zero code suppression Line coding scheme used for transmission clocking. Zero line suppression substitutes a one in the seventh bit of a string of eight consecutive zeros. See also ones density. ZIP Zone Information Protocol. AppleTalk session layer protocol that maps network numbers to zone names. See also ZIP storm and zone. ZIP storm Broadcast storm that occurs when a router running AppleTalk propagates a route for which it currently has no corresponding zone name. The route is then forwarded by downstream routers, and a ZIP storm ensues. See also ZIP. zone In AppleTalk, a logical group of network devices. See also ZIP. Zone Information Protocol See ZIP.