Memory Controller Memory Controller CPU

In its most general form, interconnection networks are a central component of all computing and communication systems from the internal interconnects of chip-scale embedded architectures to geographic-scale systems such as wide area networks and the internet. This section focuses on interconnection networks as they are used in multiprocessor and multicore systems. Specifically, the section addresses basic systems concepts and principles for interconnecting processors, cores, and memory modules. These concepts and principles are not exclusive to this application domain and in fact have also found application in networks used in storage systems, system area networks, and local area networks albeit with distinct engineering manifestations tailored to their particular domains. Interconnection networks have their roots in telephone switching networks and packet switching data networks and in fact the earliest multiprocessor networks were adaptations of those networks. They have since evolved to incorporate new principles and concepts that accommodate the distinct engineering and performance constraints of multiprocessor and multicore architectures. In particular, the lack of standards such as that found in the wide-area and local-area communities created opportunities for meeting performance goals via customized solutions which in turn has been largely responsible for the diversity of implementations. However, the shared goal of high performance multiprocessor communication has led to a common set of principles and concepts organized around a network stack that can be viewed as being comprised of the following layers: routing layer, switching layer, flow control layer, and physical layer. These layers collectively operate to realize the network performance and correctness properties, e.g., deadlock freedom. The physical layer comprises signaling techniques for synchronized transfer of data across links while switching techniques and their interaction with the flow control layer are described in the section on switching techniques in this Encyclopedia. This section describes basic interconnection network concepts covering topology, routing, correctness, and common metrics. The discussion includes the routing layer and periodically exposes dependencies on the lower level layers particularly with