Last a level of content is transmited by
Noun explanation: OSI( Open System Interconnection, the interconnection of open system) model is from the standard of the definition of ISO ( ISO ), it has defined a kind of stratified architecture, when is each layer of in which to have defined according to the agreement of different communication rank. OSI model has 7 layers, 1-7 layer is respectively: Physical layer, data link layer, network layer, transmission layer, conversation layer and expression layer and application layer. OSI model is divide into two parts logically: Lowing the 1-4 layer of layer what pay attention to is the transmission of original data; The 5-7 layer of senior level attention is the application program under network.
We may explain the concept of data pack with a vividly some examples: We when post office sends product, it does not be all right that though, product however uses product original package box only with own package box when sending to pack. Must pack the package of product box puts in the paper case special of a post office that designates , so, can just send. Here, product package box is equivalent to data pack, inside the product put is equivalent to feasible data, and the paper case special is equivalent to , and has only a data pack in a.
"pack" sounds very abstract, so is not is not evidently? Pass through surely technical means, is may the existence that perception wraps to data. For example, in Windows 2000 Server, move mouse to assume office affir fence the net card of right next angle icon goes up ( net card needs receive twinning line and company into network), may see " send: Pack, receive: Pack " hint. Through data pack, trap software may also catch data pack and analyses.
The structure
The structure of data pack is very complex , can say in a few words that settles , here our major understanding its key under one forms may , this is very important for the communication principle of the understanding agreement of TCP / IP. Data pack waits for mainly by " purpose IP address ", " source IP address " and " net year data " until part forms.
The structure of data pack writes letter usually with us is very similar, purpose IP address is to explain that this data pack is to give the whose , is equivalent to addressee address; Source IP address explains this data pack come from where, is equivalent to to post a letter person address; And net year data is equivalent to the content of mail.
It only has such structure because data wraps between, have installed the computer of the agreement of TCP / IP talent mutual communication. We when use based on the network of the agreement of TCP / IP, in network actually, what transmit is data pack. Understanding data pack has the most important meaning for the network safety of network management
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