Digital network

Advantages of digital network

Digital network has a series of advantages due to the use of digital technology: it can reduce hardware cost, improve reliability and maintainability, improve line transmission capacity, and improve user-specific The use of the line, containing information in various forms and purposes, providing buffer storage functions, and improving the interface between the terminal and the computer, etc.

PABX digital network

Digital private automatic branch exchange (PABX) can be used as a digital switch. This PABX digital network actually belongs to a new type of telephone switching network. Because the number of bits after digitizing the voice signal is much greater than the number of bits after digitizing a file. Therefore, it is relatively simple to extend the PABX digital network to process text and data. The PABX digital network has a transmission rate of only 64 kbits/sec, but it can already meet the needs of general word processing, data terminals and multi-function workbenches, as well as communication between terminals within the enterprise, or access to remote databases via public data networks. Digital exchanges can also use integrated digital exchanges (IDX), that is, program-controlled exchanges. This is the development direction of digital networks and will enable digital networks to have higher performance.

Telephone digital network

It is composed of a digital transmission system, a digital multiplexer, a digital switch, a network synchronization system, and a digital subscriber phone equipped with an encoder and decoder. Its core equipment is a digital switch. The main equipment of the switch is the control machine and the connection network. Its peripheral equipment includes clock system, user interface and relay interface equipment. The switch is connected with the user's digital phone through the subscriber line through the user interface device; it is connected with other switches through the trunk line through the relay interface device. The sending end of the relay interface device is a dedicated multiplexer, which multiplexes the multiplexing code, signaling and various service data into a relay code stream; the receiving end of the relay interface device is a branching function Frame adjuster, adjust the frequency and phase of the relay code stream. The relay code stream is usually a primary group or a secondary group code stream, which is multiplexed into a high-order group code stream by a digital multiplexer, and then transmitted to a digital switch of another network node via a high-speed digital transmission system. If you want to connect to digital networks or analog telephone networks of different standards, intercommunication or compatible equipment must be used. In a telephone integrated digital network, there are multiple streams flowing according to their own rules at the same time. Therefore, a digital telephone network can be regarded as a complex composed of several independent sub-networks. These code streams can be broadly divided into telephone signal codes, timing signals, signaling data, service data and service calls. Figure 2 depicts the flow of the first three streams. The telephone signal code flows in both directions from user to user; the timing signal is bounded by the frame adjuster at the opposite end, and flows from the timing system to all units that need timing in each network junction area, but the non-reference node must be from the reference node. The clock is extracted from the timing signal of the point; the signaling data flows bidirectionally between the control machine and between the control machine and the user's phone. Therefore, the telephone integrated digital network is an all-digital network that comprehensively transmits a variety of information.

Public Digital Network

CHINADDN is China's public digital data network operated and managed by the post and telecommunications department. At present, the network has covered all the capital cities of the country, most of the cities and some counties, and can conveniently provide you with various services of intra-city, domestic and international DDN. CHINADDN is China's public digital data network operated and managed by China Telecom. At present, the network has covered all provincial capital cities, most cities and some counties and cities in the country, and can conveniently provide you with various services of intra-city, domestic and international DDN dedicated lines.

CHINADDN is my country's medium and high-speed information national highway.

Integrated Digital Network

Introduction

Integrated Services Digital Network (ISDN) is an international standard for digital telephone networks. A typical circuit switched network system. It transmits voice and data at a higher rate and quality through ordinary copper cables. ISDN is a popular form of telephone network in Europe. The GSM mobile phone standard can also transmit data based on ISDN. Because ISDN is a fully digitized circuit, it can provide stable data services and connection speeds, unlike analog lines that are as obvious as interference. It is easier to develop more digital information services on digital lines that cannot or are more difficult to ensure quality on analog lines. For example, in addition to basic phone calls, it can also provide video, image and data services. ISDN requires an all-digital network to carry digital signals (only two states of 0 and 1). The biggest difference from ordinary analog phones is here.

In addition, ISDN also specifically refers to the use of this technology to establish a protocol suite for maintaining and disconnecting circuit switching, or isosorbidedinitrate, an abbreviation for isosorbide dinitrate. All kinds of digital networks are developing towards the integrated service digital network based on the telephone integrated digital network. Integrated Services Digital Network (ISDN) is an integrated digital network that provides end-to-end connections for voice and non-voice services by connecting users through a limited class of standard multi-purpose interfaces. The integrated service digital network is composed of its standard interface and integrated digital network (Figure 3). Among them, the integrated digital network is the main body, and various user terminals are connected to the integrated digital network through the standard interface of the integrated service digital network. A path with a prescribed rate and structure penetrates the two-layer integrated service digital network reference plane (S-side and T-side), and connects the integrated service digital network user terminal with the integrated digital network. The original terminal needs to be connected to the network, and the above-mentioned connection must be realized after being transformed into an equivalent integrated service digital network terminal through a layer of adaptation reference plane (R plane). In this way, through this general interface and integrated digital network, various communication connections can be established between various user terminals, between users and databases, and between databases and databases.

To achieve this vision, network resources will be fully utilized, network management will be significantly simplified, and the overall economics of the communication network will be fundamentally improved. Also, because the network foundation is unified, as long as appropriate procedures and adaptation devices are adopted, various possible new services can be incorporated into the network through standard interfaces, thereby improving the network's ability to adapt to new services.

ISDN structure

ISDN has two types of channels B and D: The B channel is used for data and voice information, and the D channel is used For signal and control (can also be used for data). B stands for bearer and D stands for Delta.

