Julian Munoz Dominguez wrote:
> AX25 v 2.2 specifies something similar: the data link machine ask for an
> oportunity to transmit to the link multiplexer machine, and when it
> receives the "OK" it transmits the pending acks. But it still uses T2,
> because the data link machines are separated of the medium by the Link
> Multiplexer and they don't receive information about the state of the
> carrier (and that's maybe better that way, because the data link machine
> is independent of the physical machines, i.e. you must no implement
> diferent data link machines for full duplex and half-duplex).
I'm convinced that it is wrong to have only loose coupling of the
channel access and the data link layer protocol. With the
kind of loose coupling one has with KISS TNC's, one is prone to
enqueue redundant acks, and loose opportunities to piggyback acks
with information frames. Ack frames for example need to be
generated just before they actually hit the wire, not when
you receive a frame that needs to be acked. Also, channel state
information can help the link layer make better decisions when it is best to
request the transmission of acks etc.
All commercial wireless channel access/data link protocols I know
are much more tightly coupled than what is common in amateur radio.
And the current timer mess in the AX.25 specs is a direct
consequence of the loose coupling.
> > FlexNet "prunes" the send queue (i.e. looks for redundant packets).
> > Conceptually a bit ugly, but it works well.
>
> Yes, because maybe what is redundant for tcp/ip is not redundant for
> other protocols. It's dangerous to touch whay you don't own :-)
Everyone who sends non IP data with a PID IP should be shot anyway 8-)
And with IP, you are allowed to loose packets (FlexNet doesn't
touch contents, just selectively throws away packets).
Tom
