Subject: [rohc] SigComp-extended

From: "Hans Hannu (EPL)" <[email-masked]>
Date: Mon, 29 Apr 2002 15:47:02 +0200

Hi,

FYI, the authors are working on updating the SigComp-extended draft according to what was said at the Minneapolis meeting.

The changes are made to match the current working SigComp document, e.g.
the changes to the feedback mechanism of SigComp has affected the 
acknowledgement scheme in SigComp-extended as follows: (The ones of you 
who have taken a look at the slides from Minneapolis may recognize Figure
 3 below, I think I showed that one 4 times in the presentation ;-))

"5.1.1.1. Remote compressor initiated acknowledgements

   This is the case when e.g. compressor 1 has uploaded UDVM code to
   decompressor 2. The UDVM code will use the requested and returned
   feedback fields in the announcement information to obtain knowledge
   about established states at endpoint 2.

   Consider Figure 3. An event flow for successful use of remote
   compressor initiated acknowledgements can be as follows:

   (1): Compressor 1 saves e.g. state(A).
   (2): The UDVM code to initiate a state save for state(A) is either
        carried in the compressed message, or already in place at
        decompressor 2.
   (3): As compressor 1 is the initiator of this acknowledgement it can
        use an arbitrary identifier to be returned to indicate that
        state(A) has been established. The identifier needs to consist
        of enough bits to avoid acknowledgement of wrong state. To avoid
        padding of the feedback items and for simplicity a minimum of 1
        octet should be used for the identifier.
        The identifier is placed at the location of the
        requested_feedback_item [SigComp]. The END-MESSAGE instruction
        is used to indicate the location of the requested_feedback_item
        to the state handler.
   (4): The requested feedback data is now called returned feedback data
        as it is placed into the SigComp message at compressor 2.
   (5): The returned feedback item are carried in the SigComp message
        according to Figure 4: see Section 6.1 and [SIGCOMP].
   (6): The returned feedback item are handled according to: Section 7
        of [SIGCOMP]

      +--------------+           (2)              +--------------+
      | Compressor 1 |--------------------------->|Decompressor 2|
      +------^-------+                            +-------^------+
             |    (1)                              (3)    |
         +---v---+                                    +---v---+
         |State  |                                    |State  |
         |handler|                                    |handler|
         +---^---+                                    +---^---+
             |    (6)                              (4)    |
      +------v-------+           (5)              +-------v------+
      |Decompressor 1|<---------------------------| Compressor 2 |
      +--------------+                            +--------------+
                    Figure 3. Simplified SigComp endpoints"

We are currently doing some clarifications to the shared compression 
section, such as specifying the parameters of the shared state. As soon 
as SigComp-06 ready for submission, also SigComp-Extended-03 will be 
submitted.

BR
/Hans H

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