Network architecture and protocols
The key to understand complex networks is understanding their architecture. Architecture is the most universal, high-level, and persistent elemments of structure and organization (or princciples of structuring and organizing a complex system). Protocols define how diverse modules interact, and architecture defines how sets of protocols are organized. Architecture usually involves specification of protocols (rules of interaction) more than modules (which obey protocols). In engineering, system architecture must facilitate system level functionality as well as robustness and evolvability to uncertainty and change in components, function, and environment.
Take, Internet, as an example. The Internet is an obvious example of how a protocol-based architecture facilitates evolution and robustness. The architecture of TCP/IP (Transmission Control and Internet Protocols), or the hourglass protocol stack as it’s known, has a thin, hidden “waist” of universally shared feedback control (TCP/IP) between the visible upper (application software) and lower (hardware) layers. The term “hourglass” has been used because there is a vast diversity of applications and hardware that sit above and below the thin waist of universally shared control mechanisms (TCP/IP). Roughly, IP controls the routes for packet flows and thus, available bandwidth. Applications split files into packets, and the TCP controls their rates and guarantees delivery. This allows “plug-and-play” between modules that obey shared protocols; any set of applications that “talks” TCP can run transparently and robustly on any set of hardware that “talks” IP.
In most networked systems, protocols within a layer can be visualized as “bowties,” which have large fan-ins and -outs of energy, materials, and information via a thin ‘knot’ of universal protocols specifying carriers, building blocks, or interfaces. Other engineered examples of bowties include networks which connect energy sources to diverse consumers via carriers and standard socket-plug interfaces, and raw materials to assemblies via standardized building blocks in advance manufacturing. In these and the biologic examples, the currencies, carriers, intermediates, precursors, plugs, packets, conserved residues, and interfaces in the bowtie “knot” are highly constrained by protocols. Yet their shared universality allows diverse and robust edges toadapt and evolve, as long as they have appropriate (and typically hidden) layers of feedback control such as TCP/IP.
While there does not yet exist a coherent theory of architecture, a condition we aim to change, there are now enough examples from technology and biology that suggest the required mathemtical foundations and the needed research issues along the way to a unified and coherent theory of architecture. Especially, in recent decades there has been a phenomenal increase in the wides-spread deployment and development of "communications technology", (eg., computers, the internet and the world wide web). This includes communication networks, where various protocols have been adopted and used to help with ......this upscale growth??? The architecture of these communications networks ...