On Distributed Communications Series
II. Digital Simulation of Hot-Potato Routing in a Broadband Distributed Communications Network
A sample computer output containing the map used to indicate the location of all the subroutines of the simulation program is shown in Fig. 6. The values shown are the addresses of the subroutines in the core memory and are used for checkout purposes only.
Initial Input Parameters
Under the printed heading "EXECUTION", twelve separate parameters that can be selected as input quantities and inserted into the program as a control card are shown. These separate quantities, shown in Fig. 6, are:
- An arbitrary number used to start the random number at a different selectable starting point for each run (5351 in the example shown).
- The number of columns in the rectangular array of nodes (7).
- The nuinber of rows in the rectangular array of nodes (7).
- The number of links connected to each node (8). The value of eight links corresponds to a redundancy level of R = 4.
- The number of time-frames between' computer printout snapshots (200).
- If the program is used to observe the learning occurring between two selected nodes, this parameter would indicate the "from" node (not examined in the attached printouts).
- Same as the previous input, but for the "to" node.
- Minimum path between the inputs of 6) and 7) (not used in the following printouts).
- Initial table value.
- Number of messages flowing around in the system at any time (98).
- Number of time-frames the system is to be run (3000).
- Maximum allowable handover number (60).
OutputThe next form of output, Fig. 7, presents a snapshot summary of traffic status in the network each 200 (in this case) time-frames.
- Number of messages delivered during the last 200 time-frames (271, 503, 592, etc.).
- Mean value of all handover number table entries during the last 200 time-frames (10.324723, 7.109344, 5.500000, ...).
- Percentage of messages dropped because handover numbers exceeded maximum allowable values (0, 0.001984, 0.01033, 0.004458, ...).
- Total value of the sum (modulo 131,172) of all entries on the handover number table (69422, 26960, 126426, 101382).
It is to be noted that this table suxmnation is fixed point and modulo 131,172. Thus, the first few entries of the table totals are in excess of 131,172. However, after only several cycles the values drop below 131,172 and remain below this point for the period of interest.
Handover Number TablesThe following two illustrations define the numbering procedure for node and link used in the simulation:
In the distributed network being simulated, a separate handover number table is stored at each node. Each node's table is an ordered list of desired nodes sought. For example, Node 1 would have its table ordered in terms of to Node 11, to Node 25, to Node 49, etc.
However, in the simulation it was more convenient to combine all the tables and to order it in terms of the "from" stations. Hence, Fig. 8 shows the handover number table for Node 1, which is in the upper left-hand corner of the network. Thus, it can be seen that traffic from all stations to the east of Node 1 arrived with relatively low handover numbers over Link 2 of Node 2.