Subject: RE: [rohc] Sigcomp Nack Draft -01

From: Adam Roach <[email-masked]>
Date: Wed, 10 Dec 2003 15:45:36 -0600

Surtees, Abigail [mailto:[email-masked]] wrote:

> Here are some comments on the Nack draft.
> 
> Section 2.1
> 
> Last sentence:
> The change in  behavior for a reliable transport no longer 
> involves re-transmitting the message so why would you need to 
> be able to retrieve a plain-text version of the message?

This was editorial oversight. I've removed the final sentence
of this section.

> Section 2.3.2
> 
> If the underlying TCP connection has caused SigComp to fail, 
> can it be trusted to transmit a NACK?

In my experience, most SigComp failures are caused by failures
that are independent of the underlying transport; for example,
implementations erroneously referring to previously discarded
state.

Of course, if the transport fails altogether, then the NACK
probably won't make it through either; however, transport
failures are not the focus of this mechanism.

> Section 2.4
> 
> This mechanism is a good idea.  It gives a definitive way for 
> a compressor to find out if the other end supports the nack scheme.
> 
> The probe idea is also possible but does have the limitations 
> mentioned so I don't think is worth having to the draft.

The probing was included as an aside to spur discussion, since I thought
that grabbing memory location 11 for advertising extensions might be
controversial.

> Appendix B: Changes
> 
> Moving NACK parameters:
> Isn't it impossible to have standalone feedback messages 
> (other than NACKs) because there is no way to determine for 
> which compartment the ACK is unless there is a message to go with it?
> I don't think there is any problem with the message format itself.

This particular change was made at Richard's suggestion...

If I recall correctly, standalone feedback is possible over
secured links. Presumably, compartment correlation is done on a
per-connection basis, but my memory is a bit rusty on this at
the moment.

/a

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