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End-to-End DSL Architectures by Wayne C. Vermillion

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Summary

ATM is the de facto standard for DSL transport due to its small ATM cell size, scalability, multiprotocol capability, and standardization.

An ATM cell is 53 bytes long and consists of two parts: header and payload. The header is 5 bytes long and contains six fields: GFC, VPI, VCI, PTI, CLP, and HEC. The GFC field is used for flow control information across the UNI link. The VPI/VCI fields are used for destination addressing. The PTI identifies the cell as system or user data. The CLP identifies low/high discard priorities. The HEC provides header verification.

ATM provides for multiple CoSs, but only UBR and VBR are currently used in DSL networks. Within each CoS are additional traffic parameters to define the level of service (such as ...

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