in a big ticket

உள்ள பெரிய சீட்டு

if you dont submit your holl ticket no

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Figure 1.7-2 has divided the airline functionality into layers, providing a framework in which we can discuss airline travel. Now, when we want to describe a part of airline travel we can talk about a specific, well-defined component of airline travel. For example, when we discuss gate functionality, we know we are discussing functionality that sits elow baggage handling, and above takeoff and landing. We note that each layer, combined with the layers below it, implement some functionality, some service. At the ticketing layer and below, airline-counter-to-airline-counter transfer of a person is accomplished. At the baggage layer and below, baggage-check-to-baggage-claim transfer of a person and their bags in accomplished. Note that the baggage layer provides this service only to an already ticketed person. At the gate layer, departure-gate-to-arrival-gate transfer of a person and their bags is accomplished. At the takeoff/landing layer, runway-to-runway transfer of a person (actually, many people) and their bags, is accomplished. Each layer provides its functionality (service) by (i) performing certain actions within that layer (e.g., at the gate layer, loading and unloading people from an airplane) and by (ii) using the services of the layer directly below it (e.g., in the gate layer, using the runway-to-runway passenger transfer service of the takeoff/landing layer). As noted above, a layered architecture allows us to discuss a well-defined, specific part of a large and complex system. This itself is of considerable value. When a system has a layered structure it is also much easier to change the implementation of the service provided by the layer. As long as the layer provides the same service to the layer above it, and uses the same services from the layer below it, the remainder of the system remains unchanged when a layer's implementation is changed. (Note that changing the implementation of a service is very different from changing the service itself!) For example, if the gate functions were changed (e.g., to have people board and disembark by height), the remainder of the airline system would remain unchanged since the gate layer still provides the same function (loading and unloading people); it simply implements that function in a different manner after the change. For large and complex systems that are constantly being updated, the ability to change the implementation of a service without affecting other components of the system is another important advantage of layering