CYBR1-1.1 OSI Model - MC Format (N10-008)

22. At which of the Open Systems Interconnection (OSI) model layers do switches and bridges perform their basic functions? A. Physical B. Data link C. Network D. Transport

22. B. Switches and bridges are involved in Local Area Network (LAN) communications only and therefore primarily at the data link layer. They are not primarily associated with the physical, network, or transport layers, although some switches include network layer routing capabilities.

14. At which layer of the OSI model do you find the protocol responsible for the delivery of data to its ultimate destination on an internetwork? A. Data link B. Network C. Session D. Application

14. B. On a TCP/IP network, the Internet Protocol (IP) at the network layer is the protocol responsible for the delivery of data to its final destination. Data link layer protocols are only concerned with communication between devices on a Local Area Network (LAN) or between two points connected by a Wide Area Network (WAN) link. The session and application layers are not involved in the actual delivery of data.

15. Which of the following is not a protocol operating at the network layer of the OSI model? A. IP B. ICMP C. IGMP D. IMAP

15. D. Internet Protocol (IP), Internet Control Message Protocol (ICMP), and Internet Group Message Protocol (IGMP) are all network layer protocols. Internet Message Access Protocol (IMAP) is a mail protocol that operates at the application layer.

12. At which layer of the Open Systems Interconnection (OSI) model is there a protocol that adds both a header and footer to the information that is passed down from an upper layer, thus creating a frame? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

12. B. The only layer with a protocol (such as Ethernet) that adds both a header and a footer is the data link layer. The process of adding the headers and footers is known as data encapsu- lation. All other protocol layers that encapsulate data add just a header.

10. At which layer of the Open Systems Interconnection (OSI) model are there TCP/IP protocols than can provide either connectionless or connection-oriented services to applications? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

10. D. There are two types of transport layer protocols: connection-oriented and connectionless. Connection-oriented protocols guarantee the delivery of data from source to destination by creating a connection between the sender and the receiver before any data is transmitted. Connectionless protocols do not require a connection between end systems in order to pass data. The physical layer does not use connectionless or connection-oriented protocols; it defines standards for transmitting and receiving information over a network. The data link layer provides physical addressing and final packaging of data for transmission. The network layer is responsible for logical addressing and routing. The session layer is responsible for creating and maintaining a dialogue between end systems. The presentation layer is respon- sible for the formatting, translation, and presentation of information. The application layer provides an entry point for applications to access the protocol stack and prepare information for transmission across a network.

9. Some switches can perform functions associated with two layers of the Open Systems Inter- connection (OSI) model. Which two of the following layers are often associated with net- work switching? (Choose all that apply.) A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

9. B, C. The primary function of a switch is to process packets based on their media access con- trol (MAC) addresses, which makes it a data link layer device. However, many switches can also perform routing functions based on IP addresses, which operate at the network layer.

1. At which of the following layers of the Open Systems Interconnection (OSI) model do the protocols on a typical local area network (LAN) use media access control (MAC) addresses to identify other computers on the network? A. Physical B. Data link C. Network D. Transport

1. B. The Ethernet (or IEEE 802.3) protocol at the data link layer uses MAC addresses to iden- tify computers on the local network. MAC addresses are coded into the firmware of physical network interface adapters by the manufacturer. The physical layer deals with signals and is not involved in addressing. The IP protocol at the network layer has its own addressing system. The transport layer protocols are not involved in addressing.

11. Which of the following layers of the Open Systems Interconnection (OSI) model typically have dedicated physical hardware devices associated with them? (Choose all that apply.) A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

11. A, B, C. The physical layer of the OSI model is associated with hubs, cables, and network interface adapters. The data link layer is associated with bridges and switches. The network layer is associated with routers. The transport, session, presentation, and application layers are typically not associated with dedicated hardware devices.

13. Identify the layer of the Open Systems Interconnection (OSI) model that controls the address- ing, transmission, and reception of Ethernet frames, and also identify the media access con- trol method that Ethernet uses. A. Physical layer; Carrier Sense Multiple Access with Collision Detection (CSMA/CD) B. Physical layer; Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) C. Data link layer; CSMA/CD D. Data link layer; CSMA/CA

13. C. The Ethernet protocol that handles the addressing, transmission, and reception of frames operates at the data link layer. Each frame includes hardware addresses that identify the send- ing and receiving systems on the local network. Ethernet uses the CSMA/CD media access control method. Physical layer specifications include the transmission of signals in the form of electrical or light pulses to represent binary code, not frames. CSMA/CA is a data link layer media access control method used by wireless LAN protocols, but not Ethernet.

