.1.  Source Node Data Partitioning and Padding . . . . . .   5
       2.2.2.  Source Node Outer Code Encoding Procedure . . . . . .   5
       2.2.3.  Recoding Procedures . . . . . . . . . . . . . . . . .   7
       2.2.4.  Destination Node Procedures . . . . . . . . . . . . .   7
     2.3.  Recommendation for the Parameters . . . . . . . . . . . .   8
     2.4.  Example DDP Packet Format . . . . . . . . . . . . . . . .   8
       2.4.1.  Packet Header . . . . . . . . . . . . . . . . . . . .   8
       2.4.2.  Packet Payload  . . . . . . . . . . . . . . . . . . .   9
       2.4.3.  Packet Footer . . . . . . . . . . . . . . . . . . . .  10
   3.  BATS Code Specification . . . . . . . . . . . . . . . . . . .  10
     3.1.  Common Parts  . . . . . . . . . . . . . . . . . . . . . .  10
     3.2.  Outer Code Encoder  . . . . . . . . . . . . . . . . . . .  11
     3.3.  Inner Code Encoder (Recoder)  . . . . . . . . . . . . . .  12
     3.4.  Belief Propagation Decoder  . . . . . . . . . . . . . . .  13
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
     5.1.  Provision of Confidentiality Protection . . . . . . . . .  14
     5.2.  Countermeasures against Pollution Attacks . . . . . . . .  14
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  15
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  15
   Appendix A.  Additional Stuff . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   This document specifies a BATS code [BATS] scheme for data delivery
   in multi-hop networks.  The BATS code described here includes an
   outer code and an inner code.  The outer code is a matrix
   generalization of fountain codes (see also the RapterQ code described
   in RFC 6330 [RFC6330]), which inherits the advantages of reliability
   and efficiency and possesses the extra desirable property of being
   network coding compatible.  The inner code, also called recoding, is
   formed by linear network coding for combating packet loss, improving
   the multicast efficiency, etc.  A detailed design and analysis of
   BATS codes are provided in the BATS monograph [BATSMonograph].



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   The BATS coding scheme can be applied in multi-hop networks formed by
   wireless communication links, which are inherently unreliable due to
   interference.  Existing network protocols like TCP/IP use end-to-end
   retransmission and store-and-forward at the relays, so that packet
   loss would accumulate along the way.

   The BATS coding scheme can be used for various data delivery
   applications like file transmission, video streaming over wireless
   multi-hop networks, etc.  Different from traditional forward error
   correcting (FEC) schemes that are applied either hop-by-hop or end-
   to-end, the BATS coding scheme combines the end-to-end coding (the
   outer code) with certain hop-by-hop coding (the inner code), and
   hence can potentially achieve better performance.

   The coding scheme described here can be used in a network with
   multiple communication flows.  For each flow, the source node encodes
   the data for transmission separately.  Inside the network, however,
   it is possible to mix the packets from different flows for recoding.
   In this document, we describe a simple case where recoding is
   performed within each flow.  Note that the same encoding/decoding
   scheme described here can be used with different recoding schemes as
   long as they follow the principle as we illustrate in this document.

1.1.  Requirements Language

   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 [RFC2119].

2.  Procedures

2.1.  Introduction

   A BATS coding scheme includes an outer code encoder (also called
   encoder), an inner code encoder (also called recoder) and a decoder.
   The BATS coding scheme can be used for a single data flow that
   includes a single source and one or multiple destinations.  Thus
   there exists only one encoder with multiple recoders and decoders.
   The BATS coding scheme described in this document can be used by a
   Data Delivery Protocol (DDP) with the following procedures.

      Outer Code Encoding at a source node which has the data for
      transmission:

      *  The DDP provides the data to be delivered and the related
         information to the BATS encoder.





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      *  The BATS encoder generates a sequence of batches, each
         consisting of a set of coded packets and the information
         pertaining to the batch.

      The batches generated at the source node are further recoded
      before transmitting:

      *  A BATS recoder generates recoded packets of a batch.

      *  The DDP forms and transmits the DDP packets using the batches
         and the corresponding batch information.

