Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!think!barmar
From: barmar@think.COM (Barry Margolin)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Serial TCP/IP - all the same?
Message-ID: <26204@think.UUCP>
Date: 23 Aug 88 05:32:10 GMT
References: <759@stcns3.stc.oz> <977@rlgvax.UUCP>
Sender: usenet@think.UUCP
Reply-To: barmar@kulla.think.com.UUCP (Barry Margolin)
Organization: Thinking Machines Corporation, Cambridge, MA
Lines: 26

In article <977@rlgvax.UUCP> dennis@rlgvax.UUCP (Dennis.Bednar) writes:
>	Justification of the Rules:

The justifications you gave explain why there must be SOME escape
convention (which should go without saying), but not why that
particular one was chosen.  Why is this particular escape convention
better than the old "double the special characters" convention or
preceding a special character by the escape character?  I don't think
the doubled-character convention would actually work in SLIP because
of the lack of a header (if a packet begins with FRMEND_data_char
there would be three FRMEND characters in a row, and it would look
like the FRMEND_data_char is actually the last character of the
previous packet).  But it would work to precede a FRMEND_data_char or
FRMESC_data_char with a FRMESC: when forming a packet, you search for
a FRMEND or FRMESC; if you find a FRMESC first you remove it from the
stream, read the next character into the packet buffer, and then
search again.  The only advantage I see of the chosen scheme is that
packetization and escape processing can occur as separate steps; was
this the issue that resulted in this more complex scheme?



Barry Margolin
Thinking Machines Corp.

barmar@think.com
{uunet,harvard}!think!barmar