Editing VLAN (section)

== History ==
After successful experiments with voice over Ethernet from 1981 to 1984, [[W. David Sincoskie]] joined [[Bellcore]] and began addressing the problem of scaling up Ethernet networks.  At 10&nbsp;Mbit/s, Ethernet was faster than most alternatives at the time. However, Ethernet was a broadcast network and there was no good way of connecting multiple Ethernet networks together.  This limited the total bandwidth of an Ethernet network to 10&nbsp;Mbit/s and the maximum distance between nodes to a few hundred feet.

By contrast, although the existing telephone network's speed for individual connections was limited to 56&nbsp;kbit/s (less than one hundredth of Ethernet's speed), the total bandwidth of that network was estimated at 1&nbsp;Tbit/s{{citation needed|date=June 2018}} (100,000 times greater than Ethernet).

Although it was possible to use [[IP routing]] to connect multiple Ethernet networks together, it was expensive and relatively slow.  Sincoskie started looking for alternatives that required less processing per packet.  In the process, he independently reinvented [[transparent bridging]], the technique used in modern [[Ethernet switch]]es.<ref>{{cite journal |last=Sincoskie |first=W.D. |date=July 2002 |url=https://ieeexplore.ieee.org/document/1018008 |title=Broadband packet switching: a personal perspective. |journal=IEEE Communications |volume=40 |issue=7 |pages=54–66 |doi=10.1109/MCOM.2002.1018008}}</ref> However, using switches to connect multiple Ethernet networks in a fault-tolerant fashion requires redundant paths through that network, which in turn requires a [[Spanning Tree Protocol|spanning tree]] configuration.  This ensures that there is only one ''active'' path from any source node to any destination on the network.  This causes centrally located switches to become bottlenecks, limiting scalability as more networks are interconnected.

To help alleviate this problem, Sincoskie invented VLANs by adding a tag to each Ethernet frame.  These tags could be thought of as colors, say red, green, or blue.  In this scheme, each switch could be assigned to handle frames of a single color, and ignore the rest.  The networks could be interconnected with three spanning trees, one for each color.  By sending a mix of different frame colors, the aggregate bandwidth could be improved.  Sincoskie referred to this as a ''multitree bridge''.  He and Chase Cotton created and refined the algorithms necessary to make the system feasible.<ref>{{cite journal |first1=W. D. |last1=Sincoskie |first2=C. J. |last2=Cotton |url=https://ieeexplore.ieee.org/document/3233 |title=Extended Bridge Algorithms for Large Networks |journal=IEEE Network |volume=2 |issue=1 |pages=16–24 |date=January 1988 |doi=10.1109/65.3233}}</ref> This ''color'' is what is now known in the Ethernet frame as the [[IEEE 802.1Q]] header, or the VLAN tag. While VLANs are commonly used in modern Ethernet networks, they are not used in the manner first envisioned here.{{clarify|date=March 2022}}

In 1998, Ethernet VLANs were described in the first edition of the [[IEEE 802.1Q]]-1998 standard.<ref>{{Cite book|last=|first=|url=https://standards.ieee.org/ieee/802.1Q/1039/|title=IEEE Std. 802.1Q-1998, Virtual Bridged Local Area Networks|publisher=|year=1998|isbn=|location=|pages=|access-date=2021-01-14|archive-date=2021-01-21|archive-url=https://web.archive.org/web/20210121045507/https://standards.ieee.org/standard/802_1Q-1998.html|url-status=live}}</ref> This was extended with [[IEEE 802.1ad]] to allow nested VLAN tags in service of provider bridging. This mechanism was improved with [[IEEE 802.1ah-2008]].