Chapter 9: Introduction to Metropolitan Area Networks and Wide Area Networks true/false
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| Chapter 9: Introduction to Metropolitan Area Networks and Wide Area Networks
TRUE/FALSE 1. Wide area networks share a few characteristics with local area networks. ANS: T PTS: 1 REF: 276 2. Wide area networks now carry both data and voice. ANS: T PTS: 1 REF: 276 3. Many of the same technologies and communications protocols found in local area networks are used to create metropolitan area networks. ANS: T PTS: 1 REF: 276 4. LANs cover much greater distances than MANs do. ANS: F PTS: 1 REF: 277 5. Some MAN topologies are based on a ring. ANS: T PTS: 1 REF: 277 6. Most MANs are supported by Ethernet ring technology. ANS: F PTS: 1 REF: 278 7. SONET was designed to support multiple streams of voice channels. ANS: T PTS: 1 REF: 278 8. Local area network Ethernet allows users to set their own data transfer rates. ANS: F PTS: 1 REF: 281 9. A wide area network would not exist without a sub-network. ANS: T PTS: 1 REF: 282 10. A wide area network’s sub-network, or cloud, may be categorized by the way it transfers information from one end of the sub-network to the other. ANS: T PTS: 1 REF: 282 11. A virtual circuit breaks a large amount of data into n packets. ANS: T PTS: 1 REF: 285 12. The path in a circuit-switched network exists only in the software. ANS: F PTS: 1 REF: 285 13. Broadcast networks are as common as circuit-switched and packet-switched networks. ANS: F PTS: 1 REF: 286 14. Circuit-switched networks were designed primarily for voice signals. ANS: T PTS: 1 REF: 286 15. The sub-network of a wide area network is the logical infrastructure and thus consists of nodes and various types of interconnecting media. ANS: F PTS: 1 REF: 287 16. To provide a reliable service, the network requires that a logical connection be established between the two endpoints. ANS: T PTS: 1 REF: 287 17. A common example of a connection-oriented network application is DNS. ANS: F PTS: 1 REF: 287 18. The underlying sub-network of a connectionless application cannot be a circuit-switched network. ANS: F PTS: 1 REF: 288 19. A wide area network’s underlying sub-network consists of multiple nodes, each with multiple possible connections to other nodes within the sub-network. ANS: T PTS: 1 REF: 289 20. You can assign many meanings to the weights in a weighted network graph. ANS: T PTS: 1 REF: 290 21. Most wide area networks use some form of Dijkstra’s algorithm to determine a least-cost route through a network. ANS: T PTS: 1 REF: 291 22. Compared to Dijkstra’s least-cost routing algorithm, the flooding technique seems more complex. ANS: F PTS: 1 REF: 292 23. The major disadvantage of flooding is the large number of copied packets distributed throughout the network. ANS: T PTS: 1 REF: 293 24. One disadvantage of distributed routing is related to the problems that arise if the routing tables need to be updated. ANS: T PTS: 1 REF: 295 25. When all the routing information is in one place, it is difficult to make updates to the routing information. ANS: F PTS: 1 REF: 295 26. The first routing algorithm used within the Internet was called a distance vector routing algorithm. ANS: T PTS: 1 REF: 297 27. Any network is as strong as its strongest link. ANS: F PTS: 1 REF: 297 28. Some congestion control methods are based on simple techniques such as the flow control methods. ANS: T PTS: 1 REF: 299 29. CSMA/CD is the only network technology that successfully supports connection admission control and quality of service. ANS: F PTS: 1 REF: 300 30. CSMA/CA is the most popular LAN protocol. ANS: F PTS: 1 REF: 300 31. Circuit-switched networks will someday replace packet-switched networks. ANS: F PTS: 1 REF: 284 COMPLETION 1. A network that expands into a metropolitan area and exhibits high data rates, high reliability, and low data loss is called a(n) ___________________________________. ANS:
metropolitan area network (MAN) metropolitan area network MAN MAN (metropolitan area network) PTS: 1 REF: 276 2. The ability to reroute in the event of a failure is called ____________________. ANS: failover PTS: 1 REF: 277
ANS: failover time PTS: 1 REF: 277
ANS: SONET PTS: 1 REF: 278
ANS: Metro Ethernet PTS: 1 REF: 279
ANS: bandwidth profile PTS: 1 REF: 281
ANS: burst PTS: 1 REF: 281
ANS:
wide area network (WAN) wide area network WAN WAN (wide area network) PTS: 1 REF: 281 9. A(n) ____________________ is a device that a user interacts with to access a network, and it contains the software application that allows someone to use the network for a particular purpose. ANS: station PTS: 1 REF: 282
ANS: node PTS: 1 REF: 282
ANS: sub-network, or cloud PTS: 1 REF: 282
ANS: circuit-switched PTS: 1 REF: 283
ANS: packet-switched PTS: 1 REF: 284
ANS: datagram PTS: 1 REF: 284
ANS: virtual circuit PTS: 1 REF: 285
ANS: connection-oriented PTS: 1 REF: 287
ANS: reliable PTS: 1 REF: 287
ANS: connectionless PTS: 1 REF: 287
ANS: weighted network graph PTS: 1 REF: 290
ANS: Flooding PTS: 1 REF: 292
ANS: Distributed PTS: 1 REF: 294
ANS: Adaptive PTS: 1 REF: 296
ANS:
Open Shortest Path First (OSPF) Open Shortest Path First OSPF OSPF (Open Shortest Path First) PTS: 1 REF: 297 24. When the network signals the transmitting station to slow down, this is called _________________________. ANS: explicit congestion control PTS: 1 REF: 298
ANS:
backward explicit congestion notification (BECN) backward explicit congestion notification BECN BECN (backward explicit congestion notification) PTS: 1 REF: 299 ESSAY 1. Briefly explain the most important aspects of a Metro Ethernet. ANS:
Ethernet MANs have given rise to a newer service whose popularity has grown in the last few years: Metro Ethernet. Metro Ethernet is a data transfer service that can connect your business to another business (or businesses) using a standard Ethernet connection. With Metro Ethernet, you may connect your company directly to another company using a point-to-point connection, or, for example, to two other companies using two point-to-point connections. Alternatively, you may connect your company to multiple companies as though they were all part of a large local area network. The former connection is the same as having a private connection between two points. A common example of this type of Metro Ethernet connection is found when a company is connected to an Internet service provider. All the traffic on this connection is between only two locations. The latter connection is an example of a multipoint-to-multipoint connection. Here, any company can talk to one or more (or all) connected companies. Thus, a company needs to send out only one packet to ensure that multiple companies receive this data. PTS: 1 REF: 279 2. Provide and explain an example of a circuit-switched network. ANS:
