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Chapter Objectives

Chapter Objectives. After completing this chapter you will be able to: Describe the ATM Adaptation Layer Describe quality of service (QoS) categories Outline the function of the different AAL types and sublayers. CS. Adaptation Layer. SAR. Layer two. ATM Layer. TC. Layer one.

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Chapter Objectives

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  1. Chapter Objectives • After completing this chapter you will be able to: • Describe the ATM Adaptation Layer • Describe quality of service (QoS) categories • Outline the function of the different AAL types and sublayers

  2. CS Adaptation Layer SAR Layer two ATM Layer TC Layer one Physical Layer PMD The Adaptation Layer

  3. QoS Service Catagories • CBR Constant Bit Rate • VBR-RT Variable Bit Rate - Real Time • VBR-NRT Variable Bit Rate - Non-Real Time • ABR Available Bit Rate • UBR Unspecified Bit Rate • GFR Guaranteed Frame Rate (later)

  4. Class A Class B Class C Class D Timing between Required Not required source and destination Bit rate Constant Variable Connection mode Connection-oriented Connectionless Relevant Adaptation Layer AAL 1 AAL 2 AAL 3 AAL 4 AAL 5 ATM Service Classes • Classes as defined by ITU-T rec. I 362

  5. The use of a CS is not required by all AALs Higher layer data Etc. CS T T T H H H Adaptation Layer SAR H H General Principles of Adaptation

  6. Usage of Adaptation Layer • AAL is used to adapt a source application to ATM • ATM switching takes place in the ATM Layer. Destination Source Application Application ATM Network AAL AAL ATM ATM ATM ATM PHY PHY PHY PHY UNI NNI UNI

  7. AAL 1 47 bytes 47 bytes 48 bytes 48 bytes 53 bytes

  8. AAL 1 CRC CSI 3 bit 1 bit P SN 1 bit 3 bit 47 bytes 1 byte (8 bits) 47 bytes 48 bytes 48 bytes

  9. AAL 2 Samples User 3 User 1 User 2 Initial AAL2 header 47 bytes Secondary AAL 2 header 48 bytes ATM cell header ATM cell header 53 bytes

  10. 6 bits 5 bits User 1 User 2 HEC CID LI UUI 8 bits 5 bits 3 bytes (24 bits) 47 bytes AAL 2 1 bit SN Offset 6 bits P 1 bit 1 byte (8 bits) 48 bytes

  11. AAL 3/4 44 bytes 44 bytes 44 bytes 48 bytes 48 bytes 48 bytes 53 bytes

  12. Len Control BASize Type Btag ETag Pad Seg MID CRC Len Seq 48 bytes AAL 3/4

  13. AAL5 (SEAL) Higher Layer Protocol Data Unit (PDU). Possible maximum size of 65535 bytes. 8 byte trailer plus pad added, PDU now multiple of 48 bytes Pad Trailer 48 bytes 48 bytes 48 bytes 48 bytes 48 bytes 48 bytes 53 bytes 53 bytes 53 bytes

  14. 8 bytes CRC CPI Length UU 4 bytes 1 2 bytes byte AAL5 Trailer 8 byte trailer plus pad added, PDU now multiple of 48 bytes Pad Trailer 53 bytes

  15. GFC VPI VPI VCI VCI CLP VCI PTI HEC User cell 48-byte data field SDU bit EFCI or O&M cell AAL5 Transmission • AAL5 makes use of the PTI field in ATM cell header • Bit 1 = 1 indicates this cell carries the AAL5 trailer 1 0 0 0 0 0 0

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