Introduction to Internetworking - Professional · Introduction to Internetworking ... which defines the hierarchical structure of data packets as well as each of the layers within

1Introduction toInternetworking

1.01 The Internetworking Model

1.02 Physical and Data-Link Layers

1.03 Network Layer and PathDetermination

1.04 Transport Layer

1.05 Upper-Layer Protocols

1.06 Cisco Routers, Switches, and Hubs

1.07 Configuring a Cisco Switch and Hub

TEST YOURSELF OBJECTIVES

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I n order to become a CCNA, you will need to have a solid working knowledge of the OSI model,which defines the hierarchical structure of data packets as well as each of the layers within thatseven-layer model. It is not our intention to tell you that certain layers are more important than

others, but as the CCNA is a certification that demonstrates foundational knowledge of internetworkingand Cisco equipment, the lower (or more fundamental) layers will likely be the ones about which you should possess the most knowledge. Everything starts with Layer 1. Switching happens at Layer 2,and routing at Layer 3. These are the fundamental concepts that you will use for the rest of yourinternetworking life.

TEST YOURSELF OBJECTIVE 1.01

The Internetworking ModelInternetworking is the process and methodology of connecting multiple networks without regard to their individual physical topology. Although certaininternetworking technologies have distance limitations, the overall concept of internetworking is not specifically concerned with physical distance as it relates to interconnectivity. Interconnectivity means, very simply, connecting two thingsregardless of what is between them. The Internet is the world’s largest internetworkand provides interconnectivity to millions of people, whether they use Macintosh orIBM-compatible computers, Ethernet or token ring LAN technologies, or T1s or 14.4 modems. The ability to interconnect many disparate technologies depends uponthe concept of interoperability. Interoperability is the methodology applied to makedata understandable to computers that use proprietary, or simply different, operatingsystems and languages.

The OSI model is a seven-layer protocol suite model that provides a hierarchicaltool for understanding networking technology, as well as a basis for current and futurenetwork developments. The OSI model layers are Application (7), Presentation (6),Session (5), Transport (4), Network (3), Data-Link (2), and Physical (1). A commonmnemonic device for remembering these seven layers is All People Seem To NeedData Processing. As data is passed down through the layers, each layer wraps the datain a header. This is known as wrapping the data or, more officially, as encapsulation.

� Internetworking is the process and methodology applied to connectingmultiple networks, regardless of their physical topologies and distance.

2 Chapter 1: Introduction to Internetworking

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� Interconnectivity is the means of transporting information betweencomputers—inclusive of the physical media, the data packaging mechanism,and the routing between multiple network equipment pieces—from thestarting node to the destination node.

� Interoperability is the methodology applied to make data understandable tocomputers that use proprietary, or simply different, computer operatingsystems and languages.

� The OSI model provides a hierarchical tool for understanding networkingtechnology, as well as a basis for current and future network developments.

� The OSI model is a seven-layer protocol suite model.

� Encapsulation is the process of adding a header to the data or wrapping the data.

So, exactly what is Layer 3 switching? In a word: routing. The differencesbetween Layer 3 switching and routing are largely irrelevant. For the majority ofCisco products out there, Layer 3 switching is really a clever way of saying “westuck a router into a switch,” so don’t be confused if you’ve never worked withLayer 3 switching before and see a question about it.

QQUESTIONS

1.01: The Internetworking Model1. A customer needs you to help him understand the difference between a switch

and a router. You explain to him that, unlike a switch, a router is a device thatfunctions at which layer of the OSI model?

A. Layer 1

B. Layer 2

C. Layer 3

D. Layer 4

Test Yourself Objective 1.01 3

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2. What is an internetwork?

