Chapter 2: LAN/WAN Interconnectivity

Transcription

1 Solutions Manual for A Guide to Designing and Implementing Local And Wide Area Networks 2nd Edition by Michael Palmer, Bruce Sinclair Link download full: You can see more: Test Bank for A Guide to Designing and Implementing Local And Wide Area Networks 2nd Edition by Palmer and Sinclair Link download full: Objectives Chapter 2: LAN/WAN Interconnectivity After reading this chapter and completing the exercises, you will be able to: Explain the OSI reference model, which sets standards for LAN and WAN communications Discuss communication between OSI stacks when two computers are linked through a network Apply the OSI model to realistic networking situations Describe the types of networks as represented through LAN topologies Describe major LAN transmission methods, including Ethernet, Token Ring, and FDDI Explain the basic WAN network communications topologies and transmission methods, including telecommunications, cable TV, and satellite technologies Teaching Tips The OSI Reference Model 1. Stress to students that networking standards must be in place in order to ensure compatibility among the multitudes of computer/network hardware and software vendors. Use the example from the book to show students how difficult the pre-standards days were in this field. 14

2 2. Discuss ways the OSI model has facilitated growth in network communications over the years. Note that ensuring compatibility among vendors is not the only benefit. Another compatibility issue addressed by the model is ensuring that older network equipment is compatible with newer equipment. 3. Another benefit of the OSI model that is not listed in the text is ease of learning. The OSI model takes the difficult concept of communication between two devices on a network and breaks the process down into layers. This allows students to view the complex process in smaller, more specific steps. 4. When discussing the layered aspect of the OSI model, you might want to use the following analogy: When sending a letter to someone there are steps that are followed in order to ensure that the letter will arrive to the recipient safely. First, a letter is typed. Next, it is printed and placed in an envelope. The envelope must be properly addressed and stamped. Then, the letter must be placed in a mailbox in order to be delivered to the recipient. Breaking this process up into steps is similar to what the OSI model accomplishes with its layers. 5. Make sure that students understand that communications between two network devices go up and down the layered stack at each device. Use the example in the book to describe how this occurs. Note that the word stack is often used in place of the word model. 6. Stress to students that the OSI model is not an easy concept to understand initially. Many of the functions of the layers (particularly Layers 4-6) are hard to grasp because they are usually taken care of by software and are not seen by the user. It is an important part of networking and over time, students should try to understand what exactly occurs at each layer. Physical Layer 1. Discuss the characteristics of the Physical layer. Note that most of the characteristics found at this layer are visible to the user. This layer is usually the easiest to understand. 2. Since the physical layer is responsible for the physical transfer of data signals, it is considered the foundation of a data network. Remind students of the old saying: A house is only as good as the foundation upon which it is built. Most networking professionals agree that a network is only as good as the design and implementation of the physical infrastructure. 3. Consider bringing examples of media, connectors and other Physical layer components to class to use as visual aids. 4. Remind students that computers communicate with each other using binary code (1s and 0s). Discuss how analog and digital signals are used to represent binary numbers. 5. Discuss how EMI and RFI can cause interference with signal transmission on a network. When designing a network, students should be aware of the problems posed by EMI and RFI in order to avoid them. Data-Link Layer 1. Discuss the importance of the fields of a data link frame. Point out the address field and explain how the MAC address (physical address) is used in order to deliver the frame to the intended destination. Note that this address is not the same as another common address known as an IP address. 15

