Computer Network Tutorial

Introduction of Computer Network Types of Computer Network Network Topology Computer Networking Architecture Transmission Modes (Data Flow) Basic Networking Devices Integrate Services Digital Network (ISDN)


OSI Model TCP/IP Model

Physical Layer

Digital Transmission Analog Transmission Transmission Media Switching

Data Link Layer

Error detection and Error correction Data Link Control Multiple Access Aloha

Network Layer

Network Layer - Logical Address Address Mapping Unicast Routing Protocol

Transport Layer

Process to Process Delivery User Datagram Protocol Transmission Control Protocol Stream Control Transmission Protocol Session Layer and Presentation Layer

Application Layer

Domain Name System Application Protocol E-mail Cryptography


Classes of Routing Protocols Classification of Routing Algorithms Controlled Access Protocols in Computer Networks Differences between IPv4 and IPv6 Fixed and Flooding Routing Algorithms Advantages and Disadvantages of Fibre Optics Cable APIPA Difference between Active and Passive FTP Fiber Optics and its Types Method of Joining and Fusion of Fiber Optic Cable Define Framing in Computer Network Disadvantages of Computer Network Mesh Topology Diagram in Computer Network Ring Topology in Computer Network Star Topology in Computer Networks 4G Mobile Communication Technology Advantages and Disadvantages of LAN Advantages and Disadvantages of MAN Advantages and Disadvantages of WAN Application Layer in OSI Model Cyclic Redundancy Check Example Data link layer in OSI model Difference between Transport and Network Layer Hamming Code Example Network Layer in OSI Model Session Layer in OSI Model Transport Layer in OSI Model Two Port Network in Computer Networks Uses of Computer Networks What is Computer Network What is Framing in a Computer Network Advantages and Disadvantages of Bus Topology Difference between Star Topology and Bus Topology Subnetting in Computer Network Subnetting Questions and Answers What is Bus Topology What is Network Topology and Types in Computer Networks Access Control in Networking Basic Characteristics of Computer Network Benefits of SOCKS5 Proxy in Computer Networks Computer Network viva Questions Difference between BOOTP and RARP Difference Between Network Topologies and Network Protocols Difference between NFC and RFID Difference Between Point-to-Point Link and star Topology Network Differences Between MSS and MTU Differences Between Trunk Port and Access Port Different Modes of Communication in Computer Networks MIME Protocol in Computer Networks Modes of Communication in Computer Networks Network Attack in Computer Network Port Address in Networking Simplest Protocol in Computer Network Sliding Window Protocol in Computer Network Stop And Wait Protocol in Computer Networks TCP 3-Way Handshake Process in Computer Networks What is a Proxy Server What is APPN What is ICMP Protocol What is Point-to-Point Protocol What is Port Address in Networking What is the HDLC Protocol What is VRRP Protocol Difference Between Analog and Digital Signals Difference Between Hub and Repeater Difference between Repeater and Switch Difference Between Transparent Bridge and Source Routing Bridge Source Routing Bridge in Computer Networks Transparent Bridge in Computer Networks Transport Protocol in Computer Networks Types of CSMA in Computer Networks What is Wired and Wireless Networking Network Security in Computer Network Disadvantages of Extranet Difference Between TELNET and FTP Define Protocol in Computer Networks Guided Transmission Media in Computer Network What is a Gateway in a Computer Network IGMP in Computer Networks LAN Protocols in Computer Networks MAN Meaning in Computer Modulation Techniques in Computer Networks Switching in DCN TCP/IP Applications What is IGMP? What is Modem in Networking What is Non-Persistent CSMA Difference between Cell Splitting and Cell Sectoring Forouzen Computer Network Open Loop and Closed Loop Congestion Control Types of Cluster Computing WAP-Wireless Access Point What are the elements of the Transport Protocol Difference between Gateway and Switch Flow Control in Data Link Layer Body Area Network Flooding in Computer Network Token Ring in Computer Networks VoIP in Computer Networks What is Infrared Transmission Congestion Control Techniques Forward Error Correction (FEC) Switching Techniques What is Telnet in Computer Network What are the Types of IPv4 Addresses IEEE 802.6 (DQDB) IEEE 802.15.4 Technology What is HDLC (High-level Data Link Control)? What is SMS Hubbing in Telecom? Circuit Switching in Computer Networks Communication Satellites in Computer Networks Features of HTTP Protocol IMAP4 (Internet Message Access Protocol) Internet Services How to Set up a Wireless Router Internetwork Routing in Computer Networks Distributed Computing System Features of GSM The 802.11 MAC Sublayer Protocol What is IEEE 802.3? What are Hubs and Switches in Computer Networks? What is Modem in a Computer Network? What is multicasting in Computer Networks? GSM -The Mobile Station What is Network Server? Slotted Aloha in Computer Network What is Ethernet in Computer Networks What is Arpanet? Radio Access Network (RAN) TCP 3-Way Handshake Process PING SWEEP (ICMP SWEEP) Print Server Private IP Address Security Services in Computer Networks Protocol Data Unit (PDU) CSMA with Collision Avoidance (CSMA/CA) What is Gateway in Computer Network? Advantages of Networking Data Link Layer Design Issues DHCP in Computer Networks Internet Security Association and Key Management Protocol (ISAKMP) What is Switch Hub? Telnet Full form in Networking Multimedia Systems Quality of Service in Computer Networks What is Carrier Sense Multiple Access (CSMA)? What is Circuit Switching What is Duplex Network? What is Web Protocol Network LAN Technologies Classes in Computer Network Low-Density Parity Check (LDPC) Wireless Internet Service Providers(Wisps) What is Handshaking? Cache Server What Is WSN Network? Check Sum Error Detection Linear Bus Topology Functions of the Transport Layer Infrared Transmission in Computer Networks Digital Signal in Computer Network Digital Data Transmission in Computer Networks Define Checksum with Example Computer Network Security Requirements Brust Errors in Computer Network Back Side Bus (BSB) 2-Dimension Parity Check in Computer Network Router and Brouter Microwave Transmission in Computer Networks Magnetic Media in Computer Network A One-Bit Sliding Window Protocol CDMA-Near-Far Problem Reference Models in Computer Networks Uni-cast, Broadcast, and Multicast in Computer Networks Uses Of Bridges in Computer Networks What are Gateways in Computer Network?

