Inverse Multiplexing for ATM

Inverse Multiplexing for ATM ( IMA ) is a standardized data transmission method from the telephony. Note that the data in the form of ATM cells over a bunch of ISDN lines by E1 or DS1/T1-Standard be transferred.

In parallel transmission over multiple lines, the data is divided by demultiplexer and afterwards composed to match again with a multiplexer. IMA allows for a stepwise increase or decrease the transmission capacity when multiple E1/DS1-Leitungen are available and it is not possible using a different transmission technology such as fiber optics. The maximum number of lines is 32, which / s corresponds to a total rate of 64 or 48 Mbps.

The draft standard was submitted by the ATM Forum in July 1997 and was released in the final version 1.1 in March 1999. It leads the IMA protocol that is part of the physical layer, which is below the ATM layer.

Transmitting the ATM cells is performed in a round robin fashion, and will be transparent to the terminals on the two sides. The line bundle is called the IMA group, the individual lines as IMA links. The cell stream is divided into IMA frame with usually 128 cells. IMA each frame contains a cell, the ICP cell ( IMA Control Protocol) with the group information and the link states of the sendenen side.

The addition or removal of links is possible without cell loss. An interruption of a line is automatically recognized by the IMA layer, which then automatically takes out the link from the link control. If the line is usable again, the link is re-enabled.

IMA will, inter alia, used in mobile networks to connect base stations.