< draft-ietf-lpwan-ipv6-static-context-hc-08.txt   draft-ietf-lpwan-ipv6-static-context-hc-09.txt >
lpwan Working Group A. Minaburo lpwan Working Group A. Minaburo
Internet-Draft Acklio Internet-Draft Acklio
Intended status: Informational L. Toutain Intended status: Informational L. Toutain
Expires: June 20, 2018 IMT-Atlantique Expires: June 25, 2018 IMT-Atlantique
C. Gomez C. Gomez
Universitat Politecnica de Catalunya Universitat Politecnica de Catalunya
December 17, 2017 December 22, 2017
LPWAN Static Context Header Compression (SCHC) and fragmentation for LPWAN Static Context Header Compression (SCHC) and fragmentation for
IPv6 and UDP IPv6 and UDP
draft-ietf-lpwan-ipv6-static-context-hc-08 draft-ietf-lpwan-ipv6-static-context-hc-09
Abstract Abstract
This document describes a header compression scheme and fragmentation This document describes a header compression scheme and fragmentation
functionality for very low bandwidth networks. These techniques are functionality for very low bandwidth networks. These techniques are
specially tailored for Low Power Wide Area Network (LPWAN). specially tailored for Low Power Wide Area Network (LPWAN).
The Static Context Header Compression (SCHC) offers a great level of The Static Context Header Compression (SCHC) offers a great level of
flexibility when processing the header fields. SCHC compression is flexibility when processing the header fields. SCHC compression is
based on a common static context stored in a LPWAN device and in the based on a common static context stored in a LPWAN device and in the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 20, 2018. This Internet-Draft will expire on June 25, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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4.5.1. not-sent CDA . . . . . . . . . . . . . . . . . . . . 13 4.5.1. not-sent CDA . . . . . . . . . . . . . . . . . . . . 13
4.5.2. value-sent CDA . . . . . . . . . . . . . . . . . . . 13 4.5.2. value-sent CDA . . . . . . . . . . . . . . . . . . . 13
4.5.3. mapping-sent . . . . . . . . . . . . . . . . . . . . 14 4.5.3. mapping-sent . . . . . . . . . . . . . . . . . . . . 14
4.5.4. LSB CDA . . . . . . . . . . . . . . . . . . . . . . . 14 4.5.4. LSB CDA . . . . . . . . . . . . . . . . . . . . . . . 14
4.5.5. DEViid, APPiid CDA . . . . . . . . . . . . . . . . . 14 4.5.5. DEViid, APPiid CDA . . . . . . . . . . . . . . . . . 14
4.5.6. Compute-* . . . . . . . . . . . . . . . . . . . . . . 14 4.5.6. Compute-* . . . . . . . . . . . . . . . . . . . . . . 14
5. Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . 15 5. Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15 5.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Functionalities . . . . . . . . . . . . . . . . . . . . . 15 5.2. Functionalities . . . . . . . . . . . . . . . . . . . . . 15
5.3. Delivery Reliability options . . . . . . . . . . . . . . 18 5.3. Delivery Reliability options . . . . . . . . . . . . . . 18
5.4. Fragmentation Frames Formats . . . . . . . . . . . . . . 19 5.4. Fragmentation Frame Formats . . . . . . . . . . . . . . . 20
5.4.1. Fragment format . . . . . . . . . . . . . . . . . . . 19 5.4.1. Fragment format . . . . . . . . . . . . . . . . . . . 20
5.4.2. Fragmentation formats . . . . . . . . . . . . . . . . 20 5.4.2. ACK format . . . . . . . . . . . . . . . . . . . . . 21
5.4.3. ACK format . . . . . . . . . . . . . . . . . . . . . 20 5.4.3. All-1 and All-0 formats . . . . . . . . . . . . . . . 21
5.4.4. All-1 and All-0 formats . . . . . . . . . . . . . . . 21 5.4.4. Abort formats . . . . . . . . . . . . . . . . . . . . 23
5.4.5. Abort formats . . . . . . . . . . . . . . . . . . . . 23
5.5. Baseline mechanism . . . . . . . . . . . . . . . . . . . 23 5.5. Baseline mechanism . . . . . . . . . . . . . . . . . . . 23
5.5.1. No ACK . . . . . . . . . . . . . . . . . . . . . . . 24 5.5.1. No ACK . . . . . . . . . . . . . . . . . . . . . . . 24
5.5.2. The Window modes . . . . . . . . . . . . . . . . . . 25 5.5.2. The Window modes . . . . . . . . . . . . . . . . . . 25
5.5.3. Bitmap Optimization . . . . . . . . . . . . . . . . . 28 5.5.3. Bitmap Optimization . . . . . . . . . . . . . . . . . 29
5.6. Supporting multiple window sizes . . . . . . . . . . . . 30 5.6. Supporting multiple window sizes . . . . . . . . . . . . 31
5.7. Downlink fragment transmission . . . . . . . . . . . . . 31 5.7. Downlink fragment transmission . . . . . . . . . . . . . 31
6. Padding management . . . . . . . . . . . . . . . . . . . . . 32 6. Padding management . . . . . . . . . . . . . . . . . . . . . 32
7. SCHC Compression for IPv6 and UDP headers . . . . . . . . . . 32 7. SCHC Compression for IPv6 and UDP headers . . . . . . . . . . 33
7.1. IPv6 version field . . . . . . . . . . . . . . . . . . . 32 7.1. IPv6 version field . . . . . . . . . . . . . . . . . . . 33
7.2. IPv6 Traffic class field . . . . . . . . . . . . . . . . 32 7.2. IPv6 Traffic class field . . . . . . . . . . . . . . . . 33
7.3. Flow label field . . . . . . . . . . . . . . . . . . . . 33 7.3. Flow label field . . . . . . . . . . . . . . . . . . . . 33
7.4. Payload Length field . . . . . . . . . . . . . . . . . . 33 7.4. Payload Length field . . . . . . . . . . . . . . . . . . 34
7.5. Next Header field . . . . . . . . . . . . . . . . . . . . 33 7.5. Next Header field . . . . . . . . . . . . . . . . . . . . 34
7.6. Hop Limit field . . . . . . . . . . . . . . . . . . . . . 34 7.6. Hop Limit field . . . . . . . . . . . . . . . . . . . . . 34
7.7. IPv6 addresses fields . . . . . . . . . . . . . . . . . . 34 7.7. IPv6 addresses fields . . . . . . . . . . . . . . . . . . 35
7.7.1. IPv6 source and destination prefixes . . . . . . . . 34 7.7.1. IPv6 source and destination prefixes . . . . . . . . 35
7.7.2. IPv6 source and destination IID . . . . . . . . . . . 35 7.7.2. IPv6 source and destination IID . . . . . . . . . . . 35
7.8. IPv6 extensions . . . . . . . . . . . . . . . . . . . . . 35 7.8. IPv6 extensions . . . . . . . . . . . . . . . . . . . . . 36
7.9. UDP source and destination port . . . . . . . . . . . . . 35 7.9. UDP source and destination port . . . . . . . . . . . . . 36
7.10. UDP length field . . . . . . . . . . . . . . . . . . . . 36 7.10. UDP length field . . . . . . . . . . . . . . . . . . . . 36
7.11. UDP Checksum field . . . . . . . . . . . . . . . . . . . 36 7.11. UDP Checksum field . . . . . . . . . . . . . . . . . . . 37
8. Security considerations . . . . . . . . . . . . . . . . . . . 36 8. Security considerations . . . . . . . . . . . . . . . . . . . 37
8.1. Security considerations for header compression . . . . . 36 8.1. Security considerations for header compression . . . . . 37
8.2. Security considerations for fragmentation . . . . . . . . 36 8.2. Security considerations for fragmentation . . . . . . . . 37
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . 38 10.1. Normative References . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . 38 10.2. Informative References . . . . . . . . . . . . . . . . . 39
Appendix A. SCHC Compression Examples . . . . . . . . . . . . . 38 Appendix A. SCHC Compression Examples . . . . . . . . . . . . . 39
Appendix B. Fragmentation Examples . . . . . . . . . . . . . . . 41 Appendix B. Fragmentation Examples . . . . . . . . . . . . . . . 42
Appendix C. Fragmentation State Machines . . . . . . . . . . . . 47 Appendix C. Fragmentation State Machines . . . . . . . . . . . . 48
Appendix D. Allocation of Rule IDs for fragmentation . . . . . . 54 Appendix D. Allocation of Rule IDs for fragmentation . . . . . . 55
Appendix E. Note . . . . . . . . . . . . . . . . . . . . . . . . 54 Appendix E. Note . . . . . . . . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 54 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 55
1. Introduction 1. Introduction
Header compression is mandatory to efficiently bring Internet Header compression is mandatory to efficiently bring Internet
connectivity to the node within a LPWAN network. Some LPWAN networks connectivity to the node within a LPWAN network. Some LPWAN networks
properties can be exploited to get an efficient header compression: properties can be exploited to get an efficient header compression:
o Topology is star-oriented; therefore, all the packets follow the o Topology is star-oriented; therefore, all the packets follow the
same path. For the needs of this draft, the architecture can be same path. For the needs of this draft, the architecture can be
summarized to Devices (Dev) exchanging information with LPWAN summarized to Devices (Dev) exchanging information with LPWAN
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() () () / \ +---------+ +-----------+ () () () / \ +---------+ +-----------+
Dev Radio Gateways NGW Dev Radio Gateways NGW
Figure 1: LPWAN Architecture Figure 1: LPWAN Architecture
3. Terminology 3. Terminology
This section defines the terminology and acronyms used in this This section defines the terminology and acronyms used in this
document. document.
o All-0. Fragmentation Packet format to send the last frame of a o All-0. Fragment format for the last frame of a window.
window.
o All-1. Fragmentation Packet format to send the last frame of a o All-1. Fragment format for the last frame of a packet.
packet.
o All-0 empty. Fragmentation Packet format without payload to o All-0 empty. Fragment format without payload for requesting the
request the bitmap when the Retransmission Timer expires in a Bitmap when the Retransmission Timer expires in a window that is
window. not the last one for a fragmented packet transmission.
o All-1 empty. Fragmentation Packet format without payload to o All-1 empty. Fragment format without payload for requesting the
request the bitmap when the Retransmission Timer expires in the Bitmap when the Retransmission Timer expires in the last window.
last window.
o App: LPWAN Application. An application sending/receiving IPv6 o App: LPWAN Application. An application sending/receiving IPv6
packets to/from the Device. packets to/from the Device.
o APP-IID: Application Interface Identifier. Second part of the o APP-IID: Application Interface Identifier. Second part of the
IPv6 address to identify the application interface IPv6 address to identify the application interface
o Bi: Bidirectional, a rule entry that applies in both directions. o Bi: Bidirectional, a rule entry that applies in both directions.
o C: Checked bit. Used in fragmentation header to determine when o C: Checked bit. Used in an acknowledgment (ACK) header to
the MIC is correct (1) or not (0). determine when the MIC is correct (1) or not (0).
o CDA: Compression/Decompression Action. An action that is o CDA: Compression/Decompression Action. An action that is
performed for both functionalities to compress a header field or performed for both functionalities to compress a header field or
to recover its original value in the decompression phase. to recover its original value in the decompression phase.
o Context: A set of rules used to compress/decompress headers o Context: A set of rules used to compress/decompress headers
o Dev: Device. A Node connected to the LPWAN. A Dev may implement o Dev: Device. A Node connected to the LPWAN. A Dev may implement
SCHC. SCHC.
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o FL: Field Length is a value to identify if the field is fixed or o FL: Field Length is a value to identify if the field is fixed or
variable length. variable length.
o FP: Field Position is a value that is used to identify each o FP: Field Position is a value that is used to identify each
instance a field appears in the header. instance a field appears in the header.
o IID: Interface Identifier. See the IPv6 addressing architecture o IID: Interface Identifier. See the IPv6 addressing architecture
[RFC7136] [RFC7136]
o Inactivity Timer. Timer to End the state machine when there is an o Inactivity Timer. A timer to end the fragmentation state machine
error and there is no possibility to continue the transmission. when there is an error and there is no possibility to continue an
on-going fragmented packet transmission.
o MIC: Message Integrity Check. A fragmentation header field o MIC: Message Integrity Check. A fragmentation header field
computed over an IPv6 packet before fragmentation, used for error computed over an IPv6 packet before fragmentation, used for error
detection after IPv6 packet reassembly. detection after IPv6 packet reassembly.
o MO: Matching Operator. An operator used to match a value o MO: Matching Operator. An operator used to match a value
contained in a header field with a value contained in a Rule. contained in a header field with a value contained in a Rule.
o Retransmission Timer. Timer used in the sender transmission to o Retransmission Timer. A timer used by the fragment sender during
detect error in the link when waiting for an ACK. an on-going fragmented packet transmission to detect possible link
errors when waiting for a possible incoming ACK.
o Rule: A set of header field values. o Rule: A set of header field values.
o Rule entry: A row in the rule that describes a header field. o Rule entry: A row in the rule that describes a header field.
o Rule ID: An identifier for a rule, SCHC C/D, and Dev share the o Rule ID: An identifier for a rule, SCHC C/D, and Dev share the
same Rule ID for a specific flow. A set of Rule IDs are used to same Rule ID for a specific flow. A set of Rule IDs are used to
support fragmentation functionality. support fragmentation functionality.
o SCHC C/D: Static Context Header Compression Compressor/ o SCHC C/D: Static Context Header Compression Compressor/
Decompressor. A process in the network to achieve compression/ Decompressor. A process in the network to achieve compression/
decompressing headers. SCHC C/D uses SCHC rules to perform decompressing headers. SCHC C/D uses SCHC rules to perform
compression and decompression. compression and decompression.
o TV: Target value. A value contained in the Rule that will be o TV: Target value. A value contained in the Rule that will be
matched with the value of a header field. matched with the value of a header field.
o Up: Up Link direction for compression, from Dev to SCHC C/D. o Up: Up Link direction for compression, from Dev to SCHC C/D.
o W: Window bit. A fragmentation header field used in Window mode o W: Window bit. A fragment header field used in Window mode (see
(see section 9), which carries the same value for all fragments of section 5), which carries the same value for all fragments of a
a window. window.
o Window: A subset of the fragments needed to carry a packet (see
section 5)
4. Static Context Header Compression 4. Static Context Header Compression
Static Context Header Compression (SCHC) avoids context Static Context Header Compression (SCHC) avoids context
synchronization, which is the most bandwidth-consuming operation in synchronization, which is the most bandwidth-consuming operation in
other header compression mechanisms such as RoHC [RFC5795]. Based on other header compression mechanisms such as RoHC [RFC5795]. Based on
the fact that the nature of data flows is highly predictable in LPWAN the fact that the nature of data flows is highly predictable in LPWAN
networks, some static contexts may be stored on the Device (Dev). networks, some static contexts may be stored on the Device (Dev).
