Network Layer

Class Questions 5 Router Questions 1. Which one of the seven OSI layers is specifically related to routing and what is its purpose? Answer: The network layer is specifically related to routing. Its purpose is to route messages over circuits to the appropriate destination. 2. What are the main disadvantages of dynamic routing? Answer: First, it requires more processing by each computer or router in the network. Computing resources are devoted to updating the routing table, which can slow down the network. Second, the transmission of routing information wastes network capacity. Some dynamic routing protocols transmit status information every minute, which can significantly reduce performance. (Should also define/describe dynamic routing.) 3. How does a routing table operate? Answer: In simplistic terms, routing tables operate by matching the source address with its immediate destination. A routing table can either be established by the network manager, or it can create its own table by basing its decision from stored information that it has acquired. 4. Where would you implement a high-end router and why? Answer: Corporations would implement high-end routers to allow large amounts of data to travel from one location to another in the fastest and most reliable path available. High-end routers are capable of handling millions of packets every second and are known to be scalable. 5. What is the difference between centralized and decentralized routing? Answer: With centralized routing, all routing decisions are made by one central router. Typically used in host computers where all computers are connected to the central router. With decentralized routing, all routers in the network are capable of making their own routing decisions. 802.11 1. What are the four components of an 802.11 wireless network? The four components of 802.11 networks: 1) Distribution system, 2) Access Points, 3) Wireless Medium, and 4) Stations. • • The Distribution System is responsible for communication between access points; it enables users to move from one access point to another. It is made up of one or more access points. An Access Point is connected to the distribution system, and acts as a bridge between the wired and wireless networks. It is a device that accepts and broadcasts messages from its NICs. • • The Wireless Medium for 802.11 networks is the air by use of radio frequencies. The communication can pass through walls and floors, which can be considered part of the medium. A Station is each computer on an 802.11 wireless network; it consists of the computer and the NIC. 2. What types of topologies can be used in an 802.11 wireless network? There are two basic types of network topologies used by the 802.11 networks: 1) Independent networks, and 2) Infrastructure networks. • • Independent networks (also known as ad-hoc networks) can be formed without using access points; each station can connect directly to other stations in the network. Infrastructure networks can be structured with an access point that acts much like the hub of Ethernet networks; the access point serves as a centralized control unit to the network. This allows the stations to communicate with other stations that may be out of their range, which is an advantage over an independent network 3. What are the network services that are required in 802.11 wireless networks? The 802.11 networks provide a total of nine network services to deal with its added complexity. • The Distribution service is used by the access point to deliver messages it receives to the message’s destination; all messages must travel through this service. • The Integration service is provided by the distribution service; it is used to connect the access point to the wired Ethernet network. • The Association service is a key feature of 802.11 networks, which is used to allow stations to connect to the network. In an infrastructure network, before a station can be connected to the network it must first associate itself with an access point. • The Reassociation service allows stations the flexibility to evaluate which access point can provide the best connection; the station may reassociate itself with that access point. • The Disassociation service allows stations to move from one access point to another. • The Authentication service prevents unauthorized use of the network; all stations connecting to the network must be authenticated. • The Deauthentication service terminates an authenticated relationship between a station and the network created by the authentication service. • The Privacy service of wireless networks is the Wired Equivalency Privacy (WEP); it prevents unauthorized use of the network. • The MSDU Delivery service is responsible for getting the data to the actual end point. 4. What are the four speeds that 802.11b can transmit at and what type of coding do they use? • The 802.11b uses the Direct-sequence spread-spectrum (DSSS) process for data transmission; it can transmit at 1 Mbps, 2 Mbps, 5.5 Mbps, and 11 Mbps. o The 1 and 2 Mbps speeds transmit data by converting each bit into an 11-bit Barker sequence. o The 5.5 Mbps and 11 Mbps speeds use a coding scheme called complementary code keying (CCK). 5. What process is used to transmit data with 802.11a? • The 802.11a uses the Orthogonal-Frequency Division Multiplexing (OFDM) process. The OFDM is a method of digital modulation in which a signal is split into several narrowband channels at different frequencies. It can transmit from 6 to 54 Mbps. 6. What are the issues of 802.11b security? 