3 2. Discuss how the CRC field is used to detect errors during the transmission of a frame. Consider using the Internet to research some of the calculations used in CRC checking. 3. Make sure that students understand that the Data Link layer is divided up into 2 sublayers: MAC and LLC. Explain to students the Data Link layer is where hardware components of a network device interface with software components. The MAC sublayer is the lower of the two sublayers and is used to communicate with hardware components. The LLC sublayer is used for communication with software. 4. When discussing the differences between connectionless services vs. connection-oriented services, you might want to use an analogy of sending a letter vs. placing a phone call. When connectionless services are used, the source does not contact the destination before data is sent. When connection-oriented services are used, the source has to make a connection with the destination before any data can be sent. When sending a letter we usually do not contact the recipient before sending, but, when making a phone call we are contacting the destination. Network Layer 1. Mention to students that this layer is responsible for choosing the best path to send a packet on in order for it to reach the destination. If not for this layer, the Internet would be only an idea. 2. Discuss the term virtual circuits with your students. Make sure they understand that a virtual circuit is a temporary connection between two end nodes. Transport Layer 1. Mention to students that the Transport Layer performs many functions. Error recovery is one of these functions. Explain how acknowledgements are used to make sure that all information intended for the destination has been delivered. 2. Introduce the students to the term port numbers. The text does not go into detail regarding this subject, but it is a term that networking students will need to understand. 3. Discuss the importance of flow control. Usually, a source device can send information much quicker than the destination can process it. The Transport layer has many methods that can be implemented to facilitate flow control. One of which is through the use of acknowledgements, mentioned earlier in the section. Session Layer 1. Stress to students that the Session Layer is usually the most difficult layer to comprehend. Ensure students that as they learn more about networking concepts, the functions of this layer will hopefully become clearer. 2. Explain to students that besides establishing a session between two communicating devices, this layer is also responsible for dialog control. This means setting rules on which device can communicate at a certain time. When two devices initially communicate, the session layer implements Two-way Simultaneous dialog control. This is similar to communication on a 16

4 first-come, first-served basis. Communication collisions can occur (NOTE: not the same as a collision on an Ethernet network). If the devices experience a large number of collisions, the session layer can switch to Two-way Alternate dialog control. In this mode, the devices take turns to eliminate those collisions. Presentation Layer 1. Explain the importance of managing data formatting. Explain to students that mainframes are still in use on many networks today and users typically access mainframes using PC workstations. Since the two end devices use different types of data coding, the presentation layer makes sure one format type can be read by the other. 2. Discuss the benefits of using data encryption and data compression. Explain that if data has been encrypted or compressed by the Presentation layer of the source device, it is the Presentation layer s duty of the destination to de-encrypt and decompress the data so that it can be read by the appropriate network application. Application Layer 1. Explain to students that it is at this layer where the user interfaces with network applications such as file transfer, file management, remote access, , and terminal emulation. 2. Discuss the term redirector with the students. This service makes one computer visible to another for access through the network. Use Network Neighborhood to demonstrate this concept. Quick Quiz 1. What organizations developed the OSI model to help standardize networking technologies? Answer: ISO and ANSI 2. Which layer of the OSI model organizes bits so that they are formatted into frames? Answer: Data Link 3. At which layer would you find wire, connectors, and signaling? Answer: Physical 4. Which layer of the OSI model uses acknowledgements to ensure that data is sent and received correctly? Answer: Transport Communicating Between Stacks 1. Explain to students that in order for two devices to communicate, they must be operating under the same model. Use the board to demonstrate how information travels down through the layers at the source device. Then, travels up through the layers when it is received, where the original message can be read by the destination. Each layer at the source adds instructions that are to be followed by the destination, so that the destination will know what to do with the information. 17

5 2. Discuss how peer protocols are used to enable an OSI layer on a sending node to communicate with the same layer on the receiving node. 3. Introduce the term protocol data unit (PDU) which will also be discussed in the next section. Also explain that the PDU changes as it travels through each layer. Therefore, the PDU may be called different names as it travels through each layer. Applying the OSI Model 1. Discuss with students the example from the text of how the OSI model is applied. Point out that looking at the example in steps (layers) helps us understand the difficult concept of network communication. 2. Discuss Table 2-2. Make students understand that internetworking devices and protocols can be correlated to an OSI layer. 3. Consider inviting your school s network administrator or network technician to discuss how the OSI model can be used to support and troubleshoot network problems. Types of Networks 1. Explain to students the importance of learning the types of network topologies covered in this section of the text. It is important to have knowledge of all available when designing a network. 2. Discuss the considerations students should take when choosing the type of network topology should be implemented in a design. Examples of those considerations may be: Ethernet or Token Ring, amount of potential network traffic, type of software, other networks that may be connected, speed or bandwidth requirements, and security. 3. Although the text mainly covers physical topologies, explain to students that another type of topology is a logical topology which describes how nodes gain access to the media. Bus Topology 1. Prepare design examples that show how a bus topology is configured by either drawing them or finding graphic examples. 2. Discuss why a terminator is critical on bus networks. If using a drawing from the previous tip, use the drawing to demonstrate signal reflection. 3. Make sure that students understand the advantages and disadvantages of this type of topology design. Ring Topology 1. Prepare design examples that show how a ring topology is configured. 18

