Chapter |Tech|: Network Technology
We started Chapter |Intro| by asking one of the first questions any system architect must ask:
What available technologies will serve as the underlying building blocks?
When the inventors of the Internet asked that question in the mid-1970s, there weren’t many options. The ARPANET was an experimental wide-area network, and the Ethernet had just been invented by researchers at Xerox. At the time, large mainframe computers were the norm, with Digital Equipment Corporation’s PDP-11 (a 16-bit minicomputer that would inspire Intel’s x86 and Motorola’s 68000 microprocessors) being the most influential offering in the “small and affordable” computer market.
To set a bit more historical context, demonstrating the viability of packet switching itself—as opposed to circuit switching technology used by phone companies—was the ARPANET’s main innovation. The ARPANET, in turn, was built on top of two existing technologies: (1) 64kbps digital circuits leased from AT&T, and (2) a 16-bit processor from Honeywell, a peer of the PDP-11 that was typically deployed in industrial environments. The former provided the link technology and the latter was programmed to forward packets.
Jump forward to the present day, and the technology landscape is very different. Today’s phone companies emulate voice circuits on top of a packet-switched substrate that can be directly traced back to the ARPANET. Hundreds of link technologies have been introduced (and abandoned), with Ethernet continually adapting to serve as a ubiquitous communication technology. And while some low-end packet switches are still implemented in software running on general-purpose processors, there are now domain-specific chips optimized for packet switching, analogous to the emergence of GPUs for graphics and TPUs for AI.
This chapter gives an overview of these building block technologies, which then serve as the basis for Part II. While this chapter focuses on Ethernet, we caution that other technologies do exist. We discuss some of them in the last section, but Ethernet is the example technology that we describe in detail. If you understand Ethernet in depth—both its links and switches—you can more easily digest any other technology you encounter.