Special issue on programmable switches and routers.

This Special Issue of JCN explores architectures and implementation challenges for network elements into which executable software can be safely installed and run during normal operation. Unlike traditional network elements. that are pre-programmed by manufacturers or operators. this new type of element, which is usually but not necessarily a switch or router, can be dynamically programmed and can run multiple instances of ontrol and data processing functions. The applications of multicast, traffic control, and DiffServ implementation are addressed in this issue. Many people working in this area feel that support of multiple virtual private networks. each with its own sustomized control plane. will be an important commercial application in the future. More generally. programmable network element. encourage an open market in control and traffic-processing software. promising cost savings and imaginative new services capabi lities for the operators of future networking infrastructure.