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Vint Cerf - A Brief History of Packets
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来自 University of Michigan 的课程
互联网的历史、技术和安全
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从本节课中
Technology: Internets and Packets
The Internet is designed based on a four-layer model. Each layer builds on the layers below it. The Link and Internetwork layers are the lowest layers of that model.
与讲师见面
Charles SeveranceAssociate Professor
School of Information
[music]. Packet switching was an idea which was
specifically studied by Leon Kleinrock at MIT, who was actually looking at message
switching. And he did a brilliant dissertation, on
these queuing theories, to analyze what networks of queues would look like, using
this, message switching approach. And, his analysis, although we'd never
used the word packet is, is equally applicable to packet switching as it is to
message switching, so that's one important milestone, in, around 1961.
In 62, or there about, Paul Baran is doing work for the Rand corporation, and is
deeply concerned about, the ability to preserve command and control in a
post-nuclear environment. We were seriously worried that the
Russians would actually launch, and that we would suffer a nuclear attack, and that
we had to be able to respond, and we needed command and control for that.
So Paul, in 1962, before the existence of integrated circuits or anything else is
Saying we really should be digitizing and packetizing voice and then using sort of
pole-mounted radios that are able to transmit in all directions To create a
highly connected environment. So that if holes were knocked out of it by
nuclear explosions. You would still, if it's a fabric that's
in any way connected. The information can get from 1 end to the
other. So he envisioned the notion of a message
block. And it was dynamically routed.
He used hot potato routing. If he got something, he got rid of it as
fast as he could. He chopped up the speech into little 20
millisecond pieces. He didn't talk so much about data as I
remember it. And this was supposed to be a highly
resilient voice network for command and control.
I may have just done him a disservice because later he was very much conscious
of the importance of data communication too.
So that's around 1962 it gets documented in an 11 volume series called
nondistributive communications and he can't sell it to anybody.
That at traditional telcos, AT&T in particular, and the people at what was in
the defense communications system, er defense communications agency, laughed him
out of the room, said this was a silly idea, couldn't possibly work, and so you
know he should just go away. So he never got anywhere with that in
spite of all the documentation. In 66, Larry Roberts along with one other
guy whose name I'm now not remembering, does a point-to-point experiment to test
packet switching. It was between the ANSF-Q 7 machine, at
System Development Corporation in Santa Monica, and the TX2 machine at MIT Lincoln
Laboratories, was what Larry was. They demonstrated on a 2400 you know, bit
line, bit per second line, that you can move packets back and forth.
Then in the 64 or 65 time frame. A man name Donald W.
Davies, of the National Physical Laboratory in London, also gets the bug.
Tries to get money from the science research commission at in, England.
And gets only enough to build 1 node you know, the, the 1 node network.
So he builds this packet net. He invents the term packet to describe
what these objects are and it works. He's got a bunch of you know, terminals
and other things hanging off of this 1 node.
So in, in a funny way he built the local area network if you like.
But it was you know, based on physical wires.
So those three guys, introduced packet switching, Larry and who ever it was that
he worker with demonstrate that it's possible to get very distinct kinds of
computers, talk to each other, using the standard way.
Jcr Licklider, is, is, a psychologist actually, at MIT but he's convinced in the
early 60s that computing is important to non numeric processing.
That it will allow people to work together and collaborate in ways that they never
could before. He comes and starts the information
processing techniques office at ARPA. With this bee in his mind.
And who does he encounter? He encounters Douglas Engelbart, at SRI
International, and the two bond, basically, because Engelbart was all about
nonnumeric computing and the ability of people to build up a superstructure of
communications and documents and interact with each other hyper linking.
The mouse, the portrait mode display. Black on light, black and white
presentations. I mean, the guy had a worldwide web in a
box at SRI. And Licklider understands that.
Licklider's sending out notes to his little community of, of people talking
about the intergalactic network. I mean it tongue in cheek.
So he really gets credit for having put this meme in place at ARPA.
Then Taylor comes along to pick up the, the responsibilities for running the IPT
over from Rick Leiter. And it's all hacked off because he got 3
terminals in his office at the Pentagon, connecting to 3 different machines and he
can't, why can't there be 1 terminal talking at all 3?
