On Fri, 19 Nov 1999, Henry B. Hotz wrote:

> I think it's fundamental to AppleTalk that everyone knows who else is on
> line at a given time if they want to.  In LocalTalk this is handled with
> periodic "I'm here" broadcasts and is the reason you can't put more than
> 20-30 devices on a LocalTalk segment.  EtherTalk does something to handle
> the same function which uses broadcast packets in Phase 1 and multicast in
> phase 2.

?? I know routers will do this, but hosts shouldn't.

> What I don't know is any of the details past that.  I suspect that they
> still send "I'm here" packets but have played with some of the timeouts.
> If you want to know that a device has been abruptly unplugged and isn't
> there anymore then you have to have *some* kind of background traffic to
> maintain the state of the network.  I would expect that traffic to maintain
> the network number unless something like a router exists to force a change.
> 
> On power-up a device tries to use its last node (and network?) number as a
> default (at least for LocalTalk).  I'm not sure when or how a device would
> decide to reset from routed to non-routed mode, but the total absence of
> any other devices would seem to be one likely case.

Only Ethertalk phase 2 has router & non-router modes. LocalTalk and Phase
1 don't. :-) On powerup, a phase 2 device will check for a router, and if
it times out w/o finding one, assumes there's not one. If the router were
just down, you have to power cycle (or switch to another Appletalk
interface and switch back).

All devices will try the same net & node # they used last time on powerup.
They effectivly ping the device, and if there's no response after a number
of tries, they use that address.

Take care,

Bill