Activating networks: A progress report

Active networks-networks you can add programs to or customize to particular applications-are probably most familiar as Web proxy caches and firewalls. In their more sophisticated form, however, they have become customized inf rastructures that let designers program control planes-the control software and network hardware used to manipulate the transport system's behavior. P rogramming mechanisms such as open signaling are becoming more widespread; for example. But research in active networks has taken a step beyond even these sophisti cated infrastructures. Working systems now let designers modify packet-swit ching infrastructures on the fly using either a switch-like model, which mi xes active packets with other packets, or in a capsule model, which regards all packets as programs. In surveying working systems and experimental results, the authors have fou nd that first-generation systems have opted to use modern programming langu age technologies such as Caml and Java to provide usability and safety, and cryptographic techniques to provide security. The systems differ in the de gree of flexibility and performance they offer. Many differences stem from the use of a particular security model.