Subject: [lp-wan] Ticket #29 Rephrase Bitmap Encoding section

From: ana minaburo <[email-masked]>
Date: Tue, 19 Jun 2018 15:41:49 +0200

Hello,

I'm not able to manage this ticket, here you have the solution we gave to
it, this will be published in the last version of the draft-14. And this
ticket may be closed if you agree with the changes

Ana

Section 7.4.3.1 (Bitmap Encoding) of version 13 states:

   In order to reduce the resulting frame size, the encoded Bitmap is
   shortened by applying the following algorithm: all the right-most
   contiguous bytes in the encoded Bitmap that have all their bits set
   to 1 MUST NOT be transmitted.

This phrasing gives the reader the feeling that the bitmap can be encoded
as a standalone bit string. It seems that this is not the case: the bytes
with bits set to 1 should be removed from the bit string resulting from the
concatenation of the ACK header and of the bitmap.

In Section 7.4.3.1 now it says:

The SCHC ACK that is transmitted is truncated by applying the following
algorithm: the longest contiguous sequence of bits that starts at an L2
Word boundary of the SCHC ACK, where the bits of that sequence are all set
to 1, are all part of the Bitmap and finish exactly at the end of the
Bitmap, if one such sequence exists, MUST NOT be transmitted. Because the
SCHC Fragment sender knows the actual Bitmap size, it can reconstruct the
original Bitmap from the shortened bitmap.