A. The connection of more than one network

B. The connection of three or more networks

C. The connection of five of more networks

D. All of the above

3. What is the proper order of the OSI model layers, from highest to lowest?

A. Physical, Data-Link, Network, Transport, Session, Presentation,Application

B. Application, Presentation, Session, Transport, Network, Data-Link,Physical

C. Data-Link, Physical, Session, Transport, Network, Presentation,Application

D. Application, Physical, Session, Transport, Network, Presentation, Data-Link


Physical and Data-Link LayersThe Physical layer, Layer 1, defines the mechanical and electrical specifications for abit stream (1s and 0s) and synchronizes network timing. Layer 1 defines the way datais transferred to the wire (Cat5 Cable, Fiber, etc.). V.35 is a standard Physical layerinterface suitable for relatively low-speed connections to a packet network at speeds upto 48 Kbps, and beyond, even to 4Mbps. HSSI, on the other hand, is a DTE/DCEinterface that handles high-speed communication over WAN links. Layer 2, the Data-Link layer (or the link layer), consists of two sublayers. The upper is the LLC and thelower is the MAC. Also note that encapsulated data at a layer is called a frame.

There are some differences in specifications that you should keep in mind whentaking your CCNA exam. The IEEE’s standard for Ethernet, 802.3, identifies thestandard for the framing of Ethernet (the MAC layer of Layer 2, LLC) and the


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physical cabling. DIX Ethernet does not conform to this standard and instead definesthe entire link and Physical layer attributes. IBM Token Ring networks are nearlyidentical to and compatible with the IEEE 802.5 specification that was developed laterand based on IBM’s Token Ring. The FDDI standard specifies the physical and MACportions of the Data-Link layers for a token passing, dual-ring topology using fiberoptic media at 100 Mbps.

When dealing with serial connections, especially ISDN connections, here are a fewother things to keep in mind as you head into the CCNA exam: SLIP is a legacy linklayer protocol for providing serial connections between two networks, or between anetwork and a remote node. PPP includes enhancements such as encryption, errorcontrol, authentication, dynamic IP addressing, multiprotocol support, and automaticconnection negotiation. PPP will work over serial lines, regardless of speed.

� The Physical layer, or Layer 1, defines the mechanical specifications andelectrical databit-stream.

� The Data-Link layer, or Layer 2, is also known as the link layer. It consists oftwo sublayers. The LLC is the upper level and the lower level is the MAC.

� The V.35 standard is a Physical layer protocol suitable for connections to apacket network at speeds up to 48 Kbps, and beyond, even to 4 Mbps.

� HSSI is a DTE/DCE interface that handles high-speed communication overWAN links.

� BRI is an ISDN term for an ISDN connection consisting of two B channels at64 Kbps and one D channel at 16 Kbps.

� 802.3 specifies different Physical layer MAC address portions of the layer. TheDIX Ethernet specifies one entire physical and Data-Link layer. 802.3 specifiesdifferent Physical layers, but DIX Ethernet specifies just one.

� Token Ring networks are compatible with the IEEE 802.5 specificationdeveloped later, which was based on IBM’s Token Ring.

� The FDDI standard specifies the physical and MAC portion of the Data-Linklayers for a token passing, dual-ring topology using fiber optic media at 100 Mbps.

� Synchronizing network timing is handled at the Physical layer of the OSI model.


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� SLIP is a legacy Unix Data-Link layer protocol for providing serial connectionsbetween two networks, or between a network and a remote node.

� PPP includes enhancements such as encryption, error control, security,dynamic IP addressing, multiple protocol support, and automatic connectionnegotiation. PPP will work over serial lines, ISDN, and high-speed WAN links.

� Frame Relay is a widely used packet-switched WAN protocol standardized bythe ITU-T. Frame Relay relies on the Physical and Data-Link layer interfacebetween DTE and DCE devices.

Remember when you had to learn that multiplication table in third grade? Whynot just get a calculator, right? Memorizing standards like 802.3 and 802.5 willprobably make you feel the same way. Why not just write them down somewhereand look at the piece of paper if you ever need to know? The quick answer isthat you can’t take that piece of paper into your CCNA exam. You shouldspend some time learning these and know the differences.

QQUESTIONS

1.02: Physical and Data-Link Layers4. What standard defines Ethernet?

A. 802.3

B. 802.5

C. 802.7

D. 802.11

5. What type of technology is used for 802.3 Ethernet?

A. Token passing

B. CSMA/CD


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C. Token passing with a dual-ring topology

D. CSMA/CD with token passing

6. What technology is being configured in the following example?

Router# conf t

Router(config)# interface E0/0

A. Token passing

B. CSMA/CD

C. Token passing with dual-ring topology

D. Wireless LAN


Network Layer and Path DeterminationThe Network layer, Layer 3, is where addressing is most important. The mainfunction of this layer is to provide logical addressing of the node and networksegments of a network. Routed protocols are used by end nodes to encapsulate datainto packets along with Network layer addressing information, so it can be relayedthrough an internetwork.

