Subject: [lp-wan] Ticket #2: Rule ID default size (closed)

From: Ana Minaburo <[email-masked]>
Date: Tue, 3 Apr 2018 10:58:16 +0200

The draft defines a Rule ID to identify the context that will be used for
the compression and/or fragmentation, the size in bits of this field is not
defined because the size is based on many parameters.
First, if SCHC is used only for compression, the Rule ID size is less
constrained and can be up to 1 byte (8 bits). Second, if we use
fragmentation the Rule ID default value may be 3 bits but it depends on the
SF so it could be larger. Third, we want to have the less possible padding
bits so we need to respect the byte boundary. So to do this, the Rule ID
byte boundary is shared with the Rule ID, FCN, DTag and W bit which may be
a multiple of 8 bits long.
comment:1 <https://trac.ietf.org/trac/lpwan/ticket/2#comment:1>Changed 2
months ago
<https://trac.ietf.org/trac/lpwan/timeline?from=2018-01-26T01%3A47%3A43-08%3A00&precision=second>
 by ana@…

   - *Component* changed from *coap-static-context-hc* to
   *ipv6-static-context-hc*

comment:2 <https://trac.ietf.org/trac/lpwan/ticket/2#comment:2>Changed 5
weeks ago
<https://trac.ietf.org/trac/lpwan/timeline?from=2018-02-26T10%3A25%3A59-08%3A00&precision=second>
 by ana@…

default Rule ID size? size depends on the technology.
Pascal: say at the begining that other documents will specify more specific
behaviors.
Pascal and Dominique: is Rule ID constrained by byte boundaries in any way?
See Figure 16. Clearly state if it is or it isn't, early in the document.
Edgar: depends on whether fragmentation is mandatory in all implementations.
Carles: Figure 16 and 17 are example.
Pascal: Figure 10.
JCZ: clarify that Rule ID size is not constrained by alignment.
Pascal: technology document will describe if Rule ID is constrained by
alignment for a particular technology. Generic SCHC does not place such a
constraint.
comment:3 <https://trac.ietf.org/trac/lpwan/ticket/2#comment:3>Changed 5
weeks ago
<https://trac.ietf.org/trac/lpwan/timeline?from=2018-02-26T13%3A30%3A43-08%3A00&precision=second>
 by ana@…

   - *Resolution* set to *fixed*
   - *Status* changed from *new* to *closed*

Ana: One of the comments coming over and over again: how to manage the
ruleID.
Rechartering: explain RuleID: how it will be managed, done... Pascal: HOWTO
document?
comment:4 <https://trac.ietf.org/trac/lpwan/ticket/2#comment:4>Changed 0
seconds ago
<https://trac.ietf.org/trac/lpwan/timeline?from=2018-04-03T01%3A42%3A43-07%3A00&precision=second>
 by ana@…

To fixed this question, a new section has been created to better explain
the case where Rule ID is used for.
This section is the following:

   1. Rule ID

Rule ID are identifiers used to select either the correct context to be
used for Compression/Decompression
<https://trac.ietf.org/trac/lpwan/wiki/Compression/Decompression>
functionalities
or for SCHC Fragmentation or after trying to do SCHC C/D and SCHC
fragmentation the packet is sent as is. The size of the Rule ID is not
specified
in this document, as it is implementation-specific and can vary according
to the LPWAN technology and the number of Rules, among others.

The Rule IDs identifiers are:

o In the SCHC C/D context, the Rule used to keep the Field Description of
the header packet.

o In SCHC Fragmentation to identify the specific modes and settings. In
bidirectional SCHC fragmentation, at least two Rules ID are needed.

o And at least one Rule ID MAY be reserved to the case where no SCHC C/D
nor SCHC fragmentation were possible.

Changed 1 second ago
<https://trac.ietf.org/trac/lpwan/timeline?from=2018-04-03T01%3A55%3A56-07%3A00&precision=second>
 by ana@…

In SCHC compression/decompression section, we added:

6.2. Rule ID for SCHC C/D

Rule IDs are sent by the compression function in one side and are received
for the decompression function in the other side. In SCHC
C/D, the Rule IDs are specific to a Dev. Hence, multiple Dev instances MAY
use the same Rule ID to define different header compression contexts. To
identify the correct Rule ID, the SCHC C/D needs to correlate the Rule ID
with the Dev identifier to find the appropriate Rule to be applied.

In the section 7.2 fragmentation tools we have added:
o Rule ID. The Rule ID is present in the SCHC fragment header and in the
ACK header format.

The Rule ID in an SCHC fragment header is used to identify that an SCHC
fragment is being carried, which
SCHC fragmentation reliability mode is used and which window size is used.
The Rule ID in the SCHC fragmentation header also allows interleaving
non-fragmented packets and
SCHC fragments that carry other SCHC packets. The Rule ID in an ACK
identifies the message as an ACK.