The telephone system:
When the telephone system started in 1876,
it was like (a). Each phone needs link to each other.
Soon replaced by (b). Switching office sets up
temporary circuit between
caller and callee for a call.
Switching office can only cover limited number of local phones.
To make long-distance calls (between phones served by different switching offices),
model in (c). 2nd level switching office.
Eventually 5 levels.
Irish business letterhead from 1898,
showing both telegraph and telephone contacts.
"Internet no.3" - The Internet, 1969 onwards
The Internet has been running since 1969
(a) Phone network.
Failure (or destruction) of a few key nodes can fragment network into a number of
(b) Proposed distributed network,
Each node also acts as a router.
Myth: The Internet grew
out of the military's
nuclear war communications network.
What happened was there were military-inspired studies
in the early 1960s
of how to built a robust network that could survive attack
- notably first-strike nuclear attack.
The answer is to decentralise everything,
including addressing and routing, to have no essential HQ,
and also to have
Major US academic research centres (including military research bases
with links to academia)
took this idea in the late 1960s
and built the Arpanet network that eventually evolved
into the Internet. It was full of scientists and
from the start.
Growth of Arpanet from (a) 1969
to (e) 1972.
The modern US military/intelligence/diplomatic branches
have a number of
private global networks, including:
The Internet was originally set up not for email,
not for sharing papers, documents or programs,
not really for user communication at all in fact,
but rather to allow sharing of expensive
hardware (run programs remotely on someone else's
expensive federally-funded computer).
was a surprise when it took off on Arpanet
in the early 1970s.
Later, email discussion lists started, and the
decentralised discussion-group system,
File sharing would be done between sites when they worked together
on a project.
Later came the concept of a permanent
archive of files
that anyone on the network could access at any time.
Archives of programs were set up, and later archives of
documents of all sorts.
It was not until the mid-1980s that it became clear
that an embryonic electronic "library" of documents was starting to be
built up online.
Now, of course, the library has billions of documents.
Internet had steady growth and usefulness through 1970s, 1980s,
and early 1990s,
but did not really take off until Web
As late as 1993, there was (almost) no business
and (almost) no home civilian users on the Internet.
It was still dominated by the academic, scientific, non-commercial users
that had always dominated it.
But the infrastructure was in place for an explosion in both business and civilian use.
Web invented as a system running on the Internet 1989
(Tim Berners-Lee, CERN).
But did not take off until had a mouse-driven interface
- Mosaic, 1993
(Marc Andreessen, NCSA).
Web explodes. Internet explodes.
1 server - n sites.
Common in hosting company. Sites have low to medium traffic.
Many customers may have almost no traffic.
A single powerful physical server can handle them all.
If not, split them up more.
Hosting company periodically adjusts load as traffic changes.
e.g. My website
can get 5,000 page views per day.
But it it still on a shared server:
"1,915 other sites hosted on this server."
I suspect it is one of the larger sites on the server.
90 percent of them may be very low traffic.
n servers - 1 site.
Switches between 3 machines randomly.
Or, on a larger scale, google.com.
The web address is is actually a gateway or router to many
(maybe thousands of) computers.
- Large bank of machines that serves huge number of clients per second.
Typically uses duplication
and is robust to multiple failures.
Often connected direct to backbone.