Connecting Computers With Robert E. Kahn - IEEE Xplore

SCANNING OUR PAST

Connecting Computers With Robert E. Kahn By Alexander B. Magoun

Editor’s note: This month we bring to you an article based on the IEEE Global In this month’s article, we learn about History Network’s Oral Histories series. Dr. Robert ‘‘Bob’’ E. Kahn’s education and his For the Oral Histories project, IEEE History Center’s staff and volunteers unexpected transition from academia to the burgeoning have conducted more than 600 interworld of computer networks in the 1960s and 1970s. views, all of which are available on the Center’s website, www.ieeeghn.org. Scholars in a range of fields have drawn extensively on these interviews as have writers and producers of popular books, articles, exhibits, and and supplies for nursing home chains.1 Kahn’s mother documentaries. Some editing has been done, along with the Beatrice suffered from a rheumatic heart condition that addition of a few illustrations, to make the article more suitable gave Kahn and his younger sister atypically independent for a journal publication. childhoods. He stayed close to home after completing high school in three years, graduating early from the City In 2004, Michael Geselowitz of the History Center College of New York with his B.E.E. in January 1960. interviewed Robert ‘‘Bob’’ E. Kahn (Fig. 1), corecipient While Kahn waited to hear on a National Science of the IEEE’s Alexander Graham Bell Medal (1997) with Foundation (NSF) graduate fellowship, Bell Telephone Vinton Cerf. Kahn, Chairman, Chief Executive Officer, Laboratories hired him to work at its headquarters in and President of the Corporation for National Research nearby Manhattan. His classmates joined companies Initiatives (CNRI), is renowned for his work with Cerf in working on trendy technologies like color television or inventing the standard protocols that enable communica- semiconductors, but he tions between all forms of digital computers and networks. Here he discusses his education and his unexpected opted to go into a kind of an operation with the transition from academia to the burgeoning world of research side of the business, because one, I like computer networks in the 1960s and 1970s. He also offers mathematicsVit’s more mathematical. Number two, his observations on the Internet’s growth and future. Prof. the particular job I took was in a group that was Kahn’s quotations below come from this interview, which worried about the overall structuring of the Bell is available in full at http://ieeeghn.org/wiki/index.php/ System and so it had kind of a national reach and had Oral-History:Robert_Kahn. to do with some of the macro-technological and economic issues that one had to deal with.

I. NEW YORK ROOTS Bob Kahn was born on December 23, 1938, in the Flatbush neighborhood of Brooklyn, NY, USA. His father was a certified public accountant who turned to high school teaching and administration during the Great Depression; on the side he consulted with businesses to improve their network efficiencies: truck delivery routes for a bakery,

Digital Object Identifier: 10.1109/JPROC.2014.2366209

Kahn learned about and worked on the world’s largest network in a group that was run by a fellow named Roger Wilkinson, a grand old gentleman of the Bell System.. . . He’d show up in cardigan sweaters, smoked a pipe, sailed his boat every weekend. He 1 ‘‘Oral history of Robert Kahn,’’ interviewed by Vinton Cerf, September 30, 2006, Computer History Museum ref. X3699.2007, pp. 2–3.

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System. I got to learn how to do assembly language programming as well as FORTRAN programming and to link the two together.

II. FROM MANHATTAN T O PRI CE TON When Kahn received the NSF fellowship, he decided to go to Princeton University, some 50 miles southwest of Manhattan. Still reasonably close to his parents, Princeton offered not only ‘‘an extremely good school’’ but opportunities to grow socially, live in a rural environment, and improve his golf game. I had learned to play golf while I was in high school.. . . The graduate college at Princeton was right on a premier golf course,3 so it was a no brainer. You could literally walk from your dorm room onto the course in a matter of a few hundred feet. So I used to play quite a bit of golf, . . . mainly in the interstices of writing the thesis and the like. With relaxed oversight by his advisor John B. Thomas, Kahn progressed rapidly through the doctoral program in electrical engineering. So rapidly, in fact, that Thomas and the department found he had not spent enough time in the program despite spending four months playing golf4 and completing his dissertation, and assigned Kahn to continue working with newly arrived Professor Bede Liu. His double-length thesis5 examined two questions. The first was, ‘‘how do you do simultaneous amplitude and angle modulation of a signal so as to minimize the amount of bandwidth that it occupies?’’ It