The most common example of this is the Internet. Everything connecting to theInternet, whether it is a PC, router, switch, or mobile phone, must be assigned a Layer 3address (an IP address) that is globally unique. We could use MAC addresses for thispurpose, but they tend to get “messy.” Instead, we use IP addresses. They are far moreintuitive but allow the same functionality: packets get from Point A to Point B. Thesame is true on any network, except that on private networks the address must only beunique to that network, not globally unique.

So, how do those packets get from Point A to Point B? In most internetworks theyare routed, which is a Layer 3 function. To determine the best way to send traffic fromIP address A to IP address B, a router runs a routing algorithm that defines the bestpath. The algorithm that is run depends upon the routing protocol being used, but,


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regardless of the algorithm, the best path-routing selection is made. Note that, at Layer 3, encapsulated data is called a packet.

� The main services provided at the Network layer are logical addressing of thenode and network segments.

� Layer 3, or the Network layer, is where addressing is most important.

� Routed protocols are used by end nodes to encapsulate data into packets alongwith Network layer addressing information, so it can be relayed through theinternetwork.

� A routing algorithm is the calculation that the routing protocol uses todetermine the best route to a destination network.

There is a big difference between a routing protocol and a routed protocol. Arouting protocol (such as EIGRP, RIP, or OSPF) is what routers use to exchangeinformation about a network; whereas, a routed protocol (such as TCP/IP) isthe traffic that routers actually send, using the path determined by the routingprotocol.

QQUESTIONS

1.03: Network Layer and PathDetermination

7. Your somewhat technically lacking customer needs you to help him select arouting protocol. He gives you a list of four that he is considering. Which ofthe following can you eliminate immediately because it is a routed protocol?

A. EIGRP

B. TCP/IP

C. RIP

D. OSPF


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8. What is the main function of Layer 3?

A. To provide link layer addressing

B. To provide transport services

C. To add application headers to data

D. To provide logical addressing

9. When running a dynamic routing protocol, which of the following is run todetermine the best path for data to travel from Point A to Point B?

A. The administrative distance

B. The routed protocol

C. A routing algorithm

D. A routing protocol


Transport LayerThe Transport layer, Layer 4, provides data transport services and effectively shields upper-layer protocols from data transfer issues. The main function of theTransport layer is to provide error recovery, if requested. TCP is considered a reliable,connection-oriented protocol and requests that Layer 4 provide error checking andcorrection for its data. UDP, on the other hand, is connectionless and unreliable andwill not ask for any error checking or correction. It is important to note that, like mostprotocols, TCP/UDP do not conform exactly to the OSI model. Remember, the OSImodel is a suggested model, but it is not a requirement that protocols function exactlyas specified in the model.

� The Transport layer provides data transport services, effectively shielding theupper layers from data transfer issues.

� TCP is considered a reliable, connection-oriented protocol. UDP is unreliableand connectionless.


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It is important to understand why TCP and UDP are different, and what theirbenefits and limitations are. At first glance, you might say that all of your datamust be reliable. You want to error check it all, so why not use TCP for everything?Error checking adds overhead, and that means delay—the enemy of all networkadministrators. Streaming video is a case where it is acceptable to sacrifice afew dropped video frames in order to guarantee speed. For streaming video,UDP is a great choice. On the other hand, financial data being uploaded to amainframe can handle some delay but must be absolutely accurate, so TCPwould be the proper choice for that data transmission.

QQUESTIONS

1.04: Transport Layer10. Your customer requests that you help determine him the best way to send

weekly accounting updates to the finance directors at each of his regionaloffices. What should you tell him to do?

A. Select a TCP solution because it doesn’t have error correction and will getyour data there much faster.

B. Select a UDP solution because it doesn’t have error correction and will getyour data there much faster.

C. Select a TCP solution because it has error correction and will be morereliable.

D. Select a UDP solution because it has error correction and will be morereliable.

11. What is encapsulated data called at Layer 4?

A. Frame

B. Packet

C. Segment

D. Transport


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12. What does the following diagram illustrate?

