thank you very much for your previous response, it has let me to have a
few more questions.
On Tue, 29 Feb 2000, Aman Singla wrote:
> Chris,
>
> The data hierarchy associated with Long Message transfers in STP
> is transfer->block->STU; a transfer consists of one or many blocks
> and a block consists of one or many STUs.
>
> A SCSI transaction maps to a STP transfer. The STP stack takes care
> of retransmissions for missed/dropped blocks based on timeouts (or
> any other mechanism like missed ordering of blocks etc.).
what part of the standard defines this error recovery? i was looking at
10.3 of the ST standard which says the timing out of this operation is the
responability of the ULP, which in this case is SCSI. then the ST
standard says that error recovery happens at the level of the transaction.
> Further
> the NIC h/w or firmware, if capable, may take care of STU retransmission
> for dropped STUs. For example on GbE a frame would correspond to a
> STU, and lets say a block corresponds to 64 STUs; now, if a frame is
> dropped/lost, the media/physical layer/NIC, if capable, could have
> the remote NIC resend the STU - generally resulting in the protocol
> stack on the host always getting all the blocks;
in the context of gig ethernet what defines this potential retransmision
done by the nic itself? is this something defined by STP? are you
talking about some other protocol running on gig ethernet sitting below
STP doing this retransmision?
> but if the NIC can't
> support STU retransmission, the protocol stack will observe a dropped
> block (a block isn't deemed recd. until all STUs are recd) and would
> request retransmission of the block by resending a CTS. The entire
> transfer will (generally speaking) never have to be redone.
>
do you envision the transmission of a CTS being initiated by the host or
by the nic itself? how is it anticipated that SCSI transactions would be
broken up into blocks. do you picture a SCSI transaction basically to
consist of a block or two or something closer to one block = one frame?
i would think the CTS would have to be initiated by the host itself, not
the nic. if this is the case then it would probably be prefereable to
minimize the number of blocks per transaction in order to minimize the
host/nic interaction. this would mean that a resent CTS corresponds to
the retransmission of a large number of individual frames.
chris
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