Introduction to ATM asynchronous transmission

ATMIt is a data transmission technology. It is a group exchange and multiplexing technology based on cells. It is a universal connection-oriented Transmission Mode Designed for multiple businesses. ATM is suitable for LAN and WAN, with high-speed data transmission rate and supports communication of many types of audio, Data, fax, real-time video, CD quality audio and images.

ATMAsynchronous Transfer Mode) asynchronous transmission Mode:

1) ATM was invented Based on circuit switching and group switching. It is intended for connection and Group Sending, and the effect is really good.

2) ATM uses cell as the basic unit for information transmission, reuse, and exchange. Therefore, it is a cell-based connection-oriented multiplexing and exchange technology.

3) the length of an ATM cell is fixed to 53 bytes. Five bytes constitute the cell header and contain the address information and other control information of the cell. The remaining 48 bytes are the payload.

4) ATM transmits cells through virtual circuits, and each virtual Circuit VCVirtual Circuit uses virtual Path Identifier (VPIVirtual Path Identifier) and virtual Channel Identifier VCIVirtual Channel Identifier (VCIVirtual Channel Identifier) for identification. A pair of VPI/VCI identifies the links of two directly connected ATM nodes. When a connection is released, the VPI/VCI is also released.

ATM features:

1) fixed to 53 bytes, facilitating hardware processing and practice high-speed switching.

2) connection-oriented to ensure service quality

3) the asynchronous time division multiplexing method improves the channel utilization and ensures the quality of Service (QOSQuality of Service ).

However, it provides a series of idealized technologies for connection and grouping at the same time, high bandwidth, good QOs, and so on, which require complex ATM devices, this makes it difficult to develop, configure, manage, and troubleshoot the ATM system. The most important thing is that the ATM equipment is very expensive, and the noble image of the ATM is obviously not recognized by the market, therefore, due to the impact of flexible IP technology and simple and inexpensive network devices, it gradually withdrew from the competition!

Two ATM exchange methods:

Circuit Switching: Circuit Switching refers to a dedicated communication link between two sites. This chain routes links between many network nodes. Each link has a dedicated channel for this connection. The most common example is the telephone network. However, although its communication quality is well guaranteed, it cannot share bandwidth, resulting in a waste of bandwidth.

Group exchange: group exchange transmits data in groups by reusing statistics. Each group contains data and control information, which is then sent to the vro in the network. The vro accepts and stores the group and forwards it to the next node. As a result, the service quality cannot be guaranteed and the delay is high.

ATM hierarchy:

Several layers of ATM:

1) control layer: This layer is responsible for generating and managing signaling requests. It mainly uses Signaling Protocols to establish, monitor, and remove connections.

2) user level: responsible for managing data transmission.

3) management layer: includes level management and plane management. Level Management: responsible for the management of layers in each plane, with a level structure corresponding to other layers; plane management: Responsible for system management and communication between various planes.

The ATM reference model is divided into the following four layers:

1) physical layer: similar to the OSI reference model, it mainly manages media-related transmission.

2) ATM layer: it is combined with the ATM Adaptation Layer and similar to the data link layer of the OSI reference model. Responsible for sharing virtual circuits of physical links and cell transmission in the ATM network.

(3) ATM Adaptation Layer: AALATM Adaptation Layer): it is combined with the ATM Layer and is similar to the data link Layer of the OSI reference model. The ATM adaptation layer is mainly responsible for isolating the high-level protocol from the detailed processing of the ATM. It prepares the conversion from user data to cells and splits the data into 48-byte cell payload.

4) Senior management: accept user data, arrange it into data packets, and then hand it to the ATM Adaptation Layer for processing.

In general, ATM can be used as the company's backbone network to simplify network management and eliminate complex problems caused by network interconnection between different addressing schemes and routing selection mechanisms.