ATM Adaptation Layer AAL

The AAL converts the large Service Data Unit (SDU) data packet of the upper layer to 48 bytes for the ATM cell pay load. The AAL is divided into two sublayers. They are convergence sublayer (CS) and the segmentation and Reassembly sublayer (SAR) as shown in Fig. 11.33.

Fig. 11.33. ATM adaptation layer.

ATM can be used for various applications. Therefore different types of AALs are needed to provide service to upper layer applications. The AALs are divided into four classes of traffic (class A, class B, class C and class D). Also AAL is divided into four types of AAL protocol (Type 1, Type 2, Type 3/4 and Type 5). Table 11.5 shows the service classification of ATM AAL.

Table 11.5. Service classification of ATM

Application type

Class A

Class B

Class C

Class D

AAL type

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