Re: a vote for asymmetric connections in a session

[csapuntz@cisco.com]

If I recall correctly, the windowing mechanism was put in to avoid
a deadlock condition while using multiple control connections. 
I believe the logic went as follow:

Assumption: You're not allowed to drop commands arriving in on any
connection

Because the TCP connections work at different rates, commands
may not arrive in order. Let's say you have four connections and
a command queue depth of 3. Commands #2,#3, and #4 arrive before command #1,
filling the queue. However, the queue cannot be drained
until command #1 arrives. So, deadlock.


Solution: Allow commands to be dropped

In the example above, we'd probably drop command #4 and replace it 
with command #1.

Note that using a single TCP connection for control/data is not
sufficient to solve the problem.  Imagine the case that the queue is
depth 3 and the host issues four WRITES commands in quick order.

The device stops reading the TCP connection after three commands.
Unfortunately, none of those three writes can complete until 
data is read from that connection! So, deadlock again.

CIFS, NFS, and HTTP don't have this problem because they immediately
send data after their WRITE commands.

-Costa