IEEE 802.12

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100VG AnyLAN is a standard that was developed by Hewlett-Packard and AT&T and standardized by the IEEE 802.12 committee, with the aim of becoming the successor to 10Mbit Ethernet . It was originally developed under the name 100BaseVG.

100BaseVG was specified for operation over four wire pairs of a Category 3 cable (CAT3), which is otherwise only suitable for 10 Mbit / s , as it was installed on a large scale at the time of development, especially in the USA. These cables were also known as “voice grade”. H. Telephone cable - hence the abbreviation "VG". The designation "AnyLAN" indicated that the standard also provided for the transport of Token Ring frames.

The standard was adopted in 1995. Due to the higher costs of 100VG components and their limited availability compared to 100BASE-TX , the standard did not achieve any particular acceptance; from around 1998 the corresponding products were withdrawn from the market.

functionality

100VG-AnyLan used a deterministic access method, which avoided collisions like with classic Ethernet with a common medium:

  • Each connected device / node communicates with the central hub and informs it of its transmission request. There are two possible priorities: normal and high.
  • When the hub decides that it is the device's turn to send, it notifies it that it can now send.
  • The hub runs through the devices in cyclical order and allows them to send one packet at a time ( round-robin method).
  • All high-priority devices are dealt with first, before the low-priority ones are dealt with.
  • All devices that have not submitted a request to send are ignored.
  • To prevent high priority devices from blocking the network, the hub maintains a priority timer for each device. The timer is started when the device makes a request to send with normal priority for the first time. If the timer expires before the device has a chance to send, its request is upgraded to a high priority send request.

Individual evidence

  1. ↑ HP Labs Technical Reports: An overview of IEEE 802.12 demand priority , accessed July 5, 2016