architecture for mobile computing

In the early days ofm4riftairieS, the nidintfiand many other interfaces were proprietary. Evert:Vie networked interfaces to different terminals were vendor-specific and proprietary. The most successful early TP system was the reservation system for the American Airlines.*This was over a Uniyac computer using U100 protocol. For IBM TP,.eiiviroinnent,- which runs on OS/390 known as CICS (Customer 111ft:irritation Control System), the network interface was through SNA. In India when BSNL (earlier known as DoT—Department of Telecom) launched the 197 telephone directory enquiry system in 1986, it was on TPMS (Transaction Processing Management System) running on [CL mainframe running VME operating system. The network interface was over X.25 interface. The network-centric mobile computing architecture uses a three-tier architecture Figure 2.1. In the three-tier architecture, the first layer is the User Interface or Presentation Tier. This layer deals with user facing device handling and rendering. This tier includes a user system interface where user services (such as session, text input, dialog and display management) reside. The second tier is the Process Management or Application Tier. This layer is for application programs or process management where business logic and rules are executed. This layer is capable of accommodating hundreds of users.