Windows Server 2003 Operating Systems

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The Network layer handles moving packets between devices. It makes routing decisions and forwards packets as necessary to help them travel to their intended destination. In larger net- works, there may be intermediate devices and subnetworks between any two end systems. The network layer makes it possible for the Transport layer (and layers above it) to send packets without being concerned with whether the end system is on the same piece of network cable or on the other end of a large wide area network.

To do its job, the Network layer translates logical network addresses into physical machine addresses (MAC addresses, which operate at the Data-Link layer). The Network a practice exams
layer also determines the quality of service (such as the priority of the message) and the route a message will take if there are several ways a message can get to its destination.

The Network layer also may split large packets into smaller chunks if the packet is larger than the largest data frame the Data-Link layer will accept. The Network layer reassembles the chunks into packets ...
... at the receiving end.

Intermediate systems that perform only routing and relaying functions and do not provide an environment for executing user programs can implement just the first three OSI network layers. Figure 1.5 shows how the Network layer moves packets across multiple links in a network.

The Network layer performs several important functions that enable data to arrive at its destination. The protocols at this layer may choose a specific route through an internetwork to avoid the excess traffic caused by sending data over networks and comptia a practice exams
segments that don’t need access to it. The Network layer serves to support communications between logically separate networks. This layer is concerned with the following:

Addressing, including logical network addresses and service addresses Circuit, message, and packet switching Route discovery and route selection

Connection services, including Network layer flow control, Network layer error control, and packet sequence control Gateway services