lpwan Working Group JC. Zuniga
Internet-Draft SIGFOX
Intended status: Standards Track C. Gomez
Expires: April 21, 2022 S. Aguilar
Universitat Politecnica de Catalunya
L. Toutain
IMT-Atlantique
S. Cespedes
D. Wistuba
NIC Labs, Universidad de Chile
October 18, 2021
SCHC Compound ACK
draft-ietf-lpwan-schc-compound-ack-01
Abstract
The present document describes an extension to the SCHC (Static
Header Compression and Fragmentation) protocol [RFC8724]. It defines
a SCHC Compound ACK message format, which is intended to reduce the
number of downlink transmissions (i.e., SCHC ACKs) by accumulating
bitmaps of several windows in a single SCHC message (i.e., the SCHC
Compound ACK).
The message format is generic, and can be used for instance by any
the four LWPAN technologies defined in [RFC8376], being Sigfox,
LoRaWAN, NB-IoT and IEEE 802.15.4w.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 21, 2022.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. SCHC Compound ACK . . . . . . . . . . . . . . . . . . . . . . 3
3.1. SCHC Compound ACK Message Format . . . . . . . . . . . . 3
3.2. SCHC Compound ACK Examples . . . . . . . . . . . . . . . 4
3.3. SCHC Compound ACK YANG Data Model . . . . . . . . . . . . 5
4. Security considerations . . . . . . . . . . . . . . . . . . . 7
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
6. Normative References . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The Generic Framework for Static Context Header Compression and
Fragmentation (SCHC) specification [RFC8724] describes two
mechanisms: i) an application header compression scheme, and ii) a
frame fragmentation and loss recovery functionality. Either can be
used on top of radio technologies such as the four LWPAN defined in
[RFC8376], being Sigfox, LoRaWAN, NB-IoT and IEEE 802.15.4w. These
LPWANs have similar characteristics such as star-oriented topologies,
network architecture, connected devices with built-in applications,
etc.
SCHC offers a great level of flexibility to accommodate all these
LPWAN technologies. Even though there are a great number of
similarities between them, some differences exist with respect to the
transmission characteristics, payload sizes, etc. Hence, there are
optimal parameters and modes of operation that can be used when SCHC
is used on top of a specific LPWAN technology.
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The present document describes an extension to the SCHC protocol. It
defines a SCHC Compound ACK format, which is intended to reduce the
number of downlink transmissions (i.e., SCHC ACKs) in the ACK-on-
Error mode of SCHC. The SCHC Compound ACK extends the SCHC ACK
message format so that it can contain several bitmaps, each bitmap
being identified by its corresponding window number.
The SCHC Compound ACK:
o provides feedback only for windows with fragment losses,
o has a variable size that depends on the number of windows with
fragment losses being reported in the single Compound SCHC ACK,
o includes the window number (i.e., W) of each bitmap,
o has the same SCHC ACK format defined in [RFC8724] when only one
window with losses is reported,
o might not cover all windows with fragment losses of a SCHC Packet,
o is distinguishable from the SCHC Receiver-Abort.
2. Terminology
It is assumed that the reader is familiar with the terms and
mechanisms defined in [RFC8376] and in [RFC8724].
3. SCHC Compound ACK
The SCHC Compound ACK is a SCHC ACK message that can contain several
bitmaps, each bitmap being identified by its corresponding window
number.
When the ACK-on-Error mode is used for uplink fragmentation, SCHC
Compound ACKs MAY be used in the downlink responses.
The SCHC Compound ACK groups the window number (W) with its
corresponding bitmap. The included window numbers and corresponding
bitmaps MUST be ordered from the lowest-numbered to the highest-
numbered window.
3.1. SCHC Compound ACK Message Format
Figure 1 shows the regular SCHC ACK format when all fragments have
been correctly received (C=1), as defined in [RFC8724].
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|- SCHC ACK Header --|
+ -------+---+------ + ------------ +
| RuleID | W | C=b'1 | b'0-pad(opt) |
+ ------ + - + ----- + ------------ +
Figure 1: SCHC Success ACK message format, as defined in RFC8724
In case SCHC fragment losses are found in any of the windows of the
SCHC Packet (C=0), the SCHC Compound ACK MAY be used. The SCHC
Compound ACK message format is shown in Figure 2.
The window numbered 00, if present in the SCHC Compound ACK, MUST be
placed between the Rule ID and the C bit to avoid confusion with
padding bits. If padding is needed for the SCHC Compound ACK,
padding bits MUST be 0 to make subsequent window numbers and bitmaps
distinguishable.
|-SCHC ACK Header--| W = x |...| W = x + i |
+------------------+ ------ +...+ ------- + ------ +------------+
|RuleID|W=b'x|C=b'0| Bitmap |...| W=b'x+i | Bitmap |b'0-pad(opt)|
+------+-----+-----+ ------ +...+ ------- + ------ +------------+
Losses are found in windows W = x,...,x+i
Figure 2: SCHC Compound ACK message format
Each different SCHC LPWAN technology profile MUST specify how the
SCHC Compound ACK is different from the Receiver-Abort message.
The SCHC Compound ACK MAY use a Compressed Bitmap, and bitmap fields
MAY be of variable size.
3.2. SCHC Compound ACK Examples
Figure 3 shows an example transmission of a SCHC Packet in ACK-on-
Error mode using the SCHC Compound ACK. In the example, the SCHC
Packet is fragmented in 14 tiles, with N=3, WINDOW_SIZE=7, M=2 and
two lost SCHC fragments. Only 1 compound SCHC ACK is generated.
