QUESTION: 21

Which of the following is a distributed multi-access network that helps in supporting integrated communications using a dual bus and distributed queuing?

Logical Link Control
Token Ring network
Distributed-queue dual-bus
CSMA/CA

Answer(s): C

Explanation:

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.

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QUESTION: 22

Which of the following is a distributed application architecture that partitions tasks or workloads between service providers and service requesters? Each correct answer represents a complete solution. Choose all that apply.

Client-server computing
Peer-to-peer (P2P) computing
Client-server networking
Peer-to-peer networking

Answer(s): A,C

Explanation:

Client-server networking is also known as client-server computing. It is a distributed application architecture that partitions tasks or workloads between service providers (servers) and service requesters, called clients. Often clients and servers operate over a computer network on separate hardware. A server machine is a high- performance host that is running one or more server programs which share its resources with clients. A client does not share any of its resources, but requests a server's content or service function. Clients therefore initiate communication sessions with servers which await (listen to) incoming requests.
Answer options D and B are incorrect. Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the application. They are said to form a peer-to-peer network of nodes. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have the responsibility to provide or "serve" data, and other devices consume or otherwise act as "clients" of those servers.

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QUESTION: 23

Which of the following is an attack on a website that changes the visual appearance of the site and seriously damages the trust and reputation of the website?

Website defacement
Zero-day attack
Spoofing
Buffer overflow

Answer(s): A

Explanation:

Website defacement is an attack on a website that changes the visual appearance of the site. These are typically the work of system crackers, who break into a Web server and replace the hosted website with one of their own. Sometimes, the Defacer makes fun of the system administrator for failing to maintain server security. Most times, the defacement is harmless; however, it can sometimes be used as a distraction to cover up more sinister actions such as uploading malware.
A high-profile website defacement was carried out on the website of the company SCO Group following its assertion that Linux contained stolen code. The title of the page was changed from Red Hat vs. SCO to SCO vs. World with various satirical content.
Answer option D is incorrect. Buffer overflow is a condition in which an application receives more data than it is configured to accept. This usually occurs due to programming errors in the application. Buffer overflow can terminate or crash the application.

Answer option B is incorrect. A zero-day attack, also known as zero-hour attack, is a computer threat that tries to exploit computer application vulnerabilities which are unknown to others, undisclosed to the software vendor, or for which no security fix is available. Zero-day exploits (actual code that can use a security hole to carry out an attack) are used or shared by attackers before the software vendor knows about the vulnerability. User awareness training is the most effective technique to mitigate such attacks.
Answer option C is incorrect. Spoofing is a technique that makes a transmission appear to have come from an authentic source by forging the IP address, email address, caller ID, etc. In IP spoofing, a hacker modifies packet headers by using someone else's IP address to hide his identity. However, spoofing cannot be used while surfing the Internet, chatting on-line, etc. because forging the source IP address causes the responses to be misdirected.

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QUESTION: 24

Which of the following cables is made of glass or plastic and transmits signals in the form of light?

Coaxial cable
Twisted pair cable
Plenum cable
Fiber optic cable

Answer(s): D

Explanation:

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.

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