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

[Wayland Jeong <wayland@troikanetworks.com>]

I can't speak for the authors of FCIP, but I will venture to guess, the
comment that was made regarding FCIP's ability to open as many connections
as desired between FCIP devices, was only meant to imply that an
implementation could solve the ordering problem. 

As you note, an implementation which identified source/destination flows
could bind these flows to a single TCP connection and adhere to the
sequential delivery requirement of FC fabrics. Similarly, an implementation
that allowed multiple TCP connections per src/dest flows could ensure
ordering by inserting sequence numbers in the FCIP encapsulation and
re-ordering at the destination bridge. In fact, at the interim WG meeting in
Orlando, Brocade had a proposal for a new FCIP encapsulation that seemed to
include such a sequence number (albeit for a UDP implementation). Now, I'm
not saying this would be fun to implement, but the possibility exists.

With regards to iFCP, it does ensure ordered delivery. It binds a FC login
session to a single TCP connection.

My 2 cents anyway.

-----Original Message-----
From: Santosh Rao [mailto:santoshr@cup.hp.com]
Sent: Thursday, January 18, 2001 6:19 PM
To: Sriram Rupanagunta
Cc: ips@ece.cmu.edu
Subject: Re: FCIP/iFCP : Guarantee In-Order delivery for FC N/NL_ports


Sriram Rupanagunta wrote:

> > > Can this assurance be made even while using multiple TCP
> > > connections b/n
> > > edge switch/routers ?
> > This question is N/A for FCIP, since only a single connection
> > is specified between FCIP gateways.  In iFCP, a single TCP connection
>
> Sometime back, FCIP folks mentioned that there is nothing in the
> FCIP spec that limits the number of connections to one. My
> understanding is FCIP leaves this to implementations, whether
> to use one connection or multiple.

The above is EXACTLY the reason I have raised this question. I hear
conflicting statements being made on this issue. I don't see how FCIP can
use multiple TCP connections per (S_ID, D_ID) pair and guarantee in-order
delivery without implementing buffering and re-ordering on the FC-IP
switch.

Both FCIP and iFCP MUST guarantee in-order delivery since all FC end ports
(N/NL_Ports) depend on this feature and FC-FLA Table 3 mandates this.

Regards,
Santosh


>
> Can someone clarify this once for all on this list please ?
>
> If there is no limit on the number of connections in FCIP,
> Santosh's question is valid. In that case, is it fair to
> say that FCIP does not guarentee orderly delivery ?
>
> - Sriram