DCNA

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Author:
Jacques_Botha
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191155
Filename:
DCNA
Updated:
2013-01-10 04:24:04
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Duxbury Certified Network Associate
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DCNA
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  1. What is the OSI model?
    The OSI model is a framework for standardizing communications.OSI defines the communications process as a set of SEVEN layers with specific functions isolated and associated with each layer.
  2. When was the OSI model developed?
    1977
  3. Who developed the OSI model?
    The International Standards Organization
  4. Why are there layers, what do they do?
    Each layer performs a set of functions necessary to provide a set of services to the layer above itself. Layer isolation allows a given layer to change without affecting the rest of the model.
  5. How can the SEVEN layers of the OSI model be remembered and what are they?
    • Physical - Please
    • Datalink - Do
    • Netowork - Not
    • Transport - Throw
    • Session - Sausage
    • Presentation - Pizza
    • Application - Away


  6. What does the PHYSICAL LAYER do?
    • The PHYSICAL LAYER is defines data transmission between devices.
    • It is involved in :

    • SIGNALLING,
    • TRANSPORT MEDIA &
    • CONNECTORS

    LAYER1 - Essentially everything you can TOUCH such as cabling and connectors.
  7. What is the DATALINK LAYER?
    The DATALINK LAYER is involved in:

    • Transmission,                          
    • Flow Control &
    • Error Detection

    • of the Data.

    (FRAMES are sent at LAYER 2)
  8. What does the NETWORK LAYER do?
    • The NETWORK LAYER is responsible for Logical Addressing. It translates Logical ~ to Physical Addresses.
    • (Prioritizing of Data is done at Layer 3)
  9. What is a Logical Address?
    • A Logical Address is a 48 bit address that is burned into the ROM of a NIC (Network Interface Card,which is of course part of Layer 1).  The first 24 bits are for VENDOR CODE and the next 24 bits make the SEQUENTIAL ADDRESS.  This address is commonly referred to as the MAC (Media Access Control) address.
    • REMEMBER - IP is where you are.
    •                          MAC is who you are.
  10. What is a Physical Address?
    A Physical Address is a 32 bit address assigned to each system in a network. It is also known as the IP Address.
  11. Elaborate on the PHYSICAL LAYER.
    • 1. The PHYSICAL LAYER provides for TX of info between two endpoints (1's and 0's)
    • 2. It is the "see & touch" layer.
    • 3. It defines:
    •     * TX over Physical Media
    •     * Physical Topologies (Bus, Star, Ring, Mesh & Hybrid)
    •     * Cables, NIC's and Physical aspects
    •     * Bits sent on the cable
    •     * Signal Encoding i.e. Baseband / Broadband
    •     * Components are Hubs, Repeaters & Transcievers
  12. PHYSICAL LAYER facts:
    • 1. The PHYSICAL LAYER is the most basic layer and transmits raw bits instead of packets or frames.
    • 2. No Frame Headers are added at PHYSICAL LAYER.
    • 3. The PHYSICAL LAYER performs functions requested by the DATALINK LAYER.
    • 3. The PHYSICAL LAYER determines the bit rate in bits (also known as the Bandwidth)
    • 4. The type of connectors, which frequencies to broadcast on & similar low level parameters are specified at the PHYSICAL LAYER

    REMEMBER the PHYSICAL LAYER just uses 1's and 0's and doesn't care about what's being sent.
  13. What is the DATALINK LAYER responsible for?
    The DATALINK LAYER:

    1. Provides LAN Based comms between end points including:

    creating,



    • transmitting
    •     and

    receiving frames

  14. What components are used in the DATALINK LAYER?
    In the DATALINK LAYER, Bridges and Layer 2 switches are used.

    This layer consists of two sub layers i.e.

    Logical Link Control (LLC) &

    Media Access Control (MAC)
  15. Where are Frames built?

    Frames are built in the DATALINK LAYER and consists of a SOURCE MAC & DESTINATION MAC.

  16. Elaborate on the DATALINK LAYER.
    The DATALINK LAYER provides:

    • 1. The means to transfer data between two entities & to detect and correct errors that may occur at the PHYSICAL LAYER.
    • 2. Connectivity only in a LAN for Unicast , Multicast & Broadcast traffic.
  17. In the DATALINK LAYER what happens when  data is sent?
    1. The DATALINK LAYER waits for a positive Acknowledge (ACK). If one is not received this layer assumes that the frame has been damaged or lost and another frame is sent.
  18. What does Unicast mean?
    Unicast - One-to-One Communication

    (Uni - One)
  19. What does Multicast mean?
    Multicast - One-to-Many Communication with certain exceptions such as groups.

