ATM is a connection-oriented fast packet-switching technology that combines the advantages of circuit-switching and packet-switching and is the standard transfer mode for B-ISDN. the IMA is a technique for reverse-multiplexing ATM.

In modern society, people need to transmit and process more and more information, and more and more kinds of information, in which the demand for new broadband services such as conference TV, high-speed data transmission, distance learning and so on is growing rapidly. The original various networks can only transmit one kind of service, such as telephone network can only provide telephone service, data communication network can only provide data communication service. This situation is inconvenient and uneconomical for both users and network operators. Therefore, the concept of ISDN (Integrated Services Digital Network) was proposed in the hope that a network could be used to transmit various services.

With the development and maturity of basic technologies related to communications, Asynchronous Transfer Mode (ATM) technology came into being. ATM is an asynchronous transfer mode in terms of credits, and the flow of information credits from any user does not have to be periodic.

ATM is a connection-oriented fast packet switching technology that combines the advantages of circuit switching and packet switching and is the standard transfer mode for B-ISDN (Broadband ISDN).The advantages of ATM technology are as follows:

• The use of optical communication technology improves the quality of transmission.
• Simplifies operations on network nodes and reduces network latency.
• Carrying multiple information media in a single main network, supporting multi-rate and multi-service communication services.
• Provide full QoS (Quality of Service) guarantee for real-time services.

Inverse Multiplexing for ATM (Inverse Multiplexing for ATM) is the process of inverse multiplexing a stream of higher-speed elements into multiple lower-speed physical links at the transmitter side, and then combining them into a single stream at the receiver side and delivering it to the ATM layer.

The advantages of IMA technology are as follows:

• Bandwidth saving and bandwidth convergence is achieved by multiplexing multiple lower speed links.
• Multiplexed links can be added or deleted at any time, and bandwidth configuration is flexible.

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