Network Layer
We can say, that move data from point A to point B through multiple systems. Knows the address of the neighboring nodes in the network, packages output with the correct network address information, selects routes and Quality of Service, and recognizes and forwards to the Transport layer incoming messages for local host domains.
Routes messages using the best path available. It is hadrware´s layer, but when routing is solvented by 2 network cabels, it coms like software layer.
Much of the focus here is on the all-important Internet Protocol; the section covering IP includes extensive coverage of IP version 4, IP version 6, and IP-related protocols such as IPSec, Mobile IP and IP Network Address Translation (NAT). The following three subsections cover IP support protocols such as the Internet Control Message Protocol (ICMP) and IPv6 Neighbor Discovery (ND) protocol, and the complete set of IP routing protocols.
As illustrated above, when data arrives at the Network layer, the source and destination addresses contained inside each frame are examine to determine if the data has reached its final destination. If the data has reached the final destination, the Network layer formats the data into packets delivered to the Transport layer. Otherwise, the Network layer updates the destination address and pushes the frame back down to the lower layers.
If router can’t send data frame as large as the source computer sends, the network layer compensates by breaking the data into smaller units. At the receiving end, the network layer reassembles the data.
With this model, the Network Interface Layer would then be defined according to the relevant RFC of the type "IP over ...", such as RFC 894 "Standard for the Transmission of IP Datagrams over Ethernet Networks" or RFC 2549 "IP over Avian Carriers with QoS". It is with this model in mind that the drop-down menus on the RAD University website have been organized.
Question of connection-oriented vs. connectionless services is big problem of this laeyer. It is problem, where locate all complication. All the problem was tackled, that this layer make possible to afford both of them- CONS (Connection-oriented network servies) and CLNS (Connectionless Network Services).
CLNS are realized through subnetwork, which works on base of transmission single datagrams. CONS through communications subnetwork.
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