Geographical Data Broadcast Cost Models

As discussed in Section 2.1, AT is further divided into two components, namely Probe Wait and Bcast Wait. We argue that it might be more appropriate to divide AT into four components: Index-Probe Wait (IPW), Index-Bcast Wait (IBW), Data-Probe Wait (DPW) and Data-Bcast Wait (DBW). IPW is the same as Probe Wait defined in (Imielinski, 1997), i.e., the time duration of getting to the nearest index segment. IBW is the time duration from the time when the first index segment is reached to the time when the last index segment is reached. DPW is defined as the duration from the time the last index segment is reached to the time when the first data segment is reached. DBW is defined as the duration from the time when the first data segment is reached to the time when the last data item is downloaded. The summation of IBW, DPW and DBW is equivalent to the Bcast Wait defined in (Imielinski, 1997). These four components are illustrated in Fig. 3-1 for two scenarios. We assume each index segment contains a certain number of pointers each of which points to a data segment, and each data segment contains only one data item. We use the intervals between the beginning and ending positions of data items as the measurements of the four components of access time as discussed in Chapter 2.