IEEE 802.6 (DQDB)

IEEE 802.6 is a standard for Distributed Queue Dual Bus (DQDB) network. DQDB is a MAN (Metropolitan Area Network) technology that uses two unidirectional buses to provide a two-way communication path between stations in a network.

Architecture

The DQDB network architecture consists of two unidirectional buses, each carrying traffic in opposite directions. The network is divided into multiple logical rings, with each ring having a maximum of 512 stations. The two buses are used for transmission and reception of data packets in each ring.

The DQDB network uses a distributed queueing system to manage network congestion. The stations in the network are responsible for managing their own queues and scheduling transmissions. The network uses a token-passing mechanism to grant stations the right to transmit data packets.

Benefits

DQDB provides several benefits, including:

• Higher bandwidth: DQDB supports a high data rate of up to 155 Mbps.
• Scalability: DQDB is highly scalable, allowing multiple rings to be interconnected to form a larger network.
• Fault tolerance: DQDB is designed to be fault-tolerant, with multiple routing options in case of a failure.
• Cost-effectiveness: Because DQDB uses existing copper telephone cables, it is cost-effective compared to other MAN technologies.

Implementation

DQDB is implemented using two types of components: network interface cards (NICs) and concentrators. NICs are installed in each station to provide access to the network. Concentrators are used to connect multiple rings and extend the reach of the network.

In terms of protocol architecture, DQDB uses OSI layer 1 (physical layer) and layer 2 (data link layer) protocols. The physical layer uses a Manchester encoding scheme, while the data link layer uses a modified CSMA/CD (Carrier Sense Multiple Access with Collision Detection) protocol.

Conclusion

In summary, IEEE 802.6 is a standard for DQDB network, which provides high bandwidth, scalability, fault tolerance, and cost-effectiveness. The architecture of the network is based on two unidirectional buses and a distributed queueing system. DQDB is implemented using NICs and concentrators and uses OSI layer 1 and layer 2 protocols.