We need a network. And so as he's pursuing this idea with
Charlie Hertzfeld, he's the head of ARPA at that time, Charles hands in a million
bucks over a 20 minute conversation and now Taylor's got the problem, who's going
to actually do this because Taylor's not a technologist either.
He's being another, you know, kind of psychologist type.
So he decides to get Larry Roberts, from Lincoln Laboratories, who did that packet
thing, and Larry doesn't want to come. So, he goes and complains about this to
Charlie Hertzfeld. Charlie calls up the guy that runs Lincoln
Labortories, and says, you know, we pay for a significant fraction of your
research budget every year, you should, you should tell Larry he should show up.
And in fact, I thought that maybe Larry had been forced to do this, you know, by
Charlie. I think it was probably a little less
awful than that, but Larry was persuaded to come down.
Eventually, of course, inherited the operation of the office from Bob Taylor
but in the meantime, is the guy responsible for doing the, initiating the
Internet, or the ARPAnet project. So they write an RFC, or, no an RFQ,
request for quotation. A bunch of responses come back, probably
on the order of a couple dozen, I don't know.
Personally, for sure how many. I know that I wrote one of them with my
colleague, bah, Steve Crocker, while we were still at UCLA as graduate students,
but we were consulting with a company called Jacobi Systems, in San, Santa
Monica, and Jacobi Systems wrote one of the responses.
Bolt, Baranek and Newman wrote another response, primarily written by Bob Kahn,
who'd come to BB and N from MIT. So, the responses come back and they get
evaluated and 4 of them end up. And the Jacobi Systems one isn't one of
them. Or if it was, it didn't get selected.
Bb and N got selected. So Steve Crocker and I kind of hiked back
to UCLA as graduate students. And the next thing we know, Glen
Klienmach, who's at UCLA, and who had written, you know, this original
dissertation work on packet switching, has come to UCLA to teach and explore queuing
theory is a close compatriot of Larry Roberts, because they were both in Lincoln
Labs together. So he gets the network measurement center
piece of the ARPAnet project. And Steve Crocker and I and John
Prostelle, all of us from the same high school in Santa Monica er, in San Fernando
valley. End up in Glen Kleinmach operation,
running the network measurement center. So I was the principle programmer for
that. Steve Crocker took the responsibility for
managing and leading the network working group which led to the protocols, host to
host protocols. And Jon Postel eventually becomes the
keeper of the documentation. He's the RFC editor.
Which Steve Crocker started, Request for Comments.
He's the guy that becomes the numbers czar, which is keeping track of address
spaces, and allocations, and eventually becomes the domain name manager of the
Internet Assigned Numbers Authority when the internet happens.
And that hasn't happened yet. That this period of time of the ARPAnet
program, it brings us up to 1972 and this is an important moment in this whole
history because the first demonstration of the ARPAnet happens in the Washington
Hilton Hotel basement in October, 72. A whole bunch of people from the
networking, interested networking community.
Packet-switching community at TEM not only in the US but from France and from England
and Italy and Germany and elsewhere, that group of about 25 or 30 people convenes,
sees the ARPAnet in operation, sees applications that were being done.
And including Doug Englebert's staff. And then forms this international working
group modeled after the working group that Steve Crocker managed to build the ARPAnet
system. And at this point I become the chairman of
that group because Steve is busy at ARPA doing artificial intelligence.
The next, at the end of that year Bob Connelly leaves Bolt, Bemnek and Newman
and goes down to ARPA. I leave UCLA where I'd been working with
Crinerock, and Crocker, and Pastel and I go to Stanford.
So Bob is at ARPA, I'm at Stanford and in the spring of 73, Bob comes out from ARPA
and he says, I have a problem. He says, what's your problem.
He says, well, we got this ARPAnet. He says, Yep.
But we also are working on other networking capability to make command and
control work for the military. If you're going to be serious about
putting computers in command and control, they have to be mobile, they have to be in
you know, armored personnel vehicles, and tanks, and all these other things.
They have to be seaborne so we can have ship to ship, and ship to shore
communication, which means satellite. And we so we need mobile radio, we need
satellite, in addition to the fixed-wire systems that are, are represented by the.
We have fixed installations that are not moving around.