Fig. 1. Robert ‘‘Bob’’ E. Kahn.

was a self-defined gentleman, the kind you associate with that kind of an endeavor. He ran this group in a very avuncular way, and it was really delightful. I got some fundamental jobs to deal with that involved running the program computers and doing simulations and evaluating different alternatives for operation of various parts of the Bell System. It gave me a grand overview . . . understanding how the whole system worked from a global perspective. He was exposed to programming for the first time, preparing

was essentially directly related to the solution of the Schro¨dinger wave equation from quantum mechanics.. . . I guess I really wanted to spend more time understanding, but never really got back to it. I think it’s still an open issue at this point, but it must have to do with some kind of minimization problem in nature. . ..6 The second issue

Monte Carlo simulations. They were mainly written in FORTRAN FAP . . . FORTRAN Assembly Program Linker. [T]hey had an IBM 704 . . . a vacuum tube machine. . .. Very shortly after I got there, they converted over to the solid-state version. . .. We were given desks in a room that involved four or six people. . .. Some of them were pretty world-class people, like John Riordan, the mathematician2. . .. The woman who had the desk to my right was in charge of building some of the computer programming language infrastructure for the whole Bell

dealt with representation of signals. We had known at that time all about the Nyquist theorem, or Shannon sampling theorem, as it’s sometimes called.. . . [I]f you took a signal that is limited in

2 See M. Kac, ed. ‘‘Special Issue in Honor of John RiordanV Introduction,’’ J. Combinat. Theory, Ser. A 24, no. 3, May 1978, www. sciencedirect.com/science/journal/00973165/24/3, accessed Sep. 30, 2014.

3 Springdale Golf Club was founded in 1895 as the Princeton Golf Club by members of the university. The par-71, 6380-yard, 18-hole course was designed and laid out by Gerald B. Lambert in 1911-1915, and revised by William S. Flynn in 1926-1927. See ‘‘Club History,’’ www.springdalegc. org/About-Us/Club-History.aspx, accessed Sep. 30, 2014. 4 ‘‘Oral history of Robert Kahn,’’ p. 19. 5 R. E. Kahn, ‘‘Some problems in the sampling and modulation of signals,’’ J. Bowman and B. Liu, Electr. Eng., Princeton Univ., 1964. 6 R. E. Kahn and J. Bowman, ‘‘Some bandwidth properties of simultaneous amplitude and angle modulation,’’ IEEE Trans. Inf. Theory, vol. 11, no. 4, pp. 516–120, Oct. 1965.

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I assumed would happen, but it didn’t quite work out that way.

bandwidth, that if you sample it at least twice the highest frequencies, you can perfectly reconstruct the signal. I was able to . . . show that in one of the special cases, if you took n linear operations from that signal and sampled each of them at one nth the rate, that you could still put the whole thing back together, as long as the operations were what are known as linearly independent. [It also addressed] the more general question of what was happening with signals that were not band limited and how you could deal with minimizations in that space, and also with issues having to deal with optimal choices of prefiltering to minimize error rates in nonband limited signals, and dealing with issues of time jitter in both the sampling and the reconstruction. It’s a fairly comprehensive coverage of that.7

