Flow control is the process of regulating the amount of data sent by a host to another host on the network. The
flow control mechanism controls packet flow so that a sender does not transmit more packets than a receiver
can process. TCP uses a sliding window flow control protocol. In each TCP segment, the receiver specifies in
the receive window field the amount of additional received data (in bytes) that it is willing to buffer for the
connection. The sending host can send only up to that amount of data before it must wait for an
acknowledgment and window update from the receiving host.
Answer option A is incorrect. TCP uses a sequence number for identifying each byte of data.
Answer option B is incorrect. TCP timestamp helps TCP to compute the round-trip time between the sender
and receiver.
Answer option C is incorrect. Congestion control concerns controlling traffic entry into a telecommunications
network, so as to avoid congestive collapse by attempting to avoid oversubscription of any of the processing or
link capabilities of the intermediate nodes and networks and taking resource reducing steps, such as reducing
the rate of sending packets. It should not be confused with flow control, which prevents the sender from
overwhelming the receiver.

NAT-PT (Network address translation-Protocol Translation) is useful when an IPv4-only host needs to communicate with an IPv4-only host. NAT-PT (Network Address Translation-Protocol Translation) is an implementation of RFC 2766 as specified by the IETF. NAT-PT was designed so that it can be run on low-end, commodity hardware. NAT-PT runs in user space, capturing and translating packets between the IPv6 and IPv4 networks (and vice-versa). NAT-PT uses the Address Resolution Protocol (ARP) and Neighbor Discovery (ND) on the IPv4 and IPv6 network systems, respectively.

NAT-Protocol Translation can be used to translate both the source and destination IP addresses. Answer option D is incorrect. Native IPv6 is of use when the IPv6 deployment is pervasive, with heavy traffic loads. Answer option C is incorrect. Point-to-point tunnels work well when IPv6 is needed only in a subset of sites. These point-to-point tunnels act as virtual point-to-point serial link. These are
useful when the traffic is of very high volume.
Answer option A is incorrect. The multipoint tunnels are used for IPv6 deployment even when IPv6
is needed in a subset of sites and is suitable when the traffic is infrequent and of less predictable
volume.

Fiber optic cable is also known as optical fiber. It is made of glass or plastic and transmits signals in the form of light. It is of cylindrical shape and consists of three concentric sections: the core, the cladding, and the jacket.
Optical fiber carries much more information than conventional copper wire and is in general not subject to electromagnetic interference and the need to retransmit signals. Most telephone company's long-distance lines are now made of optical fiber. Transmission over an optical fiber cable requires repeaters at distance intervals.
The glass fiber requires more protection within an outer cable than copper.
Answer option B is incorrect. Twisted pair cabling is a type of wiring in which two conductors (the forward and return conductors of a single circuit) are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources. It consists of the following twisted pair cables:
Shielded Twisted Pair: Shielded Twisted Pair (STP) is a special kind of copper telephone wiring used in some business installations. An outer covering or shield is added to the ordinary twisted pair telephone wires; the shield functions as a ground. Twisted pair is the ordinary copper wire that connects home and many business computers to the telephone company. Shielded twisted pair is often used in business installations. Unshielded Twisted Pair: Unshielded Twisted Pair (UTP) is the ordinary wire used in home. UTP cable is also the most common cable used in computer networking. Ethernet, the most common data networking standard, utilizes UTP cables. Twisted pair cabling is often used in data networks for short and medium length connections because of its relatively lower costs compared to optical fiber and coaxial cable.UTP is also finding increasing use in video applications, primarily in security cameras. Many middle to high-end cameras include a UTP output with setscrew terminals. This is made possible by the fact that UTP cable bandwidth has improved to match the baseband of television signals.
Answer option A is incorrect. Coaxial cable is the kind of copper cable used by cable TV companies between the community antenna and user homes and businesses. Coaxial cable is sometimes used by telephone companies from their central office to the telephone poles near users. It is also widely installed for use in business and corporation Ethernet and other types of local area network. Coaxial cable is called "coaxial" because it includes one physical channel that carries the signal surrounded (after a layer of insulation) by another concentric physical channel, both running along the same axis. The outer channel serves as a ground.
Many of these cables or pairs of coaxial tubes can be placed in a single outer sheathing and, with repeaters, can carry information for a great distance. It is shown in the figure below:

Answer option C is incorrect. Plenum cable is cable that is laid in the plenum spaces of buildings. The plenum is the space that can facilitate air circulation for heating and air conditioning systems, by providing pathways for either heated/conditioned or return airflows. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. However, some drop ceiling designs create a tight seal that does not allow for airflow and therefore may not be considered a plenum air-handling space. The plenum space is typically used to house the communication cables for the building's computer and telephone network.