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    Re: a vote for asymmetric connections in a session



    
    I do not know how reasonable Costa's configuration is,in the real world,
    but he has brought up a point that, I think, might be important to address.
    If his example is reasonable, then it would suggest that we NEED to enforce
    the requirement of Two connections per Session in the Asymmetric case.
    What do you all think about this?
    
    
    .
    .
    .
    John L. Hufferd
    
    
    
    csapuntz@cisco.com@ece.cmu.edu on 09/08/2000 01:01:04 PM
    
    Sent by:  owner-ips@ece.cmu.edu
    
    
    To:   ips@ece.cmu.edu
    cc:   csapuntz@cisco.com
    Subject:  Re: a vote for asymmetric connections in a session
    
    
    
    
    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
    
    
    
    
    


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