RE: FCIP: A question about framing

["KRUEGER,MARJORIE (HP-Roseville,ex1)" <marjorie_krueger@hp.com>]

Do TCP RFCs specify the behavior of the receiver regarding when to deliver
data to the application?  From what I've read, different implementations act
differently - some buffer data received data and deliver it to the app when
the buffer's full, others deliver data immediately when each packet is
received.  In either implementation, when the PUSH flag is set, all data is
delivered immediately to the application.  In a FCoIP device, could't the
receipt of the packet with the PUSH flag set indicate that this is the "end
of a frame"?  Assuming that the FC aware code can also view the TCP header.

I understand the truth of what you are saying when TCP is delivering data to
an "application", but I'm assuming that FCoTCP implementations will have
some level of mapping interaction between the TCP and the FC layer?

> -----Original Message-----
> From: Randall R. Stewart [mailto:randall@stewart.chicago.il.us]
> Sent: Thursday, November 02, 2000 11:34 AM
> To: Murali Rajagopal
> Cc: Douglas Otis; Merhar, Milan; ips@ece.cmu.edu
> Subject: Re: FCIP: A question about framing
> Murali:
> 
> Using Push does not guarantee that you will get "datagram-like"
> behavior. You
> must have some mechanism to find your "message" amongst a stream of
> bytes... this is what TCP presents you with. This usually means a 
> message/finder that can parse the incoming stream and find the
> beginning/ending of the message boundaries... Some apps have 
> been known
> to write every message in two pieces... write the number of bytes
> in this message in a 4 byte int, followed by the message with the PUSH
> flag set.  Even at that the reader side must read the 4 byte value
> and then continue to read until it has assembled a complete message.
> 
> The PUSH flag is just a hint to TCP it does not assure you 
> that you will
> get a datagram behavior depending on PUSH will not help you... been
> there ..
> . done that.. it don't work :/
> 
> R
>
 
Marjorie Krueger
Networked Storage Architecture
Hewlett-Packard Storage Organization
tel: +1 916 785 2656
fax: +1 916 785 0391
email: marjorie_krueger@hp.com