(第2空)If two communicating entities are in different hosts connected by a network，there is a risk that PDUs will not arrive in the order in which they were sent，because they may traverse( )paths through the network. If each PDUs is given a unique number，and numbers are assigned( )，then it is a logically simple task for the receiving entity to reorder( )PDUs on the basis of sequence number. A problem with this scheme is that，with a( )sequence number field，sequence number will repeat. Evidently，the maximum sequence number must be ( )than the maximum number of PDUs that could be outstanding at any time.