Modern telecommunication switching

Author: Chen Xisheng / et al.
Editor-in-Chief: Zheng Jie / et al.
Publisher:
Publish Date: 2000-05-01
Features: This book systematically introduces the main switching technologies and theories in modern telecommunications. It adopts a progressive approach, moving from telephone switching to integrated services switching, from circuit switching to packet switching, from fixed network switching to mobile and intelligent network switching, and from narrowband switching to broadband ATM switching. It analyzes and unfolds each layer from a perspective of development, focusing on the principles, methods, system structures, and organic connections among various switching technologies. The book is divided into 9 chapters, covering topics such as an introduction to switching technology, connection technology, signaling technology, control technology, packet switching, narrowband integrated services digital switching, mobile switching, frame relay switching, principles and technologies of intelligent networks, ATM switching, and IP/ATM integrated switching technology. Each chapter includes a summary and exercises. This book can serve as a textbook or reference for telecommunications higher education institutions, as well as a reference for telecommunications technicians.
Excerpt:
1. Basic Process of Circuit Switching
Circuit switching (CS: Circuit Switching) is one of the earliest switching methods. Early telephone exchanges, including manual ones, commonly used circuit switching. The basic process of circuit switching includes three stages: call setup, information transmission (call), and connection release.
2. Characteristics of Circuit Switching
Circuit switching is a real-time switching method. When one user calls another, a circuit connection is immediately established between them. If there are no idle circuits, the call cannot be established and is lost. Sufficient connection circuits must be provided to ensure that the call loss rate does not exceed the specified value. The characteristics of circuit switching can be summarized as follows:
(1) A dedicated physical connection path must be established between communicating users, which leads to the following characteristics: a connection setup process is required before communication; as long as the user does not send a release signal, the physical connection remains even if communication is temporarily suspended; any failure in the physical connection will cause communication interruption; high efficiency is only achieved when the call setup and release times are very small relative to the communication duration.
(2) Communication information is not processed (except for signaling), but is transmitted as is. Rate and code type conversion is not performed for low-speed data transmission.
(3) There are no error control measures for transmitted information.
(4) Traffic is handled based on a call loss system. When overload occurs, the call loss rate increases, but it does not affect established calls.
In summary, circuit switching allocates bandwidth statically. After a connection is established, the circuit is virtually occupied even without information transmission, resulting in low circuit utilization. A connection must be established in advance, introducing a certain connection setup delay. Once the path is established, information can be transmitted in real time, and transmission delay is generally negligible. There are no error control measures, making data exchange reliability lower than that of packet switching. Therefore, circuit switching is suitable for telephone switching, file transfer, and high-speed fax, but not for bursty services or data services sensitive to errors.