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

["Douglas Otis" <dotis@sanlight.net>]

Gaby,

> Currently, FCIP doesn't map TCP channels to FC streams.  By
> stream, I mean,
> related FCP commands and data that may require 'in order delivery' by the
> SCSI application.  Mapping TCP channels to FC addresses will
> guarantee that
> a FC-stream is fully contained within a TCP channel.

Should the application be using multiple processors with multiple FC
connections, then what you see as isolated is perhaps not.  An advantage of
using multiple TCP connections is lost if all traffic to a device is
restricted to a connection.  At what point in time would the gateway change
to a different connection if there was a problem.  All this activity is time
related and to sift through the mess, a time-stamp still seems essential.

> FCIP leaves this
> mapping to the Gateway implementation.  For example, assigning a TCP
> connection per remote D_ID address or group of address is relatively easy
> for the H/W to implement.  If we don't want to use time-stamp for
> ordering,
> the only implementation limit will be to not put a FC stream on more than
> one TCP channel, to avoid out of order delivery.

This conclusion assumes no relationship between other sources and no
fail-over will be made and all traffic will be held until a missing frame is
recovered.  A TCP interruption may recover within 20 seconds, but with
respect to FC however, this is forever.  If there are multiple working
connections, and one is briefly lost, how does one allow a fail-over?  TCP
may attempt delivery for a very long period.  Is it safe to assume no timing
relationship between FC sources?  As a TCP interruption may occur for
periods longer than the R_A_TOV, is there a violation of the FC fabric to
then release frames held for say 20 seconds?

Doug

> Gaby
>
>
> -----Original Message-----
> From: Douglas Otis [mailto:dotis@sanlight.net]
> Sent: Thursday, January 25, 2001 11:11 AM
> To: Black_David@emc.com; ips@ece.cmu.edu
> Subject: RE: FCIP/iFCP : Guarantee In-Order delivery for FC N/NL_ports
>
>
> David,
>
> For what it's worth, I am not making such fine distinctions.  I was
> attempting to discuss a reason for including a time-stamp should such
> placement be onto FC media.  (Looking to the day when there is a means to
> handle out of sequence frames.)
>
> Doug
>