    (Multi - Many)
  20. What does Broadcast mean?
    Broadcast - One-to-Many

    (Broadcast - To Transmit or Disseminate)
  21. What does the MAC Sublayer do?
    The MAC Sublayer defines :

    • * Frame Formats (Language of the packet)
    • * Media Access Methods - CSMA/CD, CSMA/CA
    • * Error Checking (Frame Check Sequence - FCS)
    • * Hardware Addressing (Physical Address)
  22. What does CSMA/CD and CSMA/CA stand for?
    • CSMA/CD - Carrier Sense Multiple Access with Collision Detection
    • CSMA/CA - Carrier Sense Multiple Access with Collision Avoidance
  23. How is a MAC Address comprised?
    • 1. A MAC Address consists of a 12 digit hexadecimal number which is 6 bytes in length. (48 bit address).
    • 2. Each MAC Address is UNIQUE to each Ethernet device.
    • 3. A MAC Address is hardcoded into the hardware of the device.
    • 4. A MAC Address is "WHO you are". (Your unique fingerprint)
  24. What does a Destination MAC Address look like?
    Two types of Destination MAC Addresses exist:

    1. Individual such as

    00-00-1D-9F-43-5A

    2. Group such as

    • FF-FF-FF-FF-FF-FF (Broadcast)
    • 01-FF-FF-FF-FF-FF (Multicast - Note that the 01 indicates Multi)
  25. What does the LLC Sublayer do?
    The LLC Sublayer:

    • 1. Shields the upper layers from any particular media or access method.
    • 2. Interfaces to upper layer protocols.
    • 3. Defines Data Frames sent between layers.
  26. How does the LLC Sublayer work with the protocols and what are some of those protocols?
    A protocol is a common set of rules or set of instructions that define how two or more systems will "talk" to one another. 

    In networking many different protocols exist such as:

    • TCP/IP
    • FTP
    • HTTP
    • IPX
    • PPP

  27. What does the NETWORK LAYER do?
    The NETWORK LAYER:

    • 1. Routes all info in a Network to a specific destination and ensures that the data arrives at the correct destination.
    • 2. Formats data for the appropriate communications method i.e. LAN, WAN.
    • 3. Determines routes & manages network traffic problems.
    • 4. Addresses messages & translates Logical Addresses (IP) into PHYSICAL ADDRESSES (MAC).
    • 5. Uses components such as:
    • * Routers
    • * Layer 3 Switches
  28. What is the symbol for a Router and what is it?


    A Router converts between Frames (Eth) and Packets (DSL).  It is the gateway OUT of a network
  29. In the NETWORK LAYER, what is an address and how is it assigned?
    • The addressing scheme is a Logical scheme and values are chosen by an Administrator.
    • This is where IPv4 or IPv6 is used. In this layer we encounter the Router which uses this logical addressing scheme to route between two Internet networks.
  30. What layer is the DATALINK LAYER and what are the sub layers?
    The DATALINK LAYER is the second layer and here you would encounter the LLC (Logical Link Control) and MAC (Media Access Control) layers.
  31. What devices function at the PHYSICAL LAYER?
    Hubs

    Repeaters

    Transceivers
  32. What is MAC the abbreviation of and what number system is used for MAC addresses?
    Media Access Control and the Hexadecimal (Base 16) Number system.
  33. What devices function at the DATALINK LAYER?
    Bridges and Layer 2 Switches
  34. What devices function at the NETWORK LAYER?
    Routers & Layer 3 Switches
  35. List the layers of the OSI model from top to bottom.
    • Application
    • Presentation
    • Session
    • Transport
    • Network
    • Datalink
    • Physical
  36. At what layer of the OSI Model do IP addresses get defined?
    Network Layer 
  37. Are layers in the OSI Model dependent on one another?
    Yes,

    Each layer responds to requests (read instructions) from the layer above it and in turn issues requests (read instructions) to the layer below it.

  38. What two parts does a MAC Address consist of?
    One half (24 bits / 3 bytes) represents VENDOR ID and the other half (24bits / 3 bytes) represent SEQUENTIAL ID
  39. At what layer do we encounter signalling?
    Physical Layer or Layer 1
  40. 05:07:01:C5:9A:E0 is an example of what type of MAC address?
    Individual 

    05:07:01:C5:9A:E0 - Individual

    FF:FF:FF:FF:FF:FF - Group (Broadcast)

    01:XX:XX:XX:XX:XX - Group (Multicast)
  41. FF:FF:FF:FF:FF:FF is an example of what type of MAC Address?
    A Group Address (Broadcast Address)

    05:07:01:C5:9A:E0 - Individual

    FF:FF:FF:FF:FF:FF - Group (Broadcast)

    01:XX:XX:XX:XX:XX - Group (Multicast)
  42. 01:XX:XX:XX:XX:XX is an example of what type of MAC Address?
    A Group Address (Multicast Address)

    05:07:01:C5:9A:E0 - Individual

    FF:FF:FF:FF:FF:FF - Group (Broadcast)

    01:XX:XX:XX:XX:XX - Group (Multicast)
  43. What type of address is assigned to a packet at Layer 3?
    Logical Address (an IP address)
  44. Where is CSMA/CD and CSMA/CA defined?
    Layer 2 - DATALINK LAYER (To be specific the MAC sublayer )
  45. Where are Frame Headers built?
    Datalink Layer - Layer 2
  46. The DATALINK LAYER responds to requests from the _________ layer and issues requests to the _________ layer? 
    The DATALINK LAYER responds to requests from the Network layer and issues requests to the Physical layer? 

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