Each zone may store {TAIL ~ instant messaging information} for a subset of the peers at {HEAD ~ locations} in the zone indicated by hashes of identifiers of the peers in the instant messaging group 
Each zone may store { TAIL ~ instant messaging information } for a subset of the peers at { HEAD ~ locations } in the zone indicated by hashes of identifiers of the peers in the instant messaging group
OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH