#555: frame synchronization


Anyone with thoughts on this? 

On 12 Jul 2014, at 4:30 am, Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:

> Another issue I don't want to raise in the current melee, but I
> think we should take it as an isssue, discuss it and close it,
> so we can claim that we thought about it:
> Has anybody considered frame-desynchronization ?
> The framing layer has neither pattern, checksum or sequence numbers
> to help us tell if the sender and receiver have become mis-synchronized,
> If we wanted to be strictly compliant with "end-to-end argument" we
> should have an integrity check, but given that we have a CRC and
> sums in the layers below I don't think that's really an overhead
> which would justify itself.
> However, it would make good sense to add a pattern or sequence
> number to the frame header to give us a "must match field" to detect
> frame misalignment.  (I looked at the current frames and there
> are no fields which lend themselves naturally to this).
> If a frame header gets misaligned one byte either way, there are
> pretty good chances that it will still look legit enough for
> processing to commence.
> Given that many people talk about processing frames while they are
> still being received, adding a more robust misalignment detection
> sounds like a good idea to me.
> The easiest is probably a single byte sequence number which just
> increments from frame to frame.  That number could be included
> in RST frames to indicate which frame caused the error.
> -- 
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk@FreeBSD.ORG         | TCP/IP since RFC 956
> FreeBSD committer       | BSD since 4.3-tahoe    
> Never attribute to malice what can adequately be explained by incompetence.

Mark Nottingham   http://www.mnot.net/

Received on Sunday, 20 July 2014 19:52:41 UTC