RE: iSCSI: RE: Framing Discussion

["Y P Cheng" <ycheng@advansys.com>]

> With respect to networks, there is more than just SCSI.  Yes, we
> can create a network interface that solves immediate needs of
> SCSI, but at the potential expense of adding a unique solution
> per each application demanding content directed services.
> IPS advocates are not allowed to discuss impact of this
> interface such as if this connection is shared with IPs or ports or
> how an application is indicated.  Once vendor specific details of SCSI are
> solved, this same connection may also then be called upon to create
another
> unique interface for VI or IPC.  Are application/vendor unique solutions
> beneficial if there is only a resemblance to the original protocol where
> different schemes employed?  As these application standards
> change, be sure to include Flash memory for your embedded processor.
> Is this how WinModem was created where application and hardware
> interface is blurred by vendor unique solutions?
>
> Doug

Doug,

What I said that "You can send anything you want, as long as rules are
followed" doesn't meant it is an incompatible solution requiring special
API.  An iSCSI adapter is both a NIC and a SCSI adapter.  As a NIC, it is
capable of RDMA to support VI and Winsock Direct.  As an iSCSI adapter it
adhere strictly to SCSI API and the IPS specifications syntactically and
semantically.  It has device drivers for different OS's providing SCSI
services with the exception of making TCP connections for logins.  However,
having said all these, each iSCSI adapter still has a unique implementation
including the ways it sends and resends TCP frames and supports multiple TCP
connections concurrently.  Being stream-oriented, TCP does give us a lot of
freedom how to segment the byte stream and how to send ACKs.

There are a lot of issues with traditional TCP implementations to support
networks with long latency delays and high probability of dropping frames.
But, if someone puts a new implementation inside an adapter, he has the
freedom to add new options like TCPRDMA and MSGBNDRY, even the SMTP protocol
to overcome the problems.  Not all implementations are created equal.  Not
everyone supports new options.  The magic word is interoperability.  The
secret is how two adapters both supporting new options talk to each other.
I thought the TCP option negotiation permits that already.  What I expect
from the IPS effort is to tell me how these new options should look like.

Yes, almost all adapters today have a flashable ROM that supports field
upgrades with new implementations for new TCP options approved by IPS WG.

Y.P.