IEEE 802.6 (DQDB)


DQDB (Distributed Queue Dual Bus), i.e IEEE 802.6 standard, is a MAN (Metropolitan Area Network) protocol. It is a bus network access control protocol that operates at a high speed across a shared media.

DQDB utilizes two unidirectional buses for transmission, enabling the concurrent transport of voice, video, and data traffic. Bandwidth allocation is achieved through time division multiplexing, where each device is assigned specific time slots for transmission.

One advantage of DQDB is its fault tolerance, facilitated by the presence of two separate buses. In case of a failure in one bus, communication can continue uninterrupted through the other bus.

The protocol supports speeds ranging from 34 to 55 Mbps and can span distances of up to 30 kilometers, making it suitable for connecting devices across a metropolitan area.

Directional Traffic

Every bus opposes the other and supports traffic in a single direction. The bus is depicted as having a square at the beginning and a triangle at the finish (Fig.1). While bus B travels from left to right (i.e., from station 5 to 1), bus A travels from right to left (i.e., from station 1 to 5).

Upstream and Downstream

The buses' direction of travel determines how the stations in the DQDB network are related to one another.

Examining bus A in Figure 1, where stations 1 and 2 are positioned upstream relative to station 3, while stations 4 and 5 are positioned downstream relative to station 3. In this instance, station 1 is at the head of bus A since there isn't an upstream station, and station 5 is at the end of bus A because it doesn't have a downstream station.


IEEE 802.6 (DQDB)

Fig. 1

Bus A's head, or station 1, creates an open slot for its usage. In a similar vein, bus B's head, or station 5, creates an open slot for bus B to use. Until the transmission station drops data into the empty slot and the intended destination reads the data, the empty slot moves along its bus.

As an illustration

Station 2 selects a slot on bus A since station 4 is downstream in bus A if it want to deliver data to station 4 (Fig. 1). There is a gap created by the head of bus A, or station 1. Station 2 inserts its address and data into the passing slot of the destination. After reading the address, Station 3 marks the slot as unread. It is recognized by station 4, which then receives the data, modifies the slot's status, and passes it along to station 5, where it is absorbed.

How do you reserve a slot?

A station at the end of the bus suffers because of the imbalance that might result in a lower quality of service. In order to send data downstream, a station must wait for the arrival of the unoccupied slot. Here is where the question of how to prevent an upstream station from manipulating the bus arises. Making a reservation at the station is the answer to this issue. Station 2 can reserve a seat on bus B for bus A here. In order to notify each station, it goes through that Station 2 is reserving a slot on Bus A, Station 2 places a reservation bit on a slot on Bus B. Every station is required to honor the downstream station's reservation and give the requested station the slot.

Advantages of IEEE 802.6 (DQDB)

Scalability: IEEE 802.6 (DQDB) is designed to scale efficiently, making it suitable for metropolitan area networks (MANs) covering large geographical areas. It can accommodate the expansion of network devices and users without significant performance degradation.

Dependability: The protocol offers high reliability and fault tolerance, crucial for maintaining uninterrupted communication within MANs. With redundant pathways and fault detection mechanisms, it ensures robust connectivity even in the event of failures.

Speed: IEEE 802.6 supports high-speed data transmission, ranging from 34 to 55 Mbps. This makes it ideal for multimedia applications such as video conferencing, online gaming, and high-speed data transfer in office or business networks.

Cost-effectiveness: DQDB can be implemented using existing LAN wiring infrastructure, reducing the need for additional investment in network infrastructure. This makes installation simpler and more cost-effective, especially for organizations looking to upgrade their networks without significant expenditure.

Disadvantages of IEEE 802.6 (DQDB)

IEEE 802.6 also has some disadvantages. The protocol is not suitable for long distance networks or large organizations because of its limited transmission reach and lack of data transfer capacity for high data transfer rates. Similarly, the convention does not preserve quality of services (QoS) for multimedia applications which may restrict its feasibility for some applications requiring high quality video or audio streaming.


IEEE 802.6 (DQDB) is a standardized communication system framework designed for metropolitan area networks (MAN's), offering fast, dependable, and efficient communication across a wide area. It is ideal for real-time applications, data transfer, and video conferencing due to its distributed queuing algorithm, dual-bus architecture, and token passing mechanism. Its dependability, scalability and cost-effectiveness make it an appealing choice for small and medium-sized organizations.

In spite of the fact that it has a few disadvantages, for example, restricted transmission range and data transmission bandwidth limitations for the exchange of data, it keeps on being a effective and flexible benchmark that affects the creation of modern communication systems. There will always be new alternatives as technology develops, but IEEE 802.6 (DQDB) remains a useful option for MANs.