Which of the following is a distributed multi-access network that helps in supporting integrated communications
using a dual bus and distributed queuing?
Correct Answer: C
In telecommunication, a distributed-queue dual-bus network (DQDB) is a distributed multi-access network that
helps in supporting integrated communications using a dual bus and distributed queuing, providing access to
local or metropolitan area networks, and supporting connectionless data transfer, connection-oriented data
transfer, and isochronous communications, such as voice communications. IEEE 802.6 is an example of a
network providing DQDB access methods. Answer option B is incorrect. A Token Ring network is a local area
network (LAN) in which all computers are connected in a ring or star topology and a bit- or token-passing
scheme is used in order to prevent the collision of data between two computers that want to send messages at
the same time. The Token Ring protocol is the second most widely-used protocol on local area networks after
Ethernet. The IBM Token Ring protocol led to a standard version, specified as IEEE 802.5. Both protocols are
used and are very similar. The IEEE 802.5 Token Ring technology provides for data transfer rates of either 4 or
16 megabits per second.
Answer option A is incorrect. The IEEE 802.2 standard defines Logical Link Control (LLC). LLC is the upper
portion of the data link layer for local area networks.
Answer option D is incorrect. Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) is an access
method used by wireless networks (IEEE 802.11). In this method, a device or computer that transmits data
needs to first listen to the channel for an amount of time to check for any activity on the channel. If the channel
is sensed as idle, the device is allowed to transmit data. If the channel is busy, the device postpones its
transmission. Once the channel is clear, the device sends a signal telling all other devices not to transmit data,
and then sends its packets. In Ethernet (IEEE 802.3) networks that use CSMA/CD, the device or computer
continues to wait for a time and checks if the channel is still free. If the channel is free, the device transmits
packets and waits for an acknowledgment signal indicating that the packets were received.
