In serial data transmission, one bit is sent after another (bit-serial) on a single transmission line. It is the
simplest method of transmitting digital information from one point to another. This transmission is suitable for
providing communication between two participants as well as for multiple participants. It is used for all long-
haul communication and provides high data rates. It is also inexpensive and beneficial in transferring data over
long distances.
Answer option D is incorrect. In parallel data transmission, several data signals are sent simultaneously over
several parallel channels. Parallel data transmission is faster than serial data transmission. It is used primarily
for transferring data between devices at the same site. For instance, communication between a computer and
printer is most often parallel, allowing the entire byte to be transferred in one operation.
Answer option A is incorrect. The unicast transmission method is used to establish communication between a
single host and a single receiver. Packets sent to a unicast address are delivered to the interface recognized
by that IP address, as shown in the following figure:

Answer option C is incorrect. The multicast transmission method is used to establish communication between
a single host and multiple receivers. Packets are sent to all interfaces recognized by that IP address, as shown
in the figure below:

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.

A demilitarized zone (DMZ) is a physical or logical subnetwork that contains and exposes external services of an organization to a larger network, usually the Internet. The purpose of a DMZ is to add an additional layer of security to an organization's Local Area Network (LAN); an external attacker only has access to equipment in the DMZ, rather than the whole of the network. Hosts in the DMZ have limited connectivity to specific hosts in the internal network, though communication with other hosts in the DMZ and to the external network is allowed.
This allows hosts in the DMZ to provide services to both the internal and external networks, while an intervening firewall controls the traffic between the DMZ servers and the internal network clients. In a DMZ configuration, most computers on the LAN run behind a firewall connected to a public network such as the Internet.