A. A TCP connection

B. A UDP connection

C. A connection-oriented protocol

D. A connectionless protocol


Upper-Layer ProtocolsThe term “upper-layer protocols” refers to the Session, Presentation, and Applicationlayer protocols. The Session layer (Layer 5) is responsible for establishing, controlling,and tearing down sessions (conversations). The Presentation layer (Layer 6) definesdata formats, such as ASCII, JPEG, and HTML. Layer 6 also defines encryption. TheApplication layer (Layer 7) defines applications that are capable of communications(e.g., if an application is capable of transferring a file, it is a Layer 7 application).

File server

Laptop computer

Ethernet

Send 1

Send 2

Send 3

Recv 4

I got the firstthree, now sendme four.

The laptop user has requested a file from the file server. This is the process by which the file server is sending the data.


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FTP, Telnet, and email programs are all examples of applications that function atLayer 7.

� The term “upper-layer protocols” refers to the Session, Presentation, andApplication layer protocols.

� The Application layer provides basic services such as file transfer and networkmanagement to applications.

� The Presentation layer handles the formatting or presentation of the data.

� The Session layer establishes, maintains, and terminates the session betweentwo network nodes.

Because the CCNA exam is an entry-level certification exam, it is going to focusheavily on fundamental concepts. You should not only know the order of theOSI model layers, but you should also be prepared to discuss what happens ateach layer. You should also know what encapsulated data is called at eachlayer.

QQUESTIONS

1.05: Upper-Layer Protocols13. Which of the following is not an upper-layer in the OSI model?

A. Session

B. Network

C. Presentation

D. Application

14. Your client is a graphic designer. She wants to know which layer defines theformat for a JPEG file. A JPEG is an example of a file format that is defined atwhich OSI layer?

A. Session

B. Transport


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C. Presentation

D. Application

15. Which layer is responsible for establishing, controlling, and tearing downconnections?

A. Application

B. Presentation

C. Session

D. Transport


Cisco Routers, Switches, and HubsDepending on the model, Cisco routers may support a combination of Ethernet, FastEthernet, Gigabit Ethernet, token ring, FDDI, T1/E1/PRI, T3, OC-3, ATM, andvarious other types of interfaces. Regardless of the types of interfaces that are supportedon any given router, almost all Cisco routers run IOS software. It is this IOS softwarethat truly provides the functionality for Cisco products. Most people would agree thatCisco only sells routers and switches to run their “real” product, IOS software.

It’s no surprise, then, that Cisco will want you to know a great deal about configuringtheir software, and the commands required to do so, for the CCNA exam. IOS has thefollowing major modes: User EXEC, Privileged EXEC, Global Configuration, andInterface/Line Configuration. There are other modes, such as Access List Configuration,but those four are the most commonly referred to by name. It is extremely importantfor you to know the differences between each of these modes.

� Cisco routers support any combination of the following interface types: ATM,channelized T3/E3, FDDI/CDDI, multichannel T1/E1/PRI, BRI, HSSI,Packet OC-3, synchronous/asynchronous serial interfaces, token ring, andEthernet/Fast Ethernet/Gigabit Ethernet.

� Cisco IOS software is the software that runs on Cisco products. This platformis integral to the interoperations of network devices in a Cisco internetwork.


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Don’t get caught by the difference between the Global Configuration mode andmore specific configuration modes, such as the Interface Configuration mode.Just keep in mind that the Global Configuration mode makes changes that affectthe entire router, not specific aspects of the router; while, for example, theInterface Configuration mode makes changes that affect a specific interface.

