OSI review test

"1. Host 1 sent a SYN packet to Host 2. What will Host 2 send in response? A. ACK B. NAK C. SYN/ACK D. SYN/NAK E. SYN

"1. C. A connection-oriented session is set up using what is called a three-way handshake. The transmitting host sends a SYN packet, the receiving host sends a SYN/ACK, and the transmitting host replies with the last ACK packet. The session is now set up.

"11. When data is encapsulated, which is the correct order? A. Data, frame, packet, segment, bits B. Segment, data, packet, frame, bits C. Data, segment, packet, frame, bits D. Data, segment, frame, packet, bits"

"11. C. The encapsulation order is data, segment, packet, frame, bits.

"12. What are two purposes for segmentation with a bridge? (Choose two.) A. To add more broadcast domains B. To create more collision domains C. To add more bandwidth for users D. To allow more broadcasts for users"

"12. B, C. Bridges and switches break up collision domains, which allows more bandwidth for users.

"16. At which layer of the OSI model would you find IP? A. Transport B. Network C. Data Link D. Physical"

"16. B. IP is a Network layer protocol. TCP is an example of a Transport layer protocol, Ethernet is an example of a Data Link layer protocol, and T1 can be considered a Physical layer protocol."

"17. Of the following, which is the highest layer in the OSI model? A. Transport B. Session C. Network" D. Presentation

"17. D. The Presentation layer is the sixth layer of the model. Only the Application layer is higher, but it is not listed. Session is Layer 5, Transport is Layer 4, and Network is Layer 3.

"20. Which IEEE standard specifies the protocol for CSMA/CD? A. 802.2 B. 802.3 C. 802.5 D. 802.11"

"20. B. The 802.3 standard, commonly associated with Ethernet, specifies the media-access method "used by Ethernet, which is known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD)."

"6. At which layers of the OSI model do bridges, hubs, and routers primarily operate, respectively? A. Physical, Physical, Data Link B. Data Link, Data Link, Network C. Data Link, Physical, Network D. Physical, Data Link, Network"

"6. C. Bridges, like switches, are Data Link layer devices. Hubs, like "repeaters, are Physical layer devices. Routers are Network layer devices"

7. "Which layer of the OSI model is responsible for converting data into signals appropriate for the transmission medium? A. Application B. Network C. Data Link D. Physical"

"7. D. The Physical layer's job is to convert data into impulses that are designed for the wired or wireless medium being used on the attached segment.

"10. Segmentation of a data stream happens at which layer of the OSI model? A. Physical B. Data Link C. Network D. Transport"

10. D. The Transport layer receives large data streams from the upper layers and breaks these up into smaller pieces called segments."

2. TCP and UDP reside at which layer of the OSI model? A. 1 B. 2 C. 3 D. 4

2. D. TCP and UDP are Transport layer protocols. The Transport layer is Layer 4 of the OSI model.

"13. Acknowledgments, sequencing, and flow control are characteristic of which OSI layer? A. Layer 2" B. Layer 3 C. Layer 4 D. Layer 7"

13. C. A reliable Transport layer connection uses acknowledgments to make sure all data is received reliably. A reliable connection is defined by the use of acknowledgments, sequencing, and flow control, which is characteristic of the Transport layer (Layer 4).

"14. Which of the following is true regarding sequencing and acknowledgments? (Choose all that apply.) A. The segments delivered are acknowledged back to the sender upon their reception. B. If a segment is not received, the virtual circuit must be restarted from the beginning at a slower transmit interval. C. Any segments not acknowledged are retransmitted. D. Segments are sequenced back into their proper order upon arrival at their destination. E. All segments are retransmitted on time slot intervals."

14. A, C, D. When sequencing and acknowledgments are used, the segments delivered are acknowledged back to the sender upon their reception. At this point, any segments not acknowledged are retransmitted, and segments are sequenced back into their proper order upon arrival at their destination.

"15. What is the purpose of flow control? A. To ensure that data is retransmit" "retransmitted if an acknowledgment is not received B. To reassemble segments in the correct order at the destination device C. To provide a means for the receiver to govern the amount of data sent by the sender D. To regulate the size of each segment"

15. C. Flow control allows the receiving device to control the pace of the transmitting device so the receiving device's buffer does not overflow."

"18. Routers perform routing at which OSI layer? A. Physical B. Data Link C. Network D. Transport E. Application"

18. C. A router is specified at the Network layer and a router routes packets. Routers can also be called Layer 3 switches.

"19. Which of the following mnemonic devices can you use to remember the first letter of the name of each layer of the OSI model in the proper order? A. All People Seem To Need Processed Data. B. Always Should People Never Threaten Dog Police. C. Please Do Not Throw Sausage Pizza Away. D. All Day People Should Try New Professions."

19. C. The phrase "Please Do Not Throw Sausage Pizza Away" contains the first letters of the layers in order, from Layer 1 through Layer 7. "All People Seem To Need Data Processing" works from the top down. The other options have all the right letters, just not in the right order."

3. Which layer of the OSI model provides a user interface in the form of an entry point for programs to access the network infrastructure?" A. Application B. Transport C. Network D. Physical"

3. The top layer of the OSI model gives applications access to the services that allow network access.

"4. You are connected to a server on the Internet and you click a link on the server and receive a time-out message. What layer could be the source of this message? A. Application B. Transport C. Network D. Physical"

4. If the remote server is busy or does not respond to your web browser request, this is an Application layer problem.

5. "Which layer of the OSI model is responsible for code and character-set conversion as well as recognizing data formats? A. Application B. Presentation C. Session" D. Network

5. B. The Presentation layer makes data "presentable" for the Application layer."

"8. A receiving host has failed to receive all the segments that it should acknowledge. What can the host do to improve the reliability of this communication session?" "A. Send a different source port number. B. Restart the virtual circuit. C. Decrease the sequence number. D. Decrease the window size."

8. D. A receiving host can control the transmitter by using flow control (TCP uses windowing by default). By decreasing the window size, the receiving host can slow down the transmitting host so the receiving host does not overflow its buffers.

9. "Which Layer 1 devices can be used to enlarge the area covered by a single LAN segment? (Choose two.) A. Firewall B. NIC C. Hub D. Repeater E. RJ-45 transceiver"

9. C, D. Not that you really want to enlarge a single collision domain, but a hub (multiport repeater) will provide this functionality for you.