RE: FCIP/iFCP : Guarantee In-Order delivery for FC N/NL_ports

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

> A point of clarification on FCIP Ordering and multiple TCP connections:
>
> The FCIP draft does not preclude multiple TCP connections.
> Somesh is right in pointing that we could result in out-of-order if we
> have more than one TCP connections between same two FCIP Gateways.

Even with just one TCP connection, when frames travel through the "IP
cloud", don't we risk out-of-order and duplicated frames at the other end?
For multiple connections, it is a sure thing.

> However, an FCIP gateway (say FCIP-A) can carry on simultaneous TCP
> connections say with FCIP-B and FCIP-C gateways without the
> danger of the out-of-order issue.

FCIP-A can take responsibility for in-order delivery of outgoing frames.
But, there is no guarantee for in-order and non-duplicated reception on
either FCIP-B or FCIP-C.

> Out-of-order is therotically possible even with FC Switch fabrics
> running a dynamic routing protocol such as FSPF, although in practice
> FC switches vendors seldom run into this condition.

I am not an expert in implementing switches.  But, in talking to both
Finisar and Brocade, I was told that the switches do see this problem and
ensure in-order delivery by buffering the frames.

> In summary, multiple TCP connections is not precluded but a solution is
> specified in the current FCIP draft. The authors of the FCIP
> draft will take an action to clarify this in the next version.
>
> Murali Rajagopal
> LightSand Communication

I always thought that FCIP can count on an E-port for frame buffering and
ordered delivery.  If not, then, FCIP even using TCP must address the same
problem of moving large amount of data on a 10Gb/100ms network like that of
iFCP and iSCSI.  One just can not assume that the TCP without help of RDMA
header and frame marker will run fast on a 10Gb/100ms network.  I thought
FCIP by leverage the effort in the fibre channel switches gets away with the
out-of-order reception problem.  But, I am not a switch expert.  Just my 2
cents' worth.

Y.P. Cheng, ConnectCom Solutions.