16. Ed is a software developer who has been given the task of creating an application that requires guaranteed delivery of information between end systems. At which layer of the Open Systems Interconnection (OSI) model does the protocol that provides the guaranteed delivery run, and what type of protocol must Ed use? A. Data link layer; connectionless B. Network layer; connection-oriented C. Transport layer; connection-oriented D. Application layer; connectionless

16. C. A connection-oriented transport layer protocol, such as Transmission Control Protocol (TCP), provides guaranteed delivery of data for upper layer applications. Connectionless protocols do not guarantee delivery of information and therefore are not a good choice. Guaranteed delivery of information is generally not a function of the data link, network, or application layer.

17. Which of the following devices operates only at the physical layer of the Open Systems Inter- connection (OSI) model? A. Hub B. Bridge C. Switch D. Router

17. A. A hub functions only at the physical layer by forwarding all incoming signals out through all of its ports. Bridges and switches operate at the data link layer by selectively propa- gating incoming data. Routers operate at the network layer by connecting local area net- works (LANs) and propagating only the traffic intended for another network, based on IP addresses.

18. Alice is a network administrator designing a new Local Area Network (LAN). She needs to determine the type of cabling and the network topology to implement. Which layers of the Open Systems Interconnection (OSI) model apply to cabling and topology elements? A. Physical and data link layers B. Data link and network layers C. Network and transport layers D. Transport and application layers

18. A. The physical layer defines the mechanical and electrical characteristics of the cables used to build a network. The data link layer defines specific network (LAN or WAN) topologies and their characteristics. The physical layer standard that Alice will implement is dependent on the data link layer protocol she selects. The network, transport, and application layers are not concerned with cables and topologies.

19. Which layers of the Open Systems Interconnection (OSI) model do not have protocols in the TCP/IP suite exclusively dedicated to them? (Choose all that apply.) A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

19. E, F. In the TCP/IP suite, the functions of the session layer are primarily implemented in the transport layer protocols: Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). The presentation layer functions are often implemented in application layer protocols, although some functions, such as encryption, can also be performed by transport or network layer protocols.

2. Which of the following organizations developed the Open Systems Interconnection (OSI) model? A. International Telecommunication Union (ITU-T) B. Comité Consultatif International Télégraphique et Téléphonique (CCITT) C. American National Standards Institute (ANSI) D. Institute of Electrical and Electronics Engineers (IEEE) E. International Organization for Standardization (ISO)

2. E. ISO developed and published the OSI model to serve as a conceptual model for soft- ware and hardware developers. The ITU-T, formerly known as the CCITT, coordinates the development and advancement of international telecommunication networks and services. ANSI is a private organization that administers and coordinates a United States-based stan- dardization and conformity assessment system. The IEEE publishes standards that define data link and physical layer standards. These standards are referred to collectively as the 802 series.

20. The protocols at which layer of the Open Systems Interconnection (OSI) model use port numbers to identify the applications that are the source and the destination of the data in the packets? A. Application B. Presentation C. Transport D. Network

20. C. Transport layer protocols, such as Transmission Control Protocol (TCP) and User Data- gram Protocol (UDP), have header fields that contain the port numbers of the applications that generated the data in the packet and which will receive it. The application, presentation, and network layers do not use port numbers.

21. Which of the following is a correct listing of the Open Systems Interconnection (OSI) model layers, in order, from top to bottom? A. Physical, data link, transport, network, session presentation, application B. Application, session, presentation, transport, network, data link, physical C. Presentation, application, transport, session, network, physical, data link D. Session, application, presentation, transport, data link, network, physical E. Application, presentation, session, transport, network, data link, physical

21. E. The correct order of the OSI model layers, from top to bottom, is application, presenta- tion, session, transport, network, data link, physical.

23. On a TCP/IP network, flow control is a function implemented in protocols operating at which layer of the Open Systems Interconnection (OSI) model? A. Presentation B. Session C. Transport D. Network

23. C. Flow control is a process that adjusts the transmission rate of a protocol based on the capability of the receiver. If the receiving system becomes overwhelmed by incoming data, the sender dynamically reduces the transmission rate. In the TCP/IP protocol suite, Transmission Control Protocol (TCP) is responsible for implementing flow control. TCP runs at the trans- port layer. None of the other layers listed have TCP/IP protocols that provide flow control.