The contexts must be stored in both ends, and it can either be The contexts must be stored in both ends, and it can either be
learned by a provisioning protocol or by out of band means or it can learned by a provisioning protocol or by out of band means or it can
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o compute-checksum: compute a checksum from the information already o compute-checksum: compute a checksum from the information already
received by the SCHC C/D. This field may be used to compute UDP received by the SCHC C/D. This field may be used to compute UDP
checksum. checksum.
5. Fragmentation 5. Fragmentation
5.1. Overview 5.1. Overview
In LPWAN technologies, the L2 data unit size typically varies from In LPWAN technologies, the L2 data unit size typically varies from
tens to hundreds of bytes. If the entire IPv6 datagram after tens to hundreds of bytes. If after applying SCHC header compression
applying SCHC header compression or when SCHC header compression is or when SCHC header compression is not possible the entire IPv6
not possible, fits within a single L2 data unit, the fragmentation datagram fits within a single L2 data unit, the fragmentation
mechanism is not used and the packet is sent. Otherwise, the mechanism is not used and the packet is sent. Otherwise, the
datagram SHALL be broken into fragments. datagram SHALL be broken into fragments.
LPWAN technologies impose some strict limitations on traffic, devices LPWAN technologies impose some strict limitations on traffic, (e.g.)
are sleeping most of the time and may receive data during a short devices are sleeping most of the time and may receive data during a
period of time after transmission to preserve battery. To adapt the short period of time after transmission to preserve battery. To
SCHC fragmentation to the capabilities of LPWAN technologies, it is adapt the SCHC fragmentation to the capabilities of LPWAN
desirable to enable optional fragment retransmission and to allow a technologies, it is desirable to enable optional fragment
gradation of fragment delivery reliability. This document does not retransmission and to allow a gradation of fragment delivery
make any decision with regard to which fragment delivery reliability reliability. This document does not make any decision with regard to
option(s) will be used over a specific LPWAN technology. which fragment delivery reliability option(s) will be used over a
specific LPWAN technology.
An important consideration is that LPWAN networks typically follow An important consideration is that LPWAN networks typically follow a
the star topology, and therefore data unit reordering is not expected the star topology, and therefore data unit reordering is not expected
in such networks. This specification assumes that reordering will in such networks. This specification assumes that reordering will
not happen between the entity performing fragmentation and the entity not happen between the entity performing fragmentation and the entity
performing reassembly. This assumption allows to reduce complexity performing reassembly. This assumption allows to reduce complexity
and overhead of the fragmentation mechanism. and overhead of the fragmentation mechanism.
5.2. Functionalities 5.2. Functionalities
This subsection describes the different fields in the fragmentation This subsection describes the different fields in the fragmentation
header frames (see the fragmentation frames format in Section 5.4) header frames (see the related formats in Section 5.4), as well as
that are used to enable the fragmentation functionalities defined in the tools that are used to enable the fragmentation functionalities
this document, and the different reliability options supported. defined in this document, and the different reliability options
supported.
o Rule ID. The Rule ID is present in the fragmentation header and o Rule ID. The Rule ID is present in the fragment header and in the
in the ACK header format. The Rule ID is a fragmentation header ACK header format. The Rule ID in a fragment header is used to
is used to identify that a fragment is being carried, the identify that a fragment is being carried, the fragmentation
fragmentation delivery reliability option used and it may indicate delivery reliability option used and it may indicate the window
the window size in use (if any). The Rule ID in the fragmentation size in use (if any). The Rule ID in the fragmentation header
header also allows to interleave non-fragmented IPv6 datagrams also allows to interleave non-fragmented IPv6 datagrams with
with fragments that carry a larger IPv6 datagram. The Rule ID in fragments that carry a larger IPv6 datagram. The Rule ID in an
an ACK allows to identify that the message is an ACK. ACK allows to identify that the message is an ACK.
o Fragment Compressed Number (FCN). The FCN is included in all o Fragment Compressed Number (FCN). The FCN is included in all
fragments. This field can be understood as a truncated, efficient fragments. This field can be understood as a truncated, efficient
representation of a larger-sized fragment number, and does not representation of a larger-sized fragment number, and does not
carry an absolute fragment number. There are two FCN reserved carry an absolute fragment number. There are two FCN reserved
values that are used for controlling the fragmentation process, as values that are used for controlling the fragmentation process, as
described next. The FCN value with all the bits equal to 1 (All- described next. The FCN value with all the bits equal to 1 (All-
1) denotes the last fragment of a packet. And the FCN value with 1) denotes the last fragment of a packet. And the FCN value with
all the bits equal to 0 (All-0) denotes the last fragment of a all the bits equal to 0 (All-0) denotes the last fragment of a
window (when such window is not the last one of the packet) in any window (when such window is not the last one of the packet) in any
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The dureation of this timer is not defined in this document and The dureation of this timer is not defined in this document and
must be defined in the corresponding technology documents (e.g. must be defined in the corresponding technology documents (e.g.
technology-specific profiles). technology-specific profiles).
o Inactivity Timer. This timer is used by a fragment receiver to o Inactivity Timer. This timer is used by a fragment receiver to
detect when there is a problem in the transmission of fragments detect when there is a problem in the transmission of fragments
and the receiver does not get any fragment during a period of time and the receiver does not get any fragment during a period of time
or a number of packets in a period of time. When this happens, an or a number of packets in a period of time. When this happens, an
Abort message needs to be sent. Initially, and each time a Abort message needs to be sent. Initially, and each time a
fragment is received the timer is reinitialized. The duration of fragment is received the timer is reinitialized. The duration of
this timer timer is not defined in this document and must be this timer is not defined in this document and must be defined in
defined in the specific technology document (e.g. technology- the specific technology document (e.g. technology-specific
specific profiles). profiles).
o Attempts. It is a counter used to request a missing ACK, and in o Attempts. It is a counter used to request a missing ACK, and in
consequence to determine when an Abort is needed, because there consequence to determine when an Abort is needed, because there
are recurrent fragment transmission errors, whose maximum value is are recurrent fragment transmission errors, whose maximum value is
MAX_ACK_REQUESTS. The default value of MAX_ACK_REQUESTS is not MAX_ACK_REQUESTS. The default value of MAX_ACK_REQUESTS is not
stated in this document, and it is expected to be defined in other stated in this document, and it is expected to be defined in other
documents (e.g. technology-specific profiles). documents (e.g. technology- specific profiles). The Attempts
counter is defined per window, it will be initialized each time a
new window is used.
o Bitmap. The Bitmap is a sequence of bits carried in an ACK for a o Bitmap. The Bitmap is a sequence of bits carried in an ACK for a
given window. Each bit in the Bitmap corresponds to a fragment of given window. Each bit in the Bitmap corresponds to a fragment of
the current window, and provides feedback on whether the fragment the current window, and provides feedback on whether the fragment
has been received or not. The right-most position on the Bitmap has been received or not. The right-most position on the Bitmap
is used to report whether the All-0 or All-1 fragments have been is used to report whether the All-0 or All-1 fragments have been
received or not. Feedback for a fragment with the highest FCN received or not. Feedback for a fragment with the highest FCN
value is provided by the left-most position in the Bitmap. In the value is provided by the left-most position in the Bitmap. In the
Bitmap, a bit set to 1 indicates that the corresponding FCN Bitmap, a bit set to 1 indicates that the corresponding FCN
fragment has been correctly sent and received. However, the fragment has been correctly sent and received. However, the
sending format of the bitmap will be truncated until a byte sending format of the Bitmap will be truncated until a byte
boundary where the last error is given. However, when all the boundary where the last error is given. However, when all the
Bitmap is transmitted, it may be truncated, see more details in Bitmap is transmitted, it may be truncated, see more details in
Section 5.5.3 Section 5.5.3
o Abort. In case of error or when the Inactivity timer expires or o Abort. In case of error or when the Inactivity timer expires or
the MAX_ACK_REQUESTS is reached the sender or the receiver may use MAX_ACK_REQUESTS is reached the sender or the receiver may use the
the Abort frames. When the receiver needs to abort the on-going Abort frames. When the receiver needs to abort the on-going
fragmented packet transmission, it uses the ACK Abort format fragmented packet transmission, it uses the ACK Abort format
packet with all the bits set to 1. The sender will use the All-1 packet with all the bits set to 1. When the sender needs to abort
Abort format to trigger the end of the transmission. the transmission it will use the All-1 Abort format, this fragment
is not acked.
o Padding (P). Padding will be used to align the last byte of a o Padding (P). Padding will be used to align the last byte of a
fragment with a byte boundary. The number of bits used for fragment with a byte boundary. The number of bits used for
padding is not defined and depends on the size of the Rule ID, padding is not defined and depends on the size of the Rule ID,
DTag and FCN fields, and on the layer two payload size. DTag and FCN fields, and on the layer two payload size.
5.3. Delivery Reliability options 5.3. Delivery Reliability options
This specification defines the following three fragment delivery This specification defines the following three fragment delivery
reliability options: reliability options:
o No ACK. No ACK is the simplest fragment delivery reliability o No ACK. No ACK is the simplest fragment delivery reliability
option. The receiver does not generate overhead in the form of option. The receiver does not generate overhead in the form of
acknowledgments (ACKs). However, this option does not enhance acknowledgments (ACKs). However, this option does not enhance
delivery reliability beyond that offered by the underlying LPWAN delivery reliability beyond that offered by the underlying LPWAN
technology. In the No ACK option, the receiver MUST NOT issue technology. In the No ACK option, the receiver MUST NOT issue
ACKs. ACKs.
o Window mode - ACK always (ACK-always). o Window mode - ACK always (ACK-Always).
The ACK-always option provides flow control. In addition, this The ACK-always option provides flow control. In addition, this
option is able to handle long bursts of lost fragments, since option is able to handle long bursts of lost fragments, since
detection of such events can be done before the end of the IPv6 detection of such events can be done before the end of the IPv6
packet transmission, as long as the window size is short enough. packet transmission, as long as the window size is short enough.
However, such benefit comes at the expense of ACK use. In ACK- However, such benefit comes at the expense of ACK use. In ACK-
always, an ACK is transmitted by the fragment receiver after a always, an ACK is transmitted by the fragment receiver after a
window of fragments has been sent. A window of fragments is a window of fragments has been sent. A window of fragments is a
subset of the full set of fragments needed to carry an IPv6 subset of the full set of fragments needed to carry an IPv6
packet. In this mode, the ACK informs the sender about received packet. In this mode, the ACK informs the sender about received
and/or missed fragments from the window of fragments. Upon and/or missed fragments from the window of fragments. Upon
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However, such benefit comes at the expense of ACK use. In ACK- However, such benefit comes at the expense of ACK use. In ACK-
always, an ACK is transmitted by the fragment receiver after a always, an ACK is transmitted by the fragment receiver after a
window of fragments has been sent. A window of fragments is a window of fragments has been sent. A window of fragments is a
subset of the full set of fragments needed to carry an IPv6 subset of the full set of fragments needed to carry an IPv6
packet. In this mode, the ACK informs the sender about received packet. In this mode, the ACK informs the sender about received
and/or missed fragments from the window of fragments. Upon and/or missed fragments from the window of fragments. Upon
receipt of an ACK that informs about any lost fragments, the receipt of an ACK that informs about any lost fragments, the
sender retransmits the lost fragments. When an ACK is not sender retransmits the lost fragments. When an ACK is not
received by the fragment sender, the latter sends an ACK request received by the fragment sender, the latter sends an ACK request
using the All-1 empty fragment. using the All-1 empty fragment.
The maximum number of ACK requests is MAX_ACK_REQUESTS. The maximum number of ACK requests is MAX_ACK_REQUESTS.
o Window mode - ACK-on-error (ACK-on-error). The ACK-on-error o Window mode - ACK-on-error (ACK-on-error). The ACK-on-error
option is suitable for links offering relatively low L2 data unit option is suitable for links offering relatively low L2 data unit
loss probability. This option reduces the number of ACKs loss probability. This option reduces the number of ACKs
transmitted by the fragment receiver. This may be especially transmitted by the fragment receiver. This may be especially
beneficial in asymmetric scenarios, e.g. where fragmented data are beneficial in asymmetric scenarios, e.g. where fragmented data are
sent uplink and the underlying LPWAN technology downlink capacity sent uplink and the underlying LPWAN technology downlink capacity
or message rate is lower than the uplink one. or message rate is lower than the uplink one.
In ACK-on-error, an ACK is transmitted by the fragment receiver In ACK-on-error, an ACK is transmitted by the fragment receiver
after a window of fragments have been sent, only if at least one after a window of fragments have been sent, only if at least one
of the fragments in the window has been lost. In this mode, the of the fragments in the window has been lost. In this mode, the
ACK informs the sender about received and/or missed fragments from ACK informs the sender about received and/or missed fragments from
the window of fragments. Upon receipt of an ACK that informs the window of fragments. Upon receipt of an ACK that informs
about any lost fragments, the sender retransmits the lost about any lost fragments, the sender retransmits the lost
fragments. However, if an ACK is lost, the sender assumes that fragments. However, if an ACK is lost, the sender assumes that
all fragments covered by the ACK have been successfully delivered. all fragments covered by the ACK have been successfully delivered,
And the receiver will abort the on-going fragmented packet and the receiver will abort the on-going fragmented packet
transmission. One exception to this behavior is in the last transmission. One exception to this behavior is in the last
window, whete the receiver MUST transmit an ACK, even if all the window, where the receiver MUST transmit an ACK, even if all the
fragments in the last window have been correctly received. fragments in the last window have been correctly received.
The same reliability option MUST be used for all fragments of a The same reliability option MUST be used for all fragments of a
packet. It is up to implementers and/or representatives of the packet. It is up to implementers and/or representatives of the
underlying LPWAN technology to decide which reliability option to use underlying LPWAN technology to decide which reliability option to use
and whether the same reliability option applies to all IPv6 packets and whether the same reliability option applies to all IPv6 packets
or not. Note that the reliability option to be used is not or not. Note that the reliability option to be used is not
necessarily tied to the particular characteristics of the underlying necessarily tied to the particular characteristics of the underlying
L2 LPWAN technology (e.g. the No ACK reliability option may be used L2 LPWAN technology (e.g. the No ACK reliability option may be used
on top of an L2 LPWAN technology with symmetric characteristics for on top of an L2 LPWAN technology with symmetric characteristics for
uplink and downlink). uplink and downlink).
This document does not make any decision as to which fragment This document does not make any decision as to which fragment
delivery reliability option(s) are supported by a specific LPWAN delivery reliability option(s) are supported by a specific LPWAN
technology. technology.
Examples of the different reliability options described are provided Examples of the different reliability options described are provided
in Appendix B. in Appendix B.
