Communications of the ACM
Cerf's Up
Connectivity Is Everything
The Turing Award Laureate for 2022, Bob Metcalfe, coined Metcalfe's Law: The value of the network grows as the square of the number of things connected to it. While some might quibble that the more realistic metric might be n log n, the point is well made. As the inventor of the Ethernet, now ubiquitous in so many forms including its wireless origins (ALOHANET) and present form as Wi-Fi as well as wired and optical versions, Metcalfe has earned the right to speak about connectivity. His premise applies equally well to the Internet: connectivity is its essential property. When Robert Kahn and I started working on the Internet in 1973, a primary assumption and driving design premise was that anything on the Internet should be able to connect to anything else, regardless of which network the source and destination happened to be on.
Part of the rationale for this position was uncertainty about all the possible applications that might evolve for interconnected, programmable devices. The original driver for the Internet design was its anticipated service as a backbone network for command and control. This included voice, video, and data transport and interaction among processes running in the attached computers. Very quickly, the implementers of this experimental system invented networked electronic mail or email as it is now known. This proved to be remarkably beneficial to allow researchers to stay current with each other's work without both having to be awake at the same time as would be the case for phone and conference calls. Mailing lists soon followed. This computer-mediated communication opened many new possibilities for software to facilitate and augment information sharing.
The ultimate information sharing tool, the World Wide Web, was developed by Sir Tim Berners-Lee, another ACM A.M. Turing Award recipient. For that to work, every Web page needed to be able to refer to any other Web page using the ubiquitous Uniform Reference Locator (URL) construct of the Web design. Once again, connectivity is everything for the success of this massive information repository. Other aspects of the Internet's design underscore the importance of connectivity. The Domain Name System allows anyone to find by domain name the Internet Protocol address of any host that is registered in the system. The Border Gateway Protocol is a critical part of the global routing system that allows Autonomous Systems to find one another and to move traffic from a source to a destination. An interesting additional conceptual evolution is the Content Distribution Network (CDN) that provides users with access to the "nearest" copy of content, reducing latency and avoiding repeated transfers of content across the global Internet.
As the inventor of the Ethernet … Metcalfe has earned the right to speak about connectivity.
An ambitious evolution of the Internet is now under way in the form of the Solar System Internet using new protocols: The Bundle Protocol Suite. These are designed to overcome the consequences of long propagation delays between the planets, thanks to the slow speed of light and disruption of connectivity owing to celestial motion. Once again, connectivity is everything. Without the ability for spacecraft and manned or robotic bases to communicate with each other and with Earth-based resources, their utility would be dramatically reduced. Although it is early days for the Solar System Internet, the space agencies of the world are actively mounting missions to return to the Moon and planning new missions to Mars and the other planets of the Solar system. In those endeavors too, connectivity will indeed be everything.
We celebrate the annual ACM Awards this month in San Francisco, CA, and I would like to extend my congratulations to all honorees. They represent the best in computer science and computer engineering. They are role models for our younger members and others interested in the science and engineering of computing.
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