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CHAPTER 18 The Network

18.3 Ethernet Frame

Ethernet traffic is transported in units of a frame, where each frame has a definite beginning and end. The form of the frame is in the figure below.

FIGURE 18.1 Ethernet Frame

In this model we define:

The data to be sent is encapsulated by each layer, from the Application down to the Physical, and each adds it's own header information. When data is received each layer strips off it's header and then passes the packet up to the next layer. The Transport Layer makes sure that the source and destination, hosts and ports, can be identified, and includes a sequence number so that a file can be broken into multiple packets and recombined on the receiving end. The Internet Layer determines how the frames will be delivered, including fragmenting them to send along a path with a smaller maximum transmission unit (MTU) or recombining them for a larger MTU path. It determines the routing used to get to the destination. The Network Layer provides the encapsulation of the datagram into the frame to be transmitted over the network. It includes the ethernet addresses of the source machine and of the next hop towards the destination. These addresses are rewritten with each hop.

Unix System Administration - 8 AUG 1996
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