ForCES TLV size

This issue was brought up by Fenggen, and was discussed by Joel in the
last meeting. Joel and I had a discussion and we came up with the
proposal below. 
Fenggen and the rest of the ForCES community please take a look and
comment. I feel this is the last issue we have before we close on the
protocol; so if we can reach a quick compromise, that would be good for
progress.

cheers,
jamal


Problem Statement:
-----------------
The TLV structure we have today for transporting data defines a 
16 bit length which makes TLVs larger than 64KB not feasible.
Although  the protocol goes at great length to ensure one can transport
(sub)objects at very granular level by using paths, and therefore
eliminating this problem, it is feasible there may be a ForCES object
that is unforseen that will not fit in 64KB. 


Proposed solution:
-----------------
We add to the path-data TLV a new flag which says "this is multipart".
The presence of the multipart flag changes the encoding of the
path-data TLV to include two new 32 bit fields:
a) a 32 bit value which carries the total content length
b) A 32 bit value which carries the offset into the total
length.

The general path-data layout with these two new fields then looks as
follows:
 T = Path-data
     |
     + -- flags (flag bit "this is multipart" is turned on)
     + -- IDCount
     + -- IDs
     + -- TotalLength
     + -- TotalOffset
     + -- SPARSE/FULLDATA TLV
          ....
	  .....

The contents of DATA TLV get concatenated to reconstruct the original
object.

Example:
-------
For the sake of explaining the example, consider that we want to use
the methodology described above with a 15 byte object and split it
into 3 5-byte messages. The message flow would be:

message 1:
 ..
 ..
 T = Path-data
     |
     + -- flags (flag bit "this is multipart" is turned on)
     + -- IDCount = ...
     + -- IDs = ...
     + -- TotalLength = 15
     + -- TotalOffset = 0
     + -- SPARSE/FULLDATA TLV
          5 byte content ..

message 2:
 ..
 ..
 T = Path-data
     |
     + -- flags (flag bit "this is multipart" is turned on)
     + -- IDCount = ...
     + -- IDs = ...
     + -- TotalLength = 15
     + -- TotalOffset = 5
     + -- SPARSE/FULLDATA TLV
          5 byte content ..

message 3:
 ..
 ..
 T = Path-data
     |
     + -- flags (flag bit "this is multipart" is turned on)
     + -- IDCount = ...
     + -- IDs = ...
     + -- TotalLength = 15
     + -- TotalOffset = 10
     + -- SPARSE/FULLDATA TLV
          5 byte content ..