Kahn had kept his hand in networks by working several summers at Bell Labs on buffers, error control, and remote controls.8 He thought that a practical engineering problem ‘‘was . . . if you were going to build a computer net, what would it look like? What are the issues you’d have to deal with, whether it’s error control or buffer management or routing or whatever. . .. I read a whole series of memoranda on those subjects.’’ He ‘‘had not even been aware of DARPA’’ until he arrived at BBN.9 His supervisor, Jerry Elkind, knew of DARPA’s interest in digital networks and suggested that Kahn visit Larry Roberts and Bob Taylor at the agency to discuss their mutual interests. Lo and behold, I would say within a year . . . they had worked up a whole package to get people to bid on building this network for them. And when the Request for Quotations came out, they pretty much thought they had specified what they wanted.10 It was general, like, ‘‘Deliver packets in a fraction of a second. They’re going to have these little nodes. They’re going to be linked together with 50 kilobits’’Vthat sort of stuff was all prepackaged. But what they did not describe was how to build the actual network itself. So these were kind of architectural decisions that they had made on a very structural level.

III . BOLT BERANEK AND NEWMAN (BBN) AND THE ARPANET After several years as one of MIT’s youngest professors, Kahn took a leave of absence in 1967 when colleague Jack Wozencraft suggested that he gain some experience to learn which theoretical questions had practical implications. I went to a little outfit . . . called Bolt Beranek and Newman (BBN), which at the time was an architectural acoustics firm, but in transit. They were interested in getting into information technology. . . . While they were building up a core competency in state-of-the-art computing, communications was something they would have liked to get into. I think I was the first person they really hired in that dimension.

[T]he package showed up at BBN. . .. I took a look . . . and they were laying out something that looked like I almost knew what to do. I had never built anything like that before, but I . . . knew how to think about it inside and out. By then, Frank Heart had taken on management of BBN’s network initiative and he met with Kahn to discuss ARPA’s request.

Little did Kahn know that his transition to the corporation marked the end of his teaching career. My thought was unequivocal. I was there to get a little practical experience, and . . . in a couple of years that I would be for sure back at MIT. Absolutely. . .. I had grown up as a kid thinking that . . . teaching was sort of the tradition in the family. My dad . . . had been a high school principal. It just seemed like the right match for me. I was very interested in things conceptual and intellectual. I liked working with kids. I liked teaching. That’s what

7 R. E. Kahn and B. Liu, ‘‘Sampling representation and the optimum reconstruction of signals,’’ IEEE Trans. Inf. Theory, vol. 11, no. 3, pp. 339– 347, Jul. 1965.

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I told him I’d be happy to share what I knew. It didn’t occur to me at that time that I would actually get involved in building the network.. . . I was thinking about winding up my tenure there and going back to MIT. He said, ‘‘Look. I’d like to put a 8

‘‘Oral history of Robert Kahn,’’ p. 29. For broader contexts to Kahn’s account, see P. H. Salus, Casting the Net: From ARPANET to INTERNET and Beyond (New York, NY, USA: Addison Wesley, 1995); K. Hafner and M. Lyon, Where the Wizards Stay up Late: The Origins of the Internet (Cambridge, MA, USA: Simon & Schuster, 1996), and J. Abbate, Inventing the Internet (Cambridge, MA, USA: MIT Press, 1999). 10 Defense Supply ServiceVWashington, Request for Quotations, Request no. DAHC15 69 Q 0002, Jul. 29, 1968, Annex B, ‘‘Specifications of interface message processors for the ARPA computer network,’’ p. 22, www.cs.utexas.edu/users/chris/DIGITAL_ARCHIVE/ARPANET/RFQARPA-IMP.pdf, accessed Sep. 30, 2014.

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proposal in on this thing. We’re going to build it.’’ I thought, well, what a great ideaVactually turn those ideas into a real proposal for an actual system. I thought that might be good.

them up and moving them all out of the way, there’s no action that can be taken. I knew that could happen in the net, but I couldn’t convince anybody. Frank and all the other people there were of the view this is like an argument that, ‘‘We better worry about an oxygen circulation system in the conference room, because of some finite probability that all the oxygen molecules will migrate up to the lower left-hand corner and we’ll suffocate.’’ They thought that was kind of ridiculous and therefore we shouldn’t worry about it. . ..

