ATM AAL Layers-Difference between AAL1,AAL2,AAL3,AAL4,AAL5



Refer Following links to subtopics on ATM tutorial:
ATM Network Architecture & Interfaces   ATM Protocol Stack  ATM services  ATM Switch  ATM Call Flow  ATM vs STM  ATM vs TDM  ATM versus Frame Relay  ATM AAL Layer Types 



This page compares ATM protocol layers AAL Type 1 to 5 i.e. AAL1, AAL2, AAL3, AAL4, AAL5 and mention difference between AAL1, AAL2, AAL3, AAL4, AAL5 ATM protocol layers. ATM Adaptation layers are classified based on their support for various service classes as well as following parameters:
• Timing between source and destination (required or not required)
• Bit rate (constant or variable)
• connection mode (whether connection oriented or connectionless)
• AAL service Classes- A/B/C/D

ATM-AAL Layers
Fig-1:ATM AAL Layers

AAL Layer in ATM is divided into two sublayers viz. Convergence Sublayer (CS) and Segmentation and Reassembly Sublayer(SAR) based on functionality of AAL layer. The function of ATM Adaptation layer in ATM protocol stack are summarized below:

CS sublayer performs following functions:
• management of lost and wrongly delivered ATM cells
• Timing recovery
• Interleaving

ATM protocol stack
Fig-2:ATM Protocol Stack

SAR sublayer performs following functions:
• Fragmentation of bit stream from upper layers into size equal to ATM cells for transmission to ATM layer in the stack.
• Reassembly of ATM cells into bit stream for delivery to upper layers.

The figure-2 depicts ATM protocol stack mentioning AAL layer. Refer ATM Protocol Stack➤.

ATM AAL1(AAL Type-1) Protocol Layer

AAL1, AAL Type-1
Fig-3:ATM AAL Type-1 (AAL1)

The figure-3 depicts ATM AAL1 (Type-1) protocol layer fields.

ATM AAL2(AAL Type-2) Protocol Layer

AAL2, AAL Type-2
Fig-4:ATM AAL Type-2 (AAL2)

The figure-4 depicts ATM AAL2 (Type-2) protocol layer fields.

ATM AAL3(AAL Type-3), AAL4(AAL Type-4) Protocol Layer

AAL3,AAL4, AAL Type-3-4
Fig-5:ATM AAL Type-3/4 (AAL3/AAL4)

The figure-5 depicts ATM AAL3/AAL4 (Type-3 and Type-4) protocol layer fields.

ATM AAL5(AAL Type-5) Protocol Layer

AAL5, AAL Type-5
Fig-6:ATM AAL Type-5 (AAL5)

The figure-6 depicts ATM AAL5 (Type-5) protocol layer fields.

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