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    Re: iFCP as an IP Storage Work Item



    Sorry,
    
    Fibre Channel, does not guarantee delivery.  The main reason is that FC does
    not have transport layer as robust as TCP.  A FC ACK simply informs that the
    frame was delivered.  FC does not have any reliable mechanism to handle
    retransmission when an ACK is not delivered.
    
    -Matt
    
    Wayland Jeong wrote:
    > 
    > I think there are some misconceptions here. As you probably know, the ANSI
    > FC standard is a collection of specifications that are thick enough to choke
    > an elephant. Of that large body of work, only a portion of it has been
    > implemented in the commercial world. I would guess from your comments that
    > you are referring to one of the ways that FC attempts to guarantee delivery.
    > The two most notable mechanisms in FC are buffer-to-buffer credit and
    > Class-2.
    > 
    > Now, BB credit is a link-layer concept which ensures that when a FC frame is
    > sent, it will not be dropped on the floor due to congestion. You can achieve
    > the same functionality in Ethernet using 802.3x flow control. That said,
    > BB-credit is a layer below what is encapsulated in iFCP. iFCP encapsulates
    > FC at frame level and largely does not concern itself with an FC primitives
    > (frame delimiters are an exception to this).
    > 
    > Fibre Channel has a class of service called Class-2 which provides an ACK
    > mechanism to guarantee delivery to the end station. It uses frame-level
    > acknowledgements of received data as well as end-to-end buffer credit. This
    > level of service ensures that data sent is delivered at the FC peer level.
    > But, Class-2 was not intended to be a congestion management solution.
    > Class-2 is an error recovery concept and it will not work well in a lossy
    > network (i.e. IP networks with congestion management through WRED and such).
    > Moreover, Class-2 is not generally deployed and the FC industry has largely
    > settled on Class-3.
    > 
    > Thus, there is nothing within a FC encapsulated in iFCP environment that
    > makes this protocol inherently reliable. iFCP specifies TCP as the transport
    > layer and mFCP uses UDP in conjunction with a well-behaved network.
    > 
    > -----Original Message-----
    > From: Stephen Byan [mailto:Stephen.Byan@quantum.com]
    > Sent: Thursday, January 04, 2001 5:47 AM
    > To: 'ips@ece.cmu.edu'
    > Subject: FW: iFCP as an IP Storage Work Item
    > 
    > -----Original Message-----
    > From: Stephen Byan
    > Sent: Thursday, January 04, 2001 8:40 AM
    > To: 'Bill Terrell'
    > Subject: RE: iFCP as an IP Storage Work Item
    > 
    > It's all the FC stuff that lets iFCP work over an unreliable data transport
    > like UDP. It's redundant when running over TCP/IP.
    > 
    > Regards,
    > -Steve
    > 
    > > -----Original Message-----
    > > From: Bill Terrell [mailto:terrell@troikanetworks.com]
    > > Sent: Wednesday, January 03, 2001 6:10 PM
    > > To: 'Stephen Byan'
    > > Subject: RE: iFCP as an IP Storage Work Item
    > >
    > >
    > > >The downside of this advantage is that native iFCP devices would be
    > > burdened
    > > >with greater complexity and cost. I therefor think iFCP
    > > should not be an IP
    > > >Storage work item.
    > > >
    > > >Regards,
    > > >-Steve
    > >
    > > How is a native iFCP endpoint (initiator or target) more
    > > complex or costly
    > > than an iSCSI native endpoint? What are the specific
    > > difficulties inherent
    > > to native iFCP devices versus native iSCSI devices?
    > >
    > > Bill
    > >
    


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Last updated: Tue Sep 04 01:05:56 2001
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