      Recoding at an intermediate node that does not need the data:

      *  The DDP extracts the batches and the corresponding batch
         information from its received DDP packets.

      *  A BATS recoder generates recoded packets of a batch.

      *  The DDP forms and transmits DDP packets using the recoded
         packets and the corresponding batch information.

      Decoding at a destination node that needs the data:

      *  The DDP extracts the batches and the corresponding batch
         information from its received DDP packets.

      *  A BATS decoder tries to recover the transmitted data using the
         received batches.

      *  The DDP sends the decoded data to the application that needs
         the data.

2.2.  Data Delivery Procedures

   Suppose that the DDP has F octets of data for transmission.  We
   describe the procedures of one BATS session for transmitting the F
   octets.  There is a limit on F of a single BATS session.  If the
   total data has more than the limit, the data needs to be transmitted
   using multiple BATS sessions.  The limit on F of a single BATS
   session depends on the MTU (maximum transmission unit) of the
   network, which MUST be known by the DDP.  We have F is no more than
   (MTU-10)2^16-1 octets.








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2.2.1.  Source Node Data Partitioning and Padding

   The DDP first determines the following parameters:

   o  Batch size (M): the number of coded packets in a batch.

   o  Recoding field size (q): the number of elements in the finite
      field for recoding. q is 2 or 2^8

   o  BATS payload size (TO): the number of payload octets in a BATS
      packet, including the coded data and the coefficient vector.

   Based on the above parameters, the parameters T, O and K are
   calculated as follows:

   o  O: the number of octets of a coefficient vector, calculated as O =
      ceil(M*log2(q)/8).

   o  T: the number of data octets of a BATS packet, calculated as T =
      TO - O.

   o  K: number of source packets, calculated as K = floor(F/T)+1.

   The data MUST be padded to have T*K octets, which will be partitioned
   into K source packets b[0], ..., b[K-1], each of T octets.  In our
   padding scheme, b[0], ..., b[K-2] are filled with data bits, and
   b[K-1] is filled with the remaining data octets and padding octets.
   Let P = K*T-F denote the number of padding octets.  We use b[K-1, 0],
   ..., b[K-1, T-P-1] to denote the T-P source octets and b[K-1, T-P],
   ..., b[K-1, T-1] to denote the P padding octets in b[K-1],
   respectively.  The padding process is shown in Figure 1.

         Z = T - P
         Let bl be the last source packet b[K-1]
         for i = 1, 2, ... do
           if Z + i >= T - 1 do
               bl[Z...T-1] = i
               break
           bl[Z...Z+i-1] = i
           Z = Z + i

                      Figure 1: Data Padding Process

2.2.2.  Source Node Outer Code Encoding Procedure

   The DDP provides the BATS encoder with the following information:

   o  Batch size (M): the number of coded packets in a batch.



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   o  Recoding field size (q): the number of elements in the finite
      field for recoding.

   o  MAX_DEG: the size of DD.

   o  The degree distribution (DD), which is an unsigned integer array
      of size MAX_DEG+1.

   o  A sequence of batch IDs (j, j = 0, 1, ...).

   o  Number of source packets (K).

   o  Packet size (T): the number of octets in a source packet.

   o  The source packets (b[i], i = 0, 1, ..., K-1).

   Using this information, the (outer code) encoder generates a batch
   for each batch ID.  For the batch ID j, the encoder returns the DDP
   that contains

   o  a sparse degree d[j], and

   o  M coded packets (x[j,i], i =0, 1, ..., M-1), each containing TO
      octets.

   The DDP will use the batches to form DDP packets to be transmitted to
   other network nodes towards the destination nodes.  The DDP MUST
   deliver with each coded packet its

   o  d: sparse degree

   o  BID: batch ID

   The DDP MUST deliver the following information to each recoder:

   o  M: batch size M

   o  q: recoding field size

   The DDP MUST deliver the following information to each decoder:

   o  M: batch size

   o  q: recoding field size

   o  K: the number of source packet

   o  T: the number of octets in a source packet



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   The BATS payload size TO MUST be known by all the nodes.

