C2 OSI reference model (Lab & Review ?s)

What do we call the PDU of the transport layer?

A PDU is a Protocol Data Unit and in the transport layer it's called a segment.

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

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

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 tranceiver

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

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

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

Layer that: manages logical device addressing tracks location of devices on the network determines the best way to move data

Network Layer (L3)

Which layer manages the transmission of data across a physical link and is primarily concerned with physical addressing and the ordered delivery of frames?

Protocol Data Units (PDUs) at the Data Link (layer 2) layer are called frames. As soon as you see the word frame in a question, you know the answer.

positive acknowledgement (with retransmission) (ACK)

In data exchange, the confirmation sent from one computer or system to another saying that the computer has received a data packet that it can read.

Which layer of the OSI model provides an entry point for programs to access the network infrastructure? A. Application B. Transport C. Network D. Physical

A. The top layer of the OSI model gives applications access to the services/software that require network access.

A receiving host has failed to received 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

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. (Transport Layer 4)

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

D. TCP and UDP (User Datagram Protocol) are Transport layer protocols. The transport layer is Layer 4 of the OSI model.

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

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.

PORT (Network or Transport Layer?)

Ports are a transport layer (layer 4) concept. Only a transport protocol such as the Transmission Control Protocol (TCP) or User Datagram Protocol (UDP) can indicate which port a packet should go to. TCP and UDP headers have a section for indicating port numbers. Network layer protocols — for instance, the Internet Protocol (IP) — are unaware of what port is in use in a given network connection. In a standard IP header, there is no place to indicate which port the data packet should go to. IP headers only indicate the destination IP address, not the port number at that IP address.

Which layer chooses and determines the availability of communicating partners along with the resources necessary to make the connection, coordinates partnering applications, and forms a consensus on procedures for controlling data integrity and error recovery?

The Application (layer 7) layer is responsible for finding the network resources broadcast from a server and adding flow control and error control (if the application developer chooses).

Which layer combines bits into bytes and bytes into frames and uses MAC addressing?

The Data Link (layer 2) layer is responsible for the framing of data packets.

Which of the following is true regarding sequencing and acknowledgements? (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

A, C, D. When sequencing and acknowledgements 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.

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

A. If the remote server is busy or does not respond to your web browse request, this is most likely an Application layer problem. The application layer reports a lack of connectivity, or the application cannot connect to the intended resource. Several users complain about a slow or sluggish network, while performance tests at the transport or network layers give good results.

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

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

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

B. IP is a Network layer 3 protocol. TCP is an example of a Transport layer 4 protocol, Ethernet is an example of a Data Link layer 2 protocol, and T1 can be considered a Physical layer protocol.

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

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).

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 D. SYN

C. A connection-oriented session is set up using what is called a 3-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. (transport Layer 4)

Acknowledgements, sequencing, and flow control are characteristics of which OSI layer? A. Layer 2 B. Layer 3 C. Layer 4 D. Layer 7

C. A reliable Transport layer 4 connection uses acknowledgements 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).

At which layers of the OSI models 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

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

What is the purpose of flow control? A. To ensure that data is retransmitted if an acknowledgement 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

C. Flow control allows the receiving device to control the pace of the transmitting device so the receiving device's buffer does not overflow. (Layer 4) see windowing too

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

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

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

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.

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

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.

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

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

Which layer provides logical addressing that routers use for path determination?

The Network (layer 2) layer provides logical addressing, typically IP addressing, and routing

At which layer is routing implemented, enabling connections and path election between two end systems?

The Network (layer 3) layer provides routing through an internetwork and logical addressing.

Which layer specifies voltage, wire speed, and connector pin-outs and moves bits between devices?

The Physical (layer 1) layer is responsible for the electrical and mechanical connections between devices.

Which layer is responsible for converting frames from the Data Link layer into electrical signals?

The Physical (layer 1) layer takes frames from the Data Link layer and encodes the 1s and 0s into a digital signal for transmission on the network medium.

Which layer defines how data is formatted, presented, encoded, and converted?

The Presentation (layer 6) layer makes sure that data is in a readable format for the Application layer.

Which layer is responsible for creating, managing, and terminating sessions between applications?

The Session (layer 5) layer sets up, maintains, and terminates sessions between applications.

Which layer is used for reliable communication between end nodes over the network and provides mechanisms for establishing, maintaining, and terminating virtual circuits as well as controlling the flow of information?

The Transport (layer 4) layer uses virtual circuits to create a reliable connection between two hosts.

connection-oriented

Used to describe the reliable nature of TCP. The connection refers to the 3-way handshake required in TCP before data transmission. (Layer 4) a service is considered connection-oriented if it has the following characteristics: ■ A virtual circuit is set up (such as a three-way handshake). ■ It uses sequencing. ■ It uses acknowledgments. ■ It uses flow control

sliding window (windowing)

technique is used by Transmission Control Protocol (TCP) to manage the flow of packets between two computers or network hosts. TCP is a core component of the Internet Protocol suite and operates at the transport layer. Windows are used to control the amount of outstanding, unacknowledged data segments. If a receiving host fails to receive all the segments that it should acknowledge, the host can improve the communication session by decreasing the window size. Layer 4