tailieunhanh - GSM Networks : Protocols, Terminology, and Implementation - Chapter 5

Hệ thống kết nối mở (OSI) mô hình tham khảo đã được chỉ định của ITU, trong hợp tác với ISO và IEC, và được ghi chép trong Khuyến nghị . Mặc dù mô hình OSI được áp dụng trong nhiều lĩnh vực, nó được sử dụng chủ yếu trong lĩnh vực thông tin liên lạc giữa các máy tính. Mục đích của nó là để tổ chức và chính thức hóa các phương pháp giao tiếp. Ý tưởng cơ bản của mô hình tham khảo OSI là để tách các phần khác nhau, trong toàn của họ, tạo thành. | 5 The OSI Reference Model Reasons for Standardization The Open System Interconnection OSI Reference Model was specified by ITU in cooperation with ISO and IEC and is documented in Recommendation . Although the OSI model is applicable in many areas it is used mostly in the area of communication between computers. Its purpose is to organize and formalize the communication method. The basic idea of the OSI Reference Model is to separate the various parts that in their totality form a communications process. Separation of concerns is achieved by layering and modularization of transactions and tasks. This approach results from the following reasoning The use of microprocessors in telecommunications not only allowed for the creation of new services but at the same time increased the requirements on communications of exchanges and computers. When humans communicate by means of telephone or letters they do not want to be concerned with the details of the physical transfer of the information. They just want to communicate. The same applies to the layers of the OSI Reference Model in which each layer has a fixed role in the process of communications. A computer is a modular structure which starts with the transistor on the lowest level and with modularity built on top of modularity ends up as a super-computer. To use such a system becomes easier when the tasks themselves can be modularized. 39 40 GSM Networks Protocols Terminology and Implementation Telephone systems are used for many applications. These applications became possible only because the application itself had become more independent of the process of pure data transmission. Modems and fax machines for instance rely on the functionality of the services of a lower layer and adapt their own functionality accordingly. The telephone network on the other hand is not concerned with the content or the representation of the transmitted data. The OSI Reference Model enables two products from different .