DQDB PROTOCOL PDF

In telecommunication , a distributed-queue dual-bus network DQDB is a distributed multi-access network that a supports integrated communications using a dual bus and distributed queuing, b provides access to local or metropolitan area networks , and c supports connectionless data transfer , connection -oriented data transfer, and isochronous communications, such as voice communications. IEEE The DQDB may be thought of as two token rings, one carrying data in each direction around the ring. They both settled on essentially a byte data frame with a 5-byte header. In the DQDB algorithm, a distributed queue was implemented by communicating queue state information via the header. Each node in a DQDB network maintains a pair of state variables which represent its position in the distributed queue and the size of the queue.

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IEEE It can be defined as a high speed shared medium access control protocol that is used over a bus network. It has two unidirectional buses, for controlling purposes, where the bus can carry data, video, and voice over a network with bandwidth being allocated as per time slots.

The advantage of using the paired bus is that it is used to tackles failure configuration. It can be extended up to 30 miles at Mbps. Directional Traffic: Each bus support traffic in only one direction and are opposite to one another. The start of the bus being represented as a square and the end of the bus being represented as a triangle Fig. Bus A traffic moves from right to left i. Upstream and Downstream: The relationship of stations of the DQDB network depends on the directional flow of traffic of the buses.

Considering bus A in Fig. Here in bus A, station 1 is head of the bus as there is no upstream station and station 5 has no downstream station and it is regarded as to end of bus A. Working: The head of the bus A i. Similarly, the head of bus B i. The empty slot travels down its bus until the transmission station drops data into it and intended destination reads the data.

For example: If station 2 wants to send data to station 4 Fig. The head of the bus A i. Station 3 reads the address and passes the slot as unread. Station 4 recognizes its address, reads the data and changes the status of the slot and passes it along with station 5 where it is absorbed. How slot reservation is done? To send data downstream, a station must wait for the arrival of the unoccupied slot, but here the question arises that how to stop an upstream station from manipulating the bus due to which the station near the end of the bus suffers, as the imbalance can lead to degraded quality of service.

The solution to this problem is to do a reservation at the station. Here station 2 can make a reservation for bus A on bus B. Station 2 sets a reservation bit on a slot on bus B to tell each station it passes through, that the station is reserving a slot on bus A.

All the station must respect the reservation of downstream station and leave the slot for requested station. GeeksforGeeks has prepared a complete interview preparation course with premium videos, theory, practice problems, TA support and many more features. Please refer Placement for details. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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IEEE It can be defined as a high speed shared medium access control protocol that is used over a bus network. It has two unidirectional buses, for controlling purposes, where the bus can carry data, video, and voice over a network with bandwidth being allocated as per time slots. The advantage of using the paired bus is that it is used to tackles failure configuration.

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