401 Guest Editorial Active and Programmable Networks D RIVEN BY advances in underlying technologies, increasing acceptance of computing and middleware paradigms in telecommunication networks, and a need to accelerate network innovation, network researchers are exploring new ways for network routers, switches, and base stations to be dynamically programmed by network applications, users, operators, and third parties. Network elements such as program controlled-switches have been programmable for

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... some time but not in the dynamic manner proposed by the current work. Active and programmable networks seek to exploit advanced software techniques and technologies in order to make network infrastructure more flexible, thereby allowing users and service providers to customize network elements to meet their own specific needs. Customizing routing, signaling, resource allocation, and accelerating information processing in this manner raises a number of significant security, reliability and performance issues. Results from this field of research have the potential for broad impact on customers, service providers, and equipment vendors across a range of telecommunication sectors, including broadband, mobile, and IP networks. Competition among existing and future Internet service providers (ISPs) may hinge on the speed at which one service provider can respond to new market demands over another. The introduction of new services is a challenging task requiring new tools for service creation, including new network programming platforms and supporting technologies. Future programmable networks are likely to be based on active networking and open signaling techniques. Both of these proposals squarely address the same problem: how to "open up" the network and accelerate its programmability in a controlled and secure manner for the deployment of new architectures, services, and protocols. The separation of communication hardware (switching fabrics, forwarding engines) from control software is fundamental to making the network more programmable. Such a separation is difficult to realize today. The reason for this is that switches and routers are vertically integrated-akin to mainframes of the 1970s. Typically, service providers do not have access to switch/router control environments (e.g., the router's operating system), algorithms (e.g., routing protocols), or states (e.g., flow states). This makes the deployment of new network services, which may be many orders of magnitude more flexible than proprietary control systems, impossible due to the closed nature of network nodes. The work on open signaling (OPENSIG) exemplifies the development of new network programming environments that explicitly recognize service creation, deployment, and management in the network infrastructure. Here, there is a clear dis-Publisher Item Identifier S 0733-8716(01)02000-5.