On 3/5/2013 8:15 AM, Brian E Carpenter wrote:
On 05/03/2013 11:55, Dearlove, Christopher (UK) wrote:
I've no idea about the example quoted, but I can see some of their motivation.
TCP's assumptions (really simplified) that loss of packet = congestion =>
backoff
aren't necessarily so in a wireless network, where packets can be lost without
congestion. This means that TCP into, out of, or across, a MANET using TCP can
be
bad. It then tends to happen that the MANET people don't fully understand TCP,
and the TCP people don't fully understand MANETs.
The effects you mention were definitely discussed in PILC.
http://www.ietf.org/wg/concluded/pilc.html
Maybe the PILC documents need revision?
Brian
TRIGTRAN tried to nail this down in more detail after PILC concluded (I
co-chaired both PILC and the TRGTRAN BOFs). This quote from the IETF 56
minutes pretty much captured where that ended up:
<quote>
Spencer summarized a private conversation with Mark Allman as, "Gee,
maybe TCP does pretty well often times on its own. You may be able to
find cases where you could do better with notifications, but by the time
you make sure the response to a notification doesn't have undesirable
side effects in other cases, TCP doesn't look so bad"
</quote>
If we had to have all the TCP responding-to-loss mechanisms in an
implementation anyway, and we could tell a sender to slow down, but not
to speed up, it wasn't clear that additional mechanisms would buy you much.
References are at
http://www.ietf.org/proceedings/55/239.htm and
http://www.ietf.org/proceedings/56/251.htm
The high order bit on this may have been that TRIGTRAN wasn't IETF-ready
and should have gone off to visit IRTF-land, but in the early 2000s, I
(at least) had no idea how to make that happen.
Spencer
I don't have a single good reference for what I say above, in particular have
things got better (or worse) as TCP evolves, and therefore which references
are still valid? But the obvious Google search (TCP MANET) throws up various
discussions.