5.4. Fragmentation Frames Formats 5.4. Fragmentation Frame Formats
This section defines the fragment format, the All-0 and All-1 frames This section defines the fragment format, the All-0 and All-1 frame
format, the ACK format and the Abort frames format. formats, the ACK format and the Abort frame formats.
5.4.1. Fragment format 5.4.1. Fragment format
A fragment comprises a fragmentation header, a fragment payload, and A fragment comprises a fragment header, a fragment payload, and
Padding bits (if any). A fragment conforms to the format shown in Padding bits (if any). A fragment conforms to the format shown in
Figure 6. The fragment payload carries a subset of either a SCHC Figure 6. The fragment payload carries a subset of either a SCHC
header or an IPv6 header or the original IPv6 packet data payload. A header or an IPv6 header or the original IPv6 packet data payload. A
fragment is the payload in the L2 protocol data unit (PDU). fragment is the payload in the L2 protocol data unit (PDU).
+-----------------+-----------------------+---------+ +-----------------+-----------------------+---------+
| Fragment Header | Fragment payload | padding | | Fragment Header | Fragment payload | padding |
+-----------------+-----------------------+---------+ +-----------------+-----------------------+---------+
Figure 6: Fragment format. Figure 6: Fragment format.
5.4.2. Fragmentation formats
In the No ACK option, fragments except the last one SHALL contain the In the No ACK option, fragments except the last one SHALL contain the
format as defined in Figure 7. The total size of the fragmentation format as defined in Figure 7. The total size of the fragment header
header is R bits. is R bits.
<------------ R ----------> <------------ R ---------->
<--T--> <--N--> <--T--> <--N-->
+-- ... --+- ... -+- ... -+---...---+-+ +-- ... --+- ... -+- ... -+---...---+-+
| Rule ID | DTag | FCN | payload |P| | Rule ID | DTag | FCN | payload |P|
+-- ... --+- ... -+- ... -+---...---+-+ +-- ... --+- ... -+- ... -+---...---+-+
Figure 7: Fragmentation Format for Fragments except the Last One, No Figure 7: Fragment Format for Fragments except the Last One, No ACK
ACK option option
In any of the Window mode options, fragments except the last one In any of the Window mode options, fragments except the last one
SHALL contain the fragmentation format as defined in Figure 8. The SHALL contain the fragmentation format as defined in Figure 8. The
total size of this fragmentation header is R bits. total size of the fragment header in this format is R bits. .
<------------ R ----------> <------------ R ---------->
<--T--> 1 <--N--> <--T--> 1 <--N-->
+-- ... --+- ... -+-+- ... -+---...---+-+ +-- ... --+- ... -+-+- ... -+---...---+-+
| Rule ID | DTag |W| FCN | payload |P| | Rule ID | DTag |W| FCN | payload |P|
+-- ... --+- ... -+-+- ... -+---...---+-+ +-- ... --+- ... -+-+- ... -+---...---+-+
Figure 8: Fragmentation Format for Fragments except the Last One, Figure 8: Fragment Format for Fragments except the Last One, Window
Window mode mode
5.4.3. ACK format 5.4.2. ACK format
The format of an ACK that acknowledges a window that is not the last The format of an ACK that acknowledges a window that is not the last
one (denoted as ALL-0 window) is shown in Figure 9. one (denoted as ALL-0 window) is shown in Figure 9.
<-------- R -------> <-------- R ------->
<- T -> 1 <- T -> 1
+---- ... --+-... -+-+----- ... ---+ +---- ... --+-... -+-+----- ... ---+
| Rule ID | DTag |W| bitmap | (no payload) | Rule ID | DTag |W| Bitmap | (no payload)
+---- ... --+-... -+-+----- ... ---+ +---- ... --+-... -+-+----- ... ---+
Figure 9: ACK format for All-0 windows Figure 9: ACK format for All-0 windows
To acknowledge the last window of a packet (denoted as All-1 window), To acknowledge the last window of a packet (denoted as All-1 window),
a C bit (i.e. MIC checked) following the W bit is set to 1 to a C bit (i.e. MIC checked) following the W bit is set to 1 to
indicate that the MIC check computed by the receiver matches the MIC indicate that the MIC check computed by the receiver matches the MIC
present in the ALL-1 fragment. If the MIC check fails, the C bit is present in the All-1 fragment. If the MIC check fails, the C bit is
set to 0 and the Bitmap for the All-1 window follows. set to 0 and the Bitmap for the All-1 window follows.
<-------- R -------> <- byte boundary -> <-------- R -------> <- byte boundary ->
<- T -> 1 1 <- T -> 1 1
+---- ... --+-... -+-+-+ +---- ... --+-... -+-+-+
| Rule ID | DTag |W|1| (MIC correct) | Rule ID | DTag |W|1| (MIC correct)
+---- ... --+-... -+-+-+ +---- ... --+-... -+-+-+
+---- ... --+-... -+-+-+------- ... -------+ +---- ... --+-... -+-+-+------- ... -------+
| Rule ID | DTag |W|0| bitmap | (MIC Incorrect) | Rule ID | DTag |W|0| Bitmap | (MIC Incorrect)
+---- ... --+-... -+-+-+------- ... -------+ +---- ... --+-... -+-+-+------- ... -------+
C C
Figure 10: Format of an ACK for All-1 windows Figure 10: Format of an ACK for All-1 windows
5.4.4. All-1 and All-0 formats 5.4.3. All-1 and All-0 formats
The All-0 format is used for the last fragment of a window that is The All-0 format is used for the last fragment of a window that is
not the last window of the packet. not the last window of the packet.
<------------ R ------------> <------------ R ------------>
<- T -> 1 <- N -> <- T -> 1 <- N ->
+-- ... --+- ... -+-+- ... -+--- ... ---+ +-- ... --+- ... -+-+- ... -+--- ... ---+
| Rule ID | DTag |W| 0..0 | payload | | Rule ID | DTag |W| 0..0 | payload |
+-- ... --+- ... -+-+- ... -+--- ... ---+ +-- ... --+- ... -+-+- ... -+--- ... ---+
skipping to change at page 22, line 4 skipping to change at page 22, line 7
<------------ R ------------> <------------ R ------------>
<- T -> 1 <- N -> <- T -> 1 <- N ->
+-- ... --+- ... -+-+- ... -+--- ... ---+ +-- ... --+- ... -+-+- ... -+--- ... ---+
| Rule ID | DTag |W| 0..0 | payload | | Rule ID | DTag |W| 0..0 | payload |
+-- ... --+- ... -+-+- ... -+--- ... ---+ +-- ... --+- ... -+-+- ... -+--- ... ---+
Figure 11: All-0 fragment format Figure 11: All-0 fragment format
The All-0 empty fragment format is used by a sender to request an ACK The All-0 empty fragment format is used by a sender to request an ACK
in ACK-Always mode in ACK-Always mode
<------------ R ------------> <------------ R ------------>
<- T -> 1 <- N -> <- T -> 1 <- N ->
+-- ... --+- ... -+-+- ... -+ +-- ... --+- ... -+-+- ... -+
| Rule ID | DTag |W| 0..0 | (no payload) | Rule ID | DTag |W| 0..0 | (no payload)
+-- ... --+- ... -+-+- ... -+ +-- ... --+- ... -+-+- ... -+
Figure 12: All-0 empty fragment format Figure 12: All-0 empty fragment format
In the No ACK option, the last fragment of an IPv6 datagram SHALL In the No ACK option, the last fragment of an IPv6 datagram SHALL
contain a fragmentation header that conforms to the format shown in contain a fragment header that conforms to the format shown in
Figure 13. The total size of this fragmentation header is R+M bits. Figure 13. The total size of this fragment header is R+M bits.
<------------- R ----------> <------------- R ---------->
<- T -> <-N-><----- M -----> <- T -> <-N-><----- M ----->
+---- ... ---+- ... -+-----+---- ... ----+---...---+ +---- ... ---+- ... -+-----+---- ... ----+---...---+
| Rule ID | DTag | 1 | MIC | payload | | Rule ID | DTag | 1 | MIC | payload |
+---- ... ---+- ... -+-----+---- ... ----+---...---+ +---- ... ---+- ... -+-----+---- ... ----+---...---+
Figure 13: All-1 Fragmentation Format for the Last Fragment, No ACK Figure 13: All-1 Fragment Format for the Last Fragment, No ACK option
option
In any of the Window modes, the last fragment of an IPv6 datagram In any of the Window modes, the last fragment of an IPv6 datagram
SHALL contain a fragmentation header that conforms to the format SHALL contain a fragment header that conforms to the format shown in
shown in Figure 14. The total size of the fragmentation header in Figure 14. The total size of the fragment header in this format is
this format is R+M bits. It is used for request a retransmission R+M bits.
<------------ R ------------> <------------ R ------------>
<- T -> 1 <- N -> <---- M -----> <- T -> 1 <- N -> <---- M ----->
+-- ... --+- ... -+-+- ... -+---- ... ----+---...---+ +-- ... --+- ... -+-+- ... -+---- ... ----+---...---+
| Rule ID | DTag |W| 11..1 | MIC | payload | | Rule ID | DTag |W| 11..1 | MIC | payload |
+-- ... --+- ... -+-+- ... -+---- ... ----+---...---+ +-- ... --+- ... -+-+- ... -+---- ... ----+---...---+
(FCN) (FCN)
Figure 14: All-1 Fragmentation Format for the Last Fragment, Window Figure 14: All-1 Fragment Format for the Last Fragment, Window mode
mode
In either ACK-Always or ACK-on-error, in order to request a In either ACK-Always or ACK-on-error, in order to request a
retransmission of the ACK for the All-1 window, the fragment sender retransmission of the ACK for the All-1 window, the fragment sender
uses the format shown in Figure 15. The total size of the uses the format shown in Figure 15. The total size of the fragment
fragmentation header in this format is R+M bits. header in this format is R+M bits.
<------------ R ------------> <------------ R ------------>
<- T -> 1 <- N -> <---- M -----> <- T -> 1 <- N -> <---- M ----->
+-- ... --+- ... -+-+- ... -+---- ... ----+ +-- ... --+- ... -+-+- ... -+---- ... ----+
| Rule ID | DTag |W| 1..1 | MIC | (no payload) | Rule ID | DTag |W| 1..1 | MIC | (no payload)
+-- ... --+- ... -+-+- ... -+---- ... ----+ +-- ... --+- ... -+-+- ... -+---- ... ----+
Figure 15: All-1 for Retries format fragment also called All-1 empty Figure 15: All-1 for Retries format, also called All-1 empty
The values for R, N, T and M are not specified in this document, and The values for R, N, T and M are not specified in this document, and
have to be determined in other documents (e.g. technology-specific have to be determined in other documents (e.g. technology-specific
profile documents). profile documents).
5.4.5. Abort formats 5.4.4. Abort formats
The All-1 Abort format and the ACK abort have the following formats. The All-1 Abort and the ACK abort messages have the following
formats.
<------ byte boundary ------><--- 1 byte ---> <------ byte boundary ------><--- 1 byte --->
+--- ... ---+- ... -+-+-...-+-+-+-+-+-+-+-+-+ +--- ... ---+- ... -+-+-...-+-+-+-+-+-+-+-+-+
| Rule ID | DTag |W| FCN | FF | (no MIC & no payload) | Rule ID | DTag |W| FCN | FF | (no MIC & no payload)
+--- ... ---+- ... -+-+-...-+-+-+-+-+-+-+-+-+ +--- ... ---+- ... -+-+-...-+-+-+-+-+-+-+-+-+
Figure 16: All-1 Abort format Figure 16: All-1 Abort format
<------ byte boundary -----><--- 1 byte ---> <------ byte boundary -----><--- 1 byte --->
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In the No ACK mode there is no feedback communication from the In the No ACK mode there is no feedback communication from the
fragment receiver. The sender will send the fragments of a packet fragment receiver. The sender will send the fragments of a packet
until the last one without any possibility to know if errors or a until the last one without any possibility to know if errors or a
losses have occurred. As in this mode there is not a need to losses have occurred. As in this mode there is not a need to
identify specific fragments a one-bit FCN is used, therefore FCN identify specific fragments a one-bit FCN is used, therefore FCN
All-0 will be used in all fragments except the last one. The latter All-0 will be used in all fragments except the last one. The latter
will carry an All-1 FCN and will also carry the MIC. The receiver will carry an All-1 FCN and will also carry the MIC. The receiver
will wait for fragments and will set the Inactivity timer. The No will wait for fragments and will set the Inactivity timer. The No
ACK mode will use the MIC contained in the last fragment to check ACK mode will use the MIC contained in the last fragment to check
error. When the Inactivity Timer expires or when the MIC check error. When the Inactivity Timer expires or when the MIC check
indicates that the reassembled packet does not match the originall indicates that the reassembled packet does not match the original
one, the receiver will release all resources allocated to reassembly one, the receiver will release all resources allocated to reassembly
of the packet. The initial value of the Inactivity Timer will be of the packet. The initial value of the Inactivity Timer will be
determined based on the characteristics of the underlying LPWAN determined based on the characteristics of the underlying LPWAN
technology and will be defined in other documents (e.g. technology- technology and will be defined in other documents (e.g. technology-
specific profile documents). specific profile documents).
5.5.2. The Window modes 5.5.2. The Window modes
In Window modes, a jumping window protocol is using two windows In Window modes, a jumping window protocol uses two windows
alternatively, 0 and 1. An FCN set to All-0 indicates that the alternatively, identified as 0 and 1. A fragment with all FCN bits
window is over (i.e. the fragment is the last one of the window) and set to 0 (i.e. an All-0 fragment) indicates that the window is over
allows to switch from one window to another. The All-1 FCN in a (i.e. the fragment is the last one of the window) and allows to
fragment indicates that it is the last fragment of the packet and switch from one window to the next one. The All-1 FCN in a fragment
therefore there will not be another window for the packet. indicates that it is the last fragment of the packet being
transmitted and therefore there will not be another window for the
packet.
The Window mode offers two different reliability options modes: ACK- The Window mode offers two different reliability option modes: ACK-
on-error and ACK-always. on-error and ACK-always.