6 2. Explain that only Token Ring or FDDI networks implement this type of physical topology. 3. Make sure that students understand the advantages and disadvantages of this type topology. Star Topology 1. Prepare design examples that show how a star topology is configured. 2. When discussing the examples from the previous tip, point out that at the center of the star topology, a hub would be placed. Explain how and why hubs are used in most network designs today. 3. Discuss how the startup costs for this type of topology compare with the other topologies. Discuss other advantages and disadvantages of implementing a star topology. Bus Networks in a Physical Star Layout 1. Discuss how logical bus communication through the use of a physical star topology is accomplished. Point out that terminators are still used. 2. Explain how multiple hubs can be connected to expand the network in multiple directions. This topology is referred to as and extended star topology. Discuss the term backbone and how it is used in an extended star topology. LAN Transmission Methods 1. Explain that although there are three main LAN transmission methods, Ethernet is installed in more places because it has the broadest options for expansion and high-speed networking. The three methods are discussed in the following sections. Ethernet 1. Begin this discussion by explaining to students that one of the biggest differences in these transmission methods is how the host or workstation gains access to the media. 2. Explain the CSMA/CD control method. Make sure that students understand collisions and how devices recover from a collision. When discussing collisions, use an example of two students asking a question at the same time. The instructor will not be able to understand both, so the students have to stop talking, and then try asking their question again. 3. Discuss the characteristics of Ethernet NICs and what is required in order for them to operate correctly. Discuss where a NIC and the characteristics of the NIC (MAC address) can be found in the OSI model. 4. Explain the two examples of frame formats listed in the text. Discuss the significance of some of the specific fields such as source and destination address and the FCS field. 19

7 5. Make sure students understand that the standard is based on IEEE s interpretation of Ethernet. The Ethernet II frame format was developed by the original creators of Ethernet. Both recognize the standard which divided the data link layer into two sublayers: MAC and LLC. 6. You might want to use a protocol analyzer to capture a few frames and demonstrate the different fields found in the results of the capture. Token Ring 1. Discuss the characteristic of Token Ring. Mention that until recently, Token Ring networks could only operate at either 4 or 16 Mbps. 2. Explain that through the use of a device called a MAU, a token ring network can have a star topology layout. Use the whiteboard to demonstrate how a packet travels through the MAU in a logical ring. To do this, use the marker to travel from port to port without picking up the marker from the board. 3. Discuss the role of the token in Token Ring networks. Explain how it allows workstations to take turns sending data. Compare this to the way Ethernet devices gained access to the media. 4. You might invite a guest speaker, with Token Ring experience, to give a lecture on the benefits of Token Ring. FDDI 1. Explain to students that FDDI is used for high-speed backbone communications. It is not used to attach individual hosts to a network. 2. Discuss the characteristics of FDDI and how it operates. Discuss the benefit of using dual rings for redundancy. WAN Network Communications 1. Explain that like LANs, there are many different WAN network transmission methods. WAN network services are typically provided by telecommunications companies, cable TV companies, and satellite providers. Discuss some of the examples listed in the book. Ask students to list ones that might be more familiar to them locally. Telecommunications WANs 1. Discuss how telcos were the earliest source of WAN connectivity. Compare the most basic WAN communications versus T-carrier lines. Mention the option of fractional T services offered by most telcos. 2. Find out the type of WAN service used by your school. Consider inviting your network administrator or a representative from a local telco to discuss T-carrier services. 20