ISDN has two access methods: Basic Rate Interface (BRI) consists of 2 B channels, each with a bandwidth of 64kbps and a D channel with a bandwidth of 16kbps. The three channels are designed as 2B+D.

Primary Rate Interface (PRI)-consists of many B channels and one D channel with a bandwidth of 64Kbps. The number of B channels depends on different countries:

North America and Japan: 23B +1D, total bit rate 1.544Mbit/s(T1)

Europe, Australia: 30B+D, total bit rate 2.048Mbit/s(E1)

Voice call through data channel (B) Transmission, control signal channel (D) is used to set up and manage the connection. When the call is established, a 64K synchronization channel is established and occupied, and the guidance call ends. Each B channel can establish an independent voice connection. Multiple B channels can be combined into a single high-bandwidth data channel through multiplexing.

The D channel can also be used to send and receive X.25 data packets and access the X.25 message network. (In fact, it is rarely widely used).

ISDN related technology and its implementation method

ISDN digital network ISDN switching system is the core of integrated service digital network. The system includes basic rate access (2B+D), primary rate access (23B+D/30B+D) and high-rate access subscriber line interface circuit, D channel processor, time division switching network, digital trunk, Packet processor call processing equipment, operation, management and maintenance equipment, common-channel signal processing equipment. The transition from multiple existing service networks to a single ISDN is a long process, so it is necessary to ensure the interconnection between ISDN and the existing communication network, which mainly includes the existing telephone network and other service networks (such as packet networks, etc.) And the communication between each ISDN network.

In order to adapt to the needs of different users and to meet the requirements of future communication business expansion, ISDN terminals should comply with all the original CCITT regulations and meet the requirements of multiple services. One terminal corresponds to multiple services, suitable for the requirements of different users. Therefore, the development of cost-effective ISDN terminals is the key to popularizing ISDN, and it is also a problem that developed countries are committed to solving in the process of developing ISDN. ISDN terminals that have been launched on the market currently have different combinations of functions, which can be divided into three types for enterprises and groups, for home users, and for public use according to their scope of application.

ISDN uses two signal systems: No. 1 digital subscriber signal system and No. 7 signaling system. Signaling System No. 1 is a brand-new signal system with comprehensive service capabilities designed for user/network interfaces; Signaling System No. 7 is an inter-office signal system adopted by the original digital telephone network. However, in order to meet the requirements of multiple services, ISDN's No. 7 signaling system must introduce functions such as ISDN user part and SCCP (signal connection control part).

ISDN services

ISDN provides users with three types of services, namely, bearer services, user terminal services, and supplementary services. The bearer service provides basic transmission functions and telecommunication functions; user terminal services include the communication capabilities provided by the network and the communication capabilities of the terminal itself; supplementary services are used to change or supplement the above two basic services. The use of supplementary services can provide many advanced functions. Brings great convenience to communication. However, the supplementary service cannot be provided to users alone, it must be provided together with the basic communication service.

Through several years of ISDN practice in the world’s telecommunications developed countries, the most important experience in developing ISDN is to develop ISDN applications and let users understand these applications. ISDN has a wide range of applications. The main application areas are local area network, multi-point screen sharing, video, voice/data integration, file exchange, remote communication, image, multimedia file access, computer-based caller number identification, etc. .

The status quo and development trend of ISDN

At present, narrowband ISDN technology has basically matured. Since ISDN was put into commercial use in various countries in 1988, during the development of ISDN, many problems such as ISDN coverage, interoperability, equipment price, and users' inadequate understanding of ISDN characteristics have caused the development of ISDN in some countries. As fast as people expect. But in recent years, the ISDN market in the world has seen a turnaround, and the growth rate of ISDN users is on the rise. The growth rate remains high. Japan and the United States are the first countries to open ISDN commercial services, and subscriber lines are increasing year by year. At the same time, many countries have accelerated ISDN interconnection between countries and opened up international ISDN services while building their own ISDN. Because narrow-band ISDN cannot comprehensively transmit broadband services such as high-definition television, high-speed data, and broadcast television, some countries with developed communication technologies have carried out research on broadband ISDN before the completion of the narrow-band ISDN field experiment. However, the research strategies and technical implementation approaches of broadband ISDN in various countries are not completely the same. The United States divides the research of broadband ISDN into two stages: the first stage focuses on data communication, and first realizes broadband local area network, municipal area network, and high-speed data network connecting these two networks; the second stage realizes ATM-based broadband ISDN. However, European countries and Japan's research on broadband ISDFN focuses on the integration of image, voice, and data. At present, all developed countries regard broadband ISDN as the long-term development direction of communication networks and have already put them into action. The research and development of key broadband ISDN technologies such as ATM (Asynchronous Transfer Mode), SDH (Synchronous Digital Sequence) and fiber subscriber loop, etc. And the application has been successful. Chinese enterprises have also made breakthroughs in the development and application of the above-mentioned products, and domestic equipment has been gradually adopted on domestic communication lines. Recently, as the ITU-T has stepped up research and formulation of relevant framework documents for the intelligent network, the intelligent technology of the network has developed the fastest. In order to welcome the advent of the multimedia communication era, the integration, intelligence, broadband and personalization of the network have received great attention. It is believed that the future information superhighway will be a broadband, highly intelligent, highly flexible network platform constructed by broadband ISDN that can fully meet the requirements of individual choices.

In short, the emergence of ISDN has solved the situation that various communication networks are independent of each other. It can provide both voice services and various non-voice services. As long as users apply for ISDN services, they can enter the integrated service digital network and use various communication services. But in ISDN to make various networks (including domestic various networks and international Internet) correctly connect and coordinate work, each communication network must be required to use the same signaling system.