ing. In packet switched networking, the sent data is divided into smaller packets that travel independently to their destinations, each transmitted through a route that seems best for a given packet at a given moment. In the Internet, the packets can travel different routes even to the same destination, can get out of order at transit, and even get completely lost, never arriving to their destination. End-to-End Principle The end-to-end principle is one of the most important principles of the Internet and of the Internet technology. It states that the network should not interfere with or alter traffic on layers that are above the network layer. Sometimes this principle is also known as 'Intelligent endpoints - dump network' principle, but that name does not do justice to the concept. Basically, what the principle states is that the network should not make any assumptions about any particular service or characteristic of the data in transit. The network must concentrate on moving the data from its source to its destination. It is up to the end points to understand the traffic and its use. This principle allows the Internet to be used for many different services and applications. Even applications and services can be supported that were at the time of the design of the Internet either technically unfeasible, completely impossible, or even unimaginable. Thus, the principle enables us to create new services without changing the network. Only the end points have to be changed to support the new service or application. Layered Architecture The layered architecture principle is closely linked to the end-to-end principle. The layered architecture principle states that there are different protocol layers that talk to each other on the same level. Figure 1.1 shows the principle in a drawing. The main idea behind the principle is that each layer does its work - no more and no less. This strict separation allows the layers to be independent of each other, and make sure that layers can be changed without changing other layers