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Protocols in multi-service networks
Protocols in multi-service networks

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4.2.3 ATM adaptation layer

The basic function of the ATM adaptation layer is to convert the user data supplied by higher layers into 48-byte blocks of data. The ATM adaptation layer is divided into two sub-layers – the convergence sub-layer, and the segmentation and re-assembly sub-layer. The convergence sub-layer provides services to higher layers through a set of protocols, but I do not need to describe these here. The segmentation and re-assembly sub-layer separates the messages from the convergence sub-layer into ATM cells. Each of the two sub-layers adds some protocol information, which is transported in the payload of ATM cells as illustrated in Figure 29.

Figure 29
Figure 29 ATM adaptation layer functions (Source: based on Tanenbaum, 1996, Figure 6.38)