I actually wrote the technical part of the proposal. . . . with some very valuable help from Severo Ornstein, who was the hardware guy.. . . I wasn’t a hardware designer, and I didn’t consider myself a real-time system programmer, but I could sit down with them and say, ‘‘Here’s how the hardware has to work. There’s this thing coming down that has to do this, this, this, this, and this.’’ He’d be designing in real time as I was talking, just manufacturing the specs on the spot. We put the whole proposal together, and it went in, and it worked. ARPA granted the contract to BBN in December, 1968, to deliver a distributed, packet-switching network connecting four differently configured ‘‘host’’ or timesharing computers in two states in nine months, with a vision of further expansion across the country. Heart encouraged Kahn to take the lead in designing, building, testing, and integrating the new interface message processors (IMPs) with each institution’s host computer and the rest of the ARPANET.11 Returning to MIT became increasingly unlikely. It was suddenly clear to me that there was another option here, namely . . . getting this thing built. Because having written the proposal, somebody still needed to figure out what to do. It was sufficiently complex at the time. . .. [T]hat was all new stuff back then. . . . I thought that was real interesting to do, so I decided I’d take another year or two. . .. One of the problems Kahn faced in building the IMPs was others’ confidence that message packet congestion would not be a problem. Do you know what the ‘‘Boston Box’’ is? This is the mechanism whereby you can have an intersection, four cars, and each one is blocking the other car from going through.. . . In the absence of a crane picking 11 BBN’s quarterly technical reports for ‘‘Interface message processors for the ARPA computer network’’ and related documents are available at the BBN Internet Engineering Timeline, http://xbbn.weebly.com/bbninternet-engineering-timeline.html, accessed Oct. 3, 2014. BBN Report 1763, ‘‘Initial design for interface message processors for the ARPA computer network,’’ Jan. 1969, is available at http://bitsavers.informatik. uni-stuttgart.de/pdf/bbn/imp/, accessed Oct. 3, 2014, along with the January 1976 update of BBN Report 1822, ‘‘Interface message processor: Specifications for the interconnection of a host and an IMP,’’ originally issued in the second quarter of 1969. The original issue of specifications does not appear to be available; it is not included in P. H. Salus, ed., The ARPAnet Sourcebook: The Unpublished Foundations of the Internet (Charlottesville, VA, USA: Peer-to-Peer Communications Inc., 2008).

When we went to do the first test of the system out in the field, the very first thing that I did was to make it lock up. We came back and reported it and they didn’t believe it. ‘‘Can’t happen,’’ they said. So I said, ‘‘You were saying in the conference room about all the molecules are in the corner?VThat’s what happened!’’ ‘‘No way!’’ . . . It was six months later before they took their own little simulation and found that, yeah, it really was a problem.

IV. DEMONSTRATING ARPANET Although the ARPANET was running successfully on fifteen nodes and 23 hosts by 1971, it was not very popular, transmitting 675 000 packets a day that fall, or 2% of capacity.12 The host operators needed additional hardware and protocol implementations to connect to the IMPs and few of them saw the incentives for sharing files or the programs on which they ran. Kahn and ARPA’s program director Lawrence Roberts began organizing a demonstration of the ARPANET’s capabilities at the First International Conference on Computer Communications in Washington, DC13 Preparation entailed months of recruiting participants and vendors; the fixed deadline of the conference forced the ARPANET community members to prepare and install the network software and protocols. I basically thought that would be a lot of fun, do a public demonstration.. . . [It] may sound pretty dull, but it involved figuring out how to put a first node of the national net into a hotel room . . . and leave it up for the better part of a week, bring all the researchers and network people who knew anything to that area. We went around and got manufacturers to deliver terminals. We had to get all the machines up and working. We had to get the protocols on the machines. It was the driving force for making the whole network work, writing scenarios. 12

