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08: Network layer - Encapsulation & logical addressing part 1

encapsulation and logical addressing

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This lesson covers the layer 4 of OSI model, the Network layer. The connection between different networks is defined at this layer. It breaks down the process of data transmission from one network to another. WANs (Wide Area Network) are to be identified with this layer on the grounds that they are the combination of different LANs by using logical addressing. The Network layer manages device addressing, tracks the location of devices on the network, and determines the best way to move data, which means that the Network layer transports traffic between devices that are not locally attached. By and large, this layer has the following functions : encapsulation, addressing, routing, decapsulation, fragmentation, and reassembly.

encapsulation and logical addressing


The above figure represents how data is encapsulated at both the Transport and Network layers. Again, when data is at the three upper layers, it is still called data, but once it is passed down to the lower layers it gets different names. At the transport layer, it is called Segment or datagram after TCP or UDP encapsulation. And at the Network layer, it is referred to as packet after being encapsulated into IP header ( either IPX, or IPv6, or Appletalk protocols). 

Encapsulation :

Accordingly, encapsulation simply means the act of packaging data or adding each layer’s header to the actual data. Simply put, when data gets at the Trasport layer, it is no longer called data, it is rather referred to as segment. Moreover, when the segment gets at the Network layer, it is no longer called a segment, it is rather known as packet. The two bottom layers also have different names, which we will see in the lesson of the Data link and Physical layers. Hence, in this lesson, data along with its header will be called packet.

Logical addressing :

Another function of the Network layer is logical addressing. Assigning an ip address to each device’s interface(s) is referred to as logical addressing. No device connected to the internet is without an ip address. Ip addresses locate devices on the network.

encapsulation and logical addressing

 As you see in the above figure, each device has a unique ip address which determines where it is located. But there is a laptop with two ip addresses ! a device can get more than one ip address depending on the interfaces it has. For example, the laptop has two ip addresses because it has two NICs ( Network Interface Card) one for wireless card (WiFi) and the other for Ethernet card. Routers may also have more than one ip address depending also on the interface they possess. Ip addresses are explained in more detail in the subnetting section.

All in all, each data to be traveled across the network is encapsulated into ip header to become a packet, and within this latter the ip address exists.
 
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08: Network layer - Encapsulation & logical addressing part 1 Reviewed by BOUFTIRA on 10:24:00 AM Rating: 5

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