Handbook of Wireless Networks and Mobile Computing phần 10

Định lý tiếp theo cho thấy rằng, ngoại trừ cho các đỉnh nguồn và đích, tất cả các đỉnh trung gian trong một con đường ngắn nhất được chứa trong các thiết lập thống trị bắt nguồn từ quá trình đánh dấu. Định lý 3 đường đi ngắn nhất giữa hai nút bất kỳ không bao gồm bất kỳ | 566 DATA MANAGEMENT IN WIRELESS MOBILE ENVIRONMENTS PERFORMANCE ANALYSIS We develop a simple model to analyze the performance of the proposed cache management scheme. Specifically we want to estimate the miss probability and mean query delay for the proposed scheme. For the purposes of analysis we consider the performance in a single cell as mobility is assumed to be transparently handled with one MSS and N mobile hosts. We make the following assumptions Total number of data items is M each of size ba bits. 6 TPequeriesgenerated by a sleeping MH . when the MH is disconnected from the MSS are lost. . Ạ s channel of I11 t c assumed feu- all transmissions takmg pla emthet cell. ll messages tra phene. to aaenss sn. -ii -ee asn soft tsnod accerficgtotha FCFS nft coma fins sereaaiscltenidinnpohey. Qaeries mtaofsinr c nitsanf invelldntions ate of size bits. Software overheads are ignored. ModeSiecQnerysUpdate Pastern TSe limeFetweeii updates to any data item is as-sumedtn follna nnesrxmantintdfetnMHoiiwMi mean r queryaccordinnlo a Poisson distribution with mean rate of A. These queries are uni-fOTmlydlst FutednyatntldrtaiSems hr the databmse. The cMna -lc it shown in Figure . uppates Mobile Clients in a Cell Figure Modeling query-update pattern. PERFORMANCE ANALYSIS 567 oo oo Awake oo Sleep l-s t st wakeup Figure Modeling sleep behavior of an MH. Modeling Sleep Pattern for an MH. An MH alternates between sleep and awake modes. The sleep wake up pattern of an MH is modeled by using two parameters see Figure 1 the fraction s 0 s 1 of the total time spent by an MH in the sleep mode 2 the frequency Ci at which it changes state sleeping or awake . We consider an exponentially distributed interval of time t with mean 1 . The MH is in the sleep mode for time st and in the awake mode for time 1 - s t. By varying the value of Ú differentfrequenciesofchangeof statecanbe obtained for the same total sleep time. We want .