Subject: RE: [rohc] sigcomp issue cabo-15

From: [email-masked]
Date: Fri, 15 Mar 2002 13:57:06 -0600

> For the remaining parameters it would be useful to get some 3GPP input on
> the range of endpoints that will be implementing SigComp. If we can persuade
> everyone to use a 64K UDVM then there's no need to announce 
> the available memory at all!

I don't think setting UDVM_memory_size to 64K is good idea. 64K is 
nothing for a laptop, but can be more than acceptable for mobiles 
today. Note that this is only about the UDVM, we still have all the 
other components in SigComp. 

Also, some application simply does not need 64K. Note that in -05, the 
maximum_state_size is represented as a multiple of UDVM_memroy_size.
That assumes we use what we need. So why trying so hard to remove the 
flexibility? Is the announcement so expensive?

BR,
Zhigang

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From: Carsten Bormann <[email-masked]>
Date: Fri, 15 Mar 2002 21:48:03 +0100 (MET)

> maximum_state_size is represented as a multiple of UDVM_memroy_size.

That sounds like a mistake.  The former scales with the number of your
peers, the latter does not (you never need more than one).  So most
implementations won't restrict UDVM memory size, but will have to
economize with the state they accrete.

> flexibility? Is the announcement so expensive?

Not really.  The expense comes from having to anticipate a multitude
of peers with bizarre combinations of all these values, and
implementing a way to do something useful for each of them.  Having a
small set of UDVM sizes (even if its cardinality is not one) is a
boon.

The likely sizes I've heard so far have been 2K (stateless), 8K
(stateful toaster) and 64K (cadillac).  Maybe 4K (stateless with
complicated algorithm), 16K (more stateful double-slot toaster), 32K
make sense, too, in some cases -- convince me *).

I believe that's it.  Let's not create more choice that only creates
more headaches.

Gruesse, Carsten

*) OK, I'm not a big fan of "proof by lack of imagination", either.
But clearly, UDVM sizes smaller than the usual MTU have very limited
applicability, and having to cope oddball intermediate sizes does not
sound very useful for the poor compressor end.