One of the best examples of a circuit-switched network is the dial-up telephone system. When someone places a call on a dial-up telephone network, a circuit, or path, is established between the person placing the call and the recipient of the call. This physical circuit is unique, or dedicated, to this one call and exists for the duration of the call. The information (the telephone conversation) follows this dedicated path from node to node within the network. A wide area network in which information follows a dedicated path from node to node within the network is a circuit-switched wide area network. When a telephone call is placed over a circuit-switched network, the network needs time to establish the circuit and to tear down the circuit. But once the circuit is established, all subsequent data travels quickly from node to node. A circuit-switched network has two key disadvantages. First, each circuit is dedicated to only one connection. Second, when the circuit is used to transfer data (as opposed to voice), it is probably not being utilized fully, because computer data transfer is often sporadic. PTS: 1 REF: 283-284 3. How does a virtual circuit packet-switched network work? ANS:
In a virtual circuit packet-switched network, all packets that belong to a logical connection can follow the same path through the network. For example, one station may want to transfer a large amount of data, such as the entire electronic contents of a book, across the network to another station. To accomplish this, a virtual circuit breaks the large amount of data into n packets and determines an optimal temporary path through the network. Each router along the path is then informed that it will be participating in a particular virtual circuit. When the data arrives with the address of that particular virtual circuit, the router simply sends the data out the router connection that is associated with that virtual circuit. When the data transfer is complete, the temporary path is dissolved (that is, each router tosses that virtual circuit information). This type of packet-switched network is called a virtual circuit because the path followed by the packets acts like a circuit but is not an actual, physical circuit like a telephone circuit. PTS: 1 REF: 285 4. How is routing through a wide area network accomplished? ANS:
Consider the Internet as an example: It is a massive collection of networks, routers, and communications lines (various types of telephone lines). When a data packet enters a router, the router examines the IP address encapsulated in the network layer of the packet and determines where the packet should go next. When there are multiple routes through a network such as the Internet, how is any one particular route selected? Although routing on the Internet is fairly complex, it is possible to examine the basic routing techniques that all types of wide area networks employ. But keep in mind that a wide area network does not use only one form of routing. The routing algorithms used within the Internet, for example, are actually combinations of several types of basic routing techniques. To begin to understand the often complex issue of routing, it is helpful to think of the sub-network as a graph consisting of nodes (computers, routers, or telephone switches) and edges (the communications links between the nodes). PTS: 1 REF: 290 5. What are the problems associated with network congestion? ANS:
Networks experience congestion for many reasons. A network failure—either failure on a communications link between nodes, or the failure of the node itself—may lead to network congestion. If the network cannot quickly detect the point of failure and dynamically route around this point, it may experience a wide range of congestion problems, from a small slowdown on an individual link to total network collapse. Even if the network were to begin the rerouting process, it might still experience congestion because one less network path would be available. But communications link and node failures are not the only causes of congestion. Insufficient buffer space at a node in a sub-network can also cause network congestion. It is not uncommon to have hundreds or even millions of packets arriving at a network node each second. If the node cannot process the packets quickly enough, incoming packets will begin to accumulate in a buffer space. When packets sit in a buffer for an appreciable amount of time, network throughput begins to suffer. If adaptive routing is employed, this congestion can be recognized, and updated routing tables can be sent to the appropriate nodes (or to a central routing facility). But changing routing tables to deflect congestion might provide only a temporary fix, if any fix at all. What is needed is a more permanent solution. Two possible more permanent solutions would be increasing the speed of the node processor responsible for processing the incoming data packets and increasing the amount of buffer space in the node. Unfortunately, both of these solutions may take a large amount of time and money to implement. Perhaps less costly alternatives are possible. What happens if the buffer space is completely full and a node cannot accept any additional packets? In many systems, packets that arrive after the buffer space is full are discarded. Although this is not a very elegant solution, it momentarily solves the problem of too many packets. Unfortunately, this is like bad medicine— it treats the symptoms, but not the disease. What is needed is a solution that reacts quickly to network congestion and addresses the real problem—too many packets. PTS: 1 REF: 298 Download 69.1 Kb. Share with your friends:
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