CompTIA Network+ N10-008 Study Guide

Chapter 2

Objectives

  • 1.1 Compare and contrast the Open Systems Interconnection (OSI) model layers and encapsulation concepts
  • 1.5 Explain common ports and protocol, their application, and encrypted alternatives

Internetworking Models

  • Open Systems Intercommunication (OSI) Standard was created by International Organization for Standardization (ISO)

Layer 1 Physical Layer

  • Examples: Physical Topology

Summary: Moves bits between devices and specifies voltage, wire speed, and pin-out of cables

  • Examples: Framing

Summary: Combines packets into bytes and bytes into frames, access to media using MAC addresses, and performs error detection, not correction

  • Responsabilities:
    • Formats messages into pieces called data frames which have a header attached which links the source and destination MAC addresses.
    • Responsabile for fingerprinting devices on a network

Layer 3 Network Layer

  • Examples: Routing

Summary: Provides logical adressing, which routers use for path determination

Data Packets - pieces of information moved throughout a network from source to destination

Route-Update Pckets - Updates about nodes in the network, their addresses, and what other nodes they are connected to

Layer 4 Transport Layer

  • Examples: End-to-end connection

Summary: Provides reliable or unreliable delivery and performs error correction before retransmition

TCP

Transmission Control Protocol (Connection oriented) uses a three way handshake (ACK -> SYN/ACK -> ACK) to establish a connection with a end system to send packets in a specific sequence.

Flow control is enabled with TCP that allows a recipient to respond with confirmation of a packet or tell the sender to wait, or slow down with sending data.

A window is the amount segments (measured in bytes) of which a sender can continue to send without an acknowledgement. Windows are used to control the amount of outstanding, unacknowledged data segments

UDP

User Datagram Protocol (Connectionless) is a protocol that sends floods of packets to it’s destination without the confirmation from the recipient

Layer 5 Session Layer

  • Examples: Dialog Control

Summary: Keeps different applications data separate

Layer 6 Presenation Layer

  • Examples: Data encryption, compression, and translation services

Summary: Presents the data and handles processing such as encryption

Layer 7 Application Layer

  • Examples: File, print, message, database, and application services

Summary: Provides a user interface

Written Lab

  1. 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?

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

  3. At which layer is routing implemented, enabling connections and path selection between two end systems

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

  5. What layer is responsible for creating, managing, and terminating sessions between applications?

  6. Which layer manages the transmission of data cross physical link and is primarily concerned with physical addressing and the order delivery of frames?

  7. 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?

  8. Which layer provides logical addressing that routers use for path determinations

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

  10. Which layer combines bits into bytes and bytes into frames and uses MAC Addressing?

Review Questions

  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. TCP and UDP reside at which layer of the OSI model?
  • A. 1
  • B. 2
  • C. 3
  • D. 4
  1. 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
  1. 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 the message?
  • A. Application
  • B. Transport
  • C. Network
  • D. Physical
  1. 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
  1. 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
  1. 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
  1. A receiving host has failed to receive all 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
  1. Which layer 1 device can be used to enlarge the area covered by a single LAN segment?
  • A. Firewall
  • B. NIC
  • C. Hub
  • D. Repeater
  • E: RJ-45 transceiver
  1. Segmentation of a data stream happens at which layer of the OSI model?
  • A. Physical
  • B. Data Link
  • C. NEtwork
  • D. Transport
  1. 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
  1. What are the 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
  1. Acknowledgements, sequencing, and flow control are characteristic of which OSI layer?
  • A. Layer 2
  • B. Layer 3
  • C. Layer 4
  • D. Layer 7
  1. Which of the following is true regarding sequencing and acknowledgements? (Chose 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 the 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
  1. Which is the purpose of flow control?
  • A. To ensure the data is retransmitted of 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
  1. At which layer of the OSI model would you find IP?
  • A. Transport
  • B. Network
  • C. Data Link
  • D. Physical
  1. Of the following, which is the highest layer in the OSI model?
  • A. Transport
  • B. Session
  • C. Network
  • D. Presentation
  1. Routers perform routing at which OSI layer?
  • A. Physical
  • B. Data Link
  • C. Network
  • D. Transport
  • E. Application
  1. Which IEEE Standard specifies the protocol for CSMA/CD?
  • A. 802.2
  • B. 802.3
  • C. 802.5
  • D. 802.11