B. Morse's regenerative repeater invention for amplifying weak telegraphic signals
has recently been resurrected and transistorized. Morse's
electrical relay permits amplification of weak binary telegraphic signals
a fixed threshold. Experiments by various organizations (primarily the Bell
Telephone Laboratories) have shown that digital data rates on the order
of 1.5 million bits
per second can be transmitted over ordinary telephone line at repeater spacings
on the order of 6,000 feet for #22 gage pulp paper insulated copper pairs.
At present, more than 20 tandemly connected amplifiers have been used in the
System T-l PCM multiplexing system without retiming synchronization problems.
to be no fundamental reason why either lines of lower loss, with corresponding
further repeater spacing, or more powerful resynchronization methods cannot be
used to extend link distances to in excess of 200 miles. Such distances would
be desired for a possible national distributed network. Power to energize the
miniature transistor amplifier is transmitted over the copper circuit itself.
Paul Baran, On
Distributed Communications, Volume I, 1964.
Ethernet provides the local
area networking technology that has spread the Internet throughout our offices
and cities. Technically, it's a physical transmission standard for
digital radio frequency communication over copper wire networks. Ethernet networking
is the most common physical networking standard. It supports TCP/IP networking
seamlessly, and provides an inexpensive, simple, high bandwidth method for interconnection
of local computers. Ethernet solved the all important "last
mile" problem, and remains the standard method of connecting personal computers
to the Internet at the office, and at home over high bandwidth connections.
the late 1960's, engineering developments were rapidly improving integrated circuit
development and computer display monitors. In order to complete the technological
triangle, Xerox PARC invented Ethernet networking, providing a fast, simple,
predictable local area networking standard. Robert
Metcalfe and David Boggs led
Who invented Ethernet? Robert Metcalfe got the idea for the Ethernet protocol
when he read a 1970 computer conference paper by Norman Abramson of the University
of Hawaii about the packet radio system called ALOHAnet linking the Hawaiian
Each node in ALOHAnet sent out its messages in streams of separate packets of
information. If it didn't get an acknowledgment back for some packets because
two radios were broadcasting at the same time, then the missing packets were
"lost in the ether".
When a packet was lost in the ether, the node would
rebroadcast them after waiting a random interval of time. Because of this randomness,
problems with collisions were quickly resolved except under the highest traffic
loads. On average, the network rarely had to retry more than once or twice to
get all of the packet to the destination, which was more efficient than trying
to implement a complex coordination system to prevent collisions in the first
Abramson's design showed that, while it worked well, ALOHAnet reached
its maximum traffic load at only 17% of its potential maximum efficiency, because
of a great increase in collisions at higher loads. Metcalfe chose this problem
for his computer science thesis, and, as a graduate student at Harvard, showed
that you could use mathematical queuing theory to achieve 90% efficiency of the
potential traffic capacity without being locked up by the packet collisions.
is a drawing that Robert Metcalfe made to present Ethernet to the National Computer
Conference in June 1976.
Ethernet is now by far the most common local area network.
Metcalfe went on to found 3Com in 1981, a maker
of Ethernet network cards and other communications products, and now one of the
largest telecommunications companies in the world.
The first version of
the Ethernet standard had a bandwidth of 2.94 Mbps, or about 300,000 characters
a second. The current version is standardized as IEEE
802.3, and provides a bandwidth of 10 Mbps or about 1,000,000 characters a
second, over normal twisted pair telephone wires, and is the most commonly deployed
local area networking standard. Recent advances in the technology have resulted
in development of 100 Mbps and 1 Gbps Ethernet standards, which are increasingly
being deployed for high bandwidth environments.
Every Ethernet network interface
has a unique MAC address.
RFC 826 describes how
to obtain an IP address from an Ethernet MAC address.
Bob Metcalfe wrote Request
For Comments 602, The Stockings Were Hung by the Chimney with Care,
in December, 1973, including descriptions of incidents of hacking only four years
after the birth of the ARPANET.
Resources. The following sites provide additional Information about Ethernet: