Network on a chip

A network on a chip or network-on-chip (NoC /ˌɛnˌoʊˈsiː/ en-oh-SEE or /nɒk/ knock) is a network-based communications subsystem on an integrated circuit ('microchip'), most typically between modules in a system on a chip (SoC). The modules on the IC are typically semiconductor IP cores schematizing various functions of the computer system, and are designed to be modular in the sense of network science. The network on chip is a router-based packet switching network between SoC modules. A network on a chip or network-on-chip (NoC /ˌɛnˌoʊˈsiː/ en-oh-SEE or /nɒk/ knock) is a network-based communications subsystem on an integrated circuit ('microchip'), most typically between modules in a system on a chip (SoC). The modules on the IC are typically semiconductor IP cores schematizing various functions of the computer system, and are designed to be modular in the sense of network science. The network on chip is a router-based packet switching network between SoC modules. NoC technology applies the theory and methods of computer networking to on-chip communication and brings notable improvements over conventional bus and crossbar communication architectures. Networks-on-chip come in many network topologies, many of which are still experimental as of 2018. Networks-on-chip improve the scalability of systems-on-chip and the power efficiency of complex SoCs compared to other communication subsystem designs. A very common NoC used in contemporary personal computers is a graphics processing unit (GPU), which is commonly used in computer graphics, video gaming and accelerating artificial intelligence. They are an emerging technology, with projections for large growth in the near future as manycore computer architectures become more common. Networks-on-chip can span synchronous and asynchronous clock domains, known as clock domain crossing, or use unclocked asynchronous logic. NoCs support globally asynchronous, locally synchronous electronics architectures, allowing each processor core or functional unit on the System-on-Chip to have its own clock domain. NoC architectures typically model sparse small-world networks (SWNs) and scale-free networks (SFNs) to limit the number, length, area and power consumption of interconnection wires and point-to-point connections. Traditionally, ICs have been designed with dedicated point-to-point connections, with one wire dedicated to each signal. This results in a dense network topology. For large designs, in particular, this has several limitations from a physical design viewpoint. It requires power quadratic in the number of interconnections. The wires occupy much of the area of the chip, and in nanometer CMOS technology, interconnects dominate both performance and dynamic power dissipation, as signal propagation in wires across the chip requires multiple clock cycles. This also allows more parasitic capacitance, resistance and inductance to accrue on the circuit. (See Rent's rule for a discussion of wiring requirements for point-to-point connections). Sparsity and locality of interconnections in the communications subsystem yield several improvements over traditional bus-based and crossbar-based systems. The wires in the links of the network-on-chip are shared by many signals. A high level of parallelism is achieved, because all data links in the NoC can operate simultaneously on different data packets. Therefore, as the complexity of integrated systems keeps growing, a NoC provides enhanced performance (such as throughput) and scalability in comparison with previous communication architectures (e.g., dedicated point-to-point signal wires, shared buses, or segmented buses with bridges). Of course, the algorithms must be designed in such a way that they offer large parallelism and can hence utilize the potential of NoC. Some researchers think that NoCs need to support quality of service (QoS), namely achieve the various requirements in terms of throughput, end-to-end delays, fairness, and deadlines. Real-time computation, including audio and video playback, is one reason for providing QoS support. However, current system implementations like VxWorks, RTLinux or QNX are able to achieve sub-millisecond real-time computing without special hardware.