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Sender Receiver
|-----W=0, FCN=6 ----->|
|-----W=0, FCN=5 ----->|
|-----W=0, FCN=4 ----->|
|-----W=0, FCN=3 ----->|
|-----W=0, FCN=2 --X-->|
|-----W=0, FCN=1 ----->|
|-----W=0, FCN=0 ----->| Bitmap: 1111011
(no ACK)
|-----W=1, FCN=6 ----->|
|-----W=1, FCN=5 ----->|
|-----W=1, FCN=4 ----->|
|-----W=1, FCN=3 ----->|
|-----W=1, FCN=2 ----->|
|-----W=1, FCN=1 --X-->|
|-- W=1, FCN=7 + RSC ->| Integrity check: failure
|<--- Compound ACK ----| C=0, W=0 - Bitmap:1111011, W=1 - Bitmap:1111101
|-----W=0, FCN=2 ----->|
|-----W=1, FCN=1 ----->| Integrity check: success
|<--- ACK, W=1, C=1 ---| C=0
(End)
Figure 3: SCHC Compound ACK message sequence example
|-- SCHC ACK Header ---|- W=00 --|----- W=01 -----|
+ -------------------- + ------- + ---- + ------- + ------------- +
| RuleID | W=00 | C=0 | 1111011 | W=01 | 1111011 | b'0-pad (opt) |
+ ------ + ------ + -- + ------- + ---- + ------- + ------------- +
On top are denoted the window numbers of the corresponding bitmap.
Losses are found in windows 00 and 01.
Figure 4: SCHC Compound ACK message format example
3.3. SCHC Compound ACK YANG Data Model
The present document also extends the YANG data model defined in
[I-D.ietf-lpwan-schc-yang-data-model] by including a new leaf in the
Ack-on-Error fragmentation mode to describe the option to use the
SCHC Compound ACK, as well as its bitmap format. Figure 5 shows this
definition:
// --- Bitmap format
identity bitmap-format-base-type {
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description "Define how the bitmap is defined in ACK messages.";
}
identity RFC8724-bitmap {
base bitmap-format-base-type;
description "Bitmap as defined in RFC8724.";
}
identity compound-ack-bitmap {
base bitmap-format-base-type;
description "Compound Ack.";
}
typedef bitmap-format-type {
type identityref {
base RCS-algorithm-base-type;
}
description "type used in rules";
}
// -------------
choice mode {
case no-ack;
case ack-always;
case ack-on-error {
leaf tile-size {
type uint8;
description "size in bit of tiles, if not specified or set to 0: tile fills the fragment.";
}
leaf tile-in-All1 {
type schc:all1-data-type;
description "When true, sender and receiver except a tile in All-1 frag";
}
leaf ack-behavior {
type schc:ack-behavior-type;
description "Sender behavior to acknowledge, after All-0, All-1 or when the
LPWAN allows it (Always)";
}
leaf bitmap-format {
type schc:bitmap-format-type,
default schc:RFC8724-bitmap;
description "how the bitmaps are included in the Ack message.";
}
}
description "RFC 8724 defines 3 fragmentation modes";
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Figure 5: SCHC Compound ACK YANG Data Model
4. Security considerations
The current document specifies a message format extension for SCHC.
Hence, the same Security Considerations defined in [RFC8724] apply.
5. Acknowledgements
Carles Gomez has been funded in part by the Spanish Government
through the Jose Castillejo CAS15/00336 grant, the TEC2016-79988-P
grant, and the PID2019-106808RA-I00 grant, and by Secretaria
d'Universitats i Recerca del Departament d'Empresa i Coneixement de
la Generalitat de Catalunya 2017 through grant SGR 376.
Sergio Aguilar has been funded by the ERDF and the Spanish Government
through project TEC2016-79988-P and project PID2019-106808RA-I00,
AEI/FEDER, EU.
Sandra Cespedes has been funded in part by the ANID Chile Project
FONDECYT Regular 1201893 and Basal Project FB0008.
Diego Wistuba has been funded by the ANID Chile Project FONDECYT
Regular 1201893.
The authors would like to thank Rafael Vidal, Julien Boite, Renaud
Marty, and Antonis Platis for their useful comments and
implementation design considerations.
6. Normative References
[I-D.ietf-lpwan-schc-yang-data-model]
Minaburo, A. and L. Toutain, "Data Model for Static
Context Header Compression (SCHC)", draft-ietf-lpwan-schc-
yang-data-model-04 (work in progress), Feb 2021.
[RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
<https://www.rfc-editor.org/info/rfc8376>.
[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.
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Authors' Addresses
Juan Carlos Zuniga
SIGFOX
Montreal QC
Canada
Email: JuanCarlos.Zuniga@sigfox.com
URI: http://www.sigfox.com/
Carles Gomez
Universitat Politecnica de Catalunya
C/Esteve Terradas, 7
08860 Castelldefels
Spain
Email: carlesgo@entel.upc.edu
Sergio Aguilar
Universitat Politecnica de Catalunya
C/Esteve Terradas, 7
08860 Castelldefels
Spain
Email: sergio.aguilar.romero@upc.edu
Laurent Toutain
IMT-Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: Laurent.Toutain@imt-atlantique.fr
Sandra Cespedes
NIC Labs, Universidad de Chile
Av. Almte. Blanco Encalada 1975
Santiago
Chile
Email: scespedes@niclabs.cl
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Diego Wistuba
NIC Labs, Universidad de Chile
Av. Almte. Blanco Encalada 1975
Santiago
Chile
Email: wistuba@niclabs.cl
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