AS/NZS 4802.6:1996

Specifies a high-speed shared medium access protocol for use over a dual, counter flowing, unidirectional bus network. This includes the physical layer, logical link control and medium access control sublayers. This Standard is identical with and has been reproduced from ISO/IEC 8802-6:1994.

This part of ISO/IEC 8802 for a Distributed Queue Dual Bus (DQDB) subnetwork of a metropolitan area network (MAN) defines a high-speed shared medium access protocol for use over a dual, counter-flowing, unidirectional bus subnetwork. This International Standard specifies the Physical Layer and DQDB Layer required to support- Logical Link Control (LLC) Sublayer, by a connectionless Medium Access Control (MAC) Sublayer service provided to support an LLC Sublayer in a manner consistent with other parts of this ISO/IEC 8802 series of International Standards.This part of ISO/IEC 8802 also specifies additional DQDB Layer functions as a framework for other services. In this edition of the standard, they are provided for completeness as part of the overall architecture; their implementation is not required for conformance.These additional functions will support- Isochronous Service Users (ISUs), by a connection-oriented service, which may be used to transport isochronous data; for example, conventional digitized voice.- Connection-Oriented Data Service Users, by an asynchronous, connection-oriented service, which may be used to transport bursty data; for example, signalling.The scope of this part of ISO/IEC 8802 is shown diagrammatically in figure 1-1.The DQDB Layer supports these services by employing the following access methods:- A Queued Arbitrated access method, with three priority queues for medium access arbitration and fixed-length slots for data transfer. Each priority level provides distributed queue access for the support of connectionless MAC service and connection-oriented data service.- A Pre-Arbitrated access method, which uses assigned octet positions in particular slots for the transfer of individual octets of data. This access method supports isochronous connection-oriented services.The Queued Arbitrated access method uses fixed-length slots for data transfer. This transfer mechanism is enhanced by a MAC convergence function to the service expected by the LLC Sublayer. The MAC convergence function is defined in this part of ISO/IEC 8802.This part of ISO/IEC 8802 defines the DQDB Layer functions to allow access to the medium to read and write data to support the isochronous service and the connection-oriented data service. The signalling procedures for establishing, maintaining, and clearing a connection are outside the scope of this part of ISO/IEC 8802.1The Physical Layer is defined to allow the use of different underlying transmission systems. This International Standard supports a DS3 interface operating at 44.736 Mbit/s, as specified in ANSI T1.102 2and T1.107. It also supports transmission systems based on CCITT Recommendation G.703 operating at 2.048 Mbit/s, 34.368 Mbit/s, and 139.264 Mbit/s, and Synchronous Digital Hierarchy (SDH) transmission systems operating at 155.520 Mbit/s, as specified in CCITT Recommendations G.707, G.708, and G.709. Other appropriate media and transmission rates may be considered for standardization in the future.Each transmission system may need to be enhanced to provide the Physical Layer service that is required by the DQDB Layer. This enhancement function, if required, is provided by a suitable Physical Layer Convergence Procedure (PLCP). This part of ISO/IEC 8802 will define a PLCP for each transmission system that is supported.

First published in Australia as AS 4802.6-1992.
Jointly revised and designated AS/NZS 4802.6:1996.