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(C) Herbert Haas
2005/03/11
History: Initial Idea
Shared media CSMA/CD as access algorithm
COAX Cables
Half duplex communication
Low latency No networking nodes
(except repeaters)
One collision domain and also one broadcast domain
10 Mbit/s shared
by 5 hosts 2
Mbit/s each !!!
The initial idea of Ethernet was completely different than what is used today
under the term "Ethernet". The original new concept of Ethernet was the use of
a shared media and an Aloha based access algorithm, called Carrier Sense
Multiple Access with Collision Detection (CSMA/CD). Coaxial cables were
used as shared medium, allowing a simple coupling of station to bus-like
topology.
Coax-cables were used in baseband mode, thus allowing only unicast
transmissions. Therefore, CSMA/CD was used to let Ethernet operate under the
events of frequent collisions.
Another important point: No intermediate network devices should be used in
order to keep latency as small as possible. Soon repeaters were invented to be the
only exception for a while.
An Ethernet segment is a coax cable, probably extended by repeaters. The
segment constitutes one collision domain (only one station may send at the same
time) and one broadcast domain (any station receives the current frame sent).
Therefore, the total bandwidth is shared by the number of devices attached to the
segment. For example 10 devices attached means that each device can send 1
Mbit/s of data on average.
Ethernet technologies at that time (1975-80s): 10Base2 and 10Base5