Subject: [rohc] Query on Feedback mechanism

From: Chan Kwang Mien <[email-masked]>
Date: Tue, 13 Aug 2002 17:36:57 +0800

hi,

i am trying to implement the Feedback mechanism described in SigComp 
internet draft ver 7.
can anyone tell me what is the difference between the returned feedback 
item stored in
Figure 3 and Figure 13 ?

if i understand correctly, the returned feedback item in Figure 3 is part 
of the SigComp message.
and the returned feedback in Figure 13 is piggybacked onto the SigComp 
message. But what is
the rationale of having the returned feedback located at 2 different location ?

can someone help me ?

Thanks,
kwang mien

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From: "Price, Richard" <[email-masked]>
Date: Tue, 13 Aug 2002 16:46:55 +0100

> item stored in Figure 3 and Figure 13 ?
> 

Hi,

Figure 3 specifies some fields that must be transmitted unmodified as
part of the SigComp message.

> message.

Figure 13 describes an area of the UDVM memory where some returned feedback
fields can be found. How these fields are transmitted in the SigComp message
is up to the compressor. It will usually be more efficient to transmit the
fields compressed, and then to decompress them by running a suitable piece
of UDVM bytecode, than to transmit them unmodified in every SigComp message.

> But what is the rationale of having the returned feedback located at 2 
> different location ?

The difference between the fields in Figure 3 and the fields in Figure 13
is that the fields in Figure 13 are compressible. So, to reduce the size of
the SigComp message we transmit a compressed version of the fields and then
decompress them at the UDVM (by running a suitable piece of UDVM bytecode).

In contrast the fields in Figure 3 are likely to be uncompressible (since
the returned feedback item should already have been compressed by the
remote endpoint). Compressing these fields twice would be pointless, so
instead we just transmit them unmodified in the SigComp message.

Regards,

Richard