These
specifications are implemented in networking hardware.
?– Data Link layer Defines the addressing of frames and the sending and
receiving of frames between two linked computers. After passing a frame to the
Figure 5-3. The OSI model describing networking between two computers
103 Chapter 5: Windows Server 2008 Networking Environment
Physical layer to be sent, the Data Link layer waits for acknowledgment that the
frame has been received before it sends another frame; if the acknowledgment
is not received, the Data Link layer resends the first frame. The Data Link layer
provides point-to-point linkage between itself and the receiving computer
by using physical addresses. The physical address at the Data Link layer is
called the media access control (MAC) address. The Data Link specifications are
implemented in a combination of hardware and dedicated networking software.
?– Network layer Defines the packaging of packets into frames and the logical
addressing (as opposed to the physical addressing used in the Data Link
layer) necessary to provide internetwork routing through multiple, connected
networks. Packets, which may be larger or smaller than frames, are broken up
or combined to create a frame in the sending computer, and are reassembled
or disassembled in the receiving computer to reproduce the original packets.
The Network layer??™s internetworking commonly uses the Internet Protocol
(IP) addressing to identify where frames should be sent.
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