2.2.3.  Recoding Procedures

   Both the source node and the intermediate nodes perform recoding on
   the batches before transmission.  At the source node, the recoder
   receives the batches from the outer code encoding procedure.  At an
   intermediate node, the DDP receives the DDP packets from the other
   network nodes, and should be able to extract coded packets and the
   corresponding batch information from these packets.

   The DDP provides the recoder with the following information:

   o  the batch size M,

   o  the recoding field size q,

   o  a number of received coded packets of the same batch, each
      containing TO octets, and

   o  link statistics, e.g., packet loss rates.

   For a received batch, the recoder determines a positive integer Mr,
   the number of recoded packets to be transmitted for the batch.  The
   recoder uses the information provided by the DDP to generate Mr
   recoded packets, each containing TO octets.  The DDP uses the Mr
   recoded packets to form the DDP packets for transmitting.

2.2.4.  Destination Node Procedures

   A destination node needs the data transmitted by the source node.  At
   the destination node, the DDP receives DDP packets from the other
   network nodes, and should be able to extract coded packets and the
   corresponding batch information from these packets.

   The DDP provides the decoder with the following information:

   o  M: batch size,

   o  q: recoding field size,

   o  K: the number of source packets

   o  T: the number of octets of a source packet

   o  A sequence of batches, each of which is formed by a number of
      coded packets belonging to the same batch, with their
      corresponding batch IDs and degrees.



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   The decoder uses this information to decode the K source packets.  If
   successful, the decoder returns the recovered K source packets to the
   DDP, which will use the K source packets to form the F octets data.
   The recommended padding process is shown as follows:

       // this procedure returns the number P of padding octets
       // at the end of b[K-1]
       Let bl be the last decoded source packet b[K-1]
       PL = bl[T-1]
       if PL == 1 do
           return P = 1
       WI = T - 1
       while bl[WI] == PL do
           WI = WI - 1
       return P = (1 + bl[WI]) * bl[WI] + T - WI - 1

                     Figure 2: Data Depadding Process

2.3.  Recommendation for the Parameters

   The recommendation for the parameters M and q is shown as follows:

   o  When q=2, M=16,32,64

   o  When q=256, M=8,16,32,64

   It is RECOMMENDED that K is at least 128.  However, the encoder/
   decoder SHALL support an arbitrary positive integer value less than
   2^16.

2.4.  Example DDP Packet Format

   A DDP can form a DDP packet with a header (5 octets), a footer (3
   octets) and a payload (TO octets).  A DDP packet has totally 8+TO
   octets.

2.4.1.  Packet Header

   The BATS packet header has 40 bits (5 octets) and includes fields
   Packet_Count, Mq, Batch_ID, and Degree.











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       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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           Packet_Count        |  Mq   |       Batch_ID        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Degree    |
       +-+-+-+-+-+-+-+-+

                   Figure 3: BATS packet header format.

   o  Packet_Count: 16-bit unsigned integer, specifying the number K of
      packets of the BATS session.

   o  Mq: 4-bit unsigned integer to specify the value of M and q as
      Table 1.

   o  Batch_ID: 12-bit unsigned integer, specifying the batch ID BID of
      the batch the packet belonging to.

   o  Degree: 8-bit unsigned integer, specifying the batch degree d of
      the batch the packet belonging to.

                         +------+----+-----+----+
                         | Mq   | M  | q   | O  |
                         +------+----+-----+----+
                         | 0010 | 16 | 2   | 2  |
                         | 0100 | 32 | 2   | 4  |
                         | 0110 | 64 | 2   | 8  |
                         | 0001 | 8  | 256 | 8  |
                         | 0011 | 16 | 256 | 16 |
                         | 0101 | 32 | 256 | 32 |
                         | 0111 | 64 | 256 | 64 |
                         +------+----+-----+----+

                        Table 1: Values of Mq field

2.4.2.  Packet Payload

                     O                         T
         +-----------------------+-------------------------------+
         |   coefficient vector  |          coded data           |
         +-----------------------+-------------------------------+

                   Figure 4: BATS packet payload format.

   The payload has TO octets, where the first O octets contain the
   coefficient vector and the remaining T octets contain the coded data.