Hafner and Lyon, p. 175. R. E. Kahn, ‘‘Demonstration at International Computer Communications Conference,’’ NWG/RFC #371, Jul. 12, 1972, http://tools.ietf. org/pdf/rfc371.pdf, accessed Oct. 3, 2014. 13

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With the success of the demonstrations to over 1000 attendees in October 1972, Kahn prepared to leave network technology at BBN for an opportunity to work on automated manufacturing at DARPA: ‘‘How do we use computers to help in design and manufacture of virtually anything?’’ However, shortly after he and his wife moved to Washington, ‘‘it was announced to me that Congress had killed the program.’’ Roberts, who had recruited Kahn, persuaded him to ‘‘figure out some new things about networking.’’

how to get it in the first machine. That’s why I asked Vint to work with me. . .. Kahn and Cerf had first met during Kahn’s efforts to measure network performance and demonstrate packet congestion at UCLA, where Cerf was a graduate student under Leonard Kleinrock.17 They worked well together then and renewed the relationship in 1973 to work out the necessary protocols to link computers from any network to computers on any other network.

I ended up setting up the packet radio program.14 I revamped the satellite program something fierce,15 ended up starting a number of other programs in what is now voice-over IP, packet-type speech recognition, and end-to-end securityVsome related problems like that.. . . Here I am sitting with the notion of multiple networks, and I’m trying to think, how would we actually do anything interesting with them if we don’t connect them? . . . If I have a radio net . . . I’ve got to get to some big machine to do anything interesting.

We had meetings at my office at DARPA. We had meetings out in California in his office and walking the streets of Roslyn, VA, and of course, that famous session where we actually wrote the TCP/IP paper, which he then had typed up and promptly threw away the manuscript. We don’t actually have a copy of the actual handwritten version that he and I wrote.. . . It would have been a nice keepsake.18 Through the interaction, what I had been proposing and what he knew from before actually got much better. The synergy between the two of us caused it to be far better than either one of us could ever have done alone. We then worked together and we [DARPA] gave contracts to Stanford, University College London, and BBN to do some initial implementations and do some testing. Of course, it started to roll out experimentally, I would say by the late 1975–1976 time frame. We did some three-node testing in 1977. . .. But there were probably two network tests that were done in either late 1975 or 1976. . ..

So I had the problem of trying to figure in those nets, and I had a basic architectural approach to deal with it, which is what became the Internet. The one problem that I did not know how to deal with back then was, how to take the functionality that I knew needed to be in the computers and actually get them into all these different machines? Because they were all different. That was exactly the problem that Vint Cerf and Steve Crocker and others had worked on in developing the original host protocol for the ARPANET.. . .16 [W]hat were you going to do in a radio case where you were behind a mountain and a signal couldn’t get there or in a tunnel or somebody jammed you . . .?

That’s sort of how things got started. The Internet really remained in a very experimental form until we decided that we would cut the ARPANET over to the use of TCP/IP in the early 1980s.

We knew we needed a better protocol, something that involved some kind of an error detection and retransmission or correction scheme.. . . I had a pretty good idea of what we needed to do, but I didn’t know how to take that and actually figure out

14 R. E. Kahn, ‘‘The organization of computer resources into a packet radio network,’’ Proc. AFIPS Nat. Comput. Conf. Expo., May 19–22, 1975, pp. 177–186; reprinted in IEEE Trans. Commun., vol. 25, no. 1, pp. 169– 178, Jan. 1977. See also R. E. Kahn, S. A. Gronemeyer, J. Burchfiel, and R. C. Kunzelman, ‘‘Advances in packet radio technology,’’ Proc. IEEE, vol. 66, no. 11, pp. 1468–1496, Nov. 1978. 15 R. E. Kahn, ‘‘The introduction of packet satellite communications,’’ Conf. Record Nat. Telecommun. Conf., Nov. 27–29, 1979, pp. 45.1.1-6, https:// archive.org/details/TheIntroductionOfPacketSatelliteCommunication, accessed Oct. 6, 2014. 16 For Cerf’s recollections, see ‘‘Dr. Vinton Cerf: An interview conducted by David Hochfelder,’’ Sec. 4.2 ‘‘ARPANET,’’ May 17, 1999, IEEE History Center Interview #355, www.ieeeghn.org/wiki/index.php/ Oral-History:Vinton_Cerf#ARPANET.

