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.