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

From: [email-masked]
Date: Thu, 18 Apr 2002 16:03:02 -0500

Hi,

Following is my understanding of the default minimum values 
of SigComp parameters according to section 3.3. Please shout
if they are incorrect.

decompression_memory_size: 2048 octets
state_memory_size: 0 octets
cycles_per_bit: 16
SigComp_version: 0
locally available state: none

Question: why do we set state_memory_size to 0? Why not
2048, which is not too large even for a low end terminal
but still large enough to be meaningfully used?

BR,
Zhigang

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From: [email-masked] (Dr. Carsten Bormann)
Date: 19 Apr 2002 00:33:01 +0200

> but still large enough to be meaningfully used?

Arguments for setting it to 0:

-- Remember that state_memory_size is per compartment/session.
   There may be many implementations that don't have a known upper
   bound on the number of sessions/compartments they have to support.
   If these are also memory-starved, they are better off with a
   default of 0 -- whenever memory permits, they can always announce a
   larger value (after allocating some space out of their limited pool
   to the specific compartment/session).

-- Some implementations may simply not want to implement state at all.
   With a default of 2048, they would have to accept at least as much.
   (Of course, this smacks like an "option", so I'm not sure I want to
   follow this reasoning too much -- on the other hand, a host may
   simply not *have* any stable storage that would survive long enough.)

Arguments for setting it to a small number like 2048:

-- The first message in an exchange can already download state; this
   allows to improve compression significantly after the first
   roundtrip.  (Otherwise, the improvement only comes after the second
   roundtrip.)  This is essentially the "avoid negotiation" argument.

A "default" different from zero could be an application specific
"default" -- so, even if the general-Internet sigcomp sets the
"default default" to zero, 3GPP could always mandate a different
default, or derive the actual state_memory_size value from any 3GPP
specific discovery process.

Gruesse, Carsten