Path: utzoo!attcan!uunet!lll-winken!lll-tis!helios.ee.lbl.gov!pasteur!ucbvax!CAM.UNISYS.COM!jonab
From: jonab@CAM.UNISYS.COM (Jonathan P. Biggar)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: FTP server question
Message-ID: <8805261929.AA04199@RHEA.CAM.UNISYS.COM>
Date: 26 May 88 19:29:14 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 21


	Re: "last byte of a packet is an URGENT boundary"
	The TCP URGENT mechanism uses a pointer; I do not think that there is
	any specification which says that packet boundaries are significant
	with respect to URGENTs.

Not so!  RFC 793 states:

        If there is urgent data the user will have been informed as soon
        as it arrived via a TCP-to-user signal.  The receiving user
        should thus be in "urgent mode".  If the URGENT flag is on,
        additional urgent data remains.  If the URGENT flag is off, this
        call to RECEIVE has returned all the urgent data, and the user
        may now leave "urgent mode".  *****Note that data following the
        urgent pointer (non-urgent data) cannot be delivered to the user
        in the same buffer with preceeding urgent data unless the
        boundary is clearly marked for the user.*****

MIL-STD 1778 has similar language.

Jon Biggar
jonab@cam.unisys.com