5.5.2.1. ACK-Always 5.5.2.1. ACK-Always
The sender starts sending fragments using the two windows procedure. In ACK-Always, the sender sends fragments by using the two-jumping
A delay between each fragment can be added to respect regulation window procedure. A delay between each fragment can be added to
rules or constraints imposed by the applications. Each time a respect regulation rules or constraints imposed by the applications.
fragment is sent the FCN is decreased by one and the sending Each time a fragment is sent, the FCN is decreased by one. When the
information is set locally. When the FCN reaches value 0 and there FCN reaches value 0 and there are more fragments to be sent, an All-0
are more fragments to be sent, an All-0 fragment is sent and the fragment is sent and the Retransmission Timer is set. The sender
retransmission timer is set. The sender waits for an ACK to know if waits for an ACK to know if transmission errors have occurred. Then,
there were some transmission errors. If there are some errors the the receiver sends an ACK reporting whether any fragments have been
receiver sends an ACK with the corresponding errors in the Bitmap, lost or not by setting the corresponding bits in the Bitmap,
otherwise, an ACK without Bitmap will be sent and a new window should otherwise, an ACK without Bitmap will be sent, allowing transmission
be sent. When the last fragment is sent, and All-1 fragment with MIC of a new window. When the last fragment of the packet is sent, an
is sent. The sender sets the retransmission timer to wait for the All-1 fragment (which includes a MIC) is used. In that case, the
ACK corresponding to the last window. During this period, the sender sender sets the Retransmission Timer to wait for the ACK
starts listening to the radio and starts an Inactivity timer, which corresponding to the last window. During this period, the sender
is dimensioned based on the received window available for the LPWAN starts listening to the radio and starts the Retransmission Timer,
technology in use. If the Inactivity timer expires an empty All-0 which needs to be dimensioned based on the received window available
(or All-1 if the last fragment has been sent) fragment is sent to ask for the LPWAN technology in use. If the Retransmission Timer
the receiver to resend its ACK. The window number is not changed. expires, an empty All-0 (or an empty All-1 if the last fragment has
been sent) fragment is sent to ask the receiver to resend its ACK.
When the sender receives an ACK, it checks the window value. The ACK The window number is not changed.
fragments carrying an unexpected W bit are discarded. If the window
number of the received ACK is correct, the sender compares the
sending information with the received Bitmap. If the sending
information is equal to the received Bitmap all the fragments sent
during the window have been well received. If at least one fragment
needs to be sent, the sender moves its sending window to the next
value and sends the last fragment. If no more fragments have to be
sent, then the fragmented packet transmission is finished.
If some fragments are missing (not set in the Bitmap) then the sender
resends the missing fragments. When the retransmission is finished,
it starts the retransmission timer (even if an All-0 or an All-1 has
not been sent during the retransmission) and waits for ACK.
If the sending information is different from the received Bitmap the When the sender receives an ACK, it checks the W bit carried by the
counter Attempts is increased and the sender resends the missing ACK. Any ACK carrying an unexpected W bit is discarded. If the W
fragments again when a MAX_ACK_REQUESTS is reached, the sender sends bit value of the received ACK is correct, the sender analyzes the
an Abort and drops the fragments. The sender Aborts the transmission received Bitmap. If all the fragments sent during the window have
when a corrupt MIC has been received or when MAX_ACK_REQUESTS has been well received, and if at least one more fragment needs to be
reached. sent, the sender moves its sending window to the next window value
and sends the next fragments. If no more fragments have to be sent,
then the fragmented packet transmission is finished.
At the beginning, the receiver side expects to receive window 0. Any However, if one or more fragments have not been received as per the
fragment not belonging to the current window is discarded. All ACK (i.e. the corresponding bits are not set in the Bitmap) then the
Fragments belonging to the correct window are accepted, the fragment sender resends the missing fragments. When all missing fragments
number is computed based on the FCN value. The receiver updates the have been retransmitted, the sender starts the Retransmission Timer
Bitmap with the correct received fragments. (even if an All-0 or an All-1 has not been sent during the
retransmission) and waits for an ACK. Upon receipt of the ACK, if
one or more fragments have not yet been received, the counter
Attempts is increased and the sender resends the missing fragments
again. When Attempts reaches MAX_ACK_REQUESTS, the sender aborts the
on-going fragmented packet transmission by sending an Abort message
and releases any resources for transmission of the packet. The
sender also aborts an on-going fragmented packet transmission when a
failed MIC check is reported by the receiver.
When All-0 fragment is received, it indicates that all the fragments On the other hand, at the beginning, the receiver side expects to
have been sent in the current window. Since the sender is not receive window 0. Any fragment received but not belonging to the
obliged to send a full window, some fragment number not set in the current window is discarded. All fragments belonging to the correct
memory may not correspond to losses. It sends the corresponding ACK window are accepted, and the actual fragment number managed by the
and the next window can start. receiver is computed based on the FCN value. The receiver prepares
the Bitmap to report the correctly received and the missing fragments
for the current window. After each fragment is received the receiver
initializes the Inactivity timer, if the Inactivity Timer expires the
transmission is aborted.
When All-1 fragment is received, it indicates that the transmission When an All-0 fragment is received, it indicates that all the
is finished. Since the last window is not full, the MIC will be used fragments have been sent in the current window. Since the sender is
to detect if all the fragments have been received. A correct MIC not obliged to always send a full window, some fragment number not
indicates the end of the transmission but the receiver must stay set in the receiver memory may not correspond to losses. The
alive an Inactivity timer period to answer to empty All-1 fragment receiver sends the corresponding ACK, the Inactivity Timer is set and
the sender may send if the ACK is lost. the transmission of the next window by the sender can start.
If All-1 fragment has not been received, the receiver expects a new If an All-0 fragment has been received and all fragments of the
window. It waits for the next fragment. If the window value has not current window have also been received, the receiver then expects a
changed, the received fragments are part of a retransmission. A new Window and waits for the next fragment. Upon receipt of a
receiver that has already received a fragment should discard it, fragment, if the window value has not changed, the received fragments
otherwise, it updates the Bitmap. If all the bits of the Bitmap are are part of a retransmission. A receiver that has already received a
set to one, the receiver may send an ACK without waiting for an All-0 fragment should discard it, otherwise, it updates the Bitmap. If all
fragment. the bits of the Bitmap are set to one, the receiver may send an ACK
without waiting for an All-0 fragment and the Inactivity Timer is
initialized.
If the window value is set to the next value, this means that the On the other hand, if the window value of the next received fragment
sender has received a correct bitmap, which means that all the is set to the next expected window value, this means that the sender
fragments have been received. The receiver changes the value of the has received a correct Bitmap reporting that all fragments have been
expected window. received. The receiver then updates the value of the next expected
window.
If the receiver receives an All-0 fragment, the sender may send one If the receiver receives an All-0 fragment, the sender may send one
or more fragments per window. Otherwise, some fragments in the or more fragments per window. Otherwise, some fragments in the
window have been lost. window have been lost.
If the receiver receives an All-1 fragment this means that the When an All-1 fragment is received, it indicates that the last
transmission should be finished. If the MIC is incorrect some fragment of the packet has been sent. Since the last window is not
fragments have been lost. It sends the ACK. In case of an incorrect always full, the MIC will be used to detect if all fragments of the
MIC, the receivers wait for fragments belonging to the same window. packet have been received. A correct MIC indicates the end of the
After MAX_ACK_REQUESTS the receiver will Abort the transmission. It transmission but the receiver must stay alive for an Inactivity Timer
can also Abort when the Inactivity timer has expired. period to answer to any empty All-1 fragments the sender may send if
ACKs sent by the receiver are lost. If the MIC is incorrect, some
fragments have been lost. The receiver sends the ACK regardless of
successful fragmented packet reception or not, the Inactitivity Timer
is set. In case of an incorrect MIC, the receiver waits for
fragments belonging to the same window. After MAX_ACK_REQUESTS, the
receiver will abort the on-going fragmented packet transmission. The
receiver also Aborts upon Inactivity Timer expiration.
5.5.2.2. ACK-on-error 5.5.2.2. ACK-on-error
The ACK-on-error is similar to the ACK-Always procedure, the The ACK-on-error sender is similar to ACK-Always, the main difference
difference is that in ACK-on-error the ACK is not sent at the end of being that in ACK-on-error the ACK is not sent at the end of each
each window but only when there is an error. In Ack-on-error mode, window but only when at least one fragment of the current window has
the retransmission timer expiration will be considered as a positive been lost (with the exception of the last window, see next
acknowledgment, it is set when receiving an All-0 or an All-1 paragraph). In Ack-on-error, the Retransmission Timer expiration
fragment. If there are no more fragments then the fragmentation is will be considered as a positive acknowledgment. The Retransmission
finished. Timer is set when sending an All-0 or an All-1 fragment. When the
All-1 fragment has been sent, then the on-going fragmented packet
When the All-1 last fragment is sent and the correct MIC have been transmission fragmentation is finished and the sender waits for the
received an ACK is sent to confirms the end of the correct last ACK. At the receiver side, when the All-1 fragment is sent and
transmission. If the retransmission timer expires an All-1 empty the MIC check indicates successful packet reception, an ACK is also
request the last ACK that MUST be sent to complete the fragmentation sent to confirm the end of a correct transmission. If the
Retransmission Timer expires, an All-1 empty request for the last ACK
MUST be sent by the sender to complete the fragmented packet
transmission. transmission.
If the sender receives an ACK, it checks the window value. ACKs with If the sender receives an ACK, it checks the window value. ACKs with
the non-expected window number are discarded. If the window number an unexpected window number are discarded. If the window number on
on the received Bitmap is correct, the sender verifies if the the received Bitmap is correct, the sender verifies if the receiver
receiver has all the fragments. When all the fragments have been has received all fragments of the current window. When at least one
received the transmission of a new window should continue. fragment has been lost, the counter Attempts is increased by one and
Otherwise, when there is an error the counter Attempts is increased the sender resends the missing fragments again. When Attempts
and the sender resends the missing fragments again. When a reaches MAX_ACK_REQUESTS, the sender sends an Abort message and
MAX_ACK_REQUESTS is reached, the sender sends an Abort. When the releases all resources for the on-going fragmented packet
retransmission is finished, it starts listening to the ACK (even if transmission. When the retransmission of missing fragments is
an All-0 or an All-1 has not been sent during the retransmission) and finished, the sender starts listening for an ACK (even if an All-0 or
set the retransmission timer. If the retransmission timer expires an All-1 has not been sent during the retransmission) and initializes
the transmission is aborted. and starts the Retransmission Timer. After sending an All-1
fragment, the sender listens for an ACK, initializes Attempts, and
initializes and starts the Retransmission Timer. If the
Retransmission Timer expires, Attempts is increased by one and an
empty All-1 fragment is sent to request the ACK for the last window.
If Attempts reaches MAX_ACK_REQUESTS, the on-going fragmented packet
transmission is aborted.
Unlike the sender, the receiver for ACK-on-error has some Unlike the sender, the receiver for ACK-on-error has a larger amount
differences. First, we are not sending ACK unless there is an error of differences compared with ACK-Always. First, an ACK is not sent
or an unexpected behavior. The receiver starts with the expected unless there is a lost fragment or an unexpected behavior (with the
window and maintains the information indicating which fragments it exception of the last window, where an ACK is always sent regardless
has received (All-0 and All-1 occupy the same position). After of fragment losses or not). The receiver starts by expecting
receiving a fragment an Inactivity timer is set, if nothing has been fragments from window 0 and maintains the information regarding which
received and the Inactivity timer expires the transmission is fragments it receives. After receiving a fragment, the Inactivity
aborted. Timer is set, if no fragment has been received and the Inactivity
Timer expires the transmission is aborted.
Any fragment not belonging to the current window is discarded. The Any fragment not belonging to the current window is discarded. The
Fragment Number is computed based on the FCN value. When an All-0 actual fragment number is computed based on the FCN value. When an
fragment is received and the Bitmap is full, the receiver changes the All-0 fragment is received and all fragments have been received, the
window value. receiver updates the expected window value.
An All-0 fragment and not a full bitmap indicate that all the
fragments have been sent in the current window. Since the sender is
not obligated to send a full window, some fragment number not used
may not correspond to losses. As the receiver does not know if the
missing fragments are lost or normal missing fragments, it sends an
ACK.
An All-1 fragment indicates that the transmission is finished. Since If an All-0 fragment is received, even if another fragment is
the last window is not full, the MIC will be used to detect if all missing, all fragments from the current window have been sent. Since
the fragments have been received. A correct MIC indicates the end of the sender is not obligated to send a full window, a fragment number
the transmission. not used may not necessarily correspond to losses. As the receiver
does not know if the missing fragments are lost or not, it sends an
ACK and reinitialises the Inactivity Timer.
If All-1 fragment has not been received, the receiver expects a new On the other hand, after receiving an All-0 fragment, the receiver
window. It waits for the next fragment. If the window value has not expects a new window and waits for the next fragment.
changed, the received fragments are part of a retransmission. A If the window value of the next fragment has not changed, the
receiver that has already received a fragment should discard it. If received fragment is a retransmission. A receiver that has already
all the bits of the Bitmap are set to one, the receiver waits for the received a fragment should discard it. If all fragments of a window
next window without waiting for an All-0 fragment and it does not (that is not the last one) have been received, the receiver does not
send an ACK either. While the receiver waits for next window and if send an ACK. While the receiver waits for the next window and if the
the window value is set to the next value, and if an All-1 fragment window value is set to the next value, and if an All-1 fragment with
with the next value window arrived the receiver goes to error and the next value window arrived the receiver aborts the on-going
abort the transmission, it drops the fragments. fragmented packet transmission, and it drops the fragments of the
aborted packet transmission.
If the receiver receives an All-1 fragment this means that the If the receiver receives an All-1 fragment, this means that the
transmission should be finished. If the MIC is incorrect some transmission should be finished. If the MIC is incorrect some
fragments have been lost. It sends an ACK. fragments have been lost. Regardless of fragment losses, the
receiver sends an ACK and initializes the Inactivity Timer.
In case of an incorrect MIC, the receivers wait for fragment Reception of an All-1 fragment indicates the last fragment of the
belonging to the same window or the expiration of the Inactivity packet has been sent. Since the last window is not always full, the
timer which will Abort the transmission. MIC will be used to detect if all fragments of the window have been
received. A correct MIC check indicates the end of the fragmented
packet transmission. An ACK is sent by the fragment receiver. In
case of an incorrect MIC, the receiver waits for fragments belonging
to the same window or the expiration of the Inactivity Timer. The
latter will lead the receiver to abort the on-going fragmented packet
transmission.
5.5.3. Bitmap Optimization 5.5.3. Bitmap Optimization
The Fragmentation Bitmap is the optmization of what has been The Bitmap is transmitted by a receiver as part of the ACK format
received. It is transmitted in the ACK format fragment when there when there are some missing fragments in a window. An ACK message
are some missing fragments. An ACK message may introduce padding at may introduce padding at the end to align transmitted data to a byte
the end to align transmitted data to a byte boundary. The first byte boundary. The first byte boundary includes one or more complete
boundary includes one or more complete bytes, depending on the size bytes, depending on the size of Rule ID and DTag.
of Rule ID and DTag.
The receiver generates the Bitmap which may have the size of a single Note that the ACK sent in response to an All-1 fragment includes the
downlink frame of the LPWAN technology used. To avoid this problem C bit. Therefore, the window size and thus the Bitmap size need to
the FCN size should be set to the corresponding downlink size minus 1 be determined taking into account the available space in the layer
bit for C bit. The C bit will be sent only in the ACK for the last two frame payload, where there will be 1 bit less for an ACK sent in
frame of the packet (All-1). response to an All-1 fragment than in other ACKs.
