peer-peer syncronization

[Francesco Orsenigo <xarvh@lombardiacom.it>]

How can syncronize a game (ie: make two simultaneous events appear 
simultaneous to all users) in a peer-peer system, using UDP?
(TCP would be slow, and i'd like to avoid the complexity of a client-server 
system).
The technique would be for each peer to send just the info about commands 
given by the player, along with the game time when the command itself is 
issued, but this may easily lead to unconsistencies between peers.

A more robust way would be for each peer to send, each game tick, a message 
with a "I'm ready for next game cycle, no command" to each other peer, OR a 
"I'm ready and the player issued the XYZ command"... But this is 
EachPlayer*EachOtherPlayer*EachGameTick... too many "each"... the network 
load would be too high even for a 5fps game.... or not?

Any ideas?
Is there any documentation about doing such things?

Thanx,
Francesco Orsenigo