What is a 2B D interface?

is also commonly called subscriber line interface circuit (slic). According to the different switch systems and application environments, there are many types of subscriber circuits. For program-controlled private branch exchange, there are mainly analog subscriber line circuits (ALC) connected with analog telephones and digital subscriber line circuits (DLC) connected with digital telephones and data terminals (or terminal adapters).

ISDN originated in 1972, but it was not clearly defined until 198. CCITT defines ISDN as follows: "ISDN is a variety of telecommunication services based on the integrated digital telephone network (IDN), and users can access the network through a limited set of standardized multi-purpose user-network interfaces." According to the above definition, the definition of ISDN can be summarized as follows:

◆ ISDN is a communication network developed on the basis of integrated digital telephone network (IDN);

◆ ISDN supports end-to-end digital connection;

◆ ISDN supports various communication services such as telephone and non-telephone;

◆ ISDN provides a standard user-network interface, which enables users to access.

ISDN is developed on the basis of IDN. The telecommunication network using digital switching and digital transmission (PCM) is called IDN for short. In IDN, communication is carried out in the form of digital signal and time division. Digital signals such as data can be transmitted directly in the digital network, while analog signals such as voice and image must be transmitted after analog/digital conversion at the sending end, and communication can be completed after digital/analog inverse conversion at the receiving end. The wide application of pulse code modulation (PCM) system and program-controlled switching equipment has laid the foundation for the development of ISDN. The access of integrated digital network is based on 64kbit/s, and ISDN uses the transmission rate of 64kbit/s to provide users with end-to-end digital connection.

the biggest difference between p>ISDN and other networks is that it can provide end-to-end digital connection. The so-called end-to-end digital connection means that the transmission from one user terminal to another is all digital, including the subscriber line. However, in the traditional telephone network, the transmission from the user terminal to the switch is analog. When users communicate digitally, they must use a Modem for digital/analog conversion before transmitting on the subscriber line. Moreover, at the opposite end, they need to use the Modem for inverse signal conversion. ISDN has changed the state of the analog subscriber loop in the traditional telecommunication network, making the digitalization of the whole network a reality, and users can obtain excellent digital performance.

ISDN supports a wide range of services, not only voice services, but also non-voice services such as data, images and faxes. It can also provide instant connection when users need communication, and it can also provide dedicated line connection.

ISDN can provide a standard user-network interface, which is the technical key to the development of ISDN. It can integrate all kinds of different terminals into ISDN network through standard interfaces, so that a pair of universal subscriber lines can connect up to 8 terminals, and provide a variety of communication integrated services for multiple terminals.

Characteristics of p>ISDN

(1) Compatibility of various services. A pair of subscriber lines can provide telephone, fax, data communication for videotex and other services. If users need higher-speed information, they can use the primary group user interface to connect the PBX, videophone, conference TV or computer local area network. In addition, ISDN users can choose the information rate and switching mode according to their needs during each call.

(2) Digital transmission ISDN can provide end-to-end digital connection, that is, the channel between terminals has been completely digitized, with excellent transmission performance and fast information transmission.

(3) The key for ISDN to provide a variety of services is to use a standardized user interface. The interface has a basic rate interface and a primary group rate interface. The basic rate interface has two 64kbit/s information paths and one 16kbit/s signaling path, which is called 2B+D for short. The primary group interface has 3 64kbit/s information paths and one 64kbit/s signaling path, which is referred to as 3B+D for short. The standardized interface can ensure the intercommunication between terminals. An ISDN basic rate user interface can connect up to 8 terminals, and it uses standardized sockets, which is easy for all kinds of terminals to access.

(4) It is convenient to use. Users can arbitrarily combine different types of terminals on a pair of subscriber lines according to their needs. For example, they can connect a telephone, a fax machine and a PC together, and can make phone calls, send faxes or transmit data at the same time.

(5) Terminal Mobility The terminal of ISDN can suspend the ongoing communication during the communication, and then resume the communication when necessary. This performance brings great convenience to users. Users can move the terminal to other rooms after communication is suspended, and then resume communication after plugging in the socket. At the same time, you can also set the identity password to resume communication.

(6) The low-cost ISDN is developed through the digitalization of the telephone network, so it can be formed by adding or changing some equipment in the existing communication network. ISDN can integrate various services in one network to improve the utilization rate of the communication network. In addition, ISDN saves the investment of subscriber lines and can obtain greater economic benefits.

Advantages of p>ISDN over traditional telephones

1) Integrated communication services: one telephone line can be used as two telephones, and two telephones can be used to dial, answer and send and receive faxes while surfing the Internet; You can also use two computers to surf the Internet at the same time. By configuring appropriate terminal equipment, the function of videophone or conference TV can also be realized.

2) fast calling speed: at present, the Internet transmission rate through Modem is low and the quality is poor; ISDN call connection speed is fast, and the subscriber line transmission rate is 64Kbps or 128Kbps. It takes about 4 seconds to surf the Internet with Modem and only 3-1 seconds with ISDN.

3) High transmission quality: ISDN adopts end-to-end digital transmission, and the voice distortion at the receiving end is very small, while the bit error rate performance of data transmission is at least ten times better than that of traditional telephone lines.

4) Flexible and convenient use: users can get a variety of services from the network by using a network interface and a common telephone number, and users can connect different kinds of terminals on this interface.

5) Appropriate cost: As a single network is used to provide various services, the utilization rate of network resources is improved, and services can be provided to users at low cost.