> I have this question for CODA ...

I really only know (disconnected) AFS, but I hope I'm correct in this.

> 1. Is there a callback mechanism from CODA server to client?

Yes, when files are updated, the client gets a message from the
server.

> 2. If so, does it happen when clients are not connected to servers?
> In that case, do CODA servers initiate TCP connections to CODA
> clients?

The communication is UDP based. This means that there are no TCP
connections between the client and the server. "Disconnected" is a
state when the network between the client and the server is not able
to forward packets (as in a offline laptop).

For obvious reasons, the server cannot contact the client when it is
offline. Coda solves this through reintegration when the client is
back on the network.

/Magnus
map_at_stacken.kth.se