<---- bitmap fragments ----> <---- Bitmap bits ---->
| Rule ID | DTag |W|C|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|0| | Rule ID | DTag |W|C|0|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|1|
|--- byte boundary ----| 1 byte next | 1 byte next | |--- byte boundary ----| 1 byte next | 1 byte next |
Figure 18: Bitmap Figure 18: Bitmap
Bitmap transmitted MUST be optimized in size to reduce frame size. The Bitmap, when transmitted, MUST be optimized in size to reduce the
The right-most bytes with all Bitmap bit set to 1 MUST be removed resulting frame size. The right-most bytes with all Bitmap bits set
from the transmission. As the receiver knows the Bitmap size, it can to 1 MUST NOT be transmitted. As the receiver knows the Bitmap size,
reconstruct the value. In the example Figure 19 the last 2 bytes of it can reconstruct the original Bitmap without this optimization. In
the bitmap are set to 1, therefore, they are not sent. the example Figure 19, the last 2 bytes of the Bitmap shown in
Figure 18 comprise all bits set to 1, therefore, the last 2 bytes of
the Bitmap are not sent.
In the last window, when checked bit C value is one, means that the In the last window, when checked bit C value is 1, it means that the
MIC is corrected and the Bitmap is not sent. Otherwise, the Bitmap received MIC matches the one computed by the receiver, and thus the
needs to be sent after the C bit. Note that the introduction of a C Bitmap is not sent. Otherwise, the Bitmap needs to be sent after the
bit may force to reduce the number of fragments to allow the bitmap C bit. Note that the introduction of a C bit may force to reduce the
to fit in a frame. number of fragments in a window to allow the bitmap to fit in a
frame.
<------- R -------> <------- R ------->
<- T -> 1 <- T -> 1
+---- ... --+-... -+-+-+-+ +---- ... --+-... -+-+-+-+
| Rule ID | DTag |W|1|0| | Rule ID | DTag |W|1|0|
+---- ... --+-... -+-+-+-+ +---- ... --+-... -+-+-+-+
|---- byte boundary -----| |---- byte boundary -----|
Figure 19: Bitmap transmitted fragment format Figure 19: Bitmap transmitted fragment format
Figure 20 shows an example of an ACK (N=3), where the Bitmap Figure 20 shows an example of an ACK (for N=3), where the Bitmap
indicates that the second and the fifth fragments have not been indicates that the second and the fifth fragments have not been
correctly received. correctly received.
<------ R ------>6 5 4 3 2 1 0 (*) <------ R ------>6 5 4 3 2 1 0 (*)
<- T -> 1 <- T -> 1
| Rule ID | DTag |W|1|0|1|1|0|1|all-0|padding| Bitmap | Rule ID | DTag |W|1|0|1|1|0|1|all-0|padding| Bitmap (before tx)
|--- byte boundary ----| 1 byte next | |--- byte boundary ----| 1 byte next |
(*)=(FCN values indicating the order) (*)=(FCN values indicating the order)
+---- ... --+-... -+-+-+-+-+-+-+-+-+-+ +---- ... --+-... -+-+-+-+-+-+-+-+-+-+
| Rule ID | DTag |W|1|0|1|1|0|1|1|P| transmitted Bitmap | Rule ID | DTag |W|1|0|1|1|0|1|1|P| transmitted Bitmap
+---- ... --+-... -+-+-+-+-+-+-+-+-+-+ +---- ... --+-... -+-+-+-+-+-+-+-+-+-+
|--- byte boundary ----| 1 byte next | |--- byte boundary ----| 1 byte next |
Figure 20: Example of the bitmap in Window mode, in any window except Figure 20: Example of a Bitmap before transmission, and the
the last one, for N=3) transmitted one, in any window except the last one, for N=3
Figure 21 shows an example of an ACK (N=3), where the bitmap Figure 21 shows an example of an ACK (for N=3), where the Bitmap
indicates that the MIC check has failed but there is no missing indicates that the MIC check has failed but there are no missing
fragments. fragments.
<------- R -------> 6 5 4 3 2 1 7 (*) <------- R -------> 6 5 4 3 2 1 7 (*)
<- T -> 1 1 <- T -> 1 1
| Rule ID | DTag |W|0|1|1|1|1|1|1|1|padding| Bitmap | Rule ID | DTag |W|0|1|1|1|1|1|1|1|padding| Bitmap (before tx)
|---- byte boundary ----| 1 byte next | 1 byte next | |---- byte boundary ----| 1 byte next | 1 byte next |
C C
+---- ... --+-... -+-+-+-+ +---- ... --+-... -+-+-+-+
| Rule ID | DTag |W|0|1| transmitted Bitmap | Rule ID | DTag |W|0|1| transmitted Bitmap
+---- ... --+-... -+-+-+-+ +---- ... --+-... -+-+-+-+
|---- byte boundary -----| |---- byte boundary -----|
(*) = (FCN values indicating the order) (*) = (FCN values indicating the order)
Figure 21: Example of the Bitmap in Window mode for the last window, Figure 21: Example of the Bitmap in Window mode for the last window,
for N=3) for N=3)
5.6. Supporting multiple window sizes 5.6. Supporting multiple window sizes
For ACK-Always or ACK-on-error, implementers may opt to support a For ACK-Always or ACK-on-error, implementers may opt to support a
single window size or multiple window sizes. The latter, when single window size or multiple window sizes. The latter, when
feasible, may provide performance optimizations. For example, a feasible, may provide performance optimizations. For example, a
large window size may be used for packets that need to be carried by large window size may be used for packets that need to be carried by
a large number of fragments. However, when the number of fragments a large number of fragments. However, when the number of fragments
required to carry a packet is low, a smaller window size, and thus a required to carry a packet is low, a smaller window size, and thus a
shorter bitmap, may be sufficient to provide feedback on all shorter Bitmap, may be sufficient to provide feedback on all
fragments. If multiple window sizes are supported, the Rule ID may fragments. If multiple window sizes are supported, the Rule ID may
be used to signal the window size in use for a specific packet be used to signal the window size in use for a specific packet
transmission. transmission.
Note that the same window size MUST be used for the transmission of Note that the same window size MUST be used for the transmission of
all fragments that belong to a packet. all fragments that belong to a packet.
5.7. Downlink fragment transmission 5.7. Downlink fragment transmission
In some LPWAN technologies, as part of energy-saving techniques, In some LPWAN technologies, as part of energy-saving techniques,
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that transmission. that transmission.
When the fragment sender transmits the All-1 fragment, it initializes When the fragment sender transmits the All-1 fragment, it initializes
and starts its retransmission timer to a long value (e.g. several and starts its retransmission timer to a long value (e.g. several
times the initial Inactivity timer). If an ACK is received before times the initial Inactivity timer). If an ACK is received before
expiration of this timer, the fragment sender retransmits any lost expiration of this timer, the fragment sender retransmits any lost
fragments reported by the ACK, or if the ACK confirms successful fragments reported by the ACK, or if the ACK confirms successful
reception of all fragments of the last window, transmission of the reception of all fragments of the last window, transmission of the
fragmented packet ends. If the timer expires, and no ACK has been fragmented packet ends. If the timer expires, and no ACK has been
received since the start of the timer, the fragment sender assumes received since the start of the timer, the fragment sender assumes
that the all-1 fragment has been successfully received (and possibly, that the All-1 fragment has been successfully received (and possibly,
the last ACK has been lost: this mechanism assumes that the the last ACK has been lost: this mechanism assumes that the
retransmission timer for the all-1 fragment is long enough to allow retransmission timer for the All-1 fragment is long enough to allow
several ACK retries if the all-1 fragment has not been received by several ACK retries if the All-1 fragment has not been received by
the fragment receiver, and it also assumes that it is unlikely that the fragment receiver, and it also assumes that it is unlikely that
several ACKs become all lost). several ACKs become all lost).
6. Padding management 6. Padding management
SCHC header, either for compression, fragmentation or acknowledgment SCHC header, either for compression, fragmentation or acknowledgment
does not preserve byte alignment. Since most of the LPWAN network does not preserve byte alignment. Since most of the LPWAN network
technologies payload is expressed in an integer number of bytes; the technologies payload is expressed in an integer number of bytes; the
sender will introduce at the end some padding bits while the receiver sender will introduce at the end some padding bits while the receiver
must be able to eliminate them. must be able to eliminate them.
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padding bits. padding bits.
7. SCHC Compression for IPv6 and UDP headers 7. SCHC Compression for IPv6 and UDP headers
This section lists the different IPv6 and UDP header fields and how This section lists the different IPv6 and UDP header fields and how
they can be compressed. they can be compressed.
7.1. IPv6 version field 7.1. IPv6 version field
This field always holds the same value. Therefore, the TV is 6, the This field always holds the same value. Therefore, the TV is 6, the
MO is "equal" and the "CDA "not-sent"". MO is "equal" and the "CDA "not-sent".
7.2. IPv6 Traffic class field 7.2. IPv6 Traffic class field
If the DiffServ field identified by the rest of the rule do not vary If the DiffServ field identified by the rest of the rule does not
and is known by both sides, the TV should contain this well-known vary and is known by both sides, the TV should contain this well-
value, the MO should be "equal" and the CDA must be "not-sent. known value, the MO should be "equal" and the CDA must be "not-sent.
If the DiffServ field identified by the rest of the rule varies over If the DiffServ field identified by the rest of the rule varies over
time or is not known by both sides, then there are two possibilities time or is not known by both sides, then there are two possibilities
depending on the variability of the value, the first one is to do not depending on the variability of the value: The first one is to do not
compressed the field and sends the original value, or the second compressed the field and sends the original value. In the second,
where the values can be computed by sending only the LSB bits: where the values can be computed by sending only the LSB bits:
o TV is not set to any value, MO is set to "ignore" and CDA is set o TV is not set to any value, MO is set to "ignore" and CDA is set
to "value-sent" to "value-sent"
o TV contains a stable value, MO is MSB(X) and CDA is set to LSB o TV contains a stable value, MO is MSB(X) and CDA is set to LSB
7.3. Flow label field 7.3. Flow label field
If the Flow Label field identified by the rest of the rule does not If the Flow Label field identified by the rest of the rule does not
vary and is known by both sides, the TV should contain this well- vary and is known by both sides, the TV should contain this well-
known value, the MO should be "equal" and the CDA should be "not- known value, the MO should be "equal" and the CDA should be "not-
sent". sent".
If the Flow Label field identified by the rest of the rule varies If the Flow Label field identified by the rest of the rule varies
during time or is not known by both sides, there are two during time or is not known by both sides, there are two
possibilities depending on the variability of the value, the first possibilities depending on the variability of the value: The first
one is without compression and then the value is sent and the second one is without compression and then the value is sent. In the
where only part of the value is sent and the decompressor needs to second, only part of the value is sent and the decompressor needs to
compute the original value: compute the original value:
o TV is not set, MO is set to "ignore" and CDA is set to "value- o TV is not set, MO is set to "ignore" and CDA is set to "value-
sent" sent"
o TV contains a stable value, MO is MSB(X) and CDA is set to LSB o TV contains a stable value, MO is MSB(X) and CDA is set to LSB
7.4. Payload Length field 7.4. Payload Length field
If the LPWAN technology does not add padding, this field can be If the LPWAN technology does not add padding, this field can be
elided for the transmission on the LPWAN network. The SCHC C/D elided for the transmission on the LPWAN network. The SCHC C/D
recomputes the original payload length value. The TV is not set, the recomputes the original payload length value. The TV is not set, the
MO is set to "ignore" and the CDA is "compute-IPv6-length". MO is set to "ignore" and the CDA is "compute-IPv6-length".
If the payload length needs to be sent and does not need to be coded If the payload length needs to be sent and does not need to be coded
in 16 bits, the TV can be set to 0x0000, the MO set to "MSB (16-s)" in 16 bits, the TV can be set to 0x0000, the MO set to "MSB (16-s)"
and the CDA to "LSB". The 's' parameter depends on the expected and the CDA to "LSB". The 's' parameter depends on the expected
maximum packet length. maximum packet length.
On other cases, the payload length field must be sent and the CDA is In other cases, the payload length field must be sent and the CDA is
replaced by "value-sent". replaced by "value-sent".
7.5. Next Header field 7.5. Next Header field
If the Next Header field identified by the rest of the rule does not If the Next Header field identified by the rest of the rule does not
vary and is known by both sides, the TV should contain this Next vary and is known by both sides, the TV should contain this Next
Header value, the MO should be "equal" and the CDA should be "not- Header value, the MO should be "equal" and the CDA should be "not-
sent". sent".
If the Next header field identified by the rest of the rule varies If the Next Header field identified by the rest of the rule varies
during time or is not known by both sides, then TV is not set, MO is during time or is not known by both sides, then TV is not set, MO is
set to "ignore" and CDA is set to "value-sent". A matching-list may set to "ignore" and CDA is set to "value-sent". A matching-list may
also be used. also be used.
7.6. Hop Limit field 7.6. Hop Limit field
The End System is generally a device and does not forward packets. The End System is generally a device and does not forward packets.
Therefore, the Hop Limit value is constant. So, the TV is set with a Therefore, the Hop Limit value is constant. So, the TV is set with a
default value, the MO is set to "equal" and the CDA is set to "not- default value, the MO is set to "equal" and the CDA is set to "not-
sent". sent".
skipping to change at page 34, line 30 skipping to change at page 35, line 9
Note that the field behavior differs in upstream and downstream. In Note that the field behavior differs in upstream and downstream. In
upstream, since there is no IP forwarding between the Dev and the upstream, since there is no IP forwarding between the Dev and the
SCHC C/D, the value is relatively constant. On the other hand, the SCHC C/D, the value is relatively constant. On the other hand, the
downstream value depends of Internet routing and may change more downstream value depends of Internet routing and may change more
frequently. One solution could be to use the Direction Indicator frequently. One solution could be to use the Direction Indicator
(DI) to distinguish both directions to elide the field in the (DI) to distinguish both directions to elide the field in the
upstream direction and send the value in the downstream direction. upstream direction and send the value in the downstream direction.
7.7. IPv6 addresses fields 7.7. IPv6 addresses fields
As in 6LoWPAN [RFC4944], IPv6 addresses are split into two 64-bit As in 6LoWPAN [RFC4944], IPv6 addresses are splitted into two 64-bit
long fields; one for the prefix and one for the Interface Identifier long fields; one for the prefix and one for the Interface Identifier
(IID). These fields should be compressed. To allow a single rule, (IID). These fields should be compressed. To allow a single rule,
these values are identified by their role (DEV or APP) and not by these values are identified by their role (DEV or APP) and not by
their position in the frame (source or destination). The SCHC C/D their position in the frame (source or destination). The SCHC C/D
must be aware of the traffic direction (upstream, downstream) to must be aware of the traffic direction (upstream, downstream) to
select the appropriate field. select the appropriate field.
