[ih] WiFi, DV, and transmission delay

[Noel Chiappa]

    > From: Dave Taht

    > The queue may not have been building at the imp but in the app.

What app? Sorry, I'm confused by this. The routing was a somewhat low-level
function in the IMPs; the hosts never saw it, or knew of it.

Or did you mean that user traffic queues were building in the IMP, and
the routing updates got buried behind them? I don't recall any more, but
routing, liveness, etc packets may have had priority over user traffic;
3803 might mention it.

    > Didn't arpanet also have some forms of flow control?

Yes, RFNM's - a network-level ACK for the delivery of a 'message' (the ARPANET
term for a user packet) to the host at the far end. 'Messages' were broken up
into smaller packets (I'm not positive of the term used for them, but I think
it may - confusingly! - have been 'packet' - let me call them 'frames here)
inside the network, so at the destination IMP a 're-assembly buffer' had to be
allocated for messages longer than a frame. RFNM's helped prevent the
network from being overloaded - but see:

    J.M. McQuillan, W.R. Crowther, B.P. Cosell, D.C. Walden, and F.E. Heart,
        "Improvements in the Design and Performance of the ARPA Network",
        Proceedings AFIPS, 1972 FJCC, Vol. 40, pp. 741-754.

for a problem which causes IMPs to wedge. (I'm pretty sure that's available
online. If not, let us know.)


    >> Alas, I don't remember any key names/titles to look up on that work
    >> ... One name that keep coming up in my mind as associate with it is
    >> Zaw-Sing Su. There's someone else who I think did more, but I just
    >> can't rember who it was.

Finally remembered who it was; Jose Garcia-Luna. He added a mechanism to DV
that basically prevented the formation of loops. I don't recall the details of
how it worked, but if you visualize a network as a pool of water, and a
connectivity change is a stone dropped into the pool, then the routing updates
are like the ripples that spread out from the point of impact.  Anyway, IIRC,
Jose's mechanism limits changes to a single ripple, so it's even better than
loop prevention, it bounds the time to respond to a connectivity change (I _think_ -
it's been decades since I looked at it).

Anyway, just Google 'routing "garcia-luna"" and a bunch of his stuff will pop up.

Anyone using a DV routing system without using his algorithm (or an equivalent)
is really missing. RIP doesn't have it because his work post-dates RIP.

   Noel