N-GEN Communications Web-based Seminars ©NGCS

Seminar - An Overview of Communications Technologies

Module 4 - ATM Technology                                                                                                                      Slide 22 of 46 _________________                                                                                  __________

                                                 ATM Adaptation Layers

                                        ATM Adaptation Layer 1 (AAL1)

                                        ATM Adaptation Layer 2 (AAL2)

                                        ATM Adaptation Layer 3/4 (AAL3/4)

                                        ATM Adaptation Layer 5 (AAL5)

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The ATM Adaptation layers, AAL1, AAL2, AAL3/4 and AAL5 provide an interface between user data and an ATM network. The ATM adaptation layer resides in the end-stations, not in the ATM switches, and is responsible for segmenting the information into 53 byte cells. It is also responsible for reassembling it back to its original form at the receiving end.

ATM Adaptation Layer 1 ( AAL1) - Suitable for Voice, Video, DS-1 and DS-3 information. A customer subscribes to a Constant Bit Rate (CBR) Service.

ATM Adaptation Layer 2 (AAL2) - Suitable for compressed video information.

ATM Adaptation Layer 3/4 (AAL3/4) - AAL3 is suitable for connection-orientated services like Frame Relay and X.25. AAL4 is suitable for connectionless services like IP and SMDS. It is suited to applications like LAN file transfers and video conferencing.

ATM Adaptation Layer 5 (AAL5) - Similar to AAL3/4 but with fewer features. It supports both Connection-orientated and connectionless data. AAL5 is used to carry Variable Bit Rate (VBR), Unspecified Bit Rate (UBR), Available Bit Rate (ABR) services data traffic.