QQUESTIONS

1.06: Cisco Routers, Switches, and Hubs16. A client wants to buy a Cisco router. He says, “If I know how to use one

model, I know how to use them all. IOS is the same on every piece of Ciscoequipment, right?” You tell him that this is

A. True. All Cisco routers run IOS.

B. False. Some Cisco router models do not run IOS.

C. True. All Cisco routers and switches run IOS.

D. False. No Cisco switches run IOS.

17. Which Cisco router mode is shown in the following example?

Router(config-if)#

A. User EXEC mode

B. Privileged EXEC mode

C. Global Configuration mode

D. Interface Configuration mode

18. Once in Line Configuration mode, what is the easiest way to get back to thePrivileged EXEC mode?

A. Type exit.

B. Type quit.

C. Press CTRL-Z.

D. Press the UP ARROW.


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Configuring a Cisco Switch and HubKeep in mind that there are specifications to be met (both site and device) wheninstalling hardware at a location. It is important to understand these before deployingthe equipment on site. For example, when patching a router’s Ethernet port to a hubor switch, be certain that you are using a straight-through cable, not a crossover cable.Additionally, the type of electrical interface that you order from the telephonecompany (e.g., V.35, RJ-45, etc.) must match the interface on your CSU. If, forexample, an internal CSU is being used, you would order an RJ-45 handoff.

� There are specifications that need to be met when installing hardware at thesite. It is important to follow these before deploying the equipment on site.

� When using patch cables, be aware of the different types: straight-through andcrossover.

There are not likely to be many questions on Cisco exams about cabling, butdon’t be surprised if you are asked to differentiate between a crossover cableand a straight-through cable. It’s really only important to know, for the CCNAexam, that a crossover cable cannot be used to connect a router to a switch,but could be used to connect two routers back to back (between Ethernet ports,of course).

QQUESTIONS

1.07: Configuring a Cisco Switch and Hub19. Ron is trying to connect a crossover cable to a 3640 router’s Ethernet0/0 port.

What is Ron doing wrong?

A. He is connecting a non-Ethernet cable to an Ethernet port.

B. He is connecting a crossover cable to a port that is already crossed over.


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C. He is connecting a crossover cable to a port that requires a straight-throughconnection.

D. He might not be doing anything wrong. In order to know if his action iscorrect, you need more information about what is going to be on the otherend of the Ethernet cable.

20. Next, Ron is trying to connect Ethernet ports of two routers back to back witha V.35 cable. What is Ron doing wrong?

A. Ron is attempting to make an Ethernet connection with a serial cable.

B. Ron is attempting to make a serial connection with an Ethernet cable.

C. Ron is attempting to make a connection that requires a crossover cablewith a straight-through cable.

D. Ron is attempting to make a connection that requires a straight-throughcable with a crossover cable.

21. If Ron has a Cisco 3640 with an Internet CSU/DSU, what type of handoffshould you request from your T1 provider?

A. G.703

B. RJ-45

C. V.35

D. X.25


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QLAB QUESTIONObjectives 1.01–1.07Lab Scenario: This chapter has reviewed the OSI model, its layers, and wherehardware and protocols are located within them. It is very important that you knowthese things for the exam, as there will be numerous questions asking on which layer aspecific hardware component or protocol will be located. There will also be questionsasking you to define specific OSI layers.

Please complete the table below, filling in each section with as much information as you can remember. As you will notice, there is a section for layer name, layerdefinition, hardware, and protocols. The layers should be listed in descending order.You must also be able to list the five-step process of data encapsulation and de-encapsulation. Feel free to reference this chapter or the CCNA, Second Edition Study Guide if necessary.

Layer Layer Name Layer Definition Hardware Protocols

7

6

5

4

3

2

1

Lab Question 17

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AQUICK ANSWER KEY

Objective 1.01

1. C

2. D

3. B

Objective 1.02

4. A

5. B

6. B

Objective 1.03

7. B

8. D

9. C

Objective 1.04

10. C

11. C

12. C

Objective 1.05

13. B

14. C

15. C

Objective 1.06

16. B

17. D

18. C

Objective 1.07

19. D

20. A

21. B


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AIN-DEPTH ANSWERS1.01: The Internetworking Mode1

1. C. A router functions at Layer 3 (a switch functions at Layer 2).

A is incorrect because Layer 1 defines physical characteristics. B is incorrectbecause Layer 2 defines Data-Link layer functions, such as switching. D isincorrect because Layer 4 defines transport services.

2. D. Technically, A is the most correct definition of an internetwork, but all of these answers are correct because they all qualify as “more than onenetwork.”

3. B. This is the only answer that is in the correct order.

A, C, and D are not correct because they do not follow the correct order.They also cannot fit into the mnemonic device “All People Seem To NeedData Processing.”

