RE: FCIP: Multiple connections

[Venkat Rangan <venkat@rhapsodynetworks.com>]

Sudhir,

For a given FC Flow (indicated by a SID, DID pair of the FC frames),
both forward and reverse directions are mapped to the same connection.
This ensures that:

1. Any TCP congestion related rate adjustment on one direction impacts the
   other direction equally. Although even a single TCP connection is subject
to
   variations introduced due to assymmetric routing, we do not want to
introduce
   more assymmetry by sending forward direction frames of one flow on one
   connection and the reverse on a different connection.

2. By allowing forward and reverse traffic flow on different connections,
   the protocol may exclude implementation of a class of products that
   rely on seeing the forward and reverse traffic on the same NIC where
   the connection is processed. If the connections end up on different
   NICs or ports and the processing is off-loaded to them, then you have
   the need to either exchange state or forward traffic to a common point.

3. Error recovery in the case of TCP connection failure may cause one of the
   two directions to be functional while the other is not. If both
directions
   are mapped to the same connection, such recovery is more easily mapped to
   a link/ISL failure.

If the protocol allows forward and reverse directions of a flow to be mapped
on
different connections, I would like to suggest that there is an option that
allows a pair of FCIP Device Endpoints to negotiate that both directions
must be
mapped on to the same connection. Implementing this "flow allegiance" is
not a significant incremental effort since in order to map all frames of a
single direction of a flow on to a particular connection, most of the
work is already done anyway.

Regards,

Venkat Rangan
Rhapsody Networks Inc.
http://www.rhapsodynetworks.com



-----Original Message-----
From: Sudhir Srinivasan [mailto:SudhirS@trebia.com]
Sent: Monday, May 14, 2001 1:53 PM
To: 'ips@ece.cmu.edu'
Cc: Sudhir Srinivasan
Subject: FCIP: Multiple connections



In Section 5.5, what is the reason to include rule (2)?
Is it not sufficient that frames in each direction be delivered
in order? Physical analogy is to have two half-duplex lines
instead of a full-duplex line. Vendor should have the choice
to go either way.

-Sudhir

Trebia Networks, Inc.                Sudhir.Srinivasan@trebia.com
978-929-0830 x139                   www.trebia.com