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OSI layers

Discussion in 'Network+' started by twizzle, Feb 15, 2006.

  1. twizzle

    twizzle Gigabyte Poster

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    Ok does anyone have an easy way to remeber the OSI layers and what happens where within them? Im having problems rembering what connects where on the osi and what protocols go with what layer... its driving me nuts. If i can crack this i might just pass the exam.
     
    Certifications: Comptia A+, N+, MS 70-271, 70-272
    WIP: Being a BILB,
  2. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    Have you tried searching our site for "OSI"? I know we've tackled this one before.
     
    Certifications: A+ and Network+
  3. Malnomates

    Malnomates Megabyte Poster

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    something like Please Do Not Throw Sausage Pizza Away...

    Remember,layer 1 is at the bottom,7 at the top.From bottom to top...PDNTSPA


    7.Application
    6.Presentation
    5.Session
    4.Transport
    3.Network
    2.Data Link
    1.Physical
     
    Certifications: A+ Network+
  4. Jakamoko
    Honorary Member

    Jakamoko On the move again ...

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    I learned it the other way around:

    All People Seem To Need Data Processing

    And I keep this link on my little homepage

    OSI Model

    Hope this helps :)
     
    Certifications: MCP, A+, Network+
    WIP: Clarity
  5. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    Thats my favourite!

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  6. Japanese Elvis

    Japanese Elvis Nibble Poster

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    I honestly don't think I'd have remembered it if it wasn't for this.

    Although I vaguely recall one which involved Australian ladies of ill repute.............

    :eek:
     
    Certifications: A+, Network+, MCSA Server 2003
    WIP: Get a job?
  7. Luddym

    Luddym Megabyte Poster

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    Hey Twizzle,

    Im studying for the Network + as well, and the OSI just throws me every time.

    What I'm currently doing is reading everything I can on it, and building up a spreadsheet. For each OSI level, Im writing a breif explanation of what each level is / does (which most wesbites seem to have) and I'm also using a column where im accumulating the protocols and processes (Ie tcp - ip - spx - hubs - routers) in the OSI level they should be in.

    I hope to finish it in the next few days (Hopefully soon anyway, as Id ment to take the N+ This week . . . cant let it drag on too long) so if it would help, you are welcome to a copy of it. Obviously don't use any one piece of material as your only study guide, but it all helps.
     
    Certifications: VCP,A+, N+, MCSA, MCSE
    WIP: Christmas Drunkard
  8. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    One of the problems with OSI which you should bear in mind is that it is more of a theoretical thing than anything else. Many popular protocol stacks have approximate mappings to OSI layers, and sometimes books will differ as to where things go.

    In addition also remember that a layer can sometimes be split into sublayers in the real world. ADSL is a classic example of this!

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  9. Pete01

    Pete01 Kilobyte Poster

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    One way to familiarise yourself with the OSI is to learn what protocols and devices function at which layer and why. As previously mentioned the OSI is an industry standard that was formed to define industry wide compatability for networking devices from different vendors.

    A very important networking function that is well illustrated by the OSI concept is encapsulation and decapsulation. As information travels down the OSI model (or any other protocol stack) each layer encapsulates the information it recieves with it's own specific header (and sometimes footer as well). When information travels back up the stack the headers (and sometimes footers) are stripped away or decapsulated.

    You may have heard of units of information being referred to as bits, packets, frames, segments- these terms aren't interchangeable. They are descriptive of the layer at which the information is at that time. Example;- At layer 3 (network layer) the information is in a layer 3 packet, as it is passed down to layer 2 it becomes a layer 2 frame.

    Another acronym to remember for encapsulation is Don't Some People Fry Bacon. This stands for Data, Segments, Packets, Frames, Bits. They map to the 7 layers like so:

    Application-----------------Data
    Presentation---------------Data
    Session--------------------Data
    Transport------------------Segments
    Network--------------------Packets
    Data Link------------------Frames
    Physical-------------------Bits

    Not wanting to confuse you further by adding more stuff to remember but hopefully. Here's a very good page explaining encapsulation and decapsulation it's even got a little movie illustrating it!:

    http://www.firewall.cx/osi-encap-decap.php

    Some more OSI links as well if you want:

    http://www.firewall.cx/osi-intro.php

    http://www.firewall.cx/protocols.php

    http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/osi_prot.htm

    Hope this helps!
     
    Certifications: MCP (NT4) CCNA
    WIP: 70-669, Learning MSI packaging
  10. simongrahamuk
    Honorary Member

    simongrahamuk Hmmmmmmm?

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    Great Stuff Pete! :thumbleft
     
  11. Boycie
    Honorary Member

    Boycie Senior Beer Tester

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    as a N+ student i have to say that this page is packed full of help, thanks to all who have contributed :clap
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  12. twizzle

    twizzle Gigabyte Poster

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    Well thanks for all the tips guys. Im hoping if i try all of em something might stick. I just cant seem to get my head around what fits where within the OSI model.... Im even getting the same questions wrong using Exam cram tests (im trying not to learn the questions but learn what thier about), and its all on the OSI layers.. If i can just squeeze 2 or 3 marks outta this i would pass more often. :eek:
     
    Certifications: Comptia A+, N+, MS 70-271, 70-272
    WIP: Being a BILB,
  13. Sandy

    Sandy Ex-Member

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  14. Jakamoko
    Honorary Member

    Jakamoko On the move again ...

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    lol - Sandy, that's still pinned to the wall above my desk since I did the N+. It remains one of the best summaries of OSI I have seen to date.

    To anyone doing the N+ or looking for OSI info - print that page off and keep it handy. Priceless.

    Nice work, Sandy. :D
     
    Certifications: MCP, A+, Network+
    WIP: Clarity
  15. arisen

    arisen Byte Poster

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    nice website Sandy.
     
    Certifications: BEng, PRINCE2, ITIL, Net+
    WIP: MSc, Linux+ 2009, RHCE

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