Làm thế nào không ATM làm việc Chương này giải thích các khái niệm cơ bản đặt nền tảng cho công nghệ ATM. Người đọc là sự hiểu biết chuyên sâu của các điều khoản như các tế bào ATM, ghép kênh thống kê, chuyển mạch ATM và chế biến lớp ATM. Các lớp của mô hình tham chiếu ATM được thảo luận và giải thích. Xem chuyên sâu bao gồm các lớp vật lý, ATM và thích ứng ATM Layer. Sự hiểu biết cơ bản của các điều khoản này được khuyến cáo trước khi đọc thông qua các chương. | Chapter 2 How Does ATM Work This chapter explains fundamental concepts that lay the basis for ATM technology. The reader is given the in-depth understanding of the terms such as ATM cells statistical multiplexing ATM switching and ATM layer processing. The layers of ATM reference model are discussed and explained. This in-depth view includes the Physical Layer the ATM and the ATM Adaptation Layer. The basic understanding of these terms is recommended prior to reading through the following chapters. ATM Protocol Reference Model As it was mentioned before ATM can be viewed as a part of the B-ISDN concept. The development of B-ISDN protocols was facilitated by the definition of the B-ISDN Protocol Reference Model PRM . The model was developed using the layered communication architecture based on the distinction between layer functions developed by the ISO International Standards Organization . ATM plays a significant role in the B-ISDN PRM. The formal ATM PRM is a three-dimensional model but the relations between layers can be better viewed using one-dimensional layer model. 9 ATM Basics Ị ApplicationJ I I I AAL I ATM PHY Fig. 2-1 Simplified ATM Protocol Reference Model It is important to understand that the layers in the ATM PRM presented in the don t have one-to-one mapping relationship with the seven layers OSI protocol reference model. Some of the layers of ATM PRM provide the functionality of more than one OSI layer. For instance the AAL ATM Adaptation Layer represent some of the features of OSI layer 4 transport control layer 5 session control and layer 7 application control . Most of the ATM PRM layers can be further subdivided into a number of sublayers. Physical Layer The physical layer PHY constitutes the lowest level of the ATM PRM. Its major task is to transmit ATM cells between ATM devices over the physical medium. ATM is designed to operate over potentially error free media. Therefore successful transmission of ATM cells between ATM .
