The popularity of the Internet and the emergence of broadband access networks is fueling the development of communications processors -devices that integrate processing, networking, and system functions into a single, low-cost, system-on-a-chip. These devices form the core of cable modems, ADSL modems, set-topboxes, smart packet phones, and a variety of Internet appliances. The conventional approach for designing communications processors is to start with a standard CPU core such as MIPS or

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... add to this several network interfaces, and tie the whole system together with a multi-channel DMA controller. In such designs the DMA controller often becomes the most complex part of the system. The integration of processing and networking into the same device offers an opportunity to rethink the way the CPU and network interface interact. In this paper we describe UNUM, an architecture for integrating communications functionality into the CPU that not only simplifies the design of communications processors, but also improves their performance and provides them with greater flexibility.