work. troduce the possibility that packets will be received out of proper sequence. For users to be protected from this form of error, the packets have to be reassembled into the same basic message structure they had upon initial transmission into the network. The process of packet reassembly is done at the destination switch-in this case, switch 3-using packet sequence numbers that must be carried through the network. 6.8 NETWORK DESIGN CONSIDERATIONS Network design requirements can be divided into two categories: 1. Existing facilities. These can be divided into the following items: Number of terminals supported 104 TELECOMMUNICATIONS Speed/code/protocol of each terminal Physical location of each terminal Physical location of the host processor Speed/code/protocol of the host processor 2. Traffic statistics. These can be divided into the following items: Average number of terminals in use at any one time Average length of input inquires Average length of output responses Peak hours in different times zones Once the basic traffic requirements (Table 6-1) are known, the next task is to organize the data. The first part of this organization Table 6-1. Network Traffic Statistics Number of terminals supported 300 baud ASCII Speed/Code/Protocol of each terminal ASYNCH. Average number of terminals in use at one time 50%/200 Average number of inquires input from a terminal per hour Average length of input inquires 6 characters Average percent of time terminal is in input Average number of responses output to a terminal from the Host per Average length of output responses Average percent of time terminal is in output Physical location of terminals: Location Number of Terminals Number Active Physical location of host Speed/Code/Protocol of host NETWORK STRUCTURES 105 is to construct a logical to/from matrix. This matrix indicates the possible source-to-destination connection. Once the logical matrix is constructed, several conclusions can be drawn that will indicate a possible network configuration (see Fig. 6-16). The n