8 Cable TV WANs 1. Discuss how the Cable TV WAN services operate. In your discussion, mention how available bandwidths may vary depending on the Cable Provider. 2. Discuss the competition between Cable TV WAN providers versus Local Internet Service Providers in regard to providing Internet access to home users. Share your opinion of the future of ISPs. 3. Consider inviting a representative from a local Cable TV provider to discuss the services that they offer. Wireless WANs 1. In many communities, licensed amateur radio operators maintain packet radio LANs. Consider having members from a local amateur radio club make a presentation in class and discuss the capabilities of wireless communication for data. WAN Transmission Methods 1. Research the methods described in the chapter. Try to find graphic representations of how the methods work. Also, give examples of which technologies use which methods. For example, ISDN uses circuit switching and Frame Relay uses packet switching. Quick Quiz 1. Which topology is considered oldest communications design method? Answer: star topology 2. What occurs when two devices on the same Ethernet network transmit at the same time? Answer: collision 3. What device is used to join each node in a Token Ring network? Answer: multistation access unit (MAU) 4. FDDI supports a data throughput rate of. Answer: 100 Mbps 5. What speed does a T-1 line offer? Answer: Mbps Class Discussion Topics 1. Discuss what happens in terms of the OSI model when a user sends an across the Internet. 21

9 2. Would networking, as we know it, be the same if we did not have the OSI model? How might things be different? 3. Why is network security a more critical issue today than it was in the mid-1980 s? 4. Compare Ethernet and Token Ring transmission methods to how students would ask questions in class. 5. Discuss why MAC addresses (physical addresses) are an important component in networking. Additional Projects 1. Have students find out the top speed at which they connect to the Internet from home. Make a chart of all of the methods and the speeds of each method. Discuss whether existing line speeds are enough for their needs. 2. Have students research the services offered by their local companies, such as: telco, cable TV and/or satellite service. Have them report on which offer the most economical method of connecting to the Internet for home users. 3. Give students a scenario for a small network. Have students decide which physical topology and LAN transmission method they would use when designing the network. Further Readings 1. Tomsho, Greg, Guide to Network Support and Troubleshooting, Course Technology 2. Spurgeon, Charles, Charles Spurgeon s Ethernet Website, 3. Webopedia Website, Online Dictionary for Computer and Internet Terms, Technical Notes for the Hands-On Projects The lab setup for Chapter 2 hands-on projects includes the following elements (see the table): HANDS-ON PROJECT A lab or other access to workstations that have Internet access and Web browsers WORKSTATION OR SERVER OPERATING SYSTEMS REQUIRED OTHER RESOURCES REQUIRED 2-1 Workstations running any OS Web browser 2-2 Test lab network with a section of exposed coax or UTP cable Electric drill or fluorescent light 22

10 2-3 Workstations running Windows 2000, XP, or Red Hat Linux 7.x 2-4 Workstations running Windows 2000 or XP 2-5 Workstations running any Microsoft OS Workgroup with shared folders and shared printers 2-6 Workstations running Windows Paint 2000 or XP 2-7 Access to an Ethernet or Token Ring networked lab 2-8 Workstations running any OS Web browser Solutions Answers to the Chapter 2 Review Questions 1. Which of the following are possible Ethernet speeds? Answer: d. all of the above 2. One aspect of the ring topology that separates it from the bus topology is that: Answer: c. it does not use terminators 3. What is the T-5 data transmission rate for T-carrier communications? Answer: d Mbps 4. What type of source address is important to the MAC sublayer? Answer: a. physical or device address 5. The cable medium and voltage levels used on the cable are important to the OSI layer. Answer: physical layer or Layer 1 6. Collisions are not an important factor in Ethernet communications. True or false? Answer: False 7. Which type of protocol is more likely to enable detection of a communications error so that a frame or packet is resent when an error does occur? Answer: b. a connection oriented protocol 8. The OSI layer employs virtual circuits to establish communications paths. Answer: network 9. What is the purpose of Ethernet SNAP? Answer: Ethernet SNAP is used to provide a way to quickly adapt protocols that are not fully compliant with standards, such as AppleTalk and DEC s LAT protocols. 10. The purpose of flow control is to: Answer: b. help keep one device from transmitting faster than another device can receive 23

