[comp.protocols.tcp-ip] user interface for urgent data.

dzoey@UMD5.UMD.EDU (09/14/87)

Hi, I was looking at the TCP spec (RFC 793) and became slightly curious
about how urgent data should be presented to the application.  Berkeley has
the application either register a function to handle the urgent data
seperately, or indicate that urgent data should be delivered as normal data.
This seems like a reasonable thing to do, but I'm curious about how other
implementations present urgent data.  I'd very much like to hear about how
other implementations do this.

Another question I have is where does the urgent data start?  Is it safe to
assume at the beginning of a packet marked as urgent?  If all the data in
a packet marked urgent is urgent data, then shouldn't urgent data be
delivered as soon as possible (i.e. not wait for sequence reassembly since
you know all data in that packet is urgent and would be delivered out of
sequence anyway)?

Is there something I should have read before asking this?


			Thanks for any info

        		Joe Herman

dzoey@umd5.umd.edu

CERF@A.ISI.EDU (09/15/87)

Joe,

In the urgent daa design, it was assumed that TCP should NOT
impose any kind of syntax on the data stream. Rather, the
flagging of urgen data meant, roughly, "start scanning the
data stream wherever you are now and go through at least
to the placed marked URGENT. Process appropriately whatever
you read, given that you know you are in URGENT mode until you
get to byte sequence number X."

It was assumed that the application using TCP would have
conventions for structuring of the TCP byte stream and
for interpreting what to do with urgent data indicator.

Vint Cerf