[e2e] What if there were no well known numbers?
day at std.com
Fri Aug 4 19:00:33 PDT 2006
I remember that we had already had conversations about
application-names and network addresses and a directory. I know that
a lot of our thinking was using operating systems as a guide to how
to do it. But since we only had 3 applications and only one
occurrence of each per host, and we needed to get something up and
running, there wasn't time to do it right. Perhaps we were having
these conversations with people other than the UCLA people. Maybe it
was the Multics crowd. I can believe that in the very very early
days that was the logic, but by 1970 or so, we knew better. From
about then, I always considered well-known sockets to be the
equivalent of "hard-wiring low core."
The port numbers in TCP and NCP function as a connection-identifier
within the scope of the (src, dest) addresses, i.e. it distinguishes
multiple connections/flows between the same two points. They do not
identify applications. The well-known idea is just an expedient
convention. It clearly doesn't generalize unless you are McKenzie
who believed that Telnet and FTP were all you needed. ;-)
At 15:54 -0700 2006/08/04, Bob Braden wrote:
>>In any event, I got the impression that TCP pretty much just followed NCP's
>>lead on this. Is there anyone here who was around for the NCP design who can
>>comment on what NCP's reasons were for well-known ports? My guess would be
>>lack of infrastructure (as DPR points out, that was before there was even
>I was around during the NCP design, in the next building over from the CS
>department where Crocker, Postel, Cerf, ... were laboring. I attended
>most of the NWG meetings and read the RFCs at the time. So, here is
>my opinion, but Steve Crocker himself is best qualified to answer this.
>Remember that at the time there was no previous experience with designing
>or implementing network protocols. (Well, I guess the Cyclades and maybe
>the Cambridge folks were doing something, but it was not well known among
>the UCLA grad students who designed NCP). Crocker et al drew nice
>schematic diagrams with process clouds communicating through ports.
>How to name these ports? Well, a 16 bit number (gosh, I forget,.. was it
>an 8 bit number?) seemed like the most obvious thing to use, so that is
>what they used. A numeric port was a string of bits with no semantic
>interpretation a priori, so it appealed to the reductionist approach that
>was common in the early network designs.
>Maybe this discussion should be posted to the history list.
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