11 11. The field uses a cyclic redundancy check in an Ethernet frame? Answer: d. frame check sequence 12. An Ethernet network uses which of the following topologies? Answer: a. bus 13. Which of the following devices can work at any level of the OSI model? Answer: a. gateway 14. The type of switching separates channels by using different frequencies. Answer: frequency division multiple access (FDMA) 15. When beaconing occurs on a token ring network, what does this mean? Answer: the network is experiencing a problem 16. What type of WAN employs a headend in the topology? Answer: c. cable TV 17. A router performs discovery at the OSI layer. Answer: network 18. What types of packets are sent by FDDI? Answer: e. only b and c 19. Packet switching is a form of switching used on WANs. True or false? Answer: true 20. Which OSI layer can provide file transfer and file management services? Answer: c. application Hands-On Projects Tips and Solutions for Chapter 2 Project 2-1 In Step 6, the general reasons for standardization are provided by the ISO under the following topics: "Worldwide progress in trade liberalization" "Interpenetration of sectors" "Worldwide communications systems" "Global standards for emerging technologies" "Developing countries" Project 2-2 An optimal design for this project is a network that does not contain a network hub or switch and that is a bus network consisting of coaxial cable connecting two or more workstations and servers. Another viable option is a network that uses unshielded twisted-pair cable and a hub or switch. One method for displaying EMI/RFI problems is to first download a file of moderate size before applying EMI/RFI to the cable segment and observing the time it takes to download the file. Then place the EMI/RFI source as close as possible to the cable segment and observe and compare the time again. Emphasize to the students that proper installation and placement of network media is vital to reliable and optimal network performance. Coaxial cable is more susceptible to EMI/RFI interference because of the cable design and individual interface design of the hardware logic contained in the network 24

12 device. Unshielded twisted pair cabling and the individual interface design of the associated hardware logic contained in the network device takes into account EMI/RFI or noise present on the cabling and can tolerate higher noise ratios by employing media filters and isolation transformers on each twisted-pair interface that acts as a filter to minimize EMI/RFI. If your test network has an intelligent hub or switch that interconnects the workstations and servers, the easiest method for detecting problems will be to look for high error counts on the interface nearest the EMI/RFI source. You can observe these error counts on the hub or switch with the management software provided by the vendor or by utilizing the console port on the hub or switch. This project also demonstrates that a network having two or more workstations or servers should be interconnected via a hub or switch, and if possible, an intelligent hub or switch, to allow for better troubleshooting tools and for easier resolution of problems. Project 2-3 This project illustrates valuable tools for your students to use in identifying address information for a NIC in Microsoft Windows and Red Hat Linux operating systems. If you have other devices running other operating systems on your network, you might have students use similar tools to provide this information. This is example of why it is imperative that you have detailed documentation about your network so that when problems arise the device or devices that are causing the problems can be quickly located and repaired. You might also emphasize that it is important to keep this information up to date as the network grows. Most intelligent network devices, such as hubs and switches, will provide network management applications either locally or remotely that will allow you to view Layer 2 MAC addresses associated with individual interfaces to quickly locate devices connected to them. This will prove very useful in locating faulty devices on your network. This will also provide you with a tool for troubleshooting problems when you first connect a device to the hub or switch so that you can make sure the hub or switch verifies the address associated with the device connected to the interface. Project 2-4 This project enables students to view the SSL settings in Internet Explorer for Windows 2000 and XP. Consider using this project to initiate a discussion about the value of network security and encryption. You might also add a project in which students view how to set up encryption for a VPN or Web server and discuss the different types of encryption. Project 2-5 Students view the Microsoft redirector at work in this project. As a supplement to the project, you might have students monitor the activities of the redirector in Windows 2000 Server through the System Monitor. They can do this by selecting to view the Redirector object and one or more of its counters. To access the System Monitor, click Start, point to Programs, point to Administrative Tools, and click Performance. Next, click the plus sign in the System Monitor, select Redirector as the performance object, and select to view one or more counters. For example, you might have students monitor Bytes Total/sec, so that student can view the total amount of activity handled by the redirector. Project 2-6 This project provides an important visual tool and direct experience for understanding how a network is designed and why a network diagram is a valuable asset for (1) future design issues and (2) troubleshooting network problems. 25