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   Information in both fields MAY be encoded in JSON (ASCII) or protobuf
   (binary) formats.

   o  coefficient vector: O octets.  The range of the value of O is in
      Table 1.

   o  coded data: T octets.  T is at most MTU - 10, where 10 is the
      total of the header and footer length plus the minimum value of O.

2.4.3.  Packet Footer

         0                   1                   2
         0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |            signature          |  parity check |
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 5: BATS packet footer format.

   The footer has three octets.

   o  signature: 2 octets.  A signature of the individual packet to
      prevent pollution attack.

   o  parity check: 1 octet.  A parity check field used to verity the
      correctness of the packet.

3.  BATS Code Specification

3.1.  Common Parts

   The T octets of a source packets are treated as a column vector of T
   elements in GF(256).  Linear algebra and matrix operations over
   finite fields are assumed in this section.

   Suppose that a pseudorandom number generator Rand() which generate an
   unsigned integer of 32 bits is shared by both encoding and decoding.
   The pseudorandom generator can be initialized by Rand_Init(S) with
   seed S.  When S is not provided, the pseudorandom generator is
   initialized arbitrarily.  One example of such a pseudorandom
   generator is defined in RFC 8682 [RFC8682].

   A function called BatchSampler is used in both encoding and decoding.
   The function takes two integers j and d as input, and generates an
   array idx of d integers and a d x M matrix G.  The function first
   initializes the pseudorandom generator with j, sample d distinct
   integers from 0 to K-1 as idx, and sample d*M integers from 0 to 255
   as G.  See the pseudocode in Figure 6.



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   function BatchSampler(j,d)
       // initialize the pseudorandom generator by seed j.
       Rand_Init(j)
       // sample d distinct integers between 0 and K-1.
       for k = 0, ..., d-1 do
           r = Rand() % K
           while r already exists in idx do
               r = Rand() % K
           idx[k] = r

       // sample d x M matrix
       for r = 0, ..., d-1 do
           for c = 0,...,M-1 do
               G[r,c] = Rand() % 256

       return idx, G

                     Figure 6: Batch Sampler Function

3.2.  Outer Code Encoder

   Define a function called DegreeSampler that return an integer d using
   the degree distribution DD.  We expect that the empirical
   distribution of the returning d converges to DD(d) when d < K.  One
   design of DegreeSampler is illustrated in Figure 7.

   function DegreeSampler(j, DD)
       Let CDF be an array
       CDF[0] = 0
       for i = 1, ..., MAX_DEG do
           CDF[i] = CDF[i-1] + DD[i]
       Rand_Init()
       r = Rand() % CDF[MAX_DEG]
       for d = 1, ..., MAX_DEG do
           if r >= CDF[d] do
               return min(d,K)
       return min(MAX_DEG,K)

                     Figure 7: Degree Sampler Function

   Let b[0], b[1], ..., b[K-1] be the K source packets.  A batch with
   BID j is generated using the following steps.

   o  Obtain a degree d by calling DegreeSampler with input j.

   o  Obtain idx and G[j] by calling BatchSampler with input j and d.





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   o  Let B[j] = (b[idx[0]], b[idx[1]], ..., b[idx[d-1]]).  Form the
      batch X[j] = B[j]*G[j], whose dimension is T x M.

   o  Form the TO x M matrix Xr[j], where the first O rows of Xr[j] form
      the M x M identity matrix I with entries in GF(q), and the last T
      rows of Xr[j] is X[j].

   See the pseudocode of the batch generating process in Figure 8.

   function GenBatch(j)
       d = DegreeSampler(j)
       (idx, G) = BatchSampler(j,d)
       B = (b[idx[0]], b[idx[i]], ..., b[idx[d-1]])
       X = B * G
       Xr = [I_M; X]
       return Xr

                    Figure 8: Batch Generation Function

3.3.  Inner Code Encoder (Recoder)

   The inner code comprises (random) linear network coding applied on
   the coded packets belonging to the same batch.  At a particular
   network node, recoded packets are generated by (random) linear
   combinations of the received coded packets of a batch.  The recoded
   packets have the same BID, sparse degree and coded packet length.

   The number Mr of recoded packets for a batch is decided first by the
   recoder.  Mr can be set as M.  When the link statistics is known, the
   recoder can try to obtain the link packet loss rate e for the link to
   transmit the recoded batch, and set Mr to be (1+e)M.