So we have all these different technologies, and Bob's brilliant idea is
not to build one network with all those technologies embedded in it.
Instead he breaks them apart and says let's build a packet satellite network.
Which optimizes the use of satellite takes into account that its got a half of second
round trip time. Let's build a packet radio network which
optimizes a system whose connectivity is changing with time as things move around
and if we get the variable the way and are also variable interference.
So these were different packet networks then the problem is how do you hop
together. You would have this problem if you put all
the technologies into 1 net but if you put them all into 1 net it makes it really
hard. To do control over all these highly
variable parameters. So instead he said break them into
different networks and connect those together.
So we design and build a gateway which today we call a router.
And that concept, also introduced a whole bunch of other things like how do you
refer to another network? Each network thinks it's the only network
in the universe. This is true of the proprietary networks
like SNA, Intechnet and so on. And you didn't have a vocabulary that
said. Take this packet and move it to another
computer on another network somewhere else, that you might not even be connected
to. So we have to invent an Internet address
space in order to solve that problem. We have to find a way to allow packet
losses in this path to be recovered which is where TCP now becomes a manager of
reliability on an end to end basis instead of relying on each net to be reliable.
The ARPAnet was built upon the assumption you can build a reliable underlying.
The internet was based on the assumption that no network was necessarily reliable
and you had to do end to end retransmissions to recover.
So during this it's 1973 period, Bob and I get the papers.
First paper written and published in IEEE Transactions and Communications, May of
1974. And I think mostly nobody paid too much
attention to it. Meanwhile,arpanet is funding us to go make
this actually work. At Stanford, I am working with my graduate
students. Some who are at Oxford, some are at, at
here at Stanford. On this detailed specifications of TCP/IP,
we published that in December of 1974 and it's the first time the word Internet
shows up in print anywhere. These are the first papers we talked about
the Internetworking. So Internet shows up in a, in a complete
spec in December of 74 and it's also got bugs but we don't know that yet until we
started implementing it in 1975 with two other organizations.
So Bob Kahn says Can't have just one implementation.
Bolt Beranek and Newman becomes one of the implementers.
University College London and Peter Kirstein's group in England is the second
or third implementation. So we have 3 implementations of TCP/IP.
In fact, by this time, it's only TCP. We haven't broken off the IP part.
Three implementations are going. We instantly find problems with the
design. And we start evolving.
So over a period from 1973 to 1978 we go through four iterations of the design and
implementation and testing, till we have a very stable thing.
And then we standardize. So 78 we fix everything.
It's, now by this time the internal protocol's been split off.
Because people like David Reed and Danny Cohen are saying we need to have real time
communications that is not necessarily reliable but which has low latency so
voice communications radar tracks and all that, you don't care where the missile was
two seconds ago. You want to know where is it now.
So and in the case of voice if you lose a packet and you just say, say that again I
missed something. So we split TCP into TCP and IP.
And we create something called user data gram protocol which is parallel to TCP and
it is the real time, low latency version of, the reliable TCP.
All of those little components, IP, TCP, and UDP, now going to the Internet
architecture, starting in 1978, and we start implementing.
For the next five years, we start, we, do everything we can, to get TCP IP
implemented on every operating system we can find.
It goes onto the IBM machines, it goes onto the digital machines, HP, goes into
Unix. We have a Unix version built by Bolt
Beranek and Newman. We sent it out to Berkeley, to the
Berkeley BSD release guys. Bill Joyce says, I don't like that code
builds his own. Puts it into BSD 4.2, and that's the
version Unix that Carries a lot of TCP/IP to the academic world because of the same
sort of time frame. Sun Microsystems comes along, builds these
fantastic work stations and they want to use open source, or at least open
protocols. And open operating systems.
So they adopt Unix, and the TCP/IP comes with it.
And they use Ethernet as a way of connecting workstations together, so they
are the engine that's driving the academic community which are all gangbusters for
workstations and high-speed local network. So all of this, course, places huge
demands on the ARPAnet backbone, which is only running at 50 kilobits a second.
And eventually leads to the need for higher speed.
Nsf jumps into the fray, seeing how valuable all this is for the academic
community, and concludes that it should build the network that runs even faster.
And it does so, and it's called NSFNet. [music]
