FWD: Re: Your SAM public comments

Charles Monia monia at am.shrmsg.shr.MTS.dec.com
Thu Apr 27 08:54:29 PDT 1995


The following is a copy of an email exchange between Rodney Van Meter and me
concerning SAM issues. With Rodney's permission, I've forwarded this for
reflector distribution.

Charles Monia

------- Forwarded message

From: "Charles Monia" <"monia%Telephone=237-6757%Location=shr3-2/c5"@am.shrmsg.shr>
App-Message-ID: <3618411226041995/A37166/DRAWRS/1194D3291100>
Precedence: Special-Delivery
To: "rdv at isi.edu"@umc.wrlmts.wrl
Subject: Re: Your SAM public comments

Hi Rod:

You wrote:

>Fine. Looks good. If it's not too late, I have three additional
>overall comments:

>* SAM defines a Target Identifier to be 64 bits. However, if we wish
>to run SCSI over IP (leaving aside for the moment the debate over
>whether this is a good idea, it _is_ covered in the GPP draft), 64
>bits will be an inadequate address when IPv6 (currently in the design
>phase) is deployed. IPv6 addresses are 128 bits. I suppose it's too
>late to change this, but it should be noted.

When the address in the native protocol is larget than the SAM address field, I
would assumed that some lower layer mapping function translates one address to
the other.

>* Authentication is not mentioned anywhere. How are devices to know
>that they are receiving commands from initiators that they _should_
>listen to? Over SPI, not a problem, since connection via a physical
>SCSI bus implies ownership of the device, but over a network, it's

Authentication falls into the class of problems that the LLP must deal with.
It's somewhat analogous to the Fibre Channel login function. 

>* Again in the case of networked SCSI (FC, SSA, GPP, what have you)
>resource discovery is also a significant problem. Over SPI,
>traditionally the host attempts to select all devices to establish
>what devices are present, but over other media this may not be

Again, in my opnion, this is an LLP problem.

>These last two issues are so big that I don't believe that they
>haven't been addressed (in fact, I vaguely recall some discussion on
>the resource discovery problem a long time ago); forgive me if I'm
>beating a dead horse.

The overarching issue here is that there are a lot of implicit LLP functions
not covered in SAM. In my opinion, while such a discussion would serve as a
useful guide to implementors and protocol designers, none of these really
effect the essential characteristics of the  model. I would therefore recommend
deferring the inclusion of such a discussion until SAM -2.

BTW: With your permission, I would like to forward this reply to the SCSI


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