802.11 networks face some of the same security issues that are also faced by wired networks: 1) denial of service, 2) unauthorized access, 3) eavesdropping, and 4) internal attacks. • Denial of Service occurs when a wireless device floods other wireless clients with bogus packets, which is a real threat to the physical security of 802.11 networks. • Unauthorized Access is a real problem since there is no sure way of preventing individuals from gaining access to a wireless network. • Eavesdropping is also a big concern for wireless networks because wireless data communication is essentially shared Ethernet. • Internal Attacks are also a concern because employees have been known to read, distribute, and alter valuable company data. LCD Monitors Question: What is the advantage of having thin Bezels on a LCD Monitor? Answer: There are professional applications that require more than one monitor to display all the data necessary for the task. A thin bezel permits multiple monitors to be tiled vertically or horizontally for superior ergonomic viewing since the eye does not have to jump past a wide break in the data presentation. This ergonomic advantage results in less eyestrain Question: Name three characteristics that differentiate an LCD and a CRT. Answer: Three characteristics that are unique to an LCD are that an LCD does not emit harmful radiation and it takes up less space at the desk/workstation and can be mounted on a wall or panel. It also consumes less power. Question: What is the contrast ratio for an LCD and which is recommended? Answer: The contrast ratio is the difference in light intensity between the brightest white and the darkest black that an LCD can produce. It helps determine how rich the color will be on on-screen images. Recommend a monitor to have a contrast ratio of 300:1 or better. Question: Name and describe three different classes of monitors? Answers: Monochrome: Monochrome monitors actually display two colors, one for the background and one for the foreground. The colors can be black and white, green and black, or amber and black. Gray-Scale: A gray-scale monitor is a special type of monochrome monitor capable of displaying different shades of gray. Color: Color monitors can display anywhere from 16 to over 1 million different colors. Color monitors are sometimes called RGB monitors because they accept three separate signals -- red, green, and blue. Question: What are 2 ways to improve viewing angles? Possible Answers: Vertical Alignment Cell Design A standard liquid crystal cell has the molecules arranged in a spiral alignment when off (black), and when turned on, the molecules align at an angle pointed toward the front of the panel. The VA design causes the crystals to all line up vertically when in the off state, and horizontally in the on state. This approach actually produces much better contrast than the standard structure, as less light leaks out in the off state. In-Plane Switching Cell Design Standard liquid crystal cells use transparent electrodes at the top and bottom of the cells to apply a voltage to the material, which causes the molecules to align in different ways. IPS panels use pairs of electrodes at the sides of each cell, and the current runs horizontally through the material. This approach keeps the liquid crystals parallel to the front of the panel, increasing viewing angle. Multi-Domain Cell Design The multi-domain design works by dividing the individual liquid crystal cell into multiple regions. The liquid crystal material is then induced to align in different ways in the different regions, using a technique that is sometimes referred to as "pre-tilt." Multi-domain technology can be used with standard liquid crystal material, or can be combined with other designs; it is often paired with VA technology to provide a display with good viewing angle and faster cell response times. LINUX 1. What is an operating system? Answer: The low-level software that handles the interface to peripheral hardware, schedules tasks, allocates storage, and presents a default interface to the user when no application program is running. 2. What is the difference between open source and commercial proprietary software? Answer: Open source means the source code is freely available to the public to modify as they choose. However, these modifications must also be freely available. The company that produces commercial proprietary software is the only one who has the access to the source code, and can modify the source code. Commercial proprietary software is not available free, and you have to pay an access fee to use it. 3. What is Linux? Answer: Linux is a UNIX clone, but is actually the kernel that is written by Linus Benedict Torvald and subsequently enhanced by other people. Some people refer to the complete operating system as Linux, but this is actually the kernel bundled with the GNU utilities. 4. What is a Kernel module? Answer: The Linux kernel comprises of modules instead of a continuous block of code, the modular design makes it possible to load only a minimum set of utilities and drivers into the memory. 5. What are the benefits of using modules? • With Modular design only utilities and drivers that are currently needed resides in memory, others modules that might be needed can be dynamically linked and unlinked at run time. This makes the OS compact and fast. • Modules are reusable e.g. a SCSI module for IBM PC can be use for Apple platform with very little modification. MPEG (Not on final exam) VPN 1. VPN stands for… VPN stands for "Virtual Private Network" or "Virtual Private Networking." A VPN is a private network in the sense that it carries controlled information, protected by various security mechanisms, between known parties. VPNs are only "virtually" private, however, because this data actually travels over shared public networks (such as the Internet) instead of fully dedicated private connections. 2. What are the acronyms for the 3 most common VPN protocols? PPTP, IPsec, and L2TP are three of today's most popular VPN tunneling protocols. Each one of these is capable of supporting a secure VPN connection. 3. What does PPTP stand for? PPTP = Point-to-Point Tunneling Protocol 4. What is the main benefit of VPNs compared to dedicated networks utilizing frame relay, leased lines, and traditional dial-up? The main benefit of a VPN is the potential for significant cost savings compared to traditional leased lines or dial up networking. These savings come with a certain amount of risk, however, particularly when using the public Internet as the delivery mechanism for VPN data. 5. In VPNs, the term "tunneling" refers to… The encapsulation of packets inside packets of a different protocol to create and maintain the virtual circuit (need to say more about what “encapsulation of packets inside packets” means)