13 Most network-drawing software vendors now provide stencils for many network devices and specific vendors. The stencils may provide detail down to the interface level for a better display of the network topology. This is a valuable add-on for network design and troubleshooting. Project 2-7 This project provides an example for your students that again shows why a thoroughly documented network is one of the most important steps in understanding how a network is designed and how it functions. The student should also completely understand how the cable plant is installed in the LAN and, if it is connected to a larger LAN or WAN, how it relates to that network. A close inspection of the network media is necessary to ensure that it meets the topology specifications for cabling types, distances, and routing of the cabling; and it will reveal the type of cable in use. Most cable vendors mark the cable type on the external cable jacket. For example, if the cable is for an Ethernet bus-type coaxial network, it will be marked as type RG58 A/U. If it is an Ethernet star-type unshielded twisted-pair network, it should be Category 3 at the minimum and hopefully Category 5. Students should inspect the connections to network devices and to the associated interfaces to determine if they match the topology specifications. For example, for Ethernet bus-type coaxial networks that are daisy-chained, each connection must contain a T-connector and an RG58, 50-ohm terminator when applicable to the last device on the chain. If the network is an Ethernet star-type unshielded twisted-pair network, RJ45 connectors should be installed and using the proper EIA/TIA 568 specification for color-coding and pin outs (students will learn more about this in the next chapter, but can begin making rudimentary observations now). Other topology specifications such as token ring or FDDI can be checked in the same fashion. When documenting their findings, students may discover that the internetworking devices provide an important key to understanding the network topology and transport method. Project 2-8 This project enables students to find out more about cable TV access, such as through two and AT&T Broadband. Due to the dynamic nature of the web pages maintained by the providers, the links may change for this project and your students may need to select other links that will provide the same information. Cable TV does provide a means for WAN access in many areas and one that is relatively easy to install and maintain. Most providers install and configure the equipment necessary to make this connection possible. The providers also supply support and instructions for problem or service change resolution. This access method is now widely available in many areas, particularly in metropolitan areas. Solutions to the Case Project Assignments In the following assignments, you work with RM Graphics to select a network transport method and the network topology. RM Graphics is a client of Network Design Consultants, your employer. You also help a new colleague to gain a better understanding of the OSI model. RM Graphics is a company that employs 19 graphic artists who reproduce the circuit designs or schematic drawings of electrical engineers. Most of RM Graphics' customers are Fortune 1000 companies that contract with RM Graphics to reproduce circuits for inclusion in customer product documentation. RM Graphics is interested in implementing a network to link the individual 26

14 workstations of the graphic artists, and has a particular need for reliability and high capacity for transmitting very large graphics files. 1. Which transport method, Ethernet or token ring, do you recommend they implement on their new network? Why? Answer: The RM Graphics company has, by their company function, some high-bandwidth requirements due to the large file size manipulations. Some of the requirements and design issues that the student should consider are: Schedule a time to visit the company and gather the following information: Meet with company administrators and employees to gather as much information as possible Focus on the administrator s wants and needs, such as network criticality and reliability Meet with a representative number of the people that work on a day-to-day basis with the applications and determine network demands Inspect the building architecture and determine the feasibility of various network topology considerations Meet with the building manager, if applicable, and determine if any present or future building design issues will present any problems. With these and other considerations in mind, the student should make his or her case for Ethernet or token ring, providing reasons for his or her selection. Note that due to the popularity of Ethernet and the many options that it offers, it is likely that this will be the best solution. 2. Given what you know about network topology, which basic topology do you recommend for RM Graphics? Answer: Using the information that the student gathers from the company, its administrators, employees, and building management, then an informed decision can be made to determine the network design, topology, and transport method. The student should consider all of the information and determine the present and future needs of the organization along with the vendor used and the related topology needed for compatibility. Students might consider the current user base for Ethernet and token ring as well as the cost and availability of related network equipment. Of course, the topology will be linked to the student s answer for part a in this case. If she or he recommends token ring, then a ring-based topology (noting that it is a physical star) should be used; and if the recommendation is for Ethernet, then the topology can be a bus or star, with star as the preferred option. 3. Brett Mason, a new colleague at Network Design Consultants, is unsure about some aspects of the OSI model. He has a list of questions for you and asks that you develop a table that he can use as a reference for the answers. Create a table containing two columns and seven rows. Label the left column "Network Function" and label the right column "OSI Layer." Enter each of the following functions in its own row under the left column and then specify the OSI layer that performs that function under the right column. Brett's questions about functions are as follows: Which layer resizes frames to match the receiving network? Which layer performs data compression? Which layer ensures data is received in the order it was sent? Which layer handles the data-carrying signal? 27