   Suppose that coded packets xr[i], i = 0, 1, ..., r-1, which have the
   same BID j, have been received at an intermediate node.  Using the
   recommended packet format, it can be verified whether the
   corresponding packet headers of these coded packets are the same.
   Then a recoded packet can be generated by one of the following two
   approaches:

   o  forwarding: when receiving xr[i], directly use xr[i] as a recoded
      packet.

   o  linear combination recoding: (randomly) choose a sequence of
      coefficients c[i], i = 0, 1, ..., r-1 from GF(q).  Generate
      c[0]xr[0]+c[1]xr[1]+...+c[r-1]xr[r-1] as a recoded packet.

   A recoder can combine these two approaches to generate recoded
   packets.  For example, the recoder will output xr[i], i = 0, 1, ...,



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   r-1 as r systematic recoded packets and generate Mr-r recoded packets
   using linear combinations of randomly chosen coefficients.

3.4.  Belief Propagation Decoder

   The decoder receives a sequence of batches Yr[j], j = 0, 1, ..., n-1,
   each of which is a TO-row matrix over GF(256).  The degree d[j] of
   batch j is also known.  Let Y[j] be the submatrix of the last T rows
   of Yr[j].  When q = 256, let H[j] be the first M rows of Yr[j]; when
   q = 2, let H[j] be the matrix over GF(256) formed by embedding each
   bit in the first M/8 rows of Yr[j] into GF(256).

   By calling BatchSampler with input j and d[j], we obtain idx[j] and
   G[j].  According to the encoding and recoding processes described in
   Section 3.2 and Section 3.3, we have the system of linear equations
   Y[j] = B[j]G[j]H[j] for each received batch with ID j, where B[j] =
   (b[idx[j,0]], b[idx[j,1]], ..., b[idx[j,d-1]]) is unknown.

   We describe a belief propagation (BP) decoder that can efficiently
   solve the source packets when a sufficient number of batches have
   been received.  A batch j is said to be decodable if rank(G[j]H[j]) =
   d[j] (i.e., the system of linear equations Y[j] = B[j]G[j]H[j] with
   B[j] as the variable matrix has a unique solution).  The BP decoding
   algorithm has multiple iterations.  Each iteration is formed by the
   following steps:

   o  Decoding step: Find a batches j that is decodable.  Solve the
      corresponding system of linear equations Y[j] = B[j]G[j]H[j] and
      decode B[j].

   o  Substitution step: Substitute the decoded source packets into
      undecodable batches.  Suppose that a decoded source packet b[k] is
      used in generating a undecodable Y[j].  The substitution involves
      1) removing the entry in idx[j] corresponding to k, 2) removing
      the row in G[j] corresponding to b[k], and 3) reducing d[j] by 1.

   The BP decoder repeats the above steps until no batches are decodable
   during the decoding step.

4.  IANA Considerations

   This memo includes no request to IANA.

5.  Security Considerations

   Subsuming both Random Linear Network Codes (RLNC) and fountain codes,
   BATS codes naturally inherit both their desirable capability of




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   offering confidentiality protection as well as their vulnerability
   towards pollution attacks.

5.1.  Provision of Confidentiality Protection

   Since the transported messages are linearly combined with random
   coefficients at each recoding node, it is statistically impossible to
   recover the individual messages by capturing the coded messages at
   any one or small number of nodes.  As long as the coding matrices of
   the transported messages cannot be fully recovered, any attempt of
   decoding is equivalent to randomly guessing the transported messages.
   Thus, with the use of BATS codes, information confidentiality
   throughout the data transport process is assured.

   The only threat towards confidentiality exists in the form of
   eavesdropping on the initial encoding process, which takes place at
   the encoding nodes.  In these nodes, the transported data are
   presented in plain text and can be read along their transfer paths.
   Hence, information isolation between the encoding process and all
   other user processes running on the node must be assured.

   In addition, the authenticity and trustworthiness of the encoding,
   recoding and decoding program running on all the nodes must be
   attested by a trusted authority.  Such a measure is also necessary in
   countering pollution attacks.

