Distributed Queue Dual Bus (IEEE 802.6 DQDB)

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DQDB Network Structure

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DQDB Application: As A Backbone Network

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DQDB Based Metropolitan Area Networks

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DQDB Node Structure

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DQDB Access Structure (Or-Write Circuit)

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Looped Bus Structure of a DQDB Network

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Network Reconfiguration Examples

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Slot Structure (Fixed Length, 53 Octets)

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Queued-Arbitraed (QA) Access Method

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l Busy Bit

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l Request Bit

Queued-Arbitrated (QA) Slot Access

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When a node does not have a QA segment to send on Bus A

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Queued-Arbitrated (QA) Slot Access

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When a node does have a QA segment to send on Bus A

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QA Access Operation Example

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A sub-network consisting of five nodes queuing for access RQ: Request Counter CD : Countdown Counter All slots passing on bus A are busy Nodes 5, 2, and 3 queue for access in that order

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QA Access Operation Example

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QA Access Operation Example

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MAC Connectionless Service PDU

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Segmentation of an IMPDU into DMPDUs

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DMPDU to Slot

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MID Page Allocation Protocol

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MID Page Allocation Protocol

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Address Format

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Isochronous Channel Concepts and PA Slot Format

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Isochronous Channels Examples

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Isochronous Channels Examples

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Establishment of Isochronous Channels

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Layer Management Message Flows at the Originating Site

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Layer Management Message Flows at the Originating Site

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Layer Management Message Flows at the Originating Site

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DQDB Access Method Characteristics

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Provides two modes of access:

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Non-Arbitrated Access (Pre-Arbitrated, PA) Queued-Arbitrated Access (QA) PA access supports Isochronous connection-oriented services QA access supports Asynchronous services QA access supports three priority levels QA access provides low access delays at low subnetwork loading and little wasted capacity at high loading The relative throughput that can be supported by QA access is independent of sub-network size or bit rate Operates as a network in a size of 50km (diameter) Slotted structure compatible with broadband-ISDN

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