Jump to content


 


Register a free account to unlock additional features at BleepingComputer.com
Welcome to BleepingComputer, a free community where people like yourself come together to discuss and learn how to use their computers. Using the site is easy and fun. As a guest, you can browse and view the various discussions in the forums, but can not create a new topic or reply to an existing one unless you are logged in. Other benefits of registering an account are subscribing to topics and forums, creating a blog, and having no ads shown anywhere on the site.


Click here to Register a free account now! or read our Welcome Guide to learn how to use this site.

Photo

packets/frames through OSI


  • Please log in to reply
2 replies to this topic

#1 techgnostic

techgnostic

  • Members
  • 12 posts
  • OFFLINE
  •  
  • Gender:Male
  • Local time:09:52 AM

Posted 04 May 2015 - 03:33 AM

I'm doing a self-study (don't have the money for school) on networking (and then I'll move on to network security), system administration (Linux), and the Python programming language.  Self-study means I don't have a teacher to ask questions.

 

I'm currently going through the "Network+ Guide to Networks" book.  I'm at a hands-on activity, but I don't understand what I'm supposed to do here.

 

Here is the entirety of the hands-on activity's instructions.

1. To begin, draw the OSI model on the left side of your paper, being certain to label each layer.

2. Above the top layer of the OSI model, write "Software".  Then, below the bottom layer, write "Network."

3. Suppose the software issues a message to the network that is 3400 bytes in size.  Next to the Application 
layer, Presentation layer, and Session layer, draw the PDU for this message as it appears at each of these layers (adding the appropriate header at each layer).  Label the fields of the PDU, including the original message 
data.  At the Session layer, how many fields does the PDU contain?

4. At the Transport layer, add a Transport layer header to the PDU.  Recall that the Transport layer is 
responsible for breaking PDUs into the smaller units--or segments--that a network can handle.  Suppose the 
network carrying this request uses Ethernet 802.3 technology, which, as you learned in Project 2-1, specifies 
that frames can be no smaller than 64 bytes and no greater than 1518 bytes in size.  However, PDUs are not 
frames, and those limits include an added minimum of 18 bytes of control information.  Thus, at the Transport 
layer, segments can be between 46 and 1500 byte in size.  Given this information, what is the minimum number of 
segments the Transport layer will divide this message into?

5.  Next to the Network layer, draw a segment after it has been broken down by the Transport layer, and add a 
field that represents this segment's sequence number and length.

6.To make the segment into a packet, next add the Network layer address fields required for the data to be routed over a network.

7. Next to the Data Link layer, add a header, frame check sequence field, and trailer to transform the packet 
into a frame.  The frame is now ready for transmission, via the Physical layer, to the network.

Up until step four, I believe the activity is merely copying a picture from the book ( http://image.slidesharecdn.com/chapter2-100915093855-phpapp01/95/chapter-2-57-728.jpg?cb=1284562293 ).  Seems kind of silly.  Getting to step four sees us doing the same thing (adding a header, which is just a little block to the diagram) and then trying to figure out some very very very simple math.  Now at step five it loses me.  "add a field that represents this segment's sequence number and length".  Just an extra box?  Then step six, adding address fields.  I haven't the slightest idea what they want me to do here.  Not a freaking clue.  And seven wants, in addition to our omnipresent header box, a frame check sequence field (just another box?) and trailer (box at the end?).  Maybe I'm just overcomplicating this.



BC AdBot (Login to Remove)

 


#2 CaveDweller2

CaveDweller2

  • Members
  • 2,629 posts
  • OFFLINE
  •  
  • Gender:Male
  • Local time:10:52 AM

Posted 04 May 2015 - 10:41 AM

You're over thinking it. They are following that diagram. Look at the Data section, first 3 layers it's data then at layer 4(step 4) it becomes Data segmented. They just want you to visualize what happens to all data, every single time it's being transmitted over a network. All of that takes place and then the reverse on the other end. The first time I saw someone break down what data does on the OSI model, I was blown away.


Hope this helps thumbup.gif

Associate in Applied Science - Network Systems Management - Trident Technical College


#3 techgnostic

techgnostic
  • Topic Starter

  • Members
  • 12 posts
  • OFFLINE
  •  
  • Gender:Male
  • Local time:09:52 AM

Posted 04 May 2015 - 07:13 PM

You're over thinking it. ... They just want you to visualize what happens to all data, every single time it's being transmitted over a network... The first time I saw someone break down what data does on the OSI model, I was blown away.

OMG, you're right.  I was obsessing over a "how to do" instead of "what to do", if that makes any sense.  Visualizing I can do, I was so worried about how to get it on paper.  Sometimes my brain just needs to be redirected, thanks for the help.

 

As for the blown away part, me too!  Before it was this unknown magic, now it all makes sense.  It's all quite clever, too.






0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users