Network layer

We have seen how network applications and services on one end device can communicate with applications and services running on another end device.
Next, as shown in the figure, we will consider how this data is communicated across the network - from the originating end device (or host) to the destination host - in an efficient way.
The protocols of the OSI model Network layer specify addressing and processes that enable Transport layer data to be packaged and transported. The Network layer encapsulation allows its contents to be passed to the destination within a network or on another network with minimum overhead.
This chapter focuses on the role of the Network layer - examining how it divides networks into groups of hosts to manage the flow of data packets within a network. We also consider how communication between networks is facilitated. This communication between networks is called routing.
Learning Objectives
Upon completion of this chapter, you will be able to:
• Identify the role of the Network layer as it describes communication from one end device to another end device.
• Examine the most common Network layer protocol, Internet Protocol (IP), and its features for providing connectionless and best-effort service.
• Understand the principles used to guide the division, or grouping, of devices into networks.
• Understand the hierarchical addressing of devices and how this allows communication between networks.
• Understand the fundamentals of routes, next-hop addresses, and packet forwarding to a destination network.