Subject: Re: [Tsvwg] Comments about prsctp-00

From: Qiaobing Xie <[email-masked]>
Date: Fri, 31 May 2002 16:29:27 -0500

Hi, Ivan,

...snip...
> 
> > Yes, agree with Randy here. To report gaps or a full list of "dropped"
> > TSNs in FORWARD TSN chunk will not be that useful because the gaps from
> > sender's view is not always the same as that from the receiver's view
> > and what really matters is what the receiver sees (this is
> > fundamentally  different from a SACK where what is reported in a SACK is the
> > receiver's view).
> >
> > For example, when the sender reports a list of "dropped" TNSs, some of
> > the "dropped" TSNs might have already been correctly received
> > and passed on to the UPL. So whether the receiver will find the additional gap
> > information useful is unclear.
> 
>         Well, you are just telling the receiver which TSNs will not retransmitted anymore... If you already got them, it does not matter. If you are still missing any of those dropped TSNs, then you should discard the user messages with at least one TSN dropped...
> 
>         But ignoring those gaps would not hurt you either (you would be exactly as we are now)...

This is exactly my point: reporting gaps is just an optimization that
*may* help the receiver *occassionally*. But the cost of doing that is
increased design and implementation complexity on both ends. In my
opinion this is hardly justifiable. Adding the following negotiations
makes the proposition even worse.

> 
>         I know you won't like this, but you could even state if you support gaps (either at the sender or receiver side) inside the Forward-TSN-Supported parameter... Thus:
> 
>         - If the INIT sender supports everything, you may send gaps if you support them at the sender side, and state in your INIT ACK if you want the INIT sender to send you gaps.
> 
>         - If the INIT sender supports gaps at the sender side, you may state in your INIT ACK if you want it to send you those gaps. But you won't send gaps as it does not support them.
> 
>         - If the INIT sender supports gaps at the receiver side, the INIT ACK sender may send them...
> 
>         It would be another level of negotiation... :-/

regards,
-Qiaobing

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