ABSTRACT
There are several different Layer 3 or Network Layer protocols available in today’s networks. However, IP is the most widely used network layer protocol. IP is a fairly complex protocol and it is often considered to be the glue that holds today’s Internet together. Even though IP has a wide variety of responsibilities, its primary task is to deliver data between the end systems in the Internet. Such data delivery may span multiple links and networks and requires that each node is uniquely identied through an IP address. An IP address identies a particular interface that connects a node to a network. In end systems or hosts, which typically contain a single interface, an IP address uniquely identies the node’s interface or the node itself and therefore is often referred to as the host’s IP address. Routers, on the other hand, are typically connected to multiple networks and therefore contain multiple interfaces. Each active interface in a router has a different IP address allocated to it. In this book, we will refer to an IP address as the address that identies a particular interface in a node. In addition to end-to-end communication, the network layer handles data encapsulation, fragmentation and reassembly, data forwarding, routing, compression, multicasting, load balancing, preferential data treatment to support various Quality of Service (QoS) requirements, and other functions. OPNET software models the majority of these features and allows for custom conguration of various aspects of IP.
