Switched Ethernet Innovations
Around 1990, many vendors offered popular devices known as intelligent multiport bridges; the first known
usage of the term switch was the Etherswitch, which Kalpana brought to the market in 1990. At the time, these
devices were used mainly to connect multiple segments—they usually did very little to improve performance
other than the inherent benefits bridges provide, such as filtering and broadcast suppression.
Kalpana changed that by positioning its devices as performance enhancers. A number of important features
made the Kalpana switches popular, such as using multiple transmission paths for network stations and
cut−through switching.
Cut−through switching reduced the delay problems associated with standard bridges by providing the means
to have multiple transmissions paths to network devices. Each device could have its own data path to the
switch and did not need to be in a shared environment.
Kalpana was able to do this by dedicating one pair of the station wiring to transmitting data and one pair to
receiving data. This improvement allowed the Kalpana designers to ignore the constraints of collision
detection and carrier sense, because the cables were dedicated to one station. Kalpana continued its history of
innovation with the introduction in 1993 of full−duplex Ethernet.

Full−Duplex Ethernet

Prior to the introduction of full−duplex (FDX) Ethernet, Ethernet stations could either transmit or receive
data; they could not do both at the same time, because there was no way to ensure a collision−free
environment. This was known as half−duplex (HDX) operation.
FDX has been a feature of WANs for years, but only the advent of advances in LAN switching technology
made it practical to now consider FDX on the LAN. In FDX operation, both the transmission and reception
paths can be used simultaneously. Because FDX operation uses a dedicated link, there are no collisions, which
greatly simplifies the MAC protocol. Some slight modifications in the way the packet header is formatted
enable FDX to maintain compatibility with HDX Ethernet.
You don’t need to replace the wiring in a 10BaseT network, because FDX operation runs on the same
two−pair wiring used by 10BaseT. It simultaneously uses one pair for transmission and another pair for
reception. A switched connection has only two stations: the station itself and the switch port. This setup
makes simultaneous transmission possible and has the net effect of doubling a 10Mbps LAN.
This last point is an important one. In theory, FDX operation can provide double the bandwidth of HDX
operation, giving 10Mbps speeds in each direction. However, achieving this speed would require that the two
stations have a constant flow of data and that the applications themselves would benefit from a two−way data
flow. FDX links are extremely beneficial in connecting switches to each other. If there were servers on both
sides of the link between switches, the traffic between switches would tend to be more symmetrical.

Fast Ethernet

Another early innovation in the switching industry was the development of Fast Ethernet. Ethernet as a
technology has been around since the early 1970s, but by the early 1990s its popularity began to wane.
Competing technologies such as FDDI running at 100Mbps showed signs of overtaking Ethernet as a de facto
standard, especially for high−speed backbones.
Grand Junction, a company founded by many of the early Ethernet pioneers, proposed a new Ethernet
technology that would run at 10 times the 10Mbps speed of Ethernet. They were joined by most of the top
networking companies—with the exception of Hewlett−Packard (HP), which had a competing product. HP’s
product, known as 100Mbps VG/AnyLAN, was in most respects far superior to the product proposed by
Grand Junction. It had a fatal flaw, though: It was incompatible with existing Ethernet standards and was not
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