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People were plugging in local area nets into the system experimentally before that. This was a way to make all of that local area network traffic and computers become actually part of a working composite system. Remember, the IBM PC didn’t really come into being until the early 1980s, and even then it didn’t have enough power to really run TCP/IP protocols. These were mainly experimental workstations.. . . By the early 1980s, there were 17 For Kleinrock’s recollections of this period, see ‘‘Leonard Kleinrock: An interview conducted by John Vardalas,’’ Sec. 4.21, Feb. 21, 2004, IEEE History Center #434, www.ieeeghn.org/wiki/index.php/Oral-History: Leonard_Kleinrock. 18 V. G. Cerf and R. E. Kahn, ‘‘A protocol for packet network interconnection,’’ presented at the 1st Int. Netw. Working Group Meeting, Univ. Sussex, U.K., Sep. 1973, and published in IEEE Trans. Commun., vol. 22, no. 5, pp. 637–648, May 1974; reprinted in ACM SIGCOMM Comput. Commun. Rev., vol. 35, no. 2, pp. 71–82, Apr. 2005.

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pockets of real capability developing, and they were all on LANs. The Internet was sort of a lot of LANs connected to the ARPANET with linkages to satellite nets.

in 2006, he anticipated three trends: increased ubiquity of wireless access to information; expansion of broadband alternatives; and the spread of digital object architecture, which was his ‘‘attempt to try and reconceptualize the Internet around the management of content.’’

The biggest surprise was the fact that they soon had to deal with thousands of LANs instead of dozens of larger networks. When we did the original addressing, the ARPANET addressing [was] fifteen-bit addressesVperfectly good for a network that might have 64 or 120 nodes. We knew with the Internet we’d need more, so we said, ‘‘Let’s make the Internet addresses 32 bits long.’’ . . . [W]e’ll make the first eight bits specify which network and the other 24 specify which machine on that net. Again, more than we thought we’d ever see in our lifetime. ‘‘We only have ten nets, we’ve got 246 more to go.’’ We thought, surely this is good enough, and very soon we realized it wasn’t. . ..

The whole idea was that you no longer are dealing with machines and files, but you’re actually identifying data structures themselves. If every data structure, which we call a digital object, has its own built-in, unique identifier, and you have a system that lets it persist . . . indefinitely, then you have the basis for managing information over the long haul. . .. It allows you to organize things in a way that doesn’t require somebody’s search mechanism to go out and find your stuff. . ..21 Looking back at what started ‘‘as a little research experiment, three nets that DARPA had been building,’’ Kahn believes that

Kahn left DARPA in 1986 and started CNRI to raise funds for the establishment of new networks, gigabit test sites,19 and a succession of other projects and initiatives to improve and expand the Internet’s capabilities.20 Speaking

The reason I think we were successful was that so few people saw it as that meaningful when we started it. . .. [W]hat happened with the Internet probably could not have happened if people understood what a big impact it was likely to have.

19 ‘‘The Gigabit Testbed Initiative: Final report,’’ Dec. 1996, www.cnri.reston.va.us/gigafr/Gigabit_Final_Rpt.pdf, accessed Oct. 6, 2014. 20 See ‘‘System and technology demonstration projects’’ at www.cnri.reston.va.us/projects.html, which links to ‘‘Earlier projects and other areas of interest.’’

21 The 100 millionth DOI was assigned in September 2014: DOI News, Sep. 2014, p. 1, www.doi.org/news/DOI_News_Sep14.pdf, accessed Oct. 6, 2014.

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