Topologies and Protocols: A Brief History
The network adapter as a commodity was first made by the 3Com Corporation. With the introduction of the EtherLink ISA Ethernet adapter, 3Com provided a relatively cheap mechanism for connecting the first PCs. IBM then entered the picture, weighing into the networking world in the mid-1980s. IBM's foray into the networking world was called Token Ring and was based on a different approach to networking. Whereas it is possible for Ethernet devices to talk at the same time (and their messages to collide, requiring them to repeat them), Token Ring circulates an electronic token around the network and devices are only allowed to "speak" when they have the token. In this way, there is never a collision of transmissions on the network. This simplicity means in theory that network communications are never slowed with retransmissions, allowing for superior throughput. This approach has merit and would later be integrated into Ethernet equipment; however, Token Ring suffered from a variety of technical and market problems.
First, Token Ring equipment was proprietary to IBM and was much more expensive than the standards-based Ethernet. That extra expense didn't provide speed superiority over Ethernet. Because of collisions and retransmissions, the maximum throughput of 10Mb/s Ethernet is considered to be 40% (or 4Mb/s). IBM's Token Ring only ran at 4Mb/s. In retrospect it seems clear that Token Ring did not offset its expense and proprietary nature with functional technical superiority; however, IBM carried great influence into the early 1990s and Token Ring was adopted by many large, high-profile institutions that had always depended on IBM for computer expertise. But by the mid-1990s, these same institutions found themselves establishing gradual replacement of their Token Ring equipment. By 1999, Token Ring held less than 10% of the network hardware market and continued to be much more expensive than Ethernet while improving at a more gradual pace.
If there was any question about Ethernet's lead over Token Ring, it disappeared with the introduction of Ethernet over unshielded twisted-pair (UTP) wiring. Approved as a standard in 1990, the new technology didn't suffer from the network fragility that Token Ring suffered. UTP wiring was also less expensive and less bulky than shielded twisted-pair wire that Token Ring required and the connectors were simpler. Finally, the 10BaseT specification allowed Ethernet to run over Level 3 UTP which was already in the wall of some offices to provide connections for the telephone system.
In the early 1990s, a company called Kalpana made three improvements to the way that Ethernet was delivered that would continue to be implemented through subsequent iterations of Ethernet.
When Kalpana introduced the EPS-700 in 1990, it was the first device that could transmit multiple conversations simultaneously through a concentrating device: the first Ethernet switch. Kalpana demonstrated their switches at conventions simultaneously transmitting two video streams through a five-port switch to underscore the availability of full bandwidth across multiple ports on the switch.
Kalpana also introduced full-duplex Ethernet on its switches in 1993. Full-duplex Ethernet is enabled by the separate transmit and receive pairs in the 10BaseT standard. Coaxial-based Ethernet could never support full-duplex operation since all transmissions occurred on the same cable. By leveraging the difference in wiring, Kalpana was able to double the potential bandwidth between the switch and the computer's Ethernet adapter.
Finally, Kalpana introduced the concept of the Etherchannel which is basically multiplexing Ethernet over multiple connections between switches. A two-wire Etherchannel with full-duplex operation could provide a theoretical bandwidth of 40Mbps between two Kalpana switches.
Kalpana was eventually acquired by Cisco Systems.