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Data takes a very specific shape when moving across the network. This shape is called the frame. So we will take a look at the structure of frames and even have those frames be used as they move across the network. Then we will actually take a look at some data in real time and break those frames down and take a look at the contest .So you can see the layout of a data frame .They start out with the very front with the preamp. This is actually a binary code that allows the recipient in all structures in between such as routers and switches to learn how to read this particular type of data frame. So our preamps will be different depending on the type of information that we are sending .Next in the data frame we see two different destinations. We have a short term destination called the destination MAC and a long term destination called the network destination .That's very important to understand the difference between the two .The destination MAC address is actually referencing that hardwired cord in each of our network devices .This is used for the small movements from one device to the next. Now because these data frames will be send very long distance we can have to have an alternate destination .So that's what this is going to do for us and depending on the network protocol this network will alternate destination is going to be different. Now an order for receiving network devices to know where the information came from and know where it sends its responses we have to have that source MAC address. Again this is going to be short term communication from one device to the next and then we have our alternate source. Again this will rely heavily on the network protocol being used. Following our destination and our source our actual data that the frame is moving will be located. Now its very possible that some problems might arise as our data frames move across the network. So in order to ensure that our data is the same as when it left we have some error detection .Now there are several different forms of this the most common of which is called Cyclic Redundancy Check or CRC. This is actually used in Ethernet frames. Then we will take a little bit better look at CRC later on down the road. So let's take a look at what our data's are going to look like as it moves across the network. So we go ahead and open up our protocol analyzer. We just want to go ahead and change a few setting here to make sure that we actually capture a data and in just a minute we will start seeing our data packets move across the network. So let's stop our capture and take a look at some of the information we have captured. We can see here we have our source, we have our destination, our protocol and our information .This is going to structure the frame. We have got our frame1 here which shows the size of the frame which is 42 bytes in this example shows that an Ethernet frame there is our destination MAC address and there is our source MAC address and this particular destination you will notice is all F's and thus referencing a broadcast .So when you see that F just happens to be the maximum hexadecimal number .So by maxing that out it denotes a broadcast. You can also see down here further into the frame we have got our MAC address we have got our IP address .So this IP address is our alternate destination where in this example our alternate source and there is our alternate destination. In our next section we will cover the different types of connections and how they are used in our networks.
Course: | CompTIA Network+ Certification (2005 Objectives) |
Author: | Brad Causey |
SKU: | 33608 |
ISBN: | 1-932808-53-1 |
Release Date: | 2005-03-22 |
Duration: | 7 hrs / 97 lessons |
Captions: | No |
Compatibility: |
Vista/XP/2000, OS X, Linux QuickTime 7, Flash 8 |