The Fuzzball

Summary:

This paper provides an overview of the Fuzzball, an operating system and application library developed by David L. Mills for the PDP11 computer family. Originally designed as a research platform for DARPA/NSF Internet development, the Fuzzball evolved into a versatile tool for network experimentation, protocol testing (including TCP/IP), and performance evaluation.

Key aspects covered in the document include:

• System Architecture: The Fuzzball utilizes a multi-process, virtual-memory environment designed to run on LSI-11 workstations. It features a sophisticated scheduler, interprocess communication mechanisms, and an emulator that allows it to run RT-11 utilities alongside network applications.
• Networking and Applications: It supports a wide array of Internet protocols and applications, including TELNET, FTP, SMTP, and various testing tools like PING and XNET.
• Experimental Impact: Fuzzballs played a pivotal role in the development and prototyping of critical Internet technologies, such as the Exterior Gateway Protocol (EGP), the Domain Name System (DNS), and the Network Time Protocol (NTP).
• Operational Roles: The system was deployed in several "enduring" networks, notably serving as traffic generators and data-processing platforms for SATNET, providing networking software for the INTELPOST electronic mail system, and functioning as backbone gateways for the NSFNET.
• Congestion and Time Synchronization: The paper details the Fuzzball's implementation of innovative congestion control, including selective preemption and quench strategies, as well as its function as a highly accurate Internet time server.

The document concludes that while the specific LSI-11 hardware became outdated, the Fuzzball's legacy lies in its instrumental role as an inexpensive, flexible tool that allowed researchers to explore the "parameter space" of early Internet architecture and protocols.