Subject: [lp-wan] Ticket #13: Terminology Sublayers

From: Ana Minaburo <[email-masked]>
Date: Mon, 26 Feb 2018 21:59:01 +0100

One topic that appears to be important (based on feedback from the
reviewers) is to better clarify the different stages and the order of the
operations defined by SCHC (for a sender, first, it is compression, then
fragmentation, if needed). This would be basically introductory material.

Also, there are terminology issues (e.g. how do we call the data unit after
compression?).

So here are some proposals.

1.- We may define that SCHC comprises two sublayers (i.e. compression
sublayer and fragmentation sublayer, as shown in the figure. Would there
be any (hidden) issues involved by adding this to the document?

+----------------+ \
| Compression | \
+----------------+ > SCHC
| Fragmentation | /
+----------------+ /

2.- Two terms are proposed below:

   - “SCHC packet”: a packet (e.g. an IPv6 packet) whose header has been
   compressed per the header compression mechanism defined in this document.
   If the header compression process is unable to actually compress the packet
   header, the packet with the uncompressed header is still called an SCHC
   packet (in this case, a Rule ID is used to indicate that the packet header
   has not been compressed).

   - “SCHC fragment”: a data unit that carries a subset of the bytes of an
   SCHC packet. Fragmentation is needed when the size of an SCHC packet
   exceeds the available payload size of the data unit of the layer underlying
   SCHC.

3.- Would the following diagram (for a sender) provide further clarity
regarding what SCHC defines?

                                   IPv6 packet

                                    |

            /                       V

           |                 +--------------+

           |                 | compression |

           |                 +--------------+

           |                           |

SCHC <                    SCHC packet

            |                          |

            |                          V

            |           +----------------+

            |            | fragmentation | (if needed)

            |            +----------------+

            |                        |

             \                       V

                       SCHC fragment (if needed)

We may include content such as the one above in the next revision of SCHC,
so please do not hesitate to provide your feedback.