5.2.  Countermeasures against Pollution Attacks

   Like all network codes, BATS codes are vulnerable under pollution
   attacks.  In these attacks, one or more compromised coding node(s)
   can pollute the coded messages or inject forged messages into the
   coding network.  These attacks can prevent the receivers from
   recovering the transported data correctly.  Although error detection
   mechanisms can be put in place to prevent the receivers from getting
   the wrong messages, detection and discard of the polluted messages
   still constitute a form of denial-of-service (DoS) attack.

   The research community has long been investigating the use of various
   signature schemes (including homomorphic signatures) to identify the
   forged messages and stall the attacks (see Zhao07 [Zhao07], Yu08
   [Yu08], Agrawal09 [Agrawal09]).  Nevertheless, these countermeasures
   are regarded as being computationally too expensive to be employed in
   broadband communications.  A practical approach to protect against
   pollution attacks consist of the following system-level
   countermeasures:

   1.  Attestation and Validation of all encoding, recoding and decoding
       nodes in the network.  Remote attestation and repetitive



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       validation of a node based on valid public key certificates with
       proper authorization MUST be a pre-requisite for admitting that
       node to a network and permitting it to remain in that network.

   2.  Attestation of all encoding, recoding and decoding programs used
       in the coding nodes.  All programs used to perform the BATS
       encoding, recoding and decoding processes MUST be remotely
       attested before they are permitted to run on any of the coding
       nodes.  Reloading or alteration of programs MUST NOT be permitted
       during an encoding session.  Programs MUST be attested or
       validated again when they are executed in new execution
       environments instantiated even in the same node.

   3.  Original Authentication of all coded messages using network or
       transport level secure protocols such as IP-sec or TLS/DTLS MUST
       be used to provide Peer or Message Origin Authentication to every
       coded message sent through the coding network.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8682]  Saito, M., Matsumoto, M., Roca, V., Ed., and E. Baccelli,
              "TinyMT32 Pseudorandom Number Generator (PRNG)", RFC 8682,
              DOI 10.17487/RFC8682, January 2020,
              <https://www.rfc-editor.org/info/rfc8682>.

6.2.  Informative References

   [Agrawal09]
              Agrawal, S. and D. Boneh, "Homomorphic MACs: MAC-based
              integrity for network coding", International Conference on
              Applied Cryptography and Network Security , 2009.

   [BATS]     Yang, S. and R. Yeung, "Batched Sparse Codes", IEEE
              Transactions on Information Theory 60(9), 5322-5346, 2014.

   [BATSMonograph]
              Yang, S. and R. Yeung, "BATS Codes: Theory and Practice",
              Morgan & Claypool Publishers , 2017.






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   [RFC6330]  Luby, M., Shokrollahi, A., Watson, M., Stockhammer, T.,
              and L. Minder, "RaptorQ Forward Error Correction Scheme
              for Object Delivery", RFC 6330, DOI 10.17487/RFC6330,
              August 2011, <https://www.rfc-editor.org/info/rfc6330>.

   [Yu08]     Yu, Z., Wei, Y., Ramkumar, B., and Y. Guan, "An Efficient
              Signature-Based Scheme for Securing Network Coding Against
              Pollution Attacks", INFOCOM , 2008.

   [Zhao07]   Zhao, F., Kalker, T., Medard, M., and K. Han, "Signatures
              for content distribution with network coding", ISIT ,
              2007.

Appendix A.  Additional Stuff

   This becomes an Appendix.

Authors' Addresses

   Shenghao Yang
   CUHK(SZ)
   Shenzhen, Guangdong
   China

   Phone: +86 755 8427 3827
   Email: shyang@cuhk.edu.cn


   Xuan Huang
   CUHK
   Hong Kong, Hong Kong SAR
   China

   Phone: +852 3943 8375
   Email: 1155136647@link.cuhk.edu.hk


   Raymond W. Yeung
   CUHK
   Hong Kong, Hong Kong SAR
   China

   Phone: +852 3943 8375
   Email: whyeung@ie.cuhk.edu.hk







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   John K. Zao
   NCTU
   Hsinchu, Taiwan
   China

   Email: jkzao@ieee.org













































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