7.7.1. IPv6 source and destination prefixes 7.7.1. IPv6 source and destination prefixes
Both ends must be synchronized with the appropriate prefixes. For a Both ends must be synchronized with the appropriate prefixes. For a
specific flow, the source and destination prefix can be unique and specific flow, the source and destination prefixes can be unique and
stored in the context. It can be either a link-local prefix or a stored in the context. It can be either a link-local prefix or a
global prefix. In that case, the TV for the source and destination global prefix. In that case, the TV for the source and destination
prefixes contain the values, the MO is set to "equal" and the CDA is prefixes contain the values, the MO is set to "equal" and the CDA is
set to "not-sent". set to "not-sent".
In case the rule allows several prefixes, mapping-list must be used. In case the rule allows several prefixes, mapping-list must be used.
The different prefixes are listed in the TV associated with a short The different prefixes are listed in the TV associated with a short
ID. The MO is set to "match-mapping" and the CDA is set to "mapping- ID. The MO is set to "match-mapping" and the CDA is set to "mapping-
sent". sent".
Otherwise the TV contains the prefix, the MO is set to "equal" and Otherwise the TV contains the prefix, the MO is set to "equal" and
the CDA is set to value-sent. the CDA is set to "value-sent".
7.7.2. IPv6 source and destination IID 7.7.2. IPv6 source and destination IID
If the DEV or APP IID are based on an LPWAN address, then the IID can If the DEV or APP IID are based on an LPWAN address, then the IID can
be reconstructed with information coming from the LPWAN header. In be reconstructed with information coming from the LPWAN header. In
that case, the TV is not set, the MO is set to "ignore" and the CDA that case, the TV is not set, the MO is set to "ignore" and the CDA
is set to "DEViid" or "APPiid". Note that the LPWAN technology is is set to "DEViid" or "APPiid". Note that the LPWAN technology is
generally carrying a single device identifier corresponding to the generally carrying a single device identifier corresponding to the
DEV. The SCHC C/D may also not be aware of these values. DEV. The SCHC C/D may also not be aware of these values.
If the DEV address has a static value that is not derived from an If the DEV address has a static value that is not derived from an
IEEE EUI-64, then TV contains the actual Dev address value, the MO IEEE EUI-64, then TV contains the actual Dev address value, the MO
operator is set to "equal" and the CDA is set to "not-sent". operator is set to "equal" and the CDA is set to "not-sent".
If several IIDs are possible, then the TV contains the list of If several IIDs are possible, then the TV contains the list of
possible IIDs, the MO is set to "match-mapping" and the CDA is set to possible IIDs, the MO is set to "match-mapping" and the CDA is set to
"mapping-sent". "mapping-sent".
Otherwise the value variation of the IID may be reduced to few bytes. Otherwise the value variation of the IID may be reduced to few bytes.
In that case, the TV is set to the stable part of the IID, the MO is In that case, the TV is set to the stable part of the IID, the MO is
set to MSB and the CDA is set to LSB. set to "MSB" and the CDA is set to "LSB".
Finally, the IID can be sent on the LPWAN. In that case, the TV is Finally, the IID can be sent on the LPWAN. In that case, the TV is
not set, the MO is set to "ignore" and the CDA is set to "value- not set, the MO is set to "ignore" and the CDA is set to "value-
sent". sent".
7.8. IPv6 extensions 7.8. IPv6 extensions
No extension rules are currently defined. They can be based on the No extension rules are currently defined. They can be based on the
MOs and CDAs described above. MOs and CDAs described above.
skipping to change at page 37, line 15 skipping to change at page 37, line 43
A node can perform a buffer reservation attack by sending a first A node can perform a buffer reservation attack by sending a first
fragment to a target. Then, the receiver will reserve buffer space fragment to a target. Then, the receiver will reserve buffer space
for the IPv6 packet. Other incoming fragmented packets will be for the IPv6 packet. Other incoming fragmented packets will be
dropped while the reassembly buffer is occupied during the reassembly dropped while the reassembly buffer is occupied during the reassembly
timeout. Once that timeout expires, the attacker can repeat the same timeout. Once that timeout expires, the attacker can repeat the same
procedure, and iterate, thus creating a denial of service attack. procedure, and iterate, thus creating a denial of service attack.
The (low) cost to mount this attack is linear with the number of The (low) cost to mount this attack is linear with the number of
buffers at the target node. However, the cost for an attacker can be buffers at the target node. However, the cost for an attacker can be
increased if individual fragments of multiple packets can be stored increased if individual fragments of multiple packets can be stored
in the reassembly buffer. To further increase the attack cost, the in the reassembly buffer. To further increase the attack cost, the
reassembly buffer can be split into fragment-sized buffer slots. reassembly buffer can be splitted into fragment-sized buffer slots.
Once a packet is complete, it is processed normally. If buffer Once a packet is complete, it is processed normally. If buffer
overload occurs, a receiver can discard packets based on the sender overload occurs, a receiver can discard packets based on the sender
behavior, which may help identify which fragments have been sent by behavior, which may help identify which fragments have been sent by
an attacker. an attacker.
In another type of attack, the malicious node is required to have In another type of attack, the malicious node is required to have
overhearing capabilities. If an attacker can overhear a fragment, it overhearing capabilities. If an attacker can overhear a fragment, it
can send a spoofed duplicate (e.g. with random payload) to the can send a spoofed duplicate (e.g. with random payload) to the
destination. If the LPWAN technology does not support suitable destination. If the LPWAN technology does not support suitable
protection (e.g. source authentication and frame counters to prevent protection (e.g. source authentication and frame counters to prevent
skipping to change at page 37, line 37 skipping to change at page 38, line 16
spoofed fragments. Therefore, the original IPv6 packet will be spoofed fragments. Therefore, the original IPv6 packet will be
considered corrupt and will be dropped. To protect resource- considered corrupt and will be dropped. To protect resource-
constrained nodes from this attack, it has been proposed to establish constrained nodes from this attack, it has been proposed to establish
a binding among the fragments to be transmitted by a node, by a binding among the fragments to be transmitted by a node, by
applying content-chaining to the different fragments, based on applying content-chaining to the different fragments, based on
cryptographic hash functionality. The aim of this technique is to cryptographic hash functionality. The aim of this technique is to
allow a receiver to identify illegitimate fragments. allow a receiver to identify illegitimate fragments.
Further attacks may involve sending overlapped fragments (i.e. Further attacks may involve sending overlapped fragments (i.e.
comprising some overlapping parts of the original IPv6 datagram). comprising some overlapping parts of the original IPv6 datagram).
Implementers should make sure that correct operation is not affected Implementers should make sure that the correct operation is not
by such event. affected by such event.
In Window mode - ACK on error, a malicious node may force a fragment In Window mode - ACK on error, a malicious node may force a fragment
sender to resend a fragment a number of times, with the aim to sender to resend a fragment a number of times, with the aim to
increase consumption of the fragment sender's resources. To this increase consumption of the fragment sender's resources. To this
end, the malicious node may repeatedly send a fake ACK to the end, the malicious node may repeatedly send a fake ACK to the
fragment sender, with a bitmap that reports that one or more fragment sender, with a Bitmap that reports that one or more
fragments have been lost. In order to mitigate this possible attack, fragments have been lost. In order to mitigate this possible attack,
MAX_FRAG_RETRIES may be set to a safe value which allows to limit the MAX_FRAG_RETRIES may be set to a safe value which allows to limit the
maximum damage of the attack to an acceptable extent. However, note maximum damage of the attack to an acceptable extent. However, note
that a high setting for MAX_FRAG_RETRIES benefits fragment delivery that a high setting for MAX_FRAG_RETRIES benefits fragment delivery
reliability, therefore the trade-off needs to be carefully reliability, therefore the trade-off needs to be carefully
considered. considered.
9. Acknowledgements 9. Acknowledgements
Thanks to Dominique Barthel, Carsten Bormann, Philippe Clavier, Thanks to Dominique Barthel, Carsten Bormann, Philippe Clavier,
Arunprabhu Kandasamy, Antony Markovski, Alexander Pelov, Pascal Eduardo Ingles Sanchez, Arunprabhu Kandasamy, Sergio Lopez Bernal,
Thubert, Juan Carlos Zuniga and Diego Dujovne for useful design Antony Markovski, Alexander Pelov, Pascal Thubert, Juan Carlos Zuniga
consideration and comments. and Diego Dujovne for useful design consideration and comments.
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>. December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
skipping to change at page 41, line 24 skipping to change at page 42, line 20
learns the prefix is not in the scope of the document. learns the prefix is not in the scope of the document.
The third rule compresses port numbers to 4 bits. The third rule compresses port numbers to 4 bits.
Appendix B. Fragmentation Examples Appendix B. Fragmentation Examples
This section provides examples of different fragment delivery This section provides examples of different fragment delivery
reliability options possible on the basis of this specification. reliability options possible on the basis of this specification.
Figure 24 illustrates the transmission of an IPv6 packet that needs Figure 24 illustrates the transmission of an IPv6 packet that needs
11 fragments in the No ACK option, FCN is always 1 bit. 11 fragments in the No ACK option. Where FCN is always 1 bit.
Sender Receiver Sender Receiver
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
|-------FCN=0-------->| |-------FCN=0-------->|
skipping to change at page 42, line 31 skipping to change at page 43, line 31
ACK-on-error, for N=3 and MAX_WIND_FCN=6, without losses. ACK-on-error, for N=3 and MAX_WIND_FCN=6, without losses.
Figure 26 illustrates the transmission of an IPv6 packet that needs Figure 26 illustrates the transmission of an IPv6 packet that needs
11 fragments ACK-on-error, for N=3, with three losses. 11 fragments ACK-on-error, for N=3, with three losses.
Sender Receiver Sender Receiver
|-----W=0, FCN=6----->| |-----W=0, FCN=6----->|
|-----W=0, FCN=5----->| |-----W=0, FCN=5----->|
|-----W=0, FCN=4--X-->| |-----W=0, FCN=4--X-->|
|-----W=0, FCN=3----->| |-----W=0, FCN=3----->|
|-----W=0, FCN=2--X-->| |-----W=0, FCN=2--X-->| 7
|-----W=0, FCN=1----->| |-----W=0, FCN=1----->| /
|-----W=0, FCN=0----->| |-----W=0, FCN=0----->| 6543210
|<-----ACK, W=0-------|Bitmap:11010111 |<-----ACK, W=0-------|Bitmap:1101011
|-----W=0, FCN=4----->| |-----W=0, FCN=4----->|
|-----W=0, FCN=2----->| |-----W=0, FCN=2----->|
(no ACK) (no ACK)
|-----W=1, FCN=6----->| |-----W=1, FCN=6----->|
|-----W=1, FCN=5----->| |-----W=1, FCN=5----->|
|-----W=1, FCN=4--X-->| |-----W=1, FCN=4--X-->|
|-----W=1, FCN=7----->|MIC checked |-----W=1, FCN=7----->|MIC checked
|<-----ACK, W=1-------|Bitmap:11000001 |<-----ACK, W=1-------|C=0 Bitmap:1100001
|-----W=1, FCN=4----->|MIC checked => |-----W=1, FCN=4----->|MIC checked =>
|<---- ACK, W=1 ------| |<---- ACK, W=1 ------|
Figure 26: Transmission of an IPv6 packet carried by 11 fragments in Figure 26: Transmission of an IPv6 packet carried by 11 fragments in
ACK-on-error, for N=3 and MAX_WIND_FCN=6, three losses. ACK-on-error, for N=3 and MAX_WIND_FCN=6, three losses.
Figure 27 illustrates the transmission of an IPv6 packet that needs Figure 27 illustrates the transmission of an IPv6 packet that needs
11 fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, without 11 fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, without
losses. Note: in Window mode, an additional bit will be needed to losses. Note: in Window mode, an additional bit will be needed to
number windows. number windows.
Sender Receiver Sender Receiver
|-----W=0, FCN=6----->| |-----W=0, FCN=6----->|
|-----W=0, FCN=5----->| |-----W=0, FCN=5----->|
|-----W=0, FCN=4----->| |-----W=0, FCN=4----->|
|-----W=0, FCN=3----->| |-----W=0, FCN=3----->|
|-----W=0, FCN=2----->| |-----W=0, FCN=2----->|
|-----W=0, FCN=1----->| |-----W=0, FCN=1----->|
|-----W=0, FCN=0----->| |-----W=0, FCN=0----->|
|<-----ACK, W=0-------|no Bitmap |<-----ACK, W=0-------| Bitmap:1111111
|-----W=1, FCN=6----->| |-----W=1, FCN=6----->|
|-----W=1, FCN=5----->| |-----W=1, FCN=5----->|
|-----W=1, FCN=4----->| |-----W=1, FCN=4----->|
|-----W=1, FCN=7----->|MIC checked => |-----W=1, FCN=7----->|MIC checked =>
|<-----ACK, W=1-------|no Bitmap |<-----ACK, W=1-------| C=1 no Bitmap
(End) (End)
Figure 27: Transmission of an IPv6 packet carried by 11 fragments in Figure 27: Transmission of an IPv6 packet carried by 11 fragments in
ACK-Always, for N=3 and MAX_WIND_FCN=6, no losses. ACK-Always, for N=3 and MAX_WIND_FCN=6, no losses.
Figure 28 illustrates the transmission of an IPv6 packet that needs Figure 28 illustrates the transmission of an IPv6 packet that needs
11 fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three 11 fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three
losses. losses.
Sender Receiver Sender Receiver
|-----W=1, FCN=6----->| |-----W=1, FCN=6----->|
|-----W=1, FCN=5----->| |-----W=1, FCN=5----->|
|-----W=1, FCN=4--X-->| |-----W=1, FCN=4--X-->|
|-----W=1, FCN=3----->| |-----W=1, FCN=3----->|
|-----W=1, FCN=2--X-->| |-----W=1, FCN=2--X-->| 7
|-----W=1, FCN=1----->| |-----W=1, FCN=1----->| /
|-----W=1, FCN=0----->| |-----W=1, FCN=0----->| 6543210
|<-----ACK, W=1-------|Bitmap:11010111 |<-----ACK, W=1-------|Bitmap:1101011
|-----W=1, FCN=4----->| |-----W=1, FCN=4----->|
|-----W=1, FCN=2----->| |-----W=1, FCN=2----->|
|<-----ACK, W=1-------|no Bitmap |<-----ACK, W=1-------|Bitmap:
|-----W=0, FCN=6----->| |-----W=0, FCN=6----->|
|-----W=0, FCN=5----->| |-----W=0, FCN=5----->|
|-----W=0, FCN=4--X-->| |-----W=0, FCN=4--X-->|
|-----W=0, FCN=7----->|MIC checked |-----W=0, FCN=7----->|MIC checked
|<-----ACK, W=0-------|Bitmap:11000001 |<-----ACK, W=0-------| C= 0 Bitmap:11000001
|-----W=0, FCN=4----->|MIC checked => |-----W=0, FCN=4----->|MIC checked =>
|<-----ACK, W=0-------|no Bitmap |<-----ACK, W=0-------| C= 1 no Bitmap
(End) (End)
Figure 28: Transmission of an IPv6 packet carried by 11 fragments in Figure 28: Transmission of an IPv6 packet carried by 11 fragments in
ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses. ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses.
