Asynchronous Transfer Mode (ATM)

Asynchronous Transfer Mode (ATM) is a data transmission technology, is the realization of B-ISDN core technology of the business. ATM is a cell-based packet switching and multiplexing, it is a business designed for a variety of common connection-oriented transport mode. It is suitable for LAN and WAN, which has high-speed data transfer rate and support the many types such as voice, data, fax, real-time video, CD quality audio and video communication.
ATM LAN or WAN, in the transmission of voice, video and data broadband technology. It is a cell relay technology, data packet size is fixed. You can be thought of as a kind of cell transport equipment, able to block from a device through the ATM switching equipment to another device. All have the same size cell, unlike frame relay and LAN system data packet size variable. Use the same size cell can provide a way to ensure that applications are expected and required bandwidth. As cars have to wait long in the busy intersection as the truck turns, variable-length packet switching equipment at easily cause traffic delays.
ATM connection-oriented transmission, the data into fixed length cells, through the exchange of virtual connections. Set ATM switching, multiplexing, transmission as a whole, in the complex asynchronous time division multiplexing is used to spend way, through information, or headers first distinguish between different channels.
ATM truly circuit switching and packet switching dual nature:
ATM connection-oriented, it requires both sides to establish a connection in the communications, telecommunications signaling the end and then removed from the connection. But it rejected the use of a synchronous circuit-switched time division multiplexing, switching asynchronous time division multiplexing, send and receive sides of the clock can be different, more efficient use of bandwidth.
ATM transmission unit is a fixed length 53byte the CELL (cell), where 5B is the cell header, the cell used to carry control information; 48B for the cell body, is used to load the user to distribute information. Header section contains a selected route using the VPI (virtual path identifier) / VCI (virtual path identifier) information, so that it has the characteristics of packet switching. It is a high-speed packet switching, the agreement on the second floor will OSI error correction, flow control functions transferred to the intelligent terminal to complete, reducing the network delay and improve the exchange rate.
ATM switching equipment is an important part of that can be used within the organization Hub, quickly transfer data packets from one node to another node; or as wide-area communications equipment, rapid transfer between remote LAN ATM cell. Ethernet, Fiber Distributed Data Interface (FDDI), token ring network with shared LAN and other traditional media, only one node at any one time can be transmitted, and ATM provides a connection between any node, the node can transmit simultaneously. Information from different nodes into a cell by multiplexing streams. In this system, ATM switches can be providers of public services within an organization owned by or part of a network.
The ATM network consists of ATM switches interconnected structure, there is the switch and the terminals, switches and switch between the two connections. Therefore, the switch supports two types of interfaces: the user interface and network UNI (Universal Network Interface) and network node interface between NNI. Corresponding to two types of interfaces, ATM cell has two different cell header.
In the ATM network introduces two key concepts: VP (Virtual Path) and VC (virtual path), which is used to describe the one-way transmission of ATM cell routing. A physical link can be reused a number of virtual channels, each virtual channel and can multiplex multiple virtual path, and with the same identifier to identify that the VPI and VCI. VPI and VCI individually numbered, VPI and VCI together can uniquely identify a virtual path.
Between two adjacent switching node cell of the VPI / VCI value of the same, the two VP nodes form a chain and between the VC chain. When the cell through the switching nodes, VPI and VCI to make corresponding changes. VPI and VCI in a separate makes no sense, only the link, form a chain and VC VP chain, before the formation of a meaningful link. In the ATM switch, a virtual connection table, each of which contains the physical port, VPI, VCI value, the table is in the process of establishing virtual circuits generated.
ATM backbone network for the company, can simplify network management, eliminating a lot of the different addressing scheme and routing mechanism for network interconnection issues arising from the complex. ATM hub can provide any two-port hub connection, and with the connected device type. The address of these devices have been pre-transformation, for example, easily from one node to another node sends a message, even without considering the type of network node. ATM management software enables users to move their place of physical workstation is very convenient.
ATM technology can be done through the corporate headquarters and branch offices and corporate local area network connectivity, enabling data transfer within the company, corporate mail services, voice services, etc., and through the United INTERNET e-business applications. ATM uses statistical multiplexing technology and because, and the access bandwidth of the original break 2M, to 2M-155M, therefore suitable for high-bandwidth, low latency and high data burst applications.
ATM is a better support for multimedia messaging technology.
Its characteristics: cell-based packet switching technologies; rapid exchange technology; connection-oriented cell switching; reservation bandwidth.
The advantage: lessons circuit switched real time, the advantages of packet switching flexibility; to take fixed-length packet (cell) as the transmission and exchange units; with excellent quality of service; the current maximum speed of 10GB / S, will reach 40GB / S.
The downside: the letter heads of the Ministry of too much overhead; technically complex and expensive.