280 CHAPTER 15 Next-generation Internet architecture overnight. Our dependence on the availability of data communication requires that the current Internet continues to be available until users, end systems, and applica- tions have transitioned to the next-generation network. Considering how many legacy-computing systems are still used today, it is likely that the current Internet will remain operational in its current form for a long time. To introduce a next-generation network, it is likely that this network will be built up in parallel to the current Internet. Some of the existing Internet infrastruc- ture can be used for the initial deployment (e.g., to tunnel traffic). Over time, more network traffic will shift to the new network and make the existing Internet increasingly obsolete. One important requirement for this transition is that there is a clear goal on what the next-generation Internet architecture looks like. At this point, there is no definite answer. Instead, industrial and academic research is still exploring alternatives. Experimental testbeds Experimental validation of different design alternatives for the next-generation Internet is essential to argue for the deployment of a particular network architec-