ARPANET Information Brochure (December 1985)

Don Hopkins don at
Tue Oct 17 02:44:33 AEST 2017

On 16 Oct 2017, at 18:09, Clem Cole <clemc at> wrote:

Don't forget the cost of the IMP itself was just the beginning.  The fees to 'TPC' for the 1/2 duplex 9600 serial lines in those days were very, very expensive.   DARPA paid for them for each site in a large deal it had with AT&T.    I don't remember where I saw it, but what sticks out in my mind for those days was that cost of a site (host) on the ARPAnet was approx $125K / year per host in an ARPA grant. 

Which really explains 'security.' In practice nobody was going to risk letting just anyone hack their system so much that it put the site at risk.   Truth is we did not try to break in because we all had access, but if it you needed a $.5-2M PDP-10 to connect to the internet, a free IMP slot (each IMP supplied 4) and the leases on the wires.  So it was just not practical to think like we do today, much less act that way.

It was not so much security by obscurity, as security by practical economics.  Moore's law, Ethernet and cheap processing power is what blow that up.

On Mon, Oct 16, 2017 at 11:38 AM, Don Hopkins <don at <mailto:don at>> wrote:
> <>

I love the way that geeky guy smugly rubs his hands together, leans back and chuckles when he say “We have our very own IMP. (Huh, huh huh, sigh.)”

I would totally chuckle that way if I had my own IMP.


My uncle worked at the German Space Operations Center, which had DATEX-P, so I asked a mailing list about how to connect with him, and got some interesting replies that give a glimpse of the topologies and costs of the time:


Date: 31-Oct-1986 0451
From: covert%covert.DEC at  (John R. Covert)
To: don at
Subject: Re: datex-p

Datex-P costs money to use.

Go to any VMS system on Telenet running PSI, and send mail to

You'll have to find someone willing to spend a buck or two for every
message you send.

You had the  breakdown of the address wrong:
2624 is for Germany (Germany leaves the 262 off within the country)
581 is for the town (the same as the telephone code for the major nearby town)
53900 is the site
37 is the subaddress

No free service to X.25 networks, sorry.


Date: Fri, 31 Oct 86 14:13:22 EST
From: rick at (Rick Adams)
To: don at
Subject: Re:  datex-p

There is nothing magic about datex-p. Its not a network anymore than C&P telephone is a network. You keep trying to make something special
out of it. Think of datex-p as MCI or ATT or SPRINT. Its just a common carrier.

For about $1500/month you could arrange a tymnet/telenet link at
maryland for them to call up. It would them cost the orignator of the
transmission $12/hour and about $.70 per kilocharacters to connect to you.

Date:  Fri, 31 Oct 86 10:03 EST
From: John C Klensin <Klensin at>
Subject:  Re: datex-p
To: Don Hopkins <don at>

This is going to get pretty complicated, and I'm at a disadvantage in
not knowing what you know already.  So, I apologize if some of the
following is obvious.  I'm going to try to anticipate questions and
answer then as a possibly-efficient way of doing this.

"...  telnet to the states":  Strictly speaking, no.  X.25 protocols,
not TCP/IP, and I think the Bundespost would have fits if someone
started passing TCP/IP traffic over their network.  Moreover, if anyone
has a VMS VAX in the entire world that is capable of accepting an
incoming X.25/X.29 call and then handling TCP/IP traffic over it, we'd
love to know about it, and how they are doing it.  But, I doubt it:  VAX
PSI could not be a more hostile environment to this sort of thing if
they had designed it with that in mind, and one cannot just write and
install X.29 software -- it has to be certified by the network vendors.
GTE Telenet might do so, Tymnet might, but I haven't heard of either of
them being asked.  And you would also need to certify the outgoing
TCP/IP over X.25 package at the far end, and the Deutschebundespost?
Well, "never" somewhat understates the situation.

How about using a datex-p connection to connect to a machine in the US
as a remote user?  Certainly feasible.  This is what is called in the
trade an X.3 -> X.25 -> X.3 or X.29 connection, should you need to know.
All you need is
 a) a machine at this end with incoming Tymnet or Telenet access (or
maybe a few other things, but I don't know).  Some universities have
them, some don't, some commercial firms have them, some don't, etc.  The
minimum charge for those connections is circa $10K per month, $5K to
some educational sites, so they are not real common in places that have
not discovered a large need.
 b) an account at that end, with Datex-P, that has international access
authorization.  That costs extra, incidentally.
 c) The machine address here (a long string of numbers, the first four
of which identify the network).
 d) And, of course, an account on the machine here, since one will be
logging into it.

What can you do once you get here?  Anything that the local user can do,
no more, no less.

Can files be transferred over the VAX/PSI (X.3) ->X.25->X.29 link?  Yep.
Either things like "go into an editor at the remote and pretend someone
is typing very fast" or things like kermit work.  The latter very slowly
because of the long packet-acknowledgement delays.

How about mail over that connection?  Not unless you invent some
protocols such as the ones MAILNET uses (this relies that you have a
daemon at the far end that you can take over and that the remote system
knows about) or cook something up yourself.  You are basically logged
into the remote machine and using yours transparently, or you are logged
into you machine and not the remote.

And how are these things tariffed?  Ignoring the fact that the charges
are for kilopackets and connect time, rather than connect time and
distance, just like long-distance voice phone:  Either originator pays
or remote machine pays ("collect call") service is possible.  Sites that
are willing to accept collect calls essentially sign up in advance,
making it more like an in-WATS service - metered, but invisible to the
caller.  The norm in the US is collect call service, although the major
packet switched networks all support login and password services for
users who need to have accounts and pay the charges themselves
(presumably because they are dealing with remote sites who refuse
"collect" incoming calls).  Internationally, there are three separate
sets of charges, each of which can be charged to either the originator
or the receiver (at least in principle).  Assuming that a call
originates in Germany and is bound for Maryland...
 a) Kilopacket and connect time charges for connecting to Datex-P.  This
is the same charge that would be incurred if you were making a local
connection in Germany.  For moderate use, it averages about $3/connect
hour, last I checked.  Datex-P does not accept any "collect" traffic at
all, so you have to pay then.
 b) Kilopacket and connect time charges for crossing from Datex-P into a
network that serves the US (the "X.75 gateway").  Here, they get you
through the nose.  Again, since Datex-P does not accept "collect"
traffic and the originating network has to be responsible for these
charges, they get passed to the Datex-P account holder.
 c) Kilopacket and connect time charges for connecting to the remote
machine in Maryland.  These charges correspond to domestic rates
(typically $5 - $9 per connect hour), and are typically charged to the
Maryland site (Telenet or Tymnet send them a bill at the end of the
month).  If the Maryland site declines to accept the collect charge,
they can be charged to the Datex-P account also, just like the voice
  The other way works the same way except that, since Datex-P refuses
any collect traffic, ALL charges are assessed to the account at the US
end.  It tends to be a bit cheaper to call from Europe to the US than
vice versa (backwards from voice), but I have not reviewed the numbers
since the dollar collapsed.

  If you can find a local GTE Telenet access number (don't know where
you are, or I could look it up), dial them up, type MAIL when you see @,
type INTL/ASSOCIATES when it asks for a user name, and give INTL as a
password.  Then track through their little menus until you find the
Federal Republic of Germany -- it should give you information on
tariffs, etc.
 (in case you wonder, those accessing instructions are public
information and appear on the second page of GTE Telenet's give-away "US
Access telephone numbers" brochure).

  that is probably about the end of my knowledge.
  good luck

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