1.02: Physical and Data-Link Layers4. A. 802.3 defines the standard for Ethernet.

B is incorrect because it is the standard for token ring. C and D make aninteresting point relating to the CCNA exam. Until now you have probablynever even seen 802.7 or 802.11. When taking the exam (provided you’vestudied an adequate amount), if you also see some bizarre number or termyou’ve never seen before, chances are it isn’t the right answer. C is incorrectbecause 802.7 defines Broadband LAN, and D is incorrect because 802.11defines wireless LAN.

5. B. Carrier Sense Multiple Access/Collision Detection is the correctanswer.

A is incorrect because token passing would be a feature of token ring orFDDI. C is incorrect because a token passing technology with a dual-ringtopology would be FDDI. D is incorrect because these two technologies aremutually exclusive and do not ever coexist on a network.

In-Depth Answers 19

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6. B. Ethernet is a CSMA/CD technology.

A is incorrect because that would be a Token Ring Interface. C is incorrectbecause that would be a FDDI Interface. D is incorrect because that would bean interface in a wireless device.

1.03: Network Layer and PathDetermination

7. B. Only TCP/IP is a routed protocol.

A, C, and D are incorrect because they are routing protocols.

8. D. The main function of the Network layer is to provide logicaladdressing.

A is incorrect because link layer addressing is a Data-Link layer (Layer 2)function. B is incorrect; transport services are provided by the Transport layer(Layer 4). C is incorrect because application headers are added only by theApplication layer.

9. C. A routing algorithm is run to convert the information learned fromother routers in the internetwork into usable information about the best pathto a given destination.

A is incorrect because the administrative distance is something that is setby the network administrator, not something that is run. B is incorrect becausethe routed protocol determines the way data is encapsulated for transmission.D is incorrect because a routing protocol determines how routers exchangeinformation about paths to various networks, but that exchange is not enoughto determine the best path. In order to determine the best path, the routingalgorithm must be run.

1.04: Transport layer10. C. TCP has error correction and will be more reliable.

A is incorrect because TCP does have error correction. B is not the bestchoice because accounting data must be accurate and should use a protocol witherror correction. D is incorrect because UDP does not have error correction.


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11. C. Encapsulated data at Layer 4 is called a segment.

A is incorrect because a frame is encapsulated data at Layer 2. B isincorrect because a packet is encapsulated data at Layer 3. D is incorrectbecause transport is the name of the layer, not the name of encapsulated data atthat layer.

12. C. This illustrates a connection-oriented protocol.

A might be correct, but there is no way of knowing if this is TCP or some other connection-oriented protocol, so A is not the best choice. B and D are incorrect because connectionless protocols (like UDP) would give noacknowledgments. The illustration clearly shows a forward acknowledgment.

1.05: Upper-Layer Protocols13. B. The Transport layer is not part of the upper layers.

A, B, and C are incorrect choices because they are the three layers that aredefined as the upper-layer protocols.

14. C. The Presentation layer defines JPEG as well as many other formats.

A is incorrect because the Session layer establishes, controls, and tearsdown connections. B is incorrect because the Transport layer is responsible forany error correction that is requested by connection-oriented protocols. D isincorrect because the Application layer defines applications that communicatewith other computers.

15. C. The Session layer is the correct answer.

A is incorrect because the Application layer defines applications that arecapable of communicating with other computers. B is incorrect because thePresentation layer defines file formatting. D is incorrect because the Transportlayer provides error-checking and correction.

16. B. Most Cisco routers run Cisco IOS, but there are some (such as the 700series routers) that do not. Don’t get caught on the CCNA exam by questionslike this. With Cisco, there is an exception to almost every rule.

A is incorrect because certain models do not run IOS. C is incorrectbecause some router models, and many Cisco switch models, do not run IOS.D is incorrect because certain Cisco switch models, like the 29xx-XL series, runIOS-based code.

In-Depth Answers 21

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17. D. The “config-if” portion tells you that this is an Interface Configurationmode.

A is incorrect; that prompt would be “Router>.” B is incorrect; that promptwould be “Router#.” C is incorrect; that prompt would be “Router(config)#.”