24. Which layer of the Open Systems Interconnection (OSI) model defines the medium, network interfaces, connecting hardware, and signaling methods used on a network? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

24. A. The physical layer of the OSI model defines the standards for the physical and mechanical characteristics of a network, such as cabling (copper and fiber), connecting hardware (hubs and switches), and signaling methods (analog and digital). All of the other layers are not involved in the mechanical characteristics of the network.

25. Which of the OSI model layers is responsible for syntax translation and compression or encryption? A. Data link B. Network C. Session D. Presentation E. Application

25. D. The presentation layer provides a syntax translation service that enables two computers to communicate, despite their use of different bit-encoding methods. This translation service also enables systems using compressed or encrypted data to communicate with each other.

26. Which layer of the Open Systems Interconnection (OSI) model is responsible for transmitting signals over the network medium? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

26. A. The physical layer of the OSI model defines the functions specific to the network medium and the transmission and reception of signals. All of the other layers are implemented in soft- ware and do not physically send or receive signals.

27. Specify the layer of the Open Systems Interconnection (OSI) model at which the Internet Pro- tocol (IP) operates and whether it is connection-oriented or connectionless. A. Network; connection-oriented B. Network; connectionless C. Transport; connection-oriented D. Transport; connectionless

27. B. IP is a connectionless protocol that operates at the network layer of the OSI model. There are no connection-oriented protocols at this layer. The protocols at the transport layer include Transmission Control Protocol (TCP), which is connection-oriented, and User Data- gram Protocol (UDP), which is connectionless.

3. Which layer of the Open Systems Interconnection (OSI) model is responsible for the logical addressing of end systems and the routing of datagrams on a network? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

3. C. Network layer protocols (such as IP) contain headers that specify logical addresses for end system communication and route datagrams across a network. The physical layer defines standards for physical and mechanical characteristics of a network. The data link layer uses media access control (MAC) or hardware addresses, not logical addresses. The transport layer uses port numbers, not logical addresses. Session layer protocols create and maintain a dialogue between end systems. Presentation layer protocols are responsible for the format- ting, translation, and presentation of information. The application layer provides an entry point for applications to access the protocol stack and prepare information for transmission across a network.

4. On a TCP/IP network, which layers of the Open Systems Interconnection (OSI) model con- tain protocols that are responsible for encapsulating the data generated by an application, creating the payload for a packet that will be transmitted over a network? (Choose all that apply.) A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

4. B, C, D. Before the payload data generated by an application can be transmitted over a TCP/ IP network, the system must encapsulate it by applying protocol headers and footers at three layers of the OSI model. The data link layer applies a header and footer to create an Ether- net frame. The network layer applies a header to create an IP datagram. The transport layer applies a TCP or UDP header to create a segment or datagram. The other model layers are involved in the payload transmission process, but they do not encapsulate the payload.

5. What layer of the Open Systems Interconnection (OSI) model is responsible for translating and formatting information? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

5. F. The presentation layer implements functions that provide formatting, translation, and presentation of information. No other layers of the OSI model translate and format appli- cation data.

6. Which of the following devices typically operates at the network layer of the Open Systems Interconnection (OSI) model? A. Proxy server B. Hub C. Network interface adapter D. Router

6. D. A router connects networks at the network layer of the OSI model. Proxy servers operate at the application layer. Network interface adapters operate at both the data link and the physical layers. Hubs are physical layer devices.

7. Which layer of the Open Systems Interconnection (OSI) model provides an entrance point to the protocol stack for applications? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

7. G. The application layer provides an entry point for applications to access the protocol stack and prepare information for transmission across a network. All other layers of the OSI model reside below this layer and rely on this entry point.

8. Which layer of the Open Systems Interconnection (OSI) model is responsible for dialogue control between two communicating end systems? A. Physical B. Data link C. Network D. Transport E. Session F. Presentation G. Application

8. E. The session layer is responsible for creating and maintaining a dialogue between end sys- tems. This dialogue can be a two-way alternate dialogue that requires end systems to take turns transmitting, or it can be a two-way simultaneous dialogue in which either end system can transmit at will. No other layers of the OSI model perform dialogue control between communicating end systems.