At 10:39 AM -0800 11/19/99, Bill Studenmund wrote:
>On Fri, 19 Nov 1999, Henry B. Hotz wrote:
>> Aren't there supposed to be multicast "I'm here" packets preiodically even
>> without a router?  Or was that eliminated in Phase 2?
>
>The multicast bits were new for Phase 2. I wasn't aware of hosts sending
>periodical packets, just routers. ??

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.

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.

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h.b.hotz@jpl.nasa.gov, or hbhotz@oxy.edu