The simple names that make up a domain may contain both upper and lower case letters (as well as digits and hyphen), but these names are not case sensitive. Hosts are generally known by names. Sometimes a host is not known to the translation function and communication is blocked. To bypass this barrier two forms of addresses are also allowed for host "names". One form is a decimal integer prefixed by a pound sign, "#". Another form, called "dotted decimal", is four small decimal integers separated by dots and enclosed by brackets, e.g., "[123.255.37.2]", which indicates a 32-bit ARPA Internet Address in four 8-bit fields. (Of course, these numeric address forms are specific to the Internet, other forms may have to be provided if this problem arises in other transport systems.)Suppose someone at A tries to initiate communication with destination H. The fully qualified destination name would be H.G.F.E.L.U Omitting common ancestors, the partially qualified name for the destination would be H.G.F To permit the case of partially qualified names, name server at A needs to resolve the simple name F, i.e., F needs to be distinct from all the other simple names in its database. To enable the name server of a domain to resolve simple names, a simple name for a child needs to be assigned distinct from those of all of its ancestors and their immediate children. However, such distinction would not be sufficient to allow simple name resolution at lower-level domains because lower-level domains could have multiple parentage below the level of this domain. In the example above, let us assume that a name is to be assigned to a new domain X by D. To allow name server at D to resolve simple names, the name for X must be distinct from L, E, D, C, F, and J. However, allowing A to resolve simple names, X needs to be also distinct from A, B, K, as well as from Q, P, N, and R. The following observations can be made. Simple names along parallel trails (distinct trails leading from one domain to the naming universe) must be distinct, e.g., N must be distinct from E for B or A to properly resolve simple names. No universal uniqueness of simple names is called for, e.g., the simple name S does not have to be distinct from that of E, F, G, H, D, C, K, Q, B, or A. The lower the level at which a domain occurs, the more immune it is to the requirement of naming uniqueness. To satisfy the required distinction of simple names for proper resolution at all levels, a naming authority needs to ensure the simple name to be assigned distinct from those in the name server databases at the endpoint naming domains within its domain. As an example, for D to assign a simple name for X, it would need to consult databases at A and K. It is, however, acceptable to have simple names under domain A identical with those under K. Failure of such distinct assignment of simple names by naming authority of one domain would jeopardize the capability of simple name resolution for entities within the subtree under that domain.