Figure 29 illustrates the transmission of an IPv6 packet that needs 6 Figure 29 illustrates the transmission of an IPv6 packet that needs 6
fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three
losses, and only one retry is needed for each lost fragment. Note losses, and only one retry is needed for each lost fragment. Note
that, since a single window is needed for transmission of the IPv6 that, since a single window is needed for transmission of the IPv6
packet in this case, the example illustrates behavior when losses packet in this case, the example illustrates behavior when losses
happen in the last window. happen in the last window.
Sender Receiver Sender Receiver
|-----W=0, CFN=6----->| |-----W=0, CFN=6----->|
|-----W=0, CFN=5----->| |-----W=0, CFN=5----->|
|-----W=0, CFN=4--X-->| |-----W=0, CFN=4--X-->|
|-----W=0, CFN=3--X-->| |-----W=0, CFN=3--X-->|
|-----W=0, CFN=2--X-->| |-----W=0, CFN=2--X-->|
|-----W=0, CFN=7----->|MIC checked |-----W=0, CFN=7----->|MIC checked
|<-----ACK, W=0-------|Bitmap:11000001 |<-----ACK, W=0-------|C= 0 Bitmap:1100001
|-----W=0, CFN=4----->|MIC checked: failed |-----W=0, CFN=4----->|MIC checked: failed
|-----W=0, CFN=3----->|MIC checked: failed |-----W=0, CFN=3----->|MIC checked: failed
|-----W=0, CFN=2----->|MIC checked: success |-----W=0, CFN=2----->|MIC checked: success
|<-----ACK, W=0-------|no Bitmap |<-----ACK, W=0-------|C=1 no Bitmap
(End) (End)
Figure 29: Transmission of an IPv6 packet carried by 11 fragments in Figure 29: Transmission of an IPv6 packet carried by 11 fragments in
ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and only ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and only
one retry is needed for each lost fragment. one retry is needed for each lost fragment.
Figure 30 illustrates the transmission of an IPv6 packet that needs 6 Figure 30 illustrates the transmission of an IPv6 packet that needs 6
fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three
losses, and the second ACK is lost. Note that, since a single window losses, and the second ACK is lost. Note that, since a single window
is needed for transmission of the IPv6 packet in this case, the is needed for transmission of the IPv6 packet in this case, the
example illustrates behavior when losses happen in the last window. example illustrates behavior when losses happen in the last window.
Sender Receiver Sender Receiver
|-----W=0, CFN=6----->| |-----W=0, CFN=6----->|
|-----W=0, CFN=5----->| |-----W=0, CFN=5----->|
|-----W=0, CFN=4--X-->| |-----W=0, CFN=4--X-->|
|-----W=0, CFN=3--X-->| |-----W=0, CFN=3--X-->|
|-----W=0, CFN=2--X-->| |-----W=0, CFN=2--X-->|
|-----W=0, CFN=7----->|MIC checked |-----W=0, CFN=7----->|MIC checked
|<-----ACK, W=0-------|Bitmap:11000001 |<-----ACK, W=0-------|C=0 Bitmap:1100001
|-----W=0, CFN=4----->|MIC checked: wrong |-----W=0, CFN=4----->|MIC checked: wrong
|-----W=0, CFN=3----->|MIC checked: wrong |-----W=0, CFN=3----->|MIC checked: wrong
|-----W=0, CFN=2----->|MIC checked: right |-----W=0, CFN=2----->|MIC checked: right
| X---ACK, W=0-------|no Bitmap | X---ACK, W=0-------|C= 1 no Bitmap
timeout | | timeout | |
|-----W=0, CFN=7----->| |-----W=0, CFN=7----->|
|<-----ACK, W=0-------|no Bitmap |<-----ACK, W=0-------|C= 1 no Bitmap
(End) (End)
Figure 30: Transmission of an IPv6 packet carried by 11 fragments in Figure 30: Transmission of an IPv6 packet carried by 11 fragments in
ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and the ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and the
second ACK is lost. second ACK is lost.
Figure 31 illustrates the transmission of an IPv6 packet that needs 6 Figure 31 illustrates the transmission of an IPv6 packet that needs 6
fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three fragments in ACK-Always, for N=3 and MAX_WIND_FCN=6, with three
losses, and one retransmitted fragment is lost. Note that, since a losses, and one retransmitted fragment is lost. Note that, since a
skipping to change at page 46, line 16 skipping to change at page 47, line 16
case, the example illustrates behavior when losses happen in the last case, the example illustrates behavior when losses happen in the last
window. window.
Sender Receiver Sender Receiver
|-----W=0, CFN=6----->| |-----W=0, CFN=6----->|
|-----W=0, CFN=5----->| |-----W=0, CFN=5----->|
|-----W=0, CFN=4--X-->| |-----W=0, CFN=4--X-->|
|-----W=0, CFN=3--X-->| |-----W=0, CFN=3--X-->|
|-----W=0, CFN=2--X-->| |-----W=0, CFN=2--X-->|
|-----W=0, CFN=7----->|MIC checked |-----W=0, CFN=7----->|MIC checked
|<-----ACK, W=0-------|Bitmap:11000001 |<-----ACK, W=0-------|C=0 Bitmap:1100001
|-----W=0, CFN=4----->|MIC checked: wrong |-----W=0, CFN=4----->|MIC checked: wrong
|-----W=0, CFN=3----->|MIC checked: wrong |-----W=0, CFN=3----->|MIC checked: wrong
|-----W=0, CFN=2--X-->| |-----W=0, CFN=2--X-->|
timeout| | timeout| |
|-----W=0, CFN=7----->|All-0 empty |-----W=0, CFN=7----->|All-0 empty
|<-----ACK, W=0-------|Bitmap:11110001 |<-----ACK, W=0-------|C=0 Bitmap: 1111101
|-----W=0, CFN=2----->|MIC checked: right |-----W=0, CFN=2----->|MIC checked: right
|<-----ACK, W=0-------|no Bitmap |<-----ACK, W=0-------|C=1 no Bitmap
(End) (End)
Figure 31: Transmission of an IPv6 packet carried by 11 fragments in Figure 31: Transmission of an IPv6 packet carried by 11 fragments in
ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and one ACK-Always, for N=3, and MAX_WIND_FCN=6, with three losses, and one
retransmitted fragment is lost. retransmitted fragment is lost.
Appendix C illustrates the transmission of an IPv6 packet that needs Appendix C illustrates the transmission of an IPv6 packet that needs
28 fragments in ACK-Always, for N=5 and MAX_WIND_FCN=23, with two 28 fragments in ACK-Always, for N=5 and MAX_WIND_FCN=23, with two
losses. Note that MAX_WIND_FCN=23 may be useful when the maximum losses. Note that MAX_WIND_FCN=23 may be useful when the maximum
possible bitmap size, considering the maximum lower layer technology possible Bitmap size, considering the maximum lower layer technology
payload size and the value of R, is 3 bytes. Note also that the FCN payload size and the value of R, is 3 bytes. Note also that the FCN
of the last fragment of the packet is the one with FCN=31 (i.e. of the last fragment of the packet is the one with FCN=31 (i.e.
FCN=2^N-1 for N=5, or equivalently, all FCN bits set to 1). FCN=2^N-1 for N=5, or equivalently, all FCN bits set to 1).
Sender Receiver Sender Receiver
|-----W=0, CFN=23----->| |-----W=0, CFN=23----->|
|-----W=0, CFN=22----->| |-----W=0, CFN=22----->|
|-----W=0, CFN=21--X-->| |-----W=0, CFN=21--X-->|
|-----W=0, CFN=20----->| |-----W=0, CFN=20----->|
|-----W=0, CFN=19----->| |-----W=0, CFN=19----->|
skipping to change at page 48, line 5 skipping to change at page 49, line 5
|-----W=1, CFN=21----->| |-----W=1, CFN=21----->|
|-----W=1, CFN=31----->|MIC checked => |-----W=1, CFN=31----->|MIC checked =>
|<------ACK, W=1-------|no Bitmap |<------ACK, W=1-------|no Bitmap
(End) (End)
Appendix C. Fragmentation State Machines Appendix C. Fragmentation State Machines
The fragmentation state machines of the sender and the receiver in The fragmentation state machines of the sender and the receiver in
the different reliability options are next in the following figures: the different reliability options are next in the following figures:
+-----------+ +===========+
+------------+ Init | +------------+ Init |
| FCN=0 +-----------+ | FCN=0 +===========+
| No Window | No Window
| No Bitmap | No Bitmap
| +-------+ | +-------+
| +--------+--+ | More Fragments | +========+==+ | More Fragments
| | | <--+ ~~~~~~~~~~~~~~~~~~~~ | | | <--+ ~~~~~~~~~~~~~~~~~~~~
+--------> | Send | send Fragment (FCN=0) +--------> | Send | send Fragment (FCN=0)
+---+-------+ +===+=======+
| last fragment | last fragment
| ~~~~~~~~~~~~ | ~~~~~~~~~~~~
| FCN = 1 | FCN = 1
v send fragment+MIC v send fragment+MIC
+------------+ +============+
| END | | END |
+------------+ +============+
Figure 32: Sender State Machine for the No ACK Mode Figure 32: Sender State Machine for the No ACK Mode
+------+ Not All-1 +------+ Not All-1
+----------+-+ | ~~~~~~~~~~~~~~~~~~~ +==========+=+ | ~~~~~~~~~~~~~~~~~~~
| + <--+ set Inactivity Timer | + <--+ set Inactivity Timer
| RCV Frag +-------+ | RCV Frag +-------+
+-+---+------+ |All-1 & +=+===+======+ |All-1 &
All-1 & | | |MIC correct All-1 & | | |MIC correct
MIC wrong | |Inactivity | MIC wrong | |Inactivity |
| |Timer Exp. | | |Timer Exp. |
v | | v | |
+----------++ | v +==========++ | v
| Error |<-+ +--------+--+ | Error |<-+ +========+==+
+-----------+ | END | +===========+ | END |
+-----------+ +===========+
Figure 33: Receiver State Machine for the No ACK Mode Figure 33: Receiver State Machine for the No ACK Mode
+-------+ +=======+
| INIT | FCN!=0 & more frags | INIT | FCN!=0 & more frags
| | ~~~~~~~~~~~~~~~~~~~~~~ | | ~~~~~~~~~~~~~~~~~~~~~~
+------++ +--+ send Window + frag(FCN) +======++ +--+ send Window + frag(FCN)
W=0 | | | FCN- W=0 | | | FCN-
Clear local bitmap | | v set local bitmap Clear local Bitmap | | v set local Bitmap
FCN=max value | ++--+--------+ FCN=max value | ++==+========+
+> | | +> | |
+---------------------> | SEND | +---------------------> | SEND |
| +--+-----+---+ | +==+=====+===+
| FCN==0 & more frags | | last frag | FCN==0 & more frags | | last frag
| ~~~~~~~~~~~~~~~~~~~~~ | | ~~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~ | | ~~~~~~~~~~~~~~~
| set local-bitmap | | set local-bitmap | set local-Bitmap | | set local-Bitmap
| send wnd + frag(all-0) | | send wnd+frag(all-1)+MIC | send wnd + frag(all-0) | | send wnd+frag(all-1)+MIC
| set Retrans_Timer | | set Retrans_Timer | set Retrans_Timer | | set Retrans_Timer
| | | | | |
|Recv_wnd == wnd & | | |Recv_wnd == wnd & | |
|Lcl_bitmap==recv_bitmap& | | +------------------------+ |Lcl_Bitmap==recv_Bitmap& | | +------------------------+
|more frag | | |local-bitmap!=rcv-bitmap| |more frag | | |local-Bitmap!=rcv-Bitmap|
|~~~~~~~~~~~~~~~~~~~~~~ | | | ~~~~~~~~~ | |~~~~~~~~~~~~~~~~~~~~~~ | | | ~~~~~~~~~ |
|Stop Retrans_Timer | | | Attemp++ v |Stop Retrans_Timer | | | Attemp++ v
|clear local_bitmap v v | +------++ |clear local_Bitmap v v | +======++
|window=next_window +----+-----+--+--+ |Resend | |window=next_window +====+=====+==+==+ |Resend |
+---------------------+ | |Missing| +---------------------+ | |Missing|
+----+ Wait | |Frag | +----+ Wait | |Frag |
not expected wnd | | bitmap | +------++ not expected wnd | | Bitmap | +======++
~~~~~~~~~~~~~~~~ +--->+ +-+Retrans_Timer Exp | ~~~~~~~~~~~~~~~~ +--->+ +-+Retrans_Timer Exp |
discard frag +--+-+---+-+---+-+ |~~~~~~~~~~~~~~~~~ | discard frag +==+=+===+=+===+=+ |~~~~~~~~~~~~~~~~~ |
| | | ^ ^ |reSend(empty)All-* | | | | ^ ^ |reSend(empty)All-* |
| | | | | |Set Retrans_Timer | | | | | | |Set Retrans_Timer |
MIC_bit==1 & | | | | +---+Attemp++ | MIC_bit==1 & | | | | +---+Attemp++ |
Recv_window==window & | | | +---------------------------+ Recv_window==window & | | | +---------------------------+
Lcl_bitmap==recv_bitmap &| | | all missing frag sent Lcl_Bitmap==recv_Bitmap &| | | all missing frag sent
no more frag| | | ~~~~~~~~~~~~~~~~~~~~~~ no more frag| | | ~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~| | | Set Retrans_Timer ~~~~~~~~~~~~~~~~~~~~~~~~| | | Set Retrans_Timer
Stop Retrans_Timer| | | Stop Retrans_Timer| | |
+-------------+ | | | +=============+ | | |
| END +<--------+ | | Attemp > MAX_ACK_REQUESTS | END +<--------+ | | Attemp > MAX_ACK_REQUESTS
