Re: Connection Startup

On Friday, October 3, 2003, at 04:48 PM, Jim Pinkerton wrote:

> The reason I bring this up so strongly is for *new* protocols, which 
> are
> designed to run on top of IWARP, and don't care about compatiblity with
> InfiniBand, I see no need for this capability. It's far more optimal to
> embed their config data in their existing configuration handshakes, and
> not add a new round-trip handshake.

That is a valid concern when adding an RDMA mode to an *existing*
protocol, such as iSCSI. And the number of *existing* protocols
that are LLP neutral is, well, pretty much zero.

Use of an RDMA negotiation message *after* other negotiations would
indeed be a wasteful additional round-trip. The intent is to support
applications that only need minimal simple parameters exchanges in
order to establish the session. When this topic has been discussed
in the DAT Collaborative, there has been little interest in engaging
in more complex session setup.

The only thing that *must* be negotiated before enabling RDMA is
the essential RDMA configuration (identifying any existing session,
RDMA read credits, maximum untagged message size, etc.) to the
extent that it is not pre-dictated as constants for that ULP.

The general conclusion I have seen application developers who
are working on an RDMA specific applications is that complex
detailed negotiations can be done *after* the connection is
established.

Now you can argue that they were merely thinking that way
because that is the only model that InfiniBand supported.
Or perhaps, that is the only model that InfiniBand
supported because it is a fine model that meets the
needs of ULP designers who are assuming RDMA capability.