The effort required to enhance the network configuration algorithm to include Virtual Network Configuration is minimal. Three new fields are added to each existing message in Table 1: antimessage toggle, send time, and receive time. Physical processes include beamforming, topology acquisition, table updates, and all processing required for configuration. Each physical process is assigned a tolerance. When the value of a real message exceeds the tolerance of a predicted message stored in the send queue, the process is rolled back.
Also, an additional packet type was created for updating an approximation of the Global Virtual Time (GVT). Because the system is composed of asynchronously executing logical processes, each working ahead as quickly as possible with its own local notion of time, it is necessary to calculate the time of the system as a whole. This system-wide time is the GVT. Since the network configuration system uses a master node as described in the physical layer setup, this is natural centralized location for a centralized GVT update method as well. RNs transmit their LVT to the master, the master calculates an approximate GVT and returns the result.
An estimate of the additional load on the orderwire packet radios using VNC is shown in Figure 8. It is assumed that virtual messages are 65 bits longer than real messages and there is one virtual message for each real message. The figure shows the prototype 19,200 bps orderwire link capacity as a function of the number of RNs, the position update rate of each RN, and the hand-off rate. The capability of the orderwire to support these rates without VNC is discussed later in detail and is shown in Figure 13. Comparing Figures 8 and 13, it is apparent that the VNC slightly more than doubles the orderwire load. However enough capacity remains to support fifteen or more users with a reasonable position update rate and handoff rate with this relatively low 19,200 bps orderwire bandwidth.
Figure 8: Orderwire Traffic Analysis with VNC.