15 Which layer provides file transfer services? Which layer enables routing? Which layer enables the receiving node to send an acknowledgment? Answer: The communication with and understanding of a new employee in any organization is vital to the firm s success. Brett should thoroughly understand the technology and how it relates to the successful completion of the project. The creation and presentation of the table showing the relationship of the OSI model and the layer functionality s will be important for Brett in designing present and future projects. Directing Brett to other sources of information such as the regulatory organization s web sites or documentation will also help Brett understand. Brett can visit the IEEE, IETF and other network related regulatory web sites for further information. There are also many different trade periodicals that Brett can consult along with numerous training courses from several different training groups. FUNCTION Resizes frames to match the receiving network Performs data compression Ensures that data is received in the order it was sent Handles the data-carrying signal Provides file transfer services Enables routing Enables the receiving node to send acknowledgement OSI LAYER Transport Presentation Transport Physical Application Network LLC at the data-link layer for connection- oriented service and the transport layer 4. Brett likes your table and has another question. He would like you to explain MAC addressing. Answer: Brett s MAC addressing question can be explained by the Organizationally Unique address assignment by the IEEE for each vendor company. Each network interface or NIC on a network device has a unique address that enables a frame to reach its destination. In this address, called the device or physical address, the first series of bytes identify the NIC vendor and are a valuable tool for network administration. The student might recommend that Brett visit the IEEE web site at and follow the standards links to the organizational unique identifiers for a downloadable document with each vendor s address. 5. RM Graphics is calling for help in developing a way to electronically receive and transmit files to their customers. Explain three ways in which they can use WAN connectivity for this purpose. Which of the three ways do you recommend for their situation? Answer: RM Graphic s request for file transfer and retrieval should be investigated with the following considerations: Company resources such as server availability, disk storage resources, and CPU resources WAN bandwidth requirements File types and security 28

16 Several types of methods for file transfer and retrieval could be: An FTP server A web-based server An outsource service provider providing file transfer and retrieval and WAN bandwidth Each of these methods can be accomplished through WAN connectivity such as: POTS/PSTN T-carrier lines Cable TV Wireless communications, such as radio or microwave communications Also, each method has advantages and disadvantages that include the following issues: Security Local or remote administration WAN bandwidth costs and availability Equipment costs Solutions for the Optional Team Case Projects 1. Western Antiques, the company with which you worked in Chapter 1, is interested in linking the LANs in five of its stores that are located in different cities in the same state. The stores are 20 to 100 miles apart. Form a team and discuss the best method for connecting the individual store LANs into a WAN. Answer: As a team assignment, it is extremely important to assemble the team with the appropriate personnel in the respective areas of expertise. Western Antiques as a retail business requires a highly reliable, secure, and cost effective network to enable each of its stores to perform business activities. The selection of the WAN topology and the provider of that topology depend on the service provider s network and bandwidth availability. Now that Western Antiques has decided to connect several different stores on a WAN, a more complex decision should be made as to the incorporation of data, voice and possibly video onto to its network. Some aspects to consider are: The cost of the bandwidth for each site Cost savings of long distance voice calls Use of video conferencing on the WAN Circuit and equipment return on investment period of incorporating data, voice and video The type of transport method such as POTS, T-carrier, cable TV, and wireless will depend on availability, costs, bandwidth requirements, and compatibility with the desired applications. These decisions are complex and need thorough decision making to provide the best services for Western Antiques in terms of reliability, security and cost effectiveness. 29

17 However, in terms of these factors, the most likely solutions studied to this point are POTS and T-carrier. 2. Several of the consultants at your company are interested in the relationship between accessing the Internet and how the OSI model is implemented. Create a team to make a presentation to the other consultants. In your presentation, consider as an example how one person uses a network browser to access the Internet. Trace the interaction of the browser and Internet to each OSI layer. You might use tables or diagrams to better illustrate your explanation. Answer: Again as a team, it is extremely important that each member of the team has a fundamental understanding of how each application or device interacts with one another. One possible presentation would be to explain and display how each network related device such as a PC and its associated web browser software, a hub, a switch, a router, and a server correspond to its respective OSI model layer. Trace the PC s browser request for Internet access through each device and how the device corresponds and interacts with the respective OSI layer, showing how it transits up and down the OSI model. Students might use tables via a word processor, overhead slides, or PowerPoint slides in their presentation. 30