Introduction
2B+D is a simple way to express the basic speed interface of Integrated Services Digital Network (ISDN). The 2B+D interface includes two voice channels B1 and B2 with a rate of 64kbit/s, and a D signaling channel with a rate of 16kbit/s.
B-Channel: Transmit data at a rate of 64Kbps per channel (or bundle two channels together at a rate of 128Kbps); each B-Channel channel is like a "pipe", Two B-Channel channels can be bundled together to download files at a faster speed. When an external call comes in, you can temporarily suspend the file download of one of the channels to give a new call request without terminating the entire download process. You can choose to resume the download after the new call request communication ends. This communication process is completely controlled by another separate D-Channel.
D-Channel: ISDN D-Channel communication is mainly used to transmit control signals, such as establishing and terminating B-Channel communication, checking whether there is an available B-Channel, and providing some useful user information ( Such as the phone number of the other party). D-Channel uses a packet-switched connection method, which makes it very suitable for intermittent data transmission. At the same time, this transmission method greatly reduces the time required to establish a connection (usually only 2 to 3 seconds, while ordinary modem protocol handshake may require 30 seconds), the transmission rate of D-Channel is generally 16Kbps (BRI ISDN) or 64Kbps (PRI ISDN). Only two devices are allowed to use simultaneously on a BRI line.
The Chinese name of ISDN (Integrated Service Digital NeTwork) is Integrated Service Digital Network, which is popularly known as "one-line communication". Existing in the telephone network switching and relaying has basically realized digitization, that is, all the digitalization from transmission to exchange between the telephone office and the telephone office is realized, but from the telephone office to the user, it is still analog, and the only thing provided to the user is The simple business of telephone. The realization of the integrated service digital network enables the use of a pair of copper wires between the telephone office and the users, which can also be digitized, and provide users with a variety of services. In addition to making calls, it can also provide such as video phones and data communications. , Conference TV and other services, so that multiple services such as telephone, fax, data, image, etc. are integrated in a unified digital network for transmission and processing.
Performance
There are two types of integrated service digital networks, narrowband and broadband. The narrowband integrated service digital network provides users with two interfaces: basic rate (2B+D, 144kbps) and primary group rate (30B+D, 2Mbps). The basic rate interface includes two independently working B channels (64Kbps) and a D channel (16kbps). The B channel is generally used to transmit voice, data and images, and the D channel is used to transmit signaling or packet information. Broadband can provide users with communication capabilities above 155Mbps.
Comprehensive communication services: Using one subscriber line, you can make calls and send and receive faxes while surfing the Internet, just like two telephone lines. By configuring the appropriate terminal equipment, you can also realize the video conferencing function to minimize the distance between you and your relatives and friends.
High-speed data transmission: In the digital subscriber line, there are multiple multiplexed channels, which are 2-8 times higher than the data transmission rate in the existing telephone network.
High transmission quality: Due to the end-to-end digital transmission, the transmission quality is significantly improved. The sound distortion at the receiving end is very small. The bit error characteristics of data transmission are at least 10 times better than that of telephone lines.
Flexible and convenient to use: You only need a network access interface and a unified number to get the various services you need to use from the network. Unified interface.
Appropriate cost: Because a single network is used to provide multiple services, ISDN greatly improves the utilization of network resources and provides users with services at a low cost; at the same time, users do not need to purchase and install different The equipment and lines are connected to different networks, so that various services can be obtained with only one interface, which greatly saves investment.
2B+D and 30B+D
There are two types of integrated service digital networks, narrowband and broadband. The narrowband integrated service digital network provides users with two interfaces: basic rate (2B+D, 144kbps) and primary group rate (30B+D, 2Mbps). The basic rate interface includes two independently working B channels (64Kbps) and a D channel (16kbps). The B channel is generally used to transmit voice, data and images, and the D channel is used to transmit signaling or packet information. Broadband can provide users with communication capabilities above 155Mbps.
The hardware design of the 2B+D digital terminal
The 2B+D digital terminal is a design proposed after a comprehensive and detailed analysis of the current situation of the terminal equipment used by domestic ships according to the needs of users The program adopts new key technologies (using MPC850 CPU, MC145572U interface transceiver, MC145480 codec integrated circuit chip, and IDL bus connection mode to form a highly integrated U interface ISDN terminal to complete voice and data terminal functions) . Improve the speed and quality of communication, and expand the range of communication.