<Dd> The internet layer exchanges datagrams across network boundaries . It provides a uniform networking interface that hides the actual topology (layout) of the underlying network connections . It is therefore also referred to as the layer that establishes internetworking . Indeed, it defines and establishes the Internet . This layer defines the addressing and routing structures used for the TCP / IP protocol suite . The primary protocol in this scope is the Internet Protocol, which defines IP addresses . Its function in routing is to transport datagrams to the next IP router that has the connectivity to a network closer to the final data destination . </Dd> <Dd> The link layer defines the networking methods within the scope of the local network link on which hosts communicate without intervening routers . This layer includes the protocols used to describe the local network topology and the interfaces needed to effect transmission of Internet layer datagrams to next - neighbor hosts . </Dd> <P> The Internet protocol suite and the layered protocol stack design were in use before the OSI model was established . Since then, the TCP / IP model has been compared with the OSI model in books and classrooms, which often results in confusion because the two models use different assumptions and goals, including the relative importance of strict layering . </P> <P> This abstraction also allows upper layers to provide services that the lower layers do not provide . While the original OSI model was extended to include connectionless services (OSIRM CL), IP is not designed to be reliable and is a best effort delivery protocol . This means that all transport layer implementations must choose whether or how to provide reliability . UDP provides data integrity via a checksum but does not guarantee delivery; TCP provides both data integrity and delivery guarantee by retransmitting until the receiver acknowledges the reception of the packet . </P>

Which came first tcp/ip or osi