18. C. Pressing CTRL-Z will immediately return you to the Privileged EXECmode.

A is incorrect because that command will return you to the GlobalConfiguration mode. B is incorrect for the same reason. D is incorrect becausethat command shows you the last command entered from the buffer.

1.07: Configuring a Cisco Switch and Hub19. D. It depends upon what is on the other end of the Ethernet cable. If he is

connecting to another router’s Ethernet port, a crossover cable is required. If heis connecting to a switch or hub, a straight-through cable is required.

A is incorrect because a crossover cable is an Ethernet cable. B is incorrectbecause Ethernet ports are not crossed over. C is incorrect because the Ethernetport doesn’t determine the type of cable required. The end-to-end connectiondetermines the type of cable that is required.

20. A. A V.35 cable is for serial connections and may not be used for Ethernetconnections.

B is incorrect because a V.35 cable is not an Ethernet cable. C is incorrectbecause a V.35 cable is not a straight-through cable in the sense that thissection discusses.

21. B. An RJ-45 connection from the DMARC to the CSU would be the bestsolution because a standard straight-through cable could be used.

A is in correct because G.703 is a European Standard Interface. C isincorrect because a V.35 handoff would require a V.35 cable and some type ofconverter for the physical interface. D is incorrect because X.25 is a type ofWAN technology, not a type of physical interface.


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ALAB ANSWERObjectives 1.01–1.07

Lab Answer 23


7 Application Gateways FTP, SMB, TELNET,TFTP, SMTP, HTTP,NNTP, CDP,GOPHER, SNMP,NDS, AFP, SAP, NCP

6 Presentation ASCII, EBCDIC,POSTSCRIPT, JPEG,MPEG, GIF

5 Session RADIUS, RPC, DNS,ASP

4 Transport TCP, UDP, SPX,Netbios, ATP

Responsible for the guaranteeddelivery of user information Itis also responsible for errordetection, correction, and flowcontrol. User information atthis layer is called datagrams.

Responsible for the setup ofthe links, maintaining of thelink, and the link tear-downbetween applications.

Responsible for the formattingof the data so that it is suitablefor presentation. Responsible forcharacter conversion (ASCII/EBCDIC), Encryption/Decryption, Compression, andVirtual Terminal Emulation.User information maintainedat this layer is called messages.

Responsible for allapplication-to-applicationcommunications. Userinformation maintained atthis layer is user data.

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Encapsulation:

1. Layer 7: User data

2. Layer 4: Datagrams

3. Layer 3: Packets

4. Layer 2: Frames

5. Layer 1: Bits

De-Encapsulation:

1. Layer 1: Bits

2. Layer 2: Frames

3. Layer 3: Packets

4. Layer 4: Datagrams

5. Layer 7: User data


3 Network Routers IP, IPX, ICMP, OSPF,IGRP, EIGRP, RIP,BOOTP, DHCP, IS-IS, ZIP, DDP, X.25

2 Data-Link Bridges, switches L2F, PPTP, L2TP,PPP, SLIP, ARP,RARP, SLARP, IARP,SNAP, BAP, PAP,CHAP, LCP, LZS,MLP, Frame Relay,Annex A, Annex D,HDLC, BPDU,LAPD, ISL

1 Physical 10BaseT, 100BaseT,1000BaseT, 10Base2,10Base5, OC-3, OC-12, DS1, DS3, E1, E3,ATM, BRI, PRI

Hubs,repeaters,cables

Responsible for the physicaltransmission of the binarydigits through the physicalmedium. This layer includesthings such as the physicalcables, interfaces, and data ratespecifications. User informationmaintained at this layer is calledbits (the 1s and 0s).

Responsible for the physicaladdressing of the network viaMAC addresses. There are twosublevels to the Data-Linklayer, MAC and LLC. TheData-Link layer has errordetection, frame ordering, andflow control. User informationmaintained at this layer iscalled frames.

Responsible for the routing ofuser data from one node toanother through the networkincluding the path selection.Logical addresses are used atthis layer. User informationmaintained at this layer iscalled packets.


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Introduction to Internetworking - Professional · Introduction to Internetworking ... which defines the hierarchical structure of data packets as well as each of the layers within