+-------------+ | | ~~~~~~~~~~~~~~~~~~ +=============+ | | ~~~~~~~~~~~~~~~~~~
All-1 Window | v Send Abort All-1 Window | v Send Abort
~~~~~~~~~~~~ | +-+-----------+ ~~~~~~~~~~~~ | +=+===========+
MIC_bit ==0 & +>| ERROR | MIC_bit ==0 & +>| ERROR |
Lcl_bitmap==recv_bitmap +-------------+ Lcl_Bitmap==recv_Bitmap +=============+
Figure 34: Sender State Machine for the ACK Always Mode Figure 34: Sender State Machine for the ACK Always Mode
Not All- & w=expected +---+ +---+w = Not expected Not All- & w=expected +---+ +---+w = Not expected
~~~~~~~~~~~~~~~~~~~~~ | | | |~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~ | | | |~~~~~~~~~~~~~~~~
Set local_bitmap(FCN) | v v |discard Set local_Bitmap(FCN) | v v |discard
++---+---+---+-+ ++===+===+===+=+
+---------------------+ Rcv +--->* ABORT +---------------------+ Rcv +--->* ABORT
| +------------------+ Window | | +------------------+ Window |
| | +-----+--+-----+ | | +=====+==+=====+
| | All-0 & w=expect | ^ w =next & not-All | | All-0 & w=expect | ^ w =next & not-All
| | ~~~~~~~~~~~~~~~~~~ | |~~~~~~~~~~~~~~~~~~~~~ | | ~~~~~~~~~~~~~~~~~~ | |~~~~~~~~~~~~~~~~~~~~~
| | set lcl_bitmap(FCN)| |expected = next window | | set lcl_Bitmap(FCN)| |expected = next window
| | send local_bitmap | |Clear local_bitmap | | send local_Bitmap | |Clear local_Bitmap
| | | | | | | |
| | w=expct & not-All | | | | w=expct & not-All | |
| | ~~~~~~~~~~~~~~~~~~ | | | | ~~~~~~~~~~~~~~~~~~ | |
| | set lcl_bitmap(FCN)+-+ | | +--+ w=next & All-0 | | set lcl_Bitmap(FCN)+-+ | | +--+ w=next & All-0
| | if lcl_bitmap full | | | | | | ~~~~~~~~~~~~~~~ | | if lcl_Bitmap full | | | | | | ~~~~~~~~~~~~~~~
| | send lcl_bitmap v | v | | | expct = nxt wnd | | send lcl_Bitmap | | | | | | expct = nxt wnd
| | +-+-+-+--+-++ | Clear lcl_bitmap | | v | v v v |
| | w=expected & +->+ Wait +<+ set lcl_bitmap(FCN) | | w=expct & All-1 +=+=+=+==+=++ | Clear lcl_Bitmap
| | All-1 | | Next | send lcl_bitmap | | ~~~~~~~~~~~ +->+ Wait +<+ set lcl_Bitmap(FCN)
| | ~~~~~~~~~~~~ +--+ Window +--->* ABORT | | discard +--| Next | send lcl_Bitmap
| | discard +--------+-++ | | All-0 +---------+ Window +--->* ABORT
| | All-1 & w=next| | All-1 & w=nxt | | ~~~~~ +-------->+========+=++
| | snd lcl_bm All-1 & w=next| | All-1 & w=nxt
| | & MIC wrong| | & MIC right | | & MIC wrong| | & MIC right
| | ~~~~~~~~~~~~~~~~~| | ~~~~~~~~~~~~~~~~~~ | | ~~~~~~~~~~~~~~~~~| | ~~~~~~~~~~~~~~~~~~
| | set local_bitmap(FCN)| |set lcl_bitmap(FCN) | | set local_Bitmap(FCN)| |set lcl_Bitmap(FCN)
| | send local_bitmap| |send local_bitmap | | send local_Bitmap| |send local_Bitmap
| | | +----------------------+ | | | +----------------------+
| |All-1 & w=expct | | | |All-1 & w=expct | |
| |& MIC wrong v +---+ w=expctd & | | |& MIC wrong v +---+ w=expctd & |
| |~~~~~~~~~~~~~~~~~~~~ +----+---+-+ | MIC wrong | | |~~~~~~~~~~~~~~~~~~~~ +====+=====+ | MIC wrong |
| |set local_bitmap(FCN) | +<+ ~~~~~~~~~~~~~~ | | |set local_Bitmap(FCN) | +<+ ~~~~~~~~~~~~~~ |
| |send local_bitmap | Wait End | set lcl_btmp(FCN)| | |send local_Bitmap | Wait End | set lcl_btmp(FCN)|
| +--------------------->+ +--->* ABORT | | +--------------------->+ +--->* ABORT |
| +---+----+-+ | | +===+====+=+-+ All-1&MIC wrong|
| w=expected & MIC right| | | | ^ | ~~~~~~~~~~~~~~~|
| | +---+ send lcl_btmp |
| w=expected & MIC right| | |
| ~~~~~~~~~~~~~~~~~~~~~~| +-+ Not All-1 | | ~~~~~~~~~~~~~~~~~~~~~~| +-+ Not All-1 |
| set local_bitmap(FCN)| | | ~~~~~~~~~ | | set local_Bitmap(FCN)| | | ~~~~~~~~~ |
| send local_bitmap| | | discard | | send local_Bitmap| | | discard |
| | | | | | | | | |
|All-1 & w=expctd & MIC right | | | +-+ All-1 | |All-1 & w=expctd & MIC right | | | +-+ All-1 |
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~ v | v | v ~~~~~~~~~ | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~ v | v | v ~~~~~~~~~ |
|set local_bitmap(FCN) +-+-+-+-+-++Send lcl_btmp | |set local_Bitmap(FCN) +=+=+=+=+=++Send lcl_btmp |
|send local_bitmap | | | |send local_Bitmap | | |
+-------------------------->+ END +<---------------+ +-------------------------->+ END +<---------------+
++--+------+ ++==+======+
--->* ABORT --->* ABORT
~~~~~~~ ~~~~~~~
Inactivity_Timer = expires Inactivity_Timer = expires
When DWN_Link When DWN_Link
IF Inactivity_Timer expires IF Inactivity_Timer expires
Send DWL Request Send DWL Request
Attemp++ Attemp++
Figure 35: Receiver State Machine for the ACK Always Mode Figure 35: Receiver State Machine for the ACK Always Mode
+-------+ +=======+
| | | |
| INIT | | INIT |
| | FCN!=0 & more frags | | FCN!=0 & more frags
+------++ +--+ ~~~~~~~~~~~~~~~~~~~~~~ +======++ +--+ ~~~~~~~~~~~~~~~~~~~~~~
W=0 | | | send Window + frag(FCN) W=0 | | | send Window + frag(FCN)
~~~~~~~~~~~~~~~~~~ | | | FCN- ~~~~~~~~~~~~~~~~~~ | | | FCN-
Clear local bitmap | | v set local bitmap Clear local Bitmap | | v set local Bitmap
FCN=max value | ++-------------+ FCN=max value | ++=============+
+> | | +> | |
| SEND | | SEND |
+-------------------------> | | +-------------------------> | |
| ++-----+-------+ | ++=====+=======+
| FCN==0 & more frags| |last frag | FCN==0 & more frags| |last frag
| ~~~~~~~~~~~~~~~~~~~~~~~| |~~~~~~~~~~~~~~~~~~~~~~~~ | ~~~~~~~~~~~~~~~~~~~~~~~| |~~~~~~~~~~~~~~~~~~~~~~~~
| set local-bitmap| |set local-bitmap | set local-Bitmap| |set local-Bitmap
| send wnd + frag(all-0)| |send wnd+frag(all-1)+MIC | send wnd + frag(all-0)| |send wnd+frag(all-1)+MIC
| set Retrans_Timer| |set Retrans_Timer | set Retrans_Timer| |set Retrans_Timer
| | | | | |
|Retrans_Timer expires & | | local-bitmap!=rcv-bitmap |Retrans_Timer expires & | | local-Bitmap!=rcv-Bitmap
|more fragments | | +-----------------+ |more fragments | | +-----------------+
|~~~~~~~~~~~~~~~~~~~~ | | | ~~~~~~~~~~~~~ | |~~~~~~~~~~~~~~~~~~~~ | | | ~~~~~~~~~~~~~ |
|stop Retrans_Timer | | | Attemp++ | |stop Retrans_Timer | | | Attemp++ |
|clear local.bitmap v v | v |clear local-Bitmap v v | v
|window = next window +-----+-----+--+--+ +----+----+ |window = next window +=====+=====+==+==+ +====+====+
+----------------------+ + | Resend | +----------------------+ + | Resend |
+--------------------->+ Wait bitmap | | Missing | +--------------------->+ Wait Bitmap | | Missing |
| +-- + | | Frag | | +-- + | | Frag |
| not expected wnd | ++-+---+---+---+--+ +------+--+ | not expected wnd | ++=+===+===+===+==+ +======+==+
| ~~~~~~~~~~~~~~~~ | ^ | | | ^ | | ~~~~~~~~~~~~~~~~ | ^ | | | ^ |
| discard frag +----+ | | | +-------------------+ | discard frag +----+ | | | +-------------------+
| | | | all missing frag sent | | | | all missing frag sent
|Retrans_Timer expires & | | | ~~~~~~~~~~~~~~~~~~~~~ |Retrans_Timer expires & | | | ~~~~~~~~~~~~~~~~~~~~~
| No more Frag | | | Set Retrans_Timer | No more Frag | | | Set Retrans_Timer
| ~~~~~~~~~~~~~~~~~~~~~~~ | | | | ~~~~~~~~~~~~~~~~~~~~~~~ | | |
| Stop Retrans_Timer | | | | Stop Retrans_Timer | | |
| Send ALL-1-empty | | | | Send ALL-1-empty | | |
+-------------------------+ | | +-------------------------+ | |
| | | |
Local_bitmap==Recv_bitmap| | Local_Bitmap==Recv_Bitmap| |
~~~~~~~~~~~~~~~~~~~~~~~~~| |Attemp > MAX_ACK_REQUESTS ~~~~~~~~~~~~~~~~~~~~~~~~~| |Attemp > MAX_ACK_REQUESTS
+---------+Stop Retrans_Timer | |~~~~~~~~~~~~~~~~~~~~~~~ +=========+Stop Retrans_Timer | |~~~~~~~~~~~~~~~~~~~~~~~
| END +<------------------+ v Send Abort | END +<------------------+ v Send Abort
+---------+ +-+---------+ +=========+ +=+=========+
| ERROR | | ERROR |
+-----------+ +===========+
Figure 36: Sender State Machine for the ACK on error Mode Figure 36: Sender State Machine for the ACK on error Mode
Not All- & w=expected +---+ +---+w = Not expected Not All- & w=expected +---+ +---+w = Not expected
~~~~~~~~~~~~~~~~~~~~~ | | | |~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~ | | | |~~~~~~~~~~~~~~~~
Set local_bitmap(FCN) | v v |discard Set local_Bitmap(FCN) | v v |discard
++---+---+---+-+ ++===+===+===+=+
+-----------------------+ +--+ All-0 & full +-----------------------+ +--+ All-0 & full
| ABORT *<---+ Rcv Window | | ~~~~~~~~~~~~ | ABORT *<---+ Rcv Window | | ~~~~~~~~~~~~
| +--------------------+ +<-+ w =next | +--------------------+ +<-+ w =next
| | +---+---+------+ clear lcl_bitmap | | +===+===+======+ clear lcl_Bitmap
| | | ^ | | | ^
| | All-0 & w=expect| |w=expct & not-All & full | | All-0 & w=expect| |w=expct & not-All & full
| | & no_full bitmap| |~~~~~~~~~~~~~~~~~~~~~~~~ | | & no_full Bitmap| |~~~~~~~~~~~~~~~~~~~~~~~~
| | ~~~~~~~~~~~~~~~~~| |clear lcl_bitmap; w =nxt | | ~~~~~~~~~~~~~~~~~| |clear lcl_Bitmap; w =nxt
| | send local_bitmap| | | | send local_Bitmap| |
| | | | +--------+ | | | | +========+
| | | | +---------->+ | | | | | +---------->+ |
| | | | |w=next | Error/ | | | | | |w=next | Error/ |
| | | | |~~~~~~~~ | Abort | | | | | |~~~~~~~~ | Abort |
| | | | |Send abort ++-------+ | | | | |Send abort ++=======+
| | v | | ^ w=expct | | v | | ^ w=expct
| | +-+---+--+------+ | & all-1 | | All-0 +=+===+==+======+ | & all-1
| | ABORT *<---+ Wait +------+ ~~~~~~~ | | ~~~~~~~~~~~~~<---+ Wait +------+ ~~~~~~~
| | | Next Window | Send abort | | send lcl_btmp | Next Window | Send abort
| | +-------+---+---+ | | +=======+===+==++
| | All-1 & w=next & MIC wrong | | | | All-1 & w=next & MIC wrong | | +---->* ABORT
| | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | +----------------+ | | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | +----------------+
| | set local_bitmap(FCN) | All-1 & w=next| | | set local_Bitmap(FCN) | All-1 & w=next|
| | send local_bitmap | & MIC right| | | send local_Bitmap | & MIC right|
| | | ~~~~~~~~~~~~~~~~~~| | | | ~~~~~~~~~~~~~~~~~~|
| | | set lcl_bitmap(FCN)| | | | set lcl_Bitmap(FCN)|
| |All-1 & w=expect & MIC wrong | | | |All-1 & w=expect & MIC wrong | |
| |~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | | | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | +-+ All-1 |
| |set local_bitmap(FCN) v +--->* ABORT | | |set local_Bitmap(FCN) v | v ~~~~~~~~~~ |
| |send local_bitmap +-------+---+--+ | | |send local_Bitmap +=======+==+===+ snd lcl_btmp|
| +--------------------->+ Wait End +-+ | | +--------------------->+ Wait End +-+ |
| +-----+------+-+ | w=expct & | | +=====+=+===+=+ | w=expct & |
| w=expected & MIC right | ^ | MIC wrong | | w=expected & MIC right | | ^ | MIC wrong |
| ~~~~~~~~~~~~~~~~~~~~~~ | +---+ ~~~~~~~~~ | | ~~~~~~~~~~~~~~~~~~~~~~ | | +---+ ~~~~~~~~~ |
| set local_bitmap(FCN) | set lcl_bitmap(FCN)| | set local_Bitmap(FCN) | | set lcl_Bitmap(FCN)|
| | | | | | |
|All-1 & w=expected & MIC right | | |All-1 & w=expected & MIC right | +-->* ABORT |
|~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ v | |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ v |
|set local_bitmap(FCN) +-+----------+ | |set local_Bitmap(FCN) +=+==========+ |
+---------------------------->+ END +<----------+ +---------------------------->+ END +<----------+
+------------+ +============+
--->* Only Uplink --->* Only Uplink
ABORT ABORT
~~~~~~~~ ~~~~~~~~
Inactivity_Timer = expires Inactivity_Timer = expires
Figure 37: Receiver State Machine for the ACK on error Mode Figure 37: Receiver State Machine for the ACK on error Mode
Appendix D. Allocation of Rule IDs for fragmentation Appendix D. Allocation of Rule IDs for fragmentation
A set of Rule IDs are allocated to support different aspects of A set of Rule IDs